Current Season Management: Latest Stock Assessments
HMS stock assessments are conducted under the auspices of international organizations involved in HMS management. These organizations are the International Scientific Committee for Tuna and Tuna-like Species in the North Pacific Ocean (ISC), which coordinates assessment of selected North Pacific HMS, and provides these scientific recommendations to the Northern Committee of the WCPFC; the Oceanic Fisheries Program of the Secretariat of the Pacific Community, which conducts assessments of tropical Western Pacific for the Scientific Committee of the WCPFC; and staff at the Inter-American Tropical Tuna Commission (IATTC), who conduct assessments of HMS stocks in the Eastern Pacific Ocean. The information below is taken from the most recent HMS Stock Assessment and Fishery Evaluation document, and reflects assessments conducted through 2008. The following table shows the recent and projected assessment schedule for HMS.
| Species (Stock) | Date (Next Anticipated) | Organization Responsible for the Assessment |
|---|---|---|
| Tunas | ||
| Albacore (north Pacific ocean, NPO) | 2006 (2011) | ISC (ISC) |
| Albacore (southern Pacific ocean, SPO) | 2008 | WCPFC |
| Bluefin (NPO) | 2008 (2012) | ISC (ISC) |
| Bigeye (eastern Pacific ocean, EPO) | 2008 (2009) | IATTC (IATTC) |
| Bigeye (western and central Pacific ocean, WCPO) | 2008 (2009) | WCPFC (WCPFC) |
| Skipjack (EPO) | 2007 (2009) | IATTC (IATTC) |
| Skipjack (WCPO) | 2008 (2009) | WCPFC (WCPFC) |
| Yellowfin (EPO) | 2008 (2009) | IATTC (IATTC) |
| Yellowfin (WCPO) | 2007 (2009) | WCPFC (WCPFC) |
| Billfishes | ||
| Striped Marlin (EPO) | 2003 (2010) | IATTC (IATTC) |
| Striped Marlin (NPO) | 2007 (2011) | ISC (ISC) |
| Swordfish (southeast Pacific ocean, SEPO) | 2006 | IATTC |
| Swordfish (NPO) | 2004 (2009) | ISC (ISC) |
| Sharks | ||
| Common Thresher (WA/OR/CA EEZ) | 2001 | NMFS |
| Pelagic Thresher | ||
| Bigeye Thresher | ||
| Shortfin Mako | ||
| Blue (NPO) | 2001 (2008) | NMFS and NRIFSF Japan (NMFS and NRIFSF Japan) |
| Other | ||
| Dorado (EPO) | ||
Conclusions from 2008 Pacific HMS stock assessments
For an explanation of fishery terms such as MSY, please see our acronyms and definitions sheet.
Albacore (north Pacific Ocean)
Stock status of North Pacific albacore is reviewed by the ISC Albacore Working Group with participating members from the United States, Mexico, Canada, Japan, and Taiwan. The latest assessment was completed in December 2006 (ISC 2007a) and finalized by the ISC in July 2007. The assessment report can be downloaded from Here.
Spawning stock biomass (SSB) estimates for the period 1966-2006 show fluctuations around an estimated time series average of roughly 100,000 mt. The assessment demonstrates a recent increase in SSB from 73,500 mt in 2002 to 153,300 mt in 2006 with a projected further increase to 165,800 mt in 2007. The recent increases are likely due to strong year classes in 2001 and 2003. Despite the high SSB estimates relative to the time series average, fishing mortality rates are high relative to most commonly used reference points. The population is being fished at roughly F17% (i.e., at a rate resulting in a reduction of the spawning potential ratio to 17 percent of the maximum spawning potential ratio in the absence of fishing). If fishing continues at the current level, and all else being equal, then SSB is projected to decline to an equilibrium level of 92,000 mt by 2015. Considering the high fishing mortality rates, and the fact that total catch has been in decline since 2002, the ISC recommended that all nations practice precautionary-based fishing practices.
The next albacore stock assessment is scheduled for 2011.
Catch of albacore by U.S. West Coast fisheries constitutes roughly 17 percent of the North Pacific-wide catch.
Albacore (western and central Pacific Ocean)
An updated assessment of albcore tuna in the WCPO was conducted by the WCPFC €™s Scientific Committee in August, 2007 (Hoyle, et al. 2008). Below is a summary of the results excerpted from the Report of the Scientific Committee meeting. The assessment can be downloaded from Here.
The stock status is assessed used MULTIFAN-CL. Current (2004-2006) fishing mortality is estimated to be below FMSY and biomass above BMSY. The current assessment identified several sources of bias that contributed to unrealistic estimates of stock size in past assessments. Although these problems were dealt with in the current assessment, additional uncertainties and biases remain. Therefore results should be viewed as highly uncertain.
Bigeye Tuna (eastern Pacific Ocean)
Stock status of bigeye tuna in the Eastern Pacific is assessed every 1 €“2 years by the IATTC. An updated assessment was conducted in May 2008 (Aires-da-Silva and Maunder 2008) and is based on the assumption that there is a single stock of bigeye tuna in the eastern Pacific Ocean (EPO). The assessment report can be downloaded from Here.
The results of the base-case stock assessment, which assumes no stock-recruitment relationship, demonstrate a continuing trend seen in the previous assessments: the biomass of 3 quarter-plus age fish was at a peak level of 626,000 mt in 1986, and has been in decline to a recent and historic low level of 270,000 mt in 2007. The current spawning biomass ratio is roughly 17 percent which is below that corresponding to maximum sustained yield (MSY). Recent catches are estimated to have been at about the levels associated with MSY. Under current fishing mortality levels and patterns of age-specific selectivity, the level of fishing effort (F) corresponding to the MSY is about 82 percent of the current level of effort.
The floating object fishery that began in 1993 catches small fish below the critical size; however, the MSY of bigeye in the EPO could be maximized if the age-specific selectivity pattern of the fishery were similar to that for the longline fishery, which catches larger individuals. The two most recent estimates indicate that the bigeye spawning stock biomass in the EPO is below SAMSY and that overfishing is taking place (F > FAMSY).
Catch of bigeye tuna by U.S. West Coast fisheries constitutes less than one percent of the Eastern Pacific-wide catch.
Bigeye Tuna (Western and central Pacific Ocean)
An updated assessment of bigeye tuna in the WCPO was conducted by the WCPFC €™s Scientific Committee in August 2007 (Langley, et al. 2008). Below is a summary of the results excerpted from the Report of the Scientific Committee meeting. The assessment can be downloaded from Here.
The stock status is assessed using MULTIFAN-CL. The biomass under equilibrium condition is 0.68 of the biomass at MSY (BMSY), indicating that the current (2003-2006) fishing mortality is above FMSY. However, current total biomass is likely still above the BMSY and spawning biomass is estimated to be near or possibly below that corresponding to MSY (SBMSY). It is also noted that longline catchability (used as primary tuning index) may have increased or that the steepness of the spawner-recruit relation may be more moderate than used that in the base case. Both of these alternatives show that the current spawning biomass is less than SBMSY.
Skipjack Tuna (eastern Pacific Ocean)
Skipjack tuna is a notoriously difficult species to assess due to uncertainties about stock structure, the vulnerabilities of all age classes, and how well fishery catch-per-unit-effort (CPUE) data tracks abundance. Thus, beginning in 2007, the IATTC has developed a simple stock assessment model to evaluate indicators of skipjack biomass, recruitment, and exploitation rate and used simple indicators of stock status based on relative values of fishery data, such as, CPUE, average weight of fish caught, and effort (Maunder and Deriso 2007). The recent assessment report (Maunder 2008) can be downloaded from Here.
The analyses showed some inconsistencies. Indicators of biomass, recruitment, and CPUE for the unassociated purse seine fishery are near the healthy reference levels; whereas, indicators for effort, exploitation rate and average fish weight are near the unhealthy reference levels. Theoretically, average fish weight could be low due to either above average recruitment or high exploitation rates. The indicators have yet to detect any adverse consequences of relatively high exploitation rates. The results of the simple stock assessment model were similar to the 2004 assessment and there still appears to be no conservation concern for skipjack in the Eastern Pacific.
Catch of skipjack tuna by U.S. West Coast fisheries constitutes less than 1 percent of the Eastern Pacific-wide catch.
Skipjack Tuna (Western and central Pacific Ocean)
An updated assessment of bigeye tuna in the WCPO was conducted by the WCPFC €™s Scientific Committee (Langley and Hampton 2008). Below is a summary of the results excerpted from the Report of the Scientific Committee meeting. The assessment can be downloaded from Here.
Stock status is assessed used MULTIFAN-CL. The status of the skipjack stock appears to be in relatively good shape. Fishing mortality is currently below FMSY and biomass is above BMSY. Recruitment is hypothesized to be largely driven by environmental factors; unless the environment becomes unfavorable the stock is likely to remain at healthy levels.
Yellowfin Tuna (eastern Pacific Ocean)
Stock status of yellowfin tuna in the Eastern Pacific is assessed every year by the IATTC. An updated assessment was conducted in May 2008 (Maunder and Aires-da-Silva 2008) and is based on the assumption that there is a single stock of yellowfin tuna in the EPO, although it is likely that there is a continuous stock throughout the Pacific Ocean. Fishing is concentrated in the east and west, making separate consideration of the EPO stock relevant for management purposes. The assessment report can be downloaded from Here.
The 2008 base case assessment, which does not include a stock-recruitment relationship, indicates that the spawning stock size was in decline during 2002-2007 from a high point in 2001 to about the level corresponding to the average MSY (AMSY). The recent fishing mortality rate (F), defined as an average of F for 2004 €“05, is near to that corresponding AMSY. Recent catches are significantly below MSY.
In general, the recruitment of yellowfin tuna in the Eastern Pacific has experienced two, or possibly three recruitment regimes: a period of low recruitment during 1975-1982; a period of high recruitment during 1983-2001; and now a period of intermediate or low recruitment during 2000 €“06. Based on the latest assessment, under the recent lower productivity regime, the spawning biomass ratio at the start of 2008 is estimated to be above AMSY and effort levels below those which would support AMSY. However, spawning biomass ratio in the period of 2002-2007 was below the levels corresponding to MSY and the 2008 estimate should be treated with caution.
The assessment in 2009 will be conducted using Stock Synthesis, which is a departure from the ASCALA model currently used to assess stock status.
Catch of yellowfin tuna by U.S. West Coast fisheries constitutes less than 1 percent of the Eastern Pacific-wide catch.
Yellowfin Tuna (western and central Pacific Ocean)
An updated assessment of yellowfin tuna in the WCPO was conducted by the WCPFC €™s Scientific Committee in August 2007 (Langley, et al. 2007). Below is a summary of the results excerpted from the Report of the Scientific Committee meeting. The assessment can be downloaded from Here.
The 2007 stock assessment conclusions differ slightly from the 2006 assessment, particularly in relation to the ratio of the current estimate of fishing mortality compared with the fishing mortality at maximum sustainable yield (F/FMSY), with the threshold in the 2007 assessment being slightly more optimistic than that in the 2006 assessment. While the point estimate of F/FMSY remains slightly less than 1.0 (0.95), the probability distribution associated with the fishing mortality-based reference point indicates that there is almost an equal probability that the value of F/FMSY is less than or greater than the reference point. Therefore, the possibility of overfishing is still relatively high (47 percent). The reference points that predict the status of the stock under equilibrium conditions are B/BMSY (1.10) and SB/SBMSY (1.12), which indicate that the long-term average biomass would remain slightly above the level capable of producing MSY at 2002 ˆ’2005 average fishing mortality. Overall, current biomass exceeds the estimated biomass at MSY (B/BMSY >1.0) indicating that the yellowfin stock in the WCPO is not in an overfished state, although there is a small probability (6.2 percent) that it is in an overfished state. The change in the estimated MSY in 2007 from that in 2006 may reflect changes in the data structure, fishery designations and levels of uncertainty in the assessment, especially in estimating absolute values, and the change in the scenarios modeled between years.
The WCPO yellowfin tuna fishery can be considered to be fully exploited. Both the 2006 and 2007 assessments indicate that there is a high probability that overfishing is occurring (73 percent for the base case 2006 assessment and 47 percent for the base case 2007 assessment). In order to reduce the likelihood of overfishing, and if the WCPFC wishes to maintain average biomass at levels greater than 5 percent above BMSY, reductions in the fishing mortality rate would be required.
Stock projections for 2007 €“2011, which attempt to simulate the conservation and management measures already adopted by the WCPFC, indicate that the point estimate of B/BMSY remains above 1.0 throughout the projection period. However, the increasing uncertainty in future projections is likely to result in an increased probability of the biomass declining below BMSY by the end of the projection period.
Bluefin Tuna (northern Pacific Ocean)
Stock status of Pacific bluefin tuna is reviewed by the ISC Pacific Bluefin Tuna Working Group with participating members from the United States, Mexico, Canada, Japan, Korea and Taiwan. The latest assessment was completed in May 2008 (ISC 2008a) and reviewed by the ISC in July 2008. The report can be downloaded from Here.
Based upon the results presented in the assessment the ISC recommended that F not be increased above the most recent levels (average 2002-2004), although that level was estimated to be above FMSY. However, due to implausible parameter estimates from the 2008 stock assessment the ISC recommended that the working group revisit the assessment in 2009. An intercessional meeting of the bluefin working group is planned for December 2009 to review possible model mis-specification. New assessment results are planned for the 2009 ISC Plenary.
Striped Marlin (northern Pacific Ocean)
The status of a hypothesized stock of striped marlin spanning the North Pacific was conducted by the ISC Marlin Working Group in 2007 (ISC 2007b). The assessment report can be downloaded Here.
The stock structure of striped marlin in the Pacific Ocean is not well known. A special session of the ISC €™s Billfish Working Group will be convened in the fall of 2009 to address the uncertainty in stock structure.
The latest stock assessment was based on analyses completed using Stock Synthesis II in 2006. The status is difficult to determine due to a range of uncertainties in the fishery data as well as biological uncertainties. Nonetheless, the results of two models demonstrate that biomass has declined to levels that are 6 to 16 percent of their level in 1952. In addition, landings and indices of abundance have declined markedly, and recruitment has been steadily declining with no evidence that strong year-classes have or are about to enter the fishery. There appears to be inconsistency in the indices developed for the Western Pacific and the Eastern Pacific, and it was recommended that stock structure in the NPO be investigated. Although there are no agreed upon biological reference points, the ISC Plenary recognized that current levels of fishing effort across the North Pacific are not likely to be sustainable. It was further recommended that a committee be formed to determine ways to reduce F on striped marlin without adversely affecting target species, and until that work is completed, that fishing effort not be increased above current levels.
The next striped marlin stock assessment is scheduled for 2011.
Catch of striped marlin by U.S. West Coast fisheries constitutes about one percent of the Eastern Pacific-wide catch.
Swordfish (northern Pacific Ocean)
The status and stock structure of NPO swordfish is planned to be assessed by the ISC Billfish Working Group in February and May 2009, respectively, and will be finalized at the July ISC Plenary meeting.