Linking community structure of small demersal fishes around Kodiak Island, Alaska, to environmental variables

Abstract

Juveniles and small adults of at least 75 species of demersal fishes rvere identified in trawl catches from the nearshore waters of Kodiak Island, Alaska, in August 1991 and 1992. We derived several indices to characterize community structure at each site, identified key environmental gradients along w h c h community structure was organized, and identified those species whose abundances varied most strongly along these gradients. tVe related species richness, species diversity, and total catch per unit effort to environmental variables observed at each site. Species richness and diversity were highly variable among sites, but decreased significantly with salinity and were significantly higher on heterogeneous sediments. Standardized catch per unit effort for all species combined differed significantly among 5 geographic areas and was significantly higher on sediments with a high sand and/or mud content. Indices of species composition for each sampling site were 0btainc.d as the Scores of ordination axes based on non-metric multidimensional scaling of Bray-Curtis dissimilarities bettveen sites. The indices summarized different aspects of community composition and werc associated with different species groups. The first and major index was primarily related to the depth-ternperature gradient and contrasted a shallow, warm water species group with a deep, cold water group. Non-linedr depth effects on most indices suggest relatively rapid changes in species composition in shallow water (0 to 50 m), and more gradual changes in the lower part of the depth range. While the depth-ternperature gradient was the most important gradient along which species composition was structured, sediment composition and geographic area accounted for a significant proportion of the variance of each of the indices. While species composition changed most strongly along the depth-temperature gradient, species richness, diversity, and total abundance tvere not related to depth or temperature, suggesting that species composition changed independently of the overail abundance and of species richness and diverstity.

Oceanographic conditions structure forage fishes into lipid-rich and lipid-poor communities in lower Cook Inlet, Alaska, USA

“…Our findings may extend to much larger spatial scales. Recent evidence indicates that water temperature plays a major role in structuring fish communities in the north Pacific, as seen in the spatial organization of nearshore demersal fish assemblages (Mueter & Norcross 1999) and a multidecadal reorganization of forage fishes and groundfishes in the Gulf of Alaska (Anderson & Piatt 1999, Mueter & Norcross 2000. Again, this structuring has resulted in longterm changes in diet composition of piscivorous predators such as seabirds and marine mammals, and corresponding changes in their biology and population size (Piatt & Anderson 1996, Francis et al 1998.…”

“…of species caught) were calculated using CPUE data. Non-metric multidimensional scaling (NMDS, Statistical Sciences 1995) was used to summarize patterns in species composition of the forage fish community based on an ordination of pairwise site dissimilarities, following Field et al (1982) and Mueter & Norcross (1999. NMDS was used to construct axes of species composition independently of environmental parameters (see below), thereby minimizing circular ambiguities about relationships between biota and physical parameters (Field et al 1982).…”

Seasonal and interannual variability in the community structure of small demersal fishes off the central Oregon coast

“…Sediment is important in structuring some demersal fish communities (e.g. Mueter & Norcross 1999), but this seems to be limited to areas with heterogeneous sediments at similar depths.…”

Modifications to a plumb staff beam trawl for sampling uneven, complex habitats

“…The PSBT has proven to be an extremely useful tool off the coast of Alaska for measuring relative abundance of juvenile and adult flatfishes (Norcross et al, 1995;Norcross et al, 1997;Abookire and Norcross, 1998;Nichol, 1998) and juvenile groundfishes (Mueter and Norcross, 1999;Abookire et al, 2000Abookire et al, , 2001Litzow et al, 2000). However, in all applications of the PSBT, sampling has been limited to relatively flat, smooth habitats with low relief and little or no emergent structure.…”

“…Although juvenile Pacific cod (Gadus macrocephalus) and juvenile walleye pollock (Theragra chalcogramma) were captured with the PSBT on relatively smooth, even benthic habitats (Mueter and Norcross, 1999;Abookire et al, 2000Abookire et al, , 2001, we wanted to sample a variety of habitats including bottom types that were uneven and had emergent structure. Certain gadid species, such as Atlantic cod (Gadus morhua), are known to be more cryptic in their juvenile stage and to use complex habitats for refuge from predation (Fraser et al, 1996;Gregory and Anderson, 1997).…”