Despite the growing number of recreational anglers targeting white seabass Atractoscion nobilis in California, no information is available on the mortality rates of juveniles following catch and release. We captured juvenile white seabass (430-577 mm total length) with 4/0 offset circle hooks (n ϭ 113) or 4/0 J-type hooks (n ϭ 108) or with a net (control, n ϭ 30) to investigate the effect of hook type on anatomical hook location. We also examined how hook location affected growth and survival for 90 d following release. Offset circle hooks penetrated the lip region significantly more frequently (73%) than did J-type hooks (41%). Hook location was directly correlated with mortality; all mortalities involved hook damage to the visceral region. A 10% postrelease mortality rate was observed for fish caught on both offset circle and J-type hooks. All mortalities occurred within 5 d postrelease. Survival was enhanced when deeply embedded hooks were left in place rather than removed from the visceral tissue. Hook-caught fish showed no reduction in growth when compared with control fish, but deeply hooked fish grew at a significantly lower rate than did fish hooked in the mouth. Angler success rates did not differ significantly between hook types. We recommend that catch-and-release mortality be incorporated into the management plan for white seabass.

Current management of the Klamath River includes prescribed minimum discharges intended partly to increase survival of juvenile coho salmon during their seaward migration in the spring. To determine if fish survival was related to river discharge, we estimated apparent survival and migration rates of yearling coho salmon in the Klamath River downstream of Iron Gate Dam. The primary goals were to determine if discharge at Iron Gate Dam affected coho salmon survival and if results from hatchery fish could be used as a surrogate for the limited supply of wild fish. Fish from hatchery and wild origins that had been surgically implanted with radio transmitters were released into the Klamath River at river kilometer 309 slightly downstream of Iron Gate Dam. Tagged fish were used to estimate apparent survival between, and passage rates at, a series of detection sites as far downstream as river kilometer 33. Conclusions were based primarily on data from hatchery fish, because wild fish were only available in 2 of the 4 years of study. Based on an information-theoretic approach, apparent survival of hatchery and wild fish was similar, despite differences in passage rates and timing, and was lowest in the 54 kilometer (km) reach between release and the Scott River. Models representing the hypothesis that a short-term tagging-or handling-related mortality occurred following release were moderately supported by data from wild fish and weakly supported by data from hatchery fish. Estimates of apparent survival of hatchery fish through the 276 km study area ranged from 0.412 (standard error [SE] 0.048) to 0.648 (SE 0.070), depending on the year, and represented an average of 0.790 per 100 km traveled. Estimates of apparent survival of wild fish through the study area were 0.645 (SE 0.058) in 2006 and 0.630 (SE 0.059) in 2009 and were nearly identical to the results from hatchery fish released on the same dates. The data and models examined supported positive effects of water temperature, river discharge, and fish weight as factors affecting apparent survival in the Klamath River upstream of the confluence with the Shasta River, but few of the variables examined were supported as factors affecting survival farther downstream. The effect of water temperature on apparent survival upstream of the Shasta River was greater than Iron Gate Dam discharge, which was greater than fish weight.

Contents-Continued implement the paired-release design, because (1) an important assumption was violated in 2007, (2) the design reduces sample sizes in the IGH-to-Shasta River reach by 50 percent, and (3) the tagging and handling mortality was negligible when the design was used in 2006. We will tag and release fish from a tank at IGH as well as hatchery fish captured in traps near the I-5 Bridge. The purpose of this added activity will be to see if the use of migrant hatchery fish will result in migration behavior more similar to the behavior of wild fish in 2006. An additional group of wild fish would improve this design, but wild fish probably will not be available in sufficient numbers for our use in 2008.

No abstract