Abstract. — The stomach con- 

 tents of 1,215 anadromous ale- 

 wives collected during winter and 

 summer groundfish research sur- 

 veys (1990-91) off Nova Scotia 

 were examined to 1) describe the 

 diet by season, area, bottom depth 

 (<101 m, 101-200 m, >200 m), 

 time of day and fish size (<151 

 mm, 151-200 mm, 201-250 mm, 

 >250 mm FL), 2) evaluate diel 

 feeding periodicity, and 3) estimate 

 daily ration. Euphausiids, particu- 

 larly Meganyctiphanes norvegica, 

 were the most important prey and 

 represented more than 82% by vol- 

 ume of total stomach contents sea- 

 sonally and geographically. Contri- 

 butions by other prey groups 

 (hyperiid amphipods, calanoid 

 copepods, crustacean larvae, poly- 

 chaetes, chaetognaths, mysids, 

 pteropods, and fish larvae) were 

 small and varied temporally and 

 spatially. The proportion of eu- 

 phausiids in the diet of alewives 

 from the Scotian Shelf (winter) 

 and Bay of Fundy (summer) 

 tended to increase with increasing 

 depth. Day and night differences 

 in diet composition indicate that 

 alewives may particulate-feed on 

 macrozooplankton when prey vis- 

 ibility is high and filter-feed on 

 microzooplankton when prey vis- 

 ibility is low. Diet composition was 

 relatively homogenous among ale- 

 wife size groups with euphausiids 

 composing most of the total food 

 volume. Alewives of different size 

 groups ate similarly sized M. 

 norvegica, generally the largest M. 

 norvegica available. Diel feeding 

 activity (stomach fullness) peaked 

 at mid-day (summer collections) 

 and mid-afternoon (winter collec- 

 tions); feeding activity was re- 

 duced at night. In all areas, feed- 

 ing activity and the proportion of 

 feeding fish was highest in regions 

 where bottom depths exceeded 200 

 m. Mean stomach fullness was 

 highest during summer in the Bay 

 of Fundy and during winter on the 

 Scotian Shelf; these regions are 

 seasonally important foraging ar- 

 eas for alewives off Nova Scotia. 

 Daily ration was 1.2% of body 

 weight during winter and 1.9% 

 during summer. 



Manuscript accepted 17 August 1993 

 Fishery Bulletin 92:157-170 (1994) 



Feeding habits of anadromous 

 alewives, Alosa pseudoharengus, 

 off the Atlantic Coast of Nova Scotia 



Heath H. Stone 



Department of Fisheries and Oceans, Biological Sciences Branch 

 PO. Box 550, Halifax. Nova Scotia B3J 2S7 CANADA 



Present address: Biological Station, Department of Fisheries and Oceans 



St. Andrews, New Brunswick, EOG 2XO CANADA 



Brian M. Jessop 



Department of Fisheries and Oceans, Biological Sciences Branch, 

 RO. Box 550, Halifax, Nova Scotia, B3J 2S7 CANADA 



The anadromous alewife, Alosa pseu- 

 doharengus, is a clupeiform fish 

 whose range extends from New- 

 foundland to North Carolina 

 (Bigelow and Schroeder, 1953). Off 

 Nova Scotia, alewives occur through- 

 out the year in regions characterized 

 by strong tidal mixing and up- 

 welling in the Bay of Fundy-east- 

 ern Gulf of Maine and are abun- 

 dant during spring in the warmer, 

 deeper waters of the central 

 Scotian Shelf and areas of warm 

 slope water intrusion along the 

 Scotian Slope and the edges of 

 Georges Bank (Stone and Jessop, 

 1992). In the Maritime provinces of 

 Canada and Atlantic coastal 

 United States, alewives and 

 blueback herring, A. aestivalis, are 

 fished commercially during their 

 spring spawning migrations and 

 are often marketed together as 

 gaspereau or river herring. Little is 

 known about the importance of ale- 

 wives as predators in the marine 

 environment or about their feeding 

 habits and food consumption rates. 

 Alewives are generally classified 

 as size-selective, particulate and 

 filter-feeding microphagists and 

 can actively feed on individual 

 zooplankton or passively feed by 

 filtering the water with their gill 

 rakers (Janssen, 1976; Durbin, 

 1979; James, 1988). Feeding mode 



depends on prey density, size, and 

 visibility, and on predator size 

 (Janssen, 1976, 1978a, 1978b; 

 Durbin, 1979). The ability to switch 

 feeding modes enables alewives to 

 consume a wide size range of prey 

 in a variety of environmental con- 

 ditions. Size-selective predation by 

 juvenile and nonanadromous fresh- 

 water alewives can shift the species 

 and size composition of zooplank- 

 ton communities towards smaller 

 forms (Brooks and Dodson, 1965; 

 Brooks, 1968; Wells, 1970; Wars- 

 haw, 1972; Vigerstad and Cobb, 

 1978). No information is available 

 on size-selective predation in the 

 ocean; however, in Minas Basin, a 

 turbid macrotidal estuary, alewives 

 were generally particulate feeders 

 of larger, benthic prey rather than 

 smaller pelagic prey (Stone and 

 Daborn, 1987). 



Information on the feeding hab- 

 its of anadromous alewives in the 

 ocean is limited to qualitative as- 

 sessments but is better known for 

 freshwater juveniles (Vigerstad 

 and Cobb, 1978; Gregory et al., 

 1983; Jessop, 1990) and estuarine 

 resident subadults during summer 

 (Stone and Daborn, 1987). Eu- 

 phausiids, calanoid copepods and, 

 to a lesser extent, hyperiid amphi- 

 pods, chaetognaths, mysids, ptero- 

 pods, decapod larvae, and salps 



157 



