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Return of the TDR

Updated: Jul 13, 2021

A long time ago in a marina far, far away……

It’s early morning when we slip the lines and the purr of the engine rises gently on our trusty RIB, Seashell. Curls of mist drift lazily up from the mirror sheen that stretches across Lough Swilly as we exit the mouth of the marina. It’s the 8th of August 2012 and today is a different day. Today is the day that the group enters the ‘big league’ in basking shark research. I steal a glance at Donal Griffin on my left and see the smile in his eyes as he squints north towards the mouth of the lough and beyond, to shark waters.

Carefully stowed onboard is a box of Timed Depth Recorder tags (TDRs) that recently arrived from Queens University, Belfast. This is a new departure for members of the group, made possible by the ‘Depth Charge’ project funded by the local Inishowen Development Partnership. Depth Charge was the first of several community-led education and awareness programmes run by the Inishowen branch of the group, with the aim of making marine science and research real for local coastal communities. These tags are a magnitude more expensive and complex than anything we have deployed before, and we hope they will bring a new perspective to our research and ultimately the protection of the species.

Left: Donal Griffin holds a prototype TDR. Right: Local fisherman Denis Glakin of Malin head with a recovered tag.

Minutes later we are trawling along a distinctive white tidal line stretching north from Dunaff to Malin Head. That’s when we see our first fin. Donal eases the throttle back as a large black triangle slides by our bow and slips below the surface. We quickly set about preparing our first tag for deployment while we wait for the shark to resurface.


The shout goes out and a quick point sets us off again. The shark is feeding lazily on the wrack- marked tidal line and I look down in the bright sunshine to see fuzzy clouds of red Calanus (the copepods these sharks like to eat) near the surface. The GoPro is rolling and a coloured visual ID tag is deployed first. Then we can all relax and sit a little easier in our seats. The shark re-surfaces moments later and the decision is made. “Let’s go for it!”. Nervous smiles return as Seashell clicks into gear once more. The shark is remarkably compliant and stays on the surface as I reach out with a shaking hand to deploy my first mini tech on a basking shark. The shark doesn’t even react, and we enjoy the moment with a celebratory cup of tea and a ginger biscuit. Yes, we know how to live it up on the water…

The IBSG deploys a TDR.


Tick tock, time flies, the world turns, and people go grey. Fast forward nine long years. I’m sitting in my office staring google eyed at the screen during a global pandemic. My inbox pings. It’s Alex McInturf, the group’s new co-coordinator, with some very welcome good news. Unbelievably, Howard, who is a keen-eyed dog walker in Orkney, Scotland, has recovered one of the TDRs that was deployed on that fateful day. In fact, it was actually found by his dogs, who likely thought they had found a new toy! After some email ping pong, we arrange to get the tag posted and I’m amazed to find that it looks in good shape. To think that it’s been washing around in the Atlantic for nearly ten years - I thought it would be practically worn away. No surprise, the battery is dead, so we have sent the tag to CEFAS in the hope that they can extract the data. Only time will tell, but all in all, fate has been kind to our early efforts. Between 2010 and 2013 we deployed 23 TDRs. This is the fourteenth recovery (not bad for a bunch of amateurs). We now have approximately 500 hours of fine scale depth and temperature data from basking sharks off Malin head. The information from TDRs we had already recovered has been used to develop a surfacing model, which explores how environmental variables (such as wind speed and sunshine) effect the surfacing behaviour of basking sharks. In time this model will be used to assess threats and risks to the species such as ship strike and by-catch. We are exploring other ideas for the data as well, looking at foraging behaviour in surface hotspots for instance. But for now, it’s just good to be back, back in the game...

May the sharks be with you.

Written by: Emmett Johnston

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