Scientists from the National Oceanic and Atmospheric Administration are investigating why bottlenose dolphins are stranding themselves at an unusually high rate in the Northern Gulf of Mexico this year
Excessive freshwater in the gulf from the Mississippi River flooding could be to blame.
More than 260 dolphins have stranded themselves across Louisiana, Mississippi, Alabama and the Florida panhandle since the beginning of February, which is approximately three-times higher than the historical average, NOAA said.
A Mississippi scientist said the spillway opening is at least partly to blame for 126 dolphin deaths across Mississippi's coastline, CBS News reports.
These strandings prompted the declaration of an unusual mortality event. or UME. Unusual mortality events are defined as "a stranding that is unexpected; involves a significant die-off of any marine mammal population; and demands immediate response."
Some report this is worse than the 2010 BP oil spill when 91 dead dolphins were found in Mississippi.
NOAA scientists said it is too early to determine any potential causes of the unusually high stranding rate this year, but they're investigating whether lingering effects from the 2010 Deepwater Horizon oil spill and salinity changes from high rivers and a Louisiana spillway opening contributed.
2019 bottlenose dolphin stranding locations by month along the northern Gulf of Mexico. Image via NOAA
NOAA reports that a number of the dolphins stranded from Louisiana to the Florida Panhandle had sores consistent with freshwater exposure, but those are common in the spring.
May 2019 went down as the wettest on record for Nebraska, Kansas and Missouri, and Oklahoma recorded its second wettest May ever, which sparked a lot of flooding especially for the Mississippi River. Flooding of the Mississippi River caused high levels of freshwater to be discharged into the Gulf of Mexico, which alters salinity levels in the ocean and affects marine life such as dolphins.
For dolphins, too much freshwater can result in eye disorders, skin lesions, abnormal blood chemistry, and in some cases death, according to NOAA. These health effects can occur over a period of days to weeks, and these conditions "can be exacerbated in dolphins with pre-existing conditions, such as injuries, infections, poor nutrition or immune suppression," NOAA said.
An investigative team is being assembled to coordinate with the Working Group on Marine Mammal Unusual Mortality Events to review the data collected and provide guidance for the investigation.
Comparison of 2019 monthly bottlenose dolphin strandings (orange) to the 17-year historical monthly average including previous UMEs (blue) and the historical monthly average excluding previous UMEs (green).
Many of the dolphins recovered are very decomposed, limiting the ability to collect samples to determine cause of illness or death.
The investigation will look at potential human factors, including the opening of spillways for flood-control purposes. For example, the Bonnet-Carre spillway, was open for 76 days between January and June, and like other spillways, it "will be investigated as a potential contributing factor to this UME," NOAA said.
Unfortunately it does not look like the worst is over yet, NOAA scientists predict that there will be a large area in the Gulf of Mexico, roughly the size of Massachusetts, of low to no oxygen that may kill fish and other marine life this summer.
The dead zone phenomenon happens every year, but NOAA scientists believe this year could be one of the largest ever, due to abnormally high levels of water being discharged from the Mississippi River system.
NOAA asks people not to push the animal back out to sea, because it may be sick or injured. If the animal is alive, keep keep its skin moist and cool by splashing water over its body. Use wet towels to help keep the skin moist and prevent sunburn; however, don't cover or obstruct the blowhole. It is also best to try to keep crowds away and noise levels down to avoid causing further stress to the animal.
Members of the public can assist investigators by immediately reporting any sightings of live dolphins in distress or stranded (floating or on the beach) by calling the 24/7 Southeast Marine Mammal Stranding Network at 877-WHALE HELP (877-942-5343).