Shovelbill shark (Sphyrna alleni), hammerhead shark (Sphyrnidae) from Caribbean and Southwest Atlantic

NEWS - Researchers have identified a new species of hammerhead shark as the shovelbill shark or Requin-marteau pelle or Tiburón Cabeza de Pala (Sphyrna alleni) collected at Robinson Point and Riversdale Village, Belize, and provided by local fishermen in 2016 and 2019. S. alleni is named after Paul G. Allen (1953-2018), a philanthropist who supported shark research and conservation.

Shovelbill shark is max 150 cm long when mature with a flat, shovel-shaped head that lacks a notch on the anterior margin, a pointed (triangular) cephalofoil in both sexes and a distinct protrusion in males. The posterior margin is lobulated.

The posterior teeth are enlarged, molar-like, the first dorsal tip is anterior to the pelvic origin and the posterior margin of the anus is shallowly concave. It differs from S. tiburo in that the anterior margin of the head is more rounded and the posterior margin lacks lobules. The number of precaudal vertebrae for S. alleni is between 80-83 (~10 more vertebrae than S. tiburo).

The distribution range is in coastal waters, estuaries, coral reefs, seagrass beds and sandy bottoms from Belize to Brazil. Its presence has been confirmed in the Caribbean in Belize, Panama, Colombia, Trinidad and Tobago and in the southwest Atlantic in Brazil.

S. alleni and S. tiburo are separated into two gene pools when examining 12 nuclear microsatellites with many private alleles observed. Visual inspection reveals a more pointed anterior margin of the cephalofoil in S. alleni which is consistent with geometric morphometric analysis and precaudal vertebrae count.

These species diverged between 3.61-5.62 million years ago which would be before the uplift of the Isthmus of Panama. It is possible that S. alleni and S. vespertina are sister lineages and S. tiburo diverged from them as it expanded into the subtropical and temperate regions of the Atlantic.

Phylogenetic reconstruction and head morphology also suggest S. tiburo is a species complex consisting of south central (Caribbean), northwestern (Gulf of Mexico, Florida, South and North Carolina) and eastern Pacific lineages.

Bonnetheads are currently rated as Globally ‘Endangered’ by the IUCN, but they have been assessed as an American amphibian species. The species is well managed in the higher latitudes of its Northern Hemisphere Atlantic range, but is heavily fished and poorly managed elsewhere.

Original research

Cindy Gonzalez, Bautisse Postaire, William Driggers, Susana Caballero & Demian Chapman (2024), Sphyrna alleni sp. nov., a new hammerhead shark (Carcharhiniformes, Sphyrnidae) from the Caribbean and the Southwest Atlantic. Zootaxa 5512 (4): 491–511, DOI: 10.11646/zootaxa.5512.4.2

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