The Inter-American Tropical Tuna Commission’s (“IATTC”) Science Advisory Committee (“SAC”) will be meeting in La Jolla this week (May 9 – 13). One of the topics up for discussion is Pacific bluefin tuna: updated assessment and management. For California’s recreational and commercial fishermen, the 2014 stock assessment update for Pacific bluefin tuna (“PBF”) had profound impacts.
- Recreational fishermen saw their daily limit reduced to two fish per day with a trip limit of six for trips three-days in length or longer in US waters. Mexico initially banned the take of PBF in their waters; but have since adopted limits which mirror those imposed by the US.
- Commercial fishermen, who had been assured access to at least 500 metric tons (“mt”) per year, saw a quota imposed which reduced landings to a combined 600 mt for the 2015 and 2016 seasons.
These reductions were the direct result of actions taken by the IATTC in response to the 2014 stock assessment update. That update found (1) the biomass of pacific bluefin was at an extremely low fraction of its unexploited biomass (around 4.2%); (2) it was highly depleted and (3) experiencing overfishing. IATTC Resolution C-14-06 included conservation measures designed to achieve a reduction in catches of 20% to 45% to address these findings.
A new stock assessment for PBF is scheduled to be finalized and published later in 2016. In advance of the SAC meeting, the International Scientific Committee for Tuna and Tuna-like Species in the North Pacific Ocean (“ISC”) provided a Draft Executive Summary of the 2016 Pacific Bluefin Stock Assessment (“Executive Summary”). IATTC staff, using the Draft Executive Summary, prepared a document for the SAC meeting entitled Updated Assessment and Management of Pacific Bluefin Tuna (“IATTC Document”).
What do these documents show and should California’s recreational and commercial fishermen be worried about further reductions?
The 2016 Stock Assessment
A full analysis of how the biomass for PBF is estimated is beyond the scope of this document. Having said that, we think a brief primer on how the stock assessment works is in order. In short, it is based on a computer model which uses catch per unit of effort and length-composition data from a number of PBF fisheries throughout the Pacific as inputs. Also accounted for are assumptions regarding natural mortality and hypothetical recruitment scenarios. After the information is input, the model produces an estimate for both total biomass and that portion of the total capable of reproducing – spawning stock biomass (“SSB”).
The 2016 stock assessment is being touted as an improved assessment model which is much better than the previous models; but is still thought to be problematic in terms of rebuilding projections. The Executive Summary makes the following statement, “In this assessment, the ratio of spawning stock biomass * * * relative to the theoretical unfished biomass * * * is 2.6%.” This is less than the 4.2% figure from the 2014 stock assessment update; and would support the idea that further management measures are necessary. However, if we delve deeper into the documents mentioned above, we see a glimmer of hope.
After giving the 2.6% value, the Executive Summary offers a comparison to the 4.2% number taken from the 2014 update. “Although the [ratio] for this assessment (2.6%) is lower that the [ratio] from the 2014 assessment (4.2%) this is due to the changes in the model assumptions because SSB gradually increased in the last four years and does not represent a decline in SSB from 2012 – 2014.” In short, it is likely that the 2.6% value currently under consideration by the ISC may represent an increase over what the 2014 value would have been had the current stock assessment methods been in use.
In December of 2015, the Western and Central Pacific Fisheries Commission (“WCPFC”) adopted Conservation and Management Measure 2015-04 which stated an initial goal of rebuilding the SSB (of PBF) to the historical median (42,592 t) within 10 years with at least 60% probability. The stock is still overfished and subject to overfishing; but is projected to meet the WCPFC mandate under current management actions. This would support a decision by the IATTC to not impose further restrictions on California’s PBF fisheries. The document prepared by IATTC staff offers a somewhat different view. Based on uncertainty in terms of how recruitment is related to spawning stock biomass and the small number of individuals that comprise the spawning stock biomass, “it is recommended that further action be taken to protect the spawning population.”
What further action(s)
When contemplating how management measures may impact PBF, we need to be mindful of the impacts the various fisheries have on the stock. The following two graphs show landings of PBF by Country and then by gear type:
Figures taken from Executive Summary, page 2.
In 2014, US Commercial vessels landed a total of 404 mt while California commercial passenger-carrying fishing vessels were thought to have landed 27,321 fish with an estimated tonnage of 423.5 mt. By comparison, the other fisheries (by nation) informing the stock assessment reported landings as follows: Japan – 9,604 mt; Korea – 1,311 mt; Taiwan – 483 mt; Mexico – 4,862 mt; Australia and New Zealand – 12. Total reported landings of PBF for 2014 was 17,076 of which the US accounted for less than 5%.
It is generally accepted that PBF spawn only in the Western North Pacific Ocean (“WPO”) and that a portion of juvenile PBF make trans-Pacific migrations to the Eastern North Pacific Ocean (“EPO”), spending up to several years of its juvenile life stage here before returning to the WPO. Last summer, when larger PBF were taken in the EPO, fishery biologists searched for evidence of spawning in the EPO but none of the fish studied showed signs of sexual maturity (ie – roe or sperm).
As to relative impacts on the stock – when comparing fisheries in the WPO to those in the EPO – the Executive Summary makes the following statement, “Historically, the WPO coastal fisheries group has had the greatest impact on the PBF stock, but since about the early 1990s the WPO purse seine fleets, in particular those targeting small fish (age 0-1), have had a greater impact, and the effect of these fleets in 2014 was greater than any of the other fishery groups. The impact of the EPO fishery was large before the mid-1980s, decreasing significantly thereafter. The WPO longline fleet has had a limited effect on the stock throughout the analysis period (Figure 7). This is because the impact of a fishery on a stock depends on both the number and size of the fish caught by each fleet; i.e., catching a high number of smaller juvenile fish can have a greater impact on future spawning stock biomass than catching the same weight of larger mature fish.” See Executive Summary Page 9.
We have already seen some conservation groups highlighting the 2.6% and how it shows further decline in the status of PBF. As discussed above, the 4.2% figure from the 2014 stock assessment update would be lower if calculated using the proposed 2016 stock assessment methodologies. The Executive Summary notes that “the decline in SSB appears to have ceased since 2010, although the stock remains near the historic low”.
If we are to assume the goal is to comply with the WCPFC’s 2015 Conservation and Management Measure of having a 60% probability of rebuilding the SSB of PBF by 2024, then no additional restrictions are necessary on California’s PBF fisheries (commercial and recreational). The Executive Summary concludes with the following statement, “Under all examined scenarios the initial goal of WCPFC, rebuilding to SSBMED by 2024 with at least 60% probability, is reached and the risk of SSB falling below Bloss at least once in 10 years was very low.” If, however, we are facing an unstated goal with loftier ambitions, our fisheries may be asked to contribute more to the rebuilding efforts.
We also must consider the international aspect of this stock. While it would be easy to point the finger at the fisheries operating in the WPO, those fisheries have been very good at convincing the international fishery management organizations (IATTC and WCPFC) that restrictions need to be implemented wherever PBF are targeted and landed. It will be incumbent upon US representatives to those Commissions to keep the relative small impact US vessels have on the PBF stock in mind as they negotiate proposed management measures. California based commercial and recreational fishermen; and the coastal communities that benefit from and rely upon those fisheries, should not be used as pawns in a larger game.
 A total of 16 Fleets were defined for use in the 2016 stock assessment model based on country/gear/season/region stratification. Thee Fleets are: (1) Japanese longline; (2) Japanese small pelagic fish purse seine fishery in the East China Sea; (3) : Korean offshore large purse seine; (4) Japanese tuna purse seine fishery in the Sea of Japan; (5) Japanese tuna purse seine fishery off the Pacific coast of Japan; (6) Japanese troll; (7) Japanese pole and line; (8 – 10) Japanese set-net fisheries; (11) Japanese other fisheries – mainly small-scale fisheries in the Tsugaru Strait; (12) Taiwanese longline fishery; (13) Eastern Pacific Ocean commercial purse seine of USA; (14) Eastern Pacific Ocean commercial purse seine of Mexico; (15) Eastern Pacific Ocean sports fishery; and (16) Japanese troll fishery for farming.
 If you really want an in-depth overview of the inputs to the 2016 Stock Assessment – see the ISC Pacific Bluefin Working Group’s document entitled, Input data of Pacific bluefin tuna fisheries for stock assessment model, Stock Synthesis 3; Update for 2016 assessment, accessible at http://isc.fra.go.jp/pdf/PBF/ISC16_PBF_1/ISC_16_PBFWG-1_03_Sakai.pdf
 See Page 8 of Executive Summary
 See Page 4 of IATTC Doc
 For 2015, US Commercial vessels landed a total of 96.1 mt and CA CPFVs are estimated to have landed 21,062 PBF.
 See Table 1 beginning on Page 15 of the Input data of Pacific bluefin tuna fisheries for stock assessment model, Stock Synthesis 3; Update for 2016 assessment at http://isc.fra.go.jp/pdf/PBF/ISC16_PBF_1/ISC_16_PBFWG-1_03_Sakai.pdf