Indirect effects

Direct effects - harvesting.

Three categories of fishing activity are of concern: the use of towed gear, the use of static gear, and rod and line angling.

Towed gear is potentially the most destructive, and has been the subject of the most intensive study (MacDonald et al., 1996, and references cited there). Nevertheless most accounts of environmental damage are anecdotal, and controlled experimental studies are only now being evaluated (Lart et al., 1993; Curry & Parrie, 1996; Hill et al., 1997). From the point of view of most CFT biotopes towed gear is generally not a major threat, since the generally steep and rocky substrata are unsuitable for both trawls and dredges. However there are types of towed gear designed for rocky areas - the rockhopper otter trawl, and the Newhaven scallop dredge - and these could pose a risk to CFT communities on gently sloping or level rock, or on mixed substrata - e.g. the low lying bedrock reefs in Papa Stour Sound. All species would be at serious risk from such heavy equipment, especially fragile long-lived ones. Currently there is considerable concern that reefs of the deep sea coral Lophelia are being destroyed by the recent upsurge in deep sea trawling. These reefs are unlikely to be a concern in any of the present SACs, but the risk to CFT biotopes from towed gear clearly exists.

Whilst towed gear may not directly cross CFT biotopes, the activities of dredging and trawling on nearby level bottoms with softer sediments could have effects on neighbouring CFT communities. Towed gear results in the suspension of fine sediment (Jones, 1992), and may leave the sediment considerably coarser in grade than before (Caddy, 1973). Experimental dredging studies off the Isle of Man (Hill et al., 1997) have shown that dredging can double the suspended matter content of the water, and that this effect is likely to persist for several days. The influence of suspended matter on CFT biotopes is discussed in section II.G. Whilst some species are adversely affected by sediment, increase in suspended particulates may benefit filter feeders (Morton, 1977). Off the Swedish west coast it is suspected that various deep rocky circalittoral communities are being affected by resuspended sediment resulting from intense otter trawling (T. Lundälv - pers. comm.). Any other activity increasing the suspended sediment loading, such as dredge spoil dumping, would have a similar impact. Thus the management of SACs must take account of fishing and similar sediment generating activities in adjacent areas.

Static gear is deployed regularly on rocky grounds, either in the form of pots or creels, or as bottom set gill or trammel nets. Whilst the potential for damage is lower per unit deployment compared to towed gear, there is a risk of cumulative damage to sensitive species if use is intensive. Damage could be caused during the setting of pots or nets and their associated ground lines and anchors, and by their movement over the bottom during rough weather and during recovery. Prior to the study by Eno et al. (1996) the impact of pots and creels had received little examination, and was generally considered to be small. They carried out observational and experimental studies on rocky substrata, and found no evidence for significant general community damage resulting from potting. Specimens of the brittle ‘ross coral’ Pentapora foliacea were broken, but the pink sea fan (Eunicella verucosa) bent under the weight of passing pots, and returned to an upright position. Based on these short-term studies potting damage would seem to be limited and specific. However long term damage may nevertheless occur as a result of cumulative sublethal damage to impacted animals, and further study is needed. Large colonies of Pentapora provide habitats for a wide variety of epibiotic species (Bunker & Mercer, 1988 recorded 94 species in 24 colonies), so in certain sites there may be a need to prohibit potting to protect this vulnerable species.

Pot fishing is notoriously difficult to monitor, in terms of both effort and catches, compounded by the fact that many boats operate simultaneously inside and outside the reserve area. In the Skomer Marine Nature Reserve there are an estimated "over 500 pots" in use at any one time over the summer months (Blaise Bullimore, pers, comm.). In the Lundy Reserve a similar estimate of about 500 pots fished has been made (Neil Downs, Devon Sea Fisheries, pers. comm.).

Rod and line angling is the least likely activity to produce incidental damage from the fishing itself - the main risk is damage from the anchoring of the angling boats. Rocky areas are often very popular with recreational anglers, due to the concentrations of fish feeding and sheltering there, and this form of activity can be locally intensive. Frequent anchoring in areas which often experience strong tidal flow is an obvious problem. Furthermore, areas where angling is common can accumulate a residue of tackle discarded after fouling the bottom, which is both unsightly, and a potential risk to divers. Lines have been observed entangling sea fan colonies, which could be at risk of damage.

The overall effects of fishing activity, and of other forms of disturbance, are to encourage a shift from long-lived and slow recruiting species to more opportunistic species. There is always uncertainty whether the original communities will return following heavy disturbance (see MacDonald, 1993, for discussion), but in any case long recovery times are anticipated.

The main traditional harvesting activity in CFT areas has been for crabs, lobsters and crayfish by potting, and by bottom-set tangle or gill nets. The latter also target fish as a by-catch. The obvious effect is the reduction in numbers of the target species, which are an important component of the aesthetic appeal of these communities. The reduction in these large predatory species will also have effects on the rest of the community, but these have not been evaluated in British waters. In South Africa, however, the removal of crayfish has been shown to have striking knock-on effects on the benthic community structure (Barkai & Branch, 1988). In the USA the effect of changes in numbers of crabs and lobsters has been debated (see discussion in section III.B.3).

More recently other CFT species have also been harvested by diving in the U.K. - it is immaterial whether by commercial divers, or incidentally by sports divers, the effects are the same. The sea urchin Echinus esculentus has been harvested commercially (Nichols, 1978). This harvesting was initially for marketing as souvenirs for the tourist trade, with subsequently the possible harvesting for human consumption, mainly for the Japanese market (Comely & Ansell, 1988). This has resulted in over-exploitation in parts of southern Britain, with a development of interest in the Scottish west coast. This activity is concentrated in the shallower infralittoral, but the substantial effects of major changes in urchin density on the plant-animal balance have been discussed above. Other species harvested for the souvenir trade include fan corals, and the large bryozoan Pentapora. Such species can very easily be stripped from an area, with regeneration being a slow process - a result which would not maintain a ‘favourable condition of interest features including typical species’.

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