By Matthew O. Berger
WASHINGTON, Jun 7, 2010 (IPS) - With their population at less than 20 percent of what it was four decades ago, bluefin tuna in the western Atlantic need a lot of things to go just right if they are going to survive as a population. Now, just as they are returning to the Gulf of Mexico to spawn, they are likely to find one of their key breeding grounds slicked-over with oil.
What effect the oil – or the dispersants used to break it up – will have on the survival of the western bluefin stocks is still an open question, but for a species many see as on a march toward extinction anything that makes life even a bit more difficult could be disastrous.
And there has been little to make life easier recently.
Biologically, bluefin are already unlucky. The fish – which can be as long as and faster than a sports car – only spawn once a year and only in certain locations. And this spawning only happens after eight to 10 years, during which time the fish grows from an egg into an adult fish averaging about 227 kilogrammes.
An effort to ban international trade in the endangered giants foundered in March when the parties to the Convention on International Trade in Endangered Species of Wild Fauna and Flora, or CITES, voted down the protections.
Pew Environment Group estimates there are only 41,000 bluefin in the whole western Atlantic. Now, those fish are returning to their natal Gulf waters to find them much different than how they left them last year.
"The spill has been going on during their peak spawning period in the only place the western population spawns, so in timing and location it's probably the worst place you could have it and during the worst time," said Lee Crocket, director of federal fisheries policy at Pew Environment.
"Now what exact impact that's going to have I don’t think we're going to know for probably a few years" when the fish being born now should be juveniles, he said. "If you don’t see fish of a certain age or you see a lot less fish of a certain age [it may be] because the spill damaged their eggs and larvae during that period."
A study released last Friday shows that the oil slick seeping out of the ruptured Deepwater Horizon well will cover key bluefin spawning waters north of that Gulf Loop current on the edge of the continental shelf.
Scientists from the Tag-A-Giant Foundation spent five years tagging and tracking bluefin and yellowfin tuna along the North American coast to determine where exactly in the gulf they breed. Their findings carry an ominous message that bluefin spawning may be directly impacted by the spill.
Bluefin release their eggs in the top 15 metres or so of water where they drift in the Gulf Loop current out to the ocean. This means eggs – as well as juvenile and adult fish – are exposed to oil and the dispersant chemicals that are now also in those upper layers of water.
The dispersants may be particularly troublesome since the eggs are mainly composed of oils, which, some studies have predicted, could be broken down by the oil-eroding dispersants.
A new era for bluefin in the Gulf?
But there is another, rosier finding in Friday's study, published in the online, peer-reviewed journal PLoS ONE. It shows that bluefin choose only specific locations in the gulf in which to spawn whereas yellowfin are dispersed throughout gulf waters. This means it should be entirely possible to protect the endangered bluefin from being accidentally caught by those fishing for yellowfin.
The catching of bluefin as bycatch has been a major problem in the gulf for decades. Fishing boats have been banned from targeting bluefin since 1982, but the miles-long longlines boats use to catch yellowfin can and do accidentally also hook bluefin – as well as marlins, sharks, birds, turtles and marine mammals.
Crockett says 300 to 500 bluefin get caught as bycatch in swordfish and yellowfin longlining each year and for those fish "there's almost a hundred percent mortality".
The visibility that the oil spill has brought to pelagic gulf species, though, may help a bit with getting action on preventing this deadly bycatch.
One of the things he is hoping is that the money that goes to compensate fishermen for lost productivity due to the oil contamination does not go to "just replicate what they've been doing, that this is an opportunity to maybe transition these fishermen into a different way of fishing for yellowfin tuna and swordfish".
He pointed to two ways in which this fishing could be done more sustainably. Alternative gear like green sticks, in which hooks are suspended on top of the water, and buoy gear, to which no more than two hooks are attached and retrieved by hand, offer methods of fishing that would target certain species much more directly and avoid most bluefin bycatch.
On the other side of the ocean, life is no easier for Atlantic bluefin.
After seeing their population drop by 82 percent over the last four decades due largely to overfishing, the western Atlantic bluefin population has more or less stabilised in the last decade, albeit at very low numbers, due to well- enforced quotas in the Gulf of Mexico and western Atlantic.
But the eastern Atlantic stock is still dropping at two to three times sustainable rates, according to the International Commission for the Conservation of Atlantic Tuna.
Those tuna spawn in the Mediterranean. Currently, the conservation groups Greenpeace and the Sea Shepherd Conservation Society are in the midst of facing off with those Mediterranean fishers. The groups have been trying to free tuna captured by boats' purse seine nets while the fish congregate to spawn.
Little can be done to free the eggs and tuna from the oil covering their Gulf of Mexico birthplaces, though, and whatever the impacts of that oil may be.