Stock Status and Conservation Information
(From ISC22 Plenary Report)
The Plenary reviewed and agreed to forward the stock status and conservation information adopted at ISC21, which was based on the 2020 stock assessment unchanged, except for the omission of accompanying figures and tables.
Click here to see the ISC21 stock status and conservation information.
Estimated female SSB exhibits an initial decline until 2003 followed by fluctuations without a clear trend through 2018. The estimated average SPR (spawners per recruit relative to the unfished population) during 2015 – 2017 is 0.50 (95% CI: 0.36 – 0.64), which corresponds to a moderate fishing intensity (i.e., 1-SPR = 0.50). The WCPFC-NC, which manages this stock together with the IATTC, adopted a biomass-based LRP in 2014 of 20% of the current spawning stock biomass when F=0 (20%SSBcurrent, F=0). The 20%SSBcurrent, F=0 LRP is based on dynamic biomass and fluctuates depending on changes in recruitment.
Stock status is depicted in relation to the LRP (20%SSBcurrent, F=0) for the stock and the equivalent fishing intensity (F20%; calculated as 1-SPR20%). Fishing intensity (F, calculated as 1-SPR) is a measure of fishing mortality expressed as the decline in the proportion of the spawning biomass produced by each recruit relative to the unfished state. The Kobe plot shows that the estimated female SSB has never fallen below the LRP since 1994, albeit with large uncertainty in the terminal year (2018) estimates. The SSB2018 was estimated to be 58,858 t (95% CI: 27,751 – 89,966 t) and 2.30 (95% CI: 1.49 – 3.11) times greater than the estimated LRP threshold of 25,573 t (95% CI: 19,150 – 31,997 t). Current fishing intensity, F2015-2017, calculated as 1- SPR2015-2017, is 0.50 (95% CI: 0.36 – 0.64;).
Based on these findings, the following information on the status of the north Pacific albacore stock is provided:
- The stock is likely not overfished relative to the limit reference point adopted by the Western and Central Pacific Fisheries Commission (20%SSBcurrent, F=0), and
- No F-based reference points have been adopted to evaluate overfishing. Stock status was evaluated against seven potential reference points. Current fishing intensity (F2015-2017) is likely at or below all seven potential reference points.
Two harvest scenarios were projected to evaluate impacts on future female SSB: F constant at the 2015-2017 rate over 10 years (F2015-2017) and (average of 2013-2017 = 69,354 t) over 10 years. Although the projections appear to underestimate the future uncertainty in female SSB trends, the probability of breaching the LRP in the future is likely small if the future fishing intensity is around current levels.
Based on these findings, the following information is provided:
- If a constant fishing intensity (F2015-2017) is applied to the stock, then median female spawning biomass is expected to increase to 62,873 t and there will be a low probability of falling below the limit reference point established by the WCPFC by 2028; and
- If a constant average catch (C2013-2017 = 69,354 t) is removed from the stock in the future, then the median female spawning biomass is also expected to increase to 66,313 t and the probability that SSB falls below the LRP by 2028 will be slightly higher than the constant fishing intensity scenario.