Stock Status and Conservation Information
(From ISC20 Plenary Report)
Shortfin Mako Shark
The reproductive capacity of the North Pacific SMA stock was calculated as spawning abundance (SA; i.e., number of mature female sharks) rather than spawning biomass, because the number of pups produced is not related to female size (i.e., larger female sharks do not produce more pups). Spawning potential ratio (SPR) was used to describe the impact of fishing on this stock. The SPR of this population is the ratio of SA per recruit under fishing to the SA per recruit under virgin (or unfished) conditions. Therefore, 1-SPR is the reduction in the SA per recruit due to fishing and can be used to describe the overall impact of fishing on a fish stock.
Click here to see the ISC19 stock status and conservation information.
- Target and limit reference points have not been established for pelagic sharks in the Pacific Ocean. Stock status is reported in relation to MSY-based reference points.
- The results from the base case model and six sensitivity analyses that represent the most important sources of uncertainty in the assessment show that the NPO shortfin mako stock is likely (>50%) not in an overfished condition and overfishing is likely (>50%) not occurring relative to MSY-based abundance and fishing intensity reference points.
Stock status was also examined under six alternative states of nature that represented the most important sources of uncertainty in the assessment. Results of these models with alternative states of nature were consistent with the base case model and showed that, relative to MSY, the stock is likely (>50%) not in an overfished condition and overfishing is likely (>50%) not occurring.
Stock projections of biomass and catch of NPO SMA from 2017 to 2026 were performed assuming three alternative constant fishing mortality scenarios:
1) status quo, average of 2013-2015 (F2013-2015);
2) F2013-2015 + 20%; and
3) F2013-2015 - 20%.
Based on these future projections, the following conservation information is provided:
- If fishing mortality remains constant at F2013-15 or is decreased 20%, then spawner abundance (SA – the number of mature female sharks) is expected to increase gradually;
- If fishing mortality is increased 20% relative to F2013-2015, then SA is expected to decrease in the final years of the projection;
- It should be noted that, given the uncertainty in fishery data and key biological processes within the model, especially the stock recruitment relationship, the models’ ability to project into the future is highly uncertain.
The ISC Plenary notes that the average annual catch of SMA by ISC members was 1,392 t in the 2013-2015 period and decreased to 1,180 t from 2016-2019