The use of estuarine habitat by the rig shark (Mustelus lenticulatus)

Abstract

The aim of this research was to understand the use of estuaries, as critical habitats, by rig shark (Mustelus lenticulatus) using Pauatahanui inlet, one arm of Te Awarua o Porirua Harbour as a study site. A total of 404 M. lenticulatus were caught, 383 were tagged with uniquely numbered tags, and 16 tagged sharks were recaptured. During the eight-month shark season, from the start of October to the end of May, individual sharks can spend up to five months within or near the estuary. There was evidence of adult M. lenticulatus, both male and female, showing nursery area philopatry. Using a self-built GPS tracking system with tags that increase a shark’s ability to swim through the water by an additional 7.3 – 8.5 % (for the most commonly-sized tagged sharks 90 – 94 cm TL). Fifty-three sharks were tracked showing that M. lenticulatus use most of the subtidal areas of Pauatahanui inlet and avoid intertidal areas. A Hidden Markov model was used to identify three different behavioural traits, the sharks spent 50 % of their time undertaking ARS (Area Restricted Searching), 44 % searching and 6 % transiting. The daily movements of M. lenticulatus were influenced by low-salinity waters, from catchment rainfall events.