Abstract
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.
Highlights
Galeorhinus galeus (Linnaeus, 1758) is a medium-sized shark that occurs in coastal and shelf temperate waters (Compagno et al, 2005; Ebert et al, 2013)
We provide new evidence on the largescale latitudinal migration of school sharks along the Southwestern Atlantic (SWA) shelves, and discuss the relationship between the observational data and the distribution and circulation of water masses in this area
The size length distribution was unimodal in both sexes, the total length (TL) of female ranged from 90 to 150 cm of TL with a peak in 120 cm of TL, and in male, the TL ranged between 100 and 130 cm of TL with a mode in 120 cm TL (Fig. 2C)
Summary
Galeorhinus galeus (Linnaeus, 1758) is a medium-sized shark that occurs in coastal and shelf temperate waters (Compagno et al, 2005; Ebert et al, 2013). Off southern Brazil (30°- 34°S), it is abundant at depths of 40-350 m, and the seasonal pattern is characterized by a fall immigration with peaks during winter (June–September) and a spring emigration (OctoberNovember), being absent during the summer months (January and February) (Peres, Vooren, 1991) On this basis, Vooren (1997) hypothesized that the school sharks spend the austral winter in the northern region of their latitudinal range (off southern Brazil), and migrate southwards to the Northern Argentine Shelf (35°- 45°S) in the austral summer. This migration could be related to reproductive habits (giving birth in nursery areas) that putatively occur in the south (Vooren, 1997; Nion, 1999; Walker, 1999; Lucifora et al, 2004)
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