Pilot study on behaviour of sharks around Saba using acoustic telemetry
Worldwide many shark populations are in strong decline mainly due to fisheries. Population status of sharks in the Caribbean is still poorly known. In order to be able to take effective measures to protect sharks, insight in their spatial behaviour during different life stages is required. Do marine parks enhance shark populations and if so at what scale?
In the Caribbean Netherlands, a unique opportunity for research on spatial behaviour is provided by the still relative high abundance of sharks on the Saba Bank, Saba and St Eustatius. To study individual movement patterns and site fidelity of sharks species that use reefs, acoustic telemetry is a proven successful technology.
As a first step, we started a pilot study with acoustic telemetry on Caribbean reef sharks and nurse sharks on the reefs directly around Saba in October 2014. Our goals were to obtain: 1) experience with using existing infrastructure and organisations in setting up a shark telemetric study; 2) experience in catching methods and insight in effort needed for these target shark species; 3) a first indication of the scale of individual movement patterns in time; and 4) raise local awareness of importance of sharks.
An array of eight detection stations (VEMCO VR2W receivers) was deployed on or near existing anchored mooring buoys at the pinnacles and the reef surrounding the island of Saba. In the last week of October 2014, in total eight Caribbean reef sharks (115-184 cm) and four nurse sharks (94-210 cm) of different life stages were implanted with VEMCO V16 transmitters (with battery life of 4.5 years) and released at the catch site. For Caribbean reef sharks, rod and line, and for nurse sharks, long-line fishing for short duration during night proved most favourable, though catching nurse sharks required more effort than Caribbean reef sharks. In addition, two nurse sharks were obtained from bycatch in lobster pot fisheries.
A first read out of the receivers was carried out in early December 2014. The first preliminary results showed that all sharks were detected after release and that most Caribbean reef sharks were detected throughout the first six weeks and mostly around only a few receivers. This suggests a very local habitat use of the reefs around Saba. Two Caribbean reef sharks appear to use a larger proportion of the reefs around the island. For the three juvenile nurse sharks habitat use appeared to be even more local since they were only detected at one receiver throughout the first six weeks. The larger female nurse shark was only detected directly after release and her spatial behaviour thereafter remains unclear as of yet.
In the coming years these sharks will yield more data on year-round habitat use. In the autumn of 2015 we will also use a mobile receiver to detect tagged sharks present at the reefs around Saba in between the stationary receivers. Furthermore, to answer research questions about dispersal, migration, connectivity and meta-population structure we aim to expand the telemetry study to the Saba Bank and given sufficient budget also surrounding islands of St. Eustatius and St. Maarten in 2015.
This pilot study could only be performed through the support of many people and organisations, e.g. the Saba Conservation Foundation. The shark research of IMARES and partners was presented at Sea & learn in Saba and the fieldwork was documented for two Dutch Caribbean TV-programmes. WWF, Wereld Natuur Fonds the Netherlands (WNF), and the Dutch Ministry of Economic Affairs provided the funding for this study.