Daniel K. Kimura

Review of Statistical Aspects of Survey Sampling for Marine Fisheries

Fishery surveys are an essential ingredient of modern fisheries stock assessment. To understand this, one must understand that the survey time series are the essential anchor that makes modern fishery stock assessment modeling possible. Without fishery surveys, fisheries stock assessment scientists would have great difficulty modeling absolute abundance, and therefore agencies would have difficulty setting levels of allowable catch. In this review, we explore the basic assumptions that need to be fulfilled for valid surveys to be accomplished. Although these assumptions are generally well understood, the complexity of survey sampling gear and the complexity of target animal behavior makes them difficult to fulfill in practice and can easily lead to problems when interpreting survey results from even the most carefully designed survey. In reviewing the literature surrounding fishery surveys, their sampling design, modeling, and methods of analysis, it became clear that fisheries scientists have long been preoccupied with coping with the intense variability found in fish catches. This variability is found within fishing hauls, between hauls, between area, time and depth strata. Coping with this variability, which is due to animal behavior, habitat variation, and the nature of fishing gear, will be a constant theme that ties together our review.

Using 210Pb/226Ra disequilibrium to validate conventional ages in Scorpaenids (genera Sebastes and Sebastolobus)

Age determination of rockfish (genera Sebastes) and thornyheads (genera Sebastolobus) is typically accomplished by counting growth zones in burnt cross-sections of the otoliths. Interpretation of patterns seen in the otolith’s growth zones is often difficult and subjective so age validation is desirable. Unfortunately, age validation has been nonexistent for many of these species. Their biology and life history often make age validation methods used on other species impossible. Therefore, we used radiometric ageing which employs the disequilibrium of 210 Pb and 226 Ra in the otolith. Two methods were used to obtain material from the otoliths: core samples and whole otolith samples. The 210 Pb/ 226 Ra ratios generally confirmed ageing criteria used for rockfish, but in some cases there was a bias between growth zone counts and radiometric ages. We investigated two potential sources of bias. First, the initial ratio of 210 Pb/ 226 Ra as incorporated into the otolith may have been overestimated. Second, the otolith core removal process may have inadvertently left excessive amounts of younger aged material not belonging to the core. Both would cause radiometric ages to be biased low. Published by Elsevier Science B.V.

Bootstrap Methods for Evaluating Sablefish Pot Index Surveys

Abstract The National Marine Fisheries Service has been conducting pot index surveys in the northeast Pacific Ocean since 1978 in an attempt to measure changes in the relative abundance of sablefish (Anoplopoma fimbria). These surveys began initially off southeast Alaska and have since been extended to the Washington-Oregon-California region. In this paper, we evaluate the available data base using analysis of variance and the relatively new method of bootstrapping (i.e., a Monte Carlo form of sample reuse). Analysis of variance indicated the between-year changes in relative abundance were not statistically significant. Bootstrap analyses indicate three or fewer sets are required for each depth stratum at a sampling location (currently five are being taken), and as many as 12 sampling locations per region may be desirable (currently four locations are sampled off southeast Alaska and six locations are sampled off Washington-Oregon-California). These recommendations may have to be altered in the future whe...