Action: Install physical barriers to prevent trawling
Key messagesRead our guidance on Key messages before continuing
- One study examined the effects of installing physical barriers to prevent trawling on subtidal benthic invertebrate populations. The study was in the Bay of Biscay (Spain).
COMMUNITY RESPONSE (1 STUDY)
- Overall community composition (1 study): One before-and-after study in the Bay of Biscay found that one to four years after installing artificial reefs as physical barriers to prevent trawling invertebrate community composition changed.
POPULATION RESPONSE (1 STUDY)
- Overall abundance (1 study): One before-and-after study in the Bay of Biscay found that one to four years after installing artificial reefs as physical barriers to prevent trawling overall invertebrate biomass increased.
- Echinoderm abundance (1 study): One before-and-after study in the Bay of Biscay found that one to four years after installing artificial reefs as physical barriers to prevent trawling the biomass of sea urchins and starfish increased.
- Molluscs abundance (1 study): One before-and-after study in the Bay of Biscay found that one to four years after installing artificial reefs as physical barriers to prevent trawling the biomass of gastropods (sea snails), of one species of cuttlefish, and of two species of octopus increased.
Fishing can impact subtidal benthic invertebrates through species removal or habitat damage from fishing gear coming into contact with the seabed (Collie et al. 2000). Some habitats, such as coral reefs and seagrass meadows, are particularly vulnerable to trawling gears. Trawling can be discouraged in certain areas through the positioning of physical barriers, such as concrete blocks or other artificial reefs, to make trawling unfeasible without damaging trawl nets (Liu et al. 2011). This may limit local trawling (and other mobile fishing) effort in the area, thereby reducing the impact on the seabed, the amount of bycatch, and overall threat to subtidal benthic invertebrates. When this intervention occurs within a marine protected area, evidence has been summarised under “Designate a Marine Protected Area and install physical barriers to prevent illegal trawling”. Evidence for related interventions is summarised under “Habitat restoration and creation – Place anthropogenic installations (e.g: windfarms) in an area such that they create artificial habitat and reduce the level of fishing activity”.
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.
Liu X.-S., Xu W.-Z., Cheung S.G. & Shin P.K.S. (2011) Response of meiofaunal community with special reference to nematodes upon deployment of artificial reefs and cessation of bottom trawling in subtropical waters, Hong Kong. Marine Pollution Bulletin, 63, 376–384.
Supporting evidence from individual studies
A before-and-after study in 1998–2007 in one area of soft seabed in the Cantabrian Sea, southern Bay of Biscay, Spain (Serrano et al. 2011) found that one to four years after installing barriers to prevent illegal trawling the biomass of invertebrates increased, and species community composition changed. Total invertebrate biomass was higher after one (3 kg/ha) and four years (7 kg/ha), compared to before installation (0–1 kg/ha). There were increases in the biomass of sea urchins (before: 12; after: 3,150 g/ha), common octopus Octopus vulgaris (before: 222; after: 920 g/ha), starfish (before: 9; after: 78 g/ha), gastropods (before: 18; after: 50 g/ha), cuttlefish Sepia spp. (before: 56; after: 131 g/ha), and curled octopus Eledone cirrhosa (before: 9; after: 18 g/ha). Invertebrate community composition was different before and after deployment (results presented as graphical analyses). Bottom trawling in the area was prohibited at depths <100 m by local legislation, but illegal trawling was common. To prevent it, artificial reefs (groups of concrete blocks 2 km apart; numbers not specified) were deployed in 2003 at 80–85 m depth. One sampling station near each group of blocks (sandy seabed without blocks) was surveyed annually in October in 1998–2007 (survey methods not specified).
- Serrano A., Rodríguez-Cabello C., Sánchez F., Velasco F., Olaso I. & Punzón A. (2011) Effects of anti-trawling artificial reefs on ecological indicators of inner shelf fish and invertebrate communities in the Cantabrian Sea (southern Bay of Biscay). Journal of the Marine Biological Association of the United Kingdom, 91, 623-633