Designate a Marine Protected Area and prohibit bottom trawling
Overall effectiveness category Unknown effectiveness (limited evidence)
Number of studies: 3
Background information and definitions
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 bottom trawls are known to be particularly damaging as they are dragged along/above the seabed, but can be prohibited within an area. Specific areas can be designated as protected, and specific management measures taken to control for impactful activities, such as bottom trawling (Huvenne et al. 2016). Inside protected areas where bottom trawling is prohibited, the threat from bottom trawling to subtidal benthic invertebrates is removed, and previously impacted populations are, in theory, able to recover over time (Hiddink et al. 2017). However, species and populations are still subjected to the effects of other fishing activities allowed (for instance commercial potting or recreational fishing).
When this intervention occurred outside of a marine protected area, evidence has been summarised under “Threat: Biological resource use – Cease or prohibit bottom trawling”. Evidence for other related interventions is summarised under “Threat: Biological resource use”.
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.
Hiddink J.G., Jennings S., Sciberras M., Szostek C.L., Hughes K.M., Ellis N., Rijnsdorp A.D., McConnaughey R.A., Mazor T., Hilborn R. & Collie J.S. (2017) Global analysis of depletion and recovery of seabed biota after bottom trawling disturbance. Proceedings of the National Academy of Sciences, 114, 8301–8306.
Huvenne V.A.I., Bett B.J., Masson D.G., Le Bas P. & Wheeler A.J. (2016) Effectiveness of a deep-sea cold-water coral Marine Protected Area, following eight years of fisheries closure. Biological Conservation, 200, 60–69.
Supporting evidence from individual studies
A replicated, site comparison study in 1997 of 14 seamounts south of Tasmania, South Pacific Ocean, Australia (Koslow et al. 2001) found that seamounts within a protected area closed to trawling tended to have different invertebrate community composition, more species and higher biomass of invertebrates, compared to shallow unprotected seamounts, but not compared to deep unprotected seamounts, after two years. Results were not tested for statistical significance. Invertebrate community composition appeared typically similar at protected seamounts and deep unprotected seamounts, but different to that of shallow unprotected seamounts (data presented as graphical analyses). Protected seamounts tended to have more invertebrate species (22 species/sample) and biomass (6 kg/sample) compared to shallow unprotected seamounts (9 species/sample; 1 kg/sample) and similar to deep unprotected seamounts (20 species/samples; 7 kg/sample). The low diversity and biomass at shallow unprotected were associated with the loss of coral substrate from intense trawling. In 1995, a protected area was established and closed to trawling. In 1997, invertebrates (including corals) (>25 mm) living on the seamounts inside (6 seamounts; 12 samples) and outside (8 seamounts; 22 samples) the protected area (peaks at approximately 660–1,700 m depths) were sampled using a dredge. Invertebrates were sorted into groups and weighed by groups. Shallow unprotected seamounts were heavily fished, but deep seamounts were only lightly fished.Study and other actions tested
A randomized, replicated, site comparison study in 1992–1993 in four areas of mixed seabed inside the Great Barrier Reef Marine Park off northern Queensland, Coral Sea, Australia (Burridge et al. 2006) found no difference in the biomass of non-commercial unwanted catch (invertebrates and fish discard) or in the number of ‘common’ and ‘rare’ discard species between areas closed to trawling and adjacent fished areas, seven to eight years after the closure. Data were reported as statistical model results. A 10,000 km2 area of the Great Barrier Reef Marine Park was closed to trawling in 1985. Two surveys were carried out, one in 1992 and one in 1993. During each survey, 25 randomly selected sites were sampled at each of four areas within the marine park, two closed areas, and two fished areas located 10 nm away, using both a benthic dredge and a prawn trawl. A total of 156 dredges (86 in closed areas, 70 in fished areas) and 122 trawls (68 in closed areas, 54 in fished areas) were towed. For each tow, discard species were collected, identified, counted, and weighed from subsamples (amount not specified). Total weight of discard was estimated from the subsamples. Species were either recorded as ‘common’ (found in at least 11 of the 25 sites) or ‘rare’ (found in 10 or fewer sites).Study and other actions tested
A replicated, site comparison study in 2006 of 25 deep-sea seamounts located south of Tasmania, South Pacific Ocean, Australia (Althaus et al. 2009) found that, four to nine years after prohibiting bottom trawling in marine protected areas, invertebrate community composition was different and abundance lower at protected seamounts compared to trawled and natural (never trawled) seamounts, and diversity and species richness was similar to trawled but lower than at natural seamounts. Community data were reported as graphical analyses and diversity data as diversity indices. Species richness was similar at protected (46 species/1,270 m2) and trawled seamounts (46), but lower than natural seamounts (52). Abundance was lowest at protected (1–3 individuals/m2), compared to trawled seamounts (3–5), and natural seamounts where abundance was the highest (5–18). Species richness, diversity, and abundance were positively related to the cover of habitat-forming corals, which was higher on protected seamounts (3%) than trawled seamounts (0.1%), but lower than on natural seamounts (52%). Invertebrates (including corals) were identified and counted at 25 seamounts from videos transects (up to 4.7 km long, from 1,100 to 1,400 m depth; 38 transects in total). Ten seamounts were located either in continuously trawled areas or in areas where trawling had stopped following establishment of reserves (at some point between 1997 and 2003), and 15 were in never-trawled natural areas. Fishing history of individual seamounts was verified using logbook data from the Australian Fisheries Management Authority.Study and other actions tested