Study Indicates Dolphin Harmed by Gulf Oil Spill

Rich DeNunzio with his 42-pound bull dolphin and the rod with the tie-wrapped spinning reel that he used to catch the fish. Photo courtesy of Steve Waters.

Rich DeNunzio with his 42-pound bull dolphin and the rod with the tie-wrapped spinning reel that he used to catch the fish. Photo courtesy of Steve Waters.

Four years after the Gulf oil spill, there is now evidence that dolphin were probably negatively affected.

A study by scientists at the University of Miami’s Rosenstiel School of Marine and Atmospheric Science showed up to a 37-percent decrease in overall swimming performance of Deepwater Horizonoil-exposed juvenile dolphin fish.

“What our study shows is that even a relatively brief, low-level exposure to oil harms the swimming capabilities of mahi-mahi, and likely other large pelagic fish, during the early life stages,” said Edward Mager, the lead author of the study. “If you harm a fish’s ability to swim you also harm its ability to perform actions that are critical for survival, such as catching prey and evading predation.”

Researchers conducted a laboratory experiment simulating the conditions during the 2010 spill and exposed dolphin larvae and juvenile dolphin to crude oil. The oil used was actually collected during the incident in July of 2010 from slicks on the surface of the Gulf of Mexico.

Two groups of dolphin were exposed to crude oil next to control fish exposed to clean seawater. One group was exposed for 48 hours during the embryonic-larval stage and then raised in clean seawater for about 25 days to the juvenile stage at the Rosenstiel School’s hatchery. The second group was raised in clean seawater to the juvenile stage and then exposed to oil for 24 hours.

The 48-hour embryonic-larval exposure group resulted in the 37-percent decrease in swimming velocity as juveniles. Juveniles exposed for the 24-hour period had a 22-percent decrease in swimming velocity.

“The study demonstrates how careful measurements of physiological performance may reveal subtle yet highly significant impacts of environmental contamination,” said Martin Grosell, a professor of ichthyology at Rosenstiel and a co-author of the study.

With a diminished capacity for catching food as well as for avoiding being caught by bigger fish, dolphin populations could decrease. The researchers suggested that a similar impairment in swimming performance may have occurred in other large, pelagic fish that live in the Gulf.

Dolphin were particularly susceptible to the ill effects of the oil spill because their fertilized eggs float near the surface of the northern Gulf of Mexico where the spill occurred and where juvenile dolphin are believed to remain during their early stages of development.

This study and others have shown that several fish embryos developed serious defects in heart development following exposure to crude oil. According to one study, “Losses of early life stages were likely for Gulf populations of tunas, amberjack, swordfish, billfish and other large predators that spawned in oiled surface habitats.”

The oil spill released more than 4 million barrels of crude oil into the surrounding waters over nearly two months, which coincided with the spawning season for many popular and economically important sportfish such as bluefin and yellowfin tunas, dolphin, kingfish and Spanish mackerel.

The study is available online at


Steve Waters has been the outdoors writer for the Sun Sentinel since August of 1990. He got his start in journalism in Charleston, S.C., where he was a sportswriter and covered sailing. In his spare time, he fished for striped bass on the famed Santee-Cooper lakes with one of the high school football coaches he knew and later bought a bass boat so he could fish there on his own. When his sports editor at his next paper, The Tuscaloosa News, found out he had a boat, he asked him if he wanted to cover the outdoors in addition to covering the Crimson Tide. It wasn't long before Waters realized that writing about fishing was way more fun than covering Alabama football. He went on to cover the outdoors for two more newspapers and a TV station, as well as sports ranging from golf and baseball to NASCAR and the NHL, before writing full-time about fishing, boating, sailing, diving, hunting, powerboat racing and environmental issues for the Sun Sentinel.

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