Action: Designate a Marine Protected Area and prohibit dredging
Key messagesRead our guidance on Key messages before continuing
- One study examined the effects of prohibiting dredging in marine protected areas on subtidal benthic invertebrates. The study was in the Firth of Lorn (UK).
COMMUNITY RESPONSE (1 STUDY)
- Overall community composition (1 study): One paired, replicated, site comparison study in the Firth of Lorn found that sites inside a protected area that had been prohibiting dredging for approximately 2.5 years had different combined invertebrate and fish community composition compared to unprotected dredged sites.
POPULATION RESPONSE (1 STUDY)
- Overall abundance (1 study): One paired, replicated, site comparison study in the Firth of Lorn found that sites inside a protected area that had been prohibiting dredging for approximately 2.5 years typically had greater combined cover of bryozoans and hydroids (combined) compared to unprotected dredged sites.
Fishing can impact subtidal benthic invertebrates through species removal or habitat damage from fishing gear entering in contact with the seabed (Collie et al. 2000). Mobile fishing gear such as towed dredges, involve towing a heavy steel frame along the bottom of the seabed, and as such are known to be particularly damaging. They are used for instance in the harvest of bivalves (e.g. mussels, clams, scallops). Recreational and artisanal bivalve fishing may cause less impact due to the smaller scale of the operations and different harvesting methods used (for instance hand-harvest). Specific areas can be designated as protected, and specific management measures taken to control scallop dredging (Blyth et al. 2002; Boulcott et al. 2014). Inside protected areas where dredging is prohibited, the threat from dredging to subtidal benthic invertebrates is removed, and previously impacted populations are, in theory, able to recover over time (Blyth et al. 2004). However, species and populations are still subjected to the effects of other fishing activities allowed (for instance commercial potting or recreational fishing).
Evidence for related intervention is summarised under “Habitat protection – Designate a Marine Protected Area and prohibit the harvest of scallops”, “Designate a Marine Protected Area and prohibit all towed (mobile) fishing gear” and “Species management – Cease or prohibit the harvest of scallops”. When this intervention occurred outside of a marine protected area, evidence has been summarised under “Threat: Biological resource use – Cease or prohibit dredging”.
Blyth R.E., Kaiser M.J., Edwards-Jones G. & Hart P.J.B. (2002) Voluntary management in an inshore fishery has conservation benefits. Environmental Conservation, 29, 493–508.
Boulcott P., Millar C.P. & Fryer R.J. (2014) Impact of scallop dredging on benthic epifauna in a mixed-substrate habitat. ICES Journal of Marine Science, 71, 834–844.
Bull M.F. (1989) The New Zealand scallop fishery: a brief review of the fishery and its management. Edited by: MLC Dredge, WF Zacharin and LM Joli, 42.
Collie J.S., Hall S.J., Kaiser M.J. & Poiner I.R. (2000) A quantitative analysis of fishing impacts on shelf‐sea benthos. Journal of Animal Ecology, 69, 785–798.
Schejter L., Bremec C.S. & Hernández D. (2008) Comparison between disturbed and undisturbed areas of the Patagonian scallop (Zygochlamys patagonica) fishing ground “Reclutas” in the Argentine Sea. Journal of Sea Research, 60, 193–200.
Supporting evidence from individual studies
A paired, replicated, site comparison study in 2009 of nine sites in three areas of sandy and rocky seabed in the Firth of Lorn, Scotland, UK (Boulcott et al. 2014) found that sites inside a protected area that had been prohibiting dredging for approximately 2.5 years typically had greater combined cover of bryozoans and hydroids and different combined invertebrate and fish community composition compared to unprotected dredged sites. In four of six comparisons, sites inside the protected area had higher cover of bryozoans and hydroids compared to dredged sites outside (inside 43 vs outside 34%; 25 vs 15%; 21 vs 10%; 22 vs 9%). In two comparisons, cover was similar inside and outside (19 vs 14%; 52 vs 54%). Community composition varied across the three areas, but within each area was always different in the protected and dredged sites (data presented as graphical analyses). Part of the Firth of Lorn was designated as a Special Area of Conservation in March 2005 and closed to scallop dredging in the boreal spring of 2007. Three areas (25–89 m depth) along the boundary of the closed area were selected. In each area, one site on each side of the boundary (i.e. one inside the closed area, one outside) was surveyed in May and again in July–August 2009. Invertebrates were surveyed using a camera at 30–40 sampling stations/area. For three photographs/station/survey, the combined area covered by erect bryozoans and hydroids was measured, and all animals (24 invertebrate species; combined with one species of skate and one group of fish species) identified and counted.