Status of Stocks & Multispecies Assessment Program
Stock Structure Symposium
A symposium entitled "The role of stock structure in the management of commercial fisheries" was held at the February 2009 meeting of the Scientific and Statistical Committee (SSC) of the North Pacific Fishery Management Council (NPFMC). The meeting was motivated by recent discussions in NPFMC Groundfish Plan Team and SSC meetings concerning stock structure for a number of Alaskan fish species.
Scientists from the AFSC, Northwest Fisheries Science Center, University of Washington, and University of Alaska presented information on techniques for incorporating spatial complexity in stock assessments, the types of information used to infer stock structure, and local adaption of fish populations to their environment. Information on spatial population structure was presented for Alaska populations of Atka mackerel, Pacific cod, and several rockfish species.
As a result of the symposium, a working group was created to develop guidelines to assist stock assessment authors, plan teams, and the SSC in determining when subregional fishing level recommendations for a species might be appropriate.
By Paul Spencer
Incorporating Stock Reproductive Potential into Stock Assessments
On 13-15 January 2009, Paul Spencer (SSMA Program) participated in a working group focused on incorporating stock reproductive potential (the capacity of a fish stock to produce eggs and larvae) into stock assessments. The working group met in Vigo, Spain, and was funded by the European Cooperation in the field of Scientific and Technical Research (COST).
The working group is one of three working groups that comprise the "Fish Reproduction and Fisheries" (FRESH) project; the other two working groups focus on 1) identifying underlying causes of variation in stock reproductive potential, and 2) standardizing methods for sampling and estimating stock reproductive potential. The aim of the FRESH project is to create a network in which stock assessment scientists and biologists studying fish reproduction can work together to address these three topics.
The working group was titled "Linking biology and assessment: Improving stock assessment through implementation of stock reproductive potential." The format of the working group meetings was to hold workshops and "training schools" where specific mechanisms for incorporating reproductive biology into assessments were presented.
At the Vigo meeting, Dr. Richard Hillary (Imperial College) led a workshop on fitting stock-recruitment relationships with Bayesian hierarchical models. Additionally, Dr. Iago Mosqueira (Centre for Environment, Fisheries, and Aquaculture Science) led a tutorial on the Fisheries Library in R (FLR) software.
Paul Spencer presented a review and progress report of maternal effects (influence of a spawner's age, size, or condition upon egg or larval quality) modeling and field research in the North Pacific. Simulation modeling conducted by Paul Spencer indicates that when a maternal effect in larval survival exists but is not recognized in an assessment model, biases in estimated productivity can be small at low and intermediate levels of fishing mortality and can increase at larger values of fishing mortality.
Additionally, results from field research on Pacific cod egg quality, conducted by Olav Ormseth (SSMA Program), and Gulf of Alaska Pacific ocean perch larval quality, conducted by Dr. Scott Heppell (Oregon State University), were presented.
