| Environmental Damage |
Boulder
Turning
Stone-turning by hand or with the use of levers at low tide is used extensively for the collection of hidden peeler and soft shell crabs (usually Carcinus maenus, but also small edible crabs Cancer pagurus and other species). Although bait collection codes promote the return of boulders to their original position in order to minimise environmental damage, a large number of collectors are unaware of the code or chose not to practice this methodology.Cryer et al. (1987) noted that replacing a boulder the right way up when searching for crab bait significantly increased the probability of finding crabs under the same boulder on subsequent tides, even when a crab was not present on the first visit. This suggests that the distribution of the population of the target species may be detrimentally affected by changes to the habitat. The impact of boulder turning on habitat has been examined in several studies (Bell et al., 1984; Cryer, 1986; Cryer et al., 1987; Liddiard et al., 1989). In very heavily used areas, close to access points and centres of population, boulders may be turned repeatedly by bait collectors searching for crab. Bell et al. (1984) demonstrated that up to 90% of all boulders in a shore transect at Mumbles Head, Swansea, could be turned within a two week period and some boulders may be turned 40-60 times during the summer. Most boulders (60%) are not replaced in their original position. Larger boulders that are upended and not overturned completely are more likely to be left as they were found. Liddiard et al. (1989) suggested that a minimum of 3,000 rocks are overturned daily during periods of reasonably low tides at both Mumbles and Oxwich. An unknown proportion involves the repeated overturning of the same rocks. No 'serious' collector was seen to replace rocks in their original position, as required by codes of conduct for anglers and collectors. Overturning boulders results in loss of habitat stability and causes significant damage, destroying underboulder, upward-facing and vertical habitats, each of which supports a distinctive community on undisturbed shores. As described above, this causes considerable damage to the species found within these habitats. Large fucoid algae may be removed from their holdfasts to expose crabs or winkles hidden within their fronds. This results in the destruction of their understory habitats, which are important for the shelter provided to small algae and invertebrates, when the algae are washed away by the incoming tide and wave action. Trampling on rocky shores also affects intertidal species composition (Brosnan and Crumrine 1994, Fletcher and Frid 1996, Quigley and Frid 1998). Foliose algal species decline and barnacles and mussels may be crushed or dislodged. Effects may arise from only small numbers of visitors to a shore, and persist for two years or more. No research has been identified to assess the impact of removal of large quantities of shore crabs for bait, on other species that may either be prey items of crabs, or whose diets include large numbers of crabs, but given what was said in the previous paragraph, this is probably limited. Large fucoid algae may be removed from their holdfasts to expose crabs or winkles hidden within their fronds. This results in the destruction of their understory habitats, which are important for the shelter provided to small algae and invertebrates, when the algae are washed away by the incoming tide and wave action. It has been suggested that despite the ubiquitous nature and abundance of the shore crabs, it is possible for heavy gathering of peelers for bait to reduce numbers locally in a popular collecting site during their moult, when breeding also takes place and they are vulnerable and quite easy to locate. Studies carried out on Mussel farms refute this however. Mussel farmers, who actively remove shore crabs from their beds, report that whilst an increase in productivity results, continued trapping is required because repopulation of the area is so swift. It must be remembered that populations of the Shore Crab in European waters can be as high as1000/m2. |
||
| Bolder Turning | |||
| Crab Shelters | |||
| Disturbance
to birds |
|||
| The Solution | |||
| Env Policy | |||
| Env Statement | |||
| The Market | |||
| Shoreline Code | |||
| Biology
of a Shore Crab |
|||
|
