A
Passion to Save the Paua
This
article was originally published in the Otago Daily Times 26 March
2005
This bay is prime paua habitat.
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Andrew
Penniket has been diving for more than 35 years around Fiordland,
Stewart Island, Chatham Islands, Otago and the subantarctic
islands. After studying marine biology at the University
of Auckland, he has spent more than 20 years filming underwater
documentaries for the Natural History Units of TVNZ and
the BBC. He has made documentaries on Otago Harbour, Fiordland,
Kaikoura, orca, octopus, reef.
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WHEN WAS the last time
you tasted paua? Not lately, I would guess. Paua stocks in the
Otago region have been in steady decline for the past 20 years,
and are now roughly a quarter of what they were in the 1970s.
Our humble paua, that
tasty icon of New Zealand gracing postage stamps and crafted into
beautiful jewellery, is now so valuable and in such demand for
export that Asian tourists can come and pay for their holiday
by smuggling back a suitcase load of the frozen delicacy. We are
faced with losing not only a traditional and once-abundant sea
food, but also a part of Kiwi culture.
Why are paua so vulnerable?
It comes down to their peculiar biology. They are a primitive
shellfish - a snail with a flat shell. Their strong shell and
slimy black foot, which is used to create powerful suction to
clamp on to rocks, allow them to live in the most exposed and
wavelashed locations. And for a shellfish they can really hoof
it, a surprising 70m an hour, but only for very short sprints
when chased by a predator, such as the 11-armed starfish.
Most of the time, however,
paua don't move much. By day juveniles hide under boulders and
in crevices, but at night they venture out to graze on carpets
of sea weeds. When they grow bigger, beyond predation by fish,
(90mm plus) paua move into the open, where they wait for currents
to deliver them drift kelp.
Tagging studies by
fisheries scientists have shown that after a year most paua are
found within 100m of their release point. At choice locations
with lots of kelp, paua group together in aggregations - in the
old days numbering hundreds of individuals.
This lifestyle predisposes
paua to overfishing. They are easy to harvest and if an area is
over-fished, they can't just repopulate it by swimming in from
elsewhere, as can fish.
Their means of reproduction
doesn't do them any favours either. Paua are what's called broadcast
spawners. They have separate sexes and each animal simply ejects
eggs or sperm into the sea, with the hope that they may meet somewhere
and fertilise. A large female paua may produce up to 7 million
eggs but the huge dilution factor in the sea means the chance
of fertilisation for each egg is very small.
It's a very ancient
and very inefficient method of reproduction, but the probability
of fertilisation is greatly improved by the way paua gather together.
Paua can sense, by taste, when neighbouring paua are spawning,
which triggers a mass spawning event, known as synchronous spawning.
This is undermined
when paua harvesters target easily-gathered aggregations, leaving
only difficult-tofind individuals scattered through the boulders
and kelp beds. For these individuals, the chances of their eggs
and sperm meeting are many orders of magnitude smaller. Paua divers,
then, are putting at risk the very means by which paua reproduce.
Most paua reach sexual
maturity at about 3-5 years, a year or two before they are legally
able to be harvested (at 125mm shell length). These young paua,
however, produce relatively few eggs compared with older and larger
paua. Most of our current paua fishery is reliant on the reproductive
output of adolescent paua, a situation likened to a farmer culling
all his breeding ewes after each sheep has had its first lamb.
Once fertilised, the
paua egg develops into a tiny planktonic larva which drifts with
the tides for just a week or two. Some experts maintain the larvae
travel only tens of metres, while others give estimates of 5km
or so. Everyone agrees, however, that paua larvae don't move very
far before settling on the bottom - which means that the entire
coastline of Otago and Southland contains hundreds of relatively
discrete populations, reliant on larvae from within their own
neighbourhood.
The obvious conclusion
from this is that once a paua stock has been fished right down,
and in some cases the term "functionally extinct" has been used,
the coastline will not be quickly repopulated from distant, more
healthy stocks. Thanks to marine reserves we now know that crayfish
can easily repopulate heavily fished areas and within a few years
bounce back to large numbers. But paua are different.
Commercial paua fisheries
have been divided by the Ministry of Fisheries into a number of
management zones. Otago and Southland have one large zone, Paua
5D, stretching 400km from the Waitaki River to Te Waewae Bay.
In the 2001-02 fishing year there was a Total Allowable Commercial
Catch (TACC) in 5D of 148.9 tonnes, but this has now been reduced
by 40% to 89 tonnes a year because of widespread acceptance that
the fishery is in serious trouble.
One problem is that
there is an overall quota for an area containing what are probably
hundreds of small populations. It is quite feasible and legal
for a single paua diver to fish a local population to functional
extinction.
It's a case of macro-managing
a fishery on the basis of bureaucratic expediency rather than
any biological rationale. In reality, the management of paua should
operate on a scale compatible to the ecology of the animal.
Reducing the commercial
quota is a start but already some commercial paua divers are saying
it is too little. Compounding this is an unknown level of poaching,
for which fisheries officials have guessed an allowance of 20
tonnes, and an unknown recreational harvest (estimated at 18 tonnes
based on 5-yearold data from diaries kept by volunteers recruited
in a nationwide telephone survey).
This is hardly robust
data on which to base the management of one of our most valuable
and vulnerable sea foods.
Like many reef creatures,
paua can live a long time, a strategy of living that is an insurance
policy for animals whose breeding success varies from year to
year. When a population is under constant high fishing pressure
it may take only one or two years of failed breeding or recruitment
to send it spiralling into a non-recovery mode.
Paua, of course, are
not alone on the reef. The reef is a constantly changing ecosystem
and fishing pressure over recent decades has greatly reduced the
density of key predators, such as blue cod and lobsters. This
may have helped paua to some extent, but it has mostly benefited
kina. Increased kina numbers decrease the coverage of kelp, creating
what are known as kina barrens. Some reefs have been denuded by
kina, leaving nothing for paua to eat. In the Goat Island Marine
Reserve, where predators such as snapper, blue cod and lobsters
are now flourishing, kina have declined and the kelp forests have
returned.
Unfortunately, we cannot
gauge the impact of kina on paua in the Otago or Southland region
because not a single square metre of reef is protected anywhere
in the Paua 5D zone.
Good science requires
control areas where fishing is excluded to gauge such events as
reef interactions and the impact of fishing. Protected areas are
also important to discern what may be natural fluctuations in
breeding, recruitment, growth and mortality. None of this research
is possible in Paua 5D because there are no marine reserves.
What hope is there
for a slow moving, slow growing animal that lives in easilylocated
groups? Not much, and even less for the average Kiwi looking for
a feed of paua. At the moment some areas are closed to commercial
paua fishing, but no statistics are available on what proportion
of coastline they cover nor, more importantly, what percentage
of paua habitat they cover.
There are some voluntary
non-commercial take areas but these are still harvested by recreational
divers, who of course target easily-gathered aggregations of breeding
paua. Suggestions of rotational temporary closure of some areas
to allow stocks to rebuild before being reopened to fishing hold
considerable merit, but neither the Ministry nor paua divers are
taking it seriously.
At the moment the only
definite tool we have for conserving paua is the outdated Marine
Reserves Act 1971. Under this legislation no marine life can be
taken except for the purposes of scientific study.
Paua poaching is a
major problem that will continue as long as the prices are high
and poachers can get away with it. In January, there were 20 incidents
relating to paua offences detected in Paua 5D alone. Poachers
do not respect size restrictions and may represent the biggest
threat of all to the future of paua.
The best strategy to
counter poachers is increased surveillance, and the best option
for that is to place marine reserves at popular locations and
tourist destinations. This gives the multiple benefit of public
enjoyment and education, increased revenue from tourism and importantly,
many extra pairs of eyes to watch for unusual activities. Obvious
places in Otago are parts of Shag Point, Moeraki, Otago Peninsula
and the Nuggets. These current-swept promontories would also have
the best chance of spreading paua larvae far and wide to recolonise
depleted stretches of coast.
Otago and Southland
have suffered the greatest decline in paua fisheries and it is
also the only region without a marine reserve. Yet marine reserves,
with complete no-take regulations, offer the best hope for paua
conservation. No other option will protect the dense groupings
of paua necessary for efficient and reliable breeding.
Without marine reserves,
paua are almost certainly destined to be a dwindling memory.
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