Threats to Marine Animals
Marine animals can become distressed or die from natural causes, but they can also die due to human activities. The work of regional response networks contribute to documenting and understanding the threats to marine animals from human activity that can help prevent and mitigate future emergencies.
Entanglement is a major source of mortality for whales, pinnipeds and sea turtles. Fishing gear entanglements are the leading cause of entanglements for whales. An entangled whale can suffer by dragging fishing gear for extended periods, as is the case with sea turtles as well. Pinnipeds, such as seals and sea lions, are often entangled in marine debris or fishing gear. While some animals are able to disentangle themselves, others, sadly, die as a result of entanglement. They can also be injured, starve due to the inability to hunt their prey or open their mouths, or drown due to heavy or anchored gear. Remember these animals all breathe air.
Entanglements can occur from several different sources. Fishing gear, including longlines, drift nets, traps, pots or gillnets are commonly found as the culprit of whale entanglements. There are currently no fishery regulations to protect these animals from entanglements in Canada, although fishermen do their best to take measures that will reduce the risk. Sea turtles can also be found entangled by fishing rope wrapped around their flippers or necks, while seals and sea lions often have line or plastic packing straps (used for shipping boxes) entangled around their necks. Entanglement in fishing gear, although unintentional, can cause distress or death to marine animals, as well as hardship to fishermen through the loss of their gear.
Whales make sounds to find each other in the immense ocean, while some also use acoustics to navigate and find food. Pinnipeds, such as seals and sea lions, also use sound for communication in their marine environment. These animals rely on a quiet ocean acoustic space to use sound effectively to communicate or capture their prey. Unfortunately, many marine industries produce large amounts of noise, some within the same frequency bands as whales. For example, seismic oil and gas exploration uses large amounts of low frequency acoustic energy to search for underground oil reserves, military use sonar to locate ships and submarines and the engines of large vessels produce loud low frequency noise. These sounds may damage animal hearing, reduce their communication space and disturb their natural behaviours.
Many species and populations of marine animals, such as whales and turtles, migrate among calving grounds in the tropics and subtropics, to feeding grounds in temperate and sub-arctic regions, where their preferred prey is abundant. Researchers know that the distribution and migration patterns depend on the location of their prey. Other cetaceans, pinnipeds and sharks’ habitat and movement is subject to food availability. As our climate warms and our polar ice caps melt, the ocean circulation patterns are expected to change. This could alter the location of the prey they so greatly rely on, and therefore impact the marine animals.
Ship strikes are a leading cause of known mortality for large whales, and all large whale species have been reported struck by ships. Many different industries operate large vessels that pose a risk to whales, including the shipping industry (did you know that 90 per cent of all our goods are transported by ship?), oil and gas (tanker transport), military, cruise ships, coast guard and recreational vessels.
The risk of ship strikes increase where whales and ships use the same areas. For example, if whales aggregate in shipping lanes, the chance of ship strikes increase. They may even be lethal if a ship’s speed is too high. Studies have shown that baleen whales do not avoid oncoming ships. They may even exhibit behavioural responses that increase their risk, like rising to the surface. Thankfully, some sensitive whale habitats have speed restrictions and rerouting measures in place to help reduce the risk.
Human pollution can impact the health of the marine environment, and negatively impact marine animals. Toxic substances include heavy metals, such as lead, mercury and cadmium, and more recently organic molecules, such as polycyclic aromatic hydrocarbon (PAHs) that is a by-product of burning coal or crude oil, dichlorodiphenyltrichloroethane (DDT) that used to be used widely as an insecticide between the 1940s and 1960s, polychlorinated biphenyl (PCBs) a chemical used in the electrical industry or as an ingredient that could be found in paint or adhesives, and insecticides and pesticides.
These toxins remain within the environment for long periods of time, and can even be found in the sediment and marine species too. Predators, like marine mammals that eat large prey, tend to have higher levels of these toxins because they store toxins from their prey within their body. Municipal sewage and wastewater from boats is also a source of pollution within the marine environment, which in large amounts can spread disease or harm cause marine life harm due to hypoxia, where not enough oxygen is available for the animal.