A global study by an international team has found that several species of tunas and billfishes are threatened and in need of further protection.
The team’s analysis - published in a recent issue of Science magazine’s Policy Forum- is the first study of global tuna and billfish populations using the methods of the International Union for Conservation of Nature (IUCN).
The study - part of the broader Global Marine Species Assessment - addresses concerns that the methods currently used to evaluate the status of tuna and billfish stocks are insufficient to sustainably manage the multi-national fisheries for these highly prized and highly priced fish.
Stock assessments for tuna and billfish are typically based on catch data collected by Regional Fisheries Management Organizations, or RFMOs.
Standardising and sharing data among RFMOs has proven difficult, thus hindering efforts to understand the overall population status of tuna and billfish species, many of which are distributed globally.
In the current study, a review team of fisheries experts from the US, Barbados, Brazil, Canada, Chile, Peru, Spain, Switzerland, and Taiwan first compiled a global database of information from fisheries reports and scientific publications. They then analysed the data using IUCN Red List criteria. Their results showed that 7 of the 61 species studied (11%) were threatened (i.e., vulnerable, endangered, or critically endangered), 4 species (7%) were “near threatened,” and 39 species (64%) were of “least concern.” Eleven species (18%) lacked adequate data and were thus classified as “data deficient.”
The seven threatened species are southern bluefin tuna, Atlantic bluefin tuna, bigeye tuna, blue marlin, white marlin, and two species of Spanish mackerels. Professor John Graves of the Virginia Institute of Marine Science, one of the study’s authors, says two main factors contribute to these fishes’ troubled status: the tunas’ high dollar value leads to heavy fishing pressure, and all the species are slow to reach sexual maturity, prolonging any recovery from over-fishing.
The proportion of threatened tuna and billfish species is higher than that of most other groups of marine bony fishes, with values closer to those recorded for other valuable and slow-reproducing species such as sharks.
Professor Graves and his co-authors write that the quickest road to recovery for the most-depleted stocks - Southern and Atlantic bluefin tunas - is to ban harvesting of these fishes until their populations can rebuild to healthy levels. They recognise that this would cause economic hardship and increase the incentive for illegal fishing, and thus call for strong deterrents such as controlled international trade through a listing of these species on the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES).
The scientists note several examples where strict monitoring and compliance measures have led to successful recovery of tuna, mackerel, and billfish species.
