An investigation of the population connectivity of sardines (Sardinops sagax) of the KZN sardine run using meristic, morphological and genetic data.

Abstract

The Sardine run occurs annually when large schools of sardine (Sardinops sagax) move from the Agulhas Bank towards KwaZulu-Natal, and has significant ecological and anthropogenic importance. Recent investigation has highlighted the nature and mechanisms resulting in the sardine run, however, critical questions about why the sardine run occurs remain unanswered. Therefore, the aim of this project was to elucidate the population diversity, connectivity and structure of sardines undertaking the sardine run. Sardines were sampled at four sites along the South African coast, and their morphology assessed using meristic data, multivariate, and geometric morphometrics. Nine exon-primed, intron-crossing (EPIC) DNA markers and the mitochondrially encoded cytochrome oxidase I (mtCOI) region of DNA were used for population and phylogeographic genetic analyses. Morphological analyses revealed significant differences between head size and shape of sardine run stock compared with other regions, and supports the delineation of a western, southern and eastern South African stock. Phylogeographic analysis using cytochrome oxidase I data, supported the idea that the Sardinops genus is monotypic. Genetic analyses using EPIC data confirmed low levels of segregation between sardines from the sardine run and the Western Cape stock. However, larvae spawned in KwaZulu-Natal demonstrated moderate levels of isolation from the Western Cape stock. The results reveal that there is successful recruitment of KwaZulu-Natal juveniles to the adult stock undertaking the sardine run. KwaZulu-Natal juveniles also recruit to the Western Cape population, although, to a lower degree. Results suggest sardines from the West Coast and Agulhas Bank partake in the sardine run. However genetic evidence suggests a certain subpopulation of the Agulhas Bank and a sub-stock of the Western Cape stock spawn successfully in KwaZulu-Natal. These results support the hypothesis that the sardine run represents a subpopulation spawning migration of Sardinops sagax in South Africa.