54 



Fishery Bulletin 88(1), 1990 



fish was mainly fall chinook salmon from 31 May 

 through the end of July. Almost all fall chinook salmon 

 captured before the first release of spring chinook 

 salmon on 19 June were less than 105 mm FL. Al- 

 though we caught some large spring chinook salmon 

 after the first release on 19 June, a large, distinct mode 

 of these fish was not apparent until 10 days later on 

 29 June. Recoveries of Anadromous, Inc. spring 

 chinook salmon with CWTs (A in Figure 2) indicated 

 that this second mode of large fish was mostly spring 

 chinook salmon. This mode of large-sized fish was also 

 obvious a week later on 7 July, but by 16 and 17 July 

 catches of large fish had decreased to low levels. 

 Catches of large chinook salmon did not increase im- 

 mediately following the 17 and 29 July releases. 



We classified fish as either fall or spring chinook 

 salmon to estimate their relative abundances in the bay. 

 On 19, 20, and 21 June fish that were < 105 mm FL 

 were considered fall chinook salmon and the larger fish 

 were considered spring chinook salmon. (Arrows in 

 Figure 2 indicate the division between these groups). 

 On 29 June and 7 July, we used the valley between the 

 two distinct modes to separate fall and spring chinook 

 salmon. To account for gi-owth of fish, we distinguished 

 fall and spring chinook salmon at slightly larger lengths 

 on 16, 17 July and 29, 30 July (120 and 125 mm FL, 

 respectively). In August, length ranges of fall and 

 spring chinook salmon overlapped and the two groups 

 could not be separated by length. However, catch per 

 set of fall chinook salmon on 29 and 30 July was lower 

 than it had been in June and earlier in July, suggesting 

 that abundance of fall chinook salmon probably peaked 

 in June and July. Catches of fin-clipped fall chinook 

 salmon (S in Figure 2) in August were also low com- 

 pared with earlier periods. Therefore, we assumed that 

 subsequent increases in catch per set of juvenile chi- 

 nook salmon in August (Fig. 2) were due almost ex- 

 clusively to releases of large spring chinook salmon 

 from Anadromous, Inc. In the following discussion we 

 have treated all fish caught starting 3 August as spring 

 chinook salmon, realizing that this probably overesti- 

 mates the abundance of spring chinook salmon in the 

 bay, especially in early August when a few marked fall 

 chinook salmon were caught. 



The proportions of adipose clipped or CWT fish in 

 our catches of spring chinook salmon were usually 

 similar to the proportions of CWT fish in the immedi- 

 ately preceding releases of spring chinook salmon from 

 Anadromous, Inc. (r tests, p>0.05) (Table 1). This 

 supports the conclusion that most fish we classified as 

 spring chinook salmon originated from the Anadro- 

 mous, Inc. facility. An exception was during the period 

 4-30 August when the proportion of CWT fish in our 

 catch of spring chinook salmon was significantly lower 

 than the proportion released by Anadromous, Inc. on 



Table I 



Percentage of coded-wire tagged (('WT) (ir adi|inse-cli|i|ied 

 fish in the catch of spring chinook salmon from Coos Bay, 

 Oregon, vs. the percentage of CWT fish in the preceding 

 release from Anadromous, Inc. 



' Includes 16 Anadromous, Inc. CWT fish, 1 1 fish with unread- 

 al)le CWTs probably from Anadromous Inc., and 5 adiposc- 

 eli|jped fish without tags. 



* Observeil frequency of tags is significantly difl'ircnt frotn 

 expected fre()uency, ;i< 0.025. 



4 August (x- = 6.14, p<0.025). This result may be 

 explained by lack of complete mixing of marked and 

 unmarked Anadromous, Inc. fish and their patchy 

 distribution. Over 77% of the catch in August occurred 

 in just five sets, three of which were on the same day. 

 Large numbers of fall chinook salmon in the bay in 

 August mistakenly classified as spring chinook salmon 

 also could have produced the low proportion of CWT 

 fish. However, there is little direct evidence that fall 

 chinook salmon were abundant in the bay during Aug- 

 ust since very few fin-clipped fish were recovered, 

 although regeneration of fins may have made recogni- 

 tion of marks difficult (R. Bender, Oreg. Dep. Fish 

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

 commun., March 1988). 



Catch distribution 



Before mid-June, roughly e(iual numbers of fall chinook 

 salmon were caught at each of the five standard sta- 

 tions (Fig. 3). After mid-June, fall chinook salmon were 

 concentrated near the mouth of the bay at station 1, 

 although they were also caught at the other stations. 

 At station 1, catch per set of fall chinook salmon peaked 

 in June and July and dropped to low levels at the end 

 of July (Fig. 3). 



Catches of Anadromous, Inc. spring chinook salmon 

 were extremely patchy, with large catches at one or 

 two stations and low catches at the others. After the 

 first release on 19 June, almost all spring chinook salm- 

 on were found upbay at station 5, but later releases 

 were caught at the lower bay stations 1, lA (not 

 shown), and 2 (Fig. 3). Catch per set of spring chinook 



