PEARCY ET AL.: JUVENILE CHUM SALMON 



taneous loss rate, k, also provided an estimate of 

 the residence time for each marked gi'oup in the 

 estuary. Solving Equation (2) for t when M/Mq = 

 V2 gave the residency half-Ufe in days, the time 

 in which the number of fish had declined by 

 50%. 



The estimated number of fish in the estuary 

 (A'^,) was multiplied by the average weight of 

 marked fish to estimate the biomass of juvenile 

 chum salmon present during each sampling peri- 

 od. These biomass estimates were multiplied by 

 the number of days between sampling periods, 

 summed over the entire period that juvenile 

 chum salmon were present, and multiplied by an 

 average instantaneous growth rate in weight of 

 the marked groups to estimate net production 

 for each year. 



RESULTS 



Emigration from Fresh water 



We estimated an outmigration of 11,900, 

 23,300, and 15,300 chum salmon fry from Whis- 

 key Creek in 1984, 1985, and 1986, respectively. 

 The early portion of the run was not sampled in 



1984. These estimates of naturally reared chum 

 salmon fry equalled 1.4%, 6.2%, and 2.3% of the 

 total chum salmon releases from the Whiskey 

 Creek Hatchery in these years (Table 1). The 

 abundances and temporal changes in catches of 

 chum salmon were similar in Jackson and 

 Whiskey Creeks in 1986 (Fig. 2). Since nearly all 

 wild chum salmon spawned in Whiskey Creek or 

 Jackson Creek, we assumed that the production 

 of fry from naturally spawning chum salmon in 

 the tributaries of Netarts Bay was about twice 

 that of Whiskey Creek. The mean length of chum 

 salmon fry caught was 40 mm in each of the three 

 years in Whiskey Creek, and 41.0 mm in 1986 in 

 Jackson Creek. Large fry (>45 mm), which were 

 indicative of rearing in freshwater (Mason 1974), 

 were not caught. 



Neai'ly all wild chum salmon fry outmigi-ated 

 into Netarts Bay by the end of April in all years 

 (Fig. 2). Peak numbers of fry were caught in 

 Whiskey Creek on 25 March 1984, 25 March 



1985, li April 1985, and 8 April 1986. Numbers 

 of emigrating fish were poorly associated with 

 any measured physical variable. Peak catches of 

 chum fry were not correlated with stream tem- 

 peratures (Fig. 2), although the second outmi- 

 gration pulse in 1985 followed an abrupt increase 

 in water temperature. Increased outmigration 

 activity of fry was not associated with phases of 



the lunar cycle as has been reported for other 

 salmonid fry (Reimers 1973; Mason 1975). 

 Stream flow estimated from stream heights ap- 

 peared positively correlated with peak numbers 

 of emigi'ating fry in 1984 when large numbers of 

 fish were sampled during or immediately after 

 three of four periods of high flow. The first peak 

 of outmigration in 1985 also occurred during high 

 stream flow; however, subsequent peaks in 1985 

 and 1986 occurred during periods of declining 

 flow. 



Distribution-Abundance in Netarts Bay 



Chum salmon were present in Netarts Bay for 

 about 21/2 months, from mid-March until early 

 June during each year (Fig. 3). The seasonal 

 abundances of juvenile chum salmon in Netarts 

 Bay were correlated with the emigration of wild 

 fish from streams and with releases of fish from 

 the Whiskey Creek Hatchery facility. Although 

 small peaks in beach seine catches during late 

 March 1984 and in early April 1986 coincided 

 with the peak of outmigi'ation of wild fish from 

 Whiskey Creek, most of the naturally reared fry 

 migrated into the bay before the major peaks in 

 beach seine catches (Figs. 2, 3). The largest 

 peaks in beach seine catches occurred within a 

 few days after releases from the Whiskey Creek 

 Hatchery in all years. 



Catches of juvenile chum salmon were greater 

 in the upper than the lower bay during March 

 and April in all years. Conversely, catches were 

 generally greater in the lower than the upper 

 bay during May and June (Fig. 4). These trends 

 indicate that juvenile chum salmon preferen- 

 tially inhabited the upper bay early in the spring 

 and then moved into the lower bay in late spring. 

 Movement into the lower bay late in spring was 

 correlated with the high water temperatures 

 that occurred in the upper bay during May of 

 each year. 



Juvenile chum salmon appeared to avoid tem- 

 peratures exceeding 14°C. Although they oc- 

 curred at most temperatures observed in the 

 upper bay during March and April, they usually 

 inhabited waters of minimum temperatures dur- 

 ing May and June, when average water tempera- 

 tures exceeded 14°C (Fig. 5, left panel). The 

 occurrence of juvenile chum salmon predomi- 

 nantly in the upper bay in early spring coincided 

 with average upper bay temperatures of <15°C. 

 Movements to the lower bay (Fig. 4) coincided 

 with upper bay temperatures exceeding 16°C 

 (Fig. 5, right panel). The percentages of chum 



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