As well as deploying tags, the team took blood samples and fin clips to help understand the health of the animals, how they fit into the systems food web and how the populations are connected to other areas.
The early morning sunlight glistens gently on the still, deep-blue waters of Dunstaffnage Marina. I’m walking along the pontoon, pushing a heavy cart of equipment down to the boat we’ve hired for the day: the Blue-Fin. The awesome mountains of the west coast stand around us; speckled snow glints on some of the tallest peaks. The nose of Ben Cruachan pokes out of the clouds for a moment, its full face then coming into focus. It’s a view you can’t beat and one of my favourite places in the world.
just here for the view though. You may be aware that populations of
elasmobranchs (sharks, skates and rays) around the world have experienced
worrying declines. But you might be less aware that there are also incredible, large
and threatened elasmobranch species closer to home. We’re here for one of Britain’s
largest and most threatened marine species: the Critically Endangered flapper
skate (Dipturus intermedius). Growing
up to about two and a half metres in size, and weighing up to one hundred
kilograms, the flapper skate is a hidden wonder in British waters. Once found
from the Mediterranean to northern Scandinavian, the flapper skate was fished
almost to extinction – even becoming the first marine species to be declared
‘locally extinct’. But the skate persist in a few small pockets of their former
distribution. And one of those is on the west coast of Scotland, where a
remarkable and inspiring synergy of citizen science, cutting-edge research and
governance is turning the tide. I can’t quite believe I’ve become part of the
slightly, I draw up the heavy cart at the boat. In the humongous, neon-yellow
oilskins and bright yellow boots I’ve borrowed for the day, I feel like a ludicrous
clown, or perhaps a lollypop. Bending over, I start to lug equipment over the
side of the boat: ultra-sound monitors, tape measures, a water pump, hose
piping, electronic acoustic tags, a blood composition monitor, antiseptics,
anaesthetic, syringes, and litres and litres of water – it all has to go in. Everything
we need in the field to catch, health check and tag flapper skate.
How do you
catch a one-hundred-kilogram fish? Amazingly (at least for someone with as much
fishing experience as me), with a hook and line. Indeed, recreational anglers
started the practice of catch-tag-and-release for flapper skate decades ago –
tagging individuals with uniquely identifiable tags, so that the capture
histories of specific individuals could be mapped across space and time. This
pioneering practice has been one of the most valuable sources of information
available to scientists and policymakers regarding the flapper skate. In
particular, it has shown that the same individuals are caught again and again
through time, suggesting that some skate are resident in the same area or at
least frequently turn again and again through time. This was the major insight
that led to the designation of the Loch Sunart to the Sound of Jura Marine Protected
Area, the only body of water in UK waters currently designated specifically for
the conservation of an elasmobranch. However, despite the enormous value of
these capture-recapture data, they don’t tell us about where skate go and what
they do in-between recapture events. And that’s why we’re back in the Marine
Protected Area today.
This is my first time on the fieldwork team, and I’m not quite sure what’s coming. The boat’s engine comes to life and we chug slowly out of the marina. The wind starts to pick up and the sun slips behind a cloud – typical Scotland! Shivering slightly, I pull my oilskins a little tighter, feeling ominous about the weather. We round the bend, out of the marina, and the boat begins to pick up pace. The wind’s rushing past my face, turning my ears and cheeks pink with the cold. A dash of sea spray catches me in the face. I steady myself as the boat begins to sway, grinning in the excitement: we’re off!
South, travelling down a deep channel to an area where skate are often found.
Our aim is to catch, health check and tag flapper skate with acoustic
transmitters. These tags transmit individual-specific acoustic pings every so
often, working in combination with an array of underwater acoustic receivers (special
hydrophones) which listen continuously for acoustic transmissions. When a skate
moves into the detection range of a receiver, the receiver logs any detections
and later, we can work out where the skate were and where they like to be using
cutting-edge statistical modelling. That’s actually my job as part of a PhD
studentship, funded jointly by Scottish Natural Heritage (through the Marine
Alliance for Science and Technology in Scotland) and the Centre for Research
into Ecological and Environmental Modelling in St. Andrews. I’m here today,
though, thanks to valuable support from Shark Guardian.
We’ve reached our site, the anchor has been deployed, the rods baited, and the reels are spinning furiously as the weights sink towards the bottom. It’s nearly 200 m deep here. Vets from the Royal Zoological Society of Scotland, Edinburgh Zoo; Adam and Georgina, are full-stations-go, checking over equipment and rehearsing protocols for when (if!) we catch a skate. Suddenly, that seems to be happening already: a rod’s nodding and Roger (our skipper) is on it, reeling it in to keep the tension, while I don a waist harness into which the rod is clipped. I feel a pull on the harness and realise that my job is to carefully bring the skate to the surface.
We use rod and line to capture skate (as opposed to long-lining) because it means that we only catch one skate at a time. Consequently, skate are brought to the surface as soon as they are caught, minimising the time that they spend on the hook. Barbless hooks also reduce the risk of damaging the skate’s mouth. Bringing the skate up isn’t easy, though, because skate initially anchor themselves to the seafloor when they are caught, before swimming up through the water column. It’s several minutes, and my back is starting to ache, but I finally I feel the skate release the bottom. I start to reel it in, slowly, to avoid bring the skate up too quickly through the different temperature zones in the water column. Sometime later, the skate breaks the surface. It’s a small juvenile female and the first one I’ve ever seen.
Using a specially-designed sling system, we carefully lift the skate onto the deck and rest it on a support pad to make sure that it is as comfortable as possible. A custom-made water pump drives oxygenated sea water through a system of hoses into the skate’s mouth so that it can breathe and the vets are straight to work, scanning the skate for scrapes and marks and taking blood samples for analysis, before surgically tagging the skate under local anaesthetic. This is a remarkably quick and simple procedure, taking just a few minutes. Meanwhile, Jane (SNH skate expert) and I are monitoring the respiratory and cardiac function of the skate; at the moment, I’m measuring the breathing rate (a breath is visible when water is pumped over from the gills) and Jane’s monitoring the heart rate by counting the number of heart beats from real-time ultrasound imaging of the heart.
The tagging is complete and it’s time to measure and photograph the skate. The photograph will be uploaded to Skatespotter: an online database that contains pictures of a large number of skate. Together with the capture-recapture data, this helps us to record the recapture history of skate, their appearance and changes through time, examine parasite loads and timing of biological events (such as pregnancy); all valuable information that can guide management.
It’s only been 15 minutes, but the skate is back in the water. I watch it flap it huge graceful wings, turning slightly as it descends once more into the depths. I suspect I won’t see that one again for a while. But, perhaps, soon enough, we’ll see it start to transmit signals to acoustic receivers that will tell us how it’s using the Marine Protected Area in years to come. I look up, panting slightly. The sun is shining, and another rod is starting to tick…
Edward Lavender is a PhD student at the University of St Andrews and a member of the Marine Alliance for Science and Technology in Scotland Graduate School. Edward acknowledges his PhD funders (Scottish Natural Heritage and the Centre for Research into Ecological and Environmental Modelling) and extends his thanks to Shark Guardian for providing the funding for his participation in the ongoing fieldwork project, designed to monitor skate habitat use in the Loch Sunart to the Sound of Jura Marine Protected Area. You can read more about the flapper skate here.