Shortfin makos
Project Leader: Dr David Sims
Background
The shortfin mako (Isurus oxyrinchus) is generally regarded as the fastest swimming shark, reaching speeds up to 50 kph. It is a warm-bodied, highly active shark with a circumglobal distribution in tropical and warm-temperate seas. However, very little is known about many aspects of its biology, including its general movements, habitat preferences and population structure.
Shortfin makos are taken as bycatch in long-lining and gill-netting operations for tuna and swordfish, activities that have expanded rapidly over the last 20 years. High demand for their fins and its good quality meat mean that makos are also now highly prized by fishers. As a result, population declines of around 25% have been recorded in the western Atlantic Ocean since 1986.
Information about the structure of shark populations is vital if conservation plans are to be successful. Shortfin makos exemplify this; there is already some evidence that they remain faithful to particular regions, with males and females apparently segregating into different regions for at least part of the year. In a conservation context, such behaviour may result in exposing the more vulnerable sharks (mature females and juveniles) to greater risk, thereby contributing to their already dramatic decline.
Shortfin makos are taken as bycatch in long-lining and gill-netting operations for tuna and swordfish, activities that have expanded rapidly over the last 20 years. High demand for their fins and its good quality meat mean that makos are also now highly prized by fishers. As a result, population declines of around 25% have been recorded in the western Atlantic Ocean since 1986.
Information about the structure of shark populations is vital if conservation plans are to be successful. Shortfin makos exemplify this; there is already some evidence that they remain faithful to particular regions, with males and females apparently segregating into different regions for at least part of the year. In a conservation context, such behaviour may result in exposing the more vulnerable sharks (mature females and juveniles) to greater risk, thereby contributing to their already dramatic decline.
In the field
Dr David Sims
SOSF is funding a 2-year study, begun in 2007, that for the first time is shedding some light on the movements and behaviour of shortfin mako sharks. Satellite tag deployments and data analyses are being conducted in parallel with the ongoing SOSF-funded project on blue shark satellite tracking.
State-of-the-art tracking technology is being used to determine the horizontal and vertical movements of mako sharks in the Atlantic, and to identify the most actively used spaces and migration routes of both males and females.
It is also plotting the geographical positions and behaviour of individual sharks against high-resolution maps of environmental variables (temperature, bathymetry, primary and secondary production, mesoscale eddies, frontal boundaries) to help quantify habitat preferences. The project team is also using geographic information systems (GIS) technology and geo-statistics to plot the extent of spatial and temporal overlap of mako shark distributions with the start and end positions of long-lines deployed by Spanish and Portuguese fishers.
State-of-the-art tracking technology is being used to determine the horizontal and vertical movements of mako sharks in the Atlantic, and to identify the most actively used spaces and migration routes of both males and females.
It is also plotting the geographical positions and behaviour of individual sharks against high-resolution maps of environmental variables (temperature, bathymetry, primary and secondary production, mesoscale eddies, frontal boundaries) to help quantify habitat preferences. The project team is also using geographic information systems (GIS) technology and geo-statistics to plot the extent of spatial and temporal overlap of mako shark distributions with the start and end positions of long-lines deployed by Spanish and Portuguese fishers.
Aims & objectives
Computer modelling aims to determine and assess the vulnerability of sharks to different fishing locations and effort scenarios. In so doing, this novel 2-year research programme is beginning to provide the first data on the long-term, large-scale movements and behaviour of the shortfin mako shark in the Atlantic Ocean.
Project Update: 2007
Research began in July 2007 with a cruise to the north of the Azores aboard a commercial long-liner but, due to appalling weather and low catch rates, no tagging of makos could take place. In late September, during a second cruise, the first mako shark was tagged with a satellite PAT tag off the coast of southern Portugal in the eastern Atlantic. This tag is due to release in early December 2007. Further deployments of tags from the Azores and southern Portugal are planned in summer 2008.