56 



Fishery Bulletin 



1990 



No consistent relationship was found between water 

 temperature and catch of juvenile chinook salmon. 

 Temperatures measured on the bottom at about 0.3 m 

 depth generally changed little between May and Octo- 

 ber but increased with distance from the mouth of the 

 bay, averaging 12.3, 11.9, 13.8, 15.0, and 16.8°C at sta- 

 tions 1-5. respectively, for all sampling dates combined. 

 The large catches of juvenile spring chinook salmon at 

 stations 1 and 2 and of juvenile fall chinook salmon at 

 station 1 (Fig. 3) occurred at water temperatures 

 between 9-14°C. However, large catches of spring 

 chinook salmon also occurred at station 5 in June and 

 July at temperatures above 17°C. Surface salinity was 

 high at all stations during the study period (usually 

 >29"/(». after mid-June), indicating little influence of 

 freshwater at our sampling sites. (See also Biu't and 

 McAlister 1959.) 



Residence in the bay 



Unmarked STEP or wild fall chinook salmon resided 

 in the shallow nearshore areas of the bay for about 1-2 

 months. Catch per set of fall chinook salmon was 

 highest between 20 June and 17 July (Fig. 3), about 

 1.0-1.5 months later than the peak catches in the river 

 systems just above the bay (R. Bender, Oreg. Dep. Fish 

 Wildl., P.O. Box 5430, Charleston, OR 97420, pers. 

 commun., March 1988). 



Mean duration of residence in the bay of 63 fin- 

 clipped STEP fall chinook salmon was about 1 month 

 (Table 2). The average number of days (weighted by 

 catch per set of the marked fish) between release of 

 the median fish in a mark gi'oup and recovery in the 



bay of fish from that same mark group was 29 days 

 (n =63, range -6 to 83 days). Eight fin-clipped fish 

 were caught more than 50 days after release. The 

 number of days between release of the last fish in a 

 mark-group and the recovery in the bay of fish from 

 that same mark-group, a minimal estimate of time since 

 release, averaged 24 days {)i =63, range - 13 to 81 

 days). Average recovery date of right-pelvic and anal 

 fin-clipped fish was 27 and 32 days, respectively, after 

 release of the median fish (Table 2). 



Peak catch per set of spring chinook salmon usually 

 occurred within 1-10 days after Anadromous, Inc. 

 releases, and catches declined ra|)idly afterwards, sug- 

 gesting that spring chinook sahiKni had a much shorter 

 period of residence in shallow waters of the bay than 

 fall chinook salmon (Fig. 3). Catches returned to low 

 levels within about 25 days following the releases on 

 19 Jime and 29 July-4 August and within 7-10 days 

 following the releases on 31 August and 3 Sej)tember. 

 The very rapid decline in catch per set after the 3 1 Aug- 

 ust and 3 September releases, together with the low 



catches of fish from the last two releases 



on 



^9 Sep- 



tember and 1 October, indicate that movement into 

 deepwater channels or out of the bay for these late 

 summer releases may have been more rapid than for 

 earlier releases. 



All but one of the 27 CWT Anadromous, Inc. spring 

 chinook salmon caught in beach seines were captured 

 10 or fewer days after release* (range 1-18 days); 



*Tags from eleven of these fish were unreadable; however, these 

 unreadable tags were prohalily from the 31 Aug. ;ind 1 Oct. releases 

 (Mary McGowan, Anadromous. Inc., P.O. Ko.\ 1(107, North Bend, 

 OR 974.'')9. pers. commun., ,Ian. 1989). 



