Integrating Biology, Genetics And Tagging Studies For The
Management And Conservation Of The Highly Vulnerable Bigeye Thresher Shark In The Atlantic Ocean
The bigeye thresher, Alopias supercilious
, is commonly caught in the Atlantic as by-catch in pelagic long-line fisheries targeting tunas and swordfish. However, there is still little information available on the biology of this species.
The bigeye thresher shark occurs circum-globally in tropical and temperate seas, ranging in habitat from oceanic epipelagic to coastal waters, preferring more oceanic and warmer waters than its congener Alopias vulpinus. It is known to usually bear only two embryos per litter (although cases of up to four embryos may occur), resulting in an extremely low fecundity and consequently, a very high vulnerability to fishing pressure.
The IUCN Shark Specialist Group (SSG) considered all members of the genus Alopias
as Vulnerable in global terms (according to the IUCN Red List Criteria), because of their declining populations. Specifically, the bigeye thresher was considered especially vulnerable to fisheries exploitation, even within the Alopias genus, due to both its exceptionally low rate of population increase and its epipelagic habitat occurring within the range of many poorly regulated waters.
Given the lack of knowledge on the biology, migrations, habitat use, population genetics and survivorship of the bigeye thresher shark in the Atlantic Ocean, there is an urgent need for a study in an ocean-wide perspective. This project was developed as a means of filling critical voids in this information needed for enlightened national and international fishery management and conservation initiatives. Based on this, the proposed project has four main objectives/tasks:
1) Determination of life history parameters including age, growth, reproduction and mortality;
2) Application of satellite telemetry tags (PAT) to study long term movements, habitat preferences and survivorship of these sharks in the Atlantic Ocean;
3) Population genetics comparing different stocks along the Atlantic Ocean
Project THRESHER has just started in February 2011 and it is a 3 year project, designed to be completed by January 2014.
We have started to collect vertebrae samples and the preliminary age and growth results will be available on this page in the near future.
The first Satellite tagging trip is planned for the summer of 2011, in the Central Eastern Atlantic Ocean (off West Africa). We are planning to tag 10 specimens during that first mission and the results on their movement patterns will be posted on this webpage.
Project THRESHER is being coordinated by Rui Coelho at CCMAR / Univ. Algarve in Portugal, and is being funded by the Portuguese Foundation for Science and Technology (Project Ref: PTDC/MAR/109915/2009)