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Providing evidence to improve practice

Action: Designate a Marine Protected Area and prohibit all towed (mobile) fishing gear Subtidal Benthic Invertebrate Conservation

Key messages

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  • Two studies examined the effects of prohibiting all towed gear in marine protected areas on subtidal benthic invertebrate populations. One study was in the Bristol Channel and the Irish Sea (UK), the other in the English Channel (UK).

 

COMMUNITY RESPONSE (1 STUDY)

  • Overall community composition (1 study): One before-and-after, site comparison study in the English Channel found that, over the three years after closing a marine protected area to all towed gears, the community composition of reef-indicative invertebrate species became different to that of unprotected fished sites.
  • Overall diversity/species richness (1 study): One before-and-after, site comparison study in the English Channel found that, over the three years after closing a marine protected area to all towed gears, the number of reef-indicative invertebrate species remained similar to unprotected fished sites.

POPULATION RESPONSE (2 STUDIES)

  • Overall abundance (1 study): One before-and-after, site comparison study in the English Channel found that, over the three years after closing a marine protected area to all towed gears, the abundance of reef-indicative invertebrate species became greater than at unprotected fished sites.
  • Crustacean abundance (1 study): One replicated, site comparison study in the Bristol Channel and the Irish Sea found that a marine protected area closed to all towed gear (only allowing potting) for 33 to 36 years had mixed effects on the abundances of lobsters and crabs depending on species.
  • Crustacean condition (1 study): One replicated, site comparison study in the Bristol Channel and the Irish Sea found that a marine protected area closed to all towed gear (only allowing potting) for 33 to 36 years had mixed effects on the sizes of lobsters and crabs depending on species.

Supporting evidence from individual studies

1 

A replicated, site comparison study in summer 2004–2007 of eight sites in four areas of rocky and sandy seabed in the Bristol Channel and the Irish Sea, UK (Hoskin et al. 2011) found that a marine protected area closed to all towed gear for 33–36 years had mixed effects on the abundances and sizes of European lobster Homarus Gammarus, and three crab species. Abundances of large lobsters (≥90 mm) did not change over time in any areas, where they were similar (1–2 lobsters/line). Abundance of small lobsters (<90 mm) increased in the protected areas by 140% (due to spill-over effects from an adjacent no-take zone; from 2 to 4–7 lobsters/line), but not in the fished areas where abundance remained constant (2–4 lobsters/line). The size of large lobsters (≥90 mm) decreased similarly in all areas by 2–3% (from 98 to 95 mm). Abundance of velvet crabs Necora puber decreased inside the protected areas (from 5–6 to 1 crab/line) but increased in the fished areas (from 0–6 to 1–7 crabs/line). Abundance of brown crabs Cancer pagarus did not change over time in any areas but was on average higher in the protected areas (1–2 crabs/line) compared to the fished areas (0.3–2 crabs/line). The average size of brown crabs did not change over time in any areas, and was not different between protected (123–128 mm) and fished areas (116–130 mm). Abundance of spider crabs Maja squinado was similar in 2004 and 2007 for all areas but varied spatially. Lundy Island marine protected area was designated as a voluntary reserve in 1971 (statutory since 1986) and only allowed crab and lobster potting (all other fishing prohibited; apart from a small 4 km2 no-take zone). In 2004–2007, lobsters and crabs were surveyed at two locations in the protected area (outside the no-take zone), and two unprotected fished locations (20–100 km away) (2 sites/location). Four lines of standard commercial baited shellfish pots were deployed (10 pots/line) at each site for 24 h. Upon retrieval, lobsters and crabs were counted and measured (carapace length). The pots were redeployed for five consecutive days each year.

2 

A before-and-after, site comparison study from 2008–2011 of 12 sites of rocky reefs and pebbly sand seabed in Lyme Bay, English Channel, southwest England, UK (Sheehan et al. 2013) found that three years after closing a marine protected area to all towed gears, community composition and abundance of reef-indicative invertebrate species became different to unprotected fished sites, but their species richness remained similar. Community data were reported as graphical analyses. Reef-indicative invertebrate species richness did not statistically change over time and was similar in closed and fished sites both before closure (closed: 8; fished: 5 species/m2) and three years after (closed: 10; fished: 5 species/m2). However, while before closure their abundance was similar in closed (6 individuals/m2) and fished sites (3 individuals/m2), it increased over time in closed sites and was greater than in fished sites after three years (closed: 16; fished: 1 individuals/m2). In particular, abundances of four key species increased in closed sites over time and became more abundant than in fished sites after three years (significantly for: bryozoans Pentapora fascialis closed 0.11 vs fished 0.01; sea squirts Phallusia mammillata 0.06 vs 0.01 and branching sponges 0.05 vs <0.01; non-significantly for hydroids 55 vs 17 individuals/m2). The 206 km2 protected area was closed to towed fishing gears in 2008. Six weeks after closure (considered the ‘before’ timepoint by the authors) and in 2011, five sites inside and seven sites outside the protected area were surveyed using a video camera (two 200 m video-transects/site). All invertebrates observed on the video present on pebbly sand, but indicative of rocky reef habitat, were identified and counted.

Referenced papers

Please cite as:

Lemasson, A.J., Pettit, L.R., Smith, R.K., and Sutherland, W.J. (2019) Subtidal Benthic Invertebrate Conservation: Global Evidence for the Effects of Interventions. Synopses of Conservation Evidence Series. University of Cambridge, Cambridge, UK.