University of Alaska Anchorage – B.A. English
Pacific halibut growth has decreased coast-wide since the late 1970s and early 1980s. This decrease in individual size-at-age has resulted in declines of observed stock biomass, relative to historical biomass averages. In all International Pacific Halibut Commission (IPHC) management areas, harvest levels and apportionments are determined using IPHC setline surveys that produce information on the observed distribution of fish >32 inches (minimum commercial retention size limit) and catch rates. The lower observed biomass of halibut, and the associated lower female spawning biomass, has resulted in decreases in the harvest levels of target and non-target halibut fisheries. The driving mechanisms behind decreasing size-at-age are not yet fully understood, and many of the relationships between them have yet to be explored. Further, while declines in mean size-at-age are well established, work remains to be done on the spatiotemporal aspects of these declines. This project’s objectives are 1) to describe the spatiotemporal distribution of halibut size-at-age in IPHC Area 3A, and to model the spatial structure of halibut growth performance (length-at-age) using geo-statistics; 2) determine the presence/absence of consistent spatiotemporal anomalies in growth performance above or below the Area 3A intra-cohort year-over-year mean size-at-age values; and 3) to explore the relationships between Pacific Halibut size-at-age and halibut diet through a method of stable isotope ratio analysis using δ 13C, δ15N, and to study the possibility of spatial variability in diet and diet tropism.