58 



Fishery Bulletin 92|1|. 1994 



have been identified as prey for alewives in conti- 

 nental shelf waters from North Carolina to Nova 

 Scotia (Holland and Yelverton, 1973; Edwards and 

 Bowman, 1979; Neves, 1981; Vinogradov, 1984; Bow- 

 man, 1986). However, none of these studies were 

 comprehensive. 



We examined the stomach contents of anadromous 

 alewives obtained from winter and summer ground- 

 fish research surveys on the Scotian Shelf, Georges 

 Bank, and in the Bay of Fundy to determine the 

 importance of these regions as foraging areas for 

 these fish. Seasonal, spatial, diel and size-related vari- 

 ability in feeding are examined. Daily ration is esti- 

 mated from information on diel feeding periodicity. 



Materials and methods 



Data collection 



Alewives were collected from seven groundfish re- 

 search surveys conducted by the Canadian Depart- 

 ment of Fisheries and Oceans in three regions 

 (Georges Bank, central Scotian Shelf, and outer Bay 

 of Fundy) during winter (February-March) and 

 summer (July) over a two-year period (1990-91) 

 (Table 1). All surveys used a Western IIA bottom 

 trawl with a 10-mm stretched-mesh liner in the cod 

 end. Thirty-minute tows at each sampling station 

 were conducted throughout the 24-hour day. Up to 

 40 fish of representative size range from each set 

 were frozen for later analysis. Bottom water tem- 

 perature CO, time of tow deployment, latitude, lon- 

 gitude, and bottom depth (m) were recorded for each 

 set. Stomach content data were grouped by season 

 and sample location: Winter-Fundy, Winter-Shelf, 

 Winter-Georges, and Summer-Fundy (Fig. 1). Stone 



and Jessop (1992) provide additional details of the 

 survey area and procedures, and seasonal distribu- 

 tion of fish. 



Fork length (mm), weight (g), sex and species (de- 

 termined by peritoneal colour (Leim and Scott, 

 1966)) were recorded for each fish. Whole digestive 

 tracts, individually identified, were preserved in 4% 

 buffered formalin. 



Diet analysis 



Stomachs were weighed (±0.01 g) and the contents 

 ranked subjectively using a fullness code (0=empty, 

 1 = 12% full, 2=25% full, 3=50% full, 4=75% full, 

 5=100% full) and a digestion code ( l=finely digested, 

 nothing recognizable; 2=medium digestion, some 

 recognizable parts; 3=some digested, some undi- 

 gested material; 4=undigested whole animals). The 

 stomach content weight was obtained by subtract- 

 ing the weight of the empty stomach from the total 

 stomach weight. Stomach content weight, as a per- 

 centage offish body weight C#BW), was used as an 

 index of fullness to evaluate feeding activity and 

 estimate daily ration. Stomach contents were iden- 

 tified (to species where possible), enumerated, and 

 the volume of each food type estimated by means of 

 a points system (Swynnerton and Worthington, 

 1940; Stone and Daborn, 1987). 



For diet analysis, prey taxa (Table 2) were 

 grouped into nine categories based on taxonomy and 

 ecology: 1) euphausiids (Meganyctiphanes norvegica 

 and some Thysanoessa spp.); 2) hyperiid amphipods 

 (Parathemisto gaudichaudiy, 3) calanoid copepods 

 (Calanus spp., Centrophoges spp. and Metridia spp.); 

 4) polychaetes (Nereis spp. and unidentifiable spe- 

 cies); 5) fish larvae (Ammodytes dubius and uniden- 

 tifiable species); 6) mysids {Neomysis americana); 1) 



