A female Great Hammerhead Shark, Sphyrna mokarran, has been found dead on a beach in Alabama. The Shark, which was found to be pregnant with 40 pups, was found floating in shallow water off Orange Beach, and pulled ashore by a group of members of the public on 20 April 2023. They informed Orange Beach Coastal Resources, who in turn contacted the Marine Fisheries Ecology Group at Mississippi State University. The Shark was taken to the university for a necropsy (the term 'autopsy' is reserved for Humans), although the cause of death could not immediately be determined. The Shark had not eaten for some time, but it is normal for female Hammerheads to fast while pregnant, so this is unlikely to have been the cause of death. Several of the Shark's organs have been sent for chemical testing. It is possible that the Shark could have been caught and then released by fishermen, only to die later of the shock, something which the species is known to be prone to.
The Shark was 4.3 m in length and was carrying 40 unborn pups, each about 40 cm in length. Given the current conservation status of the species, this represents a significant loss (although it is highly unlikely that all 40 babies would have survived till adulthood under any circumstances). The University of Mississippi intends to preserve the baby sharks for used in educational outreach programs.
Great Hammerhead Sharks are found throughout tropical and warm temperate areas of the Atlantic, Indian, and Pacific Oceans, although genetic studies have suggested that this global population is in fact made up of two genetically distinct species, one found only in the Atlantic and the other in the Indo-Pacific. Population data is available from the Northwest Atlantic, Gulf of Mexico, and Indian Ocean, and in all places the species has shown a dramatic population loss over the past three generations, for which reason it is classified as Critically Endangered under the terms of the International Union for the Conservation of Nature's Red List of Threatened Species.
The Northwest Atlantic population of Great Hammerhead Sharks is believed to have been overfished between 1983 and 1997, although there is uncertainty about how the population has fared since, with some studies suggesting that they have been spared overfishing since 2001, while others indicate that this has continued. Although the size of this population is uncertain, it is believed to have declined by at least 20% over the past three generations, a period estimated at 74.4 years for the Atlantic Ocean.
Another study, based upon data collected from long-line surveys off the coast of the US, has indicated that the population of Great Hammerhead Sharks has recovered somewhat in the Northwest Atlantic since 2005, and that this may even represent a slight increase in the population over a three generation time-span.
In the Indian Ocean, data collected by the Ocean Natal Shark’s Board's bather protection program between 1978 and 2003 suggests that the Great Hammerhead Shark population fell by an average of 6.5% per year over that time, which would equate to a 99.3% reduction over three generations (calculated as 71.1 years in the Indian Ocean).
Data on the Great Hammerhead Shark population, data gathered by the International Union for the Conservation of Nature from 20 separate fishing fleets operating in the area between 1998 and 2008 found a 61.7% decrease in the population over the ten year period, although this data was not considered reliable enough to extrapolate a three-generation trend.
In the Mediterranean, data on the Great Hammerhead as a separate species is not available, but overall data on Hammerhead Sharks, Shpyrna spp., indicates that the group has suffered a 99.99% decline in population since the early nineteenth century, effectively disappearing from this area.
In the North and West Central Pacific it was again impossible to extract information for Great Hammerheads as a species, but data collated by the International Union for the Conservation of Nature suggests that the species is caught infrequently in these regions, probably indicating that it is present at only very low levels. Data is also limited from the coast of West Africa and tropical Indian Ocean, but fishing activity here is known to have increased significantly in recent decades, presumably applyinf pressure upon the species.
Based upon the data from the Northwest Atlantic, Gulf of Mexico, and southern Indian Ocean, the Great Hammerhead Shark population has undergone significant declines in population since the mid-twentieth century, although with some signs of a limited recovery in areas where properly run management schemes have been implemented. The Atlantic Population is believed to have undergone a decline of more than 50% over three generations, with a possible recovery in the Northwest Atlantic in recent years. In the Indo-Pacific region the Great Hammerhead Shark population appears to have declined by more than 80% over the last three generations, with no sign of a recovery anywhere in this range.
Based upon this data the International Union for the Conservation of Nature classifies the Great Hammerhead Shark as Critically Endangered.
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