SBT stock assessment and projection under overcatch scenarios using the Operating Model

Stock assessments and constant catch projections under several overcatch scenarios using the operating model developed by CCSBT SC are conducted. The main factors influencing the assessment results are (1) the period over which the longline overcatch took place and (2) assumptions about the extent to which the longline overcatch necessitates CPUE adjustments. We also consider the appropriateness of the criterion used previously by the SC to evaluate short term risk

Examination of the SBT operating model to inform conditioning and projection specifications

Stock assessments and constant catch projections have been conducted using the Operating Model (OM) specified at the CCSBT technical meeting held in Seattle in July 2009. The current analysis shows that: (1) for the base case, higher steepness and lower M10 (natural mortality at age 10) are preferred in the grid sampling based on the likelihood (in contrast to the prior-based weight for steepness), and this leads to more optimistic future projections despite lower current spawning biomass (3.7% of the unfished biomass for the likelihood-based and 4.9% for the prior-based approaches), (2) when incomplete mixing of fish tagged is taken into consideration, the model fit, particularly to tag recaptures, is improved, and projection results are somewhat more optimistic, (3) the low recruitment estimate in 2006 seems to be primarily a consequence of LL1 catch-at-size data from 2008, (4) when CPUE is not adjusted for overcatch (i.e., S = 0), lower steepness and higher M are preferred, and higher S scenarios generally lead to more optimistic projection results despite worse fit to observed CPUE series, and (5) several sensitivity trials which accord less reliability to the Japanese longline CPUE favour higher M values and lead to more pessimistic results

Conditioning of the SBT operating model to inform projection specifications

The effects of updates on the operating model are examined. Because of the new growth schedule and the most recent two years’ data, the operating model prefers somewhat higher steepness compared to the previous version. This difference has little influence on the historical trajectories of spawning stock biomass, but it leads to more optimistic projection results

Further examinations of the SBT operating model to explore new tagging model and grid specifications

Stock assessments and constant catch projections were conducted using new Operating Models (OMs; sbtmod21 and sbtmod22, which have different tagging models) developed by the CCSBT ESC. The current analysis showed that: 1. a new candidate for the tagging model (incorporated in sbtmod22) led to higher M0 (natural mortality at age 0), lower M10 (natural mortality at age 10) and lower omega (non-linearity of the CPUE-abundance relationship) estimates than the previous tagging model which is used in sbtmod21, and estimated lower current stock abundance relative to the virgin unfished biomass, 2. a high S (S=0.5; S is the proportion of longline overcatch attributed to the reported effort) led to a lower M10, but the overall results were scarcely different from those for the base assumption (S=0.25), and 3. a slight change of assumptions regarding the Indonesian fishing selectivity impacted on M estimates substantially (leading to low M0 and high M10), which indicates poor ability to explain the Indonesian catch-at-age data when using a low M10 as pointed out during the 2008 SAG meeting

Further evaluation of empirical management procedures based on longline CPUE index and aerial survey index

Based on recommendations made during the third Operating Model and Management Procedure Technical Meeting (June 2010, Seattle), we have revised and evaluated “HK” Management Procedures (MPs) using empirical algorithms to determine TACs using information from the longline CPUE series and the aerial survey (AS) index. The exploration of HK variants showed that this MP can behave in a variety of ways as its control parameters and sub-algorithms are changed. As evident also from previous trials, MPs with larger TAC reduction in the early years, which might not be preferred from a socio-economic viewpoint, enable quicker stock rebuilding and greater TAC increases in later years, while still achieving the same long-term management target for spawning biomass recovery (though this comparison is complicated by transient effects)

Brief examination of conditioning results of the SBT operating model for management procedure evaluation

Updated conditioning results for the operating model used for evaluation of management procedures are examined briefly. Although no serious problems are found, the examination shows that: (1) higher steepness is preferred in the grid sampling for the reference set, which leads to slightly more optimistic future projections, and (2) based on the results of grid sampling for future projections under the current catch level, robustness trials relating to longline CPUE series often show features that differ from those for the reference set

A check of operating model predictions from the viewpoint of the management procedure implementation in 2017

Values of the core vessels’ longline CPUE and aerial survey (AS) indices (two required inputs to the Bali management procedure) are compared to projection results obtained from the SBT operating model (OM). The most recent observations for the CPUE index and the AS index fall within the 95% probability envelopes predicted by the Base case OM in 2011. As regards a decision on implementation of the recommended TAC (calculated by the MP in 2016 for the 2018-2020 fishing seasons) for the 2018 season, it is considered that no modification of the value of this TAC is required because: 1) there is no evidence to support a declaration of Exceptional Circumstances from the viewpoints of a check of the OM predictions, this year’s in-depth stock assessment/projections, and other potential reasons (Indonesian small fish catch, overcatch of reported global TAC, unaccounted catch mortality); 2) no unexpected change has been detected in the fisheries’ indicators examined; and 3) there are no indications of any appreciable decline in recruitment indices for 2017

Global status of groundfish stocks

We review the status of groundfish stocks using published scientific assessments for 349 individual stocks constituting 90% of global groundfish catch. Overall, average stock abundance is increasing and is currently above the level that would produce maximum sustainable yield (MSY). Fishing pressure for cod-like fishes (Gadiformes) and flatfishes (Pleuronectiformes) was, for several decades, on average well above levels associated with MSY, but is now at or below the level expected to produce MSY. In contrast, fishing pressure for rockfishes (Scorpaeniformes) decreased from near MSY-related levels in the mid-1990s, and since the mid-2000s has remained on average at only one third of MSY-related levels. Regions with the most depressed groundfish stocks are the Northwest Atlantic and the Pacific coast of South America, while stocks from the Northeast and Eastern Central Pacific, Northeast Atlantic, Southeast Atlantic and Southwest Pacific tend to have greatest average abundance relative to MSY-based reference points. In the most recent year available for each stock, the catch was only 61% of MSY. Equilibrium yield curves indicate that 76% of global potential groundfish yield could be achieved using current estimates of fishing pressure. 15% of this is lost by excess fishing pressure, 67% results from lower than optimal fishing pressure on healthy stocks and 18% is lost from stocks currently overfished but rebuilding. Thus, there is modest opportunity to increase catch of global groundfish fisheries by reducing overfishing on some stocks, but more by increasing harvest on others. However, there may be other reasons not to fully exploit these stocks.Fil: Hilborn, Ray. University of Washington; Estados UnidosFil: Hively, Daniel J.. University of Washington; Estados UnidosFil: Baker Loke, Nicole. University of Washington; Estados UnidosFil: de Moor, Carryn L.. University Of Cape Town; SudáfricaFil: Kurota, Hiroyuki. Japan Fisheries Research and Education Agency; JapónFil: Kathena, Johannes N.. Ministry of Fisheries and Marine Resources; NamibiaFil: Mace, Pamela M.. Ministry for Primary Industries; Nueva ZelandaFil: Minto, Cóilín. Galway-Mayo Institute of Technology; IrlandaFil: Parma, Ana María. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico. Centro para el Estudio de Sistemas Marinos; ArgentinaFil: Quiroz, Juan-Carlos. Instituto de Fomento Pesquero; ChileFil: Melnychuk, Michael C.. University of Washington; Estados Unido

Effective fisheries management instrumental in improving fish stock status

Marine fish stocks are an important part of the world food system and are particularly important for many of the poorest people of the world. Most existing analyses suggest overfishing is increasing, and there is widespread concern that fish stocks are decreasing throughout most of the world. We assembled trends in abundance and harvest rate of stocks that are scientifically assessed, constituting half of the reported globalmarine fish catch. For these stocks, on average, abundance is increasing and is at proposed target levels. Compared with regions that are intensively managed, regions with less-developed fisheries management have, on average, 3-fold greater harvest rates and half the abundance as assessed stocks. Available evidence suggests that the regions without assessments of abundance have little fisheries management, and stocks are in poor shape. Increased application of area-appropriate fisheries science recommendations and management tools are still needed for sustaining fisheries in places where they are lacking.Fil: Hilborn, Ray. University of Washington; Estados UnidosFil: Amoroso, Ricardo Oscar. University of Washington; Estados UnidosFil: Anderson, Christopher M.. University of Washington; Estados UnidosFil: Baum, Julia K.. University of Victoria; CanadáFil: Branch, Trevor A.. University of Washington; Estados UnidosFil: Costello, Christopher. University of California at Santa Barbara; Estados UnidosFil: de Moor, Carryn L.. University of Cape Town; SudáfricaFil: Faraj, Abdelmalek. Einstitut National de Recherche Halieutique; MarruecosFil: Hively, Daniel. University of Washington; Estados UnidosFil: Jensen, Olaf P.. Rutgers University; Estados UnidosFil: Kurota, Hiroyuki. Japan Fisheries Research and Education Agency; JapónFil: Little, L. Richard. Csiro Oceans and Atmosphere; AustraliaFil: Mace, Pamela. Ministry for Primary Industries; Nueva ZelandaFil: McClanahan, Tim. Wildlife Conservation Society; Estados UnidosFil: Melnychuk, Michael C.. University of Washington; Estados UnidosFil: Minto, Cóilín. Galway-Mayo Institute of Technology; IrlandaFil: Osio, Giacomo Chato. Joint Research Centre (JRC); Italia. DG Maritime Affairs and Fisheries, European Commission; BélgicaFil: Pons, Maite. University of Washington; Estados UnidosFil: Parma, Ana María. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico. Centro para el Estudio de Sistemas Marinos; ArgentinaFil: Segurado, Susana. Sustainable Fisheries Partnership; Estados UnidosFil: Szuwalski, Cody S.. University of California at Santa Barbara; Estados UnidosFil: Wilson, Jono R.. University of California at Santa Barbara; Estados Unidos. The Nature Conservancy; Estados UnidosFil: Ye, Yimin. Food and Agriculture Organization of the United Nations; Itali