FISHERY BULLETIN: VOL. 87. NO. 3, 1989 



July 1985. A 37 m long, tapered, floating beach 

 seine, set in a semicircle from the shoreline from 

 a 4.6 m boat with an 18 hp outboard motor, was 

 used for sampling. Sets encompassed about 100 

 m^. The seine had a maximum depth of 2.5 m in 

 the bunt and 0.7 m at the ends of the wings. The 

 wings were made of 2.5 cm (stretch) mesh and 

 the bag was made of 0.64 cm mesh. We sampled 

 11 high tide stations (1-11) and 10 low tide sta- 

 tions (12-21) in 1984-^5 and 11 high tide stations 

 (1-11) and 8 low tide stations (12, 13, 14, 22-26) 

 in 1986 (Fig. 1). (Specific beach seine stations are 

 described by Wilson and Pearcy (1985a) and 

 Chung and Pearcy (1986).) The numbers of beach 

 seine hauls made in 1984, 1985, and 1986 were 

 435, 333, and 388, respectively. Surface water 

 temperatures were measured to the nearest 

 0.1°C with a bucket thermometer, and surface 

 salinities were determined to the nearest 2%r 

 with an American Optical Model 10419' refrac- 

 tometer after each set. Each station was sam- 

 pled several times each month during the field 

 seasons. 



We used a Kvichak towed net^ with a 2.7 x 2.7 

 m mouth opening and a 8.2 m long body section 

 with mesh grading from 3.8 cm to 0.3 cm and a 

 cod end of 0.3 cm mesh to sample juvenile chum 

 salmon in the main tidal channel during slack 

 tide at approximately 2 wk intervals from late 

 March through late June 1985. One nighttime 

 tow was made. Two boats were used to pull the 

 net along a 900 m long transect in the main chan- 

 nel of the lower bay (Fig. 1) at speeds of about 

 1-2 m/s. 



Approximately 100 individual juvenile chum 

 salmon from each seine haul were checked for 

 fin clips. We assumed neghgible regeneration of 

 clipped fins during the 3 mo sampling period. A 

 subsample of 5-50 juvenile chum salmon was 

 preserved in 10% formaHn or 95% ethanol for 

 length measurements and stomach content anal- 

 ysis or age determination, respectively. The 

 remaining fish were released. Fork lengths of 

 all preserved fish were measured to the nearest 

 mm. These lengths were converted to fresh fish 

 lengths or weights from the regressions of indi- 

 vidual preseved lengths and weights on fresh 

 lengths and weights (Wilson and Pearcy 1985a, 

 b). 



For data analysis, the 1984, 1985, and 1986 

 field seasons were divided into 21, 17, and 18 



sampling periods, respectively, in which every 

 beach seine station was usually sampled at least 

 once. Stations were divided into the lower bay 

 (stations 1^, 12-14, and 22) and upper bay (sta- 

 tions 5-11, 15-21, and 23-26) (Fig. 1). Sand sedi- 

 ments predominate in the lower bay, whereas 

 fine sands and silt, with high organic carbon, are 

 common in the extensive tidal flats of the upper 

 bay (Kreag 1979). Ninety-five percent confi- 

 dence intervals of the median number of fish 

 caught per set were calculated by the method 

 presented in Snedecor and Cochran (1980). Mean 

 lengths of fish from different regions of the bay 

 were compared using a t-test for unequal vari- 

 ances (Sokal and Rohlf 1981). Growth rates 

 among years were estimated from regressions of 

 the size of recaptured marked fish and com- 

 pared, using analysis of co variance (Snedecor 

 and Cochran 1980). Growth in weight was calcu- 

 lated from length-weight regressions. 



The total numbers of juvenile chum salmon 

 remaining in the bay were estimated by a modi- 

 fied Peterson model (Healey 1980), where on 

 day t, 



N,= 



CM 

 R 



(1) 



where 



C 



M 



total population, 

 total catch, 



estimated number of marked fish 

 present in the bay, and 

 R = number of marked fish recap- 

 tured. 



The estimated number of marked fish present, 

 M, was calculated assuming a constant loss rate 

 of marked fish with time: 



M = Moe 



-kt 



'Reference to trade names does not imply endorsement by 

 the National Marine Fisheries Service. NOAA. 

 ^Research Nets, Inc., Bothell, WA. 



where Mq = total number of marked fish re- 

 leased, 



k = instantaneous rate of disappear- 

 ance of marked fish, and 



t = days since release. 



The actual number of marked fish recaptured 

 and the estimated number of marked fish from 

 each release group were pooled for each year and 

 used in a modified Peterson model to estimate 

 population numbers {N,). The instantaneous rate 

 of disappearance of marked fish was estimated 

 for each marked group by the slope of the re- 

 gression of time on catch per effort. This instan- 



556 



