Cease or prohibit all (mobile and static) fishing gears that catch bottom (demersal) species

Overall effectiveness category Awaiting assessment
Number of studies: 3
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Background information and definitions

Fishing gears that target fish or invertebrate species that live and feed mostly on or near the seabed (collectively called demersal or groundfish species) consist of a variety of gears, both mobile and static. Mobile gears include those actively towed on or just above the seabed by vessel, such as most types of trawls and some seine nets, and bottom seine nets pulled or drawn in by hand or vessel. Static gears include those when deployed on or near the bottom such as gillnets and longlines. These fishing gears not only selectively remove target and non-target bottom-dwelling fish species or groups, but some can cause disturbance and damage to sensitive bottom habitats, including those that fish may depend on for activities such as spawning. Ceasing or prohibiting some or all mobile and static fishing gears that catch bottom species in an area may protect demersal fish communities from overexploitation, reduce fishing mortality and help to preserve essential fish habitats.

Evidence for similar interventions relating to the use of different fishing gears to target bottom-dwelling fish are summarized under ‘Cease or prohibit mobile fishing gears that catch bottom (demersal) species and are dragged across the seafloor’, ‘Cease or prohibit fishing shellfish dredging’, ‘Cease or prohibit line fishing’ and ‘Cease or prohibit spearfishing’. See also, ‘Establish long-term fishery closures’ and ‘Establish temporary fishery closures’.

Study locations

Key messages

Three studies examined the effects of ceasing or prohibiting mobile and static fishing gears that catch bottom (demersal) species in an area on marine fish populations. One study was in each of the Greenland Sea(Iceland), the North Pacific Ocean (Canada) and the North Atlantic Ocean (USA/Canada).

COMMUNITY RESPONSE (0 STUDIES)

POPULATION RESPONSE (3 STUDIES)

Abundance (3 studies): One of three replicated, controlled studies (one paired) in the Greenland Sea, North Pacific Ocean and the North Atlantic Ocean found that an area where fishing gears targeting bottom-dwelling species had been prohibited for 15 years had higher numbers of larger and older cod than openly fished areas. One study found that fish densities in areas closed to mobile and static bottom fish gears (trawls and longlines) for at least 11 years varied between fish species/groups, and also with depth and temperature. The other study found that prohibiting mobile and static bottom fish gears (trawls and hook and line) in protected areas for 2–7 years had no effect on fish densities compared to non-protected areas.
Condition (2 studies): One of two replicated, controlled studies (one paired) in the Greenland Sea and the North Atlantic Ocean found that cod had better growth in areas closed for 5-15 years to mobile and static gears that targeted bottom-dwelling fish, compared to openly fished areas. The other study found that fish size varied between areas closed and open to bottom fish gears (trawls and longlines) and was also affected by depth and temperature.

BEHAVIOUR (0 STUDIES)

About key messages

Key messages provide a descriptive index to studies we have found that test this intervention.

Studies are not directly comparable or of equal value. When making decisions based on this evidence, you should consider factors such as study size, study design, reported metrics and relevance of the study to your situation, rather than simply counting the number of studies that support a particular interpretation.

Supporting evidence from individual studies

A replicated, paired, site comparison study in 2004–2005 of three seabed areas in the Greenland Sea, off the coast of Iceland (Jaworski et al. 2010) found that three marine protected areas closed to bottom gears (trawls and longlines) for at least 11 years had different fish densities and sizes of the most abundant bottom dwelling species, compared to adjacent areas outside, but the effect of depth or temperature was stronger than level of protection. Differences in fish density (mean log number) by size group were found inside areas closed to bottom gears compared to outside for two of nine species/groups in the closed area on the northwest coast, and for four of six in the other two closure areas on the northeast coast (see paper for species individual data). In the northwest, average fish size was similar between areas for eight of nine fish species/groups and smaller for one in the closed area; and for the two northeast areas, three of six fish species/groups were smaller inside one of the closure areas compared to the other and outside, and there were no differences for the other three (see paper for species individual data). However, the influence of temperature or depth on fish density and average size between closed and open areas was found in many cases to be higher than the level of protection (see original paper). Fish sampling was done by a research trawler: in August 2004 inside and outside one protected area off the northwest coast (41 trawl deployments); and in July 2005 inside two adjacent protected areas and one unprotected area off the northeast coast (47 deployments). The protected areas were established primarily to protect small cod and were closed to trawling and fishing with longlines in 1993 (two had been closed to trawling since the early 1970s and 1992).
Study and other actions tested
Referenced paper
Jaworski A., Solmundsson J. & Ragnarsson S.A. (2010) Fish assemblages inside and outside marine protected areas off northern Iceland: protection effects or environmental confounds? Fisheries Research, 102, 50-59.
A replicated, controlled study in 2009–2011 of four seabed areas in the northeast Pacific Ocean, off Canada (Haggarty et al. 2016) found that prohibiting bottom trawls as well as commercial and recreational hook and line fishing in protected areas for two to seven years, did not result in different densities of six of six fish species compared to outside. Densities did not differ for quillback Sebastes maliger (inside: 0.04 fish/100 m², outside: 0.04 fish/100 m²), yelloweye Sebastes ruberrimus (inside 0.02 fish/100 m², outside 0.02 fish/100 m²), copper Sebastes caurinus (inside 0.03 fish/100 m², outside 0.04 fish/100 m²), lingcod Ophiodon elongatus (inside 0.02 fish/100 m², outside 0.03 fish/100 m²), kelp greenling Hexagrammos decagrammus (inside 0.04 fish/100 m², outside 0.04 fish/100 m²) and greenstriped rockfish Sebastes elongatus (inside 0.02 fish/100 m², outside 0.02 fish/100 m²). Areas inside and outside 35 Rockfish Conservation Areas in four regions of southern British Columbia were surveyed 30 times by a remotely operated camera vehicle in 2009–2011. Data were collected during daylight from paired transects 300–900 m long inside and outside the protected areas. Fish density was calculated from fish counts and size of surveyed area. The Rockfish Conservation Areas were established between 2004–2007 and prohibited bottom trawl fisheries and commercial and recreational hook and line fisheries. Fisheries for invertebrates by trap and hand, and seining, gillnetting and mid-water trawling were permitted.
Study and other actions tested
Referenced paper
Haggarty D.R., Shurin J.B. & Yamanaka K.L. (2016) Assessing population recovery inside British Columbia's Rockfish Conservation Areas with a remotely operated vehicle. Fisheries Research, 183, 165-179.
A replicated, paired, controlled study in 2007–2009 of four bottom fishing grounds in the Gulf of Maine and Georges Bank, North Atlantic Ocean, USA (Sherwood & Grabowski 2016) found that prohibiting fishing gears that target bottom-dwelling fish (groundfish) for between five and 15 years, resulted in higher numbers of larger and older cod Gadus morhua and improved growth, compared to openly fished areas. Across all sites, in areas closed to bottom fishing gears, average cod length (inside: 55.6 cm, outside: 50.0 cm) and age (inside: 3.3 y, outside: 2.8 y) was higher, more cod age >5 were found (inside: 47, outside: 5) and cod growth was higher (data reported as growth functions and coefficients). At individual sites, cod length was significantly higher at two of four sites, and age at one. From 1994–2002, five year-round closed areas (22,000 km²) were implemented in the Gulf of Maine and Georges Bank prohibiting certain commercial bottom gears, primarily trawls and gillnets. Other fishing activities such as recreational fishing, and scallop dredging and longlining in special access areas was allowed. Four of the five closed areas were sampled from late spring to early autumn 2007–2009. Cod were collected at by rod and reel from inside (n=520) and outside (n=316) >5km away from the boundaries. Cod length, total weight and weight of removed organs was recorded, and ages determined from the otoliths (ear organs).
Study and other actions tested
Referenced paper
Sherwood G.D. & Grabowski J.H. (2016) A comparison of cod life-history parameters inside and outside of four year-round groundfish closed areas in New England, USA. ICES Journal of Marine Science, 73, 316-328.

Please cite as:

Taylor, N., Clarke, L.J., Alliji, K., Barrett, C., McIntyre, R., Smith, R.K., and Sutherland, W.J. (2021) Marine Fish Conservation: Global Evidence for the Effects of Selected Interventions. Synopses of Conservation Evidence Series. University of Cambridge, Cambridge, UK.

Where has this evidence come from?

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This Action forms part of the Action Synopsis:

Marine Fish Conservation

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