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Fishery Bulletin 97(4), 1999 



rine, inshore, and bay habitats in the northeastern 

 Pacific, it appears to be normal for five or fewer spe- 

 cies to account for more than 751 of the individuals 

 in local fish communities, even though the total num- 

 ber of species comprising these communities may be 

 much larger (e.g. Allen and Horn, 1975; Hancock, 

 1975; Horn, 1980; Allen, 1982; Gordon and Leavings, 

 1984; Orsi and Landingham, 1985). 



Although no significant differences were observed 

 in species composition between consecutive beach 

 seine sets at the same study sites, CPUE was mark- 

 edly reduced for the second sets made at both high 

 and low tides. This reduction in CPUE may have 

 resulted from avoidance by schooling species to dis- 

 turbance, or removal of most individuals during the 

 first set. As Gibson et al. (1996) observed, we found 

 marked differences in species composition between 

 tidal states, and the number of species found at low 

 tide was reduced by 26% in sets made at high tide. 

 The fact that only species that typically migrate into 

 the intertidal zone (e.g. pink salmon, sand lance, 

 great sculpin) were caught at high tide may have 

 accounted for this difference. Juvenile sand lance 

 occurred in greater numbers and were caught at 

 higher frequencies during high and flood tides, com- 

 pared with low and ebb states as observed by 

 Blackburn and Anderson (1997). These results sug- 

 gested that juvenile sand lance may have moved lat- 

 erally on each tide, by ascending from demersal habi- 

 tats to pelagic zones at flood stages, and returning 

 at ebb stages. Larval plaice (Pleuronectes platessa ) 

 of the North Sea exhibited this kind of behavior in 

 coastal nursery areas (Rijnsdorp et al., 1985). 



High-latitude fish assemblages, particularly those 

 found in shallow water habitats, are subject to large 

 seasonal variations in temperature and day length. 

 These physical factors impart a strong natural sea- 

 sonality to community structure (Nash, 1988) as ob- 

 served in the nearshore waters of Kachemak Bay. 

 Some fish species move from shallow water habitats 

 to deeper waters in winter when thermal tolerances 

 are exceeded (Allen and Horn, 1975; Allen, 1982; 

 Bennett, 1989). Decreases in catch size between 

 spring and fall peaks have also been observed by 

 many investigators (e.g. Livingston, 1976; Horn, 

 1980; Allen, 1982; Thorman, 1986b; Methven and 

 Bajdik, 1994). However, the midsummer CPUE de- 

 clines in Kachemak Bay were not accompanied by 

 declines in species diversity, as obser\^ed by Thorman 

 ( 1986b). Reduction in numbers of adult Atlantic sand 

 lance (Ammodytes marinus) has also been noted in 

 midsummer seabird diets (Monaghan et al. , 1996). 

 This change corresponds to the time when predation 

 by chick-rearing seabirds is at maximum; adult sand 

 lance may be responding to the increased presence 



of predators by avoiding nearshore and surface habi- 

 tats, or they may be coincidentally estivating in 

 preparation for spawning (Sekiguchi et al. , 1976). 



Geographic variability 



The relative abundance and distribution offish spe- 

 cies in lower Cook Inlet appears to be largely deter- 

 mined by oceanography and sediment influx. Intense 

 insular upwelling of nutrient-rich waters around the 

 Barren Islands leads to high productivity along fron- 

 tal zones that in turn results in high abundance of 

 fish. Upwelled water entering Kachemak Bay is nu- 

 trient-rich and becomes locally stratified, resulting 

 in the highest primary production recorded in lower 

 Cook Inlet ( Larrance et al. , 1977 ). In Kachemak Bay, 

 high habitat diversity and the plankton prey-base 

 provide the marine environments needed to support 

 an abundant, diverse fish community. As water cir- 

 culates around Cook Inlet to Chisik Island (Fig. 1), 

 sediment loads increase from freshwater glacial run- 

 off (Feely and Massoth, 1982), leading to maximum 

 primary production that is only about one-tenth of 

 that found in Kachemak Bay (Larrance et al., 1977). 

 The lower abundance of sand lance at Chisik Island 

 probably results from a combination of low food avail- 

 ability and deposition of glacial silt and mud (Feely 

 and Massoth, 1982) that blanket most of the local sub- 

 strates. Sand lance are known to require clean, sandy 

 nearshore substrates (e.g. Pinto et al. , 1984), and they 

 appear to favor these habitats; few were caught in the 

 offshore, oceanic waters surrounding the Barren Is- 

 lands. On the north side of the Alaska Peninsula, sand 

 lance also dominated nearshore catches and were 

 caught less frequently offshore (Houghton, 1987). 



The storm-prone Barren Islands displayed lower 

 species diversity than the other lower Cook Inlet ar- 

 eas. Species inhabiting this more exposed oceanic 

 region may avoid shallow habitats and favor slightly 

 deeper, less disturbed waters (Thorman, 1986a). lead- 

 ing to reduced nearshore diversity (Horn, 1980). Di- 

 versity of fish in the nearshore Kachemak Bay and 

 Chisik Island environments was apparently related to 

 increasing habitat diversity and reduced salinity, as 

 seen elsewhere (Thorman, 1986b; Blaber et al., 1995). 



The most notable difference observed between 

 nearshore and offshore shelf environments in lower 

 Cook Inlet was that shelf areas were dominated by 

 walleye pollock. Pollock were found in 889( of 

 midwater trawls, compared with only 39^ in beach 

 seine sets. This species does not appear to use 

 nearshore habitats as nursery areas, as does a re- 

 lated species, the Pacific cod (Houghton, 1987). The 

 presence of some pollock in nearshore areas of 

 Kachemak Bay may be related in part to the pres- 



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