Resource Ecology & Fisheries Management (REFM) Division

Status of Stocks & Multispecies Assessment Program

Evaluation of Localized Depletion for Aleutian Islands Pacific Ocean Perch

Localized depletion has been identified as a potential conservation issue for rockfish. Stock structure of certain species of rockfish could occur at relatively small spatial scales; thus, local depletions could affect these local populations to a greater degree than the overall population. Declines in fishery catch-per-unit-effort (CPUE) within small spatial areas could be indicative of population declines and thus localized depletion.

In this study, we examine Pacific ocean perch (POP) CPUE from the Aleutian Islands POP fishery in recent years, to investigate the extent to which CPUE has declined during the course
of the fishery. The POP fishery in the Aleutian Islands is characterized by relatively few vessels fishing for a few weeks in July. Data were obtained from three areas (two near Buldir Island and one near Atka Island) where large POP catches recently have occurred.

A total of 10 datasets from the three areas were examined from 2000 to 2004. Of these 10 datasets, 8 did not show a significant decline in CPUE that would be expected with a fishery-induced localized depletion. The two area-year combinations where declines in CPUE were significant were northwest Buldir in 2003 and 2004. If localized depletion occurs at temporal scales longer than 1 year, one would expect the CPUE in 2004 to be consistent with estimates observed near the end of the 2003 fishery. However, CPUE in 2004 was consistent with most of the days in 2003, suggesting that localized depletion does not seem to have carried over between years.

It appears that any population decline during the 2003 fishery has been replenished by population movement and/or recruitment before the 2004 fishery. One of the features of the POP fishery is that it is limited to only a few days each year in any given area, and the total number of hauls from which a daily CPUE can be computed may be limited to three or less for some area-day combinations. The small number of hauls can potentially have large influence on the results.

The appropriate spatial and temporal scales at which localized depletion becomes important for rockfish is a subject for future research. The extent to which localized fishing becomes problematic for rockfish is dependent upon the ability of rockfish to replenish fished areas such that local spawning populations are not negatively impacted. Considerations regarding localized depletion for rockfish should reflect the spatial scale characterizing fish movement within a year and the location and spatial extent of spawning populations, but this information is largely unknown for Aleutian Islands rockfish.

By Paul Spencer and Rebecca Reuter.

Stock Assessment Research

A growing portion of the research at the AFSC focuses on approaches to assessing groundfish stock conditions. These analyses formulate the basis of catch recommendations that are made to the North Pacific Fishery Management Council (NPFMC). The Council goes through a process of reviewing these recommendations relative to the fishery management plan (FMP) and, following extensive discussions, develops Total Allowable Catch (TAC) recommendations which are then submitted to the Secretary of Commerce for approval. These are generally accepted as is and implemented in the subsequent year by the NMFS Alaska Regional Office. The analyses at the early stages of this process are contributed in large part by the AFSC scientists.

Part of this research entails evaluating the overall management strategy, also known as a "Management Strategy Evaluation" or MSE. In an MSE, alternative hypotheses about the population dynamics and ecosystem responses can be posed in a model framework and tested using our current system of management (e.g., a "standard" stock assessment model using typically available data and managed under typical FMP/Council situations).

Large numbers of simulations can be generated and statistics evaluated to understand how well the current management system will perform under different scenarios. For example, SSMA staff developed an approach that can evaluate hypothetical productivity changes (i.e., due to short- and medium-term climate variability) for flatfish species in the eastern Bering Sea. Also, a University of Washington graduate student (Teresa A’mar) is conducting research using an MSE approach to evaluate impacts specific to Gulf of Alaska pollock. SSMA staff have held mini-workshops on MSE approaches. This is likely to be a long-term activity, particularly as the current NMFS National Standard Guidelines for fisheries management are under revision and new management strategies will need to be evaluated.

By Jim Ianelli

AFSC Quarterly Research Reports Jan-Mar 2005