Assessment of the Pacifi c halibut stock at the end of 2013

This stock assessment reports the status of the Pacific halibut resource in the northeastern Pacific, including the territorial waters of the United States and Canada. Annual removals were above the 100 year average of 64 million pounds from 1985 through 2010, dropping to 60 million pounds in 2011, and then 51 million pounds in 2012, in response to management measures intended to stabilize declining trends in the IPHC setline survey and stock assessment estimates. All data sources were updated through 2012. The 2012 setline survey showed an increase in WPUE (+12% relative to 2011), the first since the current geographically comprehensive survey began in 1997. Age distributions in 2012 from both the survey and fishery were very similar to those observed in 2011, indicating a relatively stable stock, but not showing any evidence of strong recruitments in recent years. Individual size-at-age continues to be low relative to the rest of the time-series, although there were signs of flattening in the declining trend for some ages for both males and females. For 2012, there was a full review of the data, specific model equations and general approach used to assess the stock in recent years. This effort consisted of three parts: 1) investigate and address the cause of the retrospective pattern observed in recent assessments, 2) improve the way uncertainty is propagated through data processing, model estimation and into the results used for management, and 3) identify additional work needed to create a more stable and easily reviewed stock assessment for the future. This work culminated in a successful Scientific Review Meeting, 24-26 October, 2012. Allowing for time-varying availability in the assessment model removed the retrospective bias in recent status estimates and is consistent with observed geographic and demographic trends. This change to the assessment model resulted in a much more pronounced decline in the estimated stock trend in recent years, a large reduction in the scale of current population estimates, and also a decrease in the estimated average level of productivity. The 2012 assessment indicated that the Pacific halibut stock has been declining continuously over much of the last decade as a result of decreasing size-at-age, as well as poor recruitment strengths. The population decline is estimated to have slowed and the stock trajectory is now relatively flat at 35% of the reference level, just above the harvest policy threshold (30%). Despite reductions in harvest levels in 2011 and 2012, the assessment estimates that, in retrospect, harvest rates have been well above the coastwide targets implied by the current harvest policy. The 2013 estimate of exploitable biomass is 186.49 million pounds, significantly smaller than the 2011 estimate of 260 million pounds. A bridge with the 2011 stock assessment results is provided, along with revised results from that model using the final data sets available through 2011 and through 2012 for direct comparison to the 2012 assessment results. Forecast projections were conducted for a range of alternative management actions, and probabilities of various risk metrics are reported in a decision-making table framework. The application of the current harvest policy, consistent with the approach used in recent stock assessments, results in the Blue line of the decision-making table indicating a coastwide TCEY of 36.63 million pounds and FCEY of 22.7 million pounds.

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