Current Threats to Marine Mammals By Tim Chin

Current Threats ◊ Pollution ◊ Overfishing ◊ Entanglement ◊ Other

Pollution ◊ Noise ◊ Oil ◊ Chemical ◊ Plastics and Debris ◊ The Plastic Sea

Noise Pollution ◊ Many cetaceans, such as certain whales and dolphins, rely on sound for communication and locating food. They are adversely affected by human-made noise. ◊ Noise pollution can come from a wide variety of sources, with some of those being ship traffic, seabed drilling, seismic surveys, sonars, oceanographical experiments, recreational activities, and underwater explosions.

Noise Pollution ◊ Low levels of noise pollution are enough to cause a change of behavior in whales and dolphins. They will generally try to escape from the source of the noise, which can result in them being forced out of their habitat. ◊ Higher levels of noise pollution, such as the sound of underwater explosions, can cause great discomfort and stress. It can even result in physical acoustic trauma in the form of tissue damage to the ears. ◊ Cetaceans affected by high intensity noise pollution, with sonars being an example, are likely to become stranded and die.

Oil Pollution ◊ Oil is another type of pollution that negatively impacts marine mammals. It is generally introduced into the environment through accidental spills. ◊ Oil is a compound that can destroy the insulating properties of a marine mammal’s skin.

Oil Pollution ◊ It is often the case that oil is unintentionally eaten during removal attempts. If ingested, the toxic oil can damage a marine mammal’s organs, which could result in death. ◊ If inhaled, which is usually done by whales and dolphins coming up for air, the oil can cause pneumonia. ◊ Many times it is overlooked, but oil pollution can destroy the habitats of marine mammals, forcing them to travel elsewhere or perish.

Chemical Pollution ◊ Chemical pollution is a type that can contaminate the whole of a marine food web. ◊ In a contaminated environment, as smaller fish eat plankton, and the larger fish eat the smaller fish, the toxins that exist will greatly accumulate in the bodies of large fish. ◊ Since marine mammals are at the top of their food chain, the high levels of chemical pollutants in their food will build up in their bodies, in areas such as fatty tissue and breast milk.

Chemical Pollution ◊ Marine mammals suffer from the increasing concentrations of heavy metals, PCBs, dioxins, DDT, and other persistent organic pollutants that are dumped or leaked into the ocean. ◊ Due to the bioaccumulation of chemical pollutants, marine mammals can suffer from a wide array of illnesses and disruptions to their normal body functions. Pesticides and industrial compounds usually have a negative impact on the endocrine, digestive, and nervous systems, which can lead to a decrease in health, growth and development issues, a weakened immune system, and diminished reproductive abilities. ◊ Chemical pollutants can also cause cancer.

Plastics and Debris ◊ Plastic and other debris in the ocean are a large threat to the wellbeing of marine mammals, especially due to the fact that they take a very long time to break down. ◊ Studies suggest that over 60% of the debris in the sea is plastic.

Plastics and Debris ◊ Plastic and other debris can easily trap and get tangled on various marine mammals. This can lead to numerous complications. ◊ Marine mammals sometimes mistake marine debris for food and accidentally ingest it. This can cause a blocking of the digestive tract, choking, internal injuries, and an accumulation of toxic compounds. All of these implications can be fatal.

The Plastic Sea ◊ Due to gyres, the circular currents in the ocean, it is common for plastic and other flotsam to build up in certain areas. ◊ In the Pacific Ocean, between California and Japan, there are two linked patches of garbage which are often referred to as a plastic soup. It is roughly twice the size of the continental US and is a threat to marine mammals. ◊ It is estimated that this plastic sea is the cause of death for over 100,000 marine mammals every year.

Overfishing ◊ What is Overfishing? ◊ Negative Impacts on Marine Mammals

What is Overfishing? ◊ Overfishing is the act of fishing a body of water so extensively that it depletes the supply of fish in an area. ◊ It occurs when the quantity of fish harvested exceeds the amount that can be re-supplied by growth and reproduction, which results in a population collapse of the target species.

Negative Impacts on Marine Mammals ◊ When fishing, commercial fisheries often compete for the resource of fish with their natural predators. This can make it more difficult for a population of marine mammals to obtain food. ◊ Overfishing can also cause an imbalance in an aquatic ecosystem by removing one of the links in the food chain. This in turn can result in the decline or displacement of marine mammals which depended on the harvested fish as a food source.

Entanglement ◊ What is Entanglement? ◊ Nets ◊ Debris

What is Entanglement? ◊ Entanglement is a large threat to marine mammals. It occurs when they are accidentally trapped in fishing nets, fishing lines, six-pack rings, or other snares. ◊ It is estimated that hundreds of thousands of marine mammals are entangled each year.

Nets ◊ Drift nets are one of the most threatening types of nets used by fisheries. ◊ They are essentially nets made of thin strands of nylon that are left to freely drift and catch everything in their path. ◊ They can sometimes be miles long and be left unattended for weeks. ◊ Drift nets typically catch a large amount of bycatch, or the non- target species that become tangled in the nets, such as whales, dolphins, and seals.

Nets ◊ Marine mammals that are trapped in these and other nets will often drown if they cannot escape. ◊ Those that do escape usually end up with scars or missing fins as a result of being cut by the thin nylon strands of the nets.

Debris ◊ Debris, such as plastic rings and fishing lines, mainly pose a threat to pinnipeds, or walruses and seals. ◊ These marine mammals often become trapped with debris around their necks or heads, which can restrict breathing, eating, and even swimming. Debris can also inflict physical wounds. At the very least, these negative impacts will debilitate their targets. ◊ Once snared, it is a very difficult, if not impossible task for a marine mammal to remove its bindings.

Other ◊ Collisions ◊ Climate Change

Collisions ◊ Ship traffic is another danger to marine mammals. ◊ Those that are hit by a boat will often die. ◊ However, marine mammals sometimes do survive boat collisions, but will usually end up with disfiguring wounds and scarring.

Collisions ◊ Ship strikes are not very uncommon. Many marine mammals have scar patterns that indicate multiple boat collisions. ◊ Right Whales are highly vulnerable to collisions, due to their slow surface-foraging nature.

Climate Change ◊ Due to global warming, marine mammals could lose valuable food sources and habitats. ◊ Populations of fish, which are preyed upon by marine mammals, are predicted to move into deeper and cooler water which is farther away from shore. This change is troubling to seals and other pinnipeds that require land in order to reproduce and sleep on. ◊ Migratory whales could also suffer, as they are dependent on finding certain resources at the ends of their migratory routes.

Conclusion ◊ Overall, there are many threats that oppose marine mammals, such as the numerous types of pollution, overfishing, entanglement, ship collisions, and climate change. ◊ However, these threats are not without hope of being remedied, as numerous laws, regulations, and organizations, such as the Marine Mammal Protection Act and the creation of aquatic reserves, are in place to ensure the safety and stability of the marine mammal populations.