A Review of the Literature on the Upstream Migration of Adult Salmonids

J. Fish Biol. (1969) 1, 85-136

J. W. BANKS Department of Zoology, University of Liverpool, Liverpool, England

(Received 3 December 2968)

CONTENTS

I. Introduction ...... 86 11. The homing of salmon and the formation of local races ...... 86 111. Methods of observing the upstream migration of salmonid fishes . . .. 89 IV. Migration in uncontrolled conditions ...... 91 1. Atlantic salmon Saho salar Linn...... 91 2. Sea trout Salmo trutta Linn...... 93 3. Brown trout Salmo trutfu Linn...... 93 4. Rainbow trout Salmo gairdneri Richardson ...... 96 5. Sockeye, red, blueback or Kokanee salmon Oncorhynchus nerka (Walbaum) 97 6. Pink or humpback salmon Oncorhynchus gorbuscha (Walbaum) .. 98 7. Chum or dog salmon Oncorhynchus keta (Walbaum) ...... 102 V. Migration under controlled conditions ...... 102 1. Atlantic salmon Saho salar Linn...... 102 2. Sea trout Salmo trutta Linn...... *. 112 3. Steelhead, rainbow trout Salmo gairdneri Richardson .. .. 112 4. Sockeye salmon Oncorhynchus nerka (Walbaum) ...... 112 5. Chinook or spring salmon Oncorhynchus tshawytscha (Walbaum) .. 114 VI. Discussion ...... 114 1. Rate of Flow . . *...... 114 2. Problems of flow at dams, diversions and fish passes .. .. 118 3. Temperature . . *...... 120 4. Water quality ...... 123 5. General weather, wind and tide ...... 124 6. Light intensity ...... 126 VII. The physiology of salmonids and the control of migration ...... 129 VIII. Summary and conclusions ...... 130 References ...... 132

85 A 86 J. W. BANKS

I. INTRODUCTION The literature on salmonids abounds with instances, both anecdotal and precise, which show that spawning migrations are associated with increased water flows. Doubtless this fact has been a part of fishermen's lore for a very long time. Some early references occur in Day (1887), and even then it was realized that the relationship was not straightforward, other environmental influences being involved. Subsequent work has shown that many factors like water and air temperature, turbidity, atmospheric pressure, cloud cover, pH and variations in concentrations of many dissolved ions are associated with the rate of water discharge in a more or less direct fashion. It has been more difficult in individual cases to determine the significance to the salmon of the many possible stimuli available from these covariable factors. Much of the work which has been done has involved the taking of measurements of' only a few of the parameters which are partially covariant with changes in the rate of water discharge, and therefore the conclusions reached in such work involve the assumption that other factors are not important. Where the possible importance of other covariable factors has been acknowledged, it is only rarely that the amount and statistical significance of any covariability has been considered. This is not surprising as the variables are both complex and often difficult to measure. The result is that at the present time we are still only in a position to say that in general the rate of water discharge is an important, if not dominant, stimulus to the upstream migration of salmon, but in particular instances this effect can be profoundly modified by other environmental influences. The nature of these other influences, and their effect, varies widely from place to place, with season, and with different salmonid species. Reviews of the factors controlling the migration and homing of salmon were published by Chidester (1924) and Scheer (1939). More recently, various aspects of the subject have been touched on in reviews by Hoar (1953), Pyefinch (1955), Jones (1959) and Hasler (1965), but no detailed review of this subject seems to have been attempted in recent years. The presentation of the observations on salmonid migration, which forms the bulk of this review, has been made under two headings. First under uncontrolled conditions, and second under controlled conditions. For the sake of convenience all work relating to situations where an artificial vertical ascent has been imposed on the fish will be considered under the second heading. In practice there is little difference between the ascent into a trap on a small weir, and passage through the trap in a counting fence, but this is the most convenient place to draw the line. Under these two headings the work has been presented by species, and where a publication has dealt with more than one these are mentioned separately, unless the reference is a minor one, when it has often been more convenient to place it together with the work on the species with which the paper is primarily concerned. The information which is presented in the sections on migration in uncontrolled and controlled conditions is re-examined in the discussion in a number of general categories of factors affecting salmonid migration. This section also incorporates directly some material from papers, mainly on experimental work, which do not fit easily into either of the two main sections.

II. THE HOMING OF SALMON AND THE FORMATION OF LOCAL RACES The genera SaImo and Oncorhynchus are primarily inhabitants of the north temper- ate regions surrounding the Atlantic and Pacific Oceans, respectively. Anadromous UPSTREAM MIGRATION OF ADULT SALMONIDS 87 species migrate into rivers and streams wherever suitable spawning grounds are available, and from which they have not been excluded by natural barriers, artificial obstructions, or by pollution. In this vast area, salmon habitually spawn in cold, well-oxygenated stream waters. The current speed and size of stones in the redds varies with species and size of fish. Sockeye salmon occasionally spawn on the shores of lakes, particularly where ground water seepage is coming up through the gravel, but may also spawn in areas of ground water seepage in streams. Some brown trout and rainbow trout inhabit streams and lakes, but similarly run up to cold headwaters to spawn. Others feed in the sea or estuaries, but again spawn in gravels in the streams. Suitable gravels and conditions of oxygenation are most frequently met with in the headwaters of the river system, but in mountainous areas redds may be found within a very short distance of the head of the tide. As a consequence the range of environments encountered by different individuals, even within the same species, will vary enormously. The spawning migration of some will be entirely in fresh water, others will need to make much greater physiological adjustments in moving in from the sea. The journey in fresh water may be anything from a few hundred yards to more than a thousand miles. It may involve nothing more arduous than a few stickles between pools, or can involve the passage of rapids and waterfalls, with vertical jumps of more than two metres, or fish passes on high dams where maximum swimming speeds of up to 34 m/sec may be needed repeatedly. The stream may be subject to violent fluctuations in discharge, or evenly regulated by dams and lakes. The gradients may be low or steep. Many environmental factors will vary in relation to each other, both throughout the range of the species and probably within the length of the stream. Under these conditions it is not surprising to find that there has been a tendency to develop local ‘ races ’ within each species, especially in those which are anadromous. There has been a good deal of argument about the degree to which salmonids form local ‘ races ’ by persistence in returning to their natal stream. Differences of opinion are now seen to have been the result of too much generalization from particular instances. Ward (1939) seeks to reduce the parent stream theory to a statement that it may be the rule, and that the evidence is insufficient to do more than indicate a general compliance with this practice. Much evidence, both direct and indirect, has, however, been cited in support of the stream homing hypothesis, and its concomitant, the building up of genetically different local races. Menzies (1939) cites an instance in which two neighbouring streams, apparently very similar, have a constant difference in mean length for the salmon returning to them. Dvinin (1952) cites the case of two small rivers in Kamchatka whose mouths are 5 km apart; both formerly had spawning populations of between 5000 and 12,000 chum salmon. One river was fished out many years ago and has never re-established a spawning population, while the population on the other continues to flourish. Jones (1959) described the situation in the River Bann in Ulster where destruction of the spawning grounds of the large fish in a particular reach of the main river has resulted in a steady drop of the average size of fish in the catch; Went (1946) described similar results in the River Shannon, after the hydro-electric scheme. Many years of work on the Fraser River by biologists has shown that different spawning populations of sockeye salmon are maintained in each of the major tributaries, The timing of entry from the sea varies with each tributary’s population and can be quite accurately predicted. In each instance the 88 J. W. BANKS time of entry affords the population just enough time to reach the spawning grounds before the gonads ripen. When abnormal conditions intervene, and delays occur, the effects on spawning success can be disastrous. The situation in the Fraser River was summarized by Thompson (1951). The individuals in each group of migrants are made numerically important by their survival rates and form a recognizable entity known by its home stream to the extent that this stream is itself a unit. The fact of continued favourable survival rates in their particular chain of time and space linked environments gives these groups persistence and individuality. The late race of sockeye into Adams River has maintained its numerical dominance in the cyclic year in which it occurs. Strays from its migratory path and time have been relatively unimportant, for no other major race has fluctuated in harmony with it. It had its own fluctuations in abundance and when parts of the race were caught below an obstruction in the main Fraser and forced to spawn in strange creeks, these forced transplants did not become established. Such transplants were not adapted to the conditions in the new chain of environments. Races of this kind have been studied by other means. They have characteristic periods of stay in fresh water which are reflected in scale structure. Marked individuals mainly return to their home streams. Morphometric studies show differences (Thompson, 1951). There is a possibility, as Menzies pointed out in 1939, that each river, or by exten- sion each tributary of a large river, has different environmental characteristics which call in a particular type of salmon at a particular time of year, this could explain constant differences in mean size between two adjacent and similar rivers, but not the total failure to re-establish a salmon run in the fished out stream mentioned by Dvinin. It does not invalidate the stream homing hypothesis. The return of an adult salmon to the stream in which it was born apparently results from some unknown chemical characteristics of the water. The importance of the olfactory sense in guiding adult salmon has been demonstrated by Hasler and his colleagues and associates, and has been amply reviewed in Hasler (1965). Further recent confirmatory evidence of the importance of olfactory mechanisms has been presented by Hara et al. (1965). These authors showed that when adult spawning Chinook and coho salmon arrive at the artificially constructed ' home ' pond most regions of the brain are electrically inactive, but the olfactory bulbs and posterior cerebellum are relatively highly active. Infusion of various natural waters from nearby sources produced little or no change in the electroencephalographic patterns from the olfactory bulbs. Water from the home pond, however, produced a vigorous response of high amplitude. Transplantation of ova or fry has resulted in the re-establishment of salmon runs in many rivers in which they had become extinct, e.g. the south branch of the Apple River (White & Huntsman, 1938). In this experiment the number of returns at the time of report was still small, and some fish at least went up the east branch. It is not surprising to find that when a new run is being established the salmon do not return well initially. If the arguments of Thompson are valid, several generations will be needed before the re-established run is well adapted to its new home. The attempt to establish runs of various species of Pacific salmon to the ' homing ' pond built by the College of Fisheries, Seattle, Washington, is meeting with some success (Donaldson 1961, 1965). On the other hand, the re-establishment of stocks which have been severely reduced by some calamity, but not to the point of extinction, is often very UPSTREAM MIGRATION OF ADULT SALMONIDS 89 rapid. Presumably the remnants already have a well-adapted genome and can therefore expand quickly when conditions are favourable once more. Although natal stream homing seems to be the rule with many species of salmonids, there is a good deal of evidence from marking experiments which shows that there is a variable amount of interchange between the spawning populations of different rivers. This seems to be rather more marked in Atlantic salmon and sea trout than in Pacific salmon. The fact that the genus Oncorhynchus has produced six species anadromous in the Pacific whereas S. salar is the same all round the North Atlantic would seem to suggest that S. salar is more flexible and adaptable in its spawning habits. Allan (19663) stated that an unexpectedly high proportion of the salmon going through the Axe trap had never been seen before in the river. It was possible that this was because of incomplete marking of the smolt run, or it could be that these fish had come from other rivers. It was definitely known that there was considerable interchange between sea trout in the River Axe and other South Devon rivers. This pattern also occurs in the sea trout of the Baltic where Carlin (1964) has stated ' the proportion entering other rivers is high, the homing mechanism seems to be considerably less developed than for the salmon.' Insufficient work has been published to see how universally the conclusions of these two authors can be applied to salmon and sea trout, but it seems possible that both species have a tendency to return to their home stream which is strong although less developed in some situations than that found in Pacific salmon. Although it was noted in the Second Report on Scottish Salmon and Trout Fisheries (1965) that ' when they return to fresh water to spawn practically all salmon come back to the river in which they spent their early lives. . . It is exceptional for a fish marked as a parr or smolt in its river of origin to be recaptured in any other river. We stress that homing . . . must be accepted as a basic fact when approaching salmon fishery problems.' As has already been shown the formation of local races will result in the fish of each river being well adapted to the environments usually found in that river or part of a river system, and less well adapted elsewhere. The precision of its adaptation is likely to vary with the complexity of the conditions which it has to overcome between entering the stream and spawning. An example of a very precisely adapted part of a population may have been the large salmon already mentioned which used to spawn in a particular reach of the River Bann (Jones, 1959). There is a good deal of evidence which will be cited later which shows that certain characteristics of the water discharge can profoundly affect the way in which salmon react to the water of some rivers or tributaries so that they only move into them or within them under particular conditions. One can reasonably assume that natural selection has played some part in moulding these rather precise behaviour patterns which often depend on a sequence of events unique to that particular stream, such patterns are maintained by a low rate of gene flow between the populations of different streams. The only conclusion can be that generalizations about the conditions which favour salmonid spawning migrations should be treated with the utmost caution, until they have been shown to hold good in a large number of instances.

III. METHODS OF OBSERVING THE UPSTREAM MIGRATION OF SALMONID FISHES Salmonids may be observed under three main types of circumstances: (a) during unfettered passage along a river reach, on spawning beds or in passage of a natural 90 J. W. BANKS obstacle; (b) by means of counting fences and traps; (c) in passage through fish passes over dams, weirs or natural falls. In categories (b) and (c) it is usually possible to examine fish individually for tags as well as making counts of numbers passing, although some fish passes do not incorporate traps but do enable a close watch to be kept for colour tags and the numbers of different species. There are few published accounts of observations under entirely natural conditions, since the amount of information which can be obtained is usually small, and is difficult to obtain. When counting fences are used the records are subject to a number of criticisms. There is a delay in the intervals during which the fish are allowed to collect in the trap. The fence itself is an obstruction to the fish which may not all find the trap entrance equally easily. The relative proportions of water passing through fence and trap will vary according to the water level. It is therefore impossible to calculate the effect of differences in the relative attractiveness of the trap at different water levels. A further difficulty is that siting of the trap will greatly affect the pattern of the fish movements recorded. In discussing the River Axe trap, which is situated at the head of the tide, Allan (1966~)observed that a trap situated above a shallow stickle or above obstructions surmountable only at medium or high river levels would obviously show a very different picture. Most fences are vulnerable to high floods in which the water rises above the level of the obstruction. In these circumstances an escapement of fish over the top may take place. Fences can theoretically be built high enough to overtop the biggest flood, but the weight of water and trash carried by the river under these conditions means that a great increase of the strength of the fence is needed, with a vastly increased cost for the installation. In spite of these difficulties counting fences have provided a very large amount of useful information about migration. The accuracy of guessing the numbers of ascending fish by means of angling success is clearly open to many objections. Some work using this method has been carried out in association with work using counting fences. The counting of redds is a useful method of assessing spawning populations when carried out systematically, but nothing has been published in which this method has been used to correlate the arrival of new fish on the spawning beds with particular environmental factors. Electronic counters have been successfully used instead of traps for some purposes (Stewart, 1966, 1968a, b) but the difficulty of distinguishing between species with overlapping size ranges can be a major obstacle. Allan (1966b) pointed out that if used on the Axe, electronic counters would be unable to distinguish between large sea trout, small salmon and grey mullet. In some places cameras linked to the counting mechanism might help to resolve this problem. A man-made obstruction which has to be ascended by means of a fish pass will naturally introduce an entirely artificial set of conditions. The larger the dam, the more far reaching are the changes which it will bring about. Dams used for hydro- electric power or for domestic water storage each provide special problems. The stored water will usually have differentphysicochemical properties from the normal river water above, and its use will greatly change the pattern of discharge in the river below. The flow may be deliberately manipulated to influence fish movements or these may be accidentally influenced in the course of the use of the water for its primary purpose. Alterations in the behaviour of fish on their spawning migrations, and reductions in the fish population are almost certain to result from such interferences, particularly UPSTREAM MIGRATION OF ADULT SALMONIDS 91 where large dams have been built. The changes can be kept to a minimum by good fish pass design, and could sometimes be further reduced without loss to the primary user by a more flexible approach to the release of compensation water. The evidence of these changes, and occasionally of their mitigation is presented in the section on migration in controlled conditions, and in various parts of the discussion.

IV. MIGRATION IN UNCONTROLLED CONDITIONS 1. ATLANTIC SALMON SALMO SALAR LINN. Stuart (1962) observed the passage of salmon and brown trout at the Pot of Gart- ness, and showed how different size ranges of fish attempted different falls as the rate of discharge changed. The larger fish were only attracted at higher discharges. He suggested that the attractive feature was a characteristic note produced by the falls at each water level. Jumping attempts always ceased at nightfall. Presumably the fish are dependent on some visual cues to help them gauge their leap, although the urge to move upstream was stimulated by increase in the rate of discharge, or some associated change. In 1934 The Biological Board of Canada began an investigation on the Margaree River, Nova Scotia, and noted that the numbers of salmon taken by angling during the previous decade showed good correlation with the volume of water discharge (Huntsman, 1939). The investigation on the Margaree was primarily designed to examine the effect of nets in the estuary and in the sea immediately outside, following complaints by anglers that they were unable to catch fish early in the season, although there were plenty of fish in the river by early September. Huntsman showed that northwesterly and northerly onshore winds were effective in concentrating the fish against the coast and bringing them to the estuary mouth. The set of the sea currents carried river water northwest along the coast, and the fish were associated with the masses of fresh water which issued from the estuary with each ebb tide. Fish concentrated in the estuary, or just outside, would not enter the non- tidal part of the river unless the river was in spate. Inspection of the hydrographs for the Margaree River shows that large freshets occur in late August and September when the main salmon run normally ascends. When the river had been low for some time a spate would initiate a period of increased angling success which moved gradually upstream. Unfortunately it is not clear what was the relationship between the size of the freshets and the normal dry weather flow. From an inspection of the graphs it would appear that dry weather flow was between 100 and 200 cusecs, and that natural freshets could sometimes reach 2000 cusecs. Freshets which raised the discharge from 250 to 700cusecs in June 1938 produced a negligible increase in salmon catches, but a smaller freshet in late August brought about a very large increase. Huntman’s contention that because of the shape of the estuary, very heavy freshets were needed to bring fish up the river, does not seem to be fully borne out. Experience on the Margaree led to further work on other rivers in which artificial freshets were used in an attempt to make fish ascend from the sea earlier in the season. This work will be described in the section on migration under controlled conditions. Harriman (1961) worked on the Narraguagus River in Maine, again using angling success as a measure of upstream migration. He made a comparison of hydrographs and daily rod catch statistics over a 15-year period, and reached the following conclusions. 92 J. W. BANKS

(1) A freshet prior to 15 May does not start an early run, after that date it does. (2) After 1 June a freshet will start the main run, and an increase in flow every few days will prolong it. (3) When the water level fell below 200 cusec there was no angling success. Those fish already in the river became inactive and no more moved in. An increase above 200 cusec restarted angling success provided the temperature was not too high. The Narraguagus River has a rapid run off, and very low summer levels, but has a high rate of discharge during spring. Harnman was arguing for a storage dam which would enable the discharge to be maintained at 400 cusec through late May, June and July. Allan (1966~)has described some of the results obtained at the fence and trap on the River Axe. In Table I (Allan, 1966a, Table 13), the grouped daily maxima of river

TABLEI. Numbers of salmon ascending at various river flow ranges and levels (daily maxima) in 1964. (Allan, 1966a except for the right-hand column)

~ ~ ~ ~ (a) (b) (c) (4 (d/c) Grouped daily Grouped daily maxima river maxima river Frequency Numbers flows levels of flows of salmon Salmon (cusec) (in.) (occasions) ascending per flowlday 28G 51 Oto 1.6 70 28 0.4 52 to 75 1.7 to 2.8 50 32 0.64 76 to 99 2.9 to 4.4 46 26 0.57 100to 123 4-5 to 5.6 60 19 0.32 124to 147 5.7 to 7-0 25 12 0.48 148 to 171 7.1 to 8.2 19 23 1.21 172 to 195 8.3 to 9.4 20 19 0.95 196 to 219 9.5 to 10.4 18 42 2-33 220 to 243 10.5 to 11.6 9 86 9.55 244 to 267 11.7 to 12.6 2 3 1.50 268 to 291 12.7 to 13.6 3 1 0.33 292 to 315 13-7 to 14.6 1 0 - 316 to 339 14.7 to 15.6 0 0 - 340 to 363 15.7 to 16.6 2 6 2 .o 364 to 387 16.7 to 17.7 3 50 16.67 388 to 411 17-8to 18.6 0 0 - 412 to 435 18.7 to 19.7 1 0 - 436 to 531 19.8 to 23.4 0 0 - 532 to 627 23.5 to 26.8 4 4 1-0 628 to 723 26.9 to 30.4 3 11 3 67 724 to 819 30.5 to 33.4 1 1 1.o 820 to 915 335 to 35.8 4 3 0.75 916 to 1011 35.9 to 39.2 2 11 5.50 1012 to 1107 39.3 to 42.1 0 0 - 1108 to 1203 42.2 to 45.0 0 0 - 1204 to 1299 45.1 to 47.7 0 0 - 1300 to 1395 41-8 to 50.0 1 1 1 1492 to 1683 52.4 to 56.5 3 1 0.33 1684 to 18757 56.6 to 60.9t 0 0 - 1876 to 2067 61.0 to 64.6 1 0 - 2068 to 2600 64.7 to 74-0 2 0 - ?River over banks. UPSTREAM MIGRATION OF ADULT SALMONIDS 93 flows, the frequency of these flows and the number of salmon ascending in each group are presented for 1964. It is apparent that most fish ascended through the trap at flows of 28 to 243 cusec, and although there were spates of up to 2600 cusec, these lower flows occupied 87 % of the days in the year. Allan also points out that there were 22 flood flows of over 532 cusec and that these occurred in late autumn and in the early months of the year, times when very few salmon ascend the Axe under any water conditions. Further analysis provides more information about the relationship between flow and salmon ascent in the Axe. An extra column added to Allan's Table 13 (see Table I), by dividing column (d) (numbers of salmon ascending), by column (c) (numbers of days on which a given maximum rate of discharge took place), gives a figure for the number of salmon per flow day. Up to a flow of 147 cusec the number fluctuates between 0.3 and 0.6, between 147 and 267 cusec the number of rises from 1.2 to 9.6 and falls again to 1.5, above this the flows are few and the numbers per flow day fluctuate between 0 and 17. The belief the salmon migrate upstream only or mainly on floods or freshets is not upheld by the trapping records as the author points out, but nevertheless it seems clear that, given the choice, many more ascend in the short periods of moderate freshets than do in the much longer periods of low water. It is not possible to tell from Table I how many of the fish ascending during the lower flows did so as the water subsided after a freshet, although such fish might well be said to have ascended under its influence. Huntsman (1939, 1948) and Hayes (1953) show that most Atlantic salmon ascend when the water is falling after the peak of the freshet has passed. Similar observations were made by Munro & Balmain (1956) and Stuart (1957) for brown trout, Lamond (1916) sea trout, and Davidson et al. (1943) for pink salmon. Consequently it is not possible to ascertain the complete relationship between flows and numbers of migrating salmon on the River Axe. For this, a chart in which the two parameters are presented together for some years would be needed, or possibly data grouped by seasons as suggested by Menzies (1966). Some further analysis of the data from the Axe is given in the section of the discussion on the effects of discharge, where it can be compared with work presented in other sections of this review.

2. SEA TROUT SALMO TRUTTA LINN. Very few data are available on sea trout. In the River Axe they move through the trap at low flows even more readily than salmon (Table 11) (Allan 1966a, Table 15). In common with the salmon on the Axe they show' a slight preference to move upstream at night: especially during low flows (Table 111) (Allan, 1966a, Table 12). The Axe data supports the contention of Baxter (1961) and the Second Report on Scottish Salmon and Trout Fisheries (1965) that water requirements for salmon will be adequate for sea trout.

3. BROWN TROUT SALMO TRUTTA LINN. Stuart (1953) investigated the spawning migrations of brown trout from three Scottish lochs. He concluded that spawning runs were inhibited when the temperature of the stream was higher than the temperature of the loch, that spawning runs would only occur after the stream temperature had fallen to 6 to 7" C for the first time each autumn, and that spates acted on migration indirectly by lowering the stream temper- 94 J. W. BANKS

TABLE11. Numbers of sea trout counted ascending at various water-levels (inches over weir) 1963 to 1964 (Allan, 1966~7, Table 15)

Numbers of sea trout ascending Water-levels (in.) 1963 1964

0 to 5 1334 1930 5 to 10 624 362 10 to 15 156 246 15 to 20 139 I14 20 to 25 80 6 25 to 30 6 23 30 to 35 0 1 35 to 40 88 19 40 to 45 86 0 45 to 50 43 0 50 to 55 4 8 55 to 60 1 3 60 to 65t 6 0 65 to 70 16 0 70 to 75 6 0 75 to 80 4 0 Escapement Yes Yes

?River over banks.

TABLE 111. Daylight and darkness and arrival of salmon and sea trout in the trap (Allan, 1966a, Table 12)

Salmon Sea trout A J. r V 1 Numbers caught % caught % caught % caught % caught Year Salmon Sea trout in daytime at night in daytime at night

1961 335 3121 40.7 59.3 40.5 59.5 1962 25 I 2443 45 *O 55.0 46.5 53.5 1963 480 2592 27 *7 72.3 42.4 57.6 1964 387 2818 39.5 60.5 37.9 62.1 ature. The streams were small and the size of the migration was assessed by counting the fish on the redds. Munro & Balmain (1956) recorded spawning runs of brown trout from Loch Leven into the South Quiech. No run of trout started without a rise in water level, and when the water was turbid fish ascended by day and night, but as the river cleared they ran only at night. In contrast to Stuart they found that the fish often ran when the stream temperature was higher than in the loch, although sometimes the stream temperature dropped below the loch temperature while a run was in progress. In addition to the temperature they also recorded the general weather, wind direction, alkalinity, pH and turbidity of the stream and loch, and found that changes in water level were closely associated with changes in these physical and chemical measurements. They concluded that temperature was not important in governing the migrations of brown trout into the South Quiech (Figs 1 and 2). UPSTREAM MIGRATION OF ADULT SALMONIDS 95 OC 12 I1 10 --- Stream temDeratur ..... Loch temperature

NMNMNMNMNMNMNMNMNMNMNMNM 3031 I 2 3 4 5 6 7 8 9 10 October November Date FIG.1. Four-hourly records of numbers of brown trout entering the South Quiech trap; air, stream and loch temperatures; water level and turbidity, for the period 30 October to 10 November 1953 (Munro & Balmain, 1956). (Reproduced by permission of the Controller of H.M.S.O.) OC 12 II -

3- 2- I- ppm CaC03 50 45 40 - *-_ --_- - 35 30 25 20 15 No. of fish In Turby 500 - - 400 - - - 300 -

25 26 27 28 29 30 I 2 3 4 5 6 November December Date FIG.2. Four-hourly records of numbers of brown trout entering South Quiech trap; air, stream and loch temperatures; pH and alkalinity; water level and turbidity, for the period 25 November to 6 December, 1953. (Symbols as in Fig. 1) (Munro & Balmain, 1956). (Reproduced by permission of the Controller of H.M.S.O.) 96 J. W. BANKS

A further paper by Stuart (1957) on the migration and homing behaviour of trout in the same three lochs used in his earlier work, throws a little more light on this apparent contradiction. Although recordings of the numbers of spawners was again dependent on seeing the fish in the stream, the figures which illustrate the numbers of fish running, the stream and loch heights and temperatures appear to show that the spawning migrations are closely associated with rises in water level (Fig. 3). During the time of year when the spawning runs took place, the loch temperature was almost always higher than stream temperature, so that the possibility of an inhibiting effect of higher stream temperatures would only rarely come into effect. It is probable that temperature plays an overall part in the maturation of the gonads, and it may affect migration directly from time to time in these reservoirs. In Dunalastair Reservoir (Stuart) and Loch Leven (Munro & Balmain) the brown trout seem well adapted to local conditions, regardless of whether this involves an indifference to temperature changes, as in Loch Leven, or some greater control of behaviour by temperature as at Dunalastair.

October November December FIG.3. Duration and sequence of spawning runs of brown trout in Dunalastair stream A., 1954 (Stuart, 1957). (Reproduced by permission of the Controller of H.M.S.O.)

4. RAINBOW TROUT SALMO GAZRDNERI RICHARDSON Mottley (1938) observed the spawning runs of rainbow trout from a lake in British Columbia, and showed that the peak of each run occurred in the early afternoon, and the peak of the seasonal run began during the first spell of warm bright weather after the ice left the lake. Fluctuations in intensity appeared to be related to wind direction, and migrations were highest when the wind blew into the mouth of the creek, and when relative temperatures of the creek and the lake were such that the return current created by the wind would carry the creek water with it just above the thermocline, between 5 and 10 m below the surface. Unfortunately no evidence is provided that the UPSTREAM MIGRATION OF ADULT SALMONIDS 97 fish travel to the creek at this depth, and no mention is made of the rate of discharge from the creek. The first spell of warm bright weather in spring would melt snow from the surrounding hills, and it is probable that stream discharge would be high at this time.

5. SOCKEYE, RED, BLUEBACK OR KOKANEE SALMON ONCORHYNCHUS NERKA (WALBAUM) Ellis (1962) recorded the movements of sockeye salmon and coho salmon from observation posts, and by skin and aqualung diving. He found that daytime movement through water speeds of less than 5 ft/sec (13 m/sec) was by steady swimming in schools, between 1 and 3 ft/sec (1 and 14 m/sec) this was interrupted by resting periods. Movement generally occurred along the line of the deepest channel. Above 5 ft/sec (1 4 m/sec) the fish moved individually by darting, interspersed with holding. He recorded nocturnal migration without describing it in detail. In the Paratunka River, sockeye moved upstream on a positive temperature gradient created when the fall in air temperature each night decreased the amount of snow melt water entering the river (Krogius & Krokhin, 1957). It was agreed by these authors that other factors could be involved, and they suggested work on the ionic composition of the water throughout the 24-hour cycle. It is worth noticing that a decrease in snow water would entail a fall in discharge rate. If sockeye were reacting to this change they would be doing so in the opposite manner to that which usually activates other salmonid migration. In an earlier study Krogius (1954) had shown that, in four tributaries of the Para- tunka, adult sockeye move upstream in conditions of rising temperature and pH, and falling oxygen and carbon dioxide concentration. Differences between the watersheds of the tributaries gave rise to differing diurnal cycles of these factors. All factors were simultaneously favourable only at certain times of day. Consequently in the M. Bistraya and River Dalnee the fish moved during the day, but in the Blizhee they travelled mainly during the morning and evening. Although the tributaries are all short, and contain enough water for movement at all times, sockeye already in the tributaries wait in deep pools for favourable conditions for further movement. The reasons for this behaviour were not known. The mechanism which activated the changes in temperature, pH and gas concentrations was the diurnal cycle of light intensity, which was acting indirectly through its effect on temperature and photosynthesis. The control mechanism within the fish was unknown but the author felt that it might be elucidated through work on the physiology of respiration. It is clear that in such sluggish, lake regulated streams as these, changes in discharge rate are likely to be less important than other factors. Powers (1939, 1941) came to similar conclusions to Krogius & Krokhin in stating that sockeye will turn into a stream coming from a lake in preference to one with no lake, because the former will usually have lower tensions of free carbon dioxide. Ward (1921, 1930) considered that sockeye would choose the colder stream at junc- tions, although this was shown to be not always the case, for example by Chapman (1941). Powers was concerned to show how carbon dioxide tensions could be important in homing, rather than as a stimulus to movement as had been done by Krogius. This led him to consider the whole question rather statically. He made no measurements of carbon dioxide gradients, either at different times of day or along a stretch of river, nor does he seem to have considered the possible significance of other factors. 98 J. W. BANKS

It seems unlikely that carbon dioxide, or other chemical gradients are of any importance in guiding fish up large rivers, but as Krogius, and Krogius & Krokhin showed these physicochemical gradients can be important where they are changing with time. Fluctuations of some significance are more likely in smaller streams and headwaters than in downriver zones where the variations in these factors from tributaries will tend to cancel each other. In a study of Kokanee salmon (' landlocked ' 0. nerka) Lorz & Northcote (1965) concluded that light was the most important factor in controlling the time of entry of the spawning fish into a tributary. They found that fish entered the stream when the light value dropped to 100 lux each evening. At this stage no change in stream temperature was noticeable. Apart from lake temperature they do not appear to have measured other physicochemical parameters like discharge, pH, oxygen or carbon dioxide concentrations, so indirect light effects of the type described by Krogius cannot be ruled out completely. They considered night migration to be an antipredator device, and noted that it occurs in other species, as shown by Loftus (1958) for river spawning lake trout Sulvelinus narnuycush (Walbaum) and Munro & Balmain (1956) for brown trout. However, once the stream had been entered, some Kokanee were active over a 12-hour period which included both morning and evening, although the main peak for ascent, as for entry, was during darkness. Olfaction seemed to be important in stream location. Kokanee approached the creek mouth earlier in the afternoon on days when there were strong onshore winds, but only small numbers came in on calm days. This was thought to be the result of the lateral movement of creek water brought about by wave turbulence. The creek water was thermally undetectable within a few yards, but olfactory cues are effective at very low dilutions (Walker & Hasler, 1949; Brett & MacKinnon, 1954), and olfaction is important in stream location (Wisby & Hasler, 1954; Hasler, 1965). Other work already cited (Huntsman, 1939; Davidson el al., 1943; Dvinin, 1952) supports this view.

6. PINK OR HUMPBACK SALMON ONCORH YNCHUS GORBUSCHA (WALBAUM) Pritchard (1936) showed that in McClinton Creek, British Columbia, there was a positive significant correlation between the numbers of pink salmon migrating from the sea to the stream each day, and the maximum daily water height, and the daily rainfall. Rainfall and water height were covariant, but there was no covariation with temperature (Fig. 4). In a more detailed examination of this relationship Davidson et ul. (1943) measured the pink salmon migration in two streams from southeastern Alaska and one from British Columbia. They also measured temperature in the stream and air, stream level and pH. No relationship was demonstrated between pH or temperature and numbers of pink salmon migrating. In Sashin Creek the salmon wait in the bay outside the stream mouth until sexually mature, thereafter they will enter the stream even when there is no increase in stream level, however, in most years there is a significant positive correlation between stream flow and migration (Fig. 6). In Snake Creek there was no correlation between stream level and numbers of migrating salmon. Tn fact there was in most years a slight negative correlation, possibly explained by the presence of a 10 ft (3 m) fall at the mouth of the stream which could not be ascended by pink salmon during high spates. One period of positive UPSTREAM MIGRATION OF ADULT SALMONIDS 99

FIG.4. Showing for the spawning run of 1934 the numbers of adult pink salmon reaching the weir at McClinton Creek daily, the maximum daily water height at this weir and the daily rainfall. (Reproduced with permission from the Journal of the Fisheries Research Board of Canada.)

August September October November FIG. 5. Relation of stream discharge and pink salmon upstream migration in Hooknose Creek (Hunter, 1959). (Reproduced with permission from the Journal of the Fisheries Board of Canada.) -, Actual migration; ...... ', fitted migration line 3 = 296-99 + 75.63 x - 2.59 x * +0.0241 x 3; - - - - -, stream discharge. correlation was observed, after the inshore migration had been held up by very dry weather and increase in flow was followed by the influx of 50% of the total run in a few days. In Snake Creek pink salmon mature in the quiet, deep, water above the falls after ascending them at the first suitable opportunity (Fig. 7). McClinton Creek, in contrast to the other two streams, has no lakes in its watershed and depends on surface run off and underground seepage for its flow. Pink salmon will move directly into the stream, when still immature, provided that the level has been raised by rain. When mature they will migrate regardless of stream level (Fig. 4). The authors maintained that the differences in character between the Snake Creek and Sashin Creek migrations must be explained by differences in the inherent behaviour of the two populations, as there were no apparent environmental or physicochemical differences between the two. They also state that the behaviour of the 100 J. W. BANKS

I 01 I lo

0-0

LL 50

August Sepiembar August September

FIG.6. Daily average stream temperature and stream level and number of pink salmon (daily weir count) migrating into Sashin Creek, Alaska, in 1934, 1935 and 1936 (Davidson et al., 1943). (Reproduced with the permission of the Duke University Press.)

McClinton Creek run is of the same type as in Snake Creek, but may change over to the Sashin Creek type if delayed by prolonged dry weather. Clear behaviour differences at the stream mouths were demonstrated by these authors, and they were unable to show any environmental variation which could cause them, but it is unlikely that such differences would be present as a result of chance alone. From close examination of their data one invariable fact emerges, pink salmon will ascend streams, or attempt to ascend, when they are sexually mature, regardless of the stream flow. In the description of Sashin Creek no mention is made of any suitable deep or slow water where the salmon could rest and mature. In this stream the water fluctuates around a depth of about 12 in. Thus in Sashin Creek fish can ascend, but have nowhere to mature, in Snake Creek, when they have managed the ascent, they can mature in the deep quiet water above the falls, while in McClinton UPSTREAM MIGRATION OF ADULT SALMONJDS 101

1930 1932 mN c 5 ropoo E- 8 -5c;; h 20 f 500C "0 I s-.L g - 0 0 %' 160 63 -0- E 120 Eo 47 e0- 80 32 = 40 16 0 0 6 16 59 f- 14 0 g% 12 LI Q) 6 10 30 8 1931 A 1933 'c lop00 z

f =OoO -0 --2 160 63 E 5 120 47 0- t 80 32 2 ' 40 16 0 0 16 59 ,O 14 1 EP 12 0- (r. f 10 30 c% 0 13 18 23 28 2 7 12 17 22 19 24 29 3 8 13 18 23 28 July August July August FIG.7. Daily average stream temperature and stream level and number of pink salmon (daily weir count) migrating into Snake Creek, Alaska in 1930 to 1933, inclusive (Davidson et el., 1943). (Reproduced with the permission of the Duke University Press.)

Creek they can only ascend when the water is high, but they then rest and mature in deep holes. The behavioural differences therefore appear to be a very close expression of the needs of the three populations. Davidson et al. (1943) also provided some evidence which showed that freshets are not only important in enabling the fish to enter and ascend streams, but also play a part in attracting them to the stream mouth. In reference to McClinton Creek they state that as the discharge increases, the influence of the fresh water moves further out into the bay, which enables more fish to be influenced by it. As the fish are widely distributed during dry weather, the effect of the freshet in attracting fish to the stream mouth is delayed, and the highest weir counts followed the days of high freshets. Similarly in Snake Creek in dry weather the salmon remain offshore in the open channels and only come to the falls when the influence of fresh water increases. This agrees with Huntsman's (1939) finding that the set of fresh water current along the 102 J. W. BANKS shore was an important factor in bringing the fish close in, and the findings of Lorz & Northcote (1965) for Kokanee salmon at Nicola Lake. In a further study of pink salmon, Hunter (1959) showed that in Hooknose Creek there was a significant positive correlation between discharge and migration. A third degree polynomial curve was fitted to the 1952 escapement (Fig. 5). Analysis showed that about 34% of the variation in upstream movement, apart from the seasonal trend, was associated with the level of stream discharge as measured on the same day, and 19 % of the variation with discharge of the previous day, or associated phenomena. A detailed analysis was carried out only for the pink salmon of one year, but the same relationship was evident for both pink and chum salmon in all the years studied. Thus although the fish respond to some degree to spate conditions, they are not wholly dependent on them for moving upstream. The fish did not migrate against excessive flood levels, but seemed to have a maximum current speed against which they would travel. In general the fish of this stream followed the same pattern as those in Sashin Creek. In a study of pink and chum salmon of South Sakhalin (Dvinin, 1952) it was noted that both species enter the streams when rough weather caused the sea to roll. On the west coast of Kamchatka strong offshore winds, aiding the distribution of fresh water to more remote regions of the Okhotsk Sea, caused the largest approaches of salmon towards the coast. On the west coast of South Sakhalin, where the flow of freshwater is insignificant, the reverse is true and the largest spawning runs of chum salmon coincided with onshore winds. Some possible reasons for this are discussed under the heading of general weather, wind and tide.

7. CHUM OR DOG SALMON ONCORHYNCHUS KETA (WALBAUM) Hunter (1959) gives some data for chum salmon which show that their reactions are similar to those of the pink salmon which he studied at Hooknose Creek. Dvinin (1952) also worked on pink and chum salmon, and his discussion of the importance of turbulent sea conditions in bringing fish to the mouths of the streams already has been discussed under pink salmon.

V. MIGRATION UNDER CONTROLLED CONDITIONS In an earlier section it was mentioned briefly that situations which varied greatly in the degree of their departure from the norm would be covered by the term ' controlled conditions '. Studies of these situations have frequently only been made after the artificial change has taken place. This makes it impossible to know how far the changes have affected the size of the salmonid populations, or necessitated alterations in their pre-existing behaviour patterns. The study of analogous, but unaltered environments provides the only basis for informed guesswork about the original conditions. This section will consider the migration patterns which have been observed at passes on dams, weirs and falls, also the effects of artificial freshets.

1. ATLANTIC SALMON SALMO SALAR LINN. The first recorded instance in which an artificial freshet was used to bring salmon up from the sea occurred in 1888 on the Grimersta River in Lewis. As described by Calderwood (1908), water was let down from Loch Langabat into the lowest of a chain UPSTREAM MIGRATION OF ADULT SALMONIDS 103 of four lochs, where it was held by a temporary dam. When the dam was broken, the salmon, which had been congregated at the head of the tide for a very long time in a dry season, swarmed up the river and into the loch where over 400 were caught by three rods in a week. With the arrival of rains the fish moved further up the river. Following work on the Margaree River already described in the previous section (Huntsman, 1939), the Fisheries Research Board of Canada started investigations on the Moser River, Nova Scotia, where they had the opportunity to control the rate of discharge from a lake eight miles above the head of the tide, and to count the migrants as they passed through three counting fences (Huntsman, 1948). At the end of July 1942 in a dry season, three sharp artificial freshets seemed to stimulate all the fish to ascend. The numbers of fish through the lowest fence for each freshet being 367, 140 and 23, respectively (Fig. 8). Ten days later three more freshets

July August FIG.8. Salmon ascent with artificial freshets during drought, Moser River, Nova Scotia. Histograms show numbers of salmon and the dotted lines the water levels. Head of village 3, Salmon Hole 34, and Round Lake dam 8+ miles above head of tide (Huntsman, 1948). (Reproduced by permission of the American Fisheries Society.) seemed to bring up the smaller number of fish which had accumulated in the interim. Most of the fish moved up through the lowest fence with the first freshet, but the numbers passing through the uppermost fence increased with each freshet. Presum- ably the fish did not all make the complete ascent during the short freshets which were used, but unfortunately no time is given for the duration of the freshets, and their size is only indicated by a scale of inches above some fixed point. Apparently the actual volumes of water involved were not measured. In all, more than twice the number of salmon and brook trout Salvelinus fontinalis (Mitchill) entered the river than could have been expected from proportions returning of those marked in previous years. It was suggested by Huntsman that the artificial freshets were so effective that they brought in wandering salmon from other rivers, in Windspeed and direction

e U Y ._P -m 3 W r : 4c c0 30 c E 20 0C 10 cn;

-0 June July 4 2000 cr - 1500 ._

oi -f 1000 9 .s 500 P I I I I I I 1 I 5 10 15 20 25 30 5 10 15 20 25 30 5 IC 15 20 25 30 5 10 15 20 25 30 May Jme duly August FIG.9. An assembly of data from the Le Have River 1951. Onshore winds are hatched (modified after Hayes, 1953). (Reproduced with permission from the Journal of the Fisheries Research Board of Canada.) UPSTREAM MIGRATION OF ADULT SALMONIDS 105 addition to the native stocks. In other words the increase in immigrants was at the expense of stocks in neighbouring rivers. In 1943 in a further series of experiments, the freshets were started earlier, and a sharp, though slight, artificial freshet was made every few days. The run developed steadily. On 8 July, when counting became impossible, more than three times the average annual number of salmon had gone upstream. Between 25 and 50% of the grilse returning were of foreign origin. Huntsman cites this as further evidence of the attractiveness of artificial freshets, but a similar proportion of foreign fish have been observed in the River Axe (Allan, 1966~)which has no provision for artificial freshets. It was observed that salmon started to enter the river as the freshet developed, but that the principal ascent came as the river was falling again. In shallow water fish ran chiefly for an hour after dusk, diminishing in numbers throughout the night and stopping at sunrise. In high water the fish would ascend both by day and by night. Although it is not stated, it is reasonable to assume that the high water was turbid. Similar behaviour has been noted for brown trout by Munro & Balmain (1956). As in the Margaree River, the drawback with the work on the River Moser is that it is nowhere made clear what was the relationship between the normal dry weather flow and the size of freshets used. The work of Hayes (1953) on the Le Have River, Nova Scotia, has supplied more accurate measurements of freshet volume. Figure 9 illustrates the general relationship between water volume, numbers of fish, tides, angling catches and windspeed and direction for a period in 1951. Under natural conditions the river flow might fall to under 50 cusec, but the results suggested that at least 200cusec were needed to maintain a good run of fish. In practice, the general aim was to keep the river at 400 cusec as long as supplies of water lasted, and to add four-hour freshets of up to 1600cusec at intervals. After three years work the author came to the following conclusions. (1) Large or small natural freshets are capable of moving fish when other factors like wind and tide are favourable, otherwise they have no effect. (2) Major runs can occur without the aid of natural or artificial freshets and can be maintained by a steady flow of water during the run season. (3) Artificial freshets can move fish, which happen to be at the head of tide, into fresh water, but are unable by themselves to move fish into the estuary, but if they are timed with wind and tides they could probably bring fish into the estuary as well (Fig. 10).

x0 500 G'

2 6 10 14 18 22 2 6 10 14 18 22 2 6 10 14 18 22 2 6 10 14 18 22 16 June 17 June 18 June 19 June FIG. 10. Example of the type of freshet production which appeared to be most successful in 1950. Two freshets were produced on successive days. Apparently the first one brought salmon some distance up into the estuary, and the second one took them into fresh water. Observations were made at the head-of-tidefence (Hayes, 1953). (Reproduced with permission from the Journal of the Fisheries Research Board of Canada.) 106 J. W. BANKS

(4) The reverse of a freshet, that is, cutting down river level and then increasing it again, may also act as an effective stimulus in moving fish. (5) Temperature appeared to have little effect in initiating runs. (6) Fish move out of tidal waters into fresh water at dusk and light change could be the operating factor (Fig. 13). (7) Strong onshore winds, approaching 20 m.p.h. induce salmon to concentrate in the river estuary and eventually ascend (Fig. 9). (8) Peaks in the tidal cycles representing daily increasing difference between high and low tides seem to be effective in concentrating salmon in the estuary and initiating a run into fresh water. From these conclusions Hayes proposed the following plan of water control. (1) The river should be maintained at a steady 400 cusec during summer as long as supplies last. More water would be needed at the beginning of the season. (2) Nature should be allowed to take its own course in initiating the run of fish up the river, but the run should be maintained by controlling the water level and applying a freshet stimulus when the run shows signs of dying out. (3) Water should not be wasted haphazardly on numerous early artificial freshets. (4) Positive freshets should be timed to reach the head of tide at dusk. (5) Freshets are most likely to be successful when related to spring tides and strong onshore winds. (6) Inverse or negative artificial freshets, that is cutting down river level, and then returning it to normal should be tried on two successive nights, timed to reach the head of tide at dusk or dawn, and related to favourable winds and tides. These negative freshets will be indicated when the supply of water is low. With some qualifications, many of Hayes’ conclusions can be supported for other species and other rivers. This is the most comprehensive piece of experimental work in this field, but his plan of water control can be criticized on a number of points. These criticisms stem from two allied sources, first the experiments where orientated towards the interests of anglers rather than designed to promote the salmon stock of the river, or conserve the water supply, and second the plan of control seems to aim at short term results. A flow of 400 cusec may supply continuous, excellent angling in the Le Have River, but will be far more than is necessary to maintain the stock of migratory fish. Hayes admits that the river flow may often fall naturally to only 50 cusec. A flow of perhaps 100 cusec, augmented by weekly freshets might be quite enough to prevent a large build up of fish in the estuary, and allow them to move steadily upstream to the spawning beds, giving adequate, but intermittent, angling success. Clearly, if the storage resources of the watershed are adequate to supply a volume of water which will continuously stimulate fish to ascend, then this will be beneficial to the angling but where angling is not the prime resource other interests may dictate a lower level of water release. The particular aim on all these rivers was to induce salmon to run early in the season when they are in good condition, but a system of water control which stimulated fish to ascend early, and then abandoned them to their chances in the shallow upstream waters might be disastrous in a dry season. Deoxygenation, high temperatures and disease through overcrowding would all take their toll. Hayes’ suggestion that the river should be maintained at 400cusec while supplies lasted would be extremely hazardous if analogous flows were applied uncritically elsewhere. UPSTREAM MIGRATION OF ADULT SALMONIDS 107

The use of freshets on successive nights is also recommended, but more results would be needed to justify this. In the 1950 season this technique was used once successfully. It was suggested that the first freshet brought fish up into the estuary, and the second stimulated them to enter fresh water, but although two further trials were made in 1951 they were both completely unsuccessful. Hayes’ suggestion that negative freshets should be tried when water supplies are small, is likewise based on very few actual experiments. The data from three years work on the Le Have River show that although freshets will cause salmon to run, the presence of fish in the area where they can be influenced by a freshet is dependent on suitable combinations of wind and tide. Once the stock of salmon in or near the estuary is exhausted, no freshet, natural or artificial, can cause a run of fish. Baxter (1961) examined the water requirements for migratory fish on a number of British rivers, and produced a plan of water control which took account of the likely needs of the fish at all stages in their life history. This author strongly advocates the use of freshets in any river system which has been regulated by man. Although no figures are given for the relationship between flow and migration, Baxter’s statements are based on long experience of the kinds of regime which have proved effective on the headwaters of the Tweed, and in the schemes of the North of Scotland Hydro-electric Board. The flow data from other rivers has been used to show how his conclusions would apply elsewhere. The measure by which rivers are assessed is the average daily flow (A.D.F.). At this level the river is approaching a minor spate. He shows how rivers have characteristic- ally different amounts of time during the year in which the flow is at various proportions of the A.D.F. Generally speaking, the smaller the stream the greater the proportion of the year in which it has low flows, larger rivers are more stable, but all rivers will vary according to the amount of underground or lake storage which can contribute to the flow. Another characteristic difference between large and small rivers is that the latter have much more of their bed exposed at low proportions of the A.D.F. At A.D.F. smaller streams will occupy only one-third to one-half of their bed, whereas in larger rivers at the same fraction, the only effect may be a reduction in water speed and depth. The usual minimum dry weather flow of a river usually roughly corresponds to 6 A.D.F., below this, conditions for fish life become more difficult especially at high temperatures, and in shallow water where overcrowding may be a danger. In winter, slightly lower flows can be tolerated in larger rivers without ill effect, From these considerations the author produced the following schedule of flows, stressing that it was not intended to be rigidly applied, but only a guide which could be changed to meet the needs of individual rivers (see Table IV). For small rivers this schedule represents an annual mean of 18.5 % of the A.D.F. and for larger rivers 15 %. This basic schedule is intended to provide adequate flow and bottom coverage, for example at times when these are needed for spawning, and during the early summer when a larger area of wetted river bottom will allow greater food production needed during the growing season of the parr (Carpenter, 1940; Allen, 1941). This schedule does not provide adequate conditions for the ascent of migratory fish, but it is intended that sufficient stored compensation water should be available to provide freshets. Early in the season, temperature may be the factor controlling migration, especially in the ascent of obstacles (Stuart, 1962; Menzies, 1939), the rivers are often in spate, 108 J. W. BANKS

TABLEIV. Schedule of flows, exclusive of freshets (Baxter, 1961)

Smaller rivers Larger rivers Month % A.D.F. % A.D.F. Remarks October 15 to 123 15 to 12+ in alternate weeks November 25 15 December 25 to 12+ 15 to 10 25 and 15 normally only in first 2 weeks January 123 10 February 12: 10 March 20 15 April 25 20 May 25 20 June 25 to 20 20 to 15 in alternate weeks July 20 to 15 15 to 124 in alternate weeks August 15 15 to 124 in alternate weeks September 15 to 123 15 to 12+ in alternate weeks and it is considered that freshets will be unnecessary at this time. Once the temperature has reached 42” F fish will move upstream in flows of 30 to 50% A.D.F. in lower reaches, and 70% in headwaters. In addition, early spring fish at low temperatures may require up to 70% A.D.F. to induce them to enter rivers. This view has been supported by Sedgewick (1962) who pointed out that at such times high flow for long periods was the normal condition in many rivers, and that absence of such flow in abstracted or diverted rivers could mean that the early run of fish was lost or much reduced. Where the dam is well downstream, so that there will be little natural augmentation to the compensation water, Baxter considered that weekly freshets should be provided from the time that the fish are expected to enter the river until spawning time. Where the dam is high upstream a few freshets in summer to bring fish through the fish pass may be all that is needed if there is adequate natural spate water entering below the dam. In a dry year it may be possible for extra freshets to be provided in order to avert dangerous conditions. Where the compensation water has been fixed at a moderate level, it may be invaluable in really dry years, a notable example occurred on the River Wye, where Hodges (1962) stated that at Hereford, 50 miles downstream from the Elan Reservoirs, on one occasion the compensation water accounted for 41 % of the total flow. Without this water the conditions in the Wye would have been serious. The duration of freshets need not be longer than 18 h of which only 12 should be at full rate, and the remaining six tapering off to base level. Baxter (1961) was of the opinion that fish would respond as readily to sluice water as to a natural rise, in Baxter (1962) this is modified to show that compensation water, including freshets, should be withdrawn from the upper levels of reservoirs. In thermally-stratified reservoirs the bottom water is likely to be both more deoxygenated and colder than the surface water, Law (1962) challenged this view, stating that experiments by the Fylde Water Board had shown that compensation water drawn from bottom levels in a reservoir had stabilized its oxygen concentration and temperature within 200 yd (180 m), but he gave no figures on such vital points as the degree of thermal stratification, or deoxygenation, or the depth of the reservoir. The results of the experi- UPSTREAM MIGRATION OF ADULT SALMONIDS 109 ments of the Fylde Water Board must be considered unsuitable for general application in view of the figures given by Thompson (1954) and the comments of Pearsall(1954), who pointed out that the effect of bottom water for compensation is likely to be most serious when it is drawn from reservoirs with a high mineral content and productivity. These conditions will occur most frequently in south eastern England and generally in the lowland zone of Britain. It is obvious that the conditions in which a river authority or water undertaking will want to use reservoir bottom water for compensation will be those where such water will be least desirable for the fish. For example in a drought in late summer, with deoxygenation of the lower levels of the reservoir, and minimum flow in the river, the use of bottom water could be a danger to fish life, and very probably a deterrent to upstream movement in the vicinity of the dam. A river water which is a mixture of a relatively large quantity of bottom compensation water, and a small amount of reservoir surface water coming down a fish pass, will resemble the former more closely, and as a result fish will be reluctant to enter the pass to whose water they are not acclimatized. This deterrent effect could operate in much less extreme conditions than those which actually endangered fish life. An instance of this kind was recorded by Pretious & Kersey (1957). Further work is needed to evaluate this danger on British fish passes. Andrew & Geen (1960) were of the opinion that the provision of suitable hydraulic conditions was the only method of inducing fish to use fish passes, provided that other conditions, such as the thermal barrier just mentioned, were not deterring the fish. They described a number of artificial guiding methods, but these were mostly means of guiding downstream migrants at dams, or else for repelling fish from places where they were not wanted, for example, turbine tail races, rather than attracting them to actually use fish passes. It should be noted that the effects on fish behaviour of new impoundments may not be restricted to deterrent effects of their water, or of alteration of the flow. Saunders (1960) noted that a five acre impoundment on Ellerslie Brook, Prince Edward Island, exerted a marked retaining influence on fish migrating upstream. Of those which ascended the fish pass only a much smaller proportion proceeded further upstream. The reasons for this are unknown. Andrew & Geen (1960) have expressed fears of a similar effect on the Fraser River, British Columbia, if the proposed large dams are built there. A deterrent effect of impoundments on downstream migration of smolts and kelts has also been noted by Pyefinch & Mills (1963), and Mills (1964). These authors, and Mills (1965) have investigated the migration of adult salmon in the Conon River system, which has been much altered by the building of several dams. Artificial freshets increased the flow through the fish pass from the usual 37 cusec to 121 cusec, but they were ineffective in moving fish. Heavy rain which increased the flow from a burn entering the river just above the trap, but below the dam was more effective. No correlation could be found between fish movement and air or water temperatures, barometric pressure or rainfall, although there was a general impression that most fish entered the trap during rainy weather. There are a number of factors which could influence the catches of adults in the trap on the River Meig. In order to reach it they must have ascended the TOITAchilty Dam by a Borland fish lift, passed through Loch Achonachie, and then, at the junction of the River Conon and River Meig they are presented with a choice of two streams, both of which contain water from the River 110 J. W. BANKS

Meig. The water impounded by the Meig Dam is partly diverted through a tunnel into the neighbouring watershed. If fish are influenced in their choice of stream by recog- nizing the characteristic ' taste ' of water from their natural stream, as Hasler (1954), Hasler & Wisby (1951) and Wisby & Hasler (1954) have suggested, then the junction of the River Conon and River Meig will present a very confusing situation. Further- more, the flow in the Conon itself will be very variable, as generators come on or off load at the five power stations. Mills (personal communication) states that there were so many variables and complicating factors that it was impossible to find any cor- relations between rainfall data, loch levels, and the numbers of ascending fish. The complexity of the Conon system contrasts with the situation on the River Coquet in Northumberland where the Warkworth Dam impounds water at the head of the tide, which is then abstracted for domestic purposes. Unpublished data in the possession of the Northumberland River Authority records the passage of fish over the two passes at the Warkworth Dam, and the flow rate in the river above, from 1956 onwards. Visual inspection of these records reveals a very strong correlation between runs of fish and increases in flow, except between late December and the end of March. In this river, 1961 can be taken as an example of a year in which the salmon showed a simple migration pattern. The first major flow increase, on 10 July initiated a run of fish which continued until the end of August. Although there was only one more major freshet during this time, on 7 to 9 August, a good flow of water was continuously maintained. A rise to approximately 250 cusec initiated another short run on 13 September. October freshets also brought runs, but all fish had apparently entered by early November, and there were no more until April 1962. In 1964 there was a run with a maximum of 35 fish per day in early June, just preceded by a river rise to 4 ft (1 m 20cm) approximately 1700 cusec. The river was then low through July, when it rose to 3 ft (nearly 1 m) (or 830 cusec) in mid August this was followed by a run of 228 fish. A foot rise in midSeptember produced a run of about 10 fish over 5 days, a 3 ft (1 m) rise in the first week of October produced another 87 fish, but a 5 ft (1 m 50 cm) rise 6 days later produced only another 14 fish. Heavy freshets during November and December were also associated with small runs. The flow records are estimated at a gauging station which records the water height above dry weather flow, and although an accurate calibration curve is not available at present, it seems that a rise of 1 ft (30 cm) above dry weather flow is normally needed to initiate a run of salmon. The correlation between flow and migration is strongest from late July to early September, the time when the main run of fish comes into the river, but this period may start earlier, or be extended in a dry year. A freshet which brings in a large run, as happened for example in October 1964, appears to reduce the numbers in the next freshet if this follows soon after. A close correlation between runs and flows will be subject to the availability of fish in the vicinity, this is in agreement with the findings of Hayes (1953) and Davidson et al. (1943). Stewart (1966, 1968a, b,c,d,e,f) has described the first results from the stations on the Rivers Lune and Leven at which the numbers of fish moving upstream are automatically recorded, together with fish size, water level, turbidity, humidity, barometric pressure, air temperature, water temperature and dissolved oxygen. These stations have produced a very large amount of data, and have begun to provide an objective basis for the assessment of the water requirements for fisheries in these rivers. UPSTREAM MIGRATION OF ADULT SALMONIDS 111

The relationship between movements of salmon and water levels in the Lune and Leven are discussed in Stewart (1968a, 6). From May to October at Broadraine on the Lune, where the A.D.F. is 240 cusec, 80.5% of all salmon move upstream on flows of 460 cusec or less. There is a peak of movement at 400 cusec, a flow rate naturally available for just over 8 % of the time, and there is a lesser peak at 175 cusec, a flow available for 22% of the time. These peaks correspond to the peaks of activity of summer fish and spring fish, respectively. A flow of 90 cusec, or less, is available for approximately 39 % of the time, but only 9.4 % of the fish move upstream on such flows. In the Leven, where the A.D.F. is 510 cusecs at the fish counter, the peak of fish movement is at 440 cusecs, this flow is also the peak of the percentage availability curve for water, occurring for nearly 24% of the time. It is difficult to make direct comparisons between the Lune and Leven results because the counting station on the former is 26 miles upriver, whereas the latter is at the head of tide. Moreover the Leven flow is regulated by Lake Windermere, while there is no storage on the Lune. Nevertheless, Stewart points out the similarity between the water depths below the two weirs at which the mean frequency of salmon movement takes place, although the significance of this is not yet clear. Stewart concludes that a mean flow of 245 cusec must be available at Broadraine on the Lune for 55 % of the time from April to October, and that on the Leven a mean flow of 500 cusec should be available for 55 % of the time in the same period. Radical alterations to the naturally-occurring frequencies of mean flow will be detrimental to the fisheries. The water flow requirements for angling are discussed in Stewart (1968~). The analyses are made from catches on the lower Lune, and there is therefore some uncertainty about interpreting these results in relation to movement and flow data from Broadraine. It appears, however, that the flow range at which most fish are taken is also the one in which there is most fish activity. Stewart (1968$ e,f) deals respectively with movements in relation to air and water temperatures, to darkness and daylight, and to rising, falling and steady water levels. From these reports he observes that from June to August a high proportion of fish move when air temperature is less than water temperature, but that temperature differentials are less important at other times. From June to August both the total numbers, and the numbers moving per hour, are greater during darkness, but in May the reverse is true, while in April, September and October no trend is discernible. If one takes into account the numbers of fish recorded under three main river conditions the relationship between fish movement and water levels show that on falling levels significantly more (P= <0.001) fish moved, on rising levels significantly fewer fish moved, and on steady flows the same number moved as could be expected by chance. Many of Stewart’s conclusions from this important pioneering work are necessarily tentative, and much of the analysis presented so far has been an examination of variations in numbers of fish moving, time, and one other parameter. When examinations of simultaneous variations in several parameters have been made in order to assess their interaction, much more detailed information can be expected. Without computers and suitable statistical techniques it is impossible either to make such examinations, or to cope with the very large quantities of data which become available from automatic monitoring equipment. 112 J. W. BANKS

2. SEA TROUT SALMO TRUTTA LINN. There is no work published specifically on the effects of artificially controlled discharges on sea trout, but Baxter (1961) observes that they normally occur in the same waters as salmon, and that the requirements for salmon will be more than enough to cover the needs of sea trout.

3. STEELHEAD, RAINBOW TROUT SALMO CAZR DNERZ RICHARDSON Shapovalov & Taft (1954) examined the environmental factors associated with spawning runs of steelhead in Californian coastal streams. The period of the spawning run was associated with the period of rainfall, but it was impossible to show a quantitative relationship between stream flow and run size. Although flow increases brought about spawning runs, the numbers of fish moving depended on the seasonal trend and on the nature of the particular rainstorm. Often the sudden cessation of a storm would cause fish to stop running and wait in the pools below the fish trap. No further movement would take place as long as fair weather continued, even if the fish became sexually ripe. This is in contrast to the behaviour noted for most salmonids, where sexual maturity leads to an attempt to reach the spawning beds whatever the conditions, e.g. Davidson ef al. (1943) for pink salmon, Sedgewick (1962) for Atlantic salmon. Light rain and a small river rise would then be sufficient to send them upstream. Most movements over the weir were by day, with a morning and an afternoon peak of activity. This behaviour pattern was not related to changes in discharge, although stream temperature and the light intensity must have changed. Similar patterns have been observed for sockeye salmon passing the Rock Island Dam on the Columbia River (Ward, 1939), but Chapman (1941) reported that sockeye at this dam ran up mainly in the morning, but on the middle ladder the numbers increased as the day progressed. The steelhead and Chinook salmon ran in greater numbers through the middle of the day. Chapman's conclusion that the factors influencing the movements of fish through the ladder were multiple with complex interrelationships seems fully justified. Briggs (1953) presented some observations on the behaviour of steelhead at the Sweasey Dam, California. The 1949 run did not migrate over the dam in the usual way when river level rose, apparently because the water was unusually cold. Later, a warmer rain initiated the spawning run. Brigg's conclusion that this might constitute evidence that salmonids react more closely to temperature than to fluctuations in water volume seems too general. It is more likely that in this instance the unusually low water temperature was simply inhibiting movement. It was stated by Menzies (1939) that Atlantic salmon in Britain will not readily pass obstacles when the temperature is below 5" C, and it is probable that a similar block was operating at the Sweasey Dam.

4. SOCKEYE SALMON ONCORHYNCHUS NERKA (WALBAUM) In his study of the Somass River, Ellis (1962) counted salmon jumps at a 6-ft (1-9m) log dam at the head of the tide. Periods ofjumping lasted several days but had a 24-hour rhythm. Jump counts were considered by Ellis to be a reliable indicator of migration, but when compared to environmental records they showed no relation to air or water temperatures, fluctuations in river discharge, rainfall, changes in concentration of dissolved organic matter or hours of sunshine. Increases of jumping took place within 24 hour of a change from relatively stable sunny weather to cloudy weather. Such UPSTREAM MIGRATION OF ADULT SALMONIDS 113 changes were associated with cyclonic weather conditions but only light rain or none at all, so there was no higher discharge. Removal of logs from the dam to produce a freshet had no effect, but no information is given about the size of the freshet. Many other authors have demonstrated the effect of freshets following heavy rains, which result from the passage of cyclonic weather and movement of atmospheric fronts over the watershed. Ellis concluded that the only factor common to these situations and the Somass River was the weather change arising from the approach of a warm front. He considered that this released upstream movement by salmon accumulated offshore possibly as a result of a visual cue from the presence of cloud formations. This conclusion only marginally conflicts with the evidence of the value of artificial freshets in stimulating migration since these have been shown to be most effective when other natural conditions, particularly wind and tide, are also favourable for migration. Wind was not a factor measured by Ellis, but winds, and probably strong onshore winds, might be expected to be found with a change to cyclonic conditions. Huntsman (1948) and Hayes (1953) both mention runs persisting for several weeks in the presence of high flows artificially produced from storage dams. Presumably cyclonic conditions were not maintained throughout this time, so the explanation put forward by Ellis is probably not complete. The pink salmon runs investigated by Davidson et al. (1943) sometimes showed positive reactions to freshets, but this was overridden by an urge to migrate in any conditions once the gonads were mature, some such factor as this may explain the indifference to the presence or absence of cyclones in the long con- tinuing runs cited by Huntsman and Hayes. The work of Ellis on the Somass River was largely concerned with the entry phase of salmon migration, which is likely to be the most important in short rivers. The long migration up to the spawning beds is equally or more important in large rivers like the Columbia and Fraser. Not only do such rivers have much greater length, and possibly many obstacles, but the characteristics of the water and its volume will change slowly on a seasonal basis rather than in response to short term changes in the weather. Because of their size rather little is known about the factors which affect the timing of entry of salmon into these rivers, On the Fraser River it was considered by Gilhousen (1960) that the total volume of flow for some period before the upstream migration of the lake run of sockeye to the Adams River may affect the duration of the river migration. This effect is brought about by the influence of the fresh water on oceanographic conditions in the area of the estuary. In years of high run off the main migration into the Fraser takes place between 15 and 30 September, but in low run-off years, the delay at the river mouth is extended. In such years the last part of the run may arrive upstream too late for efficient spawning because their metabolic reserves have been depleted, or they may not get there at all. The movements of salmonids have been studied at various large dams, particularly on the Columbia River. The migration of sockeye and Chinook salmon at the Rock Island Dam is controlled by the proportions of total water and turbine water, and by the location of open spillway gates with respect to the fishway ladders (Leman & Paulik, 1966). At intermediate discharges (140,000 to 300,000 cusec) it was demonstrated that the preference of the fish for either the right or centre ladders could be controlled by spilling water adjacent to the ladders. At high tailwater elevations attraction of sockeye to the spill was rapid, but at low levels there was evidence that the turbulence at the entrance to the right ladder discouraged sockeye, but not 114 J. W. BANKS

Chinook salmon. Chapman (1941) demonstrated a diurnal variation in preference for the right or centre ladder at this dam so daylight probably modifies the dominant influence of the prevailing hydraulic conditions at the fish pass entrance.

5. CHINOOK OR SPRING SALMON ONCORHYNCHUS TSHA WYTSCHA (WALBAUM) The migration of Chinook and coho salmon over a fish pass on the Cowichan River was studied by Neave (1943). The first autumn movements of fish coincided with a slight rise in water level, and the first big runs of fish came with a large increase in river volume. The number of fish per hour were counted on a pass at the Skutz falls, where there was a daily peak between noon and 3 p.m. Sometimes this single peak was replaced by morning and afternoon peaks, but very few fish ran during darkness (see Fig. 12). Changes in water temperature did not account for the diurnal fluctuations, and neither tidal cycles nor artificial light at night had any effect on the rate of migration. These observations are in agreement with the finding of Leman & Paulik (1966) that Chinook salmon at Rock Island Dam run during the middle of the day, and although it is apparent that the rate of discharge had overall importance in initiating the run on the Cowichan River, the passage of this obstruction seemed to be dependent on the presence of adequate light. In California, Chinook salmon moved mainly during the daytime (Shapovalov & Taft, 1954) but the arrival of runs of fish in the river showed a definite relationship with stream flow, although the authors were unable to express this quantitatively.

VI. DISCUSSION Having considered the observations species by species, they will be discussed under six headings: (1) rate of flow; (2) problems of flow at dams, diversions and fish passes; (3) temperature; (4) water quality; (5) general weather, wind and tide; (6) light intensity. The rate of flow is the factor most frequently cited as controlling the rate of upstream migration, but its effects are often modified by others. Under the artificial conditions of impoundments these other factors may assume greater importance, because changes in them will no longer have the same relationship to flow changes which they had under the pre-existing natural conditions to which the fish population was originally adapted. Although the rate of discharge is thus of overwhelming importance in most instances, the opportunity to vary the flow artificially depends on the presence of a storage dam. As all impoundments change the character of the water which passes through them, even if only slightly, it is necessary to understand the kinds of change which damming brings about, together with the kinds of effect which different types of water use can cause to the river below the dam, and to its chemical characteristics. These effects will influence the ease with which fish can be induced to use the passage facilities provided, and the changes in rate of upstream migration which can be brought about by artificially increased flows.

1. RATE OF FLOW A large number of the publications reviewed have been primarily concerned with the variation of migration with rate of flow. From these, the overwhelming impression gained is that this is the dominant factor in most situations, although adverse temperatures and light conditions may modify or inhibit migration under UPSTREAM MIGRATION OF ADULT SALMONIDS 115 conditions of flow which would otherwise be satisfactory. Inhibition by water temperature is particularly noticeable where the fish have to pass an obstacle. The relationship between migration and flow rate is most marked in small streams which have rapid run off, a fairly short spawning season, and a species of salmonid in which there is little overlapping of year classes on the spawning beds. If previous studies have been made in a particular stream, which indicate the likely size of the run for a given season, the numbers of salmon likely to ascend in any freshet can be predicted with some accuracy from the size and duration of the freshet, the time elapsed since the previous freshet, and the time in the season. This kind of relationship is well exemplified by the pink salmon population of McClinton Creek (Pritchard, 1936) and Hooknose Creek (Hunter, 1959) and to a lesser extent Snake Creek and Sashin Creek (Davidson et al., 1943) but on the whole, the relationship between quantity of discharge and sizes of other adult fish runs in the Pacific North West has not been well documented (Bell, personal communication). It is not known whether the above-mentioned results are typical even for the pink salmon, and the position is made more complex by the presence of at least six species of anadromous salmonid in that region. The availability of water has not been a major problem there, and research into other factors in the life history has needed a higher priority. The life cycle of the Atlantic salmon does not have the strict biennial periodicity of pink salmon. Fish hatched in a given year do not all become smolts in the same year, and their sea life may vary from a few months to three years or even more. The variation in some rivers is much greater than in others. In addition, the period during which fish enter rivers is longer, both here and on the other side of the Atlantic. In spite of this, there is a correlation between stream flow and numbers of incoming migrants, although it cannot be predicted so accurately, or reduced to a mathematical formula. This relationship is most clearly seen in Huntsman (1939, 1948), Hayes (1953), Harriman (1961) and in the data of the Northumbrian River Authority. In these investigations it can be seen that increases in flow stimulate the fish to ascend the river, both where there are physical obstacles, and where it is unobstructed. Tncreases in flow also stimulate fish to enter fresh water. This stimulus appears to result from the increase in quantity of fresh water in the sea in the vicinity of the river mouth. To be effective, the fresh water needs to be mixed with sea water and distributed in the sea, this will depend on winds and currents. This aspect is further discussed under general weather, wind and tide. Huntsman, Hayes and Harriman all proposed regimes of water control for angling which required a continuous high level of discharge to be maintained as long as possible; in practice there will seldom or never be enough water available to keep up very high flows for the long periods during which salmon enter most British rivers. Of these authors only Harriman advanced any data to show what kind of minimum flow would stimulate fish to ascend. A more economical way of using water has been proposed by Baxter (1 96 1). This sets down certain minimum flows in different kinds of rivers at different seasons, and makes provision for freshets of 70 or 100 % of the average daily flow (A.D.F.) every week during the migration season. Over the year as a whole the quantity of water which Baxter calculated would be necessary to maintain all phases of the fishes life history is approximately 20 % of the A.D.F., although he stated that variation to meet the needs of particular rivers would doubtless be necessary. These calculations only apply where there is storage in the watershed capable of supplying freshets. 116 J. W. BANKS

There are data available from two British rivers which at present lack storage, the Axe and the Lune. The A.D.F. of the Axe is not stated by Allan (19666), but rough calculations made from Table I show that in 1964 it may have been approximately 170 cusec. There were 284 days with flows below the A.D.F. on which 140 salmon passed through the trap, in other words approximately half a salmon per day. There were 82 days with a flow above 172 cusec on which 239 salmon ascended, or approximately three salmon per day. At the A.D.F., a river is approaching the conditions of a minor spate (Baxter, 1961) so in other words on this rather crude estimate, spates were about six times more effective in bringing salmon into the river than lower flows. In fact, their effectivenessis likely to have been higher still, because fish ascend both while the water is rising and especially while it is falling again after the flood crest has passed (Baxter, 1961 ; Munro & Balmain, 1956). These periods are as much part of the spate as the actual period of high flow itself, but there is no way of knowing how many salmon ran at such times from the data given. Baxter regarded $ A.D.F. as a typical dry weather flow. Table I shows that such flows occurred in the Axe on 84 days in 1964, and during these conditions 42 salmon passed through the trap. Between & A.D.F. and the A.D.F. 112 salmon, approximately 30% of the total run, passed through the trap in 258 days. Although some of these fish must have ascended during minor variations from the dry weather flow, many must have ascended as the water was rising to or falling after, a major freshet. There must have been many more days on which freshets did not reach the A.D.F., but were strong enough to stimulate fish movement. As Allan made clear, the data from the Axe show conclusively that not all salmon ascend in flood conditions, but a close examination of his data shows that the majority migrated at times when the water was above $ A.D.F., i.e. when there was at least some freshet water in the river. The water requirements of the Rivers Lune and Leven have been assessed by Stewart (1968a, b) using the criterion of mean flow requirement, rather than percentages of the A.D.F. as used by Baxter. The mean flow is probably a more relevant measure than A.D.F. in these unregulated rivers from which so much data is available. The data of Stewart for the Lune and Leven, and Allan for the Axe, show considerable similarities in the relationships between upstream movement of salmon and flow of water, despite the differing character of the runs and siting of the counting stations. The proposals of Stewart for the Lune and Leven would provide somewhat more water at most times than indicated in the schedule of flows given by Baxter (Table 4), but it should be remembered that in the unregulated Lune and Leven, Stewart was not able to make any extra provision for artificial freshets. It is assumed that natural freshets would be sufficient to provide the extra stimulus needed from time to time. The flow data make it clear that this would be true, provided that the freshets were not all absorbed by large artificial storage built in the Lune catchment, or by heavy abstraction from Windermere which would adversely affect the flow of the Leven. Generally, the minimum quantity of flow needed for fish to ascend can only be assessed experimentally where the flow can be regulated by means of stored water. None of the work done on any river system has yet fulfilled this requirement, Baxter (1961) probably comes nearest to achieving a fully worked out scheme. Although his recommendations did not have the supporting weight of experimental evidence on fish ascent, they were largely accepted by those fishery biologists with experience of these rivers which Baxter had used as examples. Nevertheless, as far as any comparison is possible with unregulated rivers, it would appear that on the Axe at least, larger UPSTREAM MIGRATION OF ADULT SALMONIDS 117 freshets than those proposed by Baxter are the most effective in bringing fish in from the sea. There is a very real conflict between the interest of anglers and other water users, this is clearly brought out in the work of Huntsman, Hayes and Harriman. These authors were primarily concerned with means of supplying good angling, and consequently advocated high levels of discharge, well above normal dry weather flow, supplemented by still larger freshets. The high levels of flow were enough to keep any salmon in the area running into the river continuously, and thus always available for anglers. Under the sort of regime proposed by Baxter, the fish would be held back at the river mouth, or at obstacles upstream, and would move slowly upstream except during the few hours each week when the freshet was released. Such a regime might well be sufficient to maintain the stock of fish, but will reduce the time during which angling is likely to be successful. Thus only a consideration of all the factors involved can resolve such a conflict of interests. Huntsman (1948) showed that as a result of artificial freshets, the run of Atlantic salmon and brook trout into the Moser River were more than twice as large as had been expected from previous studies. It has been shown by Saunders (1960) working on Ellerslie Brook, a small stream on Prince Edward Island, that annual variations in discharge determined the total number of salmon ascending the stream. Chance variations in the rainfall pattern are likely to cause variations in the annual discharge of small streams to be greater than in larger rivers in which the effects of local variations will be averaged out. It may be that in an area where there are several small streams with runs of salmonids, chance rainstorms might bring freshets favourable to salmon ascent to some streams but not others, particularly in a dry year. When this happens, it is possible that the homing of the fish breaks down to some extent, and fish ascend the stream which has freshet conditions. The results published by Huntsman and Saunders suggest that the numbers of fish each season entering the rivers which they studied were at least in part dependent on flow conditions which could be artificially altered, as was done by Huntsman, or could be subject to chance variation as was probably the case on Ellerslie Brook. These increases in numbers of fish running as a result of local changes in discharge presumably took place at the expense of the runs into neighbouring rivers. Although the evidence for homing is strong, and is undoubtedly the general rule on which most management policies must be based, it is not an invariable rule, both Allan (19660) and Carlin (1964) note that homing is not so well developed in sea trout as it is in salmon. Spawning in strange streams or tributaries is known to take place in species of Pacific salmon. It is possible that where spawning runs are small and the suitability of the water conditions for ascent, or spawning, are likely to vary greatly from year to year, it is probable that a ' race ' of salmon will exist which is more flexible in its homing tendencies than we have been accustomed to expect. One conclusion to be drawn from this is that the introduction of artificial freshets to a river may cause fish to run into that river which would otherwise have gone elsewhere. This certainly seems to have happened in the Moser River. A further possibility exists where there is a river with a large run, and a number of streams with small runs. The large river might provide a ' reservoir ' of fish which could be drawn into the smaller streams by favourable water conditions. Such conditions might be artificially produced, or be the result of chance variations in rainfall. If a large run of this kind were destroyed, for example by pollution, the potential runs into the smaller streams along the sea migration route of the large run could be

C 118 J. W. BANKS adversely affected. Much of this is supposition and could only be resolved by fish tagging on a very large scale. Generally, freshets are highly effective in stimulating fish to move upstream, but Pyefinch & Mills (1963) found them ineffective at a dam in the Conon Hydro-electric scheme. The complex conditions which now exist in this river system may be responsible, and further work will be needed to determine the best means to induce upstream migration in such circumstances.

2. PROBLEMS OF FLOW AT DAMS, DIVERSIONS AND FISH PASSES The building of dams brings many problems for the maintenance of a stock of migratory fish. These have been very thoroughly reviewed by Andrew & Geen (1960) in relation to the Fraser River system. It is unlikely that problems of the same magnitude could result at British dams, but some of the difficulties arising at the Conon Hydro-electric scheme have been discussed by Pyefinch & Mills (1963) and Mills (1965). Many of these problems are related to the effects of temperature and changes in the physicochemical condition of the water, but some of the most important arise from the need to induce fish to ascend the obstacles, the best way to achieve this is to provide suitable hydraulic conditions. Because each situation is unique, it is not always possible to determine in advance whether the conditions in any given fish pass will be suitable when translated from the drawing board into concrete. Many have had to be modified after installation, but some general principles have been formulated. It is desirable at all fish pass installations, whether at dams or natural river obstructions, to place the entrance at the farthest upstream point which the fish can reach, and to provide a high velocity water barrier immediately upstream from the fish pass (Andrew & Geen, 1960). A velocity of 4 ft/sec (1.2 m/sec) is considered minimal for fish pass entrances by Andrew & Geen, although this velocity may not be needed throughout the ladder. At McNary Dam each fish pass has a minimum discharge of lo00 cusec at the entrance, but only 165 cusec comes down the ladder, the remaining 835 cusec is introduced near the downstream end by diffusion chambers in the floors of the pools. In high water conditions when the lowest pools are drowned, further auxiliary water is added to maintain a flow of at least 2 ft/sec (0.5 m/sec) over the submerged weirs. Many features of the performance of salmon and trout in weir passes (Fig. 11) have been discussed by Collins (1958). Stuart (1962) has described performance in pool and fall fish passes. Collins listed the features which he considered necessary to achieve

Weirs IMlhfOrifices ’ 40ft End view

Ic* I Plan 16fi FIG.11. Weir fish passes used at Bonneville Dam on the Columbia River (Andrew & Geen, 1960). (Ry courtesy of the International North Pacific Salmon Fisheries Commission.) UPSTREAM MIGRATION OF ADULT SALMONIDS 119 good fish pass design and showed that angular gradients as high as 1: 8 could be negotiated successfully. He also stated that the physical performance of fish varied with season. These points were confirmed for Chinook and sockeye salmon and steelhead trout by Gauley & Thompson (1963) who also showed that when the drop between pools was 1 ft (0.3 m) the passage of these species through pool and fall passes was as fast on a gradient of 1 :8 as on a gradient of 1 : 16. When the drop between pools was increased to 1.5 ft (0.45 m) on the 1 : 8 fish pass, the passage of Chinook and sockeye became significantly slower. In experiments described by Weaver (1963) in which steelhead, Chinook and silver salmon were offered a choice between waters of different velocities they showed a significant preference for the higher velocity in most of the choices. The most extreme choice was between 3 and 13 ft/sec (0.9 and 3.9 m/ sec). The performance of these fish at high velocities was also measured. At 13.4 ft/ sec (3.98 m/sec) 92 % of steelhead and 51 % of Chinook salmon passed right through an 85 ft channel, but at 15.8 ft/sec (4.54 m/sec) these figures dropped to 51 and 5%. Large fish did noticeably better than small ones. The rate of movement over a 30 ft (9 m) section of the channel was measured at 2, 4, 6, 8, 13 and 16 ft/sec (0-6, 1-2, 1.8, 2.4, 3.9, 4.2 mjsec). The speed of passage of steelhead and silver salmon increased up to 8 ft/sec (2.4 m/sec) then declined. The speed of Chinook salmon declined at lower water velocities. The maximum observed speeds, including water velocity, were 26.8 ft/sec (8-4 m/sec) for steelhead, 2.9 ft/sec (0.87 m/sec) for Chinook, and 17-5 ft/sec (5.25 m/sec) for silver salmon. The need for stable hydraulic conditions in fish passes was emphasized by Collins who showed that all movement ceased after changes from plunging to streaming flow in weir fish passes. The observations of Leman & Paulik (1966) have already been discussed in section V. They stressed that the entrance to the ladder should be in a position where the fish could find it, and showed that species react differently to a given set of hydraulic conditions. Where these are likely to vary widely the possibility of providing more than one fish pass must be considered, so that in all states of the river which migrating fish are likely to encounter, there will always be at least one pass which they can both find and use. The quantity of water needed in pool and fall fish passes will depend on the size of the pools and this in turn will depend on the maximum numbers expected to use the pass at one time, without causing undue delay. Andrew & Geen (1960) have discussed the dangers of building fish passes too small and shown that the resulting delays could adversely affect, or even totally prevent spawning success on the Fraser River, by sapping metabolic reserves too far. The design of fish passes has been discussed by Stuart (1962) who strongly advocates the creation of the hydraulic conditions normally found at natural waterfalls, in other words a deep hole below the fall, and a standing wave from which the fish can jump, as these are the conditions which the fish are best adapted to exploit to their own advantage. Brett & MacKinnon (1954) have shown that very low concentrations of extracts of mammalian skin acts as a strong repellant to coho and Chinook salmon in fish passes, causing them to drop back down to the bottom of the pass; it therefore follows that fish passes should be designed to keep the need for manual adjustments or cleaning to a minimum. Other discharge problems associated with impoundments arise from the reduced or variable flow which results from the fluctuating use of power stations. Andrew & 120 J. W. BANKS

Geen (1960) quote the report of the Canada Department of Fisheries (1958) on the Puntledge River, Vancouver Island. A flow of 1000 cusec is diverted from the river to a power station four miles downstream. Residual flow below the diversion dam is 100 to 200 cusec. This difference in discharge at the point where the water from the turbines rejoins the original channel results in the attraction and accumulation of salmon in the power station tail race. Migration upriver has in several cases been initiated by sharp increases in discharge over the diversion dam. Reductions in flow from the power station are accompanied by a downstream retreat of the migrating coho and sockeye at Baker Dam (Ward, 1939; Andrew & Geen, 1960), but sudden reductions can cause the stranding of fish (Menzies, 1962). The best use of fish passes at dams is therefore likely to result from deliberate spilling from the dam and fish pass carefully timed to coincide with shut offs in the power station. In practice this may not be easy to arrange. It does not seem possible to make a definite statement about the quantities of spill which would be needed to attract fish towards the collection facilities. Attempts to exclude fish from tail races have met with only limited success. Sedgewick (1962) described the attempt to use electric screen in the tail races of the Shannon Hydro-electric project. Fish which entered the tail race were stunned and floated downstream, but persisted in returning after recovery. They were not attracted to the water in the old river channel. Over a period the stock of salmon in the Shannon declined and only one small run survived. The hope has been expressed that repellent extracts of mammalian skin, as described by Brett & McKinnon (1954), might be used to deter fish from entering tail races. At the present time this seems a remote possibility. Even in the low concentrations required, a very large amount of extract would be needed. As an alternative to deterrence Andrews & Geen mention supplementary fish pass facilities built into the power station, but give no indication of the extent to which they are used by the fish. One final problem introduced by reduced flows below diversions has been cited by Hourston (1958) who pointed out that below a diversion dam low flows may create points of difficult passage, generally by aggravating such points already in existence. Engineering studies at these points, including the study of water surface profiles at various discharges before diversion, are necessary to determine whether such difficulties will develop, and what remedial action will be necessary.

3. TEMPERATURE The evidence of the influence of temperature on upstream migration is both con- flicting and inconclusive. Some experimental work indicates that salmonids have preferred temperatures. Fisher & Elson (1950) showed that salmon parr respond to an electric stimulus by a sudden movement whose length is a function of the strength of the stimulus and the temperature. The maximum response occurred at 15" C for Atlantic salmon and at lo" C for speckled or brook trout. When free to move in a horizontal temperature gradient salmon select and move into a temperature of 14" C and speckled trout of 10" C. The selected temperature approximates closely to the temperature of maximum response. This selected temperature may be the result of the previous thermal history, the season, and the age of the fish (Sullivan & Fisher, 1953). These authors showed that the temperature selected by the juvenile speckled trout fell during autumn UPSTREAM MIGRATION OF ADULT SALMONIDS 121 and rose in the spring, regardless of the temperature to which the fish were acclimatized. Sullivan (1954) demonstrated that the maximum cruising speed of speckled trout, measured at different equilibration temperatures, was greatest at the temperature normally selected. These tests were carried out on juveniles, but there is no reason to suppose that adults would not behave in a similar manner. Although temperatures well away from the optimum may inhibit movement altogether, it will be difficult to measure differences in performance which result from smaller deviations from the optimum temperature. There are several instances recorded where temperature barriers have played a part in governing salmonid movements in field conditions. This is to be expected from a consideration of the experimental results given above. Salmon entered the River Tay from the estuary when there was a rise in river water temperature and level, or a rise in temperature unaccompanied by a rise in level (Calderwood, 1903). Stuart (1953) stated that if the temperature of a stream was higher than that of the loch which it fed, migration into this stream would be inhibited. Spates only stimulated migration indirectly by lowering the stream temperature. In a later paper (Stuart, 1957) it was shown that runs of migrant brown trout from the lake to the stream were closely associated with rises in water level in the stream, and that during the time when spawning runs took place the loch temperature was almost always higher than that of the stream, but he considered that the possibility of an inhibiting effect of a high stream temperature was still present. In the Columbia River there appears to be a relationship between temperature and fish movement early in the spring, this is also correlated with flow, but temperature appears to be the dominant factor (Bell, personal communication). Briggs (1953) quoted an instance of steelhead trout failing to respond to increased discharge because the water was unusually and unseasonably cold. Menzies (1939) reported that in the Rivers Tay and Spey salmon would enter from the estuary when the temperature was 34" F (1" C), but when the temperature was below 40" F (4.5" C) they would not go beyond 15 or 20 miles from the head of tide. Below 42" F (5.50 C) they would not ascend obstacles, but above this they would pass upriver freely. This has been confirmed at the fish pass on the Pitlochry Dam (Pyefinch, 1955). In the Paratunka River sockeye salmon moved upstream on the positive temperature gradient which exists in this river every evening as a result of the daytime influx of water from melting snow. It seems possible that in this instance that temperature was covariable with other factors, particularly ionic composition, and the authors said that further work was needed to clarify this. Krogius, in an earlier paper on some tributaries of the Paratunka had shown that light intensity was probably the factor controlling migration, but that it acted through its effect on photosynthesis and temperature. This kind of situation will only occur in sluggish streams and is not likely to be a frequent occurrence. Calderwood (1908) stated that the order in which salmon enter the tributaries of the Tay in spring is the same as the order in which the temperature of these tributaries reached that of the main river, but here also there is a possibility that the stimulus is not a direct result of temperature but of some covariant parameter. The statement made by Stewart (1966) that most salmon are counted at Broadraine when the air temperature falls and the river temperature rises is unexplained as yet, but also seems unlikely to be a simple effect. Several examples have been published of instances where a difference in temperature between a river and the sea, or between a stream and a lake has had no effect on 122 J. W. BANKS migration between the two, Davidson et al. (1943) for the pink salmon, Munro & Balmain (1956) for brown trout, Pyefinch & Mills (1963) for Atlantic salmon in the River Conon system, Ellis (1962) for sockeye salmon, Lorz & Northcote (1965) for Kokanee salmon. The building of dams will always affect the temperature regime in the river below, the larger the dam and the deeper the impoundment the more drastic the changes will be. Even the comparatively small dams built in Britain may have severe effects when the impounded water is deep enough to develop a thermocline, and the compensation water, or turbine water is taken from near the bottom. This will result in the river below the dam being much colder in the summer than it was before the dam was built; in addition the water from the hypolimnion may be deficient in oxygen. Water in a fish pass will be spilling from the surface of the impoundment, and will therefore be much warmer than the deep drawn compensation water. As a fish approaches the entrance to the fish pass it will be presented with a choice between a large discharge of compensation water at a lower temperature, and a relatively small volume of fish pass water at a higher temperature. There will be additional chemical differences between the two. The fish will be acclimatized to the temperature of the water which results from the mixing of the two sources, but this will be closer to the temperature of the compensation water, or the water from the turbines, since these will have the greater volume. As the experiments of Fisher & Elson (1950) and Sullivan & Fisher (1953) demonstrated, fish are likely to select the temperature to which they have been acclimatized. In warm water this problem was acute at the Pelton Dam on the Deschutes River, Oregon (Eicher, 1958 ; Pretious & Kersey, 1957). Salmon were reluctant to enter the fish pass, and had to be trapped and transported upriver by tank truck. This also happened at the Baker Dam (Ward, 1930), but was overcome by increasing surface spillage. This will raise the rate of discharge, and produce a larger body of surface water at the foot of the dam in the area of the fish pass entrance, and hence reduce the thermal barrier. Reluctance to enter fish passes could be overcome at dams which store water for purely domestic consumption by spilling all compensation water from the surface, but this solution is likely to be unpopular with water undertakings who naturally wish to discharge their deoxygenated hypolimnion as compensation water (see for example Law, 1962). The effects on river temperature of doing this will not extend far downstream, but if a sharp temperature discontinuity is created at the entrance to the fish pass, free migration may be impaired. It might be possible to eliminate this thermal barrier by passing some of the compensation water into the lower levels of the fish pass. In dams for hydro-electric power the most serious difficulty may be to get the fish as far as the fish pass, in view of the attractiveness of high flows of lower temperature water in the tail race, but once the pass is reached the same considerations apply as to dams for domestic water supply. Fluctuations in the use of turbines may also cause variation in the temperature of the river downstream, which will be unsettling to the fish. It has been surmised (Ward, 1927, 1930; Andrew & Geen, 1960), that the unstable thermal stratification of reservoirs may be a partial cause of the unexplained loss of fish during migrations through impoundments. Ward (1930) produced evidence to show that if the Baker River found its level as it entered Baker Lake, relative to the temperature in the lake it would flow at a depth of 45 ft (13.5 m). Sockeye which were acclimatized to colder water from the deep level UPSTREAM MIGRATION OF ADULT SALMONIDS 123 turbine intakes would descend to below the level of the river inflow and would be trapped there by the thermal barrier, because sockeye in the Baker River prefer cooler water when offered a choice, although they do not always do so elsewhere (Foerster, 1929; Chapman, 1941). We have not yet recognized this kind of problem in Britain. It may not have appeared so far, but it could well do so if we neglect to study the subtle influences of temperature on water quality, or the implications of the thermal choice which may be available to salmonids at dams, but only a consideration of individual examples will show whether any aspect of the temperature regime is affecting upstream migration.

4. WATER QUALITY That it is possible to head a section of this discussion as simply ' water quality ' indicates the sparseness of our knowledge on this general aspect of the environment. There are reports in which variations of concentrations of gases, trace elements and pH, have not been shown to have any effect on upstream migration, for example, Ellis (1962), Davidson et al. (1943). The concentrations of these factors are often to some extent covariable with each other and with the rate of discharge, and individual effects are difficult to isolate. Munro & Balmain (1956) reported that alkalinity, pH and turbidity varied with flow. The only separable information was that a high turbid flow encouraged daytime migration, but in clear water, movement was more restricted to the night. Strictly this is perhaps an effect of light intensity or cover, rather than water quality. The monitoring of several aspects of water quality by Stewart (1966) does not, so far, seem to have indicated any important influences on migration. However, some experimental work shows that, under certain circumstances, changes in the concentrations of various ions will affect fish movements. For example, Powers (1939, 1941), and Powers & Clark (1943) pointed out that salmonid tissues were sensitive to carbon dioxide concentration, and described experiments which led them to suppose that the concentration of carbon dioxide governed upstream migration. They were of the opinion that sockeye salmon chose waters with lower carbon dioxide tension, and moved always along a gradient from a higher to a lower carbon dioxide tension on their spawning migration. The reason for this was thought to be that lower carbon dioxide tensions would ease the physiological stress of the acidosis produced in their blood by gonad maturation. Because they were primarily concerned to show that carbon dioxide tension could be a guide in finding the home stream, they were led to consider the whole problem rather statically. No measurements were made in the field at different times of day, or along a stretch of river. Clearly such an approach could have yielded much fuller information about the kinds of situations which Powers discussed. Water quality fluctuations of some significance are more likely in small streams and headwaters, than in downriver zones where variations from tributaries are likely to cancel each other. It now seems unlikely that carbon dioxide concentration has any simple relationship with the migration of salmonids, although a constant gross difference might affect choice at a stream junction. Collins (1952) investigated some factors affecting the orientation of two species of anadromous clupeids on their spawning migration. The experiment, set up in a natural stream, allowed him to vary temperature, pH, oxygen, and carbon dioxide concentration. He found that with temperature differences of 0-5" C, 77% chose the warmer channel in the range 11 -1 to 22.3" C, but the fish were less sensitive to small temperature differences at higher temperatures. 1 24 J. W. BANKS

When the difference in carbon dioxide concentration exceeded 0.3 p.p.m.. 72% chose the water with the lower concentration. Differences of 1.1 p.p.m. of oxygen and 0.8 of pH unit had no effects. The antagonistic effects of temperature and carbon dioxide concentration could be balanced experimentally. It would be dangerous to extra- polate these results directly to salmonids, but this experiment illustrates the complexity of the effects of the relationships between the concentrations of different ions, and temperature. Because respiration is an exchange between oxygen and carbon dioxide, carbon dioxide levels are important in determining the minimum permissible level of dissolved oxygen at each temperature. Increases in concentration of carbon dioxide decrease the scope for activity of stimulated speckled trout and other fish by reducing their ability to take up oxygen (Basu, 1959). The quantity of minerals in the water will alter the osmotic stress and hence the oxygen demand. Phillips (1959) demonstrated this on trout (genus and species not named) transferred from waters with a high calcium concentration to waters with a low calcium concentration. In the Paratunka River it seems that the interplay of a rising temperature and pH together with a falling oxygen and carbon dioxide concentration, is responsible for stimulating sockeye salmon to ascend in four tributaries (Krogius, 1954). Similar interactions could occur elsewhere, either as migratory stimuli in their own right, or as modifiers to the effects of discharge. Pollution and the building of impoundments both alter the water quality of rivers, but there is at present no evidence that changes in these factors are in themselves necessarily inhibiting, except where pollution by a toxin is gross, or the oxygen concentration falls too far to support active salmonid migration. A discussion of toxic concentrations of various ions, and dangerously low concentrations of oxygen is outside the scope of this review. It is possible that more subtle effects on behaviour might prevent ascent of fish passes by fish acclimatized in water with rather different characteristics. This situation could arise at dams and has been discussed under temperature. Salmon undoubtedly rely on olfactory clues to locate their home streams, and perhaps to regulate their movement through estuaries. It is fortunate that this capacity does not seem to be seriously impaired by most man-made changes in water quality, yet this inability to appreciate danger causes fish to migrate into polluted waters where they die.

5. GENERAL WEATHER, WIND AND TIDE Location of the home stream is apparently accomplished by the olfactory discrimination of subtle characteristics of its water. Clearly the more widely this water is distributed, the more readily will returning salmon locate it. Day (1887) mentions an account of the salmon runs in the River Severn which shows that most fish ran with a strong wind blowing up the estuary. Huntsman (1939, 1948) showed how Canadian Atlantic salmon in the open sea became associated with masses of fresh water which issued at each ebb tide from the Margaree estuary and how incoming fish moved closely along the coast where this water drifted with the prevailing current, consequently the fish and Margaree water were concentrated against the coast by strong onshore winds. Hayes (1953) concluded that onshore winds, approaching 20 m.p.h., induce salmon to concentrate in the estuary, and that the ideal combination for stimulating ascent into fresh water was a freshet reaching the tidal water at a dusk high tide, when there had been a period of strong onshore UPSTREAM MIGRATION OF ADULT SALMONIDS 125 winds. The period when the difference between high- and low-water tide level was increasing, was more effective in concentrating fish into the estuary than the opposite half of the monthly tide cycle. In fresh water Mottley (1938) for rainbow trout and Lorz & Northcote (1965) for Kokanee salmon showed that onshore winds were most effective for attracting fish from lakes to the tributaries. Mottley attributed this to the optimum distribution of creek water at the right temperature, but the latter authors showed that their creek water was thermally undetectable within a few yards of its exit into the lake, and concluded that some olfactory stimulus was involved. In the light of more recent work reviewed by Hasler (1965) this now seems a possible explanation of Mottley’s results as well. At the time when he was writing the importance of olfactory stimuli was not realized. Ellis (1962) was able to show that runs of fish on the Somass River, Vancouver Island, took place within 24 hours of a change from stable sunny weather to cloudy weather. Although it may not rain, such changes are related to cyclonic weather conditions. Ellis concluded that the salmon may have been stimulated by visual cues from the presence of clouds. It is hard with our present knowledge to see why this behaviour is exhibited on the Somass River where the fish do not appear to react to freshets, changes in air or water temperatures, tides or hours of sunshine. If the fish needed a high-water level in order to enter the stream, it is easy to see that where such changes to cloudy weather precede rain, there might be some advantage to the salmon if they reacted to the presence of clouds by congregating at the stream entrance. In some other places cloudy weather will precede the rain which brings the freshets that fish need to ascend, but this is not the case on the Somass River. Never- theless, the work of Ellis indicates that such a mechanism could exist in places where it would be more obviously beneficial to the fish. Dvinin (1952) made some revealing observations on the effects of general weather. In a study of the salmon of South Sakhalin, he noticed that both pink and chum salmon entered the streams when bad weather caused rough seas. On the west coast of Kamchatka in periods of strong offshore winds, which aid the distribution of fresh water to more remote parts of the Sea of Okhotsk, the largest runs of salmon to approach the coast. On the west coast of South Sakhalin, where the flow of fresh water is insignificant, the reverse is true and the largest spawning runs of chum salmon coincided with onshore winds. Thus, it is likely that the fresh water which comes from the large rivers of Kamchatka can retain its identity and attractive power even when carried far from land. Whereas the water from the small streams of South Sakhalin can only remain sufficiently concentrated to attract fish when onshore winds keep it close to land and the set of the current distributes it laterally. This situation would thus parallel that already described by Huntsman for the Margaree River. Juveniles of five species of Pacific salmon are able to use estuarine salinity gradients as one of the directive cues in their seaward migration (McInerney, 1964). The possibility exists that returning adults are also able to use salinity gradients to regulate their movement to and through estuaries and coastal areas. At present it is difficult to generalize about the possibly complementary roles of olfactory stimuli and salinity gradients, but the observations presented here show that the effectiveness of freshets is likely to be much greater if they occur with certain combinations of wind and tide. High tides, and winds which keep the stream water concentrated close to the coast seem to be more usually favourable for inducing 126 J. W. BANKS migration, but this is not reliable because it may depend on the size of the stream, and other local conditions like currents. In McClinton Creek and Snake Creek the pink salmon were widely scattered in the bays into which these streams emptied until the influence of large volumes of freshet water spreading through the bay attracted them to the stream mouth. Once they have moved upstream beyond the influence of the tides, the weather will act upon migrating fish more directly through its effects on rainfall and temperature. Influences from factors like barometric pressure or cloud cover cannot be excluded but at present it seems probable that their importance would be small, and certainly very hard to disentangle from that of more tangible changes.

6. LIGHT INTENSITY It seems that in salmonids there is a conflict between the need for light in order to ascend obstacles, and a preference for darkness or turbid water in unobstructed passages. The latter has been interpreted as an antipredator device. Stuart (1962) observed that the leaping behaviour of salmon and trout at the Pot of Gartness ceased at nightfall. Stewart (1968e) recorded seasonal changes in numbers of fish moving at different times of day, but although daytime movement just pre- dominated in May, the bulk of the run into the Lune passed Broadraine at night. Shapovalov & Taft (1954) and Ellis (1962) found that at the small weirs which they studied few fish passed at night. Shapovalov & Taft recorded a morning and an afternoon peak of activity, but were unable to decide whether their results were purely related to light intensity or whether temperature variation also played a part. Day time activity is normal at the Stamp Falls fish pass (MacKinnon & Brett, 1953) and at the Skutz Falls fish pass (Neave, 1943); here too there were often morning and afternoon peaks, but particularly when larger numbers were running the peak period for passage was at noon (Fig. 12). Neave considered that light was the factor determining migration and found no correlation with discharge or temperature.

1400 - T 1200 - f U 6 1000 - - 25 f 800 - .._ __ _._._...... * ...... * -20- 0 15 $ -10 E -5 Oct2122 23 24 25 26 27 28 29 Nov.5 6 FIG. 12. Diurnal record of salmon migration (- ) and river discharge ( ...... ). The time scale represents 4-h intervals (Neave, 1943). (Reproduced with permission from the Journal of the Fisheries Research Board of Canada.)

Fish movements at the Rock Island Dam on the Columbia River have been studied by Ward (1939), Chapman (1941) and Leman & Paulik (1966). The reports of the first two authors are contradictory. Ward states that sockeye ran at dawn and dusk and not at all during the day yet Chapman says that ' as a whole they showed a preference for running in the early morning, the number decreasing as the day progressed, but those going through the middle ladder acted in a directly opposite manner, running predominantly in the late afternoon.' Both steelhead and Chinook UPSTREAM MIGRATION OF ADULT SALMONIDS 127 ran in large numbers through the middle of the day. Leman & Paulik have subsequently shown that the attraction of fish to the Rock Island passes is markedly influenced by the manipulation pattern of the spillway gates, a factor to which neither Ward nor Chapman referred. Fish do not run much during the night at Rock Island Dam, but the exact influence of daylight intensity is hard to define. Artificial light has been used to try to induce salmon to use fish passes at night. At the Skutz Falls passes this was completely ineffective (Neave, 1943). In a study at the Dalles Dam less than 10 % of the run passed between 20.00 and 04.00 hours regardless of the pattern of spillway manipulation or whether the fish pass was illuminated or left in darkness (Fields et al., 1964~).At the McNary Dam a further series of tests showed that salmonids did not enter the ladder at night regardless of illumination, but some of those fish already in the ladder at sunset became light adapted and continued to ascend (Fields et al., 19643). These authors also mentioned a short fish pass which was habitually used at night, but this appears to be an unusual case. When this ladder was lit, night migration stopped. In general, dark adapted fish are reluctant to enter lighted areas at night. Where there were no obstacles the evidence suggests that salmonids show a slight preference for night movement, particularly for entering a stream from an estuary or an area of open water. Slightly more salmon and sea trout passed through the Axe trap at night (Allan, 19666); this was especially true for sea trout at low flows (see Table 111). Huntsman (1948) stated that in shallow water salmon ran most strongly for an hour after dusk, diminishing during the night and stopping at dawn. Hayes (1953) showed a marked peak of salmon migration at dusk, and a lesser one at dawn (Fig. 13). Kokanee

11111111111111) 4 8 12 16 20 24 Hour of the day FIG.13. Total salmon passing the counting fence at head of tide, arranged by hours (standard time) and covering the main runs of 1950 and 1951. The interval in the latter part of June and early July spanned the longest day of the year. In all, 1685 salmon and grilse were counted. Notice the strong tendency to ascend at dusk and a less well-marked habit of ascent at dawn. The controlling factor seems to be the rate of change in light intensity (Hayes, 1953). (Reproduced with permission from the Journal of the Fisheries Research Board of Canada.) salmon would not enter a stream from a lake until the light intensity dropped to 100 lux. River spawning lake trout Salvelinus namaycush (Walbaum) only entered the streams at night, returning to the lake before dawn (Loftus, 1958). In turbid water salmonids travel as readily by day as by night. This was reported 128 J. W. BANKS by Munro & Balmain (1956) for brown trout entering the South Quiech from Loch Leven, and by Huntsman (1948) for salmon in the Moser River, Nova Scotia. In both cases once in the stream, fish seemed less reluctant to travel by day. Daytime movement was normal for sockeye in the clear water of Somass River (Ellis, 1962), and the Kokanee population examined by Lorz & Northcote (1965) would ascend during the morning and evening, although the high light intensity apparently inhibited actual entry to the stream. By contrast, the peak of the rainbow trout run from Paul Lake, British Columbia, into a creek was in the early afternoon (Mottley, 1938) showing that light intensity at a stream entrance is not necessarily always a dominating influence under clear water conditions. The suggestion of Hayes (1953) that to be most effective, artificial freshets should be timed to reach the head of the tide at dusk, is nevertheless in general agreement with these various observations. All the work dealt with so far in this section of the discussion has been concerned with direct effects of light intensity. It should not be forgotten that in the situations examined by Krogius (1954) the influence of light was indirect through its effect on photosynthesis and temperature. The result was a pattern of fish movements which was ultimately light controlled, although bearing no relationship to its diurnal cycle. The possibility that similar conditions exist elsewhere, especially in rivers or streams flowing from lakes, cannot be ignored. Finally, it is worth mentioning that there is some evidence that the maturation of the gonads in salmonids is at least partially controlled by the seasonal cycle in day length. Hatchery experiments by Hazard & Eddy (1950) showed that the spawning time of brook trout Sulvelinusfontinulis (Mitchill) could be advanced by up to 39 months by an accelerated pattern of day length shortening. Coombs et al. (1959) were able to advance the maturity of sockeye by about two weeks in a similar manner. For these fish, temperature was eliminated as an important cause of change in maturation rate. It can be concluded that sockeye maturation is largely a response to the pattern of changing length of day, and the resulting migration time is also similarly related (Gilhousen, 1960). His analysis showed that variations in migration time for a ' race ' of sockeye appear to be caused during ocean residence, and delays could be associated with sunspot cycle, through its effect on oceanic conditions. One possibility suggested by Gilhousen was that the warm water intrusions which come along the British Columbia coasts at such times could alter the latitudinal distribution of sockeye in the ocean. In higher latitudes they are subjected to longer photoperiods, which thus delay their maturation. The possibility of similar large scale influences on the Atlantic salmon by ocean water movements, whether induced by sunspot cycles or other causes, have not been investigated. If they exist they could increase our knowledge of the times during which freshets will be most efficient in inducing salmon to enter rivers, and possibly avoid water waste by applying freshets too early in a late year. Pinhorn & Andrews (1965) demonstrated that some behaviour patterns of juvenile Atlantic salmon could be altered by changing the photoperiod to which they were exposed. Fish which were experimentally accustomed to long photoperiods showed greater activity at lower light intensities than controls. This species is therefore at least susceptible to changes in photoperiod when young, but no conclusion can be drawn about the possible influences on migrating adults. UPSTREAM MIGRATION OF ADULT SALMONIDS 129 W.THE PHYSIOLOGY OF SALMONIDS AND THE CONTROL OF MIGRATION So far the fish have been considered only en masse, as numbers passing through a counting fence or fish pass. The fish as a living animal, undergoing complex physiological processes and subject to various internal controls on its behaviour has been scarcely considered at all, but it is the interaction between the external and the internal environment which gives rise to the behaviour of the animal. Our knowledge of the internal environment is growing, although still very incomplete. Parry (1966) reviewed osmotic adaptation in fishes, and recorded many observ- tions of changes taking place in the blood and muscle solutes of salmonids as they migrate into fresh water. It is unfortunate that this is also the time at which they stop feeding, so it is difficult to separate changes which are reactions to the need to re- organize the osmotic mechanisms from those which arise from the use of energy reserves for maturation and upstream migration. The changes involved are considerable, Idler & Clemens (1959) showed that the two races of sockeye salmon which they investigated use over 90 % of the body reserves of fat, and in the female up to 60% of the total protein, by the time they have died after spawning. Dunstan (1956) showed a distinct reduction in fat content of the fish as they move upstream and are held up at successive Columbia River dams. This contrasted with the gradual reduction in fat which had existed before the dams were built (Greene, 1926). To this is related the problem of fatigue, because of the intense muscular activity involved in climbing a long fish pass. After such an ascent the fish may need several hours rest before its lactic acid levels are reduced, so that it can again perform normally (Black, 1958), but there is some disagreement about the amount of fatigue caused by fishways. Collins et al. (1962) constructed an experimental ' endless ' fish pass at the Bonneville Dam on the Columbia River. Six Chinook salmon, four sockeye salmon and four steelhead trout ascended lo00 ft (300 m). One sockeye climbed over 6600 ft (2000 m) in five days on the fish pass. The level of blood lactate in the exercised fish showed no evidence of fatigue. The problems of respiratory metabolism in fish, particularly salmonids, have been reviewed by Brett (1962), who listed the following factors affecting metabolism :activity, concentrations of oxygen, carbon dioxide and ammonia, pH, temperature, salinity, size, starvation, acclimation and season. The possible interrelationships of these factors are virtually unlimited. Black (1958) listed the applications of a knowledge of energy stores and metabolism as follows: (1) a knowledge of the maximum sustained swimming rates will be of immediate use in planning fish passes; (2) an evaluation of the chemical stores of migrating adult salmon should afford useful information in evaluating the success of fish in reaching the spawning beds in a condition which will permit spawning adequate to maintain the fishery ; (3) a knowledge of the nature of muscular fatigue will serve to reduce losses in every phase of the handling of fish. The first two of these points are of immediate relevance to this review. As Brett pointed out, there is a possibility that environmental changes would so alter the pro- cedures needed in maturation, migration and spawning, that the available metabolic fuels would be exhausted before the fish were able to complete spawning. The fraction of energy stores used in maturation can be assessed, but the consequences of raised 130 J. W. BANKS temperatures and probably other environmental factors as energy drains will be hard to predict. Even within the Fraser River the danger of exhausting the metabolic reserves before spawning by means of delays, elevated temperatures, or the extra effort needed to surmount obstacles, varies from ' race ' to ' race '. The dangers to British salmon stocks from such causes are smaller, but cannot be entirely ignored. The control and timing of salmonid migration is mediated by neuro-endocrine processes, the thyroid and gonadic hormones seem to be the most likely activators according to Hoar (1953), although the possibility that hypophysis and hypothalamus are involved cannot be excluded. These hormones not only increase activity, but modify behaviour with respect to variables such as light, temperature and salinity. As maturation proceeds, changes in behaviour patterns will be controlled by the changing endocrine balance. The neuro-endocrine activity itself is directed by several variables, and each stage in migration timed by cyclic environmental variables (Hoar, 1953). Thus as each population migrates through its own series of time- and space- linked environments, its behaviour will be adapted to respond to different aspects of the environment at each stage. Many of the differences within species recorded in earlier sections of this review can be regarded as evidence for the need of individual populations to be thus adapted to the range of conditions which they normally encounter. The habit of returning to the natal stream to spawn enables each population to maintain its own adaptations to the peculiarities of its own environment, and this is necessitated by the complexity and delicacy of the stimuli which result in successful migration, maturation and spawning. Depending on its circumstances, each population may have a margin of safety within which the flexibility of its own behaviour can cope with chance variation, or new elements introduced into its environment. The presence of inappropriate stimuli, or the absence of appropriate ones, at any point in time or space along the migration route could reduce spawning success or even wipe it out completely. Obviously some parts of the environment are less susceptible to change, and the fish themselves will be more susceptible to some changes rather than others. Thus, the percentage of salmon returning to a natal stream to spawn is likely to be a good guide to the degree of adaptation needed to carry through the complete life history of the fish in those waters, although the most critical phase is likely to be the spawning migration and its timing. The higher the percentage of stream homing, the greater the degree of adaptation, the less the chance of success for any strays into the river, and the smaller the margin of safety which is implied for the ' home ' population. These physiological problems are seen in their most acute form among the ' races ' of sockeye in the Fraser River, especially those which spend a short time in the river, during which they migrate continuously, and which then spawn almost immediately after arrival. Less is known about the Atlantic salmon, much less about ' safety margins ' in the rivers in which it spawns, or the likely degree of stress which results from man made environmental alterations. The stream homing of this species in Britain appears to be less precise in some situations than, for example, the Fraser River sockeye. The time spent in the rivers is often much longer, so it can be concluded that conditions are not quite so critical as they are in some of the big rivers of the Pacific. UPSTREAM MIGRATION OF ADULT SALMONIDS 131

WI. SUMMARY AND CONCLUSIONS The following general conclusions emerge from this review. With few exceptions man-made alterations in the environment are bound to cause disturbance and some loss to the populaticn. A dam to provide storage for artificial increases in water flow constitutes such a disturbance. The amount of disturbance will depend on whether the dam is high up or low down the watercourse. Dams low down may be most efficient at stimulating stream entry, those high up will be better at assisting complete ascent, but less efficient at stimulating entry if the ' sharpness ' of the freshet is lost in its downstream passage. For British rivers the general conclusions of Baxter (1961) regarding the volume and number of freshets, and of Hayes (1953) regarding their timing, would seem to be a reasonable working basis. Special dangers may result from water diversion either by resulting in olfactory confusion for the fish or by aggravating physical obstacles in the length which has a reduced flow. Natal stream homing is well developed on many rivers, but the effects of artificially stimulating entry to one river cannot be considered in complete isolation from possible effects on others. The need to ascend dams and pass through impoundments presents new stresses for any migrant population. Little is known about metabolic reserves of British salmonids, or the degree to which they may be prematurely exhausted by these new stresses. Such knowledge would aid in predicting the likely effects of dam building on the population, and would give more data for the design of effective fish passes. The changes in water quality and temperature introduced by damming may inhibit use of a fish pass under some conditions, but could probably be mitigated by better fish pass design, and experimental examination of the extent of such effects. Stored water seems quite adequate for stimulating ascent in the watercourse as a whole. Little is known about long-term changes in Atlantic salmon populations, but work on Pacific salmon suggests that large oceanographic changes may alter the timing of migrations and the sizes of populations. If similar factors operate in the Atlantic, a knowledge of them would enable better predictions to be made of the number of salmon likely to return for a given number of freshets in any year. The sensitivity of salmon to freshets will change as maturity approaches, eventually they will usually attempt to run even in the absence of extra water in the river. Their ability to migrate decreases with approaching maturity, their flesh becomes a less desirable food as their metabolic reserves are reduced, and delays will lead to longer exposure to hazards from predators and to less successful spawning. Quantitative data on such effects are not available for Atlantic salmon. The arguments advanced in section I1 and section VII are intended to demonstrate that there is danger in the extrapolation of results from one place or species to another. Hoar (1953) said. . . ' the general timing of fish migration is no more or no less complex than the timing of seasonal cycles, and the variations which these bring to light, temperature and precipitation.' The consequences of man made changes which alter the nature or effects of these three factors can be predicted in general terms from the existing literature, but each situation is unique, and the alleviation of undesirable consequences requires studies of the special needs of each river system as well as the flexible application of general principles. I gratefully acknowledge the advice and assistance of Mr I. R. H. Allan, Chief Officer, Salmon and Freshwater Fisheries, Ministry of Agriculture, Fisheries and Food, and also Professor M. C. Bell, College of Fisheries, Seattle, Dr D. H. Mills, Nature Conservancy, Edinburgh, Mr L. Stewart, Chief Fisheries officer, Lancashire River Authority. 132 J. W. BANKS

I also wish to thank the Northumbrian River Authority and its Fisheries Superintendent Mr J. T. Percival for access to unpublished information. I am deeply indebted to Dr J. W. Jones, O.B.E., for his encouragement, advice and assistance in suggesting improvements and to the late Professor R. J. Pumphrey. The basis of this review was originally commissioned by the Water Resources Board as a literature survey, and I am most grateful to them for financial support. Any views expressed are, of course, entirely my own, and not necessarily those of the Board.

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