Evaluating the Performance of Two Salmon Management Strategies using Run Reconstruction

Abstract

Commercial salmon fisheries in Alaska are managed to obtain escapement goals within a fixed range while attempting to maximize sustained yield. Two management strategies currently being used are emergency order authority and a fixed fishing schedule. We analyzed and compared the historical performance of these two management strategies for Bristol Bay, Alaska, fisheries targeting Egegik River and Togiak River Sockeye Salmon Oncorhynchus nerka. To accomplish this, we reconstructed the daily runs to each river through the use of catch, effort, and tower count data. Our results showed that management by emergency order openings resulted in (1) the catch of a higher percentage of returning fish, (2) less yearly variation in escapement, and (3) escapements that were always above the minimum escapement goal. A fixed fishing schedule resulted in less yearly variation in catch and a harvest rate that was spread more evenly throughout the run; the more even harvest rate likely provides better protection of substocks and the sex ratio. Emergency order authority gives a manager greater control over the fishery but requires more informative data. A fixed fishing schedule provides a more predictable catch but carries a higher risk of overharvest. Each of the two management strategies was successful and was suited to the circumstances of its fishery.Received December 7, 2012; accepted September 13, 2013Published online February 10, 2014

Using model simulations to compare performance of two commercial salmon management strategies in Bristol Bay, Alaska

“…The estimated number of drift gillnet vessels and set gillnet permits (derived from the daily effort data) and the estimated daily fish arrivals (N t ) were obtained from run reconstruction techniques (Carney and Adkison 2014).…”

“…The drift fleet efficiency parameters and catchability coefficients were taken from Carney and Adkison (2014). The actual harvest fraction for day i (h i * ) was calculated as…”

“…All of the fish that escape from the Egegik fishery were assumed to reach the counting tower (i.e., c = 1). The estimate of c for Togiak was 0.9, because Togiak has an escapement goal of 20 000 fish spawning below the counting tower, which represents ϳ10% of the mean historical tower counts (Carney and Adkison 2014). The predicted escapement (Ŝ) was calculated as the sum of the proportion of each cohort in the fishing district leaving on a particular day.…”

“…The mean number of days spent pooling in the fishery was assumed to be 3.6 (i.e., k = 3 and r = 0.6) and 1.5 days for the Egegik and Togiak fisheries, respectively (Flynn et al 2006;Carney and Adkison 2014).…”

“…The mean date, y , was a 10-year running average of the mean total run timing date delayed for the time spent migrating from the fishery to the counting tower. The yearly mean total run timing dates for 1986-2010 were taken from Carney and Adkison (2014); values for previous years were calculated by assuming normal arrival timing for the cumulative catch plus escapement, with used as the standard deviation for each year. The escapement status indicator is an approximation of actual managers' behavior, because the actual managers set fishing openings and closings based on the likelihood of the final escapement being within the goal range given the escapement up-to-date and estimates of the current year's run strength and timing (based on past runs and the run strength to date of the current year).…”