Mat Mchugh has spent time studying how fish behave, what their habits are and how they react after an angler has caught them. He shares his findings in a really interesting article
Prior to getting into the fly fishing travel business I was lucky enough to study in the field of aquatic science. While I had spent most of my youth fishing and curious about water and its inhabitants I stumbled into this course of aquatic science. It taught classes on limnology, hydrology, entomology and marine and freshwater biology and ecology. At around the same time I also discovered fly fishing. As I look back now the sport of fly fishing is really an informal way of developing understanding many of the scientific subjects and theories taught in those lecture halls and class rooms. Part of the process of developing as a fly fishermen is understanding how ecosystems work and the process of fly fishing and spending time on the water and in different environments does a great job of this.
Over the last couple of years I have had the opportunity in combining both science and fly fishing to better understand the biology and ecology of both bonefish and giant trevally in a remote coral atoll environment. In conjunction with the University of Hawaii and with some generous funding from Costa sunglasses and the Tetiaroa Society we have been able to set up an acoustic tagging study of Giant trevally to try and understand their movements. Remarkably with the importance of giant trevally as not only a food source for many island communities in the tropics and as a highly regarded sportfish for both fly and popper fishermen this had never been done.
The aim was to have fly anglers participate in the research. They would visit Tetiaroa as they would normally on their fishing holiday, however this time the landed giant trevally would be tagged and followed by a scientist in order to better understand what happens after these fish are released. In September 2014 two of our clients, both very keen saltwater fly fishermen signed up to participate. They would have a week on a remote coral atoll in the middle of the Pacific Ocean and any giant trevally landed would be tagged with an acoustic transmitter and then a scientist would track their movements for the next two months.
The trip proved a great success. Over the course of six days the two anglers cast at over 65 fish, landing seven, loosing another five fish and countless heart stopping movements as fish followed and refused the fly. Five of the landed fish had an acoustic tag placed inside them by Alex Filous of the University of Hawaii and were released. The first question we hoped to answer was - Would these fish survive? This is one of the big unknowns with catch and release fishing. Does the stress of fighting and landing a fish impact on a fish's survival? Obviously different species will have different tolerances to handling and there have been many studies on other species that show poor handling can result in the death of the released fish. In this case these fish also underwent the added stress of a surgical operation to implant the tag and then the shark infested waters of the lagoon. The good news is that seven weeks after capture and release each of these fish were still swimming around the Tetiaroa lagoon. Several of them could be visually seen feeding while being tracked.
The study has also revealed some other interesting behaviours of giant trevally. Much like many of us they are very habitual creatures exhibiting a home range or territory and having very similar daily movements each day (See figure 1). But one of the most fascinating revelations of the research was that each of the fish, having been caught, tagged and released, exhibited the same response. No matter where they were caught in the lagoon, having been released, they would all swim to a small general area in the lagoon (See figure 2). This became know as the 'infirmary'. The fish would then spend 3-4 days in the infirmary recovering, before then returning to their daily rhythms. Why this area? The lagoon is eight square kilometers and there are certainly deeper areas where they could have gone to hide or recover. As with trying to understand the ecology of any species there are always more questions to be answered.
Fig 1: Territorial ranges of the 5 tagged giant trevally
Fig 2: The five fish and their initial movements after release
The work will continue next year with a similar acoustic study of bonefish movements as well as more work on giant trevally. If anglers are interested in participatng they should conact
Fly Odyssey.
Fly Odyssey would like to thank Costa for their support and contributions to this research: Alex Filous from the University of Hawaii for his scientific expertise, Jonathan Hey and Mike Youkee (the anglers), Tetiaroa Society and The Brando Hotel.
Mat Mchugh runs Fly Odyssey fly fishing holiday specialists