Stock Status and Conservation Information
(From ISC22 Plenary Report)

Shortfin Mako Shark

Based on the conclusions of the SMA indicator analysis, the Plenary agreed to forward the stock status and conservation information adopted at ISC21 unchanged, except for the omission of accompanying figures and tables.

Click here to see the ISC21 stock status and conservation information.

Stock Status

The reproductive capacity of the NPO 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.

The following information on SMA stock status is provided:

1. 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; and
2. 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 SMA 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.

Conservation Information

Stock projections of biomass and catch of NPO SMA from 2017 to 2026 were performed assuming three alternative constant fishing mortality scenarios: 1) F_current (2013-2015), average of 2013- 2015 (F_2013-2015); 2) F_2013-2015sub> + 20%; and 3) F_2013-2015 - 20%.

Based on these future projections, the following conservation information is provided:

1. In scenarios where fishing mortality remains constant at F_2013-15 or is decreased by 20%, then spawner abundance (SA – the number of mature female sharks) is expected to increase gradually;
2. If fishing mortality is increased by 20% relative to F_2013-2015, then SA is expected to decrease in the final years of the projection; and
3. 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. Catches in 2020 and 2021 were 1,101 t and 1,040 t, respectively, lower than the three-year average.