Bluefin Tuna Larvae Threatened by Gulf Oil Disaster [w/Video]

"At the same time as the Deepwater Horizon blew and started spewing oil into the water, bluefin tuna were releasing their eggs."

12-27-2010 // Jon Brett


Bluefin tuna are one of the world’s most amazing pelagic fish. Growing up to 13 feet, reaching a half ton, swimming at speeds of up to 50 miles per hour, and covering entire oceans in just weeks puts the bluefin in a category all its own.

Threatened by Overfishing

For decades, this grand species has been on the ropes due to the accepted practice of deadly efficient commercial fishing operations in the Mediterranean Sea that have the capacity to eliminate an entire school of bluefins in one fell swoop. While many conservational groups are eager to point there fingers at “greedy fisherman” the consumer demand is what truly dictates their plight.

This modernized commercial fishing practice is accomplished with the use of spotter planes, which locate the fish and transmit the precise coordinates to a fleet of million-dollar fishing boats equipped with miles of net.

According to Catherine Kilduff of Center for Biological Diversity, “Atlantic bluefin tuna have declined by more than 80 percent due to overfishing. Unfortunately, the sushi market keeps prices for tuna high — a single bluefin sold for $177,000 in 2010 — and encourages illegal and unreported fishing. A report this month by the International Consortium of Investigative Journalists valued the illegal trade between 1998 and 2007 at $4 billion.”

Bluefin Tuna Spawn and the Gulf Oil Disaster - A Case of Bad Timing

Bluefin tuna are considered to only spawn in two locations around the globe. One of these areas is the Mediterranean, and the other is the Gulf of Mexico. Regrettably, the timing of the Gulf oil disaster directly coincided with the bluefin tuna spawn, and created a tenuous and unclear situation for a species that has been on the decline for some time now.

Bruce Stein

According to Dr. Bruce Stein, NWF staff scientist, the timing of the disaster couldn’t have been worse.

“At the same time as the Deepwater Horizon blew and started spewing oil into the water, bluefin tuna were releasing their eggs. What the effect has been on their larvae is to be determined, but we can assume that many of the larvae were killed off after coming into contact with oil. What we still don’t know is the effect of losing much of this year’s recruitment of bluefin tuna will do to the long term survival of that magnificent species.”

While the Gulf oil disaster has brought about significant concern regarding what could happen to the adult population in the region, scientist’s principal fears are directed toward the impact on the young of the year, or the surviving byproduct of this years spawn. In fact, there is growing belief that the effect on this year’s class could severely undermine the future of this epic fish.

Research Team Studying Impact of Oil on Bluefin Tuna

Dr. Erik Hoffmayer, research associate at the University of Southern Mississippi’s Gulf Coast Research Lab, has been conducting a three-year project studying bluefin tuna larvae in the Gulf of Mexico. During a recent expedition in May, at the height of the Gulf oil disaster, his research team ran a number of transects around the Northern region of the Loop Current and collected more than 300 samples of bluefin tuna larvae. The samples are currently being analyzed for genetic variation, and findings should be available shortly.

“Some of the (juvenile bluefin tuna) samples were collected from areas with significant amounts of oil present,” said Dr. Hoffmayer. “These fish have certain genes which are turned on when they’re exposed to oil. We’re looking for the prevalence of those genes to see if they were exposed. Then, the next step would be to take a captive larval fish and expose it to oil and then see how many animals died, how many animals suffered from stunted growth, and reproductive issues. Those findings will give us a better understanding of what this exposure means.”

Dr. Mitchell Roffer, founder of Roffer's Ocean Fishing Forecasting Service, Inc. is a satellite fisheries oceanographic expert who helps fishing boats to locate fish. After the Deepwater Horizon rig exploded and began spewing its oil into the delicate Gulf, Dr. Roffer’s company began to provide its satellite imagery of projected distribution and movements of the oil, as well as oil-water mixture, in the Gulf. Opening his group’s data to research vessels was critical in directing them to locations where bluefin tuna were likely to occur.

“There were locations where we interacted with bluefin tuna larvae and the oil. The goal is to evaluate what percent of the habitat was influenced by the surface oil, as well as the oil water mixture," said Dr. Roffer.

Conservative estimates predict that the Gulf oil disaster killed around 10-20 percent of juvenile tuna in the area. According to Dr. Roffer, this year’s class of Atlantic juvenile bluefin tuna, along with the entire species, could be facing a monumental challenge.

“The real dilemma is that it may take years to fully understand the overall impact, and the general state of affairs for this vital fishery.”

When asked about the expected findings of the current bluefin tuna larvae research in the Gulf, Dr Roffer was not overly optimistic.

“I presume any larvae exposed to the oil are dead. Here’s a population that’s already overfished and the real possibility of losing a significant portion of this year’s recruitment is not favorable for the future of the species.”

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