ZOOPLANKTON ABUNDANCE AND FEEDING HABITS OF FRY OF 



PINK SALMON, ONCORHYNCHUS GORBUSCHA, AND CHUM SALMON, 



ONCORHYNCHUS KETA, IN TRAITORS COVE, ALASKA, WITH 



SPECULATIONS ON THE CARRYING CAPACITY OF THE AREA 



Jack E. Bailey, Bruce L. Wing, and Chester R. Mattson' 



ABSTRACT 



Juvenile pink salmon, Oncorhynchus gorbuscha, and chum salmon, 0. keta, 28 to 56 mm long (fork 

 length) from Traitors River in southeastern Alaska, fed little in freshwater but fed heavily in the 

 estuar>', mainly on pelagic zooplankters. Fry did not feed on cloudy moonless nights. The rate of 

 evacuation of pink salmon stomachs ranged from 6 h at 12.8°C to 16 h at 8.5°C. The abundance of 

 zooplankton ranged from 9 to 154 organisms per liter and quantitatively did not change noticeably 

 while fry were in the estuary. In 1964, 1965, and 1966, the estimated numbers of fry in Traitors Cove was 

 7, 1, and 4 million, respectively. An attempt was made to estimate the carrying capacity of Traitors 

 Cove, using food consumption and evacuation rates in conjunction with estimates of standing crop of 

 zooplankton. It was concluded that 50 to 100 million additional fry from hatcheries would probably 

 exceed the carrying capacity of the estuary. 



With the rapidly growing demand for animal pro- 

 tein and the emergence of new hatchery tech- 

 niques for pink salmon, Oncorhynchus gorbuscha, 

 and chum salmon, 0. keta (Bams 1972; Bailey and 

 Heard 1973; Bailey and Taylor 1974), we believe 

 that it is timely to speculate on the capacity of 

 estuaries to support more fry. The Japanese, Rus- 

 sians, and Canadians have a number of major pink 

 and chum salmon hatcheries and spawning chan- 

 nels in operation. Japanese hatcheries released 

 over 800 million pink and chum salmon fry in 1973 

 (source: Japan Fishery Agency). Individual Rus- 

 sian hatcheries are capable of releasing up to 120 

 million fry annually (Kanid'yev et al. 1970). The 

 Qualicum River in British Columbia, Canada, now 

 produces about 50 million chum salmon fry an- 

 nually through a combination of flow control in the 

 natural spawning areas and the operation of a 

 spawning channel (Eraser 1972). The problem of 

 evaluating the carrying capacity of estuaries for 

 artificially produced fry is most pertinent. What, 

 for example, would be the impact of 100 million fry 

 on the available food in Traitors Cove? 



Recent technological advances in rearing salm- 

 on in hatcheries and spawning channels now 

 make it possible to release tens of millions of pink 

 and chum salmon fry into individual estuaries, but 



'Northwest Fisheries Center Auke Bay Laboratory, National 

 Marine Fisheries Service, NOAA, P.O. Box 155, Auke Bav, AK 

 99821. 



lack of knowledge of the food requirements of 

 these two species in nature makes even the 

 immediate results of such releases uncertain. It is 

 conceivable that a spawning channel or hatchery 

 operation could produce such large numbers of fry 

 that their migratory behavior might be altered, or 

 growth and survival might be reduced because of 

 severe competition for a limited food supply. 

 Ivankov and Shershnev (1968) reported that young 

 pink and chum salmon (50 to 80 mm) had fuller 

 stomachs in years of "scarcity" of salmon than in 

 years of "abundance" in the coastal zone of the 

 southern Kuril Islands. 



The survival of fry to a large extent depends on 

 their rate of growth and on their ability to escape 

 from predators. Rapid growth requires suitable 

 temperature, an abundance of food, and a rapid 

 transition from endogenous nutrition, based on 

 yolk reserve, to exogenous feeding on small aquat- 

 ic organisms. In a study of size-selective preda- 

 tion, Parker (1971) demonstrated that predation 

 decreases with increase in size of the prey species. 



The study reported in this paper was under- 

 taken in a southeastern Alaska estuary. Traitors 

 Cove (Figure 1), in 1964-66 to gain further insight 

 into the food requirements and feeding habits of 

 pink and chum salmon fry. Questions asked were: 

 How soon in life does feeding begin? How does the 

 diet of the fry compare with the available food 

 organisms? What are the food consumption rates 



Manuscript accepted January 1975. 

 FISHERY BULLETIN: VOL. 73, NO. 4. 



846 



