Marine Fish and Benthos Studies - Knik Arm Bridge and Toll Authority

species of polychaete worm, Neanthes limnicola, for a total of just nine taxa.
Another isopod, Argeia pugettensis, is parasitic on crangonid shrimp and thus is
not a true member of the invertebrate assemblage. In addition, parasitic sea lice
of the copepod Family Caligidae, were often seen in the net following capture of
adult salmon.
Consistent among the 1983, 2004, and 2005 sampling efforts is a trend of
increasing abundance in overall invertebrate densities beginning from spring and
moving into fall. In 2004 through 2005 this trend was significant (P = 0.000;
Figure 25, Appendix B, Tables B-1 and B-4). Overall, CPUE was greatest during
late summer/fall (August through October) 2004 in comparison to either the
1983 or spring/summer 2005 surveys. When overall CPUE data for April
through July 2005 are combined with data from July through November 2004,
CPUE increases steadily over the combined year, with the exception of
November 2004. A sharp decline in total invertebrate catch in November was
in part, the result of the large quantity of gray ice shards captured by the net in
most sets. The color and size of these shards mimicked the small clear or pale
gray bodied invertebrates and made their collection very ineffective. However,
CPUE in November 2004 was similar to that in early spring (April 2005) when
ice was not a factor. Thus, there appears to have been a real drop in
invertebrate presence during the winter (November through April).
Early in the 2005 survey, the amphipod Lagunogammarus setosus dominated the
catch, but its dominance was replaced by Crangon franciscorum in early May.
The overall CPUE of Crangon species continued to increase throughout the
study period, but the dominant species C. franciscorum, dropped off significantly
in July (P = 0.000, Appendix Table B-4) and was replaced by a newly emerged
cohort of Crangon. It is probable that this new cohort also was C. franciscorum,
based on the progression of CPUE shown on Figure 26, but identification could
not be confirmed due to small size and lack of maturity. Mysid abundance was
relatively constant over the sampling period (Figure 26) until July when CPUE of
mysids reached their peak in both years sampled (P = 0.000 in 2005; Appendix
Table B-4). Species dominance shifted from Neomysis mercedis to N. rayii at the
end of June and continued through July (Figure 26).
Over the entire 2005 survey period, the mean invertebrate CPUE at each station
sampled (averaged over time) ranged from 21.5 per set (KA 5) to over 120 per
set (KA 2), but combined species CPUE did not vary significantly (Appendix
Tables B-2, B-3, and B-4). The sites with the greatest CPUE were dominated by
crangonid shrimp and were located at the northern reach of Knik Arm (sites
KA 2, KA 6, and KA 10; Figure 27, Appendix B). The only group of invertebrates
that varied significantly by station was the amphipods, which were most
prevalent at KA 13.
Pentec Environmental Page 31
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