IMAS Marine Biologist Rob French describes his important work on the post-survival release of mako sharks in Tasmania as part of a Fishwise funded project at the Institute for Marine and Antarctic Studies at UTAS.
The short fin mako shark is a highly sought after game fishing species capable of attaining sizes up to 3.95 metres. The scientific name is
which means sharp nose!
The species is known to be an excellent fighting fish capable of reaching speeds of 35 km/h and performing acrobatic jumps metres into the air. Although many anglers choose to tag and release short fin makos, the effect of the capture, tag and release process on the animal remains uncertain.
Mako sharks are important top-level predators in marine ecosystems yet relatively little is known of their ecology, population status and movements along the Australian coast. They are slow growing, reach sexual maturity at a late age and large size and produce a relatively small number of pups. As such, they are extremely susceptible to over-exploitation. Declines in the relative abundance of makos in some regions resulted in their listing as globally 'vulnerable' by the International Union of Conservation of Nature in 2007, and by the Convention on Migratory Species (CMS) in 2009. This highlighted the urgent requirement for better scientific data on mako sharks to enable legislative amendments to be scientifically based.
Mako Tagging Project
A new project being undertaken by PhD candidate Rob French, from the University of Tasmania's
Institute for Marine and Antarctic Studies
(IMAS) is aiming to fill this knowledge gap.
The three year project is funded by
Fishwise and began in January 2012. It aims to find out what proportion of released mako sharks currently survive catch-release, and if there are ways to improve survival through the development of best practice catch and release protocols. This is a great opportunity for science to work closely with Australian game anglers in an effort to improve the sustainability of the fishery so that it may be enjoyed for many years to come.
Sharks are caught by game fishers using their own techniques and gear. When the shark is landed a blood sample is quickly taken from the tail and a satellite tag is attached to the shark - in place of a standard fisheries tag. The tags operate for up to thirty days after the shark has been released and monitor movement through depth and temperature to ensure the shark is still alive and actively swimming. If the shark is still alive after thirty days the tag will pop off and transmit the data to satellites where it can be later accessed and downloaded. The tag will pop off earlier if the tag determines that the shark is dead e.g. the depth remains constant.
So far, 12 sharks have been tagged with at least another 18 to go. The tags show mixed results in terms of movement; a few sharks were swimming around the tagging area after a month at large, while others have been shown to travel great distances. For instance, one tagged off Pirates Bay, Tasmania was found around the Gascoyne Seamount, which is located about 560kms due east from the south-eastern most point of Australia's mainland coast. From Pirates Bay this is a straight line distance of 1,039km in 30 days.
The blood samples are taken so that we are able to look for signs of severe exhaustion and stress. Monitoring the physiological stress of the shark at capture and comparing this between the various fishing gears and techniques used by the anglers allows for capture methods which best limit stress, thus maximising the survival and well-being of the shark.
Contact: IMAS research on tagged mako shark and southern bluefin tuna
Sean Tracey and Rob French
Institute of Marine and Antarctic Research
University of Tasmania
Marine Research Laboratories
Phone: (03) 6227 7286
Contact: Recreational Fisheries Manager
Recreational Fisheries Manager
Wild Fisheries Management Branch
1 Franklin Wharf
HOBART TAS 7000
Phone: 03 6165 3034