204 



Abstract — The number of pelagic 

 fish eggs (cod and cunner) found in 

 stomachs of capelin tMallntus villosiis) 

 sampled in coastal Newfoundland was 

 used to estimate the encounter rates 

 between capelin and prey, and thus 

 the effective volume swept by capelin. 

 Fish eggs were found in 4-8'7f of cap- 

 elin stomachs, represented an average 

 of 1% of prey by numbers, and their 

 abundance increased as relative stom- 

 ach fullness decreased. The average 

 number of eggs per stomach doubled 

 for each 5-cm increase in length of 

 capelin. The effective volume swept 

 for eggs by capelin ranged from 0.04 

 to 0.84 m-Vh — a rate that implies 

 either very slow capelin swimming 

 speeds (<1 cm/s) or that fish eggs are 

 not strongly selected as prey. The pre- 

 dation rate estimated from stomach 

 contents was higher than that pre- 

 dicted from laboratory studies of feed- 

 ing pelagic fish and lower than that 

 predicted by a simple foraging model. 

 It remains uncertain whether capelin 

 play an important regulatory role in 

 the dynamics of early life stages of 

 other fish. 



Estimating the encounter rate of Atlantic capelin 

 (Mallotus villosus) with fish eggs, 

 based on stomach content analysis 



Pierre Pepin 



Fisheries and Oceans Canada 



P.O. Box 5667 



St Johns, NL 



Canada A1C 5X1 



E-mail address Pepinpia^dfo-mpo gc.ca 



Capelin (Mallotiis villosus (Miiller, 

 1776)) is a key species in Arctic eco- 

 systems, serving as a major prey 

 for top predators, from fish to birds 

 and whales (Akenhead et al., 1982; 

 Gj0saeter, 1998; Vilhjalmsson, 2002). 

 Off the coast of Newfoundland and 

 Labrador (eastern Canada), capelin 

 are also the dominant consumers of 

 secondary production (O'Driscoll et 

 al., 2001), as they are in other ecosys- 

 tems (Skjoldal and Rey, 1989; Hassel 

 et al., 1991). They feed on a wide 

 variety of zooplankton taxa, copepods 

 and euphausiids being the dominant 

 prey (Vesin et al., 1981; Panasenko'; 

 Huse and Toresen, 1996; Assthors- 

 son and Gislason, 1997; O'Driscoll et 

 al., 2001). The choice of prey shows 

 some degree of size-dependency; 

 copepod size increases with increas- 

 ing size of capelin, and euphausiids 

 become more frequent prey items as 

 fish size increases. In most studies 

 of the feeding habits of capelin, fish 

 eggs and larvae have been found to 

 have been eaten by capelin, although 

 these prey types generally represent 

 a minor portion of the diet, occurring 

 in less than 5% of stomachs (Huse 

 and Toresen, 1996; O'Driscoll et al., 

 2001). Because capelin are dominant 

 consumers of zooplankton in many of 

 the ecosystems in which they are pres- 

 ent, their overall impact on the sur- 

 vival of pelagic fish eggs and larvae 

 may be significant depending on their 

 encounter rates with these fish eggs 

 and larvae. 



Manuscript submitted 2 November 2004 

 to the Scientific Editor's Office. 



Manuscript approved for publication 

 10 August 200.5 by the Scientific Editor. 



Fish. Bull. 104:204-214(20061. 



' Panasenko, L. D. 1984. Feeding of 

 Barents Sea capelin. ICES CM 1984/ 

 H:6, 16 p. 



There is evidence that capelin can 

 have a significant impact on the 

 survival of ichthyoplankton through 

 predation on pelagic fish eggs and 

 larvae. In a series of patch studies, 

 Pepin et al. (20021 found that the 

 mortality rate of radiated shanny 

 (Ulvaria subbifurcata, Storer 1839) 

 larvae increased in direct relation 

 to hydroacoustic estimates of capelin 

 abundance; this loss could be attribut- 

 ed to predation by capelin on fish lar- 

 vae. In a study of two coastal areas, 

 differences in the regional patterns 

 of selective loss of radiated shanny 

 larvae, derived from sequential obser- 

 vations of the distribution of growth 

 rates, were strongly associated with 

 differences in the spatial distribution 

 and abundance of capelin (Baumann 

 et al., 2003; Pepin et al., 2003). How- 

 ever, the overall impact of capelin on 

 fish eggs and larvae has been difficult 

 to estimate (Paradis and Pepin, 2001). 

 Much of the basic foraging ecology is 

 unknown (e.g., predator's reactive dis- 

 tance, behavior of both predator and 

 prey, and selection of prey) and labo- 

 ratory experiments can only provide 

 a rough approximation of encounter 

 rates between capelin and their prey 

 (Paradis et al., 1996). 



There have been few studies to pro- 

 vide an estimate of the contribution 

 of predation by planktivorous fish 

 on the overall mortality rates of fish 

 eggs or larvae (Hunter and Kimbrell, 

 1980; Cowan et al., 1999; Koster and 

 MoUmann, 2000; Munk, 2002; Pepin 

 et al., 2002). Population studies have 

 shown that planktivorous fish can 

 play an important role in regulating 

 the stock-recruitment relationship of 

 other species (Swain and Sinclair, 



