Relationship of Variable Oceanographic Factors to Migration and Survival of Fraser River Salmon
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RELATIONSHIP OF VARIABLE OCEANOGRAPHIC FACTORS TO MIGRATION AND SURVIVAL OF FRASER RIVER SALMON 1. A. ROYAL International Pacific Salmon Fisheries Commission and J. P. TULLY Fisheries Research Board of Canada INTRODUCTION north through Queen Charlotte and Johnstone Straits. In 1957 it was noted that a larger share of Management of the various Fraser River salmon the population approached Vancouver Island from fisheries requires an intimate knowledge of the abund- the north, a larger percentage (approximately 16 ance and movements of salmon runs, which is drawn per cent) diverted through Queen Charlotte Strait largely from a detailed study of commercial catches. and it was also noted that the fish were slightly de- Abnormalities in abundance, in routes of migration layed, and migrated over a longer period of time. or times of occurrence, unless forecasted, may negate the beneficial effect of fishing regulations formulated In 1958, the sockeye run of approximately 19,000,- in advance of the fishing season. A flexible method of 000 fish failed to appear off the west coast of Van- regulatory adjustment during the course of fishing couver Island in its usual initial landfall and arrived may help rectify the adverse effects of vagaries in the northerly of Vancouver Island in the Queen Char- salmon population but it cannot be accepted as a lotte Sound area. The fish then moved in a southerly substitute for advance knowledge and planning. direction with an estimated thirty-five to forty per cent of the total population entering Queen Char- lotte Strait, thus approaching the Fraser River, from OCEANOGRAPHIC FACTORS AFFECTING the north instead of the usual route through the Juan SOCKEYE SALMON MIGRATIONS IN de Fuca Strait. In addition to the vagary in their THE NORTHEAST PACIFIC route of migration the fish appeared in the fishery ten The formulation of fishing regulations in advance days later, and oyer a longer period of time than of the fishing season requires knowledge of abund- was anticipated on the basis of previous catch rec- ance, timing and migration routes of the Fraser River ords. sockeye runs. It is known that adult sockeye abund- The effects of the radical departure from normal ance has been affected considerably by marine sur- in the route and timing of the 1958 Fraser River vival rates which have ranged from 4.22 to 18.54 per sockeye populations were serious. A surplus escape- cent in recent years. However, since there is some ment of 1,500,000 fish occurred. These could have reason to believe that freshwater and estuarial fac- been harvested had the fish followed the usual migra- tors as well as the physiological condition of seaward tion route at the usual time. The delay in the arrival migrants may influence subsequent marine survival, of the escapement on the spawning ground disturbed an oceanographic or ecological study of marine con- the normal relationship of the spawning population ditions, as related to sockeye survival, appears rather to its reproductive environment, and map have seri- impractical until these factors are more fully under- ously jeopardized its reproductive potential. The stood. While variations in survival are important, it physiological development of the fish was so disturbed is relatively simple to make compensatory adjust- in the latest arriving section of the population that ments in fishing regulations for unexpected changes an estimated ten per cent of the total escapement in abundance, provided that the timing of the runs is failed to reach their spawning grounds, some 350 inherently consistent, as it is in most years, and the miles upstream. routes of inshore migration follows a consistent pat- 111 analyzing all possible causes of the vagaries of tern. If, however, the measurement of abundance the route and timing of the 1957 and 1958 runs of from commercial catches in initial fisheries is con- sockeye to the Fraser River it is logical to conclude fused by a delay in arrival, or a change in the route that the physical marine environment, at least dur- of migration, or both, then the problem of properly ing the maturing year, must have been responsible. managing the fishery becomes most complex. Oceanographic observations over recent years show I Normally the bulk of the maturing Fraser River that when the fish went to sea the normal currents sockeye arrive off the west coast of Vancouver Island and approach the Fraser River around the south end and water masses were present off the approach to of the Island through Juan de Fuca Strait (figure 1). Juan de Fuca Strait, and that anomalous oceano- A smaller part of the population, less than ten per graphic conditions first developed off the southern cent, passes around the northern tip of Vancouver British Columbia coast in 1957 and were intensified Island and approaches the Fraser River from the in 1958. 66 CATJFORNIA COOPERATIVE OCEANIC FISHERIES ISVESTIG.\TIOXS FIGURE 1. Vancouver Island and Fraser River approaches. The trans-Pacific drift current normally flows east- sion showed that the distribution of feeding Fraser ward into the Canadian approaches. In the spring of River sockeye apparently tended to shift iiortlirrard 1957 this flow began to veer towards the north. By coincident with the warm water intrusion, and that mid-summer 1958 the flow was due north in the region no concentrations of these fish were found in the area within 600 miles of the Canadian coast. Associated westward of Vancouver Island as in precediiig years. with this change of current direction, warm water It niay be postulated that the more northerly landfall intruded northward. Tt was evident as far as the of the 1!157 and 1958 sockeye runs was the direct northern end of the Queen Charlotte Tslantls. It result of temperature preferellee on the part of the reached its maximum extent in August 1958, and has feeding sockeye in the ocean. The latenr\s in arrival degenerated somewhat since then. In the affected re- might be ascribed to the conseqnent displacenieiit of gion the seawater temperatures were 2" to 3" centi- the sockeye to more distant feeding grounds or to grade warmer than is considered normal at the sur- a circuitous migration path to avoid the warm water face. The temperature anomaly decreased with depth, iiitrusion. This concept is tenable because in l!)M arid vanished at about 500 meters. The occurrence, there was a narrow band of cooler, near normal waler, duration, and extent of the intrusion was determined close along the west coast of the Queen Charlotte by observing the temperature increase at 180 meters Islands. This would provide a coast-wise migration depth, well below the influence of seasonal heating route into Queen Charlotte Sound. A modification oB and cooling. The increase in surface temperature is this concept would be that strengthened ocenii CIII*- significant because the normal seawater temperatures rents slowed the migration rate of the fish. It can in this area, at the time of the summer shoreward be further postulated that the more northern distri- migration of sockeye salmon, are near the upper limit bution of the fish brought the sockeye into higher lati- of preference for sockeye. tudes where the days mere longer dnring the late Sampling by investigators in the northeast Pacific spring and sumnier months. This may have thc (Ift'cct during 1956, 1957 and 1958 under the sponsorship of retarding maturation and thus delaying the cor- of the International North Pacific Fisheries Commis- related migration. A study of the degree of matnra- REPORTS VOI*UAII’: 1‘111, 1 .TIJJ,Y 1959 TO 30 JUNE 1960 67 tion and energy reserves of sockeye arriving at the allow for equality in the total catch of each of the mouth of the Fraser River commencing in 1956 re- two national groups involved and €or adequate escape- veals that maturation and energy reserves were ap- ment. The pink and sockeye runs entering Juan de proximately the same in 1958 as were those of sorkeye Fuva Strait are highly vulnerable to a Canadian fish- in the preceding years, in spite of the ten day differen- ery opwating on the north side of the Strait. A U.S. tial in arrival. These findings teiid to support the lat- fishery on the south side of the Strait has never been ter of the above hypotheses. The increased temporal consistentl,~effective and its lack of siicwss has been dispersion of the run can also be explained on the attributed in a large part to the vertical distribution basis of light response. If the fish were spread over of the fish in the southern area. If the U.S. fishermen a range of latitudes wider than normal, the resultant were to develop a successful fishery in the southern greater variation of day-length encountered would side of the Strait the whole scheme of regulation account for the increased interval over which fish ~vouldhave to be revised with a major displacement arrived in the fishery. of the existing over-all fishery. Whatever the pattern of forces that created the study of the currents in Juan de Fuca Strait re- vagaries in 1957 and 1958 Fraser River sockeye runs, veals that in the northern half of the Strait the ebb a serious derangement in the management of the 1938 trilnsport of mixed salilie and land drainage water fishery resulted. The economic importance of predict- greatly exewtls the flood transport of highly saline ing these vagaries in advance has been established. ocean water. The reverse situation occurs on the southern side. Since the fish are apparently seeking THE RELATION OF OCEANOGRAPHIC waters of reduced salinity as they approach the CONDITIONS IN GEORGIA STRAIT E’raser River they probably prefer the lower salinities TO PINK SALMON SURVIVAL of the northern shore and for this reason it is highly doubtful if salmon are available at any depth or in’ Great variability in the abundance of pink salmon any great numbers on the southern side.