Estimation of Fishing Tournament Mortality and Its Sampling Variance

—The mortality of fish captured in fishing tournaments has commonly been estimated incorrectly and, thus far, only one account has presented an estimate of the standard error or confidence interval for tournament-associated mortality. In this article we describe methods for estimating the initial, delayed, and total mortality of tournament-caught fish and provide formulae for estimating the sampling variances of these estimates. The absence of such estimates from previous studies may explain an observed lack of change in tournament-associated mortality between the 1980s and the 1990s. Our methods provide insight into the design of studies of tournament-associated mortality and suggest, for example, that many previous studies have held too few fish for observation and have greatly undersampled control fish. Improved study design and reporting should increase our understanding of the factors influencing tournament-associated mortality. Fishing tournaments commonly require live release of captured fishes after weigh-in. This practice initially was adopted to reduce potential biological and social impacts of fishing tournaments (Holbrook 1975; Barnhart 1989) and assumes that a substantial proportion of angler-caught fish survives capture, handling, and release (e.g., Muoneke and Childress 1994). To date, at least 20 studies have examined tournament-associated mortality in black basses Micropterus spp. to assess this assumption, measure the magnitude of tournamentassociated mortality, and develop methods for further reducing mortality (Wilde 1998). Other studies have also examined the tournament-associated mortality of walleye Stizostedion vitreum and sauger S. canadense (e.g., Goeman 1991; Fielder and Johnson 1994; Hoffman et al. 1996). Still other studies will likely extend to additional species because of the growth in popularity of tournament angling (Shupp 1979; Duttweiler 1985; Schramm et al. 1991) and concerns for potential fishery effects of tournaments (Schramm et al. 1991; Wilde et al. 1998a). The mortality of tournament-caught fish usually is recorded at weigh-in because most tournaments are conducted with rules that penalize anglers for dead fish (e.g., Kwak and Henry 1995; Hoffman et al. 1996; Wilde et al. 1998b, 2002b). Mortality * Corresponding author: [email protected] Received April 3, 2002; accepted November 9, 2002 that occurs at or before weigh-in is variously referred to as initial mortality, prerelease mortality, and weigh-in mortality. Not all released fish survive capture, holding in live wells, and weigh-in (e.g., Holbrook 1975); therefore, several studies also have measured delayed mortality (also referred to as postrelease mortality), which occurs after tournament-caught fish are released. Generally, a sample of tournament-caught fish is collected at the release site, held in ponds, cages, or pens, and observed for several days to estimate mortality that released fish might be expected to suffer. Estimates of total tournament-associated mortality are obtained by combining estimates of initial and delayed mortality. Among the papers reviewed by Wilde (1998) that estimated total mortality in black bass tournaments and that clearly stated the methods for that calculation, several presented incorrect estimates of total mortality (May 1973; Schramm et al. 1985; and Gilliland 1997, among others). None provided an estimate of the sampling variance of total mortality. Herein, we present methods for estimating total mortality of tournament-caught fish and provide formulae for estimating the sampling variance of such estimates. We also comment on the design of studies for measuring mortality of fishes captured in tournaments.