The shortfin mako shark is the most common species of shark tagged by gamefish anglers in the south-west Pacific. In Australia, about 6400 have been tagged and 152 (2.37 per cent) recaptured, while in New Zealand, some 13,100 have been tagged and 340 recaptured (2.60 per cent).
The results of this large tagging effort have provided very important information on the movements of makos, but one unknown has always been: what is the level of post-release survival of sharks tagged and released by recreational anglers? Hopefully the answer to this question will be provided within the next three years by a new study being undertaken by The Institute for Marine and Antarctic Studies at the University of Tasmania.
To do this, PhD student Rob French hopes to tag 30 makos, all caught by usual gamefishing methods, with pop-up satellite tags. The plan is to tag 10 sharks in each of three States: Tasmania, Victoria and New South Wales, with the assistance of local recreational anglers. The tags are specifically designed to determine whether or not sharks died after release. They do so by constantly recording depth, so that when the tags release and transmit their data, it can be determined if the shark had died or had been swimming normally since release.
The study will focus on some of the variables that might affect survival, such as the gear used (circle hooks versus J-hooks, for example), line class, fight time and so on. If all goes according to plan, an anticipated benefit will be support for the mako gamefish fishery through the promotion of ‘best practice’ techniques to maximise the survival of released makos.
Rob will also be using cutting-edge science to investigate the feeding ecology of makos, including where they spend time foraging. This will involve collecting tissue samples (liver, gills, red muscle and white muscle) from makos and analysing stable isotopes of different chemical elements such as carbon and phosphorous – the ratio of which can reveal the types of prey animals the sharks have been consuming through time, and even where feeding has been occurring.
Rob is very keen to engage with the gamefishing community in conducting his studies, requesting help in deploying the pop-up tags and in collecting tissue samples from landed sharks. If you’re interested in assisting or require further information, feel free to contact Rob on: 0414 386 474 or send him an email at: Robert.French@utas.edu.au
Dr Julian Pepperell