Blue sharks
Project Leader: Dr David Sims
Background
The population structure of the blue shark (Prionace glauca) in the Atlantic appears complex, with anecdotal evidence for migrations, age and sexual segregation, and spatially discrete nursery areas. Underlying this apparent complexity is the likelihood that fisheries are significantly impacting populations. The purpose of this SOSF supported research in the north-east Atlantic is to determine the movements, behaviour and critical habitat of blue shark populations for direct use in conservation assessment of fishery interactions.
In the field
Dr David Sims
To date 12 pop-up archival transmitting (PAT) tags have been attached to blue sharks in three locations in the northeast Atlantic: seven in the English Channel, three in southern Portugal and two in the Azores. These tags archive pressure (depth), sea temperature and light intensity data and pop-off at pre-programmed times to report summary data via polar-orbiting satellites.
By September 2007, seven out of nine tags had achieved their pop-up dates and were able to relay large movement and behavioural datasets. Two of the tags deployed on female sharks in English Channel have also been physically retrieved, yielding full archival datasets of depth, temperature and light at 10-second resolution, providing an unparalleled insight into the migration behavior of blue sharks.
In addition to PAT tags, 11 smart position-only tags (SPOT) were attached to the first dorsal fins of blue sharks in the same three locations. These tags accurately pinpoint the locations where sharks break the surface during normal swimming. These have provided less reliable data with only four of 11 tags reporting positions on a regular basis.
By September 2007, seven out of nine tags had achieved their pop-up dates and were able to relay large movement and behavioural datasets. Two of the tags deployed on female sharks in English Channel have also been physically retrieved, yielding full archival datasets of depth, temperature and light at 10-second resolution, providing an unparalleled insight into the migration behavior of blue sharks.
In addition to PAT tags, 11 smart position-only tags (SPOT) were attached to the first dorsal fins of blue sharks in the same three locations. These tags accurately pinpoint the locations where sharks break the surface during normal swimming. These have provided less reliable data with only four of 11 tags reporting positions on a regular basis.
Aims & objectives
This project aims to conduct a detailed analysis of blue shark movement from the satellite data collected, including movement paths and dive behaviour.
Though at an early stage of analysis, some initial results show a high degree of sexual segregation among blue sharks in the northeast Atlantic. Using the tags Dr David Sims and his team have tracked the female-only migration within and away from the English Channel and identified specific behaviours associated with foraging and migrating. Male blue sharks were more abundant further west and a male tracked from the Azores showed directed movement towards an isolated seamount; juvenile blue sharks tracked on the continental shelf of southern Portugal were also tracked moving to oceanic seamounts, suggesting that these topographic features are probably important blue shark habitats.
Sadly, two of the six sharks tracked with SPOT tags were captured by long-lining fisheries within a month of release and tracked to ports in southern Spain, where one was physically retrieved. The death of these sharks reinforces the need for further research into the intersection of migratory routes and fisheries.
Though at an early stage of analysis, some initial results show a high degree of sexual segregation among blue sharks in the northeast Atlantic. Using the tags Dr David Sims and his team have tracked the female-only migration within and away from the English Channel and identified specific behaviours associated with foraging and migrating. Male blue sharks were more abundant further west and a male tracked from the Azores showed directed movement towards an isolated seamount; juvenile blue sharks tracked on the continental shelf of southern Portugal were also tracked moving to oceanic seamounts, suggesting that these topographic features are probably important blue shark habitats.
Sadly, two of the six sharks tracked with SPOT tags were captured by long-lining fisheries within a month of release and tracked to ports in southern Spain, where one was physically retrieved. The death of these sharks reinforces the need for further research into the intersection of migratory routes and fisheries.