Return of the Fur Seal

Forest and Bird, Issue 312, 1 May 2004, Page 12

Return of the Fur Seal

DAVE HANSFORD.

It has taken 200 years for the fur seal to recover perhaps five percent of its former numbers yet some would have it culled

again, writes

ach June, millions of hoki leave their grounds around New Zealand and make unerringly for the dark depths of the Hokitika Canyon. In the cold mid waters between 300 and 700 metres, they swarm in nuptial fervour. By the month’s end, each female will have released over a million eggs. This annual feast of riches has not gone unnoticed by others. Ashore, along the West Coast of the South Island, female New Zealand fur seals leave their pups in small créches and make the 165-kilometre journey west to the canyon to feed. The hoki teem at a fur seal’s theoretical limit of diving endurance — a limit research has shown they routinely break by plunging to over 270 metres for 10 minutes or more, making them the deepest-diving fur seals studied anywhere in the world. But their feats pale before the efforts of humans. Around early June, up to 60 New Zealand and foreign trawlers arrive at the grounds, shooting nets in midwater with a gape the size of a rugby field — lengthwise, they would comfortably hold a 14-storey building. Prior to the 1970s, any hoki they caught would have been dumped at sea, but today it’s New Zealand’s single most valuable species.

Fur seals can only pick off the shallowest stragglers of the swarming hoki — the vast bulk are beyond their reach — so they’ve found it much easier to steal a meal from the fishers, who will tell you that the seals can distinguish between the sound of a winch in freespool setting an empty net, and the groan of one hauling a full net to the surface. Which is when they pounce. As the net wallows in the trawler’s wake, the seals dash inside before it can be drawn closed. Once the net is shut, however, there is no escape. The lucky ones are drawn aboard, although they may be severely injured; the others drown or are crushed. In a workaday situation, a net may snare a couple of seals for every hundred tows, but in the rare instance when the machinery fails and the net is left trailing off the stern, seals can die in their dozens. This ‘bycatch’ is not confined to the Hokitika Canyon; seals also die, though in far fewer numbers, in fisheries on the Snares Shelf, the Bounty Islands, the Chatham Rise and Cook Strait among others. The chief executive of the Hoki Fisheries Management Company, Richard Cade, says the industry is working hard to reduce fur seal deaths. Trawler crews have changed the way they work to try to stop seals entering their nets. For instance, if seals are present, the vessel may steam flat-out for another 15 minutes before shooting the gear. Boats are instructed not to make any wide turns while the mouth of the net is still open. Crews have found it helps to keep deck lights to a minimum, and dumping offal overboard is a banned practice. But seals still get in, and hopes for them rest with an invention called a SLED or Sea Lion Excluder Device. In simple terms, the SLED is a steel grate installed near the end of the net that allows the catch to pass through, but directs trapped seals upwards and out of the net through an escape hatch. It’s been 12 years in the development, and Richard Cade says it still needs more work. The challenge has been to make sure that both seals and the valuable catch haven't been damaged against the grate. The SLED was originally designed to save New Zealand sea lions however, and Richard Cade says that because fur seals are smaller animals, the device needs a narrower grid. But hoki can grow to a metre in length and end up getting mashed against the steel bars, raising what he calls ‘fish quality issues. ‘Tm not sure how we solve those, but I want to find a solution that’s good for industry and seals. We are having some effect, but we haven't got as far as we'd like’ So while SLEDS have been tested on fur

Life History of the New Zealand Fur Seal

here are two discrete populations of New Zealand fur seals: one around the New CT coast and outlying islands, including the subantarctics; and one in southern Australia. There is growing evidence for two genetically distinct subspecies, although their ranges overlap, prompting calls for a re-evaluation of their taxonomic status. Adult females grow to about 1.2 metres in length and weigh around 40 kilograms — a petite frame beside the bulls, which can reach 1.6 metres and tip the scales at 160 kg. Fur seals are not quite at the top of the food chain; large sharks such as white pointers and orca killer whales routinely hunt seals. New Zealand sea lions have been seen taking juvenile fur seals in the subantarctic islands. They are itinerant hunters, following seasonal flushes of productivity and switching between a wide range of prey as abundance fluctuates. They take lanternfish, anchovies, jack mackerel, barracuda, and hoki, often hunting at night (those big round eyes aren't just there to make the pups look cute), when squid rise to within their diving range. In summer, they hunt over the continental shelf or near its slope diving continuously from sundown to sunrise. In autumn and winter they forage up to 200 kilometres beyond the continental slope, making their deepest dives, routinely beyond 100 metres. Outside of the breeding season, fur seals gather at haul-out grounds around the country, some well north of their breeding range. While a hauling ground can take any form, fur seals have very specific preferences for rookery (breeding) sites, normally along exposed west or northwest coasts, with a supply of rock pools for pups to learn to swim in. Males are sexually mature after five or six years but are unlikely to command a territory for at least another three. A ‘beachmaster’s’ reign may last for five years, during which he will mate with every female he can attract. From early November, bulls arrive at the rookeries to claim territory, which they then defend vigorously. The cows arrive a month later. Females reach sexual maturity between the ages of four and six, normally bearing a single pup every year until their death — on average between 14 and 17 years. Ninety-five percent of pups are born in December. A week later, the cows mate again but the fertilized egg will not implant in the uterine wall for another three months, bringing gestation back to around nine months. By mid-January, the rookeries are emptying fast but cows alternate foraging trips of one to 20 days at sea with periods of one or two days ashore to suckle their pups for around another 300 days. Pups start to feed on solid food before weaning. They spend a lot of time playing with other pups and ‘toys’ such as seaweed and reef fish, learning hunting skills for later life. Once weaned, pups disperse alone — juvenile fur seals have been found over 1000 kilometres from their natal rookery — and most reports from the public of ‘lost’ or ‘sick’ animals start coming in around this time. Although fur seals have had full protection since 1897 (with a couple of brief, local lapses), they have recovered only to an estimated five per cent of their former numbers. They are also covered by the Marine Mammal Protection Act and sections of the Fisheries Act, but continue to fall victim to trawl nets, longline hooks, discarded plastic rubbish and dogs on land.

seals, they are yet to be used in everyday hoki fishing, and Richard Cade says they may never be. He says the future safety of fur seals, in the hoki fishery at least, will probably rest with individual skippers and a code of practice. ‘That’s not good enough, says Forest and Bird’s senior researcher Barry Weeber. ‘I don’t think a code of practice is going to work. In reality, it’s the same code of practice that’s been around since 1989, and all it’s achieved is better gear deployment. He says the industry has to try harder. "We think the industry’s been very slow; they could have been more proactive than they have been. Nevertheless, fishers point to the fact that fur seal bycatch has been coming down in recent years, but that trend comes with a caveat — so has the overall fishing effort. The total allowable commercial catch for hoki has fallen from 250,000 tonnes in 1997 to 180,000 last year. That means fewer trawls and, quite simply, fewer ‘seal/vessel interactions. In all, the National Institute of Water and Atmospheric Research estimates that around 12,000 fur seals have died as fishing bycatch in trawl and longline fisheries between 1990 and 2000. Nobody knows whether this is hurting the fur seal population as a whole, because it is simply not known how many there are. A census in the early 1970s estimated a national population of 39,000 animals, but

many have questioned the accuracy of that survey and nobody has attempted one since. Barry Weeber says hard evidence shows fur seals are making a strong comeback at the Bounty Islands, and casual observation reports smaller gains in Otago, Marlborough, Nelson, and Wairarapa. He says there are probably at least 60,000 seals around our coasts today. ‘But for the big rookeries in Fiordland, the Antipodes and Stewart Island, not much has changed in the last 20 years. omething has definitely changed along S« West Coast of the South Island, next to the Hokitika Canyon hoki fishery. Long-term studies of breeding rookeries at Cape Foulwind, near Westport, and at Wekakura and Taumaka on the Open Bay Islands show that pup births are falling further every year, as are pup weights and survival. The rookeries are shrinking. Hugh Best of the Department of Conservation says that the fishery is responsible for the deaths of adult females that still have dependant pups ashore. That puts the rookery under pressure, but the knockout punch, he says, comes when bycatch coincides with an El Nino year. When the immense climatic contradiction known as the El Nino Southern Oscillation kicks in, strange things happen at sea. Fur seals make the long journey to their feeding grounds to find the huge schools gone. Cold water holds more nutrients than

warm. When El Nino drives cool waters before it, the fish go with them, moving further south or simply swimming deeper, beyond the seals’ reach. The thermal inertia of water means it can take months to return to normal. After an El Nino, Best noted that pup condition and survival plummeted as their mothers returned with empty stomachs. Furthermore, females vary as to when a blastocyst — a pre-embryonic cluster of cells — can be implanted in the uterus and there’s good evidence that a stressed cow may not bear young the following season. To understand the impact of this we need to know more about fur seals’ fidelity to their home rookery. We know that they travel vast distances — more than 750 kilometres — between breeding seasons. But if they remain loyal to their natal rookery, the West Coast colonies could conceivably fail altogether if not topped up by immigrants. Elsewhere, fur seals have come under fire, sometimes literally — from some fishers who insist that they compete for valuable commercial species and must be controlled. An outspoken proponent of a fur seal cull is the managing director of Talley’s Fisheries, Peter Talley. He maintains an ‘exploding’ seal population is ransacking fish stocks, taking 300,000 tonnes — more than the total commercial take — every year, including

8400 tonnes of hoki, worth between $18m and $20m. "They’re expanding at an ever-increasing rate. Population estimates of 60,000 are way out — by a factor of three or four, Peter Talley claims. ‘I reckon there are 60,000 in the northern South Island alone’ Peter Talley says seals pillage not just hoki but ling, crayfish, blue cod, red cod, paua, blue fin and yellow-eyed penguins. ‘A seal needs five kilograms a day to maintain its energy, but it will kill three times that because we’ve seen them biting the belly out of a fish, taking the roe and leaving the rest, he says. Again, there are few hard facts to back such assertions. A 1991 Department of Conservation study analysed seal scat and regurgitated matter at rookeries around the South Island. By identifying fishes’ earstones, or otoliths, that survive digestion, researchers found that hoki made up less than four per cent of the seals’ diet. By far the greatest component — 79 percent — was various species of lanternfish, a noncommercial midwater fish. Anchovies came in a distant second. A second study of Cook Strait haulouts by a Department of Conservation researcher, Bruce Dix, found similar results. Despite their proximity to abundant crayfish stocks, he found no trace of them in seals’ diets. Bruce Dix says their teeth are simply not designed to deal with such prey, and cites diet studies that found that seals instead target mainly smaller fish that aggregate in large shoals, particularly in the surface layers at night. Peter Talley disputes the otolith findings. ‘Seals don’t eat the heads of large fish, so why should earstones turn up in their faeces?’ Bruce Dix disagrees. He says he has recovered otoliths of ‘some very large fish’ in the course of his studies.

Nevertheless, Peter Talley wants to see seals ‘controlled’, but when pressed, he argues first for an accurate census ‘So we can sit down and talk about it with science, not emotion? here is little doubt that fur seals are steadily reclaiming their former breeding grounds. With every passing year, it seems, what were once North Island winter haulouts now clamour to the bawl of pups. Bruce Dix agrees that the fur seal population is increasing, but only steadily. ‘Not at the rate Mr Talley claims. He ignores the fact that the fur seal population is itinerant and highly mobile. They will move to areas of high productivity — just like fishers.’ The Titi Islands off Stewart Island are an example where the muttonbird harvesters of Ngai Tahu are complaining that seals are rampaging through their traditional gathering grounds, trampling vegetation and titi burrows, and menacing people as they go about their ‘customary take’ of muttonbirds. This has prompted a few to join the call for a cull, but both Ngai Tahu and the Department of Conservation are quick to distance themselves from such a suggestion. While the two are in discussion over the fur seal problem, any measures to be built into an upcoming co-management plan for the islands will most likely involve only passive management such as fences. Southland Conservator for the Department of Conservation, Kevin O’Connor, says we're simply seeing a return to a long-forgotten status quo. ‘Seal numbers crashed as a result of the sealing industry, he says. ‘In the intervening 200 or so years, plants and titi took over where the seals were. We’re now seeing a return to a more natural situation’ He says the department has no concerns ‘from an ecological perspective’ but is

sympathetic to birders living amongst seals, ‘seeing the loss of productive burrows and of vegetation that have both been there since before living memory: While the Minister of Conservation, the Hon. Chris Carter, is quick to commend fishers for their efforts to reduce fur seal bycatch, he says there’s no justification for any form of population control. ‘Fur seals are a protected species and as such we should be celebrating their gradual recovery in numbers, the Minister says. ‘Their impact on stocks of commercial fish species is negligible: The devil lies in the lack of detail; everyone — fishers and conservationist alike — agree on the urgent need for an accurate census, but the Department of Conservation has no such plans. In fact, research spending on fur seals is about to plummet. Felicity Wong of DoC’s Marine Conservation Unit says it all comes down to priorities. ‘We've got perhaps 13 breeding female southern right whales; fewer than a 100 Maui’s dolphins. Even if I had a marginal dollar — and there is a problem getting marginal dollars — I'd probably spend it on New Zealand sea lions; there are still only 12,000 of them. And there’s the rub. When you're trying to save species down in number to double figures, with budgets restricted to five figures, something has to give. We don’t even know how many seals we had to begin with, but one study has estimated that one and a quarter million watched the first sailing ships hove to. If — and it’s a big if — seals have indeed ‘exploded’ to the levels Peter Talley claims, then our total national population is still less than those killed in a single season during the peak of sealing on the Antipodes Islands. There’s an inherent paradox in the tension between fur seals and people. A sobering number of our threatened species are hovering as tiny remnant populations, and we spend millions of dollars every year trying to drag them back from the brink. But our goodwill, it seems, extends only to those that don’t require us to share the environment — that place no demands, no challenges on us. If we can’t make room — and a few of our fish — available for an animal at just five percent of its former numbers, perhaps we're the real problem. — _ DAVE HANSFORD of Origin Natural History is a writer and photographer on natural history subjects. He lives at Makara near Wellington.