Bass reach maturity at 4-6 years of age (35-40 cm) and may continue to spawn
for a further 20 years. The main spawning season extends from March in the
western English Channel until June off North Wales and the Southern North Sea.
Bass especially males will be aggregating off the South Cornwall coast prior to
March and the aggregations move further up the English Channel as the season
progresses.
Eggs are first found well offshore (outside 12 mile limit) in February (early
spawners) and appear closer inshore in May and June (but still 3 miles or more
offshore).
The larvae adopt a typical young bass lifestyle in the brackish water of
estuaries 2-3 months after hatching. It is likely that the offshore spawning
produces the young bass of 15mm upwards seen in estuaries of southern England
in June/July. The mechanism by which larvae enter the nursery area is not
known. These 'O'group bass move progressively nearer the mouth of estuaries as
they grow and are found there during there first autumn and winter.
Juvenile bass are slow growing compared to most roundfish species, reaching approximately 33cm (0.9 lb) after 4years and 41cm (1.5 lb) after 6 years. Differences in the growth rate of different year classes occur and water temperature is an important factor. Once mature they increase steadily in weight. After maturity females tend to grow faster than males and fewer males are found is bass of 11 lb upward probably due to higher mortality.
Note .This aspect of bass biology which involves the tagging of fish needs further study.
Devon and Cornwall
Most recaptures were within 20 miles of release (mainly by anglers), of the
others those released around start point tend to move westward during summer
autumn and winter and possibly eastward in spring.
The Solent and Dorset
Very few recoveries beyond 50 miles.It seems that bass of 3-6 years old move
trough the Solent towards the west in summer and autumn and remain or return to
same locality in subsequent summers.
Thames Estuary
It appears that the bass population is present chiefly between May and October
and some fish travel through the southern north sea. During the autumn the
large bass move towards the English Channel with a high proportion of adults
reaching the western channel.
The West Coast
A large proportion of adults undergo extensive migrations to the north and
south each year, as far as from North Wales to the western English Channel.
Electrophoretic analysis of tissues for 5 enzyme systems indicated no evidence of more than one genetic race in 1987. (Modern DNA analysis is now available for future studies and is more sensitive).
Bass of up to 3 years old remain close inshore in spring and summer,
usually in estuaries and move into deeper water close by during the winter. As
they approach maturity they leave the nursery areas and undergo regular
seasonal migrations eastward and northward as the water warms in spring and to
the west and south as it cools in the autumn. The movements tend to be longer
as the fish reach ages of the first spawning (4-6 years). Very very few bass
under 32 cm have been recaptured more than 3 miles offshore but of fish over 42
cm a significant number (29 out of 184) have been recaptured outside the 12
mile limit.
Local declines in catches of large fish in areas such as Portland Bill may be
due to depleations of 'isolated' adult populations which are only replenished
as maturing fish enter the area and gradually re-establish an adult population
(most likely with a large year class).
The international offshore fishery for bass started in the early 1980s. Between 1989 and 1993 this fishery took place mainly on the Trevose Head grounds, though more recently it has taken place mainly between December and early May 10-40 miles south of Lizard and Start Point. In January to March 1997 it was estimated an average of 20 French and 3 Scottish pelagic pair teams were fishing off Start Point and the Lizard. In 1998, 63 individual vessels were sighted. Over the last 11 years there has been an almost doubling of the number of vessels engaged in the fishery.
The inshore bass fishery around England and Wales relies on fish moving out of estuary nursery areas. The fishery also benefits from adult fish which have returned inshore after spawning. An estimated 180-430 full - time boats and 1300-2000 part-time are involved with a marked increase in full-time boats since 1992, particularly in the southwest and west. The fishery is mainly between April and October and small landings in November and December.
French pair trawl landings: Estimates indicate 500-1000 tonnes were taken in 1990/91 and 150-650 tonnes in 1992/93, whereas in 1996/97 a catch of 2800-5000 tonnes were taken by this fleet in area VIIe alone. Between 400 and 1600 tonnes were landed in 1998.
UK landings: Overall, landings per unit of fishing effort (which provides an index of abundance for the fishable bass population) in the UK inshore fishery have fluctuated around the average level from 1985-1996, with no clear trend, except when the exceptional 1998 year-class recruited to the fishery and catch rates trebled. Annual landings by the UK fishery as a whole were around 600 tonnes between 1985 and 1992, increased to over 2,700 tonnes in 1994 and fell back to around 1,400 tonnes in 1995 and 1996. The UK offshore pair-trawl fishery reported landings of 43 tonnes in 1998 but some 226 tonnes were landed by this fleet in 1999.
At least two bass 'stocks' are found in the Channel, one which over winters in the Channel and spawns there as the adult fish move east and north in spring to feeding grounds along the English coast and in the North Sea, and another which spends the winter around Cornwall and moves north on the west coast, spawning in the Bristol Channel in spring. The relationship between these stocks is important for fisheries management.
Please see summary of report on sampling and tagging 1999/2000