The Effects of Maritime Oil Spills on Wildlife including Non-Avian Marine Life
The following information on the effects of oil on a variety of wildlife is provided as a guide only to contingency planners and responders. The review is by no means exhaustive but is provided on the basis of current literature, open research reports and opinions in the field. Some advice on the effects of oil on wildlife provided in the literature is contradictory and a balanced approach to the reporting of this differing viewpoint is presented. (ref. 1,2 & 3)
Oil Composition and Chemistry and the Effects on Wildlife
To evaluate the consequences of oil spills on wildlife it is important to understand the properties and chemistry of crude oils and petroleum products. Oil, depending upon its form and chemistry, causes a range of physiological and toxic effects.
For example, the low molecular weight aliphatics of oil can have anaesthetic properties and aromatic components such as benzine are known carcinogens and very toxic to humans and wildlife. Some polynuclear aromatics are also carcinogenic and toxic and, are concentrated in the food chain eg. in tissues of water filter feeding shell fish like mussels and oysters.(1)
Volatile components of oil can burn eyes, burn skin, irritate or damage sensitive membranes in the nose, eyes and mouth. Hydrocarbons can trigger pneumonia if it enters lungs. Benzine, toluene and other light hydrocarbons of oil and fuels if inhaled, are transferred rapidly to the bloodstream from the lungs and can damage red blood cells, suppress immune systems, strain the liver, spleen and kidneys and even interfere with the reproductive system of animals and humans.
In general, refined petroleum products tend to be more toxic to organisms but less persistent in the environment. Crude oils and heavy fuel oils like bunker fuels tend to be less toxic but are more persistent and more likely to have physical impacts on wildlife eg coating feather, fur and skin.
This compositional variation of oil also governs its behaviour, weathering and fate after being spilt in the marine environment. For example; volatility of hydrocarbons into the air from the oil, solubility of toxic components into seawater from the slick and dispersed oil, formation and stability of emulsions, rate of natural oil dispersion, persistence, adherence to surfaces ("stickiness") and physical state, and rate of natural biodegradation.
The chemistry of crude oils and refined petroleum products varies significantly. Each spilt oil or fuel will behave differently and it is difficult to predict accurately the impacts on wildlife. For example, some oils will become more "sticky" as they weather and have a greater tendency to adhere to surfaces such as animal skins, fur, hair or feathers. Some liquid oils will form solid waxes very quickly after only a few hours of weathering at sea, others will leave little residue and other oils may contain high levels of persistent hydrocarbons.
Ambient wind and water conditions can modify the impact of oil on wildlife. For example, on a warmer sea and in high winds, evaporation may remove the lighter aromatic compounds. As a result they do not dissolve into the water column and affect marine life and are incorporated into the food chain.
Effects of Oil on Sea Birds
Many oil spills have resulted in the death of a large number of sea birds, which very sensitive to both internal and external affects of crude oil and its refined products.
Sea birds have a high risk of contact to spilled oil due to the amount of time they spend on or near the surface of the sea and on oil affected foreshores. Sea birds may also come in contact with spilled oil while searching for food, since several species of fish are able to survive beneath floating oil. (4)
Oil-coated birds can suffer hypothermia, dehydration, drowning and starvation, and become easy prey.
Sea birds are affected by oil in several ways (ref. 1,2,3,5,10,11):
- Contact with crude oil or refined fuel oils. This causes feathers to collapse and matt and change the insulation properties of feathers and down.
- Matting of feathers. This can severely hamper the ability of birds to fly.
- A breakdown in the water proofing and thermal insulation provided by the feathers. This often causes hypothermia.
- Oiled feathers. This can cause the seabirds to lose buoyancy, sink and drown because of increased weight or lack of air trapped in the feathers.
- Body weight decreases quickly as the metabolism attempts to counteract low body temperature.
- Severe irritation of the skin.
- They ingest the oil in an attempt to preen themselves.
- Irritation or ulceration of the eyes, skin, mouth, or nasal cavities
- The food searching instincts such as diving and swimming are inhibited.
- Ingestion of oil via their prey if their food chain becomes contaminated.
- Poisoning or intoxication.
Ingestion of oil can be sub-lethal or acute and will depend to a large extent on the type of oil, its weathering stage and inherent toxicity.
These internal effects can include:
- the destruction of red blood cells, important for the immune response,
- alterations of liver metabolism,
- adrenal tissue damage,
- intestinal damage,
- reduced reproduction ability,
- reduction in the number of eggs laid,
- decreased fertility of eggs,
- decreased shell thickness and
- disruption of the normal breeding and incubating behaviours (6).
It has been estimated that as little as four microlitres of petroleum contaminating a fertile egg can cause the embryo to die (4).
Impact of Oil Spills on Marine Mammals
Mammals are a special group of vertebrates, with a combination of characteristics that separate them from all other animals. (1,2,7,8,9)
- may breathe air through lungs,
- bear live young,
- produce milk for their young,
- are warm-blooded,
- can have smooth skins, hair or fur,
- have relatively large brains,
- have a variety of tooth sizes and shapes or sift food in the sea using baleen
- and are often protected by conservation laws.
There are five distinct zoological groups of mammals and their life cycles, patterns of habitat use and responses to oil are very different.
Within the large class of animals known as mammals is a small specialised group called marine mammals. These include sea otters, sea lions, seals, walruses, sea cows (dugongs), dolphins, porpoises and whales. They not only suckle their young, as do all mammals, but millions of years ago they adapted to life in the sea.
CETACEANS include all whales, dolphins, and porpoises.
There are two main types:
- Toothed whales (suborder odontoceti) include dolphins, porpoises, sperm whales, orcas or killer whales, and narwhals. These whales have from two to more than 50 teeth, and breathe through a single blowhole.
- Baleen whales (suborder mysticeti) include the blue, gray, humpback, and bowhead whales. Instead of teeth, baleen whales have plates of baleen arranged in a row along the upper jaw, which filter their food. Baleen whales breathe through a pair of blowholes.
SIRENIANS include two species of plant-eating marine mammals that inhabit tropical and subtropical waters. Dugongs (family Dugongidae) are found in the Indo-West Pacific, including Australia and China. Manatees (family Trichechidae) are found in the Caribbean, Florida, the Amazon and West Africa.
PINNIPEDS are flipper-footed marine mammals. This group includes Sea lions and fur seals (family Otariidae). True seals (family Phocidae) include harbour seals, elephant seals and Walruses (family Odobenidae).
Marine mammals are vulnerable to oil spills because of their amphibious habits and their dependence on air. Some marine mammals live and migrate in small groupings while others exist in large localised colonies. These feeding and behavioural differences mean that oil spills will have varying impacts, may be very seasonal and will affect a few individuals or large colonies.
The rough skin surface, body hair and grooming habits of some species increase the possibility of oil contact, ingestion and associated toxicological effects.
Contrary to some reports, most marine mammals do not necessarily avoid oil slicks or contaminated shorelines. Whales and seals have been seen swimming and feeding in or near oil, while others have been able to detect slicks and move away from harm.
Accurate data on the effects of oil on mammals is limited due to public and scientific concerns about unnecessary and inhumane controlled laboratory experiments on mammals. Data from actual spills therefore appears to provide the only source of physiological effects.
Effects of oil on marine mammals are dependent upon species but may include:
- hypothermia due to conductance changes in skin, resulting in metabolic shock,
- toxic effects and secondary organ dysfunction due to ingestion of oil,
- congested lungs,
- damaged airways,
- interstitial emphysema due to inhalation of oil droplets and vapour,
- gastrointestinal ulceration and haemorrhaging due to ingestion of oil during grooming and feeding,
- eye and skin lesions from continuous exposure to oil,
- decreased body mass due to restricted diet and
- stress due to oil exposure and behavioural changes.
The nature of the oil and how much it has weathered will also be an important factor in determining impacts on wildlife.
Individuals oiled early in a spill may be exposed to the more toxic components of the oil by direct contact and ingestion and suffer greater toxicity than those affected by a more weathered oil. The thermoregulatory problems for oiled wildlife would not change.
Effects of Oil on Cetaceans
There is little documented evidence of cetaceans (whales) being affected by oil spills. This is because of their reclusive and migratory behaviour. Some reports indicate there is a tendency for dead cetaceans to sink in the ocean. Other reports indicate dead whales eg Southern Right would float. The migratory nature of most whales and the movement away from an impacted area would also cause problems in cause/effect studies on oiled cetaceans.
During the Exxon Valdez oil spill observers reported the deaths of a number of killer whales as a result of oil exposure, and their numbers declined after the spill. However, some researchers argue this was purely coincidental.
Cetaceans have mostly smooth skins with limited areas of pelage (hair covered skin) or rough surfaces such as barnacled skin. Oil tends to adhere to rough surfaces, hair or calluses of animals, so contact with oil by whales may cause only minor oil adherence.
The way a cetacean consumes its food affects the likelihood of its ingesting oil. Baleen whales, which skim the surface are more likely to ingest oil than "gulp feeders" or toothed whales.
Baleen whales are particularly vulnerable to oil while feeding, as oil may stick to the baleen while the whales "filter feed" near oil slicks. They plunge, take in huge quantities of water then filter out their feed of plankton and krill. Sticky, tar-like residues are particularly likely to foul the whales baleen plates.
Cetaceans such as humpbacked whales are pelagic (move freely in the oceans) and because of their migratory patterns may only be occasionally affected by oil spills.
It has been stated that pelagic species will avoid oil, mainly because of its noxious odours, but this has not been proven. The strong attraction to specific areas for breeding or feeding may override any tendency for cetaceans to avoid the noxious presence of oil. So weathered or tar-like oil residues can still present a problem by fouling baleen whales feeding systems.
Researchers have also indicated that inhalation of oil droplets, vapours and fumes is a distinct possibility if whales surface in slicks to breathe. Exposure to oil in this way could damage mucous membranes, damage airways or even cause death.
Dolphins are toothed whales which feed on fish and squid and spend much of their time in waters close to shore.
It has been found in some oil spill incidents that dolphins have detected oil and avoided it, but at other times have not done so and have been exposed to floating oil.
Dolphins are smooth-skinned, hairless mammals, so oil tends not to stick to their skin, but they can inhale oil and oil vapour. This is most likely to occur when they surface to breathe. This leads to damaging of the airways, lung ailments, mucous membrane damage or even death. A stressed or panicking dolphin would move faster, breathe more rapidly and therefore surface more frequently into oil and so increase exposure.
Dolphins eyesight may also be affected by oil. They might also consume oil-affected food or may even starve due to the lack of available food or an inability to find food.
Chronic ingestion of subtoxic quantities of oil may have subtle effects which would only become apparent through long-term monitoring. The transfer of petroleum hydrocarbons through the mothers milk to sucking young is another way oil affects dolphins.
It is also possible that oil pollution impairs dolphins immune system and causes secondary bacterial and fungal infections.
Sirenians are "Sea-Cows", a group of mammals including Dugongs, found in tropical waters of Australia. It is believed the largest surviving populations of dugongs live in the waters of the Great Barrier Reef and Torres Strait. In general they are found in coastal waters from Broome in Western Australia to Moreton Bay in Queensland.
Dugongs are fully herbivorous and feed on sea grass beds in shallow waters. Therefore their habitats are low energy inshore regions of coastline that support seagrasses.
The dugongs head is heavy and blunt, with the mouth on the underside of the head designed for grazing. They have smooth skins but coarse hairs around their mouths which serve as sensors as they search for edible sea grasses.
Dugongs have smooth skin surfaces and are less likely to suffer from skin adherence. Oil tends to stick to the pelage or rough areas of an animals skin. If surfacing in slicks with the head out to breathe, dugongs may foul these sensory hairs and also get oil in their eyes. This could cause inflammation and infections, and affecting their ability to feed and breed.
There has been little research on the effects of oil on the dugong, but it is thought they could suffer "lipid pneumonia" if they inhale oil droplets and oil vapour when they surface through oil slicks to breathe.
Dugongs may also suffer from long term chronic effects such as liver problems if they consume oil droplets or oil-affected sea grasses. Depending upon the amount and composition of the ingested oil, the effects could range from acute, to subtle, to progressive organ damage.
Aromatics and other low molecular weight hydrocarbons can be absorbed from the intestine and transported via the bloodstream to various target organs within the dugong.
PINNIPEDS are flipper-footed marine mammals. There are three groups of Pinnipeds:
1. Sea lions and fur seals (family Otariidae). They have external ear flaps and can "walk" on all four flippers. Their swimming power comes from their large front flippers.
2. True seals (family Phocidae) include harbour seals and elephant seals. True seals have no external ear flaps and must crawl on land somewhat like inchworms. Their front flippers are small and their swimming power comes from their rear flippers.
3. Walruses (family Odobenidae) have no external ear flaps and walk when on land. The upper canines of both the male and female grow into long tusks. Walruses inhabit the Artic seas and are not found in Australian waters.
The Australian Sea Lion (Neophoca cinerea) is the only true Australian endemic pinniped.
Seals and sea lions inhabit rocky shores and are efficient swimmers. They prey on fish they catch underwater and come ashore to rest and breed.
Seals are very vulnerable to oil pollution because they have to spend much of their time on or near the surface of the water. They need to surface every few minutes to breathe, and regularly haul out on to beaches. During the course of an oil pollution incident they are at risk both when surfacing and when hauling out.
It has been stated that pinnipeds will avoid oil. However, seals, sea lions and fur seals have been seen swimming in oil slicks during a number of documented spills (3). Pinnipeds will stay near established colonies and haul out areas. Oil also tends to collect in natural inlets on foreshores used by seals as haul out points.
Fur seals are more vulnerable due to the likelihood of oil adhering to fur. Heavy oil coating and tar deposits on fur seals may result in reduced swimming ability and lack of mobility out of the water.
Most pinnipeds scratch themselves vigorously with their flippers but do not lick or groom themselves so are less likely to ingest oil from skin surfaces. However, a pinniped mother trying to clean an oiled pup and may ingest oil.
During oil spill incidents, some seal pups have been seen to be so encased in oil that their flippers have been stuck to their bodies. This can lead to drowning or increased predation. Sand and other detritus may adhere to the oil and tarry residues. This increases body weight and density and leads to buoyancy problems.
The risk of oiling increases for pinniped pups. They spend much of their time in rocky shore areas and tidal pools, compared to adults who swim in open water.
Recent evidence suggests that pinniped pups are very vulnerable during oil spills because the mother/pup bond is affected by the odour. Pinnipeds use smells to identify their young. If the mother cannot identify its pup by smell in the large colony it may not feed it or it might even reject attempts by the pup to suckle. This leads to starvation and abandonment.
The ingestion of oiled food or the inhalation of oil droplets is also a possibility. Oil, especially light oils, will attack exposed sensitive tissues. These include mucous membranes that surround the eyes and line the oral cavity, respiratory surfaces, anal and urogenital orifices. This can cause corneal abrasions, conjunctivitis and ulcers. Consumption of oil-contaminated prey will lead to the accumulation of hydrocarbons in tissues and organs.
Pinnipeds with thick layers of blubber and low-conductance skin do not suffer from hypothermia like fur-covered animals. But pups of some pinnipeds are furry (they have woolly fur called lanugo) and may be vulnerable to hypothermia if oiled.
Sea turtles are of particular concern because their numbers are declining worldwide. Little information is available on the effects of oil on sea turtles but the following effects are likely.
If turtles surface in an oil slick to breathe oil will affect their eyes and damage airways or lungs.
Sea turtles will also be affected by oil through contamination of the food supply or by absorption through the skin.
Turtles are very vulnerable at beach nesting sites during the breeding season.
Nesting sites are typically on sandy beaches, which, if oiled, can lead to the following problems:
- Digestion/absorption of oil through food contamination or direct physical contact, leading to damage to the digestive tract and other organs.
- Irritation of mucous membranes (such as those in the nose, throat and eyes) leading to inflammation and infection.
- Eggs may be contaminated, either because there is oil in the sand high up on the beach at the nesting site, or because the adult turtles are oiled as they make their way across the oiled beach to the nesting site. Oiling of eggs may inhibit their development.
- Newly hatched turtles, after emerging from the nests, make their way over the beach to the water and may become oiled.
There are many fish species in Australian waters, of varying species have physiology and feeding behaviour. They also have varying habitats - the open sea, shores, coral reefs or in estuaries or mangroves. Some live close to the surface and some on the bottom of the sea. Therefore only general observations can be made on the impact of oil on fish.
The eggs, larvae and young fish are comparatively sensitive to oil (particularly dispersed oil), as demonstrated in laboratory toxicity tests. But there is no definite evidence from case histories to suggest that oil pollution has significant effects on fish populations in the open sea. This is partly because fish may take avoiding action and partly because the oil-induced deaths of young fish are often of little significance compared with huge natural losses each year through natural predation and fishing.
Reports also suggest that some fish species do not avoid oil but are actually attracted to oil because it resembles "floating objects".
Fish have often been seen associated with floating objects on the sea surface. This could be a result of reduced light intensity under the object (slick shadow), some floating objects providing food eg. smaller fish, crustaceans and algae, shade also making prey less visible to predators, objects providing shelter from diving birds, objects damping wave action so less energy is used swimming, objects providing an orientation point, or point of reference in an optically homogeneous sea.
This association of some fish with floating objects such as slicks could cause problems for seabirds, such as cormorants, attracted by schools of fish under oil slicks.
There are increased risks to some species and life stages of fish (and crustaceans such as prawns) in shallow nearshore waters such as estuaries, coral reefs, seagrass and mangrove habitats. These foreshores are believed to function as essential feeding and "nursery" breeding grounds for many fish and crustaceans.
This results in the tainting of fish, and in some cases loss of sales because clean fish are presumed to be tainted if they come from a spill area. The worst tainting problems may arise with fish, crustaceans, molluscs and algae in aquaculture facilities such as fish cages and, in the case of shellfish, in intertidal beds. Oil on the water may affect the supply to aquaculture ponds.
It is also common for fishing to be banned for a short time in the region of an oil spill, in order to maintain market confidence and protect fishing gear.
In regard to assessing the contamination of fish by oil, the water soluble fraction (WSF) of the oil is the most important toxic component. This WSF chemistry and toxicity will vary from oil to oil and, for example, may only be a minor proportion of the total weight. But in the case of oils such benzine, toluene and xylenes, this is often the most toxic fraction.
Sea birds appear to be the most frequent victims of maritime oil spills but mammals such as seals, whales, dolphins and dugong and reptiles like sea turtles may also be impacted during spills.
There is no clear relationship between the amount of oil spilled in the marine environment and the likely impact on wildlife.
Important factors related to the impact of oil spills on wildlife are:
- the spread of the oil slick,
- the type of oil spilled, its movement and weathering characteristics
- the location of the spill,
- the area of estuary, sea and foreshore impacted by oil,
- the sensitivity of the regional environment, eg proximity to bird breeding colony,
- the number of different habitats impacted, such as rock shore, beach, mangrove, wetland,
- the timing of the incident (during seasonal breeding, bird migration),
- the nature, toxicity and persistence of the oil,
- and the variety of species at the spill location.
To plan and implement an effective oiled wildlife response it is vitally important to assess the scale of and likely impact on wildlife during a marine pollution incident, both from a marine and foreshore perspective. It is also important to respond to the number and type of species impacted or likely to be impacted by the oil spill rather than to the quantity of oil spilled.
The types and numbers of animals impacted by the oil will determine the resources required during a spill. But once wildlife have been impacted by an oil spill, those responding have a moral and legal obligation to provide timely and humane treatment and care for affected species.
Contingency arrangements for oiled wildlife are being developed at both the Commonwealth and State/Territory level under the National Plan to Combat Pollution of the Sea by Oil and Other Noxious and Hazardous Substances.
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- Geraci J.R and St.Aubins D.J. (1990) Sea Mammals and Oil. Confronting the Risks, Academic Press. ISBN-0-12-280600-X
- Kerley, G.I.H., Bowen, L. and Erasmus, T. (1987). Fish behaviour - a possible role in the oiling of seabirds. S. Afr. J. Wildl. Res. 17, 128-130.
- Walraven E. (1992). Rescue and Rehabilitation of Oiled Birds (Pub. Zoological Parks Board of NSW, Taronga Zoo Sydney)
- Leighton, F.A. (1995). The toxicity of petroleum oils to birds: an overview. In: Wildlife and Oil Spills. Frink, L., Ball-Weir, K. and Smith, C. (eds), Tri-State Bird Rescue and Research, Inc., Newark, Delaware.
- Baker, A N (1983) Whales and Dolphins of New Zealand and Australia: An Identification Guide, Victoria University Press, Wellington.
- Harrison, Sir R and Bryden, M M (eds) 1988, Whales, Dolphins and Porpoises. Golden Press Pty Ltd, Sydney.
- Leatherwood, S and Reeves R 1983, The Sierra Club Handbook of Whales and Dolphins, Sierra Club Books, San Francisco.
- IBRRC (1985) Rehabilitating Oiled Sea Birds - A field Manual by IBRRC Pub. API Publications # 4407, 1985.
- 11. Jessop R. et al (1993). Regime for Treating Sick and Injured Penguins (- Pub. Phillip Island Penguin Reserve.
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