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

Over the two sample periods, 18 species of fish including 7 species of adult and
juvenile salmonids were captured with the beach seine. Total catches in the two
July samplings were comparable (17.2 and 18.8 fish per set in 2004 and 2005,
respectively). Species composition and relative abundances also were generally
consistent from 2004 and 2005 with the notable exceptions of some seasonal
anadromous fish migrations, such as juvenile and adult salmon (Oncorhynchus
spp.) and eulachon (Thaleichthys pacificus) that were more abundant in the
spring of 2005 than in the later sampling in 2004 (Table 3).
The following sections describe the catch of individual species in greater detail
during both sampling periods.
3.3.2.1 Juvenile Salmonids
In total, 167 juvenile salmonids were captured by the 120-foot beach seine
during the July to November 2004 study period (Tables 4 and 5) and over 900
were collected during the April to July 2005 study period in Knik Arm (Tables 6
and 7; Figure 6). All species of juvenile and adult salmonids showed significant
variation in CPUE by month sampled (Table 8), a result of their seasonal
migration patterns.
Sockeye Salmon – 2004. Sockeye (O. nerka) were the most abundant juvenile
salmonid observed during the July to November sampling period in 2004,
comprising 55 percent of all juvenile salmonids captured. However, many
(43 percent) of these fish came from stations KA 1 and KA 3 (Figure 1, Table 5),
which were only sampled in August. Juvenile sockeye were widespread in the
project area, collected at all stations except KA 5A (sampled November only),
but were most abundant at stations in the inner Arm (Stations KA 1, KA 3, KA 7,
and KA 10). Sockeye CPUE was highest in August, although this statement is
again biased by the high catches at upper Arm stations KA 1 and KA 3.
Numbers decreased sharply in September (Figure 6).
Length frequency histograms show most juvenile sockeye were between 21 and
80 mm over the whole 2004 sampling period. Examination of length frequency
data over time (Figure 7) suggests steady growth through the latter half of 2004
as numbers declined in the nearshore. Most juveniles, believed to represent Age
0 fish, were between 31 and 50 mm in July, 41 and 50 mm in August, and 41 to
70 mm in September. During May and June sampling in 1983, most sockeye
were between 60 and 80 mm and were likely Age 1 migrants. The very few fish
under 50 mm in spring 1983 were likely Age 0 fish that correspond to the Age 0
group of 31 to 50 mm fish in July 2004. Growth in this cohort can be tracked
through August and into October 2004. The groups of larger sockeye (61 mm
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