Another Life: First catch your fish – the science of tracking sea life

Once it was just binoculars. Then hidden cameras and infrared video. Today, keeping an even closer eye on nature, computerised mini electronics and spies in the sky track the travels and habits of creatures great and small.

Bulky radio collars are just about tolerated by lions, tigers, wolves and bears. Miniature lightweight transmitters are stuck to the backs of birds, bats and even butterflies. Now deep-ocean animals report on their wanderings by attachments that pop up to the surface, on command, and send radio packages of data to satellites. These trace the course of long journeys, the nursery and feeding grounds, the depths of dives, the temperature and salinity of the water, and levels of light.

Around Ireland such “tags” have been fixed to basking sharks, porbeagles and blue sharks, bluefin tuna, leatherback turtles and sunfish. Some of these tags have tracked transatlantic migrations. But some species can be less accommodating. Leatherback turtles, for example, need to be captured first – often rescued from entanglement in nets or ropes – and fitted with a harness to carry the tag.

But how do you engineer a 50cm fish to report on its travels? This summer has seen more tracking of the movements of sea bass, Ireland's most prized catch of inshore angling and a fish in dire need of conservation. A collaboration of the Marine Institute and University College Cork mounted a study that began in Cork Harbour and has since widened to the coast of Co Wexford. Implanting the bass with tiny acoustic transmitters, it tracks their signals by receivers mounted on buoys around the southeast and retrieved, once a fortnight, by computer at UCC.

The fish are caught by the region’s many bass enthusiasts – the sort of angler found in winter braced waist deep in tables of windblown surf to cast a lure beyond the third wave. In summer, however, bass move into estuaries to chase shoals of sand eels, which makes catching them a more comfortable challenge.

Fitting the tiny transmitter involves delicate surgery, with a preliminary anaesthetic bath and fresh seawater piped through the gills. An incision in the belly implants the transmitter, the skin is stitched up, and the bass, after recovery in a bucket of oxygenated seawater, then swims strongly to freedom (so I am assured), its progress marked by electronic pings.

This silvery, muscular, but slow-growing fish – a five-kilo female might be 16 years old – was once prolific around the southern coasts of Ireland. Commercial overfishing through the later 20th century concentrated on Wexford Harbour, the estuary of the River Slaney, but was halted by government order in 1990, with a two-fish-a-day bag limit also extended to anglers.

That protection was echoed this spring by an EU ban on commercial fishing of bass around most of Ireland and Britain, and a recreational-angling limit of three bass a day from the top of the North Sea around the south to Dingle, including the Irish Sea.

The Irish conservation laws did indeed produce a local rise in bass numbers, as young females grew to maturity, and a new influx of tourist anglers to Wexford and the southeast. But the good years have not held up since 2007. Among delegates to a conference at Dublin Castle last September was the Wexford angling writer and bass enthusiast Ashley Hayden. After 24 years of conservation, he declared, "estuaries, headlands, beaches and tide races from Carnsore Point to Galway Bay should be alive with midweight bass in the four- to six-pound bracket. Sadly and mysteriously they are not."

40 Foot Walruses

My recent column about the playful grey seals of Dublin Bay nipping at the toes of swimmers at the Forty Foot brought an email from a reader, Barry O’Connor, offering some fascinating testimony. He and friends in the

[ 40 Forty-Foot Walruses Swimming Sea Swimming Club ]

, beefy masochists all, also specialise in foreign trips to compete in swimming through ice.

To build up their tolerance to cold they take long night swims from the Forty Foot in winter’s squally seas, dressed only in brief togs, an activity that attracts the close attention of wandering pups and adolescent seals. “There are times,” he writes, “when we have had to shoo them away, as the constant tickle of whiskers on our feet, interspersed with the odd slap from flippers, becomes a bit too much. You do feel initially vulnerable, but increasingly irritated.”

This winter, he adds, he and his colleagues Allen Evans and Ger Kennedy are off to swim in Siberia. There, in the White Sea, the harp seal is numerous and common, a bit smaller than the grey seal, but with even more bristly whiskers, detecting any movement in the dark.