Another Life: A prickly ocean bonanza

A rather pretty little fish with quite the wrong name keeps swimming into my attention. "Boarfish" isn't at all what Linnaeus had in mind in coining Capros aper from the Latin, though what's exactly goatlike, either, about its prickly presence or tubular snout is hard to see. The Cornish fishermen, who've known it longer than we have, call it the Zulu fish, which seems to speak for the sinuous, orange lines that bar the male's flanks in the mating season. Not that goats or boars ever glowed with such bright vermilion and silver — or even the tribal Zulus, to my knowledge, in Britain's Boer War.

These diminutive fish, swimming vertically in big, tight-packed, ball-shaped shoals like some you’ve seen underwater on telly, are heralded as a special gift from a warming ocean to the trawlermen of Killybegs, Co Donegal. Once regarded as a minor nuisance in mackerel hauls, where their spiny dorsal fins damaged the other fish, a dramatic explosion in numbers has made them a staple catch.

As yet another survey vessel, chartered jointly by the Marine Institute and the Killybegs Fishermen's Organisation, sets sail next month to study their abundance and life-cycle, the home port is completing the world's largest bio-marine ingredients plant to process some 50,000 tonnes of boarfish. In partnership with Norway's Biomarine Science Technology (BST) it will pulverise these shiny, 23cm miniatures into their constituent proteins, oils and calcium as food ingredients or athletes' energy supplements.

Alternatively, as An Bord Iascaigh Mhara advertises, the fish's "amiable qualities" make it "perfect for eating off the bone". Headed, gutted, skinned, finned and pan-fried or breaded for tapas, it becomes, as BIM's sales leaflet promises (in a 500g bag, blast-frozen), "an excellent option for 'straight from the sea'." Such morsels were handed round by fisheries minister Simon Coveney at China's last big seafood bazaar.

All this has to be preferable to the fish's current fate, which is to be landed abroad for mincing into fishmeal, food for farmed salmon. The Killybegs Fishermen's Organisation, working with the Marine Institute, has, to its credit, been taking the ecological issues seriously. By the time it contracted UCD biology graduate Dr Edward Farrell five years ago to study this still unexamined fish, the Irish catch had risen in a decade from 120 to 137,500 tonnes. As the EU brought in precautionary controls, the need for proper knowledge became clear.

The boarfish feeds mainly on zooplankton, sucking it in by pouting out its tube-like mouth. The trigger for its exponential increase seems to have been the warming of the ocean in the Bay of Biscay and the Celtic Sea, especially in the spawning season. This increased food supply, raising stronger boarfish with high survival rates and reproduction, in waters where the fish’s spiny dorsal and anal fins found few predators.

Its nursery areas are close to the seabed on the Atlantic shelf. After spawning, the adults form dense shoals over seabed banks or at the shelf edge and these have spread spectacularly northwards, perhaps following the drift of particular zooplankton species.

Boarfish particularly like Calanus, a crustacean zooplankton whose northward shift is attracting other warm-water species, such as sardines, anchovies and sea bass.

The survey next month will use echo-sounding to plot and sample boarfish shoals from the north-west of Ireland to the Atlantic shelf edge off Brittany. The western sweep will be carried out by the Marine Institute's big RV Celtic Explorer. A trawler, chartered jointly with Killybegs, will take over the survey southwards for another 21 days. This follows the pattern set first in 2012, when the map of boarfish abundance showed huge shoals clustered at the edge of the Porcupine Seabight, due west of Connacht, and more at the shelf-edge of the southern Celtic Sea.

The vessels’ trawls also snared boarfish for scrutiny and the extraction of 600 otoliths – the tiny “earstones” of fish – to read their ages and growth-rates, like the rings in a tree.

How boarfish fit in into the ecosystem of the ocean is still virtually unknown. It could easily eat lots of eggs and larvae of commercial fish, but seems not to.

As to potential predators, its spines seem not to deter conger eels, thornback ray, barracuda and swordfish in the Azores, where they may not have a very wide choice. Around those islands they are also targeted by diving seabirds, especially when shoals are driven near the surface by attacking barracuda.

Given warm conditions and plenty of food, boarfish keep spawning again and again for long periods – in aquariums, males have spawned every day and females every two or three days over nine consecutive months.

In the ocean, as Dr Farrell reports, spawning is restricted to the summer months, with a peak in July. How far boarfish sustain their “enhanced recruitment” rests in the capacious lap of climate change.