Basking sharks (Cetorhinus maximus) are present in oceans all over the world. The eastern North Pacific subpopulation, however, appears to be isolated from other populations. And basking sharks in this area are still not being found in any significant numbers, despite decades of management by both Canada and the US fisheries agencies.
Recently the National Marine Fisheries Service designated the eastern North Pacific population of basking shark as a species of concern, reflecting the lack of recovery. Efforts to help this endangered species are hampered by lack of knowledge of its natural history and continued interest in basking sharks for the Asian shark fin soup market.
Present Protection for Endangered Basking Sharks Around the World
The US National Marine Fisheries Service ruling on Atlantic shark fisheries and UK wildlife legislation protect basking sharks in portions of the Atlantic. This vulnerable shark species is also protected in the Mediterranean and in New Zealand waters. The eastern North Pacific subpopulation is listed as Endangered on the IUCN Red List along with the Northeast Atlantic subpopulation.
Decline in Basking Sharks Linked to Heavy Fishing Pressure
Basking sharks on migration to Canada from central California were taken by both the US and Canadian fisheries as sources of fishmeal, shark liver oil and shark cartilage until the 1970s. Their large dorsal fins continue to make them a target for the shark fin soup fishery. Basking sharks are also particularly vulnerable to entanglement in salmon fishing gear. In Canada they were targeted for eradication to protect salmon fishing interests.
Natural Behaviors Increase Threats to Basking Sharks
Some basking shark natural behaviors likely add to the species vulnerability. The name basking shark comes from the species' tendency to rest on the surface. Like the whale shark, these plankton eating sharks are also surface feeders, increasing the time spent on the surface and making them doubly vulnerable targets for the shark fishing industry and increasing the risk of entanglement in fishing gear or being hit in boating accidents.
The failure to recover may also be linked to historically small numbers and highly social lifestyle. If there were never large numbers of basking sharks and most of those animals congregated in areas that were heavily fished, there may be few animals to restock those areas that were heavily fished in the past.
Lack of Knowledge of Basking Shark Life History Adds to the Problem
Compounding the issue for basking sharks is their slow reproductive rate and a lack of understanding of their natural history. These sharks appear to only give birth every 18 months to three years with litter size only one to six pups. Age of reproductive maturity is unknown. Habitat use by basking sharks is poorly understood at best and population structure data is also lacking. Because so little is known about population structure, it is unclear whether these sharks ever existed in large numbers or whether they merely congregated in certain areas at specific times giving the appearance of a larger population. The apparent lack of interaction between the eastern North Pacific basking sharks and other subpopulations is also a concern.
Efforts are underway to increase knowledge of basking shark natural history and population dynamics. The National Marine Fisheries Service, the Monterey Bay Aquarium Research Institute, the Pelagic Shark Research Foundation and several universities are involved in this work, but with only 300 – 500 eastern North Pacific basking sharks estimated to be left, it may be some time before this species recovers, despite special protections.
Dawn M. Smith - A vet nurse, Dawn has worked in wildlife rehabilitation and conservation around the world in addition to her veterinary hospital ...
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