[image-1]But other animals, from amphibians to mammals, have either already been collected by recovery teams or will be feeling the effects of the oil spill soon, and those effects may continue for quite some time. Nine visibly oiled and 338 “pending” dead sea turtles have been reported as of June 27; 92 oiled and 2 “pending” turtles have so far been found alive. Turtles can be affected by oil as they swim toward shore for nesting, and eggs can be damaged if an oiled adult lies on the nest.
Three oiled and five “pending” dead mammals have been reported as well — the Deepwater Horizon Response chart is unclear about what species of mammals have been found, but a separate report from the National Oceanic and Atmospheric Administration (NOAA) confirms that the deceased mammals included in the report are dolphins. Searches continue for more wildlife potentially harmed by the spill.
And those are just animals that touch the surface of the water. Absorbent booms may be helpful in sopping up oil on top of the water, but oil also can sink into deeper oceanic currents, especially if chemical dispersants are used. Dispersants cause oil to bead up into tiny droplets that can mix into water and disperse into deeper areas of water, where currents can theoretically dilute the oil and its environmental risks. While this is positive for surface-dwellers like birds and otters, as oil drifts downward and through currents, it falls on fish and underwater eggs and creates further damage to those lower ecosystems.
[image-2]Peter Hodson, a fish toxicologist at Queen’s University in Kingston, Ontario, has performed lab experiments with Corexit 9500, the “standard” oil dispersant, being exposed to Atlantic herring embryos. According to the study, the dispersant greatly increased the amount of hydrocarbons that could affect fish; plus, that extra dose of exposure made the oil significantly more toxic to the fish (measured as an elevated enzyme response in the fish’s livers).
In a telephone interview, Hodson explained how using chemical oil dispersants can create a more dangerous environment for fish and bottom-feeders.
“You see two kinds of toxicity. In the immediate aftermath of an oil spill, it contains elements that are very volatile, which can kill fish. Think of ‘dead bodies in the street.’ These volatiles act like narcotics… like an anesthetic. … Benzene, toluene, they usually evaporate quickly -- we cannot study that because it’s very short-lived.
“The more common toxicity is after those volatile materials have gone. The residual material sinks in the water and associates with spawning areas. In the case of the Exxon Valdez [1989 accident], it gets in the gravel… or might get associated with vegetation, which is the case with herring. The embryonic stages and stages just after hatching get exposed for a long period of time because the oil isn’t moving.”
This means that exposure to dispersed oil has a greater impact on the younger members of fish populations, damaging population numbers by limiting healthy birth and maturation. And while the majority of people see birds, turtles and dolphins washing up covered in oil, they don’t really get to see the destruction of the fish population.
Hodson could only guess at how long it could take a population to come back from a hit like this.
“With the Exxon Valdez, two species were badly affected — the Pacific herring and pink salmon. … Fish eggs developed in the presence of oil and caused a decline in numbers that survived. Fewer fish grew to maturity, and we saw a decline in pink salmon in streams that were affected. They came back after three to five years; because of so much wave action, oil tends to get washed out and diluted. But there was a noticeable impact.”
[image-3]The effects in the Gulf could vary greatly from this example, simply because the Gulf’s wave action may not allow for such a constant “dilution” in an impacted area.
Hodson expressed that his big concern was with bluefin tuna, as the Gulf of Mexico is a very important spawning ground for them, and they even have adult feeding grounds all the way up in Nova Scotia. This species is a “broadcast spawner” – meaning that eggs float freely in the water.
“Those eggs can … drift along with dispersed oil. … If you get a hit on those fish, you can get major problems.”
Those concerned can stay updated daily with fish and wildlife collection reports from the Deepwater Horizon Response website and with NOAA’s incident response documents.
