The basking shark is not extinct. This species, the second-largest fish in the world, still roams the temperate oceans across the globe. However, their populations have been so drastically reduced that sightings are rare, leading many to believe they have vanished entirely. Their continued existence is a testament to their resilience, yet their future remains precarious.
Current Global Conservation Status
The International Union for Conservation of Nature (IUCN) Red List of Threatened Species classifies the basking shark, Cetorhinus maximus, as Endangered. This global designation signifies that the species faces a very high risk of extinction in the wild. Their population numbers are severely depleted across their range in both the northern and southern hemispheres.
The conservation status is even more concerning in specific regions, such as the Northeast Atlantic, where the population has also been assessed as Endangered. This regional variation reflects the fragmented nature of their remaining groups and the localized pressures they face. All current data indicates a dramatic decrease in overall numbers, though scientists lack a definitive global population count.
The Reason for Rarity and Misconception
The perception of the basking sharkâs rarity is rooted in their natural history and a legacy of intense human exploitation. For centuries, targeted fisheries pursued these sharks for their massive livers, which can account for up to 25% of their body weight. The liver oil was rich in squalene, a compound used for lighting, industrial lubricants, and cosmetics.
Commercial fisheries operated on a “boom and bust” cycle, decimating regional populations in the 20th century. Notably, in the Northeast Atlantic, the last fishery closed in 1995. It is estimated that nearly 100,000 basking sharks were harvested during this period. The species’ naturally slow recovery rate means they are still struggling to rebound from this historical exploitation.
Their behavior also contributes to the difficulty of consistent sightings. Basking sharks are highly migratory, moving between coastal surface waters in the summer and deeper, offshore areas during the winter months. Satellite tagging has shown they often descend to depths of 900 meters or more for long periods, making them functionally invisible to surface observers for much of the year.
Unique Basking Shark Biology and Behavior
The basking shark is a giant of the ocean, typically reaching lengths of 22 to 29 feet, with some individuals exceeding 40 feet. It is second in size only to the whale shark, yet it is entirely harmless to humans, feeding exclusively on tiny organisms. Their feeding mechanism is a unique form of passive filtration.
They are known as “ram feeders,” swimming slowly with their enormous mouths wide open to push water through their gill rakers. These specialized structures strain zooplankton, such as copepods, from the water column. A large shark can filter up to 2,000 tons of seawater per hour. This surface feeding behavior is what gives them their common name, as they appear to be basking in the sun.
Their reproductive biology limits their ability to recover from population collapse. Basking sharks are ovoviviparous, meaning the embryos develop inside the mother and are born live, but litters are small. Females reach sexual maturity late, possibly between 12 and 16 years of age, and their gestation period is thought to be extremely long. This combination of late maturity and low reproductive output means that every individual lost significantly hinders recovery.
Ongoing Threats and Protective Measures
Despite the end of most targeted commercial hunting, basking sharks continue to face threats that prevent their recovery. Accidental entanglement and bycatch in commercial fishing gear, such as trawls and gillnets, represent a major source of mortality. Their habit of feeding near the surface also makes them vulnerable to vessel strikes from large commercial ships and recreational boats.
Another threat is the ingestion of marine debris and microplastics, which they inadvertently filter out of the water along with their plankton food. Climate change is also impacting the distribution and timing of the zooplankton blooms they rely on, potentially disrupting their migratory and feeding patterns.
In response, several protective measures have been implemented globally and regionally. The basking shark is listed under Appendix II of the Convention on International Trade in Endangered Species (CITES). This listing regulates international trade of their parts to ensure it does not threaten the species’ survival. Targeting the species is illegal in the waters of many nations, including the United Kingdom and all European Union waters. Some areas, such as the Sea of the Hebrides in Scotland, have been designated as Marine Protected Areas (MPAs), offering a safe haven.