Robards et al : Variation in fish communities of lower Cook Inlet, Alaska 



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Figure 5 



Species composition l^i of total catch I in the 

 nearshorc (■) and shelf ( I areas of Kachemak 

 Bav, Chisik Island, and the Barren Islands. 



colder than average through the 1970s to warmer 

 than average through the 1980s and 1990s (Royer, 

 1993). Temperatiu-e changes have been linked to El 

 Nino Southern Oscillation (ENSO) events and shifts 

 in the location and intensity of the Aleutian low-pres- 

 sure cell (Niebauer, 1983). This climatic "regime 

 shift'" caused a major reorganization of North Pa- 

 cific biota (Francis et al., 1998). Phytoplankton and 

 zooplankton abundance increased in the Gulf of 

 Alaska, and this may have increased availability of 

 food to larval stages of salmon and other groundfish, 

 leading to enhanced recruitment (Francis et al., 

 1998). The timing of peak production of zooplankton 

 biomass also changed, and this may have influenced 

 recruitment in a suite of fish and invertebrates by 

 altering the survival of larvae ("match-mismatch" 

 hypothesis; Anderson and Piatt, in press). However, 

 not all species appear to have been affected by chang- 

 ing climate. It is notable that the most abundant fish 

 jn Kachemak Bay, sand lance, exhibited no signifi- 

 cant change in abundance or frequency of occurrence 

 between 1976 and 1995-96. Sand lance have a unique 



life history. They spawn during the fall and larvae 

 emerge in January or February, much earlier than 

 the spring plankton blooms or larvae of many other 

 Gulf of Alaska fish species. This strategy may be 

 adaptive in situations where prey availability is un- 

 predictable (Haldorson et al. , 1993). Therefore, sand 

 lance recruitment may have been little affected by 

 changes in the timing or magnitude of zooplankton 

 abundance during spring and early summer. 



Capelin abundance declined sharply throughout 

 the Gulf of Alaska after the late 1970s (Bechtol, 1997; 

 Piatt and Anderson, 1996) but may have started to 

 rebound in Cook Inlet waters during the early 1990s 

 (Roseneau et al.'-). Apart from catches in 10 beach 

 seine sets ( three sets in Kachemak Bay and at Chisik 

 Island, and four at the Barren Islands), there is little 

 evidence that capelin occur in nearshore areas of 

 Cook Inlet. However, they were the third most com- 

 mon species caught in midwater trawls, and capelin 

 were widely consumed by halibut and seabirds in 

 Cook Inlet in 1995 and 1996 (Roseneau and Byrd, 

 1997; Roseneau et al.^). This species may occupy 

 habitats offshore of the littoral zone, but largely in- 

 shore of where we made midwater trawls and may 

 therefore be under-represented by this study. 



The diversity of species in Kachemak Bay is com- 

 parable to that of other subarctic areas of Alaska. 

 Isakson et al. (1971) caught 40 species in the 

 nearshore waters of Amchitka Island and Orsi and 

 Landingham (1985) found 42 species in southeast- 

 ern Alaska. About 20-30 species are typically present 

 in nearshore habitats in the more temperate regions 

 of Sweden (Thorman, 1986a), Norway (Nash, 1988), 

 Scotland (Gibson et al., 1996), and California (Allen 

 and Horn. 1975; Horn, 1980; Allen, 1982). 



In Kachemak Bay, four species accounted for over 

 92% of the catch in 1995-96, and two species repre- 

 sented over 937f of the 1976 catch. One species (sand 

 lance) made up more than 99*7^^ of Barren Islands 

 catch, and even at Chisik Island, where species eq- 

 uity was high, only five species accounted for 79^^ of 

 the total numbers. As might be expected from these 

 patterns of relative abundance, these fish were pre- 

 dominantly juveniles (Gibson et al.,1996) and typi- 

 cally low in the trophic web (Allen, 1982). In estua- 



- Roseneau, D. R. A. B. Kettle, and G. V. Byrd. 1995 and 1996. 

 Common murrc restoration monitoring in the Barren Islands, 

 Alaska. 1993 and 1994. Ex.xon Valdez Oil Spill Restoration 

 Projects 93049 and 94039. Unpubl. final reports. 



' Roseneau, D. G., A. B. Kettle, and G. V. Byrd. 1996 and 

 1997. Barren Islands seabird studies. In D. C. Duffy (com- 

 piler I, APEX: Alaska Predator Ecosystem E.\periment. Exxon 

 Valdez Oil Spill Restoration Project. Alaska Natural Heritage Pro- 

 gram, University of Alaska, Anchorage. Appendix J. Unpubl. an- 

 nual reports. 



