Fish Assemblages in Nearshore Habitats of Prince William Sound, Alaska

We sampled fish at eight locations in western Prince William Sound (PWS), Alaska, in April, July, and September 2006, and July 2007, to identify species assemblages and habitat use. At each location, fish were sampled with a 37-m long variable mesh beach seine in three nearshore habitats: bedrock outcrops, eelgrass meadows, and cobble beaches with kelp. A total of 49,060 fish representing 45 species were captured in 95 beach seine hauls. Catch-per-unit-effort (CPUE, all species) did not differ by season but did differ by habitat type–CPUE was greater in eelgrass and kelp than in bedrock. Seasonal pulses in catch were evident for some species; pink salmon were captured only in spring and summer, Pacific herring only in summer and fall, and capelin only in fall. Species richness was greater in summer (34) than in spring (23) or fall (28), and greater in eelgrass (34) than in bedrock (22) or kelp (33). Species that were good discriminators among seasonal collections were pink salmon, saffron cod, crescent gunnel, and Pacific herring, whereas species that were good discriminators among habitat collections were crescent gunnel, tubesnout, bay pipefish, saffron cod, and Arctic shanny. Of the most abundant species captured, most were juveniles based on estimated size at maturity. The summer fish assemblage in western PWS has changed over the last 20 years, especially with the appearance in large numbers of saffron cod. Sites in this study can be monitored periodically to track future changes in fish assemblages and habitat that may result from local and regional human disturbance. 1Author to whom correspondence should be addressed. E-mail: [email protected] Introduction Alaska has about 55,000 km of shoreline (Heard and Andersen 1999) and a wide diversity of nearshore habitats available to fish including eelgrass (Zostera marina) meadows, kelps, and exposed bedrock outcrops. These habitats are ecologically important for many fish species, providing shelter from predators and abundant food resources (Pollard 1984, Beck et al. 2003, Spalding et al. 2003). Prince William Sound (PWS), a large embayment with numerous islands, provides extensive nearshore habitats that are protected from more exposed conditions on the outer coast (Laur and Haldorson 1996). Although it is well established that over 100 fish species use the nearshore environment in Alaska (NOAA Fisheries 2009a), often in large numbers, what is unknown is their use of specific habitats and how that changes seasonally and with life stage. Most coastal fish surveys in PWS have been in deeper water of embayments (Norcross and Frandsen 1996, Stokesbury et al. 1999, Ostrand et al. 2004) and not in shallow, nearshore habitats (<5 m deep and <20 m offshore). In the few nearshore surveys in PWS using SCUBA or beach seine, juvenile pink salmon (Oncorhynchus gorbuscha), Pacific cod (Gadus macrocephalus), Pacific tomcod (Microgadus proximus), and walleye pollock (Theragra chalcogramma) were observed or captured in large numbers (Laur and Haldorson 1996, Wertheimer and Celewycz 1996, Dean et al. 2000). Other species that use shallow, nearshore habitats in PWS for spawning or rearing include capelin (Mallotus villosus), Pacific herring (Clupea pallasii), and Pacific sand lance (Ammodytes hexapterus) (Robards et al. 1999, Norcross et al. 2001, Brown 2002, Cooney 2007). Of all the fish species in PWS, Pacific herring is the most studied, largely in response to research needs identified by the Exxon Valdez oil spill (Brown et al. 1996, Johnson et al. 1997). The primary objective of this study was to compare fish assemblages by season and habitat type in shallow, nearshore waters of PWS. We focused our efforts in western PWS where 1543 km of shoreline were mapped with the ShoreZone protocol in 2004 (NOAA Fisheries 2009b). ShoreZone uses aerial video imagery to classify and map intertidal and shallow sub-tidal geomorphology and biota across wide geographic ranges. These data enabled us to identify the dominant nearshore habitats available to fish. Our study is Northwest Science, Vol. 84, No. 3, 2010 267 Fish Assemblages in Prince William Sound unique because we concentrated our efforts in shallow, nearshore habitats (<5 m deep and <20 m offshore) that are often ignored in fisheries surveys. Because the nearshore is vulnerable to local and global human disturbances, including global climate change (Lubchenco et al. 1993, Johnson et al. 2003), a better understanding of how the nearshore supports living marine resources is needed to help managers protect essential habitats.