Fish populations unaffected by Deepwater oil spill

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The Deepwater Horizon spill in the Gulf of Mexico may not be the environmental disaster it is made out to be, at least for fishes. This is the result of a study published by two American scientists in a recent issue of the online journal PLoS ONE.

The Deepwater Horizon explosion and subsequent spill over a three-month period released nearly 5 m barrels of crude oil into the Gulf of Mexico, causing extensive damage to marine and coastal ecosystems.

Joel Fodrie and Kenneth Heck used data obtained over a period of five years (2006–2010) to examine the impacts of the the Deepwater Horizon spill on the populations of coastal fishes in the northern Gulf of Mexico.

As much of the oil spilled was emulsified throughout the water column, the authors hypothesised that the juvenile cohort of May–September 2010 would be negatively affected by the oil spill (ie. a drop in the number of fishes born during this period was expected).

The authors obtained data from 853 trawls made in the seagrass meadows of the northern Gulf of Mexico (which lies within the area affected by the spill), collecting 167,740 fishes representing 86 species. They then analysed their data using statistical methods, comparing data from 2006–2009 as the undisturbed condition with data from 2010 as the disturbed condition.

Contrary to expectations, the authors did not find reductions in the abundance of juvenile fish following the spill, but found that 12 of the 20 most commonly-encountered species were in fact more abundant after the spill (there was no difference in abundance for the other eight species).

They also found no statistical difference in the composition of the juvenile fish communities in the affected area before and after the spill.

The authors hypothesised that the lack of a significant negative impact on the fish populations of the area could be due to the fact that most of the oil spilled remained in deeper waters.

The authors also found some signs that the difference in abundance for some species might be due in part to management actions enacted after the spill (chiefly fishery closures), although they encountered no statistically significant differences in the response of fished or unfished species to the spill or to fishery closures (implying that fishery closures did not have a large-scale impact on fish populations).

The authors cautioned that while their results provide reason for early optimism, attention should be given to possible chronic effects of oil exposure on fishes as well as delayed indirect effects cascading through the post-spill Gulf of Mexico.

For more information, see the paper: Fodrie FJ and KL Jr, Heck (2011) Response of coastal fishes to the Gulf of Mexico oil disaster. PLoS ONE 6, e21609. doi:10.1371/journal.pone.0021609

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