David B. Sampson

Bias and Precision of Estimates from an Age-Structured Stock Assessment Program in Relation to Stock and Data Characteristics

Abstract Assessments for many U.S. Pacific coast groundfish stocks have been developed using the statistical catch-at-age method known as Stock Synthesis. This study used Monte Carlo simulation and a fractional factorial experiment to evaluate the effects of input data errors and stock characteristics on bias and precision in estimates of ending exploitable biomass, rate of fishing mortality, depletion, and other output variables. Nine factors were examined: length of the data series, rate of natural mortality, shape of the fishery selectivity curve, trend in fishing mortality, recruitment pattern, and level of sampling error in the data for catch, fishing effort, a survey biomass index, and sample size for fishery and survey age compositions. Length of the data series, age composition sample size, survey biomass variability, and fishing effort variability were the most influential factors for most of the output variables. The estimates of depletion had the least bias and the estimates of starting biomass...

Gear-Related Mortality in Selective Fisheries for Ocean Salmon

Abstract In ocean fisheries for Pacific salmon Oncorhynchus spp., there can be several forms of gear-related mortality. Much research effort has been directed at estimating mortality rates for salmon that are hooked and then released. Also potentially important but not easily measured is mortality of fish that escape from the hook before being brought to the boat or fish that are removed from the hook by predators, so-called “drop offs.” In selective fisheries in which some hatchery-bred fish are marked for retention and unmarked fish legally must be released, the actual mortality rate suffered by unmarked fish depends on the harvest rate for the marked fish, the accuracy of mark recognition, and the proportion of marked and unmarked fish when fishing begins. This paper develops a model for evaluating gear-related mortality in selective fisheries and explores the potential importance of several sources of mortality. Mortality rates for unmarked fish are generally lower than the apparent harvest rates but ...

The Center for Independent Experts: The national external peer review program of NOAA's National Marine Fisheries Service

Abstract Requirements are growing for peer review of the science used for governmental management decisions. This is particularly true for fisheries science, where management decisions are often controversial. The National Oceanic and Atmospheric Administrations National Marine Fisheries Service instituted the Center for Independent Experts (CIE) in 1998 as a national peer-review program. Operations of the CIE, run under a contract with the University of Miami, maintain the independence of reviewers from the agency, and follow strict conflict of interest guidelines. Reviews by the CIE fulfill the requirements of the Information Quality Act and the Office of Management and Budgets Peer Review Bulletin. The CIE completed 101 reviews between 1999 and September 2006. Ninety-eight reviewers have participated in CIE reviews, with 72% of them coming from overseas. Case studies involving groundfish data and stock assessments, and marine-mammal abundance, are described, including the scientific issues, CIE opera...