718 



Fishery Bulletin 98(4) 



■D 

 (D 



10 



Age (years) 



Figure 6 



Total fish aged for each year class from random samples of Gymnocan- 

 thus pistilliger collected during 1997 (n=588) and 1998 (n=404l. Males 

 and females were combined for each vear 



Diet 



Gymnocanthus pistilliger preys upon benthic amphipods, 

 polychaetes, crangonid shrimp, and fish. A diet shift from 

 amphipods to shrimp and fish with increased body size 

 represents the sculpin's abihty to capture and ingest larger 

 prey items with increased body size, an abihty that lessens 

 the likelihood of intraspecific competition and increases 

 efficiency in feeding. 



Tokranov ( 19851 reported on the diets of G. pistilliger from 

 off the western coast of the Kamchatka Peninsula. He found 

 diets consisted mainly of polychaete and Echiurus (~lQ'7c fre- 

 quency and weight) and amphipods (contributing little to 

 the diet). Gymnocanthus pistilliger from Kamchatka increas- 

 ingly consumed mollusks, decapods, and juvenile capelin as 

 it grew, and polychaetes and Echiurus decreased as impor- 

 tant items in the diet. Tokranov (1985) also found a shift to 

 larger prey items with increasing fish size. 



Commercially important flatfish also use shallow waters 

 in Bristol Bay as spawning and nursery grounds (Fadeev, 

 1968; Grigorev and Fadeev, 1995). The diet composition of 

 G. pistilliger overlaps with that of flatfish species, such 

 as Limanda aspera (yellowfin sole), Limanda proboscidea 

 (long-head dab), Pleuronectes bilineatus (rock sole), and 

 Pleuronectes quadrituberculatus (Alaska plaice), where 

 competitive interactions may occur. These flatflsh diets 

 also consist of benthic amphipods, polychaetes, and Echi- 

 urus (>50'7f by weight) (Livingston et al., 1986; Brodeur 

 and Livingston. 1988; Corcobado-Onate, 1991; Lang et al., 

 1995). However, Holladay and Norcross ( 1995) found that 

 these flatfish species e.xhibit a diverse diet ( 10-57 groups) 

 and show diet preferences based on substrate. Dietary 

 shifts such as these may lessen the likelihood of prey com- 

 petition in densely populated areas such as Bristol Bay. 



Gymnocanthus pistilliger is also potentially an impor- 

 tant resource to larger predators because of its small size 



