674 



Fishery Bulletin 89(4). 1991 



Cod captured with jigs at sites a few kilometers from 

 shore on shallow (46-51 m) gravel bottom (samples 10 

 and 12) consumed negligible amounts of snow crab (Fig. 

 5; Table 1). In contrast, the percentage by weight of 

 toad crab in samples 10 and 12 was 40.8 and 48.8%, 

 respectively, and the mean number of toad crab per 

 cod stomach was 1.57 and 1.96, respectively (Fig. 5; 

 Table 1). Other important prey in the diet of these cod 

 were invertebrates (25.4 and 34.7%) (amphipods, 

 euphausiids, and molluscs) and fish (20.2 and 23.3%) 

 [pleuronectids, mackerel Scomber scombrus, and small 

 gadids]. 



Cod captured with jigs at sites closer to shore on 

 shallower (33-46 m) gravel bottom (samples 13 and 14) 

 also consumed negligible amounts of snow crab (Fig. 

 5; Table 1). However, the percentage by weight of toad 

 crab was lower, 5.5 and 9.7%, as was the mean number 

 per stomach, 0.49 and 0.78 (Fig. 5; Table 1). In addi- 

 tion, stomachs contained Cancer crab and a lobster 

 Homarus americanus, but the main prey once again 

 was fish (67.7 and 73.2%) (Fig. 5). 



Skate stomach analyses 



All skate were collected during spring 1981 and fall 

 1982 by Danish seines or concord trawls over sandy 

 and muddy bottoms (Fig. 1) (samples 1, 2, 9, 11, and 

 15). During spring 1981 (samples 1 and 2), the percent- 

 age by weight of snow crab found in skate stomachs 

 was 37.7 and 64.3%, and the mean number of snow 

 crab per stomach was 0.30 and 2.26 (Fig. 6; Table 2). 

 The large percentage by weight of snow crab present 

 was large soft-shelled males. Besides crab, skate fed 

 on fish (27.4 and 46.9%) such as cod, hake Urophysis 

 tenuis, herring Clupea harengus, and sand lance Am- 

 modytes americanus. 



During September 1982 (samples 9, 11, and 15), the 

 percentage by weight of snow crab had decreased to 

 between 3.5 and 27.6%, but the mean number of snow 

 crab per skate stomach had increased to between 1.44 

 and 4.81 (Fig. 6; Table 2). The overall average number 

 of crab per stomach was twice as high during the fall 

 as in spring. During fall 1982, skate diet also included 

 large quantities of other invertebrates (up to 52%) 

 (polychaetes, amphipods, euphausiids, gastropods, 

 cephalopods, hermit crab Pagurus longicarpus, and 

 brittle stars Ophiopholis aculeata) and fish (up to 35%) 

 (Fig. 6) such as mackerel Scomber scombrus and 

 pleuronectids. 



Comparisons between cod and 

 skate as crab predators 



The percentage by weight of toad crab in the diet of 

 skate was small (0-1.3%) (Fig. 6; Table 2). However, 



5 - 

 * 4 - 



3 - 

 2 



1 

 



6 - 

 5 - 



4 - 

 3 - 



Sample 1 5 



Concord Trawl 

 70 Cod 4 



04/2 1 /81 

 (101m) 3 



Sample 3 



Danish Seine 



207 Cod 



05/ 10/82 



(101m) 



=□_ 



Sample 2 



Danish Seine 



53 Cod 



05/05/8 1 



(130-14 1m) 



O "O ,0 



4C 

 05/ 



M 



Sample 4 



Jig 



40 Cod 



05/28/82 



(55m) 



*■ 



sF 





Figure 6 



Percentage by weight of prey categories against total weight 

 of stomach contents from skate sampled in April/May 1981 

 and September 1982. Dark bar represents the percentage by 

 weight of total toad crabs (Hyas araneus, H. coarctatus, 

 unidentified Hyas). 



the mean numbers of toad crab per stomach for cod 

 and skate captured at the same sampling sites in the 

 same tows were similar (0.28 and 0.30 for cod and 

 skate, respectively) (Table 3, samples 1, 2, and 9). In 

 these same samples, the mean number of snow crab 

 found in skate stomachs was on average 4.9 times 

 higher than the mean number of toad crab (Table 3), 

 whereas the mean numbers of snow crab and toad crab 

 found in cod stomachs were similar (0.30 and 0.28, 

 respectively). Skate also appeared to consume up to five 

 times more snow crab than cod (1.60 and 0.30 per skate 

 and cod, respectively) (Table 3). 



Influence of season and substratum type 



The quantity of crab consumed by cod varied between 

 bottom types. In the stomachs of cod captured on sand 

 and mud bottoms, the overall mean numbers of snow 

 crab and toad crab per stomach were generally similar 



