A shark washed ashore can be unsettling, sparking concern and mystery. While uncommon, various factors lead to shark strandings. Understanding these reasons sheds light on the complex lives of marine predators and their ecosystems.
Natural Biological Factors
Sharks can strand due to health issues. Illnesses, such as parasitic infections or bacterial diseases, can weaken a shark, impairing its ability to navigate or swim effectively. Brain inflammation, potentially caused by an infectious disease, has been observed in some stranded great white sharks.
Injuries from interactions with other marine life also contribute to strandings. Sharks might be wounded during encounters with larger predators, such as orcas, or from struggles with their prey. These injuries can leave a shark disoriented or too debilitated to return to deeper waters, making it susceptible to currents that push it ashore. Old age can also diminish a shark’s capabilities, leading to a decline in health and increased likelihood of stranding.
In rare instances, birthing complications for pregnant female sharks can result in stranding. Female sharks sometimes utilize shallow coastal waters as nursery grounds, and birthing difficulties could leave them vulnerable and unable to swim away from shore. These biological vulnerabilities highlight the challenges sharks face.
Environmental Conditions and Phenomena
External natural forces play a significant role in shark strandings. Severe weather events, including strong storms and hurricanes, can disorient sharks, pushing them into shallow waters from which they cannot escape. Such turbulent conditions can overwhelm even healthy sharks, trapping them as tides recede.
Extreme temperature changes in oceanic waters can also affect sharks, leading to cold stunning or heat stress. When water temperatures drop rapidly, sharks can become lethargic and disoriented, losing their ability to swim and regulate their bodies, making them vulnerable to being washed ashore. Conversely, unusually warm waters can also stress sharks, forcing them into less suitable areas.
Harmful algal blooms (HABs), often called “red tides,” are another environmental factor that can cause strandings. These blooms produce toxins that can affect a shark’s nervous system, leading to disorientation, neurological issues, and even death. Sharks can ingest these toxins directly or indirectly by consuming contaminated prey, causing them to become unable to swim. Unusual currents or tidal patterns can also trap sharks that have ventured close to shore, leaving them stranded as the water recedes.
Human-Induced Impacts
Human activities significantly contribute to shark strandings. Interactions with fisheries are a notable cause, including bycatch where sharks are accidentally caught in fishing gear. Even if released, the stress and injuries from entanglement can weaken a shark, making it unable to survive. Lost or discarded fishing gear, often called “ghost gear,” poses a long-term threat as it continues to entangle marine life indiscriminately.
Vessel strikes, where sharks are hit by boats, can cause severe internal and external injuries, leading to incapacitation or death. Evidence of such strikes is often difficult to obtain, but satellite tracking has revealed instances where whale shark transmissions end abruptly in busy shipping lanes, suggesting fatal collisions. The increasing size and number of commercial vessels heighten this risk, especially in areas where shipping lanes overlap with shark feeding grounds.
Pollution also impacts shark health and can lead to stranding. Ingestion of plastics, from microplastics to larger debris, can cause blockages in the digestive system, lead to a false sense of fullness, and result in malnutrition or starvation. Chemical contamination, including persistent organic pollutants and heavy metals, can bioaccumulate in sharks, causing illness and disorientation. Habitat degradation, such such as the destruction of coastal ecosystems, can force sharks into less suitable areas, increasing their vulnerability to stranding.
What to Do When You Encounter a Stranded Shark
Encountering a stranded shark requires a cautious approach for your safety and the animal’s welfare. Maintain a safe distance and never attempt to approach or handle the shark. Even a seemingly docile or injured shark can pose a threat, as wild animals may bite if they feel threatened, resulting in severe injury.
The immediate step is to contact local authorities or marine wildlife rescue organizations. In the United States, this often includes local animal control, the Coast Guard, or regional marine mammal stranding networks. A quick online search for “marine animal rescue” followed by your location can provide relevant contact information. These professionals are equipped to assess the situation and determine the appropriate course of action, which might involve relocation, medical treatment, or euthanasia.
When reporting, provide precise details about the shark’s location, such as the beach name, nearby landmarks, or GPS coordinates. Describe the shark’s estimated size, species if identifiable from a safe distance, and its apparent condition, noting any visible injuries or signs of distress. Observing tidal conditions can also be helpful for responders. This information assists experts in their response and contributes to scientific data collection on stranding events.