52 



Birds — Our Living Restiurces 



20 - 



Pollock 



Fig. 4. Temporal changes in 

 marine fish stocks of the Gulf of 

 Alaska: total pollock biomass 

 (age 2+) from stock assessment 

 surveys by the National Marine 

 Fisheries Service, 197S-40 (above, 

 Marasco and Aron 1991 ), and 

 catch per unit effort of capelin in 

 midwater trawls in Pavlov Bay, 

 western Gulf of Alaska, 1972-92 

 (below; P. Anderson, NMFS, 

 unpublished data). 



For further information: 



Scott A. Hatch 



National Biological Service 



Alaska Science Center 



Anchorage, AK 99503 



to pollock-based (Piatl, unpublished data), 

 Seabiid deeiines and bieeding failures corfe- 

 spond to the shift, as do drastic declines in har- 

 bor seals (Phoca vltiilina) and nonhern sea lions 

 {Eiinieloplas jiihaiiis) in the Gulf of Alaska 

 (MeiTick et al. 1987; Pitcher 1990). 



The wholesale removal of large quantities of 

 fish biomass from the ocean is likely to have 

 major, if poorly known, effects on the marine 

 ecosystem. An emerging issue is whether fish 

 harvests are altering marine ecosystems to the 

 detriment of seabirds and other consumers like 

 pinnipeds and whales. 



The relative role of fishing and natural envi- 

 ronmental variation in regulating these systems 

 is another matter for long-term research. In any 

 case, seabird monitoring will continue to pro- 

 vide valuable insights into marine food webs, 

 especially changes that affect the ocean's 

 top-level consumers, including humans. 



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