Unravelling the mystery of smooth-hound sharks
Two species of smooth-hound sharks – common and white-spotted – are targeted by fishermen along South Africa’s coast. Simo is examining their physical and genetic differences to help us understand the relationship between these species.
Simo Maduna
Unravelling the mystery of the genus Mustelus in southern Africa
This project’s key objective is to investigate the evolutionary origin of the genus Mustelus in southern Africa, and the influence of selective and demographic factors on intra- and inter-population genomic and phenotypic variation in two commercially important, sympatric Mustelus species, M. Mustelus and M. palumbes.
Misidentification of sharks is a prominent issue in fishing operations, particularly in long-line and trawl fisheries, where there is a high rate of incidental capture of non-target shark species. This hinders the collection of reliable, species-specific data for shark catches and trade making robust stock assessments and identification of overfished and potentially threatened species nearly impossible in most situations. Understanding species boundaries and evolutionary history will thus be useful for the conservation management of various shark species.
Mustelus is a species-rich and commercially important genus of circumglobally distributed small- to medium-sized demersal sharks found in temperate and tropical waters. Mustelus species are collectively termed smoothhounds, houndsharks, gummy sharks or palombos, and some share a high degree of external morphology, which leads to confusion in distinguishing between species. Consequently the genus has historically been deemed taxonomically and systematically challenging. The scarcity of informative morphological variation and limited genetic knowledge have hindered the delineation of species boundaries and the understanding of their evolutionary origin, which has important implications for conservation management.
In southern Africa there are two socio-economically important, sympatric Mustelus species: the common smoothhound shark M. mustelus and whitespotted smoothhound shark M. palumbes. Currently M. mustelus is listed as Near Threatened by the IUCN Red List; M. palumbes is listed as Data Deficient. M. mustelus is a cosmopolitan species with widespread distribution from the Mediterranean Sea and eastern Atlantic Ocean to the South-West Indian Ocean. M. palumbes is endemic to southern Africa and the species’ range overlaps with that of M. mustelus from Namibia to northern KwaZulu-Natal. In KwaZulu-Natal these species co-occur with an isolated population of the north-west Indian Ocean Mustelus species, the hardnose smoothhound shark M. mosis.
It is suggested that the observed peculiar distribution of Mustelus species is due to the interaction of different oceanographic phenomena and the limited migratory ability of these animals, thus they are restricted to isolated geographic ranges. It is imperative that future population genomics and phylogenetic studies clearly explain the distribution patterns and speciation exhibited by these species.
The aims and objectives of this project are to:
- Collect fin-clippings and muscle tissue samples from at least eight individuals of each Mustelus species in the north-east Atlantic (M. asterias, M. Mustelus and M. punctulatus), south-east Atlantic (M. palumbes) and south-west Indian Ocean (M. mosis), respectively, for phylogenetic analyses.
- Collect samples and phenotypic data, based on morphological, morphometric and meristic characters, from at least seven sites across the geographic range of M. mustelus and M. palumbes (15 to 25 individuals per population per species) for population genomics analyses.
- Develop restriction-associated DNA (RAD) sequencing and molecular markers for M. mustelus and M. palumbes.
- Analyse phylogenetics of Mustelus species occurring in the eastern Atlantic and south-west Indian Ocean.
- Determine the influence of selective and demographic factors on intra- and inter-population genomic and phenotypic variation.