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Stranded whales and dolphins have high toxin levels in their bodies

Marine mammals such as whales and dolphins rely on their diet, which consists of fish, squid, octopus, crustaceans, and other marine animals, to obtain necessary nutrients and elements. This diet, however, also exposes them to hazardous heavy metals.

Human health implications 

Research has shown that dolphins and whales stranded along the Southeastern Coast of the U.S. have high toxin levels.

The importance of tracking these contaminants in stranded marine animals, which are key indicators of oceanic pollution and may have implications for human health, cannot be overstated.

Despite the critical nature of this issue, comprehensive data on how these toxins distribute within the bodies of these animals, particularly for less commonly encountered species, and how toxin levels vary with the animal’s sex, species, age, and other demographic details is lacking.

Studying toxins in stranded whales and dolphins

A study led by the Harbor Branch Oceanographic Institute at Florida Atlantic University, sought to investigate the presence, concentrations, and distribution of essential and non-essential trace elements, including heavy metals, in various tissues (blubber, kidney, liver, muscle, skin) and fecal samples from 90 stranded whales and dolphins in Georgia and Florida between 2007 and 2021.

This investigation analyzed 319 samples from nine species – including pygmy sperm whales, dwarf sperm whales, Gervais’ beaked whales, Risso’s dolphins, short-finned pilot whales, sperm whales, melon-headed whales, a Blainville’s beaked whale, and a false killer whale – for seven essential (cobalt, copper, iron, manganese, molybdenum, selenium, zinc) and five non-essential (arsenic, cadmium, lead, mercury, thallium) elements.

The species studied were of high and similar trophic levels, subsisting on a diet of cephalopods and fish.

Varying levels of contamination 

The experts found that Risso’s dolphins and short-finned pilot whales exhibited the highest median concentrations of mercury, cadmium, and lead. In contrast, dwarf sperm whales showed the lowest levels of these contaminants.

Significantly, adult pygmy and dwarf sperm whales stranded from 2019 to 2021 demonstrated increased concentrations of several heavy metals compared to those stranded from 2010 to 2018, indicating a growing exposure risk.

“When we separated phylogenetic groups into age classes and compared median concentrations of heavy metals in specific tissue types between adult specimens of species, we found some interesting trends,” said senior author Annie Page, an associate research professor and clinical veterinarian at FAU Harbor Branch.

Fecal samples, which are collected non-invasively, had the highest concentrations of many elements. Besides fecal samples, the liver or hepatic tissues contained the most iron, manganese, mercury, molybdenum, and selenium; kidneys or renal tissues had the highest cadmium levels; skin had the highest zinc levels; and the liver and kidneys primarily contained copper, arsenic, and lead.

The researchers found the lowest median concentrations of mercury and cadmium in liver, kidney, blubber, and muscle samples, with dwarf sperm whales having the lowest skin mercury concentration and the lowest liver lead concentration.

Heavy metal exposure

Mercury, a particularly toxic element in marine environments, can accumulate and magnify through the food web, with cetaceans ingesting mercury mainly through contaminated prey.

“Exposure to heavy metal contaminants can result in oxidative stress, which can impair protein function, damage DNA and disrupt membrane lipids,” Page explained. “Heavy metal exposure has been linked to degenerative heart disease, immunodeficiency and increased parasite infestations, among other disease risks.”

“Because tissue concentrations of heavy metal contaminants also vary based on an individual animal’s sex, age class, trophic level and location, among other factors, it is important to first establish baseline values and then continue to monitor cetacean populations for exposure to these toxicants,” Page concluded.

More about stranded whales and dolphins

As discussed above, the phenomenon of whales and dolphins stranding on beaches has captured global attention, sparking concern and mobilizing rescue efforts from communities around the world.

These majestic creatures, known for their intelligence and complex social structures, face numerous challenges in their natural habitats, with stranding events highlighting the urgent need for research, conservation, and intervention strategies.

Understanding the causes

Stranding, also known as beaching, occurs when whales or dolphins wash ashore and are unable to return to the water.

These incidents can involve individual animals or mass strandings, where dozens or even hundreds of animals beach themselves simultaneously. Researchers identify several potential causes behind these distressing events:

Environmental and health factors

Changes in the marine environment, such as extreme weather, shifting tides, and alterations in the ocean floor, can disorient marine mammals, leading to accidental strandings. Additionally, unhealthy water conditions, including pollution and harmful algal blooms, contribute to the distress of these animals.

Diseases and injuries can weaken whales and dolphins, making it difficult for them to swim and navigate effectively. Parasitic infections, malnutrition, and physical trauma are common health issues that may lead to stranding.

Human activities and responses

Human activities, including shipping, fishing, and naval exercises, significantly impact marine mammals. Noise pollution from ships and sonar disrupts the echolocation abilities of dolphins and whales, leading to disorientation and stranding. Fishing nets and gear also pose entanglement risks, which can result in injury or death.

When whales or dolphins strand, time is of the essence. Rescue operations require coordinated efforts from trained volunteers, wildlife experts, and local communities. The primary goals are to keep the animals comfortable, hydrated, and to attempt refloating them back to the sea when conditions allow.

Rescue teams and monitoring stranded whales and dolphins

Specialized rescue organizations and local authorities often lead these efforts, employing techniques and equipment designed to safely assist stranded animals.

Public involvement is crucial, with community members providing support through monitoring beaches, reporting strandings, and participating in rescue activities under expert guidance.

Scientists seize the opportunity to study stranded animals, collecting data that can shed light on the health of marine populations and the challenges they face. Autopsies of deceased animals offer valuable insights into causes of death and disease prevalence, informing conservation strategies.

Stranded whales and dolphins: The path forward

Addressing the root causes of strandings requires a multifaceted approach. Reducing pollution, regulating fishing practices, and minimizing noise pollution are critical steps toward safeguarding marine habitats.

Public education and awareness campaigns play a vital role in fostering a sense of stewardship for the ocean and its inhabitants.

Protecting marine mammals is a global challenge that demands international collaboration. Agreements and policies that promote marine conservation and regulate human activities at sea are essential for the well-being of whales, dolphins, and other marine life.

Local communities can contribute significantly to conservation efforts. Participating in beach clean-ups, supporting marine protected areas, and advocating for responsible practices can all help mitigate the factors leading to strandings.

In summary, the stranding of whales and dolphins is a complex issue that reflects broader environmental challenges. Through research, conservation efforts, and global cooperation, it is possible to reduce the frequency of these tragic events.

Each stranding is a reminder of our shared responsibility to protect marine life and the ecosystems that support it. By working together, we can ensure a healthier future for these magnificent creatures and the ocean they call home.

The study is published in the journal Heliyon.


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