North Pacific Research Board
Age validation of Pacific cod using high resolution stable isotope signatures in otoliths
This project will conduct high resolution micro-milling and microchemistry analysis of otoliths for age validation and ageing error estimation of Pacific cod. Pacific cod (Gadus macrocephalus) is the second most important groundfish managed by the North Pacific fishery Management Council, with harvests totaling more than 250,000 mt annually and recent ex-vessel values of more than $250 million. Pacific cod are assessed using age-structured models where age data are key to estimating mortality, recruitment, and harvest. However, Pacific cod age determination uncertainty has lead to assessment model uncertainty in which models with and without age data have been proposed as alternative competing models. Such uncertainty has resulted in as much as a 40,000 mt discrepancy in projected allowable biological catches between models with and without the inclusion of age data. The North Pacific Fishery Management Council has identified the need to validate and improve age determination methods for Pacific cod in its five-year research priorities. In response to this need our goal is to resolve Pacific cod ageing inaccuracy, particularly in the first 2-4 otolith growth bands, using stable oxygen isotope (δ18O) signatures in Pacific cod otoliths. Because variability in δ18O is inversely related to temperature the δ18O signature in an otolith from high resolution micro-sampling provides a proxy for seasonal temperature cycles and therefore a tool for age validation. This innovative approach is similar to that of Weidman and Millner (2000) who successfully applied this technique to North Atlantic cod.
Data and Resources
Start Date: 2011/09/01
End Date: 2013/07/31