162 



Fishery Bulletin 92(1), 1994 



Winter-Fundy 



(n = 58) 



Winter-Georges 



(n = 147) 



%N 



%v 



Winter-Shelf 



%N 



%v 



%N 



%v 



t— I = 20% FO 



Figure 2 



Relative importance of prey categories in the diet of alewives, Alosa 

 pseudoharengus, collected from groundfish research surveys off 

 Nova Scotia (1990-91), ranked from highest Index of Relative Im- 

 portance (left to right) by season and area, n = number of stom- 

 achs with prey; '#FO = % frequency of occurrence; %N = % of total 

 prey number; %V = % of total prey volume; Eup = euphausiids; Cop 

 = calanoid copepods; Pter = pteropods; Amp = hyperiid amphipods; 

 CruLar = crustacean larvae; FishLar = fish larvae; Chaet = cha- 

 etognaths; Mys = mysids; Poly = polychaetes. 



bottom depths exceeding 101 m (no fish were ob- 

 tained at bottom depths less than 101 ml. IRI 

 rankings of" prey categories between depth groups 

 r Georg nk collections were highly correlated 



• .=0 !9, P fi.01 ' / prey i igorie n 



present for analysis of Winter-Fundy collections. In 



both winter and summer, most euphausiids con- 



med at depths less than 101 m were Thysanoessa 



pp. v than M. m vegica a) 



f, r shallower regions < (Table 3). 



el vari< t 



t h ou gh i 



numbers and volumes were ingested 

 during the day (7rN=74, %V=92) than 

 at night ( r /rN=16, %V=85) (Fig. 4). IRI 

 values for day and night collections 

 were not significantly correlated 

 (r s =0.26, P>0.05) reflecting the 

 greater consumption of hyperiid am- 

 phipods during the day and copepods, 

 crustacean larvae and fish larvae at 

 night. 



Diet composition by size class 



Diet composition was relatively homo- 

 geneous among alewife size groups 

 (<151 mm, 151-200 mm, 201-250 

 mm, >250 mm) with euphausiids com- 

 posing most of the total food volume 

 (Fig. 5). Multiple correlations of IRI 

 values for prey categories (excluding 

 euphausiids) by fish length group 

 were significant for both the Scotian 

 Shelf (u;=0. 58, P=0.024) and Georges 

 Bank (w=0.65, P=0.011). For Sum- 

 mer-Fundy collections, diets of the 

 two largest size groups were nearly 

 identical; IRI values were not signifi- 

 cantly correlated (r s =0.38, P>0.05) 

 due to slight differences in the 

 rankings of minor prey categories 

 (i.e., amphipods, mysids, polychaetes, 

 chaetognaths). 



Prey size composition 



Alewives ingested similar sizes of M. 

 norvegica during winter (Georges 

 Bank, Scotian Shelf) and summer 

 (Bay of Fundy) (Fig. 6). Modal peaks 

 in euphausiid size appeared at 25-27 

 mm and 30 mm on the Scotian Shelf and at 30-35 

 mm for Georges Bank and the Bay of Fundy. In com- 

 parison, M. norvegica from Emerald Basin 

 BIONESS collections in June 1991 were bimodally 

 ibut( it 25-27 mm and 34 mm. Euphausiids 

 larger than 29 mm were proportionately less fre- 

 quent than in stomach contents. 



Mean lengths of M. norvegica consumed by ale- 

 vives varied by season/area group (F._, 7II| =65.5, 

 P<0.001), although differences between means were 

 small (Winter-Georges: mean=32.1±3.13; Winter- 

 Shelf: mean=28.7±3.72; Summer-Fundy: mean 

 ll.2±3.64). The average size of euphausiids con- 

 d did not differ (F, 50 =3.31, P =0.075) with ale- 



wife stum;. I tion -ize i ran<i;.>: 225-300 mm FL). 



