Impacts on other species

Impacts on habitat

Impacts on other shore users

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. 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 as well as by direct removal. Collection does not take place throughout the year and recovery of populations of this common species is considered to be relatively swift.

The other bait species are not under serious threat from collection either, although their populations may be depleted. They are usually common (i.e. mussels, winkles, limpets Patella species and slipper limpets Crepidula fornicata) or only a small proportion of the population is available for exploitation, because the species mainly occurs in sublittoral areas. McKay and Fowler (1997 a) review the collection of mussels from the shore in Scotland, which is not considered to pose a significant impact on stocks. Hand collection of winkles targets the largest individuals, which are often those no longer contributing to recruitment because of infestation by flukes – in many populations it is the winkles in their first reproductive year that provide the main source of eggs and larvae. Provided that small winkles are not removed from the shore, the rate of recruitment to the population will barely be affected by collection (McKay and Fowler 1997 b)

It is possible that collectors from other ethnic backgrounds may increase collection pressures on these and other shoreline species in future for personal use. Appendix 1 lists other species that may be targeted in future.

Boulder turning and removal of large algae during peeler crab or winkle collection has a serious effect upon the flora and fauna of rocky shores. A rich under-boulder fauna is associated with stable boulder shore habitats. Sponges, coelenterates and ascidians encrust the undersides of rocks, with numerous other mobile invertebrates (worms, crustacea and echinoderms) sheltering here. These communities are dependent upon the shelter provided by this habitat. Seaweeds and a range of dependent fauna are found on the upper surfaces of the boulders. When boulders are overturned, the algae on the (formerly) upper side are smothered and the underboulder communities exposed to predation, wave action and desiccation. On heavily used shores, boulders are so regularly turned as to severely reduce their species diversity. Liddiard et al. (1989) noted that there was a marked reduction in the diversity of species recorded on rocks at disturbed sites, in comparison with undisturbed control sites.

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. Very heavy depletion of crab populations as a result of collection could have unforeseen ecological effects. Studies on the impact of winkles as important grazers in the intertidal were reviewed by McKay and Fowler (1997 b).

The impact of boulder turning on this 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.

Archaeological remains such as drowned field walls and fish traps may be damaged and dismantled by collectors in some areas. The appearance of the shore and its value for field studies is also affected by extensive collection.

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