Natal source contributions of Pacific cod (Gadus macrocephalus) recruits in the southeastern Bering Sea

• Main Author: DiMaria, Ruth A.
• Other Authors: Miller, Jessica M., Hurst, Thomas P., Ciannelli, Lorenzo, Boehlert, George, Fisheries and Wildlife, Oregon State University. Graduate School
• Format: Master Thesis
• Language: English; unknown
• Published: Oregon State University
• Subjects: Pacific cod > Bering Sea; Pacific cod > Alaska > Alaska; Gulf of; Otoliths; Fish stock identification > Genetic aspects; Pacific cod > North Pacific Ocean; Bering Sea; Alaska
• Online Access: https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/08612s22f

Effective and sustainable fisheries management not only depends on identifying and defining stocks (fundamental unit of management), but also on having knowledge of factors influencing the abundance, distribution and connectivity of stocks. Population structure of Pacific cod (Gadus macrocephalus) in the southeastern Bering Sea (EBS) remains unresolved although genetic data indicate isolation-by-distance throughout the species range across the North Pacific Ocean. Pacific cod are fished on their spawning grounds, therefore, it is important to evaluate whether particular spawning sources are more critical than others in sustaining the productivity of fished populations. Chemical analysis of otoliths can provide information on mixing among groups of fish on ecological time scales and at finer spatial scales than genetic analyses. Therefore, I completed laboratory and field research on the otolith elemental composition of larval and juvenile cod to: (1) investigate temperature and growth-rate effects on otolith elemental incorporation to aid interpretations of field data; (2) evaluate the potential to detect larval exchange between the Gulf of Alaska (GOA) and the EBS; (3) quantify spatial scales at which there was significant variation in otolith elemental composition; and (4) quantify the number of larval sources (chemically distinct groups) contributing to juvenile recruits in the EBS. In the laboratory study, I observed higher rates of incorporation at lower temperatures for both Sr and Ba but similar ranges of Mg incorporation at 2°C, 6°C and 8°C. There was no significant effect of somatic growth or otolith precipitation rate on elemental incorporation detected, indicating that variation in individual growth rates should not confound interpretations of field data. In two years of field collections (2006 & 2008), otolith elemental signatures (Mg:Ca, Mn:Ca, Zn:Ca, Sr:Ca, and Ba:Ca) differed between larvae collected in the EBS and GOA, and over 70% of the larvae were correctly classified to source. ...