facts and myths about marine mammals and oil spills

FACTS AND MYTHS ABOUT MARINE MAMMALSAND OIL SPILLS

SEA ALARM FOUNDATION

When oil is spilled at sea, attention immediatelyfocuses on birds, which are often affected when oilis spilled where they are feeding, breeding or

migrating. Birds also are most likely to wash up on beachesand, thus, be easily seen. But what about marine mammals-seals, sea lions, sea otters, whales, dolphins, porpoises, polarbears and walrus? The good news is that some of theseanimals are minimally affected by contact with oil, and forothers preventive measures may help reduce the numbers ofanimals affected. Some facts and myths about how oil affectsthese fascinating sea creatures follow.

FACT:The true seals, sea lions and walrus are least affected bycontact with oil.

These animals have thick blubber layers and have short,dense fur, which they don’t groom and which they molt(shed) annually. The thick blubber layer means they don’tdevelop hypothermia when coated in oil and, since theydon’t groom, they ingest less oil. Also, with their short, densecoats it is less likely that oiling will inhibit their movement.These animals are at some risk if they are caught in areaswhere the volatilised oils are near the surface as they swimthrough. But they don’t spend much time at the surface, sothe risk is much less than other species. These animals willgenerally be a low priority for rescue and adults will often bedifficult to capture, should response be considered.

FACT:Young true seals, sea lions and walrus are at higher risk thanadults until they finish nursing and develop a blubber layer.

For the first few months of life, these pups have very littleblubber layer, putting them at risk of hypothermia. However,many of the true seal pups (common, ringed, spotted, ribbon,grey, elephant, harp, hooded, etc.,) do not go into the waterwhile they are nursing so protecting nursery beaches duringa spill may help significantly, provided it is possible to do sowithout too much disturbance to the nursery group.

FACT:Sea otters and polar bears are the marine mammals mostsignificantly impacted by oil.

Sea otters have almost no blubber, relying on their thick furcoat for insulation and they spend much of their time on thesurface of the water, where volatised fuels cause respiratorydamage. This species grooms nearly constantly, greatlyincreasing the amount of oil they ingest. During the ExxonValdez spill in 1989, over 1,000 oiled otter carcasses wererecovered and, of the 361 animals brought in for cleaning,only 197 survived. Most of the survivors were captured laterin the spill, when levels of volatiles were lower. The ExxonValdez was the first oil spill where rehabilitation wasattempted on large numbers of sea otters. Just as survivalrates for seabirds have gone up as cleaning and rehabilitationtechniques have advanced, future sea otter rehabilitationefforts are likely to be more successful.

Pre-emptive capture may be considered but this species oftendoes not do well in captivity. Hazing or other forms ofdeterrence might also be an option.

Polar bears not only suffer from the effects of the oil itself,they are also very sensitive to human disturbance during oilspill clean-up activities. Like sea otters, they are reliant ontheir fur for thermoregulation. Hair loss and skin damageresult from exposure to oil, putting them at risk ofhypothermia. Polar bears also seem to be particularlysensitive to oil they ingest while grooming. They may becomeanorexic, dehydrated and sometimes suffer renal failure,which may lead to death. Protecting denning sites and othercritical polar bear habitat, as well as developing effectivedeterrent methods are two options being explored forprotecting polar bears from oil.

Polar Bears, courtesy USFWS

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Spotted Seal, courtesy NOAA

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MYTH:Adult fur seals (northern, southern, South American,Australian, Guadalupe, etc.) have a blubber layer so they arenot at risk during an oil spill.

Unfortunately, the blubber layer on these species is muchthinner than that of the true seals, sea lions and walrus. Andtheir long, thick fur can hold a great deal of oil, which theywill ingest when they groom. Unfortunately, adult fur sealscan be difficult to capture and handle so there is limitedpossibility of being able to treat them. Prevention throughdeterrence may be the best option for them.

FACT:Pre-emptive capture has been successfully used to protectyoung fur seals from oiling.

Young fur seals are more easily handled than adults. In 1991,following the Sanko Harvest spill in the Archipelago of theRecherche a colony of young fur seals became oiled as thegently sloping beach they needed to use to get in and out ofthe water was affected. The fur seals were washed on siteand held in pens until the beach was safe to use. Taking thisa step further, during the Rena spill in 2011, some pups werepre-emptively captured and prevented from being oiled.

MYTH:Cetaceans (whales, dolphins and porpoises) avoid oil spills.

This myth grew from a couple of very limited studies ofcaptive animals. In the wild, whales, dolphins and porpoisesgenerally do not avoid oil. But measuring the impact of oil onthese species is difficult, as they spend most of their timeoffshore and underwater. There are some reports coming outof the Deepwater Horizon incident regarding the impact ofthe oil spill on marine mammals, including one survey whichreported 5 sperm whales (listed as vulnerable on the IUCNRed List of Threatened Species) of which, at least one wasconfirmed to be covered in oil sheen.

It has also been shown that Orca (killer whales) are unlikelyto detect and avoid oil. Whether there are species ofcetaceans who do avoid oil is not known. One promisingpreventive measure may work for some dolphins. In Cape CodBay, one of the three top ‘hot spots’ for mass strandings ofdolphins and whales, ‘pingers’, small noise making devicesoriginally designed to keep marine mammals out of fishfarms, have been successfully used to keep dolphins fromcoming ashore. The response does vary from species tospecies but it offers one more possible deterrent. Preventingthese animals from coming in contact with oil will always bethe best option.

FACT:Long term impacts of oil spills on cetaceans are now beingstudied.

In Alaska, some populations of Orca from the area of the1989 Exxon Valdez spill are still not reproducing at pre-spilllevels. Whether this is from actual contact with oil during thespill or whether they are being affected by contaminatedfood sources is not yet known. Understanding the reasonswhy some populations are recovering, but not others, willtake time and further research.

In the Gulf of Mexico, one year after the Deepwater Horizonspill, dolphins captured in a bay in Louisiana were found tobe underweight, anemic and some had lung and liver disease,along with low levels of hormones involved in stressresponse, metabolism and immune function. Longer termmonitoring of animals from this area may further ourunderstanding of how oil impacts cetaceans.

MYTH:All dead marine mammals found covered in oil were killed bythe spill.

In reality it can be very hard to determine whether the oilkilled these animals, particularly if they have been dead formore than a day or two, or whether the carcasses of alreadydead animals became covered in oil when drifting throughthe spill zone. Full post mortem examinations help to betterdetermine cause of death but only if the carcasses are fresh.Collecting carcasses during spill response is, therefore, animportant part of an accurate oiled wildlife impactassessment.

Walrus, courtesy NOAA

Sea Otters, courtesy Michael L. Baird, flickr.bairdphotos.com

Polar Bear Family, courtesy NOAA

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