INTERACTIONS AMONG MARINE BIRDS AND COMMERCIAL FISH 



205 



Table 2. Fish of worldwide commercial importance in the diets of some marine birds. 



Fish 



Shearwaters 



Murres 



Puffins 



Fulmars 



Gulls 



on the feeding behavior of the birds and on the 

 life history of the fish (e.g., distribution, abun- 

 dance, growth, and adult size). Pursuit diving 

 birds, such as murres and puffins, can con- 

 sume fish at greater depths than can birds 

 that feed near the surface, such as shear- 

 waters, kittiwakes, fulmars, and gulls. 



torn as adults have pelagic stages during 

 which they are vulnerable to predation by 

 marine birds. Juveniles of some demersal 

 species (pollock, cod, halibut, some species of 

 sole, and king crabs) are sometimes found in 

 shallow water where they might be subject to 

 predation by birds. 



SHEARWATERS 

 FULMARS 



FEEDING BEHAVIOR 



V S 







w 



OF MINOR IMPORTANCE 



OF MODERATE IMPORTANCE 



OF MAJOR IMPORTANCE 



Fig. 5. Feeding behavior and relative importance of 

 food of some groups of marine birds that occur in 

 the eastern Bering Sea. 



Aspects of the Life 

 Histories of Fish Related to 

 Predation by Marine Birds 



Fish that are pelagic during part of their 

 lives, such as salmon and herring, and forage 

 fish like smelt, capelin, and sand lance, are 

 vulnerable to greater predation by a wider 

 variety of marine birds that are bottom-dwell- 

 ing demersal fish, such as pollock, cod, sole, 

 ocean perch, and halibut, as well as king and 

 snow crabs. Some species that live on the bot- 



Demersal Fish and Shellfish 



The early life histories of the commercially 

 important demersal fish of the eastern Bering 

 Sea are quite different (Table 3). For example, 

 the eggs and larvae of Pacific halibut (Hippo- 

 glossus stenolepis) generally occur at depths 

 greater than 100 m (Hart 1973), whereas 

 those of pollock and yellowfin sole are found 

 at or near the surface (Musienko 1963, 1970). 

 The eggs of Pacific cod are demersal, but the 

 larvae are oceanic (pelagic) and occur from 25- 

 150 m (Mukhacheva and Zviagina 1960). 



In their juvenile stages, many demersal fish 

 frequent the near-surface waters (Table 3), 

 where they become vulnerable to predation by 

 piscivorous marine birds. Juvenile pollock, for 

 example, form into small schools that usually 

 move about close to the bottom but some- 

 times move into areas as shallow as 3 m. 

 Juvenile Pacific cod prefer the warmer water 

 close to shore and may be found within 10 m 

 of the surface (Moiseev 1953). The young of 

 many species of flatfish, such as yellowfin 

 sole, rock sole (Lepidopsetta bilineata), and 

 flathead sole (Hippo glosoides elassodon), re- 

 main for a time in shallow warm water after 

 assuming a demersal existence. Yellowfin sole 

 2-2.5 cm in total length may be found in abun- 



