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

(Figure 8), the larger size of the Age 0 coho in July 2004 may be the result of the
later sampling in 2004 (end of the month cf mid-month in July 2005).
Chinook. Like coho, Chinook salmon were represented by several year classes
in the springs of 1983 and 2005. Small numbers of very small (less than 50 mm)
young-of-the-year migrants were present in April 2005, but seemed to be absent
in May 2005. Poor survival from this life history strategy has been reported in
Puget Sound estuaries (Beamer and Larsen 2004) that likely have much more
favorable conditions for growth and survival than does Knik Arm (see
Section 4.4). In May 2005, all Chinook taken in the large beach seine appeared
to be Age 1 or 2 outmigrants, although two Age 0 were taken in the small beach
seine at Port MacKenzie in June and in the large seine in July 2004. A cohort of
Chinook centered around 70 mm in July 2004, appeared to have grown
considerably by August 2004 (Figure 9).
Sockeye. Like coho and Chinook, sockeye salmon seem to exhibit a number of
different life history strategies in their use of and passage through Knik Arm. No
sockeye were taken in April 2005 beach seine samples. The small number of
sockeye taken in May 2005 (and in May/June 1983; Dames & Moore 1983)
ranged widely in size (Figure 7), likely representing fry, Age 1, and Age 2
outmigrations from their natal streams. The Age 0 cohort from May 2005,
displayed some apparent growth in June (or larger fish had entered the Arm) but
little change by July 2005. These fish (size peak at 60 mm in June and July 2005)
were considerably larger than the smallest cohort present in summer 2004,
which did not reach this size distribution until September (Figure 7).
A similar apparent growth pattern was observed in both offshore tow net
samples and with the fixed position net off the Port MacKenzie pier. Again, few
sockeye were captured in May with a wide size range likely representing two or
more age groups. Apparent growth was evident with Age 0 outmigrants, which
increased in size over the June and July time period (Figure 19).
Chum and Pink. Residency of pink and chum salmon juveniles in the Arm is
brief, but a steady increase in the maximum size of chum was apparent from
April through June 2005, both inshore in the beach seine samples and in
offshore tow net samples (Figures 10 and 19). This steady growth during their
brief residency was also observed by Moultan (1997) in offshore tow net
samples.
Very few pinks were observed in the nearshore, but a substantial number were
found in offshore tow net samples and apparent growth was seen from May to
June (Figure 19).
Pentec Environmental Page 41
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