Crab and lobster: have we reached the critical point?
(Based on an article first published in Fishing News, 10
September 1999)
Thirty years ago shellfish
contributed a mere 5% of the total first sale value of our
fisheries. Now the share is an unprecedented 30%.
Dr Colin Bannister, scientific advisor on
shellfisheries at Cefas Lowestoft, discusses why action should be
taken now to manage the important lobster and edible crab
fisheries, together worth at least £21m in England and Wales.
Lobster fisheries
Lobsters are common but not abundant. They occupy shelter at all
stages of their lives, and are mainly active at night in the
vicinity of boulders, breakwaters and wrecks, when they leave these
hideouts to forage and feed. Some lobsters migrate over distances
of 10-30 miles, but most move only a mile or two, and although
potting occurs along most coasts, the stocks are limited in
extent.
The main landings come from the North Sea and the Channel
(Figure 1). Landings from the east coast dominated the 1960s, then
declined in Northumberland, before increasing again in the 1990s
especially in Yorkshire and East Anglia.
Figure 1. Lobster landings in England and Wales 1960 to the
present.
Landings from the Channel increased in the 1980s, especially in
Dorset and Sussex. On the west coast, landings have increased in
South Wales, but dwindled in Cardigan Bay and in North Wales,
Traditional lobster fishermen use 10 m boats and generally work
within sight of land, but in the last ten years the use of keel
boats and fast work boats has extended the fisheries further
offshore. Aided by the increased efficiency of the steel parlour
pot, many fishermen are using more and more pots, and are working
longer set-over times and a longer season.
Edible crab fisheries
Crabs like shelter too but they are more widespread than lobster
and occur at a higher density. Over the last 20 years inshore crab
fisheries in Northumberland, Yorkshire and parts of the West
Country have declined, but offshore crabbing has spread throughout
the western Channel, off the Humber, East Anglia, and South Wales.
Many of the larger mobile crab potters now work 1500 to 2000 pots,
and since the 1960s crab landings have doubled (Figure 2). The
French Channel Island, Scottish and Irish crab fisheries have seen
similar trends.
Figure 2. Edible crab landings in England and Wales 1960 to the
present.
Assessing stocks
When stocks are lightly fished, animals survive quite well into the
larger sizes, but when stocks are heavily fished, fewer large
animals are left. The proportion of small and large animals in the
size measurements is therefore a good guide to the harvesting rate.
When linked to information on growth rate, maturity, and egg
number, size measurements are also used to assess how a change in
the minimum size or the harvesting rate can benefit stocks. Trends
in catch per effort (e.g. from fishermen's log book data) also
indicate trends in the stock.
State of the stocks
On traditional lobster grounds where potting effort is heavy, catch
per effort has been low for a number of years, and large lobsters
are uncommon. In most districts landings depend on animals between
85 mm and about 110 mm carapace length (CL) (say 1 lb to 2 lb in
weight). Sizes are even more restricted on some parts of the east
coast and the eastern Channel. In some areas, lobstermen can still
find large lobsters of 120-150 mm CL on offshore grounds, where
catch per effort is higher, but it is only a matter of time before
the offshore refuges are fished down. The size range on the
traditional grounds shows we could be harvesting over 50% of the
population each year, which is high.
For edible crab, the main size range in the landings varies from
115-150 mm carapace width (CW) in East Anglia, through 125-170 mm
along the north east coast to 140-190 mm CW in the Channel. These
sizes partly reflect regional differences in growth rate, hence the
regional differences in the national minimum size for crab. As with
lobster, landings concentrate on animals just above the minimum
landing size except in the Channel, where the size range available
is wider. Taking into account the regional differences in growth
rate, it appears that we could be harvesting over 60% of a crab
population each year along both the east coast and in the Channel.
This is double the rate estimated by my predecessors in the
1960s.
Minimum landing sizes
A basic principle of good management for crustacea is to set a
landing size (MLS) in order to prevent animals being captured
before they reach maturity. EU Regulation 850/98 will raise the
lobster MLS from the present 85 mm CL to 87 mm CL, but not until 1
January 2002.
For UK vessels, however, national legislation will bring this
size in earlier, on 1 January 2000, which will benefit the stocks
along our coasts. Some sea fisheries committees already have 87 mm
CL lobster bye-laws. As with the previous increase in legal size
from 80 to 85 mm, the new increase should produce two kinds of
conservation benefit.
First, more hen lobsters will mature before they can be legally
caught, and egg number per female at the legal size will be
slightly higher.
Secondly, although landings will initially fall for a year or
two, increased survival and the extra moult increment will increase
them again after two or three years, and, more importantly, mature
stock will increase by 10% to 30%. A higher mature stock is very
important for conservation. These are average figures for a range
of districts. They assume that fishing effort stays unchanged, but
there is concern that if fishing effort rises then the benefits of
raising the MLS will fall.
For edible crab, research indicates that 75% of hen crabs will
mature at 115 mm carapace width (CW) in Norfolk, and at 110 mm CW
in Yorkshire. In the Channel most hens will be mature at 140 mm CW.
EU regulation 850/98 and prospective national legislation will
combine to produce the regional minimum sizes available on the
grounds. The EU regulation is a step forward, applying a crab MLS
to Europe for the first time, and marking the acceptance of
carapace width as a measure. Some EU crab sizes are less strict
than existing UK national legislation, as in the Channel and the
North Sea, for example, so new national legislation aims to either
maintain or increase the present UK crab sizes.
There may be little scope for further MLS changes in these
fisheries. For crab, the proposed minimum sizes are probably as
high as they can go without curtailing some fisheries too severely.
For lobster, to ensure that all hens mature before capture would
require an MLS above 90 mm CL. Cefas knows that in some areas
fishers already fear that the changes to 87 mm will cause them more
losses than gains, so any further increases in lobster MLS will
have to he looked at very carefully indeed.
Are lobster and crab stocks sustainable?
Effective fisheries management ensures that the harvesting rate
leaves enough mature stock at the end of the year to provide for
next year's catch, to maintain egg production, and to offset years
when juvenile survival is poor. Are the present lobster and crab
fisheries sustainable in this way? For lobster, the annual harvest
rate is over 50%. For crab, it is over 60%. Biological models show
that these high harvest rates reduce spawning stocks to well below
a quarter of their unfished level. Juvenile numbers therefore
depend on the increased survival rate that comes when total egg
production is greatly reduced. In the United States, such low
stocks would trigger conservation action, by law.
So far, the numbers of juvenile lobster and crab appear be
holding up in the main UK fisheries, but for how long? There is
nothing to control the number of potting vessels or their pots, so
that overcrowding on the grounds, stock depletion, and the negation
of MLS increases, can all continue.
A female crab produces up to three million eggs, but the major
Channel crab fisheries catch mainly spawning females, which is an
obvious threat to stocks. The spread of effort to offshore stocks
hits refuges of older animals of both crab and lobster, and this is
particularly serious for the lobster, which carries less than
50,000 eggs per female.
Fisheries science is also rather imprecise: we simply do not
know how much extra potting effort can be tolerated before stocks
will collapse. Because of this I believe that we are taking serious
risks. It is as if we are walking towards a cliff edge in the dark.
The margin for error is low, and we can all hear the sound of
breakers below. I suggest that finding the collapse point the hard
way, by letting it happen, is not an acceptable option: prudent
action must now be the way forward.
Balancing act
A balancing act between different viewpoints and obligations is
needed if the shellfish story is to continue. Established fishermen
want to maintain their income, and keep their share of the fishery.
New fishermen, or those working outside the sector, want in.
Processors and the markets will probably settle for stable
supplies. The public and some retailers want to see responsible
fishing. Managers have an international obligation to conserve
resources. Scientists have to advise on what this means, with
imperfect information. With this plethora of interests, where is
the balance point?
Controlling harvest rate
Some fishermen say that juveniles are plentiful on the grounds.
This simply strengthens the case for action: if there were no
juveniles, it would already be too late. Harvest rates must be
controlled, and since the TAC approach is inappropriate for these
fisheries, it must be achieved in some other way.
There is a very good case for reducing potting effort. High
effort produces diminishing financial returns, and a reduction
would increase stocks, produce a higher catch rate, and increase
overall landings and profitability. A simpler and more pragmatic
first step, however, is to prevent potting effort from increasing
further by capping it at present levels. This will not promote
recovery, but it should reduce the risk of stock collapse.
Previous efforts to discuss this approach in 1995 and 1996
failed, but three years on we still stand at a crucial point for
these economically important fisheries. Agreeing to limit effort
now should prevent the pain of much more drastic reductions later.
There may not be another chance.
V-notching
Because lobsters produce relatively few eggs, fishermen and SFCs
are keen to protect hen lobsters by V-notching. In Europe the
benefits of doing this are not fully known, but Cefas scientists
have given their support to national V-notching legislation, and to
regional schemes like the North Eastern SFC V-notching programme.
Such schemes do not control fishing effort, however, and indeed the
prospective benefits of V-notching could be lost if there are
effort increases. Irrespective of V-notching, the case for limiting
effort remains, therefore.
Other conservation information
This article has only dealt with the lobster and edible crab
fisheries. Colin Bannister's Dr Walne Memorial Lecture entitled A
Review of Shellfish Resources and their Management, can also be
found in the Proceedings of The Thirtieth Annual Shellfish
Conference 1999, published by the Shellfish Association of Great
Britain, Fishmongers' Hall, London Bridge, London EC4R 9EL.