Stock Assessment Updates the Status of the Bottomfish Resources of American Samoa, Commonwealth of the Northern Mariana Islands, and Guam for 2012

Establishment of catch limits for bottomfish stocks in American Samoa, Commonwealth of the Northern Mariana Islands (CNMI) and Guam requires the best available information on status of the stocks. Stock status information for bottomfish complexes in these U.S. Pacific Island jurisdictions was recently updated based on the same mathematical modeling approach used in the previous stock assessment of these resources. A Bayesian statistical framework was applied to estimate parameters of a biological surplus production model fit to local indices of bottomfish abundance – time series of annual bottomfish catch-per-unit-effort (CPUE) statistics. This approach provides direct estimates of uncertainty for parameters fundamental to stock status determination. The surplus production model incorporates both process error in biomass production dynamics and observation error in the CPUE data. Alternative models with differing prior assumptions about carrying capacity and the ratio of initial stock biomass (at the beginning of the assessment time period) to carrying capacity were evaluated using the Deviance Information Criterion. The sensitivity of status determination results to catch data and model assumptions was also evaluated.

Stock status determinations, based on the base case production model with the best fit to the CPUE data, appear relatively robust. The results indicate that the bottomfish complexes in American Samoa, Commonwealth of the Northern Mariana Islands, and Guam were not depleted or experiencing overfishing in 2010, the most recent year of the stock assessment estimates.

The production models were used to project bottomfish stock levels in each area for 2013 and 2014 and to compute levels of Total Allowable Catch (TAC) associated with specified levels of overfishing risk. For the American Samoa stock complex, assuming a hypothesized 2-year TAC would be harvested from the stock, the projections indicated that the TAC to produce a 25% (1 out of 4) chance of overfishing in 2013 was 95,000 pounds and the TAC to produce a 50% (1 out of 2) chance of overfishing was 124,000 pounds. Similar stock projections for the Commonwealth of the Northern Mariana Islands bottomfish complex indicated that the TAC to produce a 25% chance of overfishing in 2013 was 219,000 pounds and the TAC to produce a 50% chance of overfishing was 293,000 pounds. Projections for the Guam bottomfish complex indicated that the TAC to produce a 25% chance of overfishing in 2013 was 65,000 pounds and the TAC to produce a 50% chance of overfishing was 81,000 pounds. Actual landings in all three jurisdictions have been substantially less.

Estimated bottomfish TAC associated with specified chance of overfishing the bottomfish resource in 2013 (in 1,000's pounds)
 
Chance of overfishing
  25% 50%
American Samoa 95 124
CNMI 219 293
Guam 65 81