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THOUSANDS of young seabirds are dying in the Shetland isles. The colonies
are of international importance, and the largest in the European community.
This is the sixth successive year that many birds have been unable to rear
their young. The chicks are dying because there are not enough sand eels
for them to eat. Evidence is growing that the recent, rapid development
of industrial fishing of sand eels is to blame. The crash of sand eels was
foreseen by fisheries biologists, but the government did nothing to prevent
it.

No one has yet proved that the shortage of sand eels is caused by the
fishing boats, which takes sand eels for processing into oil and fish meal.
But because sand eels are naturally short-lived, it is inherently difficult
to prove that fishing is causing the decline until after the damage has
been done.

This uncertainty about the effects of fishing suggests that the Department
of Agriculture and Fisheries Scotland (DAFS) should carefully regulate the
early stages of exploitation. Instead, it has provided the DAFS with an
excuse for doing nothing.

Ornithologists first noticed that seabirds were faring badly on the
Shetlands when Arctic terns had a poor breeding season in 1984. Breeding
failed again in 1985 and 1986 all over Shetland. In 1987, the Nature Conservancy
Council and the Royal Society for the Protection of Birds joined together
to try to find out what was happening, funding a three-year study. The work,
by Pat Monaghan, Martin Burns and John Uttley of the University of Glasgow,
confirmed that the chicks were starving to death.

The colonies they studied in Shetland reared no chicks in either 1987
or 1988. The terns were much more successful in colonies away from Shetland,
on RSPB reserves in nearby Orkney and on Coquet Island in Northumberland.
At these colonies, pairs each reared on average between 0.5 and 0.9 young
to fledgling. This year the RSPB’s survey team has found Arctic tern chicks
dead in colonies all over Shetland, and the few surviving chicks are underweight
and unlikely to fledge.

Arctic terns feed by plunging to catch small fish near the surface of
the sea. Along with many other seabirds on Shetland, they feed mainly on
sand eels: small shoaling fish that spawn in sandy sediments in winter.

Sand-eel larvae float in the sea as tiny plankton from February to April,
and metamorphose as they reach a length of 3 or 4 centimetres in April and
May. The young fish of the year, known by biologists as O-group, first appear
in fishing nets in late June and July. Those that escape become sexually
mature when two years old.

O-group sand eels are the main prey for Arctic terns in late June and
July, when their young are hatching. Monaghan and her colleagues have shown
that adult terns on Shetland now find it difficult to provide enough food
for their chicks. On Coquet Island, where breeding success is good, the
terns supply their young with three times as much food.

The number of young Arctic terns produced in Shetland as a whole is
strongly linked to the number of young sand eels in the sea: the number
of chicks that ringers mark every year reflects the estimated ‘recruitment’
of O-group sand eels – that is, the entry of young fish into the stock that
is caught by fishermen. But the relationship between sand eels and terns
is probably more complicated.

The chicks appear to depend almost entirely on the O-group fish brought
in by the parents. But the lack of fish a year older (1-group) early in
the season may prevent adults from gaining enough energy to lay eggs or
to incubate them efficiently. The researchers from Glasgow have weighed
adult Arctic terns, using electronic balances disguised as rocks, and shown
that breeding birds are in poor condition. This may explain why breeding
sometimes fails before the eggs hatch.

Other surface-feeding seabirds that prey on sand eels are also finding
it hard to rear young. In recent years, kittiwakes have been leaving their
chicks unattended on the cliffs for long periods: many chicks have starved
to death or been taken by predators.

In 1986 and 1987, Martin Heubeck of the University of Aberdeen monitored
kittiwake colonies all around Shetland. Breeding success, measured by the
proportion of nests occupied towards the end of the breeding season, has
been low, slumping from 0.69 chicks fledged per nest in 1986 to 0.09 in
1988. Breeding failed completely in the south and east of Shetland, and
partially in the north and west.

Tony Martin, a marine biologist based in Cambridge, has looked at the
percentage of sand eels in the food puffins feed to their chicks. His results
show a drop from between 80 and 100 per cent in 1973 to 1986, down to 19
per cent and 36 per cent in 1987 and 1988 respectively.

Individual fish as well as the total loads brought ashore by puffins
have become lighter in recent years, and chicks have starved in their burrows.
As a result, the 25 000 pairs of puffins at the Hermaness colony have apparently
failed to rear any young in 1987 and 1988.

Martin has suggested that some species, such as gannets, have been able
to shift their diet as the number of sand eels dwindled. But a range of
other species including red-throated divers, black guillemots, fulmars,
great skuas and Arctic skuas still depend on sand eels. These too have shown
signs of lower breeding success.

What has happened to the sand eels? The commercial fishing of sand eels
started in Shetland in 1974. Landings quickly grew from 8000 tonnes to 52
600 tonnes in 1982. Since then, catches have slumped, and only 4800 tonnes
were landed in 1988.

The Shetland sand-eel fishery is unlike others in the North Sea. It
relies heavily on catches of O-group fish, which become big enough to be
vulnerable to the fishing gear only from July onwards. Other sand-eel fisheries
in the North Sea concentrate on older fish from the previous year, cutting
down on fishing after the end of June.

But until the end of June this year, the DAFS did nothing to reduce
fishing pressure on the Shetland sand-eel stock, despite clear indications
that the fishery was crashing and in the face of warnings from its own biologists.

The department’s position, stated at a meeting of the Shetland Bird
Club in October 1988, has been that fishing has nothing to do with the decline.
It has said the same in answers to parliamentary questions from Labour’s
fishery spokesman, Norman Godman. But as long ago as 1983, a fisheries biologist
at the DAFS, Roger Bailey, gave a clear warning: ‘. . . the dependence of
the fishery on young immature fish makes it very vulnerable to changes in
the level of recruitment . . . and a succession of only two years of poor
recruitment would result in a big decrease in stock abundance and hence
in the productivity of the fishery’.

Bailey added that this would be all the more likely if the intensity
of fishing was to increase ‘significantly above the level of recent years’.
Yet the proportion of O-group sand eels taken by the fishery remained at
a high level or even increased.

At much the same time, a working group of the International Council
for the Exploration of the Seas, composed of government fisheries biologists
from countries around the North Sea, decided that the most effective way
to limit the exploitation of O-group fish would be to close the fishery
at the end of June when the sand eels first appear in the catches. Still
the DAFS did nothing to limit catches.

In 1984 Bailey again warned that high catches of O-group fish reduce
the yield of the fishery and increase the chance of depleting the stock.
In 1986 he repeated his warning: ‘To protect the small sand eels until they
have had a chance to spawn, there is a very strong case for putting a restraint
on catches of the O-group.’

Bailey later reminded the DAFS of his earlier warning that ‘a severe
reduction in the catches in the months of July and August is the only practicable
method of bringing this about’. The DAFS refused to take action until 28
June this year, when it banned sand-eel fishing around Shetland for the
rest of the season.

The Shetland Fishermen’s Association has hosted several seminars on
stocks over the years to examine the advice from the DAFS. It did consider
a voluntary close season to protect O-group fish, but failed to introduce
one. Instead, the association introduced voluntary restrictions on the size
of fish that could be landed in 1987.

These measures banned boats from landing sand eel if more than 25 per
cent by weight were less than 3 inches (7.6 centimetres) long. But most
O-group sand eels are longer than this from the end of July onwards, so
this step would have had little effect.

The sand-eel population has now crashed. The recruitment of O-group
fish was below average between 1984 and 1987, when Arctic terns began to
breed poorly. The indications are that it was low in 1988 and is low again
this year.

Sand eels are naturally short-lived fish, so the total biomass of the
stock and the biomass of the breeding population (the ‘spawning stock’)
are both strongly influenced by recent recruitment – that is, by how many
young O-group fish came into the population in a given year. So the size
of the spawning stock around Shetland is almost certain to fall for the
next two years.

It is notoriously hard to prove that a naturally short-lived species
is being overfished. The role of overfishing in dramatic declines such as
those that hit Californian sardines and Peruvian anchovies has become well
established only in retrospect. It is all a question of numbers.

Accurate measures of the abundance of fish are crucial to an assessment
of the effects of any fishery, but especially so in short-lived species
such as the sand eel. Regulatory measures must be implemented rapidly because
the level of recruitment can vary widely from year to year.

The DAFS relies on stock estimates based on ‘cohort analysis’: the method
uses the age structure of commercial catches and assumptions about natural
mortality to estimate the number of fish in an age group or cohort. This
approach enables biologists to estimate the number of O-group recruits very
roughly in a particular year.

The advantage of the system is that the estimate improves as time goes
on, once we know how many 1-group fish were caught in the next year, and
how many 2-group fish were caught in the year after that. So as cohorts
age, their original strength is more accurately known, provided that the
assumptions about natural mortality are accurate. The trouble with this
method is that although it gives a better and better picture of what was
happening several years ago, it may give an inaccurate idea of what is happening
now. The assumptions built into the model, including the crucial ones about
natural mortality, compound the uncertainty.

All these problems are well known to fisheries biologists. In a standard
textbook, Fish Population Dynamics (edited by John Gulland and published
by John Wiley in 1988), J. Csirke of the Food and Agriculture Organisation
discussed short-lived species such as sand eels where recruitment varies
greatly from year to year. He wrote that fisheries should adopt a policy
of prudent exploitation to reduce the risk of collapse. To do this authorities
must set the fishing level below the level estimated to provide a maximum
sustainable yield, and carefully monitor the fishery, preferably using data
that can be subdivided according to month and fishing ground. And the authorities
must take strong action at the first sign of any deterioration of the fish
stock.

The closure of the Shetland sand-eel fishery this year is one small,
belated step. If implemented when Bailey first advised it, in 1983, the
ban might have prevented the crash of the fishery. It might now help the
stocks to recover. However, many fear that it may be too little too late.
Indeed, if fishing is allowed to start again next spring, the O-group fish
not taken during this year’s closed season might simply be taken as 1-group
fish before they have had a chance to spawn.

The DAFS has not proposed conservation measures in the other important
Scottish sand-eel fishery, in the Minch off northwest Scotland. There the
fishery started in 1980, much later than in Shetland, and has grown enormously,
just as the Shetland fishery did. Will the same pattern of falling recruitment
and dying seabirds recur there? What is needed is a better understanding
of what affects the number of sand eels, both as the food supply of breeding
seabirds and as a resource for people to exploit. But it is difficult to
identify who should be responsible for funding such research. Although the
Natural Environment Research Council has recently given Monaghan and her
colleagues substantial funding for more studies of seabirds, who is studying
the fish? All the information on the fish population comes from the statistics
on commercial fishery that the DAFS collects. The department carries out
research on fisheries being heavily exploited, but it rarely studies unexploited
stocks in anticipation of a future fishery, or fish stocks that can no longer
be exploited profitably.

Yet studies of this kind are vital for predicting when we are overfishing
short-lives species such as sand eels. Under the Ramsar convention and the
EC Birds Directive, Britain is responsible for protecting internationally
important populations of seabirds, so it ought to find a way to fund such
research.

The DAFS’ attitude to the failure of seabird colonies has always been
that they are irrelevant. Its responsibility is to regulate the fishery,
not to uphold the British government’s obligations to protect birds.

The lesson seems to be that fisheries should always be exploited cautiously
until we know enough to identify how much fishing they can take without
damaging local wildlife or the long-term future of the fishery itself. But
such a reversal of the current policy of proceeding with exploitation until
it can be shown to be harmful is certain to be opposed by short-term commercial
interests.

Dr Mark Avery and Dr Rhys Green work for the Royal Society for the Protection
of Birds, The Lodge, Sandy, Bedfordshire.