C-18 



Fish . The fish abundance estimate in Figure 2 is 

 an indirect calculation. The amount of fish consumed by 

 fish predators, as in Figure 3, is 14- x 10° tons per year. 

 Derivation of this value will be discussed later. Assuming 

 conservatively that annual production is equal to standing 

 stock for fish, biomass is 14 x 10^ tons. If annual pro- 

 duction is less than the average standing stock, then the 

 biomass estimate should be revised upward. 



From a study on fish in the South Orkney Islands 

 (Everson, 1970), an annual consumption rate of 6.5 times 

 body weight is derived. A fish stock of 14 million tons 

 then consumes 91 x 10" tons of food per year, about two- 

 thirds krill and the remainder other organisms. Values for 

 fish standing stock and krill consumption are educated 

 guesses, and are most likely to be underestimates. 



Squid . The biomass estimate in Figure 2 is based on 

 predation on squid, another indirect estimate. Previous 

 estimates of Antarctic squid biomass have been based on 

 the population size required to support predation by sperm 

 whales, a major squid predator. However, from Figure 3, 

 seals, birds, and possibly fish together consume at least 

 twice as much squid as do sperm whales. Therefore, squid 

 population estimates have been revised upward (Green, 1977). 

 Estimated yearly predation on squid in the southern ocean 

 amounts to about 19 x 10^ tons. On the assumption that 

 squid populations turn over faster than fish do and that 

 annual production is one and a half times standing stock, 

 a squid standing stock of 12.4 x 10^ tons was derived. 

 This estimate is speculative S.nd not reliable. It is higher 

 than previous estimates, but may still be conservative. 



An annual consumption rate of eleven times average 

 body weight is extrapolated from laboratory studies (Van 

 Heukelem, 1973; Hurley, 1976). The total consumption by 

 a stock of 12.4 x 10^ tons of squid would be 136 x 10^ tons 

 of food per year. Squid may consume 100 x 10 tons of 

 krill annually (D. Tranter, Woods Hole Conference). 



Fish and squid estimates are the least reliable num- 

 bers in Figure 2 since they are not based on any direct 

 data. One concern expressed at the Woods Hole Conference 

 was the need for improved data on fish and cephalopod 

 stocks. This information is essential, because fish and 

 squid feed extensively on krill and they are potentially 

 harvestable resources. 



Birds. From an extensive review of population and 

 physiological data available for Antarctic birds (Prevost, 

 in press), a standing stock of 0.27 x 10^ tons for waters 



