Fisher and Pearcy Distribution and residence of juvenile chinook salmon 



57 



another indication that residence of spring chinook 

 salmon in the bay is relatively short. Moreover, CWT 

 spring chinook salmon from each release were recov- 

 ered only during the period before the next release. 



Growth rates 



Growth rates of anal and right-pelvic clipped fall chi- 

 nook salmon, estimated from the slopes of the linear 

 regressions of fork length on days since release of the 

 median fish, were 0.54 mm/day {n = 19, r- =0.74) and 

 0.29 mm/day (h =33, r- = 0.33), respectively. Because 

 emigration from the bay may be positively related to 

 fish size, these observed growth rates probably under- 

 estimate the true average rates of growth of fish in the 

 mark groups. 



Discussion 



Our data indicate that small fall chinook salmon reside 

 in Coos Bay for a longer period than do larger spring 

 chinook salmon. Duration of residence in estuaries may 

 be related to the size or stock of fish. Dawley et al. 

 (1986) found that rates of downstream movement of 

 subyearling chinook salmon from lower Columbia River 

 stocks were positively related to fish length. Movement 

 of small subyearling fish through the Columbia River 

 estuary decreased by 30% relative to movement rates 

 farther upstream, while larger yearling fish moved 

 through the estuary at the same rate as through the 

 river. Neither subyearling nor yearling fish, however, 

 reared for long periods in the Columbia River estuary. 

 Because our collections were made by beach seine in 

 shallow nearshore areas of Coos Bay, we can say little 

 about the utilization of deeper channel areas by juvenile 

 fall and spring chinook salmon. We do not know whe- 

 ther peak abundances of fall or spring chinook salmon 

 in channels coincide with peak abundances in shallow 

 areas. Neither do we know what fraction of fall or 

 spring chinook salmon at any given time are in shallow 

 or channel areas. Temporal and size-related differences 

 in utilization of nearshore and channel areas by juvenile 

 chinook salmon have been found in other estuaries and 

 also may occur in Coos Bay. (See Figure 1 for locations 

 of other estuaries discussed.) In Yaquina Bay, Myers 

 (1980) found that although catches in shallow areas 

 peaked in late July and early August, catches continued 

 to increase in channels into October. In both Yaquina 

 Bay and the Columbia River estuary, small fish and 

 large fish preferentially utilized nearshore and chan- 

 nel areas, respectively. The mean lengths of wild juve- 

 nile chinook salmon in beach seine (nearshore) and lam- 

 para net (channel) catches in Yaquina Bay during June 

 were 88 and 106 mm FL, respectively (Myers 1980). 

 In the upper Columbia River estuary, many more year- 



ling chinook salmon (large fish) were caught in chan- 

 nels than in nearshore areas and, conversely, more 

 subyearling chinook salmon (smaller fish) were found 

 in nearshore areas than in channels (Dawley et al. 

 1986). In addition, subyearling fall chinook salmon 

 caught in nearshore areas were 10-20 mm shorter than 

 those caught in channel areas, and catch rates of sub- 

 yearling chinook salmon in nearshore areas were in- 

 versely related to length (Dawley et al. 1986). If similar 

 size-related distributional patterns occur in Coos Bay, 

 then the large spring chinook salmon released from 

 Anadromous, Inc. may utilize channel areas much more 

 extensively than shallow nearshore areas. 



Delays of up to 10 days occurred between releases 

 of spring chinook salmon from the Anadromous, Inc. 

 facility and peak catches of juvenile spring chinook 

 salmon in nearby (<8 km distant) shallow areas (Figs. 

 2 and 3). This suggests that spring chinook salmon may 

 stay in channels for several days following release and 

 then disperse into shallow waters. Some of the spring 

 chinook salmon occurring at stations 1 and 2 near the 

 mouth of the bay, especially those found several days 

 after a release, may even have reentered the shallows 

 from the ocean. Two CWT juvenile chinook salmon 

 released earlier in 1987 in Yaquina Bay were found 

 later in Coos Bay at station 1. This demonstrates that 

 juvenile chinook salmon, after they have entered the 

 ocean, sometimes reenter estuaries. 



The apparent rates of growth in length for two 

 groups of fin-clipped STEP fall chinook salmon caught 

 in Coos Bay (0.29 and 0.54 mm/day) were similar to 

 rates reported for a group of marked subyearling fish 

 caught in the upper Columbia River estuary (Dawley 

 et al. 1986; 0.60 mm/day) and reported by Levings et al. 

 (1986) for fry caught in the Campbell River estuary 

 (0.46-0.70 mm/day) but lower than reported by Healey 

 (1980) for fry in Nanaimo Estuary (1.32 mm/day) or 

 by Argue et al. (1986) for smolts in Cowichan Bay (0.97 

 mm/day). All these calculations of growth rates were 

 based on changes in length of marked fish with time 

 and should have a similar bias (i.e., possible faster 

 emigi-ation of fast-growing or large fish that results in 

 underestimates of actual mean growth rates attained 

 in the bay). Reimers (1973) reported little change in 

 size of marked and unmarked fish in the Sixes estuary 

 June through August, after which growth rates in- 

 creased dramatically. He attributed the slow growth 

 of juvenile fish during the June- August period to their 

 high densities in the bay. Myers (1980) found substan- 

 tial increases in size of wild chinook salmon with time 

 and between the upper and lower bay, indicating sub- 

 stantial growth of wild chinook salmon. Thus growth 

 of juvenile chinook salmon appears to vary among 

 estuaries, perhaps depending on their density and food 

 supply. 



