Bigeye Tuna Severity of the Atlantic Population's Decline and its Causes

The Atlantic Ocean's bigeye tuna population has declined in abundance from a healthy level in 1961 (and even as recently as 1986) to an overfished condition by 2002. See figure below, left, showing catch per unit effort for the extensive Japanese longline fleet which targets bigeye and the U.S. longline fleet. However, the population has not yet reached a dangerously low level (which begins at 50% of the MSY level). Its overall abundance has declined by about 58%, and it is declining moderately rapidly. The cause is overfishing allowed by ICCAT by thousands of commercial vessels from many nations, but primarily those of the European Union (EU). They land vast numbers of tiny bigeye in violation of their pledge to abide by ICCAT agreements setting minimum size limits (3.2 kg or 6.4 lbs.) and quotas. Almost 80% of Spain's recent landings of bigeye tuna have been smaller than the minimum size limit. ICCAT has yet to find the courage needed to force compliance by its members which routinely ignore its binding recommendations - recommendations they agreed to comply with as members of ICCAT.

As depicted in the graph to the upper right, the percentage of catch that is composed of juveniles weighing less than ICCAT's minimum size has reached 60% of the total bigeye tuna landed by all 39 member states. They are targeted primarily by Spain using purse seines in the bigeye's primary nursery areas off west Africa (particularly off Ghana) and by the other EU members in their nursery areas off Italy. The purse seines are set around Fish Aggregation Devices (FADs) that attract vast numbers of juvenile bigeye but also large numbers of juvenile sailfish, blue marlin, wahoo, dolphin, swordfish, etc., which are shoveled overboard dead and dying. The graph to the right shows the decline in biomass of Atlantic bigeye tuna since 1980. Responsible fishery managers would never allow a population to remain below the Maximum Sustainable Yield level (indicated by the horizontal dashed line at 1.0). This model shows the anticipated population change under various future catch levels with 100,000 metric tons being the recommended total allowable catch.

Source:  Marlin magazine, Jan 2004

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Daily "Kill-o-Meter"

Longliners fish most heavily during the periods when the moon is brightest. So, this real-time image of the moon phase shows when the kill of swordfish is greatest and least. It also shows when the kill of blue marlin, white marlin, sailfish, sharks, tunas, sea turtles, marine mammals and a host of other marine life is also greatest - even though they are not even targeted. For more, see link above.

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