by John Bell
When 'Lilly' and 'JoAnn' the shortfin mako sharks were caught, satellite tagged and released off the coast of Isla Mujeres, Mexico nearly six months ago, marine scientist Dr. Guy Harvey and his team from the Guy Harvey Research Institute (GHRI) had little idea of the path that they would take.
The juvenile sharks, with a satellite reporting SPOT tag attached, disappeared quietly back into their environment in the Gulf of Mexico, but are now providing multiple and accurate detections of their journey, giving scientists a high resolution view of their migration patterns.
This week, Dr. Mahmood Shivji, Director of Guy Harvey Research Institute at Nova Southeastern University, reported that 'Lilly' had returned close to the original tagging site after 5.8 months and over 2,600 miles of travel.
Dr. Shivji said 'JoAnn' when released took a different and even longer journey (over 4,500 miles in 5.3 months) that has included both the Caribbean Sea and Gulf of Mexico. Amazingly, 'JoAnn', has now passed near where she was originally tagged three separate times during her extensive journey.
'What we are learning from 'Lilly' and 'JoAnn' is that these sharks do not roam randomly, but exhibit a finely tuned sense of place,' said Dr. Shivji. 'Longer term tracking will tell us if they are also exhibiting a sense of time as well as place.'
Lilly and JoAnn are still being tracked and their travels can be followed on the GHRI interactive website.
Is the tagged makos’ sense of place timed on mating cycles, seasonal availability of specific food sources or some other factor?
'We certainly see a finely tuned sense of place and time in the travels of tiger sharks we have tracked for long periods,' said Dr. Harvey. 'Time will tell if makos show the same navigational skills.'
Given the high fishing pressure on makos for their meat and fins, this species is showing declining population trends in parts of its range, which has resulted in the species being listed as 'Vulnerable' on the IUCN Red List of threatened species.
GHRI at NSU