A number of studies are finding links to oil exposure as a factor in wildlife population health over time. Much of the recent research has focused on fish and benthic invertebrates but work continues on determining the role of the Deepwater Horizon incident in dolphin deaths in Barataria Bay, Louisiana and great northern diver populations that overwinter in the Gulf.
Exxon Valdez and Alaskan fish health
New information from studying fish after the Deepwater Horizon spill led to research on salmon and herring embryos and juvenile fish in Alaska. The results of that study suggest that the population crashes occurring in these species four years after the Exxon Valdez were possibly related to exposure of embryos to crude oil, in particular polycyclic aromatic hydrocarbons (PAHs).
The study animals looked normal externally but they grew and swam more slowly as a result of changes in the structural development of the heart. Small and slow swimming fish are more susceptible to predators. These more subtle effects on embryos and juvenile fish may explain the delayed population declines in the two species.
Norwegian study looks at dispersants and cod
Not all the news is negative. A Norwegian study found that the careful use of dispersants may reduce the risk of oil having an impact on cod spawning grounds. By combining models of where released oil travels with models of where cod eggs and larvae drift, then looking at PAH concentrations in the water column under various scenarios, they determined dispersants can moderately decrease the proportion of eggs and larvae exposed to lethal and sublethal PAH concentrations.
Despite this positive impact, the work also showed that the decision to use dispersants must be made in combination with information on timing and location of the spill and what other effects the oil and dispersant might have on the habitats and species found there.
The full study can be accessed on PubMed.
Great northern divers come of age after Deepwater Horizon
A population of great northern divers (known as common loons in the US) that spends summers in Minnesota, on the Canadian border is being monitored by the Department of Natural Resources for contaminant levels and reproductive success as they winter in the Gulf of Mexico. 200 Minnesota based birds died as a result of the spill. After the Deepwater Horizon incident, contaminants were detected in the blood and tissue samples of 30% of the birds returning to Minnesota. Eggs were also affected.
This year the young that hatched in 2008/2009 are entering the breeding population. Having been exposed to the spill as first and second year birds, this group is of special interest. In addition to monitoring their long-term survival, their reproductive success will be tracked over time to give a clearer picture of how oil exposure affects development.
More news on dolphin mortality in the wake of the Deepwater Horizon event
In the ongoing effort to understand what role the BP spill played in the ongoing Unusual Mortality Event (UME) in the Gulf of Mexico, scientists looked at 22 samples from dolphins stranded in Barataria Bay as compared to those from 106 animals found in areas not affected by the spill.
In that comparative study, the dolphins from Barataria had higher incidences of lung and adrenal gland damage than animals outside of the Deepwater Horizon footprint. While the overall UME began before the spill, scientists are beginning to separate out various groups of animals in different regions of the Gulf as post mortem findings differ between groups suggesting several separate causes for the UMEs.
The full paper can be found on PLoS One.
Delayed effects of oil compromise long-term fish survival. NOAA Northwest Fisheries Center News. Accessed online 20.9.15
Toxin Affecting Cod Breeding Not Increased by Oil Spill Dispersants. The Fish Site. Accessed online 20.9.15
DNR continues study of BP spill effects on Minn. loons. Northland News Center. Accessed online 20.9.15
BP oil spill contributed to dead dolphins scientists say, citing tissue samples. The Times Picayune. Accessed online 20.9.15