Large-scale migration of a school shark, Galeorhinus galeus , in the Southwestern Atlantic

Abstract

Knowledge of the spatial and temporal distribution patterns of chondrichthyans is critical for their effective management. In this study we report and analyze a large-scale latitudinal migration (~ 1,425 km) of a female school shark in the Southwestern Atlantic shelf where it is currently classified as Critically Endangered. During the austral summer (February 15, 2015), ninety-four school sharks were captured (75 females and 19 males) and tagged with fin tags in Nuevo Gulf (~ 42°43’S, 64°53’W, Argentina). A female of 112 cm total length was recaptured in Uruguayan shelf waters in the austral winter (August 17, 2015). This long displacement represents the first direct evidence to support Vooren and Lucifora’s hypothesis of a single transnational population of Galeorhinus galeus in the Southwestern Atlantic. The good agreement found between the school shark habitat conditions (salinity 33-34, temperature 12-17°C) and the warmer member of Subantarctic Shelf Waters suggests that the seasonal variation in school shark abundance within this region could be related to water masses movements.

Uso de BRUVS para describir el ensamble de peces y su estacionalidad en dos caletas marinas poco profundas dentro de áreas protegidas de la Patagonia, Argentina

“…It is noteworthy that the seasonal patterns for N. cepedianus and G. galeus were only statistically significant in the southern study site (CM), since the two species were not recorded in the area during winter. This observation agrees with recent evidence on the migratory pathways for G. galeus (Jaureguizar et al 2018) and N. cepedianus (De Wysiecki et al 2020), characterized by northward displacements during colder months, possibly explaining why they were not found in CM in winter. However, a previous study in CV using fishing technics recorded N. cepedianus year-round, but with marked seasonality in catches (Irigoyen et al 2018).…”

Extensive oceanic mesopelagic habitat use of a migratory continental shark species

“…Additionally, tope are considered highly migratory, and variable movement patterns of adult tope within their regional subpopulations have been described, including movements into and across oceanic waters 28 , 30 , 32 , partial migration of females between pupping and nursery grounds 31 , residency near known aggregation areas 31 , oceanic migrations between coastal areas 31 , 33 , large-scale seasonal latitudinal migrations 34 , 35 and along-coast migrations 36 . These movements of adult tope are often seasonal in nature and regularly related to their reproductive cycle 31 , 36 , or shifts in habitat conditions, such as the displacement of warm water masses 34 , 35 . With periods spent on the continental shelf and occasional excursions in deep-water, some evidence of crepuscular vertical migrations have been presented for tope in deep water areas 29 , 30 .…”

“…Generally considered a benthopelagic species with a mainly coastal distribution on continental shelves and slopes, offshore and pelagic distribution in open ocean habitats have also been observed in tope [28][29][30][31] . Additionally, tope are considered highly migratory, and variable movement patterns of adult tope within their regional subpopulations have been described, including movements into and across oceanic waters 28,30,32 , partial migration of females between pupping and nursery grounds 31 , residency near known aggregation areas 31 , oceanic migrations between coastal areas 31,33 , large-scale seasonal latitudinal migrations 34,35 and along-coast migrations 36 . These movements of adult tope are often seasonal in nature and regularly related to their reproductive cycle 31,36 , or shifts in habitat conditions, such as the displacement of warm water masses 34,35 .…”