FISHERY BULLETIN: VOL. 73. NO. 4 



were not collected outside Traitors Cove in Behm 

 Canal. Several years later extensive plankton 

 collections were made in open channels and several 

 small adjacent bays of northern southeastern 

 Alaska as a part of the 1972 MARMAP  investiga- 

 tion. Within the May 1972 samples, average 

 zooplankton abundance was nearly twice as great 

 at 14 outside stations as at 4 stations within bays. 

 Therefore, our estimates of carrying capacity 

 based on influx of zooplankton from Behm Canal 

 would be conservative. 



2. Salmon fry were the only predators on 

 zooplankton. We ignored the requirements of all 

 other planktivorous animals of the area. The 

 requirement of local planktivores other than salm- 

 on are only qualitatively and poorly known. 

 Herring were not seen in large numbers during 

 the years of this food study. A school of herring 

 entered the inner bay in 1967 while being fed on by 

 a whale. We do not know how long these herring 

 remained in Traitors Cove, but they were not 

 conspicuous 2 wk after their entry. 



3. Zooplankton concentrations were constant. 

 We ignored the strong seasonality of reproduction 

 and growth in the holoplankton and the fact that 

 meroplankton may be present for only a limited 

 time. We ignored the probability that some larval 

 forms reach a life history stage where their 

 behavior would make them unavailable to the salm- 

 on fry. We ignored natural mortality of larval 

 forms other than from predation by salmon fry. 

 Some of these factors would increase zooplankton 

 concentrations while others would decrease them. 

 In the absence of information on reproduction, 

 growth, mortality, and life histories, we assumed 

 these factors would balance so that the zooplank- 

 ton concentration would be constant. 



4. Distribution of the zooplankton was uniform. 

 Physical and biological factors controlling the 

 patchiness of zooplankton in estuaries and near- 

 shore environments are poorly understood and not 

 easily modeled. 



5. All zooplankton were equally available, 

 equally desirable, and of equal quality as feed for 

 salmon fry. We ignored the size selectivity and 

 preference for calanoid copepods shown in our own 

 data. It is highly probable that the species of 

 zooplankton vary in quality as food. 



6. Salmon fry had a constant feeding 

 requirement of 544 zooplankters per day. This is 



Marine Resources Monitoring, Assessment, and Predic- 

 tion-program sponsored by National Marine Fisheries Service 

 on a nationwide scale. 



the highest of our estimates of pink salmon feed- 

 ing rates and ignores variations in food 

 requirements that would accompany variations in 

 physical environment and physiological state. 



7. No behavioral changes in either the salmon 

 fry or zooplankton were induced by changes in 

 densities, physical environment, or biological 

 states. 



8. The number of salmon fry was constant. 



9. All the zooplankton would be utilized as food. 

 If this actually occurred, no survivors would be left 

 to produce new zooplankton crops or to replenish 

 stocks of other resources that have planktonic lar- 

 val stages such as herring, crabs, and shrimp. 



10. Models of circulation in the estuary would be 

 of the simplest type. We do not know the flushing 

 rates in Traitors Cove or the potential of transport 

 of zooplankton food to and from the bay by es- 

 tuarine circulation. 



Some additional assumptions peculiar to each 

 estimate are described with each estimate. Only 

 the outer bay is considered because fry in Traitors 

 Cove appeared to move quickly through the inner 

 bay and then spend a longer time in the outer bay. 



Our first estimate of carrying capacity is based 

 on standing stock of zooplankton in the top meter 

 of water of the outer bay. Fry were in the outer 

 bay in relatively high densities for about 30 days 

 each year. The surface area of the outer bay is 

 about 7.6x10^ m^, and the average density of 

 zooplankters was estimated to be 24,000 per cubic 

 meter or higher. The product of area and plankton 

 density divided by 544 (the estimated maximal 

 number of organisms consumed per day by pink 

 salmon fry) results in a plankton stock equivalent 

 to 335 X 10^ fry feeding days. This estimate divid- 

 ed by 30 days expresses the food supply in fry 

 months— 11 million fry could feed for 1 mo on the 

 standing stock of food in the surface meter of 

 outer bay. This establishes a lower limit for the 

 carrying capacity of Traitors Cove because it ig- 

 nores saltwater entrainment by outflowing fresh- 

 water and the consequent addition of plankton 

 from deeper water. 



For our second estimate, we calculated the 

 quantity of zooplankton that would be brought 

 into the outer bay from Behm Canal each day by a 

 combination of two factors: circulation due to 

 freshwater runoff from Traitors River and cir- 

 culation due to tidal action. Records of the U.S. 

 Geological Survey indicate that discharge from 

 Traitors River generally averages about 8 mVs in 



858 



