Publication Abstract

Crab and lobster: have we reached the critical point? 

(Based on an article first published in Fishing News, 10 September 1999)

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.

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.