BAILEY ET AL.: ZOOPLANKTON ABUNDANCE AND FEEDING HABITS OF FRY 



at the rate of about 3.5 liter/min. Even at the 

 lowest observed abundance of 1 zooplankter per 

 Hter (Table 5), each fry would theoretically en- 

 counter about 3.5 zooplankters per minute, which 

 is slightly greater than the estimated feeding rate 

 of 3 zooplankters per minute in floating aquaria at 

 10°C. At this rate of feeding, a single fry could fill 

 its stomach in about 39 to 155 min and could 

 therefore easily ingest zooplankters faster than 

 they could be evacuated. 



Abundance of zooplankton in the outer bay of 

 Traitors Cove ranged from 4 to 563 organisms per 

 liter (Table 7), and this was theoretically enough to 

 satiate feeding fry as shown above. Furthermore, 

 the abundance of zooplankton as estimated from 

 Clarke-Bumpus samples did not decrease during 

 the time that salmon fry were in the estuary. 

 Therefore, we conclude that there was an abun- 

 dant food supply in Traitors Cove for salmon fry. 

 LeBrasseur et al. (1969), who conducted feeding 

 experiments with wild juvenile pink and chum 

 salmon in the Eraser River estuary in 1967 (an 

 off-cycle year of pink salmon in the Eraser sys- 

 tem), arrived at a similar conclusion for that area. 



Carrying Capacity of Traitors Cove 



Fry of pink and chum salmon emerged from the 

 gravel of Traitors River at night, and most of 

 them migrated to the estuary before dawn. Some 

 of the fry, as evidenced by their size and the con- 

 tents of their digestive tracts, lingered a few days 

 in the stream where they fed on freshwater or- 

 ganisms. The tendency to linger and feed in 

 freshwater, most pronounced for chum salmon, 

 has been described by Mason (1974). After the fry 

 left Traitors River, they gathered in schools close 

 to shore and began feeding and migrating ocean- 

 ward. The time spent in the estuary is unknown 

 but was probably from a few days to a few weeks. 



We estimated the abundance of pink and chum 

 salmon fry in Traitors Cove by making counts each 

 day along the shore from a moving skiff or by a 

 mark-and-recapture technique. In 1965, the great- 

 est number estimated from counts on any day 

 was 7 million fry, but in 1966 the greatest estimate 

 was under 1 million fry. The number of salmon fry 

 in Traitors Cove in 1968 was estimated by mark 

 and recapture to be 4 million (il.3 million, 95% 

 confidence limits). The mark-and-recapture es- 

 timate was made on a different annual fry 

 migration than those covered by this study of 

 feeding habits, but it strengthened our confidence 



in the visual estimates of fry abundance in 1965 

 and 1966. 



It did not appear that the Traitors Cove estuary 

 was overgrazed by wild fry at the time of this 

 study. In 1966, zooplankton abundance was always 

 greater than 1.0 zooplankter per liter, which would 

 allow maximum feeding rates by fry. During May 

 and June 1966, when 1 million fry were present, 

 the average abundance was about 29 zooplankters 

 per liter. In June 1965, abundance was 154 

 zooplankters per liter after 7 million fry passed 

 through the estuary. 



The number of fry that migrate through Trai- 

 tors Cove each year is probably limited to less than 

 20 million by the productivity of the spawning 

 grounds in Traitors River and Margaret Creek, 

 the major salmon streams in the cove. We used 

 stream survey data from Martin (1959) and 

 applied a correction factor of 0.5 to correct for 

 pools and stream bottoms of mud, sand, and 

 bedrock to calculate 66,000 m^ of spawning 

 grounds-55,000 m2in Traitors River and 11,000 m2 

 in Margaret Creek. These spawning grounds 

 would yield about 7 million fry if they produced 

 100 fry per square meter or about 20 million fry if 

 they produced 300 fry per square meter. Fry den- 

 sities of 0.1 to 589 per square meter (average 250 

 fry per square meter) have been observed in Trai- 

 tors River,''' but these densities were in sections of 

 the stream consistently favored by spawning salm- 

 on. Less favored areas were not sampled. 



The installation of a hatchery or spawning 

 channel in a drainage system such as Traitors 

 River could potentially result in a production of 

 100 million fry annually, or 5 to 100 times the es- 

 timated production of wild fry. Available data are 

 inadequate to determine the carrying capacity of 

 Traitors Cove with certainty, but it is possible to 

 make very speculative estimates based on the 

 standing crop of zooplankton. 



Before presenting the estimates of carrying 

 capacity, we wish to cite 10 necessary assumptions 

 (required because we lack knowledge of the 

 ecology of estuarine nursery areas) and some of 

 the factors which may invalidate the estimates. 



1. Zooplankton abundance was the same in 

 Behm Canal as in Traitors Cove. Plankton samples 



''Mattson, C. R., and J. E. Bailey. 1966. Chum and pink salmon 

 studies at Traitors Cove, September 1963 to September 1964. On 

 file, Auke Bay Laboratory. 



'Mattson, C. R., and R. G. Rowland. 1963. Chum salmon studies 

 at Traitors Cove Field Station June 1960 to March 1963. On file, 

 Auke Bay Laboratory. 



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