Analyses/Maps

Fish

Integration of Community Metrics

The sections showing species diversity, species richness, and rockfish richness have provided results relevant to managing resources. The overlay of the top 17-20% of trawls for high species diversity, species richness, or rockfish richness is provided. The background of the map shows the bathymetric complexity discussed in another section. The overlay of the points provides visual representation of the results.

Richness calculates the number of fish species present in each trawl, while diversity takes into account the abundance of fish species as well. Diversity and richness are correlated (r2=0.06), but trawls with high diversity are not necessarily trawls with high richness. Trawls which were high in overall richness and diversity were distinguished, and show areas important to demersal fish. A cluster of trawls with high diversity and high richness straddle the boundary between Gulf of the Farallones and Monterey Bay NMS, as well as along the 200 meter contour north of Cordell Bank NMS. Small clusters of high diversity and high richness trawls are present within each sanctuary. Depth varied between the three community metrics, with high richness, rockfish richness, and diversity progressing from shallow to deep. The mean depth for trawls with the top 17% of rockfish richness was 221±87, with 43% of the trawls between 200 and 300 meters depth. Showing these trawls reemphasizes the interaction between rockfish richness and the edge of the continental shelf. The trawls with high species richness show much more variability with depth (mean depth 212±225 meters), but 64% of them are in water less than 200 meters deep. The trawls with high species diversity were deeper (mean depth 372±289 meters), with 52% of them greater than 300 meters depth. Overall, the trawls with high diversity were deeper than the trawls with high richness. A good example of this split by depth can be found south of the Monterey Bay NMS. This suggests that trawls with high species richness found just east of the 200 meter contour are dominated by a few influential species. Conversely, the areas of high diversity just west of the 200 meter contour might have one or two fewer species, but overall the species are evenly distributed.

Results from the assemblage analyses were significantly tied to depth; therefore, maps show bands of similar sites along depth contours and do not delineate areas important to demersal fish. Conversely, the results from the community metrics do delineate hot spots. Results are limited by collection method since rocky, highly sloped, or shallow (less than 50 meters depth) areas were not sampled. Managers could use the interaction of the community metrics to decide on proper management strategies. For example, management is often tasked with protecting biodiversity, and is therefore interested in delineating areas that contain the highest number of species. However, if an area is high in richness, but is dominated by one economically important species, protecting this area could contribute to resource use conflicts. The interplay between diversity and richness should be carefully evaluated.