BAYS TUNAS
The SCRS completed a stock assessment of Atlantic bigeye tuna in October 1999. The assessment utilized catch and effort information submitted by ICCAT member and non-member nations. This section provides a summary interpretation of the stock assessment results.
The 1999 SCRS report/stock assessment for bigeye tuna indicates (as have previous SCRS reports) that the catch of undersized fish remains a major problem in the Atlantic bigeye tuna fishery. The share of bigeye tuna less than the ICCAT minimum size (3.2 kg) is approximately 55 percent, by number, of all bigeye tuna harvested. This number has stabilized since with the time/area closure for purse seining in the eastern tropical Atlantic area (detailed in Section 4.2.3), but still remains a concern (SCRS 1999b)
1.1 Life History/Species Biology Information
Compared to other tuna and tuna-like species, less research has been conducted on bigeye tuna. The lack of reasonable estimates of some biological parameters considerably hinders the stock assessment process. The Bigeye Tuna Year Program, which calls for extensive research on bigeye tuna, was adopted in 1996 and began its operation in 1999 as funds became available. Additional information on the life history of Atlantic bigeye tuna can be found in the HMS FMP (Sections 2.2.1 and 6.3.1.2).
1.2 Most Recent Stock Assessment Data
ICCAT currently manages Atlantic bigeye tuna based on an Atlantic-wide single stock hypothesis. However, the possibility of other scenarios, including north and south stocks, does exist, and should not be disregarded (SCRS 1999b)
Table 1 Summary Table for Atlantic Bigeye Tuna
| Age/size at Maturity | Age 3/~100 cm curved fork length |
| Spawning Sites | Tropical waters |
| Current Relative Biomass Level* Minimum Stock Size Threshold | SSB98/SSBMSY = 0.57 - 0.63 0.6BMSY (age 2+) |
| Current Relative Fishing Mortality Rate* F1998/FMSY Maximum Fishing Mortality Threshold | F98/FMSY = 1.50 - 1.82 FMSY |
| Outlook | Overfished; overfishing is occurring |
| Management Measures in Place | Minimum sizes; time/area closures for fish aggregating device (FAD) fishing; limit on number of vessels > 24 m length overall (LOA) (not applicable to countries catching less than 2000 mt/year); catch and vessel limit for Chinese Taipei. No specific rebuilding program is in place. |
*B/BMSY and F/FMSY ranges are ranges of estimates from different model formulations rather than confidence intervals around an estimate
2.1 Life History/Species Biology Information
2.2 Most Recent Stock Assessment Data
Based on migration patterns, as well as other information (e.g., time-area size frequency distributions and locations of fishing ground), ICCAT currently manages Atlantic yellowfin tuna based on an Atlantic-wide single stock hypothesis.
Table 2 Summary Table for Atlantic Yellowfin Tuna
| Age/size at Maturity | Age 3/~110 cm curved fork length |
| Spawning Sites | Tropical waters |
| Current Relative Biomass Level Minimum Stock Size Threshold | unknown 0.5BMSY (age 2+) |
| Current Relative Fishing Mortality Rate F1997/FMSY Maximum Fishing Mortality Threshold | F97/FMSY = 0.97-1.35 FMSY |
| Outlook | Stock not overfished, overfishing may be occurring |
| Management Measures in Place | Minimum sizes; ICCAT recommendation for effective fishing effort not to exceed 1992 levels; recreational retention limit in the United States. |
3 NORTH ATLANTIC ALBACORE TUNA
The SCRS did not conduct a new stock assessment for Atlantic (northern, southern, or Mediterranean) albacore tuna in 1999. The latest stock assessment was conducted in 1998. The HMS FMP includes a summary of the status of the stock of northern Atlantic albacore tuna (Section 2.2.1). The next assessment for both North Atlantic and South Atlantic albacore tuna is scheduled for October 2000.
3.1 Life History/Species Biology Information
3.2 Most Recent Stock Assessment Data
On the basis of the available biological information, the existence of three stocks of albacore tuna is assumed for assessment and management purposes; northern and southern Atlantic stocks (separated at 5 N) and a Mediterranean stock. The United States primarily fishes on the north Atlantic stock/management unit, with very minor catches (~ 1 mt) of south Atlantic albacore.
Table 3 Summary Table for the North Atlantic Albacore Tuna
| Age/size at Maturity | Age 5/~90 cm curved fork length |
| Spawning Sites | Subtropical western waters of the Northern Hemisphere |
| Current Relative Biomass Level Minimum Stock Size Threshold | B97/BMSY = 0.47 (0.34 - 0.63) B90-94/B75-80 = 0.72 0.7BMSY |
| Current Relative Fishing Mortality Rate F1997/FMSY Maximum Fishing Mortality Threshold | F97/FMSY = 1.39 (uncertain) F97/FMAX = 0.91 F97/F0.1 = 1.60 FMSY |
| Outlook | Overfished; overfishing is occurring |
| Management Measures in Place | Limit number of vessels to average number 1993-1995 |
2.3.4.1 Life History/Species Biology Information
No new life history information is available regarding Atlantic skipjack tuna. Please refer to the HMS FMP (Sections 2.2.1 and 6.3.1.4) for more information on the life history of skipjack tuna.
2.3.4.2 Most Recent Stock Assessment Data
Table 4 Summary Table for West Atlantic Skipjack Tuna
| Age/size at Maturity | Age 1 to 2/~50 cm curved fork length |
| Spawning Sites | Opportunistically in tropical and subtropical waters |
| Current Relative Biomass Level Minimum Stock Size Threshold | unknown unknown |
| Current Relative Fishing Mortality Rate F1998/FMSY Maximum Fishing Mortality Threshold | unknown FMSY |
| Outlook | unknown |
Source :
2000 Stock Assessment and Fishery Evaluation for Atlantic Highly Migratory Species
U.S. Department of Commerce
National Oceanic and Atmospheric Administration
National Marine Fisheries Service
Office of Sustainable Fisheries
Highly Migratory Species Management Division
1315 East-West Highway
Silver Spring, MD 20910
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