A new study published last month reveals how the 2010 BP Deepwater Horizon oil disaster likely caused life-threatening heart deformities and irregular function in the fish embryos of yellowfin tuna, bluefin tuna, amberjack and swordfish.

If you’re thinking that this sounds like another study we reported on last month, then you’re right. A number of different studies have been conducted on fish hearts, and each of them is an important piece of the puzzle that scientists are assembling to understand the impacts of the BP Deepwater Horizon oil disaster.

This latest study conducted by Dr. John Incardona and others clarifies how the oil from the BP oil disaster affects the embryos of large predatory fish living in the open ocean (or pelagic zone) of the Gulf of Mexico. Previous studies have determined that crude oil can be toxic or have delayed fatal effects on fish living in cold Arctic waters, such as pink salmon, or in warm freshwaters, such as zebrafish. We’ve also recently learned that Gulf killifish living in oiled areas of coastal Louisiana are suffering from deformed hearts and reduced chances of survival; another study helped us better understood the mechanism by which crude oil affects tuna hearts. Collectively, this research allowed scientists to make assumptions about how oil might affect fish living in the warm offshore waters of the Gulf.

These new findings draw a solid line between the crude oil released by the BP oil disaster and possible impacts to the pelagic fish spawning in the Gulf, meaning that the puzzle is coming together and fewer assumptions will need to be made about impacts. The implications for Gulf fish were summarized by the authors, who said that the “losses of early life stages were therefore likely for Gulf populations of tunas, amberjack, swordfish, billfish, and other large predators that spawned in oiled surface habitats.” Depending on how many fish eggs and larvae were killed or damaged as a result of oil exposure, a loss of these young life stages could translate to a reduction in the total population of impacted fish.

What I found most alarming in the study results was the low concentration of oil needed to cause irregular heart function. Using water quality data collected for the Natural Resources Damage Assessment, the authors estimated that 20 percent of the water samples collected in the pelagic spill area met this low threshold for oil contamination.

Other fish species such as king and Spanish mackerels, mahi mahi, sailfish, blue marlin and cobia were also spawning in the Gulf at the time of the BP oil disaster. All of these fish are crucially important to the Gulf ecosystem as top ocean predators and to the Gulf economy as valuable fisheries resources.

The total impact to the wild populations of tuna, amberjack and other large pelagic fish is yet to be determined, and is one of the reasons why it is critically important that we continue to research and monitor the impacts of the BP oil disaster throughout the ecosystem. We need more research to determine how experimental findings like those of Dr. John Incardona and others translate to the trends we are seeing in wild populations, and we need continued long-term monitoring to observe those trends and track how fish populations are changing.

The impacts of the BP oil disaster are still unfolding, and hundreds of studies are underway to determine the total impact. Ocean Conservancy continues to track this research, and we will continue to post updates on emerging impacts and trends.