Identification and Distribution of Morphologically Conserved Smoothhound Sharks in the Northern Gulf of Mexico

Abstract

AbstractIdentification of sharks within the genus Mustelus (smoothhound sharks) is problematic because of extensive overlap in external morphology among species. Consequently, species‐specific management of smoothhound shark resources is difficult when multiple species inhabit the same geographic region. The species identification and distribution of smoothhound sharks in the northern Gulf of Mexico (the Gulf) were assessed using sequences of mitochondrial DNA, nuclear‐encoded microsatellites, and catch data. Phylogenetic analysis of 1,047 base pairs of mitochondrially encoded ND‐2 sequences and Bayesian clustering of multilocus genotypes at 15 microsatellites revealed three genetically distinct monophyletic lineages (clades) of smoothhound sharks in the Gulf. Examination of external morphology revealed characters that distinguished each genetically distinct clade, and based on species descriptions and comparisons with the type and other specimens in established collections, the lineages were identified as Smooth Dogfish Mustelus canis, Florida Smoothhound Mustelus norrisi, and Gulf Smoothhound Mustelus sinusmexicanus. Two hundred and eighty‐seven smoothhound sharks sampled from across the Gulf were then assigned unequivocally, based on genetic data, to one of the three species. Multifactorial analysis and homogeneity tests of species‐specific means versus grand means of spatiotemporal factors (depth, longitude, and month) at capture indicated significant differences among the three species with respect to all three factors. On average, the Smooth Dogfish is found in deeper waters than the Gulf Smoothhound, whereas the Florida Smoothhound inhabits relatively shallow waters. A diagnostic key for the field identification of adult specimens of each species is provided.