1/S3 S7
A Biological Study of the Influence of the Bridge River Rapids on the Sockoye Runs of the Upper Fraser Watersheds
by
Stanley Reginald Killiok
A Thesis submitted in Partial Fulfilment of The Requirements for the Degree of
MASTER OF SCIENCE IN AGRICULTURE in the Department of ZOOLOGY
The University of British Columbia
APRIL* 1948 A Biological Study of the Influence of the Bridge River Rapids on the Sockeye Huns of the Upper Fraser Watershed. by
Stanley Reginald Killick.
•ABSTRACT
The significance of obstructed passage of sockeye up the Fraser river was not realized fully until, the very dlsast- erous effect^of Hell's Gate were revealed by the international -Pacific Salmon Fisheries Commission in 1941; After the import• ance of the Hell's Gate obstruction was established, evidence on the conditions at the Bridge River Rapids were reviewed and a study commenced in 1942. These Rapids are located on the Fraser river, 76 miles north of Hell's Gate and must be passed by all the sockeye races destined for the upper Fraser water• shed. The Rapids consist of two separate falls, and have been reported to have caused difficult and block passage to salmon as early as 19IS.
The study, commenced by the Commission in 1942, was outlined to determine the direct influence of the Rapids on the current sockeye populations and to make such adjustments in the contour of the itapids as to allow unobstructed passage of salmon at all water levels, should blockade conditions be revealed. The problem involved four separate tagging experi• ments from 1942 to 1946. No tagging was done in 1943. The results of the various experiments revealed that Or the sockeye ?*ere delayed art seriously blocked m some years during low water levels occurring in September and October. The late-running Chllko and Stellako sockeye were the only races that were effected as the other runs to the Stuart, Bow- ron and Horsefly districts pas.sed through the Rapids early in the summer when the water levels were high. After the completion of the analysis of the tagging experiments up to 1945, a recommendation, that two fishways be constructed at the Kapids, was submitted for the considera• tion of the Commission. The installation of fishways was ap• proved and their construction completed for the salmon runs of 1946. The efficiency of the fishways w^e tested in that year and a complete change in the pattern of tagsrecoveries was recorded. Whereas, block conditions were previously shown by sudden increases in the number of tags recovered below the Rapids; practically no tags were recovered below during low water periods after the fishways were built. The same methods of analysis that were used to determine block conditions were . repeated in 1946 to test the fishways and in each case a noticeable improvement in passage was recorded; Therefore, it was concluded that the fishways built at the Bridge Hjver Kap• ids were successful in passing sockeye salmon, through the previously known block periods that were revealed by tagging
in 1942j 1944 and 1945.
Frontpiece General view of the lower and upper falls at the Bridge River Rapids looking upstream. September 6, 1944. .Vater level RI gauge - 655 feet. CONTENTS
I INTRODUCTION 1 II REVIEW OF LITERATURE ...... v.. 3 Reports of J. P. Babcock ...... 3 (1) Condition of sockeye salmon in Seton Creek in 1912...... 3 (2) Observations at the Rapids 1912 and 1925 ...... 4 Dominion Fisheries report ...... i. 5 (1) No cohoe salmon present in the Upper Fraser watershed ...... 5 (2) Fluctuations in the Seton Creek populations ... 5 Investigations-of the International Pacific Salmon Fisheries Commission 7 (1) Reports of H. S. Tremper . *...... 7 (2) Bulletin #1 - W. F. Thompson ...... 8
III METHODS 10 Method and location of tagging ...... 10 Water levels ....•* 11 Theory of conducting a tagging experiment to. evaluate blockades ...... » 11 IV RESULTS ...... • 13 Number of Sockeye tagged 1942 - 1946 13 Section'A - Evidence of obstruction from the analysis of tagging 1942 - 1945 14 (a) Fishing intensity and races of sockeye ...... 14 CI) 1942 .... *...... i ...... 16 (2) 1944 .... ; . 18 " (3) 1945 18 (b) Percentage recovery of tags below and above the Rapids 20 (1) 1942 ...... r.21 (2) 1944 23 (3) 1945 25 (c) Time out before recovery of tags below ...... 27 (1) 1942 ...... 28 (2) 1944 30 (3) 1945 .. 30 (d) influence of water levels on percentage recovery below...... 33 (1) 1942 ...... 35 (2) 1944 . 35 (3) 1945 i. 37 The effect of Hell's Gate 39 Summation of the evidence of difficult and block conditions 45 Recommendations for f1shways 47 Section B - The. analysis of the 1946 tagging experi• ment to test the efficiency of the fishways. 48 (a) Fishing intensity and the races of sockeye.48 (b) Percentage recovery of tags below ahdabove.52 (c) Period of delay of tags below the Rapids .... 52 (d) Cummulative percentage of tags recovered below the Rapi ds...... 54
V SUMMARY AND' CONCLUSIONS 56 Before the fishways were constructed 57 After the fishways were constructed ...... 59 VI ACKNO'ffLSDG'EMENTS ...... 60 VII LITERATURE CITED 61 % Biological Study of the Influence of the Bridge River Raplda on the Sockeye Runs of the Upper
Fraser 'Watershed. 1
by
Stanley Reginald Killick
INTRODUCTION
The biological and engineering study of the Bridge River Rapids, and subsequent remedial measures taken by the International Pacific Salmon Commission represents the sec• ond major program for the removal of serious obstructions to the migration of sockeye salmon within the Fraser River water• shed. The first task was the discovery and definition of the block at Hell's Gate and the construction of fishways designed to pass salmon through a wide range of water levels. The significance of obstructed passage of sockeye up the Fraser River was not realized fully until the very dis- asterous effects of Hell's Gate were revealed in 1941. In that year it became apparent that water levels acted as a major control of the numbers of salmon reaching the various spawning grounds. After the importance of the Hell's Gate block was established, evidence on the conditions at Bridge River Rapids was reviewed more thoroughly and it became evldr ent that a study should be atarted at this point immediately. In the summer of 1943, the writer was stationed at the Rapids, and an extensive tagging program was commenced below and,above the Rapids. This study was designed to obtain information on the following phases of the problem:
(1) Dates of the arrival, peak, and end of the various runs through the Rapids. (2) Evidence as to whether sockeye dropped downstream and entered Seton Creek upon being blocked at the Rapids. (3) Dates and.durations of blockades.
(4) Precise water levels causing blocks.; ;
(5) Influence of Hell's Gate on the movements of sock• eye and its relationship to the Bridge River Rapids. The problem as defined by the Commission was to det• ermine the direct influence of the Rapids on the current sock• eye populations and to make such adjustments in the contour of the Rapids as to allow unobstructed passage of salmon to the
Upper Fraser, should blockade conditions be revealed as a re• sult of their study. It is the purpose of this paper to pre• sent accumulated'evidence of blockade conditions at the Bridge
River Rapids together with the results obtained after the installation of the fishways in 1946.
Referring to the map, the critical position of the
Bridge River Rapids is readily noted with respect to all the
Fraser River runs that, spawn above the confluence of the Thom• pson River at Lytton. Apart from the three runs into the
Thompson River watershed (Adams-Little River, Raft and Seymour) all the sockeye populations of the Fraser above Hell's Gate must pass through the Bridge River Rapids except for the small 3 Seton-Anders on run. To ssvoid confusion-, it must be noted that the Rapids are not on Bridge River despite the name but are on the Fraser proper, one-half mile upstream from the mouth of Bridge River and six miles north of the town of Lillooet. The Rapids consist of two separate falls approximately 900 feet apart. These have been designated as the "lower" and "upper" falls, both of which appear to become difficult or impossible for salmon to ascend during certain years when the water level of the Fraser River becomes low in. September and October. Details on the height of the drop through the two falls and -a3L other required data pertaining to profiles and rise and fall, of water levels have been studied by the engineering division of the Commission and are Included In an unpublished manuscri• pt by Milo Bell (1945). Plates I and II illustrate the turb• ulence and drop through the lower and upper falls. REVIEW OF LITERATURE A review of the literature and historical background of the Bridge River Rapids has aided materially in determining the method of study and defining the objectives to be achieved. Unfortunately, no precise studies of the Rapids had been under• taken prior to the work of the Commission but the sum of the accumulated evidence left little doubt that some factor or factors had influenced the passage of salmon at this location for many years. Reports of J. P. Baboock
(1) Condition of sockeye salmon in Seton Creek in 1912. 4 In the report of the Commissioner of Fisheries for British Columbia for 1913, Babcock made the following state• ments :
"The first sockeye entered our hatchery weirs at the outlet of Seton Lake on July 35. Between that date and August 17, when this run ended, 3,000 unusually large prime fish had entered the weirs. On September 1 the sockeye again began, entering the hatchery weirs, and by the 17th of the month up• wards of 10,000 were impounded in the seining pool. The run continued until October 8. The fish which passed'through the weirs after September 10 were in poor condition, being badly scarred about the head and many showed hook and spear wounds. It was estimated that more than half of the fish between the 15th and 30th were mutilated more or less by hook or spear. Many were so badly waunded that they died. During September 6,700 dead sockeye were removed from the weirs." "We attribute the exceptionally large - collect!on of sockeye eggs at the Seton Lake hatchery this year, and the battered and wounded condition of the f-ish that came to the station after September 10th, to the low stage of water in the Fraser River, which prevented their passing through the canyon half a mile above the mouth of the Bridge River". In 1937 and 1940 considerable numbers of sockeye were again found dead and unspawned in Seton Creek, This finding agreed with observations made in the strBams below Hell's Gate where many salmon were examined during block years and found dead and unspawned,
(3) Observations at the Rapids 1913 and 1935. In conduction of Mr. Babcock's report on the:jpopulations in Seton Creek (Cayoosh Cr.), he made a few actualyobservations on the Bridge River Rapids themselves. After a visit to the Rapids in 1913, Mr. Babcock reported that: "The river bed of the Fraser where the blockade occur• red is so narrow and so filled with projecting rocks, that even during ordinary stages the water rushed through with such velocity as to give the sockeye considerable difficulty in passing. The water was so low that the sockeye found their passage completely blocked by September 10. The waters of the Fraser were too discoloured to trace the movements of these salmon from the canyon back to Cayoosh Creek, but the fish 5 that reached the hatchery the last of September and the first of October were so scarred about the head as to convince any• one who had seen the bruised fish in the pools below the canyon (Rapids) that they received their injuries there, and being unable to pass up the Fraser had turned back to enter the first available lake-fed tributary stream".
Upon another visit to the Rapids in 1925 Babcock stat• es ' ed; "At such low stages of water as existed there this year the fish encountered as much difficulty as they did at Hell*s Gate. They (sockeye) were blocked for two weeks and during that time most of them that escaped capture by Indians dropped down-stream and entered Cayoosh Creek. Five hundred" sockeye entered Seton. All were in advanced condition and believed to be all blocked sockeye."
Dominion Fisheries Reports. (1) No Cohoe salmon present in the Upper Fraser watershed. In reviewing some of the pertinent literature in the
Dominion Fisheries report It was found that ishoro. aro no Cohoe salmon (Oncorhychus kisutch) have ever been reported in the upper Fraser river district; however, they are present in the South Thompson watershed which is accessible without pas• sing through the Bridge River Rapids. The cohoe is a fall-run salmon and would inevitably arrive at the Rapids In late Oct• ober and November if they passed the Thompson River junction.
(2) Fluctuations in the Seton Creek Populations A more direct indication of a blockade at the Rapids is found in a review of the sizes of the Seton Creek populat• ions. One important consideration, to be described in the subsequent analysis of the tagging data, was the tracing,of blocked sockeye from below Bridge River Rapids down the Fraser and into the Seton-Anders'on watershed. In 1942,this behaviour- was actually proved, by the recovery,in Seton and Portage creek, of tagged sockeye that were held up by. low water at the Rapid during September and October. This phenomenon was strongly suspected in 1912, 1925, 1937 and 1940 by various observers but lacked proof until tags could be traced from the Rapids to Seton creek. With, the knowledge of this movement, it is possible to indicate certain years in the past in which block conditions must have existed at the Rapids.
The estimated sockeye populations of Seton Creek have been tabulated from the records of the Dominion Department of
Fisheries for all years from 1901 to 1946 (Table I). In those years in wMch Seton creek had an unusually large run, the presence of blocked sockeye was indicated by the fact that the brood year was too small to warrant the great increase.
Furthermore,the run four years later showed no improvement as a result of the influx of blocked fish. Those years in which the populations of Seton Creek were thus increased are marked with a double asterisk For example, the year 1937 showed a population of approximately 50,000 sockeye, yet the brood year of 1933, showed only a run of 100. Still more evident was the fact that the 1941 populations which should be the progeny of the 50,000 sockeye In 1937 consisted of only 50 salmon. The block at Bridge River Rapids must have been ser• ious in 1937 as indicated by the Seton population. In 1942, when the Rapids were under daily observation, tagged sockeye were.traced back to Seton but the fish were not as abundant in that year as they were in 1937. TABLE I
ESTIMATED SOCKEYE POPULATIONS OF SETON CREEK
Year Population Year Population
-
1901 1,000,000- " 1924 -• 50 1902 0 1925 66,000*-*- 1903 971 1926 40G 1904 1,000 1927 200 1905 200,000 1928 700 1906 15,000** 1929 200 1907 — •' 1930 100 1908 - 1931 100 1909 1,000,000 1932 100 1910 - 1933 100 1911 90 1934 400 1912 10,000 1935 200 1913 30,000 1936 15,000** 1914 300 1937 50,000** 1915 200 1938 500 1916 100 1939 20 1917 - 200 1940 2,000** 1918 100 1941 50 1919 200 1942 1,000** 1920 0 1943 800 1921 0 1944 100 1922 0 1945 20 1923 0 1946 75
** Block at Bridge River Rapids indicated. Investigations by the internatipnal Pacific Salmon Fisheries Commissdon
. (1) Reports of H. S; Tremper. • The following observations were made by the Commiss• ions observer stationed at the Rapids in 1940; "A slight blockade to the migrating salmon at Bridge River Rapids was evident on September 26. This partial block- lasted two days. From then (September 28) until October 4 the 8 Rapids were a very serious obstacle to the migrating sockeye. There were large numbers of sockeye which were weakened to such a state that it did not seem possible that they could ascend the Rapidsi It then seems obvious that the Rapids had a deter- ant effect on large numbers of sockeye at certain water levels. Weak, battered sockeye were observed attempting the Rapids and two days later, cleaner, fresher sockeye appeared in the eddies;"
The observer states in conclusion:
"It is evident that the Bridge River Rapids represents a problem of near equal magnitude as Hell's Gate. It should be studied in'a similar manner and with equal vigouri"
(2) Bulletin §1 - W. F* Thompson.
The above brief review of some of the early history
as quoted chiefly from Babcock is sufficient to demonstrate
that difficult passage at Bridge River Rapids has been effect•
ive for many years. Investigation conducted by the Internatio- af Hell's Gate from 1939 'to nal Pacific Salmon Commission/1942 has further indicated that
some interrupting factors have influenced the distribution of
the, sockeye races in the Fraser River system. Thompson (1945)
described the fluctuating populations of the Seton-Anderson watershed and also showed the major division of the sockeye races into the Upper Fraser and the Thompson area by the recov•
ery of Hell's Gate tags on the spawning grounds. The pattern
of race segregation Into the two systems noted above Is an
important factor in the appreciation of the seriousness of the
Bridge River Rapids.
Reference may be made to figure 21 in Thompson's re•
port where the recoveries of Hell's Gate tags on the various-
spawning grounds have been plotted. From this figure it is
apparent that at present there are two main divisions of the
sockeye runs within the Fraser River system. The first divis- 9
ion passing Hell's Gate before September 18 is comprised of
sockeye going to the Upper Fraser watershed. The "3econd divi•
sion passes Hell's Gate after September 18 and is destined for
the South Thompson district. With only minor exceptions this
pattern of division holds true for every cycle of t»he present
day runs. However, the history of the Thompson river runs has
shown that sockeye formerly migrated during the period before
September 18 and Thompson'(1945) presents various reasons for
their decline almost to the point.of complete extinction. It
then remains to be shown what factor or factors could restrict
the passage of sockeye after September 18 to the Upper Fraser,
A strong clue as to the fate of some of these late
runs to the Upper Fraser is found in the sudden appearance of
.large, unexpected runs into the Seton-Anderson watershed*
Further evidence of the obstruction of late runs will be brought
out in the analysis of the tagging in the following sections of
this paper.
Vital evldenoe was furnished by the investigations of
Babcock, Thompson and Tremper indicating that difficult passage
and often serious block conditions to the salmon migrating to
the Upper Fraser have been in effect for many years. However,
only the dates of difficult passage were given and no definite
water levels were assigned to the periods of slight delay and
periods of serious obstruction. Thus, the apparent need for
adequate data on accumulations of fishj dates of blockade and
accurate water levels became evident. The determination of the seriousness of any suspected 10 obstruction to the migration of salmon presents a difficult problem that requires study from every possible approach. To date, only limited means are available to accurately determine difficult passage of fish in any other watershed than the
Fraser river. Thus, the method of tagging as employed by the
Salmon Commission at Hell's Gate was used again at the Bridge
River Rapids as the best method so far available for solving this type of problem. Certain modifications"and adjustments have been made to suit the particular conditions at the .Rapids but essentially the evidence of blockade is Interpreted by the pattern of the tag recoveriesi
METHOD
Method and Location of Tagging
The method of affixing the tags to the sockeye at the
Rapids was the same as that'uaed In all the tagging program conducted by the Commission and may be referred.to in the report of MacKay, Howard and Killick (1944). The sockeye were captured for tagging in Indian dip nets. All fish tagged were kept out of the water for as short a time as possible and sel• dom more than 45 seconds was required for the whole operation.
Details on the condition, total length and scars were recorded and ;a':.scale sample taken from each fish;
Fishing stations were located below and above the
Rapids so that comparisons of the fishing intensities and re• covery of tags could be made* In 1944, tagging was limited to the stations below the Rapids only, because of a reduced crew. Sockeye were tagged at both the right and left banks 11
below the falls. In the analysis of the tag recoveries it was
found that there was no significant difference between the numbers of recoveries from the two banks; therefore, a combin•
ation of both groups of tags was used.
Water Levels
Consistent water level readings were recorded since
1942^ from a single gauge below the Rapids^ during the salmon migrations. These readingsj taken dally except on Sundays, for the months of JulyAugust, September and October will be found at the appendix of this paper. During the 1944 season, more extensive water level readings were taken by the Commiss• ion engineers at ten separate locations below and above the
Rapids on both right and left banks-'! The gauge;used in the interpretation of the biological data^ is located on the right bank of the river below the lower falls. (Gauge Rl)
As it was desirable to have water level readings for years previous to 1942, the rate of flow of the river as rec• orded at Jesmond was interpolated into gauge readings at the
Rapids as far backa as 1935. Jesmond is located approximately
30 miles north of Llllobet . For the purposes of the block• ade analysis, the water level readings at the Rapids as calcu• lated from Jesmond and correlated with gauge Rl will be used throughout this report.
Theory of conducting a Tagging Experiment to evaluate blockades. As it is impossible to actually observe the salmon 12 within the Fraser river, some mark or identification must be attached to the fish in order that their movements may be traced, .in this case, numbered celluloid tags were attached to as many salmon as possible both below and above the site under study* The salmon, when caught unselectlvely, tagged and returned to the river, represent the best known means of demonstrating what is happening to the population as a whole.
In conjunction with the tagging operation, accurate water level readings were taken each day and the developement of any falls or turbulent waters recorded. It then remains to be seen where and when these tags will be recovered and in what numbers they will be taken above and below the tagging site*
The place of recovery of the tags put on below will be considered first. In this regard it is quite logical to assume that if some tags are recovered above and h£ tags are recaptu• red at the place of tagging or at any downstream point then these tagged fish have proceeded upstream without difficulty.
It is equally logical to reason that If these tags were recov• ered In significant numbers at the place of tagging below or at any downstream point then some factor has impeded their pro gress passed-the site under study. Concurrent with the abun• dance of tags recovered below, there may be a corresponding scarcity in the numbers of recoveries above*
in addition to the analysis of tags put on below, the tags put on above are studied. If no obstruction is in effect, the pattern of upriver returns from the tagging below and above should be the same. If on the othec hand an obstruction 13
occurs, it has been found that the sockeye tagged.above during
block periods were recovered in reduced numbers on the spawn•
ing as were those sockeye tagged below during the same period.
It would appear that an extended delay, caused by the obstruc•
tion, reduced the vitality of the fish to such an extent that,
even though some sockeye were able to surmount the Rapids and be tagged above, they were unable to reach the spawning grounds.
If a differential recovery of tags occurred within the season then an explaination should be sought to account for the various recovery fluctuations. The first thing to look for is undoubtably the influence of the river through which the salm• on must swim* ThuSj the water levels have been gauged and plotted against the pattern of tag recoveries. This process was repeated over a period of years to find out what relation• ship exists between the water levels and the success of pass• age of migrating salmon.
RESULTS
Number of Sockeye tagged 1942-46
A summary of the total numbers of sockeye tagged is shown in the following table II:
Year Tagged below Tagged above No. in crew
1942 1173 469 3 1944 3341 0 2 1945 1980 931 4 1946 1808 651 4
Totals 7301 2041 14 A
Each year the maximum numbers of sockeye were taeyeu tagged and every effort wiss made "to secure at least 10 sockeye on each day of tagging. Details on the relative abundance of tags applied throughout the season are given in the sections on the fishing intensity.
Section A Evidence of obstruction from the analysis of tagg• ing 1942-1945.
In this section of the paper the results of the taggi• ng experiments for the years 1942, 1944 and 1945 will be pres• ented to show how the Rapids influenced the passage of sockeye salmon to the Upper Fraser; The various means of illustrating the distribution of tags and the numbers of recoveries below and above the Rapids are included for each year of tagging.
The results will then be summarized and a general statement given as to the seriousness of the Rapids and the recommend• ation for. remedial measures*
RESULTS.
(a) Fishing intensity and Races of sockeye.
In figures 1-3 it is shown that the sockeye populations arriving at the Bridge River Rapids are comprised of a number of distinct and separate races. The segregation of these races has been clearly illustrated by Thompson (1945) and has been confirmed by the results of the present Bridge River Rapids tagging experiment. The figures indicate which runs might be effected by a block at the Rapids. They also Illustrate the varying abundance of sockeye of the Rapids throughout the f season and the period of passage or range of the various races 15
Figure 1 Daily catches of sockeye above and below Bridge River Rapids plotted against the water levels and ranges of the runs of the Upper Fraser sockeye population in 1943. 1942
30 10 20 30 10
H STELLAKO
GHILKO
4 BOWRON
H STUART
120 DAILY CATCHES
Below Above
10 20 30 10 20 30 10 20 30 10
JULY. AUGUST • SEPTEMBER OCTOBER 16 destined for the spawning ground of the Upper Fraser river. (1) 1942 With reference to figure 1 it will be noted that tag• ging commenced on July 10 and ended on October 16. The catches of the tagging crews indicate that these dates include the full range of the sockeye migration to the Upper Fraser river spawning grounds passed the Bridge River Rapids during 1942. Fishing was continued to October 28 but no sockeye were caught after October 16.
It is shown that the catches were erratic through July and August and at no time except July 31 were the sockeye abundant. However, on September -2 and 3 a sudden, heavy influx of sockeye occurred and large catches were made until September 21. This abundance of fish consisted of a wave of blocked salmon that were released from a block at Hell's Gate when the water level dropped below 28 feet on August 31st. These fish then ran into low water at Bridge River: Rapids and large num• bers were seen accumulating in the eddy below the lower and- upper falls and accounted for the heavy catches occurlng in September; It is interesting to note a sudden increase in the catches about the Rapids on September 19 which coincided with a rise in water level to 652.8 feet on this date. Comparing the catches of fish below and above the
Rapids on figure 1, it was noted that practically no sockeye were taken at the upper station after September 22, yet sock• eye were still being caught in some numbers below. It was at this time that the water level had dropped below a gauge 17
Figure 3
Daily catches of sockeye below the Bridge River Rapids plotted against the water levels and ranges of the runs of the Upper Fraser sockeye populations In 1944. 1944
20 30
STELLAKO
H CHILKO
BOWRON
200 DAILY CATCHES 80 Below
60
40
20
100
80
60
40
20
0 10 20 30 10 .20 30 10 20 30 10 JULY AUGUST SEPTEMBER 18
reading of 650 feet and remained low for the remainder of the season. It should also he realized that no sockeye tagged at the Rapids after September 27 were recovered on the spawning grounds despite the fact that sockeye were tagged in signifi• cant numbers up to October 12. (2) 1944
In 1944, the tagging was confined to the stations bel• ow the falls. The first sockeye were caught and tagged on July 12 and operations were terminated on September 24. The daily catches in 1944 present a markedly different picture from those of 1942, but again the influence of Hellas Gate was ref• lected. With reference to unpublished data complied by G. B. Talbot(1948)on the effect of blockade, at Hell's Gate, It was reported that salmon were delayed until August 14 after which the water rose suddenly and good passage was permitted until August 25. This opening at the Gate between August 14 - .25 was reflected in the large catches at the Rapids from August 18 to September 3. None of the sockeye tagged after September 17 was recovered on the spawning grounds even though tagging continued until September 24.
It should be #oted that the 1944 water levels were high throughout the sockeye migration period and no large accummulation of fish was observed below the Rapids.
(3) 1945 A crew of four men commenced fishing at the Rapids on July 5* The first catch of sockeye occurred on July 7 when 4 sockeye were tagged. As far as was possible to determine, 19
Figure 5
Daily catches of sockeye above and below the Bridge River Rapids plotted against the water levels and ranges of the runs of the Upper Fraser sockeye populations in .1945. 1945
WATER LEVELS BRR
30 \ STELLAKO
^ CHILKO
H MIDDLE RIVER
H HORSEFLY
-I BOWRON
-I EARLY STUART
120 DAILY CATCHES Below Above
JULY AUGUST SEPTEMBER so no sockeye were taken at the Rapids before July 7. On July 8 the sockeye run increased and 25 sockeye were tagged on that day* Consistent tagging continued from July 8 to the end of the salmon migration on October 24. The catches made by the tagging crews below and above the Rapids have been plotted separately to illustrate the effects of possible blocks of salmon below the falls; Obser- ing the daily oatches above and below the Rapids it is seen that the bulk of the sockeye were caught during July and Aug• ust. The good catches made during July were attributed to the Stuart Lake run and to a lesser extent the Bowron sockeye; The largest catches were made between August 10 and August 16 when the peak of the Chilko run was passing through.
From August 20 to 30, the catches were poor and no large run of fish appeared after that date. One point of major importance was the fact that no lengthy breaks occurred in the catches at the Rapids this year as often happened in the past. This steady passage of sockeye was credited to the improved passage at Hell's Gate.
The most important conclusion drawn from figure 3 is that no sockeye tagged at the Rapids after September 12 were recovered from the spawning grounds of the Upper Fraser, despite the fact that sockeye were still being tagged at the Rapids until October 5. It would therefore appear that the Rapids were blocked after September 12. (Water level on Sept• ember 12 - 651 feet).
(b) Percentage Recovery of Tags Below and Above the
Kapld3 t 21 The recovery of the tags was divided into two main groups; namely, recoveries below and recoveries above the Rapids. The recoveries below the Rapids were tags recovered immediately below the Rapids or at any downstream point; The recoveries above were made mostly on the northern spawning ground but include small numbers of recoveries from Indian fishing stations located along the route of the salmon migra• tion. The total recovery of tags was broken down into the number of each dayfs tagged sockeye that were recovered either below or above and are presented as percentages in figures 4-6. ,
In the earlier section of this paper dealing with the theory of tagging it was stated that if no tags were recovered below the tagging location then the passage of salmon could be regarded as being unobstructed; However, if tags were re• captured below, then they should be studied as to abundance, time out and their relationship to the water-levels. The figures on the percentage recovery of tags below and above the Rapids illustrate the; fluctuations occurring throughout the season, but the extent of the delay occurring before the tags were actually recovered is. not shown. This factor of time will be dealt with later, (see pages 27.-33} (1) 1942
The fluctuating pattern of the recovery of the tags put on in 1942 is illustrated in figure 4i ) . It is seen that ~ some sockeye were recaptured below the Rapids throughout the whole season. It is also noted that the percentage of recov- 22
Figure 4
Percentage recoveries of tags from each day of tagging as recovered above and below the Bridge River Rapids 194S.
Blank columns represent days when less than 10 sockeye were tagged. 1942
640' • ' 1 1 r 10 20 30 10 20 30 10 20 30 10 JULY AUGUST SEPTEMBER OCTOBER
0 10 20. 30 10 20 30 10 20 30 10
Date of Tagging at Right Bank Above
10 20 • 30 10 20 30 10 20 30 10 JULY AUGUST SEPTEMBER OCTOBER Date of Tagging at Right Bank Below 23 ery below, fluctuates,, widely'from 0 to 68% for any one day of tagging. Through July and August the number of recoveries was fairly uniform except for slight increases in recovery on July 26 and 29 and August 17* On August 24 and 31 the number of re• coveries increased; but the samples were too small to warrent consideration. However, commencing on September 2, wide fluct• uations became apparent* it appears that the number of recov• eries increased as the water dropped below the 650 foot water level on September 2,4 and 7* With the sudden rise in water level to 652.8 feet between September 17-19 the recaptures bel• ow decreased* By September 20 the water again dropped below the 650 foot mark and remained low for the remainder of the season. With the onset of low water the number of recoveries below the Rapids increased rapidly and the presence of a block
became apparent. The influence of the critical water levels around the 650 foot level was also reflected in the patter on the recover• ies above the Rapids* Corresponding to the rise in water level above 650 feet there was a rise in the percentage recovery of tags above and._a similar reduction in the recoveries below. It is the association of these three factors that provides some
of the basic evidence in the definition of the presence of a blockade at the Rapids* This alone,, however, is not sufficient evidence as it must be known how long the fish were out before being recaptured below the place of obstruction. (2) 1944 The recoveries made during 1944 are plotted &nfigure 5* Again the percentages fluctuate widely throughout the sea• son especially through July to the middle of August; No assoc• iations jvarsi noted between the recoveries below and above 24
Figure 5
Percentage recoveries of tags from each day of tagging as recovered above and below the Bridge River Rapids 1944. Blank columns represent days when less than 10 sockeye were tagged. 1944
WATER LEVEL 670
660
650 10 20 30 1( 10 20 30
% RECOVERED ABOVE 60
40 -
20 -
L 0 I T— r 10 20 30 10 20 30 10 20 30
6*0 RECOVERED BELOW 60
40
20
0 10 . 20 30 10 20 30 10 20 30 JULY AUGUST SEPTEMBER
Date of Tagging Below Rapids 85 the Rapids until.the end of August and during September; Com• mencing on August 18, it is shown that a steady increase occur• red in the recoveries below and a corresponding decline in the recoveries above. The recoveries indicate that some sockeye tagged after August 30 were delayed long enough to have prevented them from reaching the spawning grounds. After Sept• ember 5 the small percentage recovered above became evident*, however,the bulk of the sockeye passed through the Rapids from
August 18 to September 3. During this, period a high percentage of recoveries was made above; therefore, only a small propor• tion of the runs was effected by the Rapids at the end of the season.
As will be shown later in the analysis of the data on the days-out before recapture of the fish below the Rapids, the salmon were not seriously delayed during the 1944 season despite the volume of recoveries below; (3) 1945
Referring to figure 6 it is seen that a radical cha• nge occurred in the patted of tag recoveries taken above and below the Rapids in 1945; It was found that there was cons• iderable variation in the. daily percentage recovery of tags above the Rapids. However, this variation was not caused by the block conditions alone, but also depends on the extent and efficiency of the recovery operations on the various spawning grounds. This is best illustrated by the high percentage recoveries made above the Rapids in July on the sockeye run to Stuart lake where approximately 80$ of the dead fish were r
Figure 6
Percentage recoveries of tags from each day of tagging as recovered above and below the Bridge River Rapids 1945.
Blank columns represent days 'when less
than 10 sockeye were tagged* 10 20 ' 30 10 20 30 10 20 30
% I RECOVERED BELOW
JULY AUGUST SEPTEMBER Dates of Tagging Below Lower Rapids 27 examined. In contrast only about 25$ of the Chilko sockeye - which pass /through the Rapids In August were examined on the spawning grounds* Were the small sample of dead fish at Chilko not taken into account it would be suspected that the August run of salmon were subject to a heavy mortality. Low percentage recovery of tags below during both July and August indicates good passage; therefore the varying percentage recovery above is influenced mostly by the variation in ability to recover _ tagged fish on the spawning grounds. Having accounted for the variations in tag recovery
during July and August, we find greatly reduced recoveries in
September far below what could have been recovered on the
spawning grounds had the tagged fish passed the Rapids. Direct•
ly corresponding to the declining recoveries above, were the
rapidly increasing percentages recoveries of tags below. At
this same time the water level had dropped below the 650 foot
mark.
In contrast to the recoveries above, the percentage
of recaptures below was low during July and August* indicating
a good ascent of the Salmon through the Rapids. Recaptures
were few below the Rapids during the passing of the main part
of the Chilko run. It was not until September 5 that the
higher percentages of tags were recovered. From September 5
to the end of the season, the daily percentage of recaptures
below the Rapids was high and block conditions were In effect*
(c) Time out before recovery of tags below. 28
The varying abundance of tagged sockeye recovered below the Rapids and the length of the delay period before the tags were recovered is shown on figures 7-9.' Each recovered tag is represented by a straight line drawn from the date of recovery on the right to the date of tagging on the left. The numbers of recaptures below the falls were few during open periods at the Rapids^ also, the tags that were recovered had only been out a few days; When periods of difficulty and block occur, the number of recaptures will be large and the number of days out before recapture will be extended. The recaptures are plotted against the water levels to show when the open and closed periods occuri (1) 1942
Upon analysis of Figure 7, it is evident that the vc recaptures during August were few, indicating good passage of salmon through the Rapids. Following the drop in water levels at the end of August, Hell*s Gate opened and a large run of sockeye arrived at the Rapids on September 3. By this date the water at the Rapids had dropped below the 650 foot level and the sockeye found passage up-stream difficult. Between
September 3 and September 17 the numbers of recaptured salmon greatly increased and the sockeye were subjected to a delay of
1 to 6 days or an average of approximately 3 days. Two tagged sockeye dropped downstream and entered Seton Creek during this period. Water levels below 648 feet were most serious and the period of delay became much greater when this level was reached 29
Figure 7
Periods of delay as shown by tagged fish recaptured below the Rapids. The lines are plotted.from the date of recovery on the right to date of tagging on the left. Broken lines represent tags recovered from Seton and Portage Creeks, 1942. 1942
TAG RECOVERIES AT POINT OF TAGGING BELOW BRIDGE RIVER RAPIDS
10 20 30 10 20 30 10 20 3Q 10, 20 30 JULY ' AUGUST SEPTEMBER OCTOBER . 30 The block remained into October and an additional 9 sockeye dropped downstream and were recovered in Seton Creek during the month* (see -f-igure 7) The rise in water level during
October would have relieved the block conditions somewhat had it occurred earlier in the season* By this date the sock• eye were so weakened that further migration was unlikely.
(2) 1944
It has already been demonstrated in figure 5j that a considerable number of tagged sockeye were recovered below the Rapids; however, the lapse of time from the date of tagging to date of recovery was short in most cases as shown in figure
8. Only a few of the fish recaptured below the Rapids had been out for more than 2 or 3 days. The first sign of any delay occurred on August 6 at which time the lower east bank was difficult to ascend. (Water level 657 feet). An 18 foot rise in water level between August 14 and August 18 permitted all d delayed sockeye to pass upstream. A short delay commenced on
September 1 and lasted until September 8; however, these sock• eye disappeared without a rise in water level* In general, a slight' difficulty to migrating sockeye occurred at a water level of approximately 658 feet in 1944.
(3) 1945 Observing the pattern of recoveries in figure 9 it becomes apparent that a relatively good passage of salmon occ• urred during July and August. Some evidence of delay and accumulation was indicated which may have been caused by diff• icult passage on the east bank, e.g. August 10 and August 26. 31
Figure 8
Periods of delay as shown by tagged fish recaptured below the Rapids. The lines are plotted from, the date of recovery on the right to date of tagging on the left. 1944. 1944
TAG RECOVERIES AT POINT
OF TAGGING
BELOW BRIDGE RIVER RAPIDS
T 1 I 1 1 1 I I 1 1 1 I 10 20 30 10 20 30 10 20 30 10 20 30
JULY AUGUST SEPTEMBER OCTOBER 32
Figure 9
Periods of delay as shown by tagged fish recaptured below the Rapids. The lines are plotted from the date of recovery on the right to date of tagging on the left. 1945. 1945
TAG RECOVERIES AT POINT
OF.TAGGING
BELOW BRIDGE RIVER RAPIDS
10 20 30 10 20 30 10 20 30 10 20 30
JULY AUGUST SEPTEMBER OCTOBER 33 The most important conclusion to be drawn from figure 9 is the effect of the obstruction on the salmon during September* Commencing September 5 and even more apparent on September 8 a block condition was indicated by the large numb• ers of recaptures and the extended period of delay. The water dropped below the 650 foot level on September 4 and except for slight rise to less than 651 feet between September 11 and September 15 the water continued to drop through the remainder of the season* (d) influence of Water Levels on Percentage Recovery Below It may be realized from the tagging analysis pres• ented so far that one method alone can not be relied upon to illustrate the total effect of a block. The method used to show the varying percentage recoveries below the Rapids was useful but did not establish the duration of the delay before the tagged sockeye were recovered. The second method used to demonstrate the time of the block, by means of the line graph, provided information on the duration of the delay but did not allow for the differences in'the numbers of tags applied on the different days* It was necessary to combine the two types of analysis to show clearly how the various water levels influence the passage of sockeye through the Rapids. In figures 10-12, the water levels have been groups ed into 5 foot intervals so that the samples will be sufficien• tly large to demonstrate what occurs as the water level drops* The line between the points is actually a reversed cumulative curve and was established by subtracting one days recovery of 34
Figure 10
Percentage recovery of all tags put on below and recovered below the Rapids at different water levels. The percentage recovery of tags out for varying number of days is also shown. 194E. 1942
DAYS OUT 1 2 3 4 5 6 7 B 9 10-15-20 20 r
12 34 56 78 9 10-15-20 20 ! 1
35
tags from the accumulation of all those taken including the day to be subtracted.- For example, in 1942 at the 650-646 foot water level, 23.2$ of all the tags put on were eventually recovered below the Rapids. The.number of tags that were only 1 day out then substracted, leaving 21.5$ of the tags out g.t least 2 days. This procedure was continued until it was seen that 2.6$ of the tags were out for more than 20 days. The significance of this type of figure is that the percentage of the recovery is readily noted for all tags and also the percentage of recovery for all periods of delay can beoaeen. This is important because a block was only serious when a delay of considerable length was caused. Thus if the line dropped to a low percentage after a delay of only one or two days then no serious damage will be likely to, occur*
(1) 1942 • Observing the figure 10 it appears that there was no delay above water levels of.665 feet; Some difficulty in the passage of sockeye occurred during water-levels 665-651, and serious delay in significant numbers occurred in the 650-646 levels. The high percentage of recoveries and the extent of delay below 650 feet appeared to be the critical stage in the passage of sockeye in 1942. This confirmed the conclusions reached by the other methods of analysis. (2) 1944 The average water levels were high in 1944 and no serious.delay was noted at the Rapids; yet, a considerable number of tags were recaptured below the Rapids. The pattern 36
Figure 11
Percentage recovery of all tags put on below and recovered below the Rapids at different water levels. The percentage recovery of tags out for varying number of days is also shown. 1944. 1944
DAYS OUT 1 2 3 4 5 6 7 8 9 10-15-20 20 +
665-66 1 -
* °—-o .
66O-65 6
655-65 1
itiiii r 7 I 1 1 I i ' 12 3 4 5 6 7 8 9 10-15-20 20 of these recoveries is showng on figure 11. The range of water levels through the season was small and at no time during the sockeye migration did the water level drop below 650 feet. Some delay was evident between water levels 660-651 feet but only up to a period of 4 days. It is considered that although it would be ideal to have absolutely no delay, the conditions in 1944 would not cause serious harm.
(3) 1945
The extreme range of water-levels were found in 1945. Above the water level of 655 only a few tagged sockeye were recovered below the Rapids. With few exceptions, these socke• ye were recovered within 3 days. Between 655-650 some diffic• ulty was shown; however, only a small percentage of the sockeye were delayed longer than 5 days. The most signiglcant influe• nce of serious obstruction was evident In the water levels of 650-646 and 645-641. During these periods, slightly over 34$ of all tags put on were recovered below the Rapids. Equally important was the entent of the delay of these obstructed sockeye* The curves do not drop to the base line rapidly, illustrating that a considerable number of sockeye were delayed for a long period o£ time, (see figure 12)
On the basis of these illustrations it was evident that some factor was influencing the success of passage of sockeye through the Rapids. Further, it was evident that there was a differential effect on the degree of passage during different water levels. Some difficulty was illustrated during water levels above 650 feet vrtien delays of 3 to 5 days were 38
Figure 12
Percentage recovery of all tags put on below and recovered below the Rapids at different water levels. The percentage recovery of tags out for varying number of days is also shown. 1945. DAYS OUT 1945 g 12 3 4 5 6 7$? 10-15-20,20*
3 665-66I 0 3 66O-656 0
5 h
0
30
25
20
15 h
10
5
0
645-641 30
25
20
15
10
5
0 —1 1 r- 1 1 r 1 r 1— 1 1 r~—S— 123 45 6 7 J 9 10-15-20 20 39 found; howeverj the major periods of obstruction occurred below the 650 foot water level and were apparent in each of the methods of analysis* It then remained to be shown what would happen after the fishways were installed for the passage of the 1946 run of sockeye salmon* The Effect of Hell's Gate
It has been stated in the introduction to this paper that there was the possibility that a delay of sockeye at Hell's Gate may have weakened the salmon to. such an extent that they would be unable to pass the turbulent waters of the Rapids located 76 miles upstream. It might be further sugges• ted that, after the construction of the'Hell's'Gate fishways^ the unobstructed sockeye would be sufficiently strong to over• come the difficult waters of the Rapids above* While this possibility existed-^ a definite statement of the seriousness of the Rapids could not be made on the basis of the 1942 and
1944 data* It remained to be seen what the circumstances would be during the season of 1945 at which time the Hell's Gate fishways would be nearly complete. The analysis of each tag• ging experiment at the Rapids has been presented and it was evident that difficult and blockade conditions persisted at the Rapids during the 1945 season to the same or greater extent than those occurring in 1942 and 1944. Thus it was concluded that even with improved passage of sockeye through Hell's Gate, the block stages at the Rapids remained as serious as they had in previous years. Upon the completion of the analysis, of the 1945 data, recommendations for fishways at the Rapids were 40 first submitted.
This problem of defining obstruction conditions at any point above a previous obstruction point further downstream is sufficiently important to warrant brief discussion and the inclusion of figures 13 and 14. If it is reasoned that the salmon were weakened at the first barrier sufficiently to act as their only cause of delay at a second barrier, then it must be demonstrated what weakening has occurred and which group or groups of salmon were thus effected. If it can be shown that weakened fish were always held up at the second obstruction and strpng fish were never delayed, then it is probable that the second location would not be a serious factor when the first location had been cleared. It is equally probable that if previously weakened fish did pass the second barrier at certain times and that both weakened and strong fish were delayed at other times then each barrier represents an independent factor.
To demonstrate the circumstances between barrier #1 at Hell's Gate and barrier #2 at the Bridge River Rapids, two measurements of possible weakness of the salmon have been investigated. In an earlier unpublished report (Killick 1945), the condition of the sockeye, recorded by the taggers as "green", "pink" and "red'% was analysed. It was found that that there were few salmon in "red" condition and that the fish noted as "green" and."pink" were equally delayed during water levels below 650 feet. It was also noted that the maj• ority of the tagged sockeye that dropped downstream from the
Rapids during blocked stages and entered Seton and Portage t 41
creeks were in "green" condition when tagged. However, this measure of the weakness or strength of the salmon is open to criticisim, inasmuch as the appearance of "green" and "pink" sockeye may not actually represent their true condition; A second and more positive criterion of the condition of the sockeye when they arrive at the Rapids is the number of days it takes for the salmon to travel between Hell's Gate and the Rapids. Weakened fish will be those fish taking the long• est time to arrive at the Rapids. The figures 13 and 14 illustrate the number of days required for sockeye to pass from Hell's Gate to the Highway' bridge located six miles below the Rapids. Hell's Gate tags recovered at the Rapids themselves have been plotted m a sep• arate manuscript but are not used here as it is impossible to distinguish between the time enroute and the time of delay be• low the Rapids. As there is no reason to suspect delays, dur• ing any water levels, between the Highway bridge and theiRapids it was concluded that the days - out presented on the figures represent j within a few hours, migration rate to the Rapids;
Observing figure 13 for the year 1942, it is apparent that a wide range in the speed of migration from 3 to 49 days was required for sockeye to travel from Hell's Gate to the Hi• ghway bridge* Fish arriving at the bridge up to August 10 were out 12 days or less and were considered to be in good physical condition; After August 10 and during September, a consider-; able number of sockeye were out a long time before reaching the Highway Bridge and these salmon were possibly weakened by a delay below Hell's Gate; However, sockeye were 42
Figure 15
The migration rate of sockeye tagged at Hell's Gate and recovered at the Highway bridge at Lillooet, 1942 and 1944. 19^2
T r
M-0
£> 30 o %20
• « 12.22 ... _ - - - V. o__o _ 10 * o*
10 20 30 10 20 30 10 20 30 JULY AUGUST SEPTEMBER DATES OF RECOVERY
i r -> : r
ho
EH 30 O
CO _ 13.5lJ- f —.—— ...... , 4 10 10 20 30 10 20 30 10 26 30~ JULY AUGUST SEPTEMBER DATES OF RECOVERY 43 not obstructed at the Rapids in August as they should have been if weak fish are suspected of being delayed at the second barrier. Further, there was a block at the Rapids during September and it effected all fish whether previously delayed or not. By the pattern of the days out of fish from Hell's Gate in 1942, it appears doubtful that the block at the Rapids was the result of only the presence of weakened sockeye as these were present during the full month of August when no evidence of a block was occurred at the Rapids.
In 1944-, the data were not conclusive as the numb• ers of recoveries were small; however, it does appear that the sockeye arriving after August 24 were previously delayed suf• ficiently to cause some weakening. Low block levels were not encountered at the Rapids in that year.
The season of 1945 was of major importance in the final definition of the Bridge River Rapids obstruction as the fishways at Hell's Gate were in operation during that year* The possibility existed that, with the improved passage of sockeye through the Gate,^ the Rapids would no longer act as an obstacle to the salmon* The fact that the passage through Hell's Gate in 1945 was improved has been clearly demonstrated by data on file in the laboratory of the International Pacific Salmon Commission. This improvement passage was reflected def• initely in the more concentrated pattern of quick recoveries of Hell's Gate tags at the Highway Bridge as shown in figure 14. Despite the improved passage and condition of sockeye after Hell's Gate was remedied, it was found that block con- 44
Figure 14
The migration rate of sockeye tagged at Hell's Gate and recovered at the Highway bridge at Lillooet. 1945 and 1946. 19^5
-
o CQ •* • • « • • 10 - •* • • •• 8.59 • •• 0 • • •1 ••• • • •
1 .0 20 30 10 20 30 10 20 30 JULY AUGUST SEPTEMBER DATES OF RECOVERY
19^6
• i 1 1 1 1 1 1 r-
• S 30 • o • CQ • g 20 • • • • - • • • 10 • • * • - jo." ~.V •• — • A - • g.55 * * • •
L0 20 30 10 20 30 10 20 30 JULY AUGUST SEPTEMBER DATES OF RECOVERY 45 ditiona still persisted at the Rapids in 1945; It was then evident that even when no previous delay has been encountered by the sockeye at a downstream point they still were unable to pass the Rapids during certain low water levels stages occur•
ring in September and October4
The means of the number of days-out throughout the season was also significant* Whereas in 1942 and 1944 it took on average of 12.22 and 13.54 days for sockeye tagged at Hell's Gate to reach the Highway Bridge, it required only 8.59 and 8.55 days to cover this same distance in 1945 and 1946*
llhe pattern of the rate of migratlonfrom Hell's Gate to t;he Highway Bridge during 1946 has been included as an additional check on the Hell's Gate fishways* Figure 14 Illustrates that the bulk of thesrockeye passed undelayed between the two points the same as they had in 1945. The num• ber of days required for the migration during 1945 and 1946 show a remarkable similarity; thus it was possible to compare the Bridge River tagging results for these two years without question as to the condition of the salmon. Summation of the evidence of difficult and block conditions.
In reviewing the evidence of difficult and block conditions at the Bridge River Rapidsj it must be realized that, as yet, there is no single test sufficiently accurate to produce the required answers to the problem. Information from every possible source must be considered. Thus, the review of the literature was presented to express the opinions of earlier investigators. The analysis of the tagging programs " 46 of 1942, 1944 and 1945 follows and represents the more exten•
sive study, the results of which form the basis for precise
conclusions and the recommendation of a solution to the problem.
Three years of tagging were required before a de• finite statement could be made regarding the success of passage of sockeye salmon through the Rapids. In 1942, direct obser• vations and the pattern of tag returns pointed strongly to a state of serious obstruction during low water levels. In 1944, water levels remained high during the sockeye migration making it impossible to test the results obtained in 1942 during low water stages; The tagging conducted during 1945 supplied the final answers by confirming earlier suspicions and avoiding the possibility that Hell's Gate was a factor in the definition of a block at the Rapids.
Various methods of analysing the tagging data have been employed to test the presence of obstructed passage; and in each case the periods of delay and block occur at the same water levels in each year.
Upon summarizing each method of analysis it was found that above water levels of 665 feet less than 1% of the sockeye were delayed longer than 1 day below the Rapids. Below 665 feet and above 650 feet, up to 10% of the sockeye were delayed at least 1 day; however, only 5$ of the fish were delayed from 2 to 4 days. Delays of over 20 days were record• ed for a few individuals during water levels between 665 - 650 but not in sufficient numbers to be important. These water 47 levels were classed as difficult and were considered in the recommendations for the installation of fishways.
Water levels below 650 feet were then considered and a remarkable change in the patternof tag returns was noted.' The recovery of tags below the Rapids increased to as high as 34% of all tags applied. Recoveries above the Rapids showed a corresponding decline and it was apparent fchat block conditions
were in effect. The period of delay was extended and sockeye were traced from below the Rapids down into Seton and Portage creeks. The numbers of sockeye reaching the spawning-grounds dropped to nearly zero during the extended block periods in 1942 and 1945. Every method of analysis showed the same results and clearly illustrated that water levels below 650 feet at the Rapids were critical and acted as a serious barrier to the sockeye salmon migrating to the spawning grounds of the Upper Fraser watershed. Recommendations for fjshways. A summary report on the tagging experiments for the years 1942, 1944 and 1945 was submitted for the consideration of the Commission in the fall of 1945. Included in this report, was a recommendation that fishways be constructed at the Rapids, to pass salmon during periods of difficult and block water levels. It was proposed that fishways be built at both the lower and upper Rapids and that they should function from a top level of 665 feet to a bottom level of 642 feet. After careful consideration of the biological evidence and the results of an extensive engineering survey the proposed fish- 48
ways were approved* Constuction of the flshways was started in the spring of 1946 and completed for the salmon runs of that year.
Section B-- The analysis of the 1946 tagging experiment. to test, the efficiency of the fjshwaya.
The fishways, shown in plates III and 17, were constructed early in the spring of 1946; They were designed to permit unobstructed passage of sockeye salmon to the Upper Fraser spawning grounds.through the entire period of the sock• eye salmon migration. To test their efficiency, it was nec• essary to repeat the earlier tagging experiments and record any changes in the pattern of tag returns. The results of the 1946 tagging at the Rapids are presented and include each method of study used in the earlier programs.
(a) Fishing intensity and the races of sockeye
The varying abundance of sockeye as caught at the Rapids is shown in figure 15. The catches made by the tagging crews below and above the Rapids have been plotted separately.
It was noted that the peaks of abundance of sockeye correspond closely to mid-points.of the passage of the dlffer- en#£r*uns. The peaks of the runs as they occurred at the Rapids were as follows: Stuart-July 27 j Bowron-August 3, Chilko-August 17, Stellako- September 3. The time of passage of the various runs was determ• ined from the Bridge River tags that were actually recovered on the spawning grounds and traced back to the date of tagging at the Rapids. Observing the ranges of the runs and the daily 49
Figure 15
Dally catches of sockeye above and below the Bridge River Rapids plotted agains the water levels and ranges of the Upper Fraser sockeye runs in 1946 1946
H STELLAKO
H GHILKO
BOWRON
H STUART
120 DAILY CATCHES Below —— 100 Above
80
60
40
20
0 —i r 10 20 30 10 20 30 10 20 30 ! JULY AUGUST SEPTEMBER 50 catches, it was noted that there were no extended periods of poor catches followed by a mass of fish as has occurred in the past when Hell's Gate delayed passage.
Catches above the Rapids, dropped almost to zero during September, yet sockeye were still being caught below in small numbers. It would appear that the decline in the catches above indicated a block at the Rapids, however it was found that sockeye tagged at the Rapids during September below the 650 foot water level succeeded in reaching the northern spawning ground. It was then realized that a comparison of the abundances in the catches above and below the Rapids cannot be relied up to measure the success of passage.
Sockeye tagged on the last day of tagging, September 28, were recovered on the Stellako river district, (see figure 15) This finding was in direct contrast to the pattern of recoveries in 1945 when not a single tagged sockeye was recov• ered from the spawning grounds of the Upper Fraser river after September 12 (water level-650 feet), although sockeye were tagged at the Rapids until October 5. It would therefore in 1946 - appear that the sockeye were not blocked below the Rapids/de• spite the fact that the water level dropped below the block level of 650 feet on September 11, and continued to remain low throughout the remainder of the season. This was the first time since biological studies were started at the Rapids that tagged sockeye from below the falls were recovered on the northern ground after continuous block conditions were in effect. 51
Figure 16
Percentage recoveries of tags from each day of tagging as recovered above and below the Bridge Klver Kapids 1946. Blank columns represent days when less than 10 sockeye were tagged. 1946 53 (b) Percentage recovery of taga below and above the Rapids. A comparison of the water levels and tags recoveries for 1945 and 1946 provides a striking illustration as to what occurred after the fishways were installed. The water levels were similar for the two years; therefore the periods of block, i as reflected by the recovery of tags above and below the Rapids, should have been approximately the same; such was not the case. In 1945, the recovery of tagged sockeye below the Rapids incre• ased noticeably with the advent of low water below 650; whereas in 1946j practically no tagged sockeye were recovered below during similar low water level conditions. (Figure 16). in all years previous to the construction of the fishways, there had been a distinct increase in the percentage recovery of tags below the Rapids and a corresponding decrease in the percentage recoveries above when the water level dropped below 650 feet. Such was not the case after the fishways were put in and high recoveries above persisted despite a drop in water level down as low as 643.4 feet by September 38. Thus, it was found that the pattern of recoveries of tags above and below the Rapids had distinctly changed and sockeye were able to pass undelaye:d through the Rapids at water levels below the 650 foot water level. Good ascent was recorded during water levels down as low as 643.4 feet. (c) Period of delay of tags below the Rapids. In studying the tag returns for 1946 on figure 17, it was found that few tagged sockeye were retaken below the 53
Figure 17.
Periods of delay as shown by tagged fish recaptured below the Rapids. The lines are plotted from the date of recovery on the right to date of tagging on the left, 1946. WATER LEVELS 1946
i r TAG RECOVERIES AT PLACE OF TAGGING BELOW BRIDGE RIVER RAPIDS
10 20 . 30 10 20 30 10 20 30 JULY ; AUGUST SEPTEMBER 54 falls which indicated unobstructed passage with only chance recaptures being made on the same day as they were tagged; Passage in August appears to be free from definite block periods. However, some delay was caused the sockeye-about. August IE* Tt was on this date that the east bank of the lower falls appear• ed to become difficult to ascend and the delay indicated, pro• bably represents the time it took for the sockeye to overcome the east bank falls or to cross over the west bank where the fishway was functioning.
The most striking feature shown on figure 17 is the few recaptures occurring in September when the water level dropped to below 650 feet on September 11* Sockeye were being tagged all through September below the Rapids and had the fish- ways not been in operation, recaptures would have probably reached a maximum during this month* (see figures 7 and 9)
(d) Cumulative percentage of tags recovered below the Rapids at different water levels. -Figure 18
The recoveries below the Rapids in 1946 have been plotted exactly the same as those for previous years. When observing all recoveries it appears that there was some delay between 665 - 656; however, when only those recoveries out 3 days or more were considered, there were no significant num• bers of sockeye recaptured below throughout the entire season* Of greatest significance was the drastic change in the pattern of recoveries below 650. feet* In 1943 and 1945 the recoveries 55
Figure 18,
Percentage recovery of all tags put on
below and recovered below the Rapids at different water levels. The percentage recovery of tags
out for varying number of days is also shown. 1946 1946
DAYS OUT 12 34 56 7 8 9 10-15-20 20 +
670-6 66 5
0
665-6 61 5 \
> O 0 C 0 660-6 56 5 -
0
655-6 51 5 -
0 65O-6 46 5
0 o 645-6 41 5"
1 1 12 34 56 7 8 9 10-15-20 20 56 below 650 feet were numerous and periods of extended delay were recorded; however, in 1946 there were no tags recovered from tagging in the levels 650 - 646 and practically none recovered between 645-641. It was evident that whereas a block previous• ly occurred below 650 feet before the fishways were installed, the passage was almost completely cleared after the fishways were constructed.
SUMMARY AND CONCLUSIONS Discussion and investigation on the success of the upstream migration of adult sockeye salmon within the Fraser fiver watershed has been of vital interest for at least the last forty-five years. Hell's Gate attracted particular atten• tion in the years 1913 to 1915 but the extent to which water levels acted as a major contfiol of the numbers of salmon reach• ing the various northern spawning grounds was not realized until 1941. As soon as the International Pacific Salmon Com• mission became aware of the great losses of salmon at Hell's Gate then all the evidence on the conditions at the Bridge River Rapids were reviewed ^thoroughly and a biological study was commenced at the Rapids in 1942. The purpose^ of this study was to determine the direct influence of the Rapids on the current sockeye populations and to recommend such measures as to provide unobstructed passage.for salmon should blockade con• ditions be revealed. A program of tagging was outlined and carried on in 1942. The 1942 experiment was repeated in 1944 and the results reported for each of these years. It was then thought that 57
the delayed passage of salmon at Hell's Gate might have been a factor m the conditions at the Rapids; therefore, a third tagging program was conducted at the Rapids after the fishways at Hell's Gate has been constructed. At the conclusion of the 1945 study, it was apparent that difficult passage and block conditions were still effective at the Rapids and two fishways were recommended. After careful consideration of the biologi• cal and engineering reports on the Rapids, the recommendations were approved^, and the two fishways constructed in the spring " of 1946. A fourth tagging experiment was conducted in the summer of 1946, to test the effeclency of the fishways. This paper presents the most pertinent facfis revealed by the analy• sis of each of the four tagging experiments.
The most important conclusions are outlined below: A..-Before the fishways were constructed.
(1) A review of the reports of J. P. Babcock indicated o that serious block conditions existed at the Rapids as early as 1912. He stated that the sockeye entering Seton Creek late in the season were battered and wounded after being blocked at the Rapids.
(2) The fact that no cohoe have yet been found in the upper Fraser may be attributed to block conditions at the
Rapids.
(3) The irregular fluctuations in the Seton Creek sock•
eye population strongly indicate that block conditions at the
Rapids have been effective for many years. (4) Figure 21 in Bulletin No.l of the international 58
Pacific Salmon Commission shows that there are two main div•
isions of sockeye runs within the upper Fraser river system.
The first division passes Hell's Gate before September 18 and
goes to the Upper Fraser while the second division passes the
Gate after September 18 and goes to the Thompson district* Thompson suggests that blocks during September and October, at the Bridge River, Rapids may have prevented the occurance of a fall run of sockeye in the upper Fraser. (5) Block conditions were indicated below the 650 foot water level in 1942 and 1945 when the daily catches above the
Rapids became poor while fair catches, were still being made below.
(6) A loss of sockeye f.r,omthe Stellako and Chllko runs was indicated in 1942 and 1945. After the water level dropped below 650 feet, sockeye were still being tagged at the Rapids until October 12 in 1942 and October 5 in 1945; yet, none of the sockeye tagged after September 27 in 1942 and September 12 in
1945 were recovered from the spawning grounds.' A loss of the last part of the Chllko run was indicated in 1944; however only a small portion of the run was effected.
(7) . The percentage recovery of tags below the Rapids increased rapidly in 1942 and 1945 during water levels below
650 feet. Recoveries of tags above-.the Rapids showed a corres• ponding decline during these same water levels; , . (8) Less than 1% of the sockeye were delayed longer than 1 day when the water levels at the Rapids were above 665 feet. 59 /
(9) Below ©65 feet and above 650 feet, up to 10$ of the sockeye were delayed at least 1 day; however, only 5% of the fish were delayed from 2 to 4 days* (10) When the water level dropped below 650 feet, the recovery of tags below the Rapids increased to as high as 34$ of all fish tagged.
(11) During extended periods of block, sockeye tagged at the Rapids were recovered in Seton arid Portage Greeks.
' (12) The numbers of tagged sockeye reaching the spawn• ing ground dropped to nearly zero during the block periods of
1942 and 1945. (13) Fishvmys were recommended to provide passage for salmon during the low water period. These were constructed by the Commission in 1946.
(14) After studying the migration times from Hell*!s Gate to the Highway Bridge located 6 miles below the Rapids, It was concluded that the Rapids would act as a barrier to sal• mon irrespective of a previous block at Hell's Gate* B - After the Fjshways were constructed. (1) After the flshways at ths; Rapids were built for the salmon runs of 1946 it was found that sockeye tagged during water levels below 650 feet were not recovered below* (2) Up to the last day of tagging, sockeye were recover• ed on the northern spawning grounds*
(3) Sockeye were known to have passed through the Rapids undelayed even when the water level dropped as low as 643.4 feet*
t • ; 60
(4) Between•water'levels 665 - 656 feet a slight delay still remained; however, when only tags out more than 3 days were considered the number of recoveries became insignificant* (5) Wo tags were recovered below the Rapids from tagg• ing in levels 650-646 feet and practically none recovered be• tween 645-641* (6) From the sum of the 1946 analysis it was concluded that difficult passage above 650 feet was relieved and previous block conditions below 650 feet' were completely remedied after the fishways were constructed.
i
ACKNO WLEDGEMBNT3 The writer wishes to express his appreciation to Mr'. B. M. Brennan, Director of the international Pacific Salmon Fisheries Commission, for permission to use the material con• tained in this paper and to Dr. R. Yan Cleve for his critlsim of the manuscript. In addition, the author is indebted to Dr. Wi A. Clemens for his encouragement and advice during the analysis of the data* Sincere thanks are extended to Mr. R. I. Jackson for the development of the plates. LITERATURE CITED
Babcock, J. P. 1913• The spawning beds of the Fraser. Report of Commissioner of Fisheries for British Columbia. 1912, p.28.
1926. The spawning beds of the Fraser. Report of Commissioner of Fisheries for British Columbia. 1925. p. 41.
Bell, M. I945• Preliminary report on Bridge River Rapids remedial work, Fraser River. International Pacific Salmon Fisheries Commission.. Manuscript.
Canada. Department of Fisheries. • 1901 - 1946.. Various field reports on file at the Dominion Fisheries Office, New Westminster, B. C
Killick, S. R. 1945* The obstruction at the Bridge River Rapids. International Pacific Salmon Fisheries Commission. Manuscript.
MacKay, D.C.G., G. V. Howard, and S. R. Killick. 1944* Sockeye tagging at Sooke and Johnstone Strait. International Pacific Salmon Fisheries Commission. Annual Report, 1943» p. 21-22. New Westminster, B.C.,
Talbot, G. B. 1948. A biological study of the effectiveness of the Hell's Gate fishways. International Pacific Salmon Fisheries Commission." Manuscript.
Thompson, W. F. 1945. Effect of the obstruction at Hell's Gate on the sockeye salmon of the Fraser River. International Pacific Salmon Fisheries Commission. .Bulletin 1, 1945* P. 101-113. New Westminster, B.. C. 2.
Tremper, H. S. 1940. Season's report for the Seton-Anderson watershed. , International Pacific Salmon Fisheries Commission. Manuscript. Water Levels at Bridge River Rapids - 1942
Calculated from. Jesmond
Day July August September October 1 666.6 661.5 649.5 646.2 2 667.0 660.9 649.3 646 ;0 3 667.3 660.5 649.2 645.8 4 668.0 659.8 648.8 645.6 5 669.1 659.4 648.5 646.0 6 670.0 658.9 648.1 647.4 7 670.1 658.7 648.1 647.1 8 670.1 658.9 647.9 646*9 9 669,7 658.9 649.0 647*4 10 670.0 658.7 649.3 648*3 11 668.0 658.7 649*8 649.2 12 667.3 658.7 649.8 650*1 13 666.8 658.4 649.5 650;0 14 666.4 658; 2 649.3 650 ;0 15 666.1 657.9 649.2 650.0 16 665.5 656;7 649.0 649.0 17 665.5 655.8 649; 5 648.1 18 667.0 655; 4 651.5 647.4 19 667.5 655.6 652.8 646.6 20 667.7 656.5 650*8 645.6 21 667.0 657.4 649*6 644.9 22 666.1 657.9 649.2 644.7 23 665.5 658.4 649.0 644.5 24 665.2 657.9 649*0 646 ;0 25 665 ;0 656.9 649.0 647.4 26 664.7 655.6 648; 7 647; 6 27 664.1 654.4 648.1 646*3 28 663.1 653;9 647.7 645*6 29 662.5 652.8 647.1 645.6 30 662.0 651.1 646.9 645.6 31 661.7 650.0 645*8 Water Levels at Bridge River Rapids - 1944
Calculated from Jesmond
Day " July August September October 1 661.-0 658.4 656,9 3 663.5 660.0 657*9 656.6 3 663.3 658;-8 656*8 655.4 4 663.0 657.3 656.6 655*3 5 662.6 656.7 655 *• 7 661.7 6 661.6 656.5 654*• 9 663*9 7 661.0 656*5 653*8 665.4 8 660.8 656*6 653*3 662*5 9 660*7 656.5 653.0 659*3 10 660*5 656.1 652.9 656.3 11 659.7 655*5 653 .-1 655*3 12 659*4 658.2 653.1 653.6 13 659*1 664.6 653.0 653.4 14 659.7 670.2 653.7 650*7 15 660*4 652;-7 649.9 16 660.7 670.1 653*1 649*7 17 660 i 5 667.6 654*0 648*9 18 661.4 664.9 655*1 648; 6 19 663;6 663,"7 655*3 648.3 20 662.1 663*8 654*3 647.8 21 661 il 662.6 654*1 647*3 22 660*8 663.4 653*8 647*0 23 660.8 661.-6 654*- 5 646*8 24 661*0 659.-7 653*1 646.8 25 661.0 658 .-4 653 s 7 647.3 26 663.3 657*0 653 i 2 647*4 27 665*4 656*'6 653 i 3 647*3 28 664.6 655; 9 659i6 647.0 29 663.2 657.0 659 .-7 646.5 30 661.9 657.-6 657 i8 646.0 31 661.4 657i6 645*5 Water Levels at Bridge River Rapids 1945 Calculated from Jesmond
Day July August September October
1 . 658.0 652.6 642.3 2 668.4 657.8 642.2 3 667.3 656,4 651.1 642.5
4 66607 655.2 650.2 642.7 5 667.0 649.7 642.9 6 666
20 660o8 654,6 647.4 646.1 21 659*8 653.8 647.8 22 653*8 646.6 645.4 23 659.4 653.3 644.3 24 658.2 652.0 645.6 644.1 25 658.5 651.1 645.3 643.6 26 659.1 651.3 644.5 642.4 27 658.8 651.4 643.6 642.3 28 658.1 651.6 643.3 641.9 29 652.6 643.0 641.7 30 658.2 653,2 641.4 1946 Water Levels - Gauge R, I
Bridge River Rapids
Day July August September October
1 664.3 653.5 . 643.5 2 670.5 664.3 643.7 3 670* 1 652.5 642*4 4 669; 7 652.1 642.8 5 669.9 664*,5 651.9 642; 5 6 663.2 651.8 643.0 7 661.4 651.6 641.8 8 669.5 660 *.l 651.3 641.5 9 669.3 660*3 641.1 10 669.0 650.5 640*7 11 668.6 648.8 . 640,* 4 12 668.0 659.4 648,. 3 640; 2 13 ' 658.4 648.5 639; 9 14 658.9 639,. 8 15 668.0 658*9 640.1 16 668.7 658; 8 647.9 640.3 17 668.8 658.3 647.7 640.2 18 668.8 647.6 639*9 19 671*4 658.0 647.5 639*5 20 657 i'O 646*9 639.2 21 655.7 645.7 639.4 22 668.7 655*0 645.1 639.1 23 667.9 655*0 639.4 24 667.4 655.2 644^. 1 639.8 25 666.9 655.1 644.2 640.2 26 666.2 644.0 640.4 27 655.4 643.7 640.4 28 V--' <, '.. * vj 655.0 643.4 640-.8 29 664;2 654.6 643.4 640.4 30 664.1 654*2 640*0 31 664.3 653.6 640.7
Plate II The upper falls at the Bridge River Rapids and the lower section of the upper fishway under construction. March 5, 1946. Water level Rl gauge - 634 feet. Plate III The upper falls at the Bridge River Rapids and the completed upper fishway. April 25, 1946. v/ater level RI gauge - 647 feet. Plate IV General view of the lower and upper falls at the Bridge River Rapids and the completed flshways. April 25, 1946. Water level RI gauge - 647 feet.