PREDATION ON CAPITELLA SPP. BY SMALL-MOUTHED PLEURONECTIDS 



IN PUGET SOUND, WASHINGTON^ 



D. Scott Becker^ and Kenneth K. Chew^ 



ABSTRACT 



This study examined the predation patterns of three flatfishes (English sole, Dover sole, and rex sole) 

 on the opportunistic polychaetes Capitella spp. in disturbed soft-bottom habitats of Puget Sound, 

 Washington. Sampling was conducted throughout the diel cycle during May and June 1981. All three 

 fishes exhibited some degree of selective predation on Capitella spp. based on both number and size 

 of these prey. Numerical dietary contribution by Capitella spp. was greatest at night for all three 

 fishes, suggesting that these polychaetes become more accessible to predators at night. Predation on 

 Capitella spp. allowed English sole to alter their normal diurnal feeding chronology and forage 

 successfully at night. This study supports the hypothesis that some demersal fishes can exploit 

 opportunistic prey in disturbed habitats. 



The composition of soft-bottom marine benthic in- 

 vertebrate assemblages can be altered by a vari- 

 ety of natural and anthropogenic disturbances, 

 including salinity reduction (Boesch et al. 1981), 

 storm-induced surge (Rees et al. 1977), hypoxia 

 (Santos and Simon 1980), dredge-spoil dumping 

 (Rhoads et al. 1978), sewage disposal (Pearson 

 and Rosenberg 1978), and oil spills (Sanders et al. 

 1980). To predict the effects of these events on 

 demersal fishes, predator-prey relationships be- 

 tween benthic invertebrates and their piscine 

 predators must be understood. Unfortunately, 

 this kind of information is rare for marine ecosys- 

 tems (Mills 1975). 



Frequently, benthic invertebrate assemblages 

 in disturbed habitats are dominated by one or 

 more opportunistic species (e.g., Grassle and 

 Grassle 1974; McCall 1977; Pearson and Rosen- 

 berg 1978; Rhoads et al. 1978). These oppor- 

 tunists are adapted to rapidly colonize disturbed 

 environments and often attain exceptionally high 

 population densities. Because many of these spe- 

 cies reside at or near the sediment-water inter- 

 face, they represent a potential food bonanza to 

 bottom-feeding demersal fishes. When fishes en- 

 counter such an abundant and accessible food 

 source, it seems likely that those species capable 

 of modifying their foraging behavior to fully ex- 



ploit this windfall will do so. Such opportunistic 

 predation on temporally or spatially variable 

 superabundant prey has been found for a variety 

 of fishes (e.g., Nilsson 1960; Ivlev 1961; Zaret and 

 Rand 1971; Murdoch et al. 1975), and is one pre- 

 diction of optimal foraging theory (review in Pyke 

 et al. 1977). 



As an example of how a group of demersal fishes 

 responds to a disturbed soft-bottom habitat domi- 

 nated by opportunistic benthic invertebrates, we 

 describe the foraging patterns of three flatfishes 

 (Pleuronectidae) in Puget Sound, WA on 

 Capitella spp., a well-known group of opportunis- 

 tic polychaetes (Grassle and Grassle 1974; Pear- 

 son and Rosenberg 1978). The flatfishes targeted 

 for study were English sole, Parophrys uetulus; 

 Dover sole, Microstomus pacificus ; and rex sole, 

 Glyptocephalus zachirus. These fishes belong to 

 the small-mouthed subgroup of pleuronectids 

 identified by Moiseev (1953) and, as such, prey 

 primarily upon small infaunal and epifaunal ben- 

 thic invertebrates. These species also form a major 

 component of demersal fish assemblages in Puget 

 Sound (Miller et al. 1977; Wingert and Miller 

 1979; Becker 1984), as well as in most nearshore 

 areas along the west coasts of the United States 

 and Canada (e.g., Alverson et al. 1964; Day and 

 Pearcy 1968; Hart 1973; Allen 1982). 



iContribution No. 723, School of Fisheries, University of 

 Washington, Seattle. WA 98195. 



2School of Fisheries, University of Washington, Seattle, WA 

 98195; present address: Tetra 'Tech, Inc., 11820 Northup, 

 Bellevue, WA 98005. 



3School of Fisheries, University of Washington, Seattle, WA 

 98195. 



Manuscript accepted March 1987. 



FISHERY BULLETIN: VOL. 8.5, NO. 3. 1987. 



MATERIALS AND METHODS 



Field Sampling 



The study was conducted on the delta of the 



471 



