Past stock status and conservation advice
(From ISC9 Plenary Report)
After discussion of the ALBWG conclusions (Annex 9) and consideration of comments raised by Plenary members, the ISC offers no new conservation advice for North Pacific albacore above and beyond that which was provided to ISC7 in July 2007, pending the results of a new stock assessment, planned for 2011. To reiterate, the advice provided at ISC7 was:
“Previous scientific advice, based on the 2004 stock assessment, recommended that current fishing mortality rate (F) should not be increased. It was noted that management objectives for the IATTC and WCPFC are based on maintaining population levels which produce maximum sustainable yield. Due to updating, and improvements and refinements in data and models used in the 2006 stock assessment, it is now recognized that F2002-2004 (0.75) is high relative to most of the F reference points [commonly used in fisheries management] (see Table 5a in Annex 5) [of the ISC7 Plenary Report].
On the other hand, the same analysis indicates that the current estimate of the SSB is the second highest in history but that keeping the current F would gradually reduce the SSB to the long-term average by the mid 2010s. Therefore, the recommendation of not increasing F from current level (F2002-2004=0.75) is still valid. However, with the projection based on the continued current high F, the fishing mortality rate will have to be reduced.”
The NC adopted an interim management objective at NC4 (September 2008) to maintain the spawning stock biomass (SSB) above the average level of its 10 historically lowest points (ATHL) with a probability of 50% until reference points are established. The associated F-based threshold (FSSB-ATHL) was not estimated during the last stock assessment, but the ISC-ALBWG was requested to conduct its assessments, and to express the results of its assessments, such that they include the information necessary to achieve this interim management objective.
Based on analyses conducted by the ALBWG since ISC8, the following points are highlighted:
- The ISC9 Plenary notes that there is increasing uncertainty concerning the status of North Pacific albacore in the absence of a new stock assessment.
- The estimated value of FSSB-ATHL is 0.75 yr-1 for a 25-year projection period using fishery data through 2008. This value is similar to the most recent estimate of F (F2002-2004 = 0.75 yr-1) from the last stock assessment.
- The ALBWG did not determine the proximity of F2008 to this reference point.
- The ALBWG has generally interpreted FSSB-ATHL as a limit reference point, however, further guidance is required from the Northern Committee to clarify whether FSSB-ATHL is considered a target or limit reference point. If FSSB-ATHL is intended to be a limit reference point, then further consideration about the probability of falling below the threshold may be needed.
Pacific Bluefin Tuna
After discussion of the PBFWG’s assessment reports (Annexes 4 and 10) and consideration of comments raised by Plenary members, the ISC offers the following conservation advice:
- If F remains at the current level and environmental conditions remain favourable, the recruitment should be sufficient to maintain current yield well into the future.
- A reduction in F in combination with favourable environmental conditions, should lead to greater SPR.
- Increases in F above the current level, and/or unfavourable changes in environmental conditions, may result in recruitment levels which are insufficient to sustain the current productivity of the stock.
With regard to advice on the current level of F, differing viewpoints were expressed. Some members concurred with the findings of the PBFWG which stated:
- Given the conclusions of the May-June 2008 stock assessment with regard to the current level of F relative to potential target and limit reference points, and residual uncertainties associated with key model parameters, it is important that the current level of F is not increased.
In contrast, other members suggested that the following statement better reflects the current understanding of the stock status relative to the range of reference points considered:
- Given the conclusions of the July 2009 PBFWG, the current level of F relative to potential biological reference points, and increasing trend of juvenile F, it is important that the current level of F is decreased below the 2002-2004 levels on juvenile age classes.
In the absence of further information and analysis regarding the stock status of North Pacific striped marlin, the ISC Plenary agreed to maintain the conservation advice from ISC7, i.e.:
“While further guidance from the management authority is necessary, including guidance on reference points and the desirable degree of reduction, the fishing mortality rate of striped marlin (which can be converted into effort or catch in management) should be reduced from the current level (2003 or before), taking into consideration various factors associated with this species and its fishery. Until appropriate measures in this regard are taken, the fishing mortality rate should not be increased.”
The WCPO and EPO stocks of swordfish are healthy and well above the level required to sustain recent catches.