Graduation Date

Spring 2019

Document Type

Thesis

Program

Master of Science degree with a major in Natural Resources, option Fisheries

Committee Chair Name

Dr. Eric Bjorkstedt

Committee Chair Affiliation

HSU Faculty or Staff

Second Committee Member Name

Dr. Mark Henderson

Second Committee Member Affiliation

HSU Faculty or Staff

Third Committee Member Name

Dr. Andre Buchheister

Third Committee Member Affiliation

HSU Faculty or Staff

Subject Categories

Fisheries

Abstract

Properly describing variability in population dynamics (e.g., growth, fecundity, recruitment) is expected to improve management of important fisheries stocks (Maunder & Piner, 2014). As recruitment to most fish stocks is determined during early life history stages (Houde, 1997; Iles & Beverton, 2000), and early life history stages are influenced by oceanographic conditions (Bjorkstedt et al. 2002; Laidig, 2010), understanding how environmental stochasticity influences recruitment deviations has potential to improve estimates of stock productivity and how productivity might change over time to support more effective management. Chilipepper Rockfish (Sebastes goodei) are an important commercial species that is managed as a single population throughout the continental US (Field et al. 2015), yet spatiotemporal heterogeneity of oceanographic conditions is likely to cause variability in recruitment deviations throughout this range. Field and Ralston (2005) used region-based catch-at-age data from 1967-1997 to determine that 72% of recruitment deviations were shared throughout their range, though a substantial amount of the variability was coherent over smaller scales. I extended and enhanced the analysis presented in Field and Ralston (2005) to encompass data from the last two decades, a period in which there was considerable rebuilding of stocks, generally favorable oceanographic conditions, and a rise in the understanding of spatial oceanography in the California Current System (CCS). In doing so, we confirmed results from Field and Ralston (2005), demonstrating that 70% of the variability in Chilipepper Rockfish recruitment deviations were shared coastwide between 1973 and 2015, though north-south and core (approximate center of biomass) -boundary spatial patterns did emerge. Generalized additive models were then used to examine oceanographic conditions as predictors of both coastwide coherence and spatial heterogeneity in recruitment deviations. Spatial patterns in recruitment emerged as a product of oceanographic conditions in the winter, at least in part due to high- and low-frequency transport dynamics, captured by sea level anomalies and the North Pacific Gyre Oscillation, respectively. Magnitude of recruitment success, which was generally shared coastwide, was best captured by upwelling anomalies during spring. This work demonstrates a method to empirically estimate spatial variability in recruitment deviations, which may facilitate current efforts to develop spatially-explicit stock assessment models, which are currently forced to make the assumption that recruitment is equally distributed across space (Thorson and Wetzel, 2013). Furthermore, understanding how oceanographic conditions may predict temporal shifts in that recruitment distribution may enhance the effectiveness of these stock assessment models.

Citation Style

APA

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