Analyses/Maps
Fish
National Marine Fisheries Service (NMFS) Demersal Trawls on the Continental Slope
Little
is known about the deep slope species, especially information on
which species are found together on what habitats. Multivariate
statistics were used to analyze species assemblages over trawlable
habitats between 190 and 1280 meters depth off California. This
is the first attempt to exclusively define species assemblages on
the deep slope community. For an introduction to the continental
slope ecosystem, see section VII G in the Ecological Linkages Report.
Eight species assemblages (Figure) and seven site groups (Table,
Map) were identified. The average frequency of occurrence of species
assemblages (percent occurrence calculated for each species and
then averaged for each fish assemblage) within each site group was
calculated to analyze the interaction between the species assemblages
and site groups (Table). As with all data sets, the most significant
result was the effect of depth on species assemblages. All attempts
to isolate and remove the effects of depth in order to determine
secondary effects were unsuccessful. Certainly secondary effects
exist, but at the scale of this study, they were not discernible.
Our results support previous results by Williams and Ralston (2002),
Sullivan (1995), Field et al. (2002), Gabriel and Tyler (1980),
and Matthews and Richards (1991), who found bathymetry to be an
important factor in defining demersal fish assemblages on the west
coast. Through this analysis a large amount of information has been
condensed down to assemblages of co-occurring species, as well as
groups of similar locations. A map is provided to visually portray
the spatial arrangement of the results.
Table. Site group results for slope trawl data. The number of trawls associated with each group as well as average depth ± standard deviation are provided. Different letters signify a significant difference using Tukey's pairwise comparison on log adjusted depth with overall a set at 0.001. Average frequency of occurrence of fish species assemblages (percent occurrence calculated for each species and then averaged for each fish assemblage) for each slope site group are also provided. Numbers in bold represent influential species assemblages.
| |
Group 263 meters |
Group 410 meters |
Group 530 meters |
Group 622 meters |
Group 733 meters |
Group 931 meters |
Group 1112 meters |
| Depth±SD (meters) |
263±49a |
410±46b |
530±42c |
622±27d |
733±71e |
931±132f |
1112±95g |
| N |
84 |
86 |
43 |
29 |
48 |
90 |
74 |
| Sablefish Assemblage |
0.41 |
0.78 |
0.87 |
0.97 |
0.95 |
0.84 |
0.68 |
| Aurora Rockfish Assemblage |
0.40 |
0.75 |
0.55 |
0.31 |
0.27 |
0.25 |
0.17 |
| Stripetail Rockfish Assemblage |
0.51 |
0.08 |
0.00 |
0.00 |
0.00 |
0.00 |
0.00 |
| Splitnose Rockfish Assemblage |
0.88 |
0.92 |
0.64 |
0.36 |
0.18 |
0.04 |
0.06 |
| Filetail Catshark Assemblage |
0.03 |
0.33 |
0.51 |
0.43 |
0.23 |
0.08 |
0.05 |
| Longspine Thornyhead Assemblage |
0.01 |
0.05 |
0.22 |
0.41 |
0.65 |
0.87 |
0.84 |
| Pacific Viperfish Assemblage |
0.01 |
0.02 |
0.06 |
0.09 |
0.14 |
0.16 |
0.27 |
| Market Squid Assemblage |
0.14 |
0.15 |
0.13 |
0.07 |
0.07 |
0.03 |
0.05 |
Average frequency of occurrence of fish species assemblages (percent occurrence calculated for each species and then averaged for each fish assemblage) for each slope site group are also provided. Numbers in bold represent influential species assemblages.
| |
Group 263 meters |
Group 410 meters |
Group 530 meters |
Group 622 meters |
Group 733 meters |
Group 931 meters |
Group 1112 meters |
| Sablefish Assemblage |
0.41 |
0.78 |
0.87 |
0.97 |
0.95 |
0.84 |
0.68 |
| Aurora Rockfish Assemblage |
0.40 |
0.75 |
0.55 |
0.31 |
0.27 |
0.25 |
0.17 |
| Stripetail Rockfish Assemblage |
0.51 |
0.08 |
0.00 |
0.00 |
0.00 |
0.00 |
0.00 |
| Splitnose Rockfish Assemblage |
0.88 |
0.92 |
0.64 |
0.36 |
0.18 |
0.04 |
0.06 |
| Filetail Catshark Assemblage |
0.03 |
0.33 |
0.51 |
0.43 |
0.23 |
0.08 |
0.05 |
| Longspine Thornyhead Assemblage |
0.01 |
0.05 |
0.22 |
0.41 |
0.65 |
0.87 |
0.84 |
| Pacific Viperfish Assemblage |
0.01 |
0.02 |
0.06 |
0.09 |
0.14 |
0.16 |
0.27 |
| Market Squid Assemblage |
0.14 |
0.15 |
0.13 |
0.07 |
0.07 |
0.03 |
0.05 |
