Several rocky shore species are exploited by man in the UK. The main commercial species
are seaweeds (knotted wrack, Ascophyllum nodosum and kelps, Laminaria spp),
winkles (Littorina littorea), mussels (Mytilus edulis) and edible crabs (Cancer
pagurus). Knotted wrack is traditionally harvested from the sheltered shores of sea
lochs in the Western Isles. It is used in the industrial production of alginates. Kelp
plants are collected from the strand line for use as fertilisers and animal feed. Winkles,
mussels and crabs are harvested primarily for food. Invertebrates are also collected for
use as bait by sport fishermen. Any species of crab which is about to moult
(peelers) or has recently moulted (soft shells) are popular.
Mussels are also used in some areas (Fowler, 1992).
The removal of any species can have unforeseen effects on other members of the
community (Wells and Alcala, 1987). These effects are expected to be greatest when key
species are removed. Seaweeds are responsible for much of the primary production on rocky
shores and are important providers of microhabitat for other species. Winkles are an
important grazer and mussels are a particularly important space occupying species. The
recovery of any population will depend on the degree of exploitation. Mechanical
harvesting of kelps like Laminaria hyperborea by dredging removes the whole plant.
Clumps of Ascophyllum spp., on the other hand, can regrow after careful hand
cutting. Such careful harvesting is necessary since Ascophyllum spp. is slow to
recruit after it has been completely removed. A review of the impact of kelp harvesting is
provided by Wilkinson (1995). Dredging trials for Laminaria hyperborea for alginate
production were successfully carried out in Scotland in recent years but have not
Historically, large quantities of mussels have been harvested from UK shores.
Collecting now occurs at much lower levels (McKay and Fowler, 1997a). Thus the impact is
probably limited to low level disturbance. Substantial winkle collecting still occurs.
This is a largely unrecorded black economy activity. Official figures suggest
that the annual harvest for Scotland amounts to approximately 2000 tonnes. Figures based
on buyers estimates suggest that the annual harvest could be over 4,000 tonnes
(McKay and Fowler, 1997b). Declines have been reported in the winkle population in areas
where it is heavily exploited. Elsewhere in Europe the impact of exploitation of many
rocky-shore species is high. Sea urchins are extensively collected in France, Spain and
Italy, while stalked barnacles (Pollicipes species) are gathered in Spain and
Portugal. Even limpets are harvested in Southern Portugal, the Azores, Madeira and the
Canaries (Raffaelli and Hawkins, 1996). Historically, they were once heavily collected in
the British Isles, as evidenced by various shell middens.
An additional problem associated with harvesting and bait collection is
disturbance. Rocks turned over during the collection of peeler crabs might not be replaced
and the removal of mussels can destabilise neighbouring animals. The impact of any
harvesting or collecting activity will vary depending on the species exploited, how it is
done and to what extent. It is strongly recommended that any such activities occurring in
or close to marine conservation sites should be closely monitored.