This study was carried out during January - March 1999, funded by the MAFF Chief Scientist's Group (CSG) (contract CTS 0891), and in ,Jan -April 2000 under the MAFF MA contract.
A Pilot Study was carried out in 1999 to develop and initiate a sampling programme for the UK winter bass fishery, collecting information on bass catch and effort, length and age distribution in catches, and biological data. Using the experience thus gained, a more comprehensive sampling programme was carried out in 2000, which also included tagging bass on the spawning grounds.
Ten UK pair trawlers took part in the 1999 bass fishery offshore in mid-Channel to the south of Plymouth and landed around 240 t of bass, whilst only 42 t were landed by 8 vessels in 2000. An individual vessel quota (5 t per vessel per week) was set in January 2000 in order to limit excess landings of bass, though catches by Scottish pair teams never approached that level. Bass landings in the winter inshore fishery in the Southwest of England were 18 t in 1999 and 22 t in 2000. Useful information on fishing activity by the French component of the fleet was obtained by direct observation and MAFF surveillance, though details of French catch and effort are not yet available for either 1999 or 2000.
Bass appeared to begin spawning in mid-February and spawning peaked in early March an length, age and maturity data were collected throughout this period. The bass caught in the offshore fishery were mainly in the length range 40 - 65 cm, whereas bass caught at the same time inshore in the western English Channel were generally below 50 cm.
The North-west European bass fishery is important to a wide variety of people. It has generally been prosecuted by small, inshore commercial vessels and private and charter angling boats and shore anglers in the UK, the Channel Isles, France and Ireland. Since the early 1980s, however, there has been a steady development in pelagic pair-trawling for this species in wintering and spawning areas, particularly in the western English Channel (ICES Division VIIe) and also on the Trevose Head grounds in the eastern Celtic Sea (Divisions VIIf,g). Over the last 12 years, this fishery has been prosecuted by an average of 20-25 French vessels operating out of the Biscay ports of Lorient and La Turballe, along with others from Channel ports such as Cherbourg, Granville and St Malo. A few Scottish vessels have taken bass as a by-catch since the early 1980s during the autumn/winter mackerel fishery off south-west England, sometimes staying to fish for bass for a few weeks. More recently, 3-6 Scottish pair teams have been involved in this fishery either switching, over from mackerel and scad after Christmas, or coming to specifically target bass in February, March and April.
Exploitation has increased since the mid 1980s, and UK surveillance and inspection data indicate that 150-650 tonnes of bass were taken by the French fleet in 1992, and 500-1600 tonnes in 1998 (Scott, 1999). These offshore catches are normally made up of mature bass (>40 cm), and the fishery is particularly intensive when these fish shoal to spawn, generally in March or early April (Masski, 1998).
This exploitation of bass by UK vessels fishing in the offshore spawning area has been essentially uncontrolled. There are no direct effort or catch restrictions, although there is an EC Minimum Landing Size (MLS) of 36 cm aimed at protecting juvenile bass which occur predominantly inshore. On the 6th December 1999, the Fisheries Minister announced a new precautionary measure to conserve sea bass. From lst January 2000, a weekly landing limit of five tonnes per vessel was imposed as a licence condition for all UK vessels. Alternatively, vessel owners could chose to be licensed to land up to 15 tonnes a month. The aim was to limit exploitation of adult bass in this fishery until sufficient information was gathered on stock status to advise on appropriate management. These measures were similar to the French weekly quota of 5 tonnes per vessel, which was first implemented for producers' companies' trawlers in 1996 to sustain market prices, and extended in 1997, with the agreement of the European Commission, to all trawlers landing in France between 1 January-30 April.
Adult bass are now perceived by artisanal and recreational fishermen on both sides of the English Channel to be returning inshore in the warmer months in much reduced numbers. In the UK, this appears to be causing inshore commercial fishermen to intensify effort on juvenile bass, thus undermining the existing conservation package (36 cm MLS, 37 inshore nursery areas closed to bass fishing and mesh size regulations for enmeshing nets). These measures were designed to reduce the mortality of juvenile bass and thus improve yields to the fishery and the recruitment to the adult stock. Although there has been a number of above average year-classes in UK waters in recent years, there is a strong association between recruitment and sea temperatures (Pawson, 1992), and a favourable climate change could be masking any effect that directed exploitation of the spawning stock may have on juvenile production and future recruitment.
The combined effects of the exploitation of bass by the seasonal offshore,
inshore and recreational fisheries is an important element in decisions
relating to management of this resource. CEFAS , Lowestoft, has monitored the
UK inshore commercial fishery since the early 1980s, but until recently has had
little access to international catch and effort data. A desk study by CEFAS,
based on aerial surveillance and Fisheries Protection Squadron boarding
reports, provided estimates of the number and distribution of vessels in the
French pair-trawl fleet fishing in the UK sector, along with estimates of
catches, over the period 1988-98 (Scott, 1999). A pilot study, to develop means
of collecting biological information and catch and effort data relating to the
offshore fishery, was implemented by CEFAS in early 1999. This 3-month
programme was undertaken by a sea-going scientist, based at Plymouth, the main
UK landing port for this fishery. In May 1999, a joint proposal for a study to
gain a better scientific understanding of this fishery and it's interaction
with other bass fisheries , was prepared by CEFAS (with France and Ireland) and
submitted for funding under the EC call for studies in support of the CFP. In
the event, the Commission did not make the funds available, but both CEFAS and
IFREMER (France) have been allocated national funds to monitor the winter bass
fishery in 2000 and to tag adult bass. Two sea-going sampling officers were
employed by CEFAS from early January to the end of April to carry out this
work.
This report describes the results of the pilot study and the sampling
programmes in 1999 and 2000, from the point of view of compiling information
which can be used to assess the impact which the offshore fishery on spawning
bass may be having on the stock. These data will be made available to the Study
Group on bass stock assessment set up by the International Council for the
Exploration of the Seas (ICES) in October 2000.
To obtain information with which to ascertain the effect of exploitation by
the offshore fishery on the bass spawning stock in the Channel, and the impact
which this may be having on coastal fisheries.
Following a pilot study in 1999 two graduate marine biologists were employed
for 4 months in 2000 to accompany UK vessels between Jan and April 2000 and
record data on 10% by volume or 200 bass, if less, on each tow. They were to
weigh and take scale samples from 5 bass per centimeter group per month and
sample bass landings from UK inshore fishery on markets and direct from vessels
in port. Also the maturity stages of bass were to be sampled at two week
intervals and tag a total of 500 bass in each of Divisions VIIe and VIIf/g
during commercial voyages.
Updated information on the results of tagging can be found at the CEFAS web site http://www.cefas.co.uk/Basstagging.htm
Sampling the winter bass fishery in the western English Channel for the first time in 1999 produce valuable experience of organising and carrying out offshore sampling and safety procedures. This was used to plan a more comprehensive sampling programme in 2000, and to offer useful advice for IFREMER's own sampling of the French winter bass fishery. Both 1999 and 2000 sampling programmes achieved most of their targets and produced catch, fishing effort and biological data for two years in the winter bass fishery as conducted by UK vessels.
Plymouth proved to be an ideal base for the UK sampling programme, being an active commercial fishing port with a large market which is central to the UK offshore bass fishery, and the base for the Scottish pair trawl fleet during the winter fishery. Good sampling and laboratory facilities (for example at the University of Plymouth), and willing assistance from local MAFF SFI, the staff of Plymouth Trawler Agents and others associated with the port, have proved invaluable throughout the study . Bass were available at a range of merchants for full biological sampling, and it was of great benefit to base the sampling officer at Plymouth for the duration of the winter fishery, rather than for staff based at Lowestoft to pay visits.
Any operation involving working at sea carries an element of risk, both to the sea-goer and for the project itself should prolong severe weather restrict fishing activity and catches. This is especially the case in the western English Channel and Western Approaches during winter, but the large size of the Scottish pelagic vessels reduced the risk of trip cancellations and provided a comfortable and safe working environment for sea-goers. The safety protocol employed by CEFAS for this study proved to be practicable, though some minor modification were recommended for future studies.
Onboard sampling has many advantages compared to sampling at markets. The main ones are:
The data collected were sufficient to provide a full description of the UK winter bass fisheries in terms of disposition of fleets, catching methods and catch and fishing effort. In addition, the biological data obtained provided the first clear picture of the population structure of bass caught on the spawning rounds during the first quarter of the year. The 1989 year class, at 10 and 11 years old in 1999 and 2000 respectively , predominated in catches, fish which had probably spawned for the first time in 1996. The results also showed that the offshore fishery targets fish which are in the process of spawning either because the fish are more vulnerable to capture at this time, or are aggregated, such that larger catches can be taken.
Although a comparison of 2 year's catch at age per effort data would, theoretically, make it possible to estimate the level of fishing mortality on this part of the stock, this requires that the catch and age samples are representative of the whole fishery (UK and French vessels) and that the pattern of exploitation on the stock has been the same in both years. This is clearly not the case, given the steep decline in catch rates by the Scottish pair-trawl fleet between 1999 and 2000, which was not matched by the provisional estimates of French landings. Consequently, it will not be possible to draw firm conclusions as to the overall impact of exploitation on wintering bass stocks until similar data are available (at the ICES Bass Study Group) for the larger French component of the fishery.
The presence of sea-going samplers aboard both UK and French vessels provided a valuable opportunity to tag bass offshore in 2000. It is too soon to know whether these releases will yield sufficient recaptures to show the extent to which bass taken in the offshore winter fishery are exploited/recruit to other fisheries during the rest of the year. A reciprocal scheme, tagging adult bass in a range of summer and autumn fisheries in the UK, Ireland and Channel Islands, is under way at the time of writing, aimed at elucidating the pattern of winter recaptures.