207 



Abstract — Nurseries play an impor- 

 tant part in the production of marine 

 fishes. Determining the relative 

 importance of different nurseries in 

 maintaining the parental population, 

 however, can be difficult. In the west- 

 ern Gulf of Alaska, the Kodiak Island 

 vicinity may be particularly well 

 suited as a pollock nursery because of a 

 prey-rich nearshore environment. Our 

 objectives were 1) to examine age-0 

 pollock body condition, growth, and 

 diet for evidence of a nearshore-shelf 

 effect, and 2) to determine if variation 

 in the potential prey field of zooplank- 

 ton was associated with this effect. 

 This was a pilot study that occurred 

 in three bays and over the adjacent 

 shelf off east Kodiak Island during 

 5-18 September 1993. Sampling 

 occurred only during night at loca- 

 tions where echo sign indicated the 

 presence of age-0 pollock. Echo sign 

 was targeted to increase the chance of 

 collecting fish given the limited vessel 

 time. Fish condition was indicated by 

 length-specific body weight. Growth 

 rate indices were estimated for three 

 different periods by using fish length- 

 age data and daily otolith increment 

 widths: 1) from hatching date to cap- 

 ture, 2) 1-5 d before capture, and 3) 

 6-10 d before capture. Fish diet was 

 determined from gut content analysis. 

 Considerable variation among areas 

 was evident in zooplankton composi- 

 tion, and fish condition, growth, and 

 diet. However, relatively high prey 

 densities, as well as fish condition 

 and growth rates indicated that Chin- 

 iak Bay was particularly well suited 

 as a pollock nursery. Hatching-date 

 distributions indicated that most of 

 the age-0 walleye pollock from bays 

 were spawned earlier than were those 

 from the shelf. The benefit of being 

 reared in nearshore areas is therefore 

 realized more by individuals that were 

 spawned early than by individuals 

 spawned relatively late. 



Geographic variation among age-0 

 walleye pollock (Theragra chalcogramma)'. 

 evidence of mesoscale variation in nursery quality?* 



Matthew T. Wilson 



Annette L. Brown 



Kathryn L. Mier 



Alaska Fisheries Science Center 



National Marine Fisheries Service, NOAA 



7600 Sand Point Way. NE 



Seattle, Washington 98115 



E-mail address (for M T Wilson) matt wilson(a>noaa gov 



Manuscript submitted 20 November 2003 

 to the Scientific Editor's Office. 



Manuscript approved for publication 



16 September 2004 by the Scientific Editor. 



Fish. Bull. 103:207-218 (2005). 



The location of suitable fish nurseries 

 has long been of interest to fishery 

 scientists (Kendall and Duker, 1998). 

 Such areas are a link in the chain of 

 resources that sustain the produc- 

 tivity of a population and shape its 

 evolution. Although the presence of 

 juvenile fish in an area may indicate 

 a nursery, relative importance among 

 nursery areas ultimately depends 

 on the number and reproductive fit- 

 ness of reared individuals that con- 

 tribute to the parental population. 

 These qualities, however, are usually 

 not measurable. Instead, we focus 

 on measuring the size of juveniles, 

 their body condition, diet, growth, and 

 other characteristics that are acces- 

 sible and relevant to fish survival. 

 However, because these indices are 

 not free of measurement error, it is 

 advisable to consider more than one 

 index (Suthers, 1998). 



In the North Pacific Ocean, wall- 

 eye pollock {Theragra chalcogramma) 

 have adapted to the heterogeneity and 

 productivity of coastal areas; they 

 now support one of the world's most 

 productive fisheries. Walleye pollock 

 are a semidemersal gadid. Spawning 

 typically occurs in mid-water during 

 the spring at locations near, or over, 

 the continental shelf (Kendall and 

 Picquelle, 1989; Bailey et al., 1997). 

 Fertilization is external. The eggs 

 and larvae are pelagic, remaining in 

 the plankton for ca. 4 months while 

 they are dispersed over large areas. 

 At 25-40 mm standard length (SL), 

 larvae transform to juveniles (Brown 

 et al., 2001) and become increasingly 



nektonic. Juveniles are referred to as 

 "age-0" when they are between tran- 

 sition and 12-months old (40-130 mm 

 SL, Brodeur and Wilson, 1996a). They 

 are zooplanktivorous, feeding mostly 

 on copepods and euphausiids, but 

 other taxa sometimes dominate their 

 diet (Brodeur and Wilson, 1996a). 

 Age-0 juveniles commonly occur in 

 various habitats from nearshore to 

 the outer continental shelf (Nakatani 

 and Maeda, 1987; Sobolevskiy et al., 

 1992; Carlson, 1995; Natsume and 

 Sasaki, 1995; Brodeur and Wilson, 

 1996a; Wilson, 2000). Occasionally, 

 they are found farther offshore (Tang 

 et al., 1995), but probably in small 

 numbers (Brodeur et al., 1999; Shida 

 et al., 1999). 



The early life stages of walleye pol- 

 lock have been extensively studied in 

 the Gulf of Alaska (GOA) (Kendall et 

 al., 1996). In the Gulf, young pollock 

 are most abundant in the western 

 region (Brodeur and Wilson, 1996a). 

 This region is naturally divided into 

 two areas by the Shelikof Sea Val- 

 ley, which cuts through the shelf at 

 ca.l56°N longitude (Fig. 1). To the 

 east, the Kodiak vicinity includes the 

 continental shelf around the Kodiak 

 Island Archipelago. To the west, the 

 lower Alaska Peninsula vicinity ex- 

 tends to Unimak Pass at the Penin- 

 sula's southwestern terminus. During 

 the 1980s, age-0 abundance in the 



Contribution FOCI-0417 to NOAA's 

 Fisheries- Oceanography Coordinated 

 Investigations, 7600 Sand Point Way 

 NE, Seattle, WA 98115. 



