Named for the unusual and distinctive form of their heads, hammerhead sharks belong to the family Sphyrnidae.<\/p>\n
They are found worldwide, preferring life in warmer waters along coastlines and continental shelves.<\/p>\n
\u201cHammerhead sharks are a monophyletic lineage of carcharhiniform sharks first appearing in the Miocene epoch,\u201d said Florida International University researcher Cindy Gonzalez and her colleagues from the United States and Canada.<\/p>\n
\u201cThey are characterized by their laterally expanded, dorsoventrally compressed head or \u2018cephalofoil\u2019 and currently comprise nine named species.\u201d<\/p>\n
\u201cHammerhead sharks are one of the most threatened shark families mainly due to overexploitation, with all species but one (Sphyrna gilberti) being globally listed as Vulnerable, Endangered, or Critically Endangered by the IUCN,\u201d they added.<\/p>\n
\u201cThere are four species of small-bodied hammerheads (less than 1.5 m total length at first maturity) that are endemic to the Americas: Sphyrna tiburo, Sphyrna tudes, Sphyrna corona, and Sphyrna media.\u201d<\/p>\n
\u201cSphyrna corona occurs only in the Eastern Pacific, Sphyrna tudes occurs only in the Western Atlantic, and two species occur in both oceanic basins, including the scoophead shark (Sphyrna media) and the bonnethead shark (Sphyrna tiburo).\u201d<\/p>\n
The newly-described Sphyrna species is a small hammerhead shark less than 1.5 m in length.<\/p>\n
Scientifically named Sphyrna alleni (common name is the shovelbill shark), it has a flat, shovel shaped head that lacks indentations on its anterior edge.<\/p>\n
\u201cSphyrna alleni is distinct from Sphyrna tiburo because in this species the anterior margin of the head is more rounded and the lobules on the posterior margin are not present,\u201d the researchers said.<\/p>\n
\u201cPrecaudal vertebral counts for Sphyrna alleni are between 80 and 83 \u2014 around 10 more vertebrae than in Sphyrna tiburo.\u201d<\/p>\n
\u201cGiven some similarity in cephalofoil shape in Sphyrna alleni and Sphyrna vespertina it is possible that they are sister lineages and Sphyrna tiburo diverged from them as it expanded into the subtropical and temperate Atlantic, with a later separation of Sphyrna vespertina and the incipient Sphyrna alleni by the Isthmus closure.\u201d<\/p>\n
Sphyrna alleni is distributed in coastal waters, estuaries, coral reefs, seagrass beds, and sand bottoms from Belize to Brazil.<\/p>\n
The presence of the species has been confirmed in the Caribbean in Belize, Panama, Colombia, Trinidad and Tobago, and in the southwestern Atlantic in Brazil.<\/p>\n
\u201cBonnetheads are currently assessed as Globally Endangered by the IUCN but they have been assessed as one amphi-American species,\u201d the scientists said.<\/p>\n
\u201cThe assessment highlights that the species is well managed in higher latitude parts of its northern hemisphere Atlantic range (U.S., Bahamas) but heavily fished and poorly managed elsewhere, with evidence of population collapse in Brazil and throughout much of the Tropical Eastern Pacific.\u201d<\/p>\n
\u201cReevaluating this assessment considering the geographic distribution of Sphyrna tiburo and Sphyrna alleni is now warranted,\u201d they said.<\/p>\n
\u201cGiven how fishing and management is distributed it is likely that the IUCN status of Sphyrna tiburo would improve and Sphyrna alleni would warrant a highly threatened status.\u201d<\/p>\n
\u201cGreater management attention is necessary to rebuild populations of Sphyrna alleni, which could take the form of restrictions on gillnets and trawls as these gear types are responsible for most catches of this coastal species.\u201d<\/p>\n
The discovery of Sphyrna alleni is reported in a paper in the journal Zootaxa.<\/p>\n
Cindy Gonzalez et al. 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<\/p>\n