Whales face threats from their natural environment and human activities. Studying whale mortality provides insights into ocean health and informs conservation efforts.
Natural Causes of Whale Mortality
Whales are subject to natural processes that contribute to their mortality. Old age is a factor, as whales eventually succumb to the natural end of their lifespan, which can range from a few decades to over 200 years for bowhead whales. With age, susceptibility to disease increases.
Disease and illness are natural causes of death. Pathogens, parasites, and health conditions can weaken individuals. For instance, a study found that nearly half of St. Lawrence Estuary belugas that died between 2009 and 2012 were infected with Toxoplasma gondii, a parasite that could compromise their immune systems. Complications during birth can also be fatal for both mother and calf.
Predation is a natural element of the marine food web, with killer whales and sharks preying on vulnerable individuals, especially calves. Fluctuations in prey availability can impact whale health and survival, leading to starvation. Environmental shifts, such as changes in ocean currents, can alter prey distribution, forcing whales into less favorable areas.
Human-Induced Threats to Whales
Human activities exert preventable pressures on whale populations, leading to mortality. Ship strikes are a leading cause of death for large whales. These impacts result in blunt force trauma or propeller injuries, which can be fatal.
Entanglement in fishing gear is a major threat. Whales can become ensnared in active fishing lines or ghost gear, leading to exhaustion, starvation, physical trauma, and infection. This entanglement can impede a whale’s ability to feed, travel, or surface to breathe.
Pollution affects whales through chemical contamination, plastic ingestion, and noise disruption. Chemical pollutants, such as persistent organic pollutants (POPs), accumulate in whale blubber through the food chain, causing immune system suppression, reproductive issues, and hormonal imbalances. Whales can ingest large plastic debris, leading to blockages, internal injuries, or starvation.
Noise pollution from human activities, including shipping, seismic surveys, and military sonar, impacts whales that rely on sound. Loud underwater noises can cause stress, disrupt behavior, mask natural sounds, and lead to hearing damage. Climate change presents indirect threats by altering ocean temperatures, increasing acidification, and shifting prey distributions, which can stress whales and force them into unfamiliar habitats. Commercial whaling historically reduced many whale populations, and while largely regulated, illegal hunting still poses a threat.
Whale Strandings: A Complex Phenomenon
Whale strandings are complex events with multiple contributing factors. Strandings can be categorized as single, or mass strandings, where multiple animals come ashore together.
Natural factors contribute to strandings, including disease, injury, or weakness due to old age. Disorientation can occur from geomagnetic anomalies, affecting navigation. Navigational errors can arise from chasing prey too close to shore or from ineffective echolocation systems. Strong social bonds among toothed whales can lead to “follow-me” strandings.
Human-related factors contribute to strandings. Underwater noise has been linked to mass strandings of deep-diving whales, causing disorientation, tissue damage, or rapid ascents. Habitat degradation, entanglement in fishing gear, and pollution can weaken whales or impair their navigation, making them more susceptible. Once stranded, whales often die from dehydration, organ failure, overheating, or drowning.
Investigating and Mitigating Whale Deaths
Investigating whale deaths helps understand threats and develop conservation strategies. When a deceased whale is found, scientists conduct necropsies to ascertain the cause of death. This forensic analysis involves examining internal organs and tissues for signs of disease, trauma, or exposure to pollutants. Necropsies help identify patterns, such as the prevalence of ship strikes or entanglement injuries.
Monitoring and data collection track whale populations and mortality events. Researchers collect information on stranded or deceased whales, contributing to databases that highlight trends in mortality causes and geographic hotspots. This systematic approach allows scientists to assess the health of whale populations and the impacts of various stressors.
Conservation and mitigation strategies are implemented globally to reduce human-induced threats. To prevent ship strikes, measures include vessel speed restrictions in whale habitats and rerouting shipping lanes away from high-traffic whale areas. Developing whale-safe fishing gear aims to reduce entanglements.
Regulations on ocean noise minimize acoustic disturbances from shipping, military sonar, and industrial activities. This includes establishing acoustic buffer zones and utilizing quieter technologies. International cooperation establishes marine protected areas that safeguard whale habitats and controls transboundary pollution. Rescue and rehabilitation efforts for live stranded or entangled whales involve trained teams providing specialized assistance.