Whale Sharks Depend on Their Skin Microbes for Health and Conservation

Whale sharks are the largest fish in the world, reaching lengths of up to 18 meters and weights of up to 15 tons.

These gentle giants are filter feeders, sucking in large volumes of water and filtering out plankton, krill, fish eggs, and other small organisms.

They are also highly migratory, traveling thousands of kilometers across the oceans to find food and mates. But what factors affect their health and survival in a changing world?

Habitat loss and human threats

(Photo : EDIER ROSADO CHERREZ/AFP via Getty Images)

Whale sharks are endangered by habitat loss and human activities such as fishing and shipping. They depend on productive areas where plankton blooms occur, such as coral reefs, coastal waters, and oceanic islands.

However, these habitats are threatened by pollution, overfishing, climate change, and coastal development.

Whale sharks are also vulnerable to accidental entanglement in fishing nets and collisions with boats, which can cause serious injuries or death.

Furthermore, some whale sharks are targeted by illegal fisheries for their meat, fins, oil, and skin.

According to the International Union for Conservation of Nature (IUCN), whale sharks are classified as endangered, meaning that their population has declined by more than 50% in the past three generations.

The global population size and trend of whale sharks are unknown, but some regional studies have reported significant declines in recent decades.

For example, a study in the Indian Ocean found that whale shark sightings decreased by 79% between 1994 and 2014.

Another study in the Gulf of Mexico estimated that the population declined by 30% between 1999 and 2005.

To protect whale sharks from further decline, conservation efforts are needed at local, national, and international levels. Some of the measures that have been implemented or proposed include:

•  Establishing marine protected areas where whale sharks can feed and breed without disturbance.
•  Regulating fishing activities and enforcing bans on whale shark trade and consumption.
•  Educating fishermen and boat operators on how to avoid or minimize interactions with whale sharks.
•  Promoting ecotourism and research opportunities that benefit both whale sharks and local communities.
•  Monitoring whale shark movements and population trends using satellite tags, photo-identification, and genetic analysis.

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Microbial health and diversity

Whale sharks are not only affected by external factors, but also by internal factors such as their microbial health.

Microbes are microscopic organisms that live on or inside other organisms, performing various functions that affect their host's well-being. For example, microbes can help digest food, produce vitamins, fight infections, or cause diseases.

Whale sharks have a diverse and abundant community of microbes on their skin surface, called the epidermal microbiome.

This microbiome plays a crucial role in maintaining the skin's integrity and immunity against pathogens and parasites.

However, little is known about how the microbiome varies across different whale shark populations and habitats, and how it responds to environmental changes.

A recent study by scientists from around the world has shed some light on this topic.

The study sampled microbes from the skin surface of 74 whale sharks at five of the most famous diving sites around the world: Ningaloo Reef in Western Australia, Oslob in the Philippines, Mafia Island in Tanzania, La Paz, and Cancún in Mexico.

The study used cutting-edge genomic sequencing technology to identify the types of microbes on the whale shark skin surface.

The study found that while microbial species differ across the world, they work together to form a balanced network that contributes to the health of the sharks.

The study also revealed characteristics of what comprises a balanced or unbalanced microbiome. For example, a balanced microbiome has a high diversity of microbes that interact positively with each other and with the host.

An unbalanced microbiome has a low diversity of microbes that interact negatively with each other or with the host.

The study also discovered 34 new species of microbes that have never been described before. The whale sharks from Ningaloo had the highest number of novel microbial species, suggesting that there is still much to learn about the microbial diversity of marine animals.

The study concluded that measuring and analyzing the epidermal microbiome of whale sharks is important for understanding how microbes affect their health and survival.

It also suggested that microbial health could be used as an indicator of environmental health, as changes in the microbiome could reflect changes in water quality or temperature.

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