Marine experts working in the Gulf of Mexico report that the mass die-off of dolphins in the coast region has steadily declined five years since the Deepwater Horizon oil spill occurred in 2010.

Research biologist Jenny Litz from the National Marine Fisheries Service (NMFS) announced on Friday, Oct. 16, that the number of dolphin mortalities in the Gulf has dropped this year since reaching its peak between 2010 and 2014.

When the BP-owned Deepwater Horizon oil rig exploded in April of 2010, it killed 11 people working on the offshore platform and spilled around 4.9 million barrels' worth of unprocessed oil into the surrounding ocean before it was finally sealed five months later.

Despite the mishap, BP refuses to be held accountable for the die-off, asserting that the frequent deaths of marine animals in the area in the past were caused by the spread of bacterial diseases in the region.

In response to a report by the National Oceanic and Atmospheric Administration (NOAA), BP said it is important to consider that the mass die-offs of dolphins in the Gulf are not unusual.

The London-based company pointed out that while the Unusual Mortality Event (UME) overlapped in certain areas affected by the oil spill, there is no indication that it was caused related to the mishap.

NOAA scientists, however, disagree with BP's stance, stating that the population of dolphins in the region has been prone to such mass die-offs in the past, but it has never been occurred for as long as it did following the oil spill. They said the accident has affected a wide range of marine mammals, particularly their calves.

"No feasible alternatives remain that can reasonably explain the timing, location and nature of this increase in death," Stephanie Venn-Watson, NOAA scientist and one of the co-authors of the report, said.

Die-offs of Marine Animals in the Gulf

According to reports, the average number of animal deaths in the Gulf of Mexico typically reaches around 74 individual dolphins each year. This number, however, grew to about 248 marine mammals during the five-year span following the oil spill.

NMFS estimates state that there have already been 1,433 dolphins and whales killed in the aftermath of the 2010 oil spill. Out of this number, 1,246 (87 percent) of those affected happened to be bottlenose dolphins.

The adverse effects of the oil spill on the environment were far reaching, but populations of dolphins have proved to be especially sensitive to waters damaged by the accident.

The NOAA explained that many of the dolphin species in the Gulf are shallow-water or coastal-dwelling animals that appear to stay in specific areas of the waters, making it possible for the sea creatures not to abandon even a severely damaged habitat.

Marine experts believe that even though there has been progress, the reliance of dolphins on the Gulf as a habitat means that there is still much work to be done in order to make the waters safer.

 In May, the NOAA said that similar to what has been observed in the Exxon Valdez oil spill, the breakdown of oil products can affect the food chain, build up in the tissues of creatures, produce cascading effects on ecosystems as well as impact populations of wildlife for many years to come.

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