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SURVIVP...L OF PINK AND CHUM

SA!JlON EGGS Al~ ALEVINS

_j - ..... p '-_.. -~

WII LIAM J. McNEIL Oregon State Unive ..-sity Department of Fisheries and Wildlife

Survival of Pink and Eggs and A1evins 1

ABSTRACT The production of pink (Oncorhynchus gorbuscha' and chum (0. keta) salmon fry is controlled by density-dependent mortality. Production from Sash in Creek, Little Port Walter, :;outheastern , approaches a na.ximum of about 5 00 fzy perm 2 of spawning ground at an egg deposition of 2,000 to 3,000 egg'i per m2. The production curve for Sashin Creek is dome shaped. Mortality from droughts, floods, or freezing temperatures may exceed 50 percent of the eggs and alevins in spawning gravels, but such mortality appears, for the most part, to be independent of population size. Superimposition of redds, on the other hand, causes density-dependent mortality: studies at Sashin Creek indicate that survival of eggs and alevins is higher when spawning is early than when it is late. Thus, a dome-shapped production curve in freshwater may result from repllicement of more viable eggs from early spawners by less viable eggs from late sn3.wners as ihe total number of spawners increases beyond the level where superimposition of redds becomes a frequent ocwrrence. INTRODUCTION Freshwater production of pink (On~orhynchus gorbuscha) and chum (0. keta) salmon is detennined largely by survival of eggs and alevins because the fry seek the sea immediately after they emerge from spawning: !Jeds. Fn~shwater production of sockeye (0. nerka), chinook (0. tshawytscha), and crilo (0. kisutch) salmon, on the other hand, may be determined by the availability of space and food for juveniles in freshwater nursery areas as well as by survival of eggs and alevins. Although we have yet to determine if mortality of pink and chum salmon is density dependent at sea, successful forecasts of the number of spawners returning to Prince William Sound, Alaska (Roys, 1967), suggest that total production is controlled more by factors i!' streams than in the sea. ~Cnfortunately, counts ot' fry entering the sea fr()m individual streams and adults returning to spawn have thus far failed to describe a production curve in salt water, possibly because measurements of rates of exploitation have lacked precision for separate spawning populations.

1 A contribution oi t11e Bureau of Commercial Fisheries Biological Laboratory, Auke Bay, Alaska 99821.

101 Symposium on Salmon and Trout in Streams

This paper considers some of the important factors that affect survival of pink and chum salmon eggs and alevins in spawning beds. Much of the work described was done by the U.S. Bureau of Commercial Fisheries in Sashin Creek, Little Port Walter. Alaska, where research on pink and chum salmon has been underway since 1934. Sashin Creek drains a 13.4 km2 (5.2 square mile) watershed on southeastern Baranof 1 Island. The terrain is mountainous and only partially ti..nbered. Much of the watershed t consists of muskeg, alpine meadows, and rock outcroppings. Lakes provide temporary storage for the runoff during frequent periods of heavy precipitation and maintain a relatively uniform flow in SashL.1 Creek. Precipitation at Little Port Walter averages 561 em (221 inches) per year. October, the wettest month, averages 94 em (37 inches). Salmon are denied access to upper Sashin Creek by a high waterfall about 1.1 km (0.7 mile) above Little Port Walter Bay, and spawning is therefore restticted to the lower portion of the stream. Little or no spawning occurs in a canyon extending 300 m downstream from the waterfall or in the intertidal portion of Sashin Creek. In both areas, the streambed is precipitous and consists of bed rock. A weir is operated at the head of tide to count adult salmon into the creek, and seaward migrating fry fmm the creek. Pink and chum salmon spawn in late August and September; most fry .emerge in late April and May. Since JQ59, spawning ground studies have bt:en conducted in a 13,084 m2 area which includes ar unn~r (2,945 m2), middle (4,06i~ ~·~2), and alower(6,072 m2) segment. The Upper segment has a high gradient and coarse material~ iil the bed; the middle segment has an intermediate gradient and medium..-sized materials; and the lower segment has a low I gradient and fine materials (Fig. 1). In this paper I will emphasize comparisons between BED MATERIALS (mm) 1.68-12.7 )12.7 \ ~ e- 5.9 ------.. _------Q) "'0 =4.4 ------"------::: 0 \, c 3.5 ------o 3. I MIDDLE Q) LOWER E 2.4 I Q) > 0 I .Q 0 13% I I I 0 I i -> 0~~9~1------~4~9~0~------~7~6~0~----9~8~0~-- cu I! Distance upstrttam from weir (m) lJJ I I FIGURE I i GRADIENT AND SIZE CO~! POSITION OF BED ~fATERIALS IN THREE SEG!I.tENTS i; OF THE SASHIN C'REEJ.: SPAWNING GROt:~D. \ 102

s.\ ~· , !.,., ~ \ -

\- : ' . . " \.,. .. ------..-----~...... ~

Survival of Pink and Chum Salmon hggs and A lev ins the upper and lower segments of the Sashin Creek spawning ground because the contrasting conditions best ciemonstr::ltc the effects of environment and behavior of spawners on the survival of eggs and alevins.

MORTALITY PROCESSES Before discus .ing specific factors that affect survival of pink and chum salmon eggs and alevins, I will disc\'ss briefly the nature of mortality processes. A popular school of population ecology states that population size is ultimately rt!gulated by density-dependent mortality processes. For fishes the rate of mortality is highest and most variable dux!ng early stages of life. Models of the clymanics of exploited populat!0ns of fish sometimes are based on the assumption that the number of fish recruited to an expi~1t~1bJc population is independent of the number of spawners, i.e. the number added each year tends to remain co:~stant over a wide range of population size. Gulland (1965) has correctly pointed out that this assumption is equivalent to arguing that the avemge survival from spawning to recruitment of juveniles to the population decreases w~th increasing numbers of spawners, i.e. direct density-dependent mortality operates to limit recruitment. Theoretical production curves that relate the number of fish constituting a population at some late life-history stage to potential egg deposition have been formulated by Ricker (1954, 1958a, and 1958b), Beverton and Holt (1957), and Larkin et al., (1964). The shapes of the curves vary according to their underlying assumptions, but all of them imposv an upper limit to the size of the population. The definition of the production curve and the determination of the number of spawners required for the maximum number of recru~ted to a population are vital for effective management of a fishery resource and represent major chaUenges to fishery science. Potential egg deposition and the number of seaward migrating salmon fry have been estimated in Sashin Creek at Little Port Walter since 1941 (1940 brood year). Tltc ~:-eriods of spawning and fry migration in s~.shin Creek are the same for pink and cliam salmon, and the two specie~ mix freely on the spawning ground. Because their behavior is similar, pink and chum salmon have a similar exposure to mortality factors in freshwater, and r have combined observations on potential egg deposition and fry production for the two species to examine general relationships. The number of spawners has ranged from 46 to 92,000; have predominated in years of abundance, churn salmon in some of the years of scarcity. The number of seaward migrating fry has ranged from 50 t.: 6,000,000. Potential egg deposition and fry production per m2 of spawning ground in Sashin Creek are summarizeq in Table 1. Production of pink and chum salmon fry in S~:~shin Creek approaches a maximum of about 500 per m2 of spawning ground when about 2,000 to 3,000 eggs per m2 are available for deposition (about 1 female spawner pe•. m2). Fry production decreases rapidly with a potential egg deposition below 2,000 or above 3,000 per m2, giving a dome-shaped production curve (Fig. 2). Points would have been sc<.-ttered amund almost any cuiVe fitted to the observations on potential egg deposition and fry production. Tlle curve of figure 2 may describe broadly a density-dependent relation, but the scattering of points around the curve is considerable. Fry production varied greatly, for example, even at similar levels of potential egg deposition. Some of the scattering may adse from errors of measurement, but other mortality factors, only in part or not at all density-dependent, most probably were important. It becomes necessary, therefore, to understand the relation of important mortality factors to population density.

103 Symp,Jsium on Salmon and Trout in Streams

TABLE 1 POTENTiAL EGG DEPOSITION AND FRY PRODUCTION OF PINK AND CHUM SALMON IN SASHIN CREEK, ~94Q THROUGH 1965 BROOD YEARS. (DATA ARE FROM CLSEN AND McNEIL, 1967).

,...-. ' Potennal egg Fry production Broodyear deposition per m2 perm-?

Number Number

1940 3,878 249 1941 6,507 75 1942 5,789 49 1943 1,114 17 1944 325 10 1945 384 3 1946 55 (1 1947 112 2 1948 76 1 . 1949 365 13 1950 13 0 1951 324 31 t 1952 7 <1 ~. 1953 108 8 1954 3 (1 1955 756 93 1956 83 (1 1957 204 43 1958 17 1 1959 2,964 391 1960 16 1 1961 2,29$ 463 1962 0

EFFECT OF ENVIRONMENT ON EGGS AND ALEVINS To survive, a fertilized egg must be protected agaiut mechanical disturbance: must receive ~~dequate water having a high content of dissolved oxygen, a low content of toxic substances, and a suitable temperature; and must be protected against attack from ;redators, pathogens, and parasites. Obviously, all of these requirements are ne\,er fully satisfied for all fertilized eggs in nature; accordingly the survival of pink and chum salmon eggs and alevins in spawning beds is normally less than 25 percent of the po ten tital egg deposition. SURVIVAL TO END OF SPAWNING Factors which affect survival during spawning include coarseness of bed materials and streamflow as deml'nstrated in the upper and lower segments of the Sashin Creek spawning ground in 1963 and 1965 (McNeil, 1968). The densities of spawning t~mulcs were similar in both segments in 1963 and 1965. However, the coarser bed materials of the upper segment contained more eggs at the end of spawning than the finer bed mulerials of the lower segment (Table II). Furthermore, a muc!1 higher percentage of the potential egg deposition was present in the spa\vr ing ground in 1965 ( 78 percent) than in

i 963 (50 percent).

I 0-~ Symrh ·.~um on Salmon and Trout in Streams

TABLE 1 POTENTIAL EGG ")£POSITJON ANO FRY PRODUCtiON OF PINK AND CHUM SALMON I~ SASHi'-c CREEK, 1940 THROUGH 1965 BROOD YEARS. (DATA ARE FROM OLSEN AND McNEIL, 1967).

Potential egg · Fry productic•rz I "1 Brood yea;: I deposition per m2 per n;- --~~ Number Number

1940 3,878 249 1941 6,507 75 1942 5,789 49 1943 1,114 17 1944 325 10 1945 184 3 1946 55 (1 1947 112 2 1948 76 1 . 1949 365 13 1950 i 13 0 1951 n4 31 1952 7 ., ... 1964 171 -.l 1965 931 164 -- l i i EFFECT OF ENVIROi'!;~J.ENT 0?-J EGGS AND ALEVINS I f To survive, a ferWized egg must be protected ag~inst mechanical di~turbance: must 1 i I receive adequate water having a high content of dissolved oxygen,~ low content of toxic 1 1 substances, and a suitable temperature; and must be rrotected. against attack from l predators, pathogens, and parasites. Obviously, all of these requh~·ments are never fully ! satisfied for all fertilized eggs in nature; accor ;~;igly the ~urvival of pi-k and chum salmon j l eggs and alevins in spawning beds is norm~B:r- less than 25 percent of the potentital egg l deposition. j SURVIVAL TO END OF SPAWNING 1 Factors which affect survival during spawning include coarseness of bed materials and i l ! l 1 streamfl0w as demonstrated in the upper and lower segments of the Sash in Creek ! ! spawn in!] ground in 1963 and 196"' 'McNeil, 1968). The densities uf spawning females I l j, i were simllur in both segments in 1963 ami 1965. However, the ~oarser bed materials of I I ~ the upper segment contained more eggs at the end of sp~:twning than the finer bed I materials of the lower segment {Table fl). Furthermore, a mud1 higher percentage of the I l I potential egg deposition was present in the spawning ground ·in 1965 (78 percent) than in ' 1963 (50 percent). I t I, I JQ.:~ li I -l \~' l ...... I .<;t;' I ,_ \

Survival of Pink and Chum Salmon hggs and A leJ,ins

5 -en 0 "0 ..,P-, cu ~ / .,, 4 I o' \ c:: I \ ::s .r:. I \ - 3 I \ I \ NE o\ ol \ '- I ~ I ' Q. I ' ~ ' ' u..'- ' ' ...... 0 0 ......

0 2 3 4 6 7 Potential egg deposition per (thousands) FIGURE 2 REPRODUCTION OF PINK AND CHUM SALMON IN SASHIN CREEK. THE CURVE IS fiTTED BY EYE. POINTS WITH POTENTIAL EGG DEPOSiTION LESS THAN 100 PER m2 ARE NOT PLOTTED. TABLE II SUCC'ESS OF PINK AND CHUJ\f SAU,ION SPAWNING IN UPPER AND LOWER SEGMENTS OF SASHIN CREEK SPAWNING GROUND, 1963 AND 1965.

,. 1963 1965 Potcllti.:d Potential Segment egg Portion of egg Portion of of spawning deposition.., ~ggs in deposition.., eggs in ground perm- spawning bed perm- spawning bed

Number Percent Number Percent

~--· Upper 1,150 78"!:14 1,030 93!21 ' Lower 1,150 38!8 780 69!23

50 78 I Average values arc calculated from the total number of eggs in the upper and lower scgmcttb combined~ hence, they arc voei~hted by the &rea of each segment.

In both years~ less than five percent of the potential egg deposition was retained in the body cavities of the parent spawners, so egg retention was not a significant factor. Streamflow is tho·lght to have caused the difference in survival since the lowest September rainfall on record at Little Port Walter (?8 years) was in 1965 (5 em) and the highest on record was in ! .:63 ( 133 CJP'.

105 Symposium on Salmon and Trout in Streams I SURVIVAL TO EMERGENCE OF FRY I Questions which bear importantly on whether or not the spawn will survive to hatch l and et'nerge as fry include: Will dissolved oxygen become depleted to a lethal level? Will predators feed extensively on eggs and alevins? 'Nilllow streamflow expose spawning: beds to drying or freezing? Will sediment smother the eggs or prevent the alevins fror. emerging? Df'

I Survival of Pink and ::Jwm Salmon Eggs and A Ievins

The rate of interchange between stream water and intragravel water is h.~h in the upper segment of the Sashin Creek spawning ground even at low streamflow because of water turbulence over coarse bed materials. Interchange of water in the lower segment at low streamflow is restricted by a low gradient and fine sediments in the bed. Higher quality intragravel water in the upper creek segment than in the luwer is demonstrated by the higher percentage of eggs hatching there in two years ( 1963 and 1965) when the intensity of spawning was similar between the two segments (Table Ill).

TABLE III ....·- :.: "'.-..:;.:.. SUCCESS OF ... CHING OF PINK AND CHUM SALMON EGGS IN UPPER AND LOWER ~~ -

Number Number Percent Number Number Percent

Upper 0.6 885 81 0.6 966 69 Lower 0.6 433 0.4 539 J 34 2Avetage _t_1 LJ 1 Estimated with hydraulic sampler (McNeil, 1964a). 2 The average value for each year is calculated from the total number of eggs in the upper and lower segments combined; hence, these value~· have been weighted by the area of each segment. This difference in the percentage of eggs hatching in the two segments was especially pronounced in 1965 when streamflow was low throughout September. Th~ low percentage of eggs hatching in 1965 was very likely due to low dissolved oxygen in intragravel water. Measurements at 25 random points in each segment on two dates in 1965 gave the following percentages of saturation values of dissolved oxygen~ Segment September 13 September 22

Upper 56 percent 71 percent

Lower 20 percent 27 percent Predation Although coarse bed materials accommodate more eggs and allow better interchange between stream and intragravel water than do fine bed materials, they also may allow predators (and scavengers) better access to eggs than do fine bed materials. This difference is indicated by observatior.s in Sashin Creek during the autumns of 1963 and 1965. An estimated 32 percent of eggs were unaccounted for in samples collected with the hydraulic sampler from the upper segment of the spawning ground in autumn 1963 and 24 percent in autumn 1965; all eggs were accounted for in the lower segment (McNeil, 1968). Thus, certain mortality factors which cause the removal of spawn operate in autumn irt coarse bed materials of the upper segment but not in fine bed materials of the lower segment. ( aleuticus) and possibly other fish predators may be involved. McLarney (1964) and Phillips and Claire. (1966) have shown that sculpins are capable of penetrating deeply into streambeds to feed on salmon eggs and al:!vins where the gravel is coarse and free of fine sediments. In his studies at Sashin Creek, McLarney (1967)

107 Symposium on Salmon and Trout in Streams r I found scutpms dispersed over the spawning ground in summer before the salmon r spawned: whereas, in September, at the peak of pink and chum salmon spawning, they were concentrated in the coarse bed materials of the upper segment of the spawning ground. He estimated that thu population of sculpins in Sashin Creek was between 15,000 and 20,000 fish 5 em or longer total length; fish of this size fed on salmon eggs. Cooling of stream water would curtail the rate of feeding by predatory fish in winter. The temperature of Sashin Creek characteristically declines from about 8°C in October to about 2°C in December and remains below 2°C until April. Relatively few eggs and alevins disapJ,Jear during winter (McNeil, et a!., 1964; McNeil, 196Gb), although the 1965-66 winter was an exception (McNeil, 1968). The low streamflow in September 1965 may have been indirectly responsible for the disappearance of eggs over winter. In 1965, the carcasses of 14,000 salmon decomposed in the creek; rhey are usually removed from Sashin Creek every few days by freshets. The large quantity of decomposing flesh in the stream may have provided nutrients necessary for organisms which attack dead eggs and lllevins to reproduce rapidly in summer and autumn and become abundant. No studies have been made, to my knowledge, to test this hypothesis. High Streamflow In studies at Indian Creek, Twelvemile Creek, and Harris River, southeastern Alaska, I recorded the disappearance of eggs and alevi'1s from spawning grounds during high streamflow (McNeil, 1966a). Disappearance from these streams during strong freshets t often exceeded 50 percent of the eggs and alevins in the streambed and on one occasion l the loss exceeded 90 percent. Lakes on Sashin Creek watershed store water during freshets and maintain a relatively I steady streamflow. Discharge of Sashin Creek rarely exceeds 17m3 per second (600 cfs), r which is about 60 times the minimum flow. Removal of eggs and alevim: by high streamflow may be less serious in Sashin Creek than in many other pink and chum salmon spawning streams. It appears, however, that high streamflow contributes to the disappearance of eggs from the upper segment of the Sashin Creek spawning ground in autumn, even though there is little or no mechanical disturbance of the bed. McLarney ( 1967) detected eggs near l.he surface of the streambed by stirring the overlying w1ter within a 0.2 m2 circular screen and collecnng eggs which had become suspended in the stream. He tested between 80 and 90 random points per segment of spawning ground in September I 965 and obtained 19 times more eggs from the coarse bed materials of the upper segment than from the t1ne bed materials of the lower~ this shows that eggs are susceptible to removal from coarse bed materials by turbulent water as well as by predation. II Freezing I have attributed high mortJlity of pink and chum salmon eggs and alevins to freeziag ~ in only one stream (Indian Creek) studied. The average daily stream discharge of Indian r Creek fluctuated from 0.11 to 55 m3 per second (500-fold difference). Mortality during the cold winter of 1956-57 was four to five times higher in Indian Creek than in nearby I Twelvemile Creek.., (McNeil, l966a), where the fluctuation in d::~i~y discharge was SO-fold (0.34 to 28m.) per second). We have nu evidence of unusually high mortality from prolonged freezing weather in I Sashht Creek, where the fluctuation in daily discharge was only 60-fold (0.28 to 17 m3 per second). Freezing weather persisted for five weeks at Little Port Walter in the winter of 1964-65, and a thkk layer of ice fanned over the creek. r obtuim;d 54 percent of live I alcvins in the total number of eggs :.md alevins collected from the three segrnents of the spawning rround in :v1urch 1965. Similar sampling after the warmer winters of 19tJ 1-<,2. I!

108 \

- --~"""~~ ..... -~ .. ~---.."~~~-~ ~--- .... -~- -~----·~ ·--... ~~ ~~ _.,. ·b-~ .... ~,."""' ,,..,..,._,,_. ·----1"'""" -- ,-~- ~--~-~------...... t p.

Sun•ipaf of Pink and Chum Salmon Eggs and A Ievins

1963-64, and 1965-6o yielded 51, 60 and 4::! percent of1ive alevins. Thus, the 54 perc~nt live alevins after an exceptionally colg wimer was near the average of 51 percent for the tl)ree warmer winters. Sedimentation It is well known that flow of water through spawning beds may be restricted by fine sediments and may cause impainnent of water quality for salmon eggs and alevins (see review by Cordone and Kelly, 1961). Other studies show that fine sediments can impede the emergencr. of fry (Koski, 1965). McNeil a.r:d Ahnell ( 1964) compared amounts of fine sediments in spawning beds of six southeastl~rn Alaska pink and chum salmon spawning streams from measurements of the volum~ of sediments in the top 15 em of bed materials. The amount of sediments passing through a 0.833 Huu sieve ranged from five perc~nt of the total volume of solids ~n a productive spawning grol!nQ tR :!Q p~rcent in an unproductive spawning ground. Similar measurements in Sashin Creek gave values ra~1ging from only two percent of fine sediments in the upper segment of the spawning ground to 11 percent in the lower. Althot!f'Jl the lower segment of the Sashin Creek spawning ground contained about six times more fine sediments per volume of spawning gravel than the upper, success of fry emergence d!d not appear to differ in the two segments. In spring, I 964, I estimated the number of dead pink salmon alevins in the upper and lower segments of the spawning ground at the beginning of fry emergence (April 2) and one month later (May 2) after 43 percent of the total number of fry had left the stream. Dead alevins, expressed as a percentage of total live and dead alevins at the beginning of fry emergence, increased on.ly three percent in each segment during the one-month period (Table IV). TABLE IV DEAD PINK AND CHUM SALMON ALEV1NS Of THE l96313ROOD YEAR FOUND lN SASHIN CREEK, EXPRESSED AS A P~RCENTAGE OF TOTAL LIVE AND DEAD ALEVINS AT THE BEGINl~lNG OF FRY EMERGENCE.

Total live and Dead alevins dead alcvins Segment of per m2 at At beginning After 43 percent spawning beginning of of emergence offry migration ground fry emergence (April 2, 1964) (May 2, 1964) Difference

Number Percent Percent Percent

Upper 364 1 4 3

Lower 186 6 9 3

Further evidence of Jaw mortality of Sashin Creek pink and chum salmon fry during emergence in the spring of 1964 Q~e from estimates of alevins in early spring and subsequent counts of seaward migrating fry passing the weir at the head of tidewater. Alevins were estimated to number 3,342,000 just before the fry emerged. The number of fry counted at the weir was 3,256,000; the slight decrease from the number of alevins was not statistically significant at p = .1 0. EFFECT OF BEHAVIOR OF SPAWNER£ ON EGGS AND ALEVINS Although the environment ultin1ately determines if a fertilized egg will survive to produce a fry, the opportunity to survive may be influenced to a large extent by the behavior of the parents. Of special significance are ti..-ne of spawning and distribution and crowding on spawning beds.

109 Symposium on Salmon and Trout in Streams

TIME OF SPAWNING Most pink and chum salmon are sexually mti.ture when they enter Sashin Creek, so that early entry to the stream results in early spawning. Survival of pink salmon eggs and alevins in Sashin Creek has been high when entry of spawners was early and low when entry was late (Skud, 1959; Merrell, 1962). The negative regression of total freshwater survival on the time 50 percent of parents enter Sashin Creek to spawn is significant for pink salmon, p = 0.01 (Fig. 3), and for chum salmon, p = 0.05 (Fig. 4).

25 ' ,;, .

~ 0 -~ 20 ~ 0 0 ~. > ?- > ~.J> ).,. 15 :l U) C) ._ 0 OJ 10 -tl 3 0 I 0 .s:: 0 5 CD.... u.

10 20 30 9 19 August September FIGURE 3 REGRESSION OF TOTAL FRESHWATER SURVIVAL OF SASHIN CREEK PINK SALMON ON THE DATE 50 PERCENT OF THE PARENTS HAD ENTERED THE STREAM TO SPAWN. THE CURVE 'J = 26.66 • 0.72x IS FITTED BY LEAST SQUARES, LETTING AUGUST 10 CORRESPOND TO x = 0.

It is not krr.own why early spawning results in better survival of eggs than late spawning, but Merrell (1962) suggested that water temperature might be a contributing factor. Water temperature in Sashin Creek typically reaches its maximum (about 15°C) in mid August and declines steadily to about 8°C in early October. Spawning normally occurs in Sashin Creek from August to October; the eggs begin incubation at water temperatures that vary from about IS°C to 8°C. The temperature ofSashin Creek drops below 8°C before mid October and sometimes as early as mid September. Merrell's suggestion has been supported by experiments with sockeye salmon by Andrew and Geen (1960), who showed that eggs which began incubation at 7°C exrerienced higher mortality than eggs which began incubation at 10°, 130, and I6°C. Combs ( 1965) obtained similar results with chinook and sockeye salmon eggs, Some indication exists also that early spawning pink salmon concentrate in the upper segment of the Sashin Creek spawning ground (McNeil. 1968). The existence of highly favorable environmental conditions tbr eggs and alevins in this area has already been described. This behavior. if common, could contribute significantly to high survival of spawn in years when the adults enter the stream early. but confirmation of this hypothesis will require ndditional observ on and testing.

110 ..... ---·- ______, ------\'"-'···'--~----·...,.r,C: .• ~ ..:..I

-~ - ! Survival of Pink and Chum Salmon l:.'ggs and A Ievins l - -l -~ I 25

- 20 -~ 0 > 15 > ~ :::1 Cl) y • IO 0 10 ~ -- ·ICJ.- -- ~ 0, CD ...... __ 2A,.-1 0 -0 0 ::: 0 I 5 .c: Cl) cu 0 ... C!. LL 0 10 20 30 9 19 August September FIGURE 4 REGRESSION OF TOTAL FRESHWATER SURVIVAL OF SASHIN CREEK CHUfll SALMON ON THE DATE 50 PERCENT OF THE PARENTS HAD ENTERED THE STREAM TO SPAWN. THE CURVE y = 10.14 - 0.24 x IS FITTED BY LEAST SQUARES, LETTING AUGUST 10 CORRESPOND TO x = 0.

DISTRIBUTION ON THE SPAWNiNG GROUND The full potential of a stream to produce pink and chum salmon fry can be realized only if all segments of the available spawning ground are optimally utilized by spawners. VF!ry often spawners are too few to occupy fully the available spawning area. It has been argued by several workers that areas not used when runs are small have relatively poor conditions for eggs and alevins., but studies at Sashin Creek show that this may not always be true (McNeil, 1966b). The upper and lower segments of the Sashin Creek :\pawning ground are used extensively by pink and chum salmon spawners in years when the runs are large. but fry production per m2 of spawning ground has been at least twice as high in the upper segment as in the lower (Table V). When runs are small, pink aQd chum salmon spawn in TABLE V PINK AND CHUM SALMON FRY PRODUCTION FROM THE UPPER AND LOWER SEGMENTS OF THE SASHIN CREEK SPAWNING GROUND DURING FOUR YEARS WHEN ESCAPEMENTS OF SPAWNERS WE~E LARGE.

Brood Fry production per m2 year Spawners Upper segment Lower segment

Number Number Numh.::r

1959 35,400 330 140

1961 30,100 600 230

1963 16,900 360 180

1965 14,900 230 110

Ill Symposium on Salnion and Trout in Streams the lower segment and often ignore the upper (Merrell, 1962; McNeil, I 968). Thus when spawners are few, those present tend to concentrate where condit~~ms of water flow and oxygen supply are less favorable for eggs and alevins; but by doing so, they avoid a.1 area where their eggs are most vulnerable to predation. Perhaps this behavior 1s advantageous; for if predators were able to satiate themselves with eggs obtainable from r,oarse bed materials but not from fine bed materials, mortality would Le inversely density dependent. A large percentage of eggs under this circumstance would be lost from a small population and a small percentage from a large population. CROWDING ON THE SPAWNING GROUND Egg retention by spawned pink and chum sa}mon is usually less than five percent of the potential egg deposition but may ?.pproach 40 percent where the numbers of spawners on the spawning grounci at the same time are excessive. Experiments with penned sockeye and pink salmon show that a high percentage of eggs are retained where more than one female per m2 is present at the same time (Mathisen, 1962; Hanavan and Skud, 1954). Such high densities of spawners are unusual even where large numbers of salmon enter a spawning ground, because the spawning period often lasts 6 to 8 weeks and individual females survive only one or two weeks aft::., !: :;• spawn. Nevertheless, 40 percent egg retentk·n by female salmon has been reported at least twice where the density of pink and chum salmon spawners became unusually high (Semko, 1954; Helle, et al., 1964). Perhaps the most serious mortality factor during spawning is the super-imposition of redds. In Fig. 5, I compare for three southeastern Alaska streams the number of eggs in spawning beds at the end of spawning with the potential egg deposition. Spawning grounds were sampled with a hydraulic sampler (rvlcNeil, 1964a), and potential egg depositions were estimated from the counts of female spawners. If 100 percent of potential egg deposition had been recruited to the spawning grounds, I would expect the points (Fig. 5) to be scattered about y =x. Except for very low densities. of spawners, considerably fewer eggs were found at the end of spawning than were available for deposition. As suggested by the dotted curve, the disparity between actual and potential egg deposition increCtses with increased potential egg deposition; it appears that the loss is density dependent. A mathematical model describing density-det:endent mortaiity from redd superimposition has been developed (McNeil, 1964b) by assuming that redds are located randomly and that the number of eggs recruited to a spawning ground approaches an upper limit asym;·totically. On the basis of data from Harris River, the model predicted that about 33 percent of the potential egg deposition would have been lost from redd superimposition when the density of female pink salmon spawners was 1 per m2; about 50 percent when the density was 2 females per m2; and about 67 percent when the density was 3 females per m2, Sernko 0954) estimated that between 50 and 75 percent ~:a~~e~or~~;c~~:~ ~g~e:~~:i~~~2~uld have been lost when the. density of pink salmon

PRODUCTION CURVE IN FRESHWATER Spawning ground studies reveal that many factors can contribute to the mortality of pink and chum salmon eggs and aleyins. Those such as oxygen privation, mechanical dis­ turbance of the streambed, and freezing appear to induce essentially a density­ independent mortality. Under certain circumstances, individual density-independenr n~ctors may cause the death of 50 percent or rnore of eggs and alevins in a spawning ground, (t should not be surprising, therefore. to encounter difficulties in describ.ing production curves for pink and chum salmon from data on potential egg deposition and

112 Survival of Pink and Chum Salmon Eggs and A Ievins

0 c c ~ c o Q. Harris R. en a ln~ian Cr...... 0 A Sashin Cr .

"0 c Q)

..c -en "0 (\J c E c .... cn CIJ ::J 0 c.. .c Cl) .... Cl' 0 - 2 Q) ...... - .... - ---0 """0 . ---- .... I (',) .Q E ~ :::::p :.0 z 0 2 3 4 5 6 •, 2 Potential egg deposition per m (thousands)

FIGURE 5 OBSERVATIONS ON DENSITY OF PINK AND CI-IU~t SALMON EGGS IN SPAWNING GROUNDS AT END OF SPAWNING AND POTENTIAL EGG DEPOSITION. THE CURVE y = x REPRESENTS 100 PERCENT OF POTENTIAL EGG DEPOSITION. f.y migration without first understanding how and to what extent these density-independent factors are influencing mortality. Sashin Creek, because of its uniform flow, appears to be little affected by mechanical disturbance of the streambed or by freezing. This situation helps to reduce the variability in the number of fry migrants that result from any given ievel of potential egg deposition. The available data show the production curve for Sashin pink and chum salmon to be dome shaped (Fig. 2). Studies in Sashin Creek and elsewhere have indicated that the number of eggs in the spawning ground at the end of the spawning period becomes limited ultimately by the amount of space for redds, and that the number of eggs in a streambed approaches an upper limit asymptotically. I have proposed a simple model to descril:le recruitment of eggs to a spawning ground (McNeil, 1964b). On the assumption that re tds are dispersed randomly, the following equation is obtained:

113 Symposium on Salmon al'id Trout in Streams

R = L (1-eE/L), where R is the number of eggs per m2 in the streambed, E is the potential egg deposition per m2, Lis the asymptotic upper limit of egg deposition, and e is the base of the natural logarithm Figure 6 illustrates the relationship of the number of eggs remaining in the spawning ground (R) to the number which have been lost {E-R). The "random model" may be a suitable first approximation of a mathematical description of the recruitment of eggs to a spawning ground. A recent test of the model in a spawning channel at Lovers Cove Creek near Little Port Walter (McNeil, 1967) has revealed, however, that redds are dispersed in a contageous fashion, i.e. they becom€ clustered at particular locations. If this behavior is common, the random model will tend to overestimate egg deposition and underestimate mortality, although the error is not necessarily large. The number of fry produced obviously eannot exceed the number of eggs recruited to a spawning ground. Thus, a relationship between egg recruitment and potential egg deposition similar to that shown by Fig. 6 can lead directly to an asymptotic production curve. Observations at Sashin Creek indicate, however, that fry production approaches a maximum where potential egg deposition is in the range 2,000 to 3,000 eggs per m2 of spawning ground (Fig. 2) and the production curve is dome shaped rather than asymptotic. It is believed that low dissolved oxygen levels in spawning beds are seasonal and the result of factors other than large populations of eggs (Smirnov, 1947). Low concentrations of dissolved oxygen in pink and chum salmon spawning beds have been described where the population density of eggs was low (M.cNeil, 1966a; McNeil, et al., 1 )64). The rapid removal of dissolved oxygen from spawning beds by biochemical processes even in the absence of eggs and alevins has been demonstrated by Sheridan (1962) who found that the dissolved oxyge!l content of in tragravel water remained high so long as stream water flowed over a gravel bed but soon became low after the stream level had dropped and water no longer flowed over the bed. Interchange between stream and intragravel water is necessary to maintain high levels of dissolved oxygen in the streambed (Vaux, 1968). The superimposition of redds at high densities of spawners wot!ld limit, and may possibly prevent, the overcrowding of eggs and alevins in spawning beds. Disturbance of bed materials from redd digging activities of females also enhances conditions for eggs and alevins by removing silt and organic detritus, thus increasing the porosity and permeability of gravel beds (Sernko, 1954; McNeil and Ahnell, 1964). If intense spawning activity improves the quality of spawning beds, it is conceivable that some factor or factors other than overcrowding of eggs and alevins may cause the production curve to be dome shaped. With high spawning density, eggs remaining in the streambed at the end of spawning may originate predominantly from the late spawning females whose eggs may be less vulnerable to loss from superimposition of redds than those from early-spawning females. Should late deposition of eggs result in lowered survival (see Fig. 3, 4), fry production may diminish as the density of spawners increases beyond a level where superimposition of redds becomes common. Should spawners be less numerous, on the other hand, eggs from early-spawning females should experience lower mortality from superimposition or redds: an optimum density of spawners may exist, therefore. which would insure adequate usc of the

114 Su!'lJival of Pink and Clzum Salmon Eggs and Ale1·ins

·-c:: .-. 0 c ..._c:: ·-c ·-0 "0 E c Q) ::s flo. 0 flo.

Cl) C» (E- R) 0 L 0 0' CD c

'1- ·-c 0 ~ ... c Q) c. ..c Cl) E R ::s z 0 •• I= ) Potential egg deposi.tion (""" FIGURE 6 RELATIONSHIP BE1WEEN THE NUMBER OF EGGS REMAINING IN A SPAWNING GROUND (R) AND THE NUMBER LOST FROM SUPERIMPOSITION OF REDDS (E-R). THE ASYMPTOTIC LIMIT OF EGG RECRUITMENT TO THE SPAWNING GROUND IS L. available spawning ground, yet not present a major threat to eggs deposited by early spawners. Long-term observations at Sashin Creek suggest that two spawners (both sexes) per m2 of spawning ground is near the optimum density. This represents an escapemenL of about 27,000 pink and chum salmon spawners to Sashin Creek. ACKNOWLEDGEMENTS Continuation of long-term studies at Little Port Walter has been made possible through the participation of many pen;ons. The program of research was initiated under Frederick A. Davidson (1934-43) and has since been directed by Samuel J. Hutchinson (1943-48), Mitchell G. Hanavan (1948-56), RichardT. Myren (1956-59), Theodore R. Merrell, Jr. (1959-62), and William J. McNeil (1962-66). The daily operation of the field station has been assigned to five station foremen since permanent living facilities were completed in 1940: Richard F. Shuman (1940-43), Gomer W. Hilsinger (194346), Jerrold M. Olson (1946-60), Dennis A. Shepperd (1960..154), and Henry Kopperman · ( 1964-presen t).

115 Survh•a/ of Pink ami Chum Salmon Eggs and Alel'ins

·-c D -0:: c ...... ·-c: ·-0 '"C E c Q) ::s ...... 0 en 0 (E- R) 0 0 0 Q) ·-c ~ c 0 ~ .... c Cl) a. .c en E R :::s z 0 Pot e n t i a I e g g de p o s i. t i o n ( E } FIGURE 6 RELATIONSHIP BETWEEN THE NUMBER OF EGGS REMAINING IN A SPAWNING GROUND (R) AND THE NUMBER LOST FROM SUPERIMPOSITION OF RI.::DDS (E-R). THE ASY!IIPTOTIC LIMIT OF EGG RECRUITMENT TO THE SPAWNING GROU~D IS L. availabl~ spawning ground, yet not present a major threat to eggs depo•;ited by early spaWners. Long-~erm observations at Sashin Creek suggest that two spawnms (both sexes) per m2 of spawni!lg i;iOtmd is near the optimum density. This represents an escapement of about 27,000 pink and chum salmon spawners to Sashin Creek. ACKNOWLEDGEMENTS Continuation of long-term studies at Little Port Walter has been made possible through the participation of many persons. The program of research was initiated under Frederick A. Davidson ( 193443) and has since been directed by Samuel J. Hutchinson (194348), Mitchell G. Hanavan (1948-56), RichardT. Myren (1956-59), Th~odore R. Merrell, Jr. (1959-62), aP.d William J. McNeil ( 1962-66). The d?ily operation of the field station has been assigned to five fltation foremen since permanent living facilities were completed in 1940: Richard F. Shuman (194043), Gomer W. Hilsinger (1943-46), Jerrold M. Olson (1946-60), Dennis A. Shepperd (1960-64), and Henry Koppennan · ( 1964-presen t).

115 Symposium on Safrnon and Trout in Streams

David Brickell, Robert Coats, Richard Crone, Clark Fontaine, William McLarney, and Ralph Wells assisted in spawning ground studies over the period 1962-66. Dean Shumway and John Donaldson of Oregon State University and fheodore Merrell, Jr., William Heard, Robert J. Ellis, and Wilbur Hartman of the Bureau of Commercial Fisheries, provided many helpful suggestions on the organization und content of this paper.

LITERATURE CITED ALDERDICE, D.F., W.P. WICKETT and J.R. BRETT. 1958. Some effects of temporary exposure to low dissolved oxygen levels on Pacific salmon eggs. 1. Fish. Res. Bd. Can. 15: 229-250. ANDREW, F.J. and G.H. GEEN. 1%0. Sockeye and pink salmon production in relation to proposed dams in the Fraser River system. Int. Pac. Salmon Fish. Comm. Bull. 11,259 pp. BEVERTON, R.J.H. and S.J. HOLT. 1957. On the dynamics of exploited fish populations. U.K. Ministry Agr., Fish., Food. Fish. Invest. (Ser. 2) 19, 533 pp. BRANNON, E. L. 1965. The influence of physical factors on the development and weight of sockeye salmon embryos and alevins. Int. Pac. Salmon Fish. Comm., Prog. Rep. 12, 26 pp. COMBS, Bobby D. 1965. Effect of temperature on the development of salmon eggs. Progr. Fish-Cult. 2/: 134-137. CORDONE, .~lr o J. and })on W. KELLY. 1961. The int1uence of inorgantc sediment on the aquatic life of streams. Calif. Fish Game 47: 189-228. GULLAND, J.A. 1965. Survival of the youngest stages of fish and its relation to year-class strength. Int. Comm. Northwest Atlantic Fish., Spec. Publ. 6: 363-371. HANAVAN, Mitchell G. and Bernard Einar SKUD. 1954. Intertidal spawning of pink salmon. U.S. Fish and Wild!. Serv., Fish. Bull. 56: 167-185. HAYES, F.R., l.R. WILMOT and D.A. LIVINGSTONE. 1951. The oxygen consumption of the salmon egg in relation to development and activity. J. Exp. Zool. 116: 377-395. HELLE, John R., RichardS. WILLIAMSON and Jack E. BAILEY. 1964. Intertidal ecology and life histozy of piitk salmon at Olsen Creek, Prince William Sound, Alaska. U.S. Fish Wildl. Serv., Spec. Sci. Rep. Fish. 483, 26 pp. KOSKI, K. Victor. 1965. The survival of (0ncorhynchu8 kisutch) from egg deposition to emergence in three Oregon coastal streams, Thesis, Oreg. State Univ., Corvallis, 84 pp. LARKIN, P.A., R.R. RALEIGH and N.J. WILIMOVSKY. 1964. Some alternative premises for constiucting theoretical production curves. J. Fish. Res. Bd. Can. 21: 477-484. MATHISEN, Ole. 1962. The effect of altered sex ratios on the spawni~ of red salmon. Univ. Wash., Seattle, Pub!. Fish. 1: 137-246. McLARNEY, William 0. 1964. The coastrange , Cottus aleuticus: Structure of a population and predation on eggs of the pink salmon, Oncorhync!:us gorbuscha. M.S. Thesis Umv. Mich., Ann Arbor, 83 pp. McLARNEY, William 0. 1967. Intra-stream movement, feeding habits, and population of th~ coastrange sculpin, Cottus aleuticus, in realtion to egg3 of the pink salmon, Oncorhynchus gorbuscha, in Alaska. Ph.D. Thesis, Univ. Mich., Ann Arbor,l31 pp. McNEIL, William J. 1964a. A method of measuring mortality of pink salmon eggs and larvae. U.S. Fish Wild. Serv., Fish. Bull. 63: 575-588. McNEIL, William!, 1964b. Rcdd superimposition and egg capacity of pink salmon spawning beds. J. Fish. Res. Bd, Can. 21: 1385·1396. McNEIL, WiHiam J. 1966a. Effect of the ~pawning bed environment on reproduction of pink and ·.. chum salmon. U.S. Fish. Wildl. Serv., Fish. Bull. 64: 495-523. McNEIL, Willi~m J. 1966b. Distributio11 of spawning pink Salmon in Sashin Creek, southeastern Alaska, and survivat of their progeny. U.S. Fish Wildt. Sen•., Spec. Sci. Rep. Fish. 583, 12-pp. McNEIL, William J. 1967. Randomness in distribution of pink salmon redds. J. Fish. Res. Bd. Can. 24: 1629-1634. McNEIL, William J. 1968. Migration and distribution of pink salmon spawners in Sash in Czeek in 1965 and survival of their progeny. U.S. Fish Wildl. Serv., Fish. Bull. 66: 575-586. McNEIL, William J. and Warren H. AHNELL. 196 ~.Success of pink salmon. spawning relaHve to size of spawning bed materials. U.S. Fish. Wildt. Serv ., Spec. Sci. Rep, Fish. 469, 15 pp. McNEIL, William J ., Ralph A. WELLS and David C. BRICKELL. 1964, Disappearance of dead pink salmon eggs and larvae from Sushin Creek, Baranof Island, Alaska. U.S. Fish. Wildl. Sl!rv., Spec. Sci. Rep. Fish. 485, 13 pp. \ 116 \

I DUWflts. I .~-----_·--=-·-_~.. -_---_- .. _---_----_--'--_·~..:-______:.;_;..:. --::.\ I -I I 1 i Survival of Pink and Chum Salmon Eggs and A Ievins -t •• J l i MERRELL, Theodore R., Jr. 1962. Freshwater survival of pink salmon of Sashin Creek, Alaska. in ; N.J. Willimovsky (editor), Sympmium on pink salmon, pp. 59-72. H.R. MacMillan Lect. Fish .. Univ. , Vancouver. OLSON, Jerrold M. and William J. McNEIL. 1967. Research on pink salmon at Little Port Walter, Alaska. 1934-64. U.S. Fish Wildl. Serv., Data Rept. 17,5 microfiches. PHILLIPS, Robert \V. and Errol W. CLAIRE. 1966. lntragravel movement of the reticulate sculpin, Cottus perplexus, and its potential as a predator on salmonid embryos. Trans. Amer. Fish. Soc. 95: 210-21::!. RICKER, William E. 1954. Stock ami recruitment. J. Fish. Res. Bd. Can. 11: 559-623. RICKER, William E. 1958a. Handbook of computations for biological statistics of fish populations. Fish. Res. Bd. Can., BulL 119, 300 pp. RICKER. William E. 1958b. Maximum sustained yields from fluctuating environments and mixed stocks. J. Fish. Res. Bd. Can. 15: 991-1006. ROYS, Robert S. 1967. Forecast of 1967 pink and chum salmon runs in Prince William Sound. Alaska Dep. Fish Game, Inform. Leafl. 104, 49 pp. SEMKO, R.S. 1954. The west Kamchatka salmon reserves and their industrial utilization. Izv. Tikhook. Nauch.-Issled. Inst. Rybn. Khoz. Okea~ogr. 41: 3-109. (Fish. Res. Bd. Can., Transl. Ser. 288). SHERIDAN, William L. 1962. Wa~erflow through a salmon spawning rit'fle in Southeastern Alaska, U.S. Fish. Wildl. Serv., Spec. Sci. Rep. Fish. 407, 20 pp. SHUMWAY, Dean L., Charles E. WARREN and Peter DOUDOROFF. 1964. Influence of oxygen concentration and water movement on the growth of steelhead trout and coho salmon embryos. Trans. Amer. Fish. Soc. 93: 342-356. SILVER, Stuart J., Charles E. WARREN, and Peter DOUDOROFF. 1963. Dissolved oxygen requirements of developing steelhead trout and chinook salmon embryos at different water velocities. Trans. Amer. Fish. Soc. 92: 327-343. SKUD, Bernard Einar. 1958. Relation of adult pink s:llmon size to time of migration and fresh-water survival. Copeia, 1958(3): 170-176. SMIRNOV, A.G. 1947. Composition of the stocks of Amur salmon and the causes of their fluctuations in abundance. Izv. Tikhook. Nauch. Issled. Inst. Rybn, Khoz. Okeanogr. 25: 33-51. (Translation in Pacific Salmon, Nat. Sci. Found. and U S. Dep. Int., Israel Program for Scientific , Translations, Jerusalem.) VAUX, W.G. 1961}. Jntragravel flow and interchange in a streambed. U.S. Fish Wild. Serv., Fish. Wild). Serv., Fish. Bull. 66: 479-489.

117