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13.3 Threat: Biological resource use

p. 651-675


Texte intégral

13.3.1 Spatial and Temporal Management

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Beneficial

Cease or prohibit all towed (mobile) fishing gear

1Eight studies examined the effects of ceasing or prohibiting all towed fishing gear on subtidal benthic invertebrate populations. One study was in the Limfjord (Denmark), two in the English Channel (UK), three in Georges Bank in the North Atlantic Ocean (USA and Canada), one in the Ria Formosa lagoon (Portugal), and one in the Irish Sea (Isle of Man).

2COMMUNITY RESPONSE (4 STUDIES)

3Overall community composition (3 studies): Two of three replicated, site comparison studies in the Limfjord and the English Channel, found that areas excluding towed fishing gear for either an unspecified amount of time or two to 23 years had different overall invertebrate community composition compared to areas where towed-fishing occurred and one found that ceasing towed-gear fishing for nine years had mixed effects.

4Overall species richness/diversity (3 studies): Two replicated, site comparison studies in the English Channel reported that areas excluding towed fishing gear for either an unspecified amount of time or two to 23 years had different or greater invertebrate species richness and diversity to areas where towed-fishing occurred. One site comparison study in Georges Bank found no difference in invertebrate species richness between an area closed to mobile fishing gear for 10 to 14 years and a fished area.

5POPULATION RESPONSE (3 STUDIES)

6Overall abundance (3 studies): Two site comparison studies (one replicated) in the English Channel and Georges Bank found that sites excluding towed gear for either two to 23 years or 10 to 14 years had greater overall invertebrate biomass compared to sites where towed-gear fishing occurred, but one also found that abundance was similar in both areas. One replicated, controlled, before-and-after study in the Ria Formosa lagoon found that ceasing towed gear for 10 months led to increases in the cover of mobile but not sessile

7Mollusc abundance (2 studies): Two site comparison studies (one replicated) in the Irish Sea and the English Channel found that areas closed to towed fishing gear for either two to 23 years or 14 years had more scallops compared to adjacent fished areas.

8Mollusc condition (1 study): One site comparison study the Irish Sea found that an area closed to towed fishing gear for 14 years had higher proportions of older and larger scallops compared to an adjacent fished area.

9Starfish abundance (1 study): One replicated, site comparison study in Georges Bank found more starfish in areas closed to towed fishing gear for five to nine years compared to adjacent fished areas.

10Starfish condition (1 study): One replicated, site comparison study in Georges Bank found that starfish arm length was similar in areas closed to towed fishing gear for five to nine years and adjacent fished areas.

11OTHER (1 STUDY)

12Overall community biological production (1 study): One before-and-after, site comparison study in Georges Bank found an increase in the biological production from invertebrate in sites closed to towed fishing gear for approximately five years compared to adjacent fished sites.

13Assessment: beneficial (effectiveness 70 %; certainty 70 %; harms 0 %).

http://www.conservationevidence.com/actions/2102

Likely to be beneficial

Cease or prohibit all types of fishing

14Five studies examined the effects of ceasing or prohibiting all types of fishing on subtidal benthic invertebrate populations. All studies were in the North Sea (Belgium, Germany, Netherlands, UK).

15COMMUNITY RESPONSE (2 STUDIES)

16Overall community composition (2 studies): Two site comparison studies (one before-and-after) in the North Sea found that areas closed to all fishing developed different overall invertebrate community compositions compared to fished areas.

17Overall species richness/diversity (2 studies): One of two site comparison studies (one before-and-after) in the North Sea found that areas closed to all fishing did not develop different overall invertebrate species richness and diversity compared to fished areas after three years, but the other found higher species richness in the closed areas after 20 years.

18POPULATION RESPONSE (3 STUDIES)

19Overall abundance (2 studies): Two site comparison studies (one before-and-after) in the North Sea found that areas closed to all fishing had similar overall invertebrate abundance and biomass compared to fished areas after three and five years.

20Crustacean abundance (1 study): One before-and-after, site comparison study in the North Sea found that closing a site to all fishing led to similar numbers of lobster compared to a fished site after 20 months.

21Crustacean condition (1 study): One before-and-after, site comparison study in the North Sea found that closing a site to all fishing led to larger sizes of lobster compared to a fished site after 20 months.

22OTHER (1 STUDY)

23Overall community energy flow (1 study): One before-after, site comparison study in the North Sea found that, during the 12–14 months after closing an area to all fishing, the invertebrate community structure (measured as energy flow) at sites within the closed area did not change, but that it increased in nearby fished sites.

24Species energy flow (1 study): One before-and-after, site comparison study in the North Sea found that closing an area to all fishing for 12–14 months had mixed effects on species-level energy flow.

25Assessment: likely to be beneficial (effectiveness 55 %; certainty 50 %; harms 0 %).

http://www.conservationevidence.com/actions/2096

Cease or prohibit bottom trawling

26Four studies examined the effects of ceasing or prohibiting bottom trawling on subtidal benthic invertebrate populations. Two studies were in the Bering Sea (USA), one in the North Sea, and one in the Mediterranean Sea (Italy). COMMUNITY RESPONSE (3 STUDIES)

27Overall community composition (2 studies): Two site comparison studies (one before-and-after, one replicated) in the North Sea and the Mediterranean Sea found that in areas prohibiting trawling for either 15 or 20 years, overall invertebrate community composition was different to that of trawled areas. Overall species richness/diversity (3 studies): Two of three site comparison studies (one paired, one before-and-after, one replicated) in the Bering Sea, the North Sea, and the Mediterranean Sea found that invertebrate diversity was higher in sites closed to trawling compared to trawled sites after either 37 or 15 years, but the other found no differences after 20 years.

28POPULATION RESPONSE (3 STUDIES)

29Overall abundance (2 studies): One of two site comparison studies (one paired, one replicated) in the Bering Sea and the Mediterranean Sea found that total invertebrate abundance was higher in sites closed to trawling compared to trawled sites after 37 years, but the other found no differences after 20 years. Both found no differences in total invertebrate biomass.

30Unwanted catch overall abundance (1 study): One replicated, before-and-after, site comparison study in the Bering Sea found that during the three years after closing areas to all bottom trawling, unwanted catch of crabs appeared to have decreased, while no changes appeared to have occurred in nearby trawled areas.

31Assessment: likely to be beneficial (effectiveness 55 %; certainty 50 %; harms 5 %).

https://www.conservationevidence.com/actions/2099

Cease or prohibit dredging

32Four studies examined the effects of ceasing or prohibiting dredging on subtidal benthic invertebrate populations. One study was in the North Atlantic Ocean (Portugal), one in the South Atlantic Ocean (Argentina), one in the English Channel and one in the Irish Sea (UK).

33COMMUNITY RESPONSE (3 STUDIES)

34Overall community composition (3 studies): One of three site comparison studies (one replicated, one before-and-after) in Atlantic Ocean and the Irish Sea found that after ceasing dredging, overall invertebrate community composition was different to that in dredged areas. The other two found that communities remained similar in dredged and non-dredged areas.

35Overall richness/diversity (3 studies): One of three site comparison studies (one replicated, one before-and-after) in Atlantic Ocean and the Irish Sea found that after ceasing dredging, large (macro-) invertebrate diversity was higher but small (meio-) invertebrate diversity was lower compared to dredged areas. The other two found that overall diversity remained similar in dredged and non-dredged areas.

36POPULATION RESPONSE (3 STUDIES)

37Overall abundance (3 studies): One of three site comparison studies (one replicated, one before-and-after) in Atlantic Ocean and the Irish Sea found that four years after ceasing dredging, large (macro-) and small (meio-) invertebrate abundance and/or biomass appeared higher to that in dredged areas. The other two found that abundance and/or biomass remained similar in dredged and non-dredged areas after either two or six years.

38Tunicate abundance (1 study): One replicated, site comparison study in the English Channel found that a year after ceasing dredging in three areas, abundance of ascidians/sea squirts (tunicates) was similar to that in dredged areas.

39Bryozoan abundance (1 study): One replicated, site comparison study in the English Channel found that a year after ceasing dredging in three areas, abundance of bryozoan was higher than in dredged areas.

40Crustacean abundance (1 study): One replicated, site comparison study in the English Channel found that a year after ceasing dredging in three areas, abundance of spider crabs was higher than in dredged areas, but abundance of edible crab was similar.

41Cnidarian abundance (1 study): One replicated, site comparison study in the English Channel found that a year after ceasing dredging in three areas, abundance of sea fans was higher than in dredged areas.

42Sponge abundance (1 study): One replicated, site comparison study in the English Channel found that a year after ceasing dredging in three areas, abundance of sponges was higher than in dredged areas.

43Assessment: likely to be beneficial (effectiveness 75 %; certainty 55 %; harms 0 %).

https://www.conservationevidence.com/actions/2101

Unknown effectiveness

Cease or prohibit commercial fishing

44Three studies examined the effects of ceasing or prohibiting commercial fishing on subtidal benthic invertebrate populations. Two studies were in the Tasman Sea (New Zealand), the third on Gorges Bank in the North Atlantic Ocean (USA).

45COMMUNITY RESPONSE (2 STUDIES)

46Overall community composition (1 study): One site comparison study in the Tasman Sea found that an area closed to commercial trawling and dredging for 28 years had different overall invertebrate communities than an area subject to commercial fishing.

47Overall species richness/diversity (1 study): One site comparison study on Georges Bank found no difference in invertebrate species richness between an area closed to commercial fishing for 10 to 14 years and a fished area.

48POPULATION RESPONSE (3 STUDIES)

49Overall abundance (2 studies): Two site comparison studies in the Tasman Sea and on Georges Bank found that areas prohibiting commercial fishing for 10 to 14 years and 28 years had greater overall invertebrate abundance compared to areas where commercial fishing occurred. One of the studies also found higher biomass, while the other found similar biomass in closed and fished areas.

50Crustacean abundance (1 study): One replicated, site comparison study in the Tasman Sea found that in commercial fishing exclusion zones lobster abundance was not different to adjacent fished areas after up to two years. OTHER (1 STUDY)

51Overall community biological production (1 study): One site comparison study in the Tasman Sea found that an area closed to commercial trawling and dredging for 28 years had greater biological production from invertebrates than an area where commercial fishing occurred.

52Assessment: unknown effectiveness (effectiveness 55 %; certainty 34 %; harms 0 %).

https://www.conservationevidence.com/actions/2097

Establish temporary fisheries closures

53Six studies examined the effects of establishing temporary fisheries closures on subtidal benthic invertebrates. One study was in the English Channel (UK), one in the D’Entrecasteaux Channel (Australia), one in the North Pacific Ocean (USA), two in the Mozambique Channel (Madagascar), and one in the North Sea (UK).

54COMMUNITY RESPONSE (2 STUDIES)

55Overall species richness/diversity (1 study): One replicated, site comparison study in the English Channel found that sites seasonally closed to towed-gear fishing did not have greater invertebrate species richness than sites where towed-fishing occurred year-round.

56Mollusc community composition (1 study): One replicated, before-and after study in the D’Entrecasteaux Channel found that temporarily reopening an area previously closed to all fishing for 12 years only to recreational fishing led to changes in scallop species community composition over four fishing seasons.

57POPULATION RESPONSE (1 STUDY)

58Overall abundance (1 study): One replicated, site comparison study in the English Channel found that sites seasonally closed to towed-gear fishing did not have a greater invertebrate biomass than sites where towed-fishing occurred year-round.

59Crustacean abundance (1 study): One before-and-after, site comparison study in the North Sea found that reopening a site to fishing following a temporary 20-month closure led to lower total abundance but similar marketable abundance of European lobsters compared to a continuously-fished site after a month.

60Mollusc abundance (5 studies): One replicated, site comparison study English Channel found that sites seasonally closed to towed gear did not have higher abundance of great scallops than sites where towed-fishing occurred year-round. Two before-and after, site comparison studies (one replicated) in the Mozambique Channel found that temporarily closing an area to reef octopus fishing did not increase octopus abundance/biomass compared to before closure and to continuously fished areas. Two replicated, before-and after studies in the D’Entrecasteaux Channel and the North Pacific Ocean found that temporarily reopening an area previously closed to all fishing to recreational fishing only led to a decline in scallop abundance after four fishing seasons and in red abalone after three years.

61Mollusc condition (3 studies): One replicated, before-and after study in the North Pacific Ocean found that temporarily reopening an area previously closed to fishing led to a decline in the size of red abalone after three years. Two before-and after, site comparison studies (one replicated) in the Mozambique Channel found that temporarily closing an area to reef octopus fishing increased the weight of octopus compared to before closure and to continuously fished areas, but one also found that this effect did not last once fishing resumed.

62Assessment: unknown effectiveness (effectiveness 30 %; certainty 36 %; harms 10 %).

http://www.conservationevidence.com/actions/2098

No evidence found (no assessment)

63We have captured no evidence for the following interventions:

  • Cease or prohibit midwater/semi-pelagic trawling

  • Cease or prohibit static fishing gear.

13.3.2 Effort and Capacity Reduction

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Unknown effectiveness

Establish territorial user rights for fisheries

64One study examined the effects of establishing territorial user rights for fisheries on subtidal benthic invertebrate populations. The study was in the South Pacific Ocean (Chile).

65COMMUNITY RESPONSE (0 STUDIES)

66POPULATION RESPONSE (1 STUDY)

67Mollusc reproductive success (1 study): One site comparison study in South Pacific Ocean found that an area with territorial user rights for fisheries had larger-sized and more numerous egg capsules, and more larvae of the Chilean abalone up to 21 months after establishing fishing restrictions compared to an open-access area.

68Assessment: unknown effectiveness (effectiveness 65 %; certainty 10 %; harms 0 %).

https://www.conservationevidence.com/actions/2104

Install physical barriers to prevent trawling

69One 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).

70COMMUNITY RESPONSE (1 STUDY)

71Overall 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.

72POPULATION RESPONSE (1 STUDY)

73Overall 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.

74Echinoderm 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.

75Assessment: unknown effectiveness (effectiveness 75 %; certainty 32 %; harms 0 %).

https://www.conservationevidence.com/actions/2112

No evidence found (no assessment)

76We have captured no evidence for the following interventions:

  • Eliminate fisheries subsidies that encourage overfishing

  • Introduce catch shares

  • Limit the density of traps

  • Limit the number of fishing days

  • Limit the number of fishing vessels

  • Limit the number of traps per fishing vessels

  • Purchase fishing permits and/or vessels from fishers

  • Set commercial catch quotas

  • Set commercial catch quotas and habitat credits systems

  • Set habitat credits systems.

13.3.3 Reduce Unwanted catch, Discards and Impacts on seabed communities

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Likely to be beneficial

Fit one or more mesh escape panels/windows to trawl nets

77Seven studies examined the effects of adding one or more mesh escape panels/ windows to trawl nets on subtidal benthic invertebrate populations. Six were in the North Sea (Belgium, Netherlands, UK), two in the Thames estuary (UK), one in the English Channel (UK), and one in the Gulf of Carpentaria (Australia).

78COMMUNITY RESPONSE (0 STUDIES)

79POPULATION RESPONSE (7 STUDIES)

80Overall survival (1 study): One replicated, paired, controlled study in the English Channel and the North Sea found that fitting nets with either one of seven designs of square mesh escape panels (varying mesh size and twine type) led to higher survival rates of invertebrates that escaped the nets compared to unmodified nets.

81Unwanted catch overall abundance (7 studies): Three of seven replicated, paired, controlled studies in the North Sea, the Thames estuary, the English Channel and the Gulf of Carpentaria found that trawl nets fitted with one or more mesh escape panels/windows/zones reduced the unwanted catch of invertebrates compared to unmodified nets. Two found mixed effects of fitting escape panels on the unwanted catch of invertebrates and fish depending on the panel design. Two found that trawl nets fitted with escape panels caught similar amounts of unwanted invertebrates and fish compared to unmodified nets.

82OTHERS (7 STUDIES)

83Commercially targeted catch abundance (7 studies): Three of seven replicated, paired, controlled studies in the North Sea, the Thames estuary, the English Channel and the Gulf of Carpentaria, found that trawl nets fitted with one or more mesh escape panels/windows/zones caught similar amounts of all or most commercial species to unmodified nets. Three found mixed effects of fitting escape panels on the catch of all or most commercial species depending on the species and/or panel design. One found that trawl nets fitted with escape panels reduced the catch of commercial species compared to unmodified nets.

84Assessment: likely to be beneficial (effectiveness 60 %; certainty 50 %; harms 5 %).

http://www.conservationevidence.com/actions/2132

Fit one or more soft, semi-rigid, or rigid grids or frames to trawl nets

85Two studies examined the effects of fitting one or more soft, semi-rigid, or rigid grids or frames to trawl nets on subtidal benthic invertebrate populations. The studies were in the Gulf of Carpentaria and Spencer Gulf (Australia). COMMUNITY RESPONSE (0 STUDIES)

86POPULATION RESPONSE (2 STUDIES)

87Unwanted catch abundance (1 study): Two replicated, paired, controlled studies in the Gulf of Carpentaria and in Spencer Gulf found that nets fitted with a ‘downward’-oriented grid but not an ‘upward’-oriented grid reduced the weight of small unwanted catch and that both grid orientations caught fewer unwanted large sponges, and that nets fitted with two sizes of grids reduced the number and biomass of unwanted blue swimmer crabs and giant cuttlefish caught, compared to unmodified nets.

88OTHER (2 STUDIES)

89Commercial catch abundance (2 studies): Two replicated, paired, controlled studies in the Gulf of Carpentaria and Spencer Gulf found that nets fitted with a ‘downward’-oriented grid or a small grid reduced the catch of commercially targeted prawns, compared to unmodified nets, but those fitted with an ‘upward’-oriented grid or a large grid caught similar amounts to unmodified nets.

90Assessment: likely to be beneficial (effectiveness 60 %; certainty 40 %; harms 0 %).

https://www.conservationevidence.com/actions/2133

Modify the design of dredges

91Six studies examined the effects of modifying the design of dredges on subtidal benthic invertebrate populations. Four were in the North Atlantic Ocean (Portugal) and two were in the Irish Sea (Isle of Man).

92COMMUNITY RESPONSE (1 STUDY)

93Unwanted catch overall composition (1 study): One replicated, controlled, study in the Irish Sea found that a new design of scallop dredge caught a similar species composition of unwanted catch to a traditional dredge.

94POPULATION RESPONSE (3 STUDIES)

95Overall abundance (2 studies): One of two controlled studies in the North Atlantic Ocean and in the Irish Sea found that a new dredge design damaged or killed fewer invertebrates left in the sediment tracks following dredging. The other found no difference in total invertebrate abundance or biomass living in or on the sediment tracks following fishing with two dredge designs. Unwanted catch overall abundance (2 studies): Two controlled studies (one replicated) in the North Atlantic Ocean and the Irish Sea found that a modified or a new design of bivalve dredge caught less unwanted catch compared to traditional unmodified dredges.

96Unwanted catch condition (6 studies): Six controlled studies (one replicated and paired, four replicated) in the North Atlantic Ocean and the Irish Sea found that new or modified bivalve dredges damaged or killed similar proportions of unwanted catch (retained and/or escaped) compared to traditional or unmodified designs, three of which also found that they did not reduce the proportion of damaged or dead unwanted crabs (retained and/or escaped). OTHER (1 study)

97Commercial catch abundance (1 study): One replicated, controlled, study in the Irish Sea found that a new dredge design caught a similar amount of commercially targeted queen scallops compared to a traditional dredge. Assessment: likely to be beneficial (effectiveness 40 %; certainty 42 %; harms 19 %).

https://www.conservationevidence.com/actions/2119

Modify the position of traps

98Two studies examined the effects of modifying the position of traps on subtidal benthic invertebrate populations. One study was in the Varangerfjord (Norway), the other in the North Atlantic Ocean (Spain).

99COMMUNITY RESPONSE (1 STUDY)

100Unwanted catch species richness/diversity (1 study): One replicated, controlled study in the North Atlantic found that semi-floating traps caught fewer unwanted catch species compared to standard bottom traps.

101POPULATION RESPONSE (2 STUDIES)

102Unwanted catch abundance (2 studies): Two replicated, controlled studies in the Varangerfjord and the North Atlantic found that floating or semi-floating traps caught fewer unwanted invertebrates compared to standard bottom traps.

103OTHER (2 STUDIES)

104Commercial catch abundance (2 studies): Two replicated, controlled studies in the Varangerfjord and the North Atlantic found that floating or semi-floating traps caught similar amounts (abundance and biomass) of commercially targeted species as standard bottom traps.

105Assessment: likely to be beneficial (effectiveness 65 %; certainty 40 %; harms 0 %).

http://www.conservationevidence.com/actions/2144

Use a larger codend mesh size on trawl nets

106One study examined the effects of using a larger codend mesh size on trawl nets on unwanted catch of subtidal benthic invertebrate populations. The study was in the Gulf of Mexico (Mexico).

107COMMUNITY RESPONSE (1 STUDY)

108Unwanted catch species richness/diversity (1 study): One replicated, paired, controlled study in the Gulf of Mexico found that trawl nets fitted with a larger mesh codend caught fewer combined species of non-commercial unwanted invertebrates and fish compared to a traditional codend.

109POPULATION RESPONSE (1 STUDY)

110Unwanted catch abundance (1 study): One replicated, paired, controlled study in the Gulf of Mexico found that trawl nets fitted with a larger mesh codend caught lower combined biomass and abundance of non-commercial unwanted invertebrates and fish compared to a traditional codend.

111OTHER (1 STUDY)

112Commercial catch abundance (1 study): One replicated, paired, controlled study in the Gulf of Mexico found that trawl nets fitted with a larger mesh codend caught less biomass and abundance of commercially targeted shrimps compared to a traditional codend, but that the biomass ratios of commercially targeted to discard species was similar for both.

113Assessment: likely to be beneficial (effectiveness 65 %; certainty 42 %; harms 0 %).

https://www.conservationevidence.com/actions/2135

Use a midwater/semi-pelagic trawl instead of bottom/ demersal trawl

114One study examined the effects of using a semi-pelagic trawl instead of a demersal trawl on subtidal benthic invertebrates. The study was in the Indian Ocean (Australia).

115COMMUNITY RESPONSE (0 STUDIES)

116POPULATION RESPONSE (1 STUDY)

117Overall abundance (1 study): One replicated, controlled, study in the Indian Ocean found that fishing with a semi-pelagic trawl did not reduce the abundance of large sessile invertebrates, which was similar to non-trawled plots, but a demersal trawl did.

118OTHER (1 STUDY)

119Commercial catch abundance (1 study): One replicated, controlled, study in the Indian Ocean found that fishing with a semi-pelagic trawl reduced the abundance of retained commercially targeted fish compared to fishing with a demersal trawl.

120Assessment: likely to be beneficial (effectiveness 70 %; certainty 41 %; harms 0 %).

https://www.conservationevidence.com/actions/2118

Unknown effectiveness

Fit a funnel (such as a sievenet) or other escape devices on shrimp/prawn trawl nets

121One study examined the effects of fitting a funnel, sievenet, or other escape devices on trawl nets on marine subtidal invertebrate. The study was in the North Sea (UK).

122COMMUNITY RESPONSE (0 STUDIES)

123POPULATION RESPONSE (1 STUDY)

124Unwanted catch abundance (1 study): One replicated, paired, controlled study in the North Sea found that trawl nets fitted with a sievenet appeared to catch fewer unwanted catch of non-commercial invertebrates compared to unmodified nets.

125Assessment: unknown effectiveness (effectiveness 65 %; certainty 20 %; harms 0 %).

https://www.conservationevidence.com/actions/2131

Fit one or more mesh escape panels/windows and one or more soft, rigid or semi-rigid grids or frames to trawl nets

126One study examined the effects on subtidal benthic invertebrate populations of fitting one or more mesh escape panels/windows and one or more soft, rigid or semi-rigid grids or frames to trawl nets. The study was in the Gulf of Carpentaria (Australia).

127COMMUNITY RESPONSE (0 STUDIES)

128POPULATION RESPONSE (1 STUDY)

129Unwanted catch abundance (1 study): One replicated, paired, controlled study in Gulf of Carpentaria found that trawl nets fitted with an escape window and a grid reduced the total weight of small unwanted catch and caught fewer unwanted large sponges, compared to unmodified nets.

130OTHER (1 STUDY)

131Commercial catch abundance (1 study): One replicated, paired, controlled study in Carpentaria found that trawl nets fitted with an escape window and a grid reduced the catch of commercially targeted prawns, compared to unmodified nets.

132Assessment: unknown effectiveness (effectiveness 65 %; certainty 32 %; harms 0 %).

https://www.conservationevidence.com/actions/2134

Fit one or more mesh escape panels/windows to trawl nets and use a square mesh instead of a diamond mesh codend

133One study examined the effects of fitting one or more mesh escape panels to trawl nets and using a square mesh instead of a diamond mesh codend on subtidal benthic invertebrate populations. The study was in the English Channel (UK).

134COMMUNITY RESPONSE (0 STUDIES)

135POPULATION RESPONSE (1 STUDY)

136Unwanted catch abundance (1 study): One replicated, paired, controlled study in the English Channel found that trawl nets fitted with two large square mesh release panels and a square mesh codend caught fewer unwanted catch of non-commercial invertebrates compared to standard trawl nets.

137OTHER (1 STUDY)

138Commercial catch abundance (1 study): One replicated, paired, controlled study in the English Channel found that trawl nets fitted with two large square mesh release panels and a square mesh codend caught fewer commercial shellfish, and fewer but more valuable commercially important fish, compared to standard trawl nets.

139Assessment: unknown effectiveness (effectiveness 65 %; certainty 30 %; harms 0 %).

https://www.conservationevidence.com/actions/2138

Fit one or more soft, semi-rigid, or rigid grids or frames and increase the mesh size of pots and traps

140One study examined the effects of fitting one or more soft, semi-rigid, or rigid grids or frames and increasing the mesh size of pots and traps on subtidal benthic invertebrates. The study took place in the Corindi River system (Australia).

141COMMUNITY RESPONSE (0 STUDIES)

142POPULATION RESPONSE (1 STUDY)

143Unwanted catch abundance (1 study): One replicated, controlled study in the Corindi River system found that traps fitted with escape frames and designed with larger mesh appeared to reduce the proportion of unwanted undersized mud crabs caught, compared to conventional traps without escape frames and smaller mesh.

144Assessment: unknown effectiveness (effectiveness 50 %; certainty 20 %; harms 10 %).

https://www.conservationevidence.com/actions/2149

Fit one or more soft, semi-rigid, or rigid grids or frames on pots and traps

145One study examined the effects of fitting one or more soft, semi-rigid, or rigid grids or frames on pots and traps on subtidal benthic invertebrates. The study took place in the Corindi River system (Australia).

146COMMUNITY RESPONSE (0 STUDIES)

147POPULATION RESPONSE (1 STUDY)

148Unwanted catch abundance (1 study): One replicated, controlled study in the Corindi River system found that traps fitted with escape frames appeared to reduce the proportion of unwanted undersized mud crabs caught, compared to conventional traps without escape frames.

149Assessment: unknown effectiveness (effectiveness 55 %; certainty 20 %; harms 0 %).

https://www.conservationevidence.com/actions/2146

Fit one or more soft, semi-rigid, or rigid grids or frames to trawl nets and use square mesh instead of a diamond mesh at the codend

150One study examined the effects of fitting one or more soft, semi-rigid, or rigid grids or frames to trawl nets and using a square mesh codend on subtidal benthic invertebrates. The study was in the Gulf of St Vincent (Australia). COMMUNITY RESPONSE (0 STUDIES)

151POPULATION RESPONSE (1 STUDY)

152Unwanted catch abundance (1 study): One replicated, paired, controlled study in Gulf of St Vincent found that trawl nets fitted with a rigid U-shaped grid and a square-oriented mesh codend reduced the catch rates of three dominant groups of unwanted invertebrate catch species, compared to unmodified nets.

153OTHER (1 STUDY)

154Commercial catch abundance (1 study): One replicated, paired, controlled study in the Gulf of St Vincent found that trawl nets fitted with a rigid U-shaped grid and a square-oriented mesh codend reduced the catch rates of the commercially targeted western king prawn, due to reduced catch of less valuable smaller-sized prawns, compared to unmodified nets.

155Assessment: unknown effectiveness (effectiveness 70 %; certainty 20 %; harms 0 %).

https://www.conservationevidence.com/actions/2137

Hand harvest instead of using a dredge

156Two studies examined the effects of hand harvesting instead of using a dredge on subtidal benthic invertebrate populations. Both were in San Matías Gulf, South Atlantic Ocean (Argentina).

157COMMUNITY RESPONSE (2 STUDIES)

158Unwanted catch community composition (1 study): One replicated, controlled study in San Matías Gulf found that, when harvesting mussels, the community composition of the unwanted catch was similar by hand harvesting and by using a dredge.

159Unwanted catch richness/diversity (1 study): One replicated, controlled study in San Matías Gulf found that, when harvesting mussels, hand harvesting caught fewer species of unwanted catch compared to using a dredge.

160POPULATION RESPONSE (2 STUDIES)

161Unwanted catch abundance (1 study): One replicated, controlled study in San Matías Gulf found that, when harvesting mussels, hand harvesting caught fewer unwanted sea urchins and brittle stars compared to using a dredge. Unwanted catch condition (1 study): One replicated, controlled study in San Matías Gulf found that, when harvesting mussels, the damage caused to unwanted sea urchins and brittle stars was similar by hand harvesting and by using a dredge.

162OTHER 1 STUDY)

163Commercial catch abundance (1 study): One replicated, controlled study in San Matías Gulf found that more commercially targeted mussels were caught by hand harvesting than by using a dredge.

164Assessment: unknown effectiveness (effectiveness 45 %; certainty 18 %; harms 10 %).

https://www.conservationevidence.com/actions/2121

Increase the mesh size of pots and traps

165One study examined the effects of increasing the mesh size of pots and traps on subtidal benthic invertebrates. The study took place in the Corindi River system (Australia).

166COMMUNITY RESPONSE (0 STUDIES)

167POPULATION RESPONSE (1 STUDY)

168Unwanted catch abundance (1 study): One replicated, controlled study in the Corindi River system found that traps designed with larger mesh appeared to reduce the proportion of unwanted undersized mud crabs caught, compared to conventional traps of smaller mesh.

169Assessment: unknown effectiveness (effectiveness 61 %; certainty 29 %; harms 0 %).

https://www.conservationevidence.com/actions/2148

Modify the design of traps

170Two studies examined the effects of modifying the design of traps on subtidal benthic invertebrates. One study took place in the Mediterranean Sea (Spain), and one in the South Pacific Ocean (New Zealand).

171COMMUNITY RESPONSE (0 STUDIES)

172POPULATION RESPONSE (2 STUDIES)

173Unwanted catch abundance (2 studies): Two replicated, controlled studies in the Mediterranean Sea and the South Pacific Ocean found that the amount of combined unwanted catch of invertebrates and fish varied with the type of trap design used and the area.

174OTHER (1 STUDY)

175Commercial catch abundance (1 study): One replicated, controlled study in the Mediterranean Sea found that plastic traps caught some legal-size commercially targeted lobsters while collapsible traps caught none.

176Assessment: unknown effectiveness (effectiveness 40 %; certainty 21 %; harms 20 %).

https://www.conservationevidence.com/actions/2143

Modify the design/attachments of a shrimp/prawn W-trawl net

177One study examined the effects of modifying the design/attachments of a W-trawl net used in shrimp/prawn fisheries on unwanted catch of subtidal benthic invertebrate. The study was in Moreton Bay (Australia).

178COMMUNITY RESPONSE (0 STUDIES)

179POPULATION RESPONSE (1 STUDY)

180Unwanted catch overall abundance (1 study): One replicated, paired, controlled study in Moreton Bay found that four designs of W-trawl nets used in shrimp/prawn fisheries caught less non-commercial unwanted catch of crustaceans compared to a traditional Florida Flyer trawl net.

181OTHERS (1 STUDY)

182Commercial catch abundance (1 study): One replicated, paired, controlled study in Moreton Bay found that four designs of W-trawl nets used in shrimp/ prawn fisheries caught lower amounts of the commercially targeted prawn species compared to a traditional Florida Flyer trawl net.

183Assessment: unknown effectiveness (effectiveness 61 %; certainty 24 %; harms 0 %).

https://www.conservationevidence.com/actions/2139

Reduce the number or modify the arrangement of tickler chains/chain mats on trawl nets

184Three studies examined the effects of reducing the number or modifying the arrangement of tickler chains/chain mats on subtidal benthic invertebrates. All studies were in the North Sea (Germany and Netherlands).

185COMMUNITY RESPONSE (0 STUDIES)

186POPULATION RESPONSE (3 STUDIES)

187Overall abundance (1 study): One replicated, paired, controlled study in the North Sea found that using a beam trawl with a chain mat caused lower mortality of benthic invertebrates in the trawl tracks compared to using a beam trawl with tickler chains.

188Unwanted catch abundance (2 studies): One of two replicated, paired, controlled studies in the North Sea found that all three modified parallel tickler chain arrangements reduced the combined amount of non-commercial unwanted invertebrate and fish catch compared to unmodified trawl nets, but the other found that none of three modified parabolic tickler chain arrangements reduced it.

189OTHER (2 STUDIES)

190Commercial catch abundance (2 studies): One of two replicated, paired, controlled studies in the North Sea found that three modified parabolic tickler chain arrangements caught similar amounts of commercial species to unmodified nets, but the other found that three modified parallel tickler chain arrangements caught lower amounts.

191Assessment: unknown effectiveness (effectiveness 43 %; certainty 32 %; harms 10 %).

https://www.conservationevidence.com/actions/2140

Use a larger mesh size on trammel nets

192One study examined the effects of using a larger mesh size on trammel nets on subtidal benthic invertebrates. The study was in the North Atlantic Ocean (Portugal).

193COMMUNITY RESPONSE (1 STUDY)

194Unwanted catch community composition (1 study): One replicated, controlled, study in the North Atlantic Ocean found that using larger mesh sizes in the inner and/or outer panels of trammel nets did not affect the community composition of unwanted catch of non-commercial invertebrates (discard). POPULATION RESPONSE (1 STUDY)

195Unwanted catch abundance (1 study): One replicated, controlled, study in the North Atlantic Ocean found that using larger mesh sizes in the inner and/ or outer panels of trammel nets did not reduce the abundance of unwanted catch of non-commercial invertebrates (discard).

196Assessment: unknown effectiveness (effectiveness 20 %; certainty 36 %; harms 0 %).

https://www.conservationevidence.com/actions/2141

Use a pulse trawl instead of a beam trawl

197One study examined the effects of using a pulse trawl instead of a beam trawl on subtidal benthic invertebrates. The study was in the North Sea (Netherlands).

198COMMUNITY RESPONSE (0 STUDIES)

199POPULATION RESPONSE (1 STUDY)

200Unwanted catch abundance (1 study): One replicated, controlled, study in the North Sea found that pulse trawls caught less unwanted invertebrate catch compared to traditional beam trawls, but the effects varied with species. OTHER (1 STUDY)

201Commercial catch abundance (1 study): One replicated, controlled, study in the North Sea found that pulse trawls reduced the volume of commercial catch by 19 % compared to beam trawls.

202Assessment: unknown effectiveness (effectiveness 41 %; certainty 34 %; harms 15 %).

https://www.conservationevidence.com/actions/2126

Use a smaller beam trawl

203One study examined the effects of using a smaller beam trawl on subtidal benthic invertebrates. The study was in the North Sea (Germany and Netherlands).

204COMMUNITY RESPONSE (0 STUDIES)

205POPULATION RESPONSE (1 STUDY)

206Overall abundance (1 study): One replicated, paired, controlled study in the North Sea found that a smaller beam trawl caused similar mortality of invertebrates in the trawl tracks compared to a larger beam trawl.

207Assessment: unknown effectiveness (effectiveness 30 %; certainty 35 %; harms 0 %).

http://www.conservationevidence.com/actions/2127

Use a square mesh instead of a diamond mesh codend on trawl nets

208One study examined the effects of using a square mesh instead of a diamond mesh codend on trawl nets on unwanted catch of subtidal benthic invertebrate populations. The study was in the English Channel (UK).

209COMMUNITY RESPONSE (0 STUDIES)

210POPULATION RESPONSE (1 STUDY)

211Unwanted catch abundance (1 study): One replicated, paired, controlled study in the English Channel found that a trawl net with a square mesh codend caught less non-commercial unwanted invertebrates in one of two areas, and similar amounts in the other area, compared to a standard diamond mesh codend.

212OTHER (1 STUDY)

213Commercial catch abundance (1 study): One replicated, paired, controlled study in the English Channel found that a trawl net with a square mesh codend caught similar amounts of commercially targeted fish species in two areas, and that in one of two areas it caught more commercially important shellfish, compared to a standard diamond mesh codend.

214Assessment: unknown effectiveness (effectiveness 50 %; certainty 20 %; harms 10 %).

https://www.conservationevidence.com/actions/2136

Use an otter trawl instead of a beam trawl

215One study examined the effects of using an otter trawl instead of a beam trawl on subtidal benthic invertebrates. The study was in the North Sea (Germany and Netherlands).

216COMMUNITY RESPONSE (0 STUDIES)

217POPULATION RESPONSE (1 STUDY)

218Overall abundance (1 study): One replicated, paired, controlled study in the North Sea found that otter trawls caused similar mortality of invertebrates in the trawl tracks compared to beam trawls in sandy areas but lower mortality in silty areas.

219Assessment: unknown effectiveness (effectiveness 50 %; certainty 34 %; harms 10 %).

https://www.conservationevidence.com/actions/2125

Use an otter trawl instead of a dredge

220One study examined the effects of using an otter trawl instead of a dredge on subtidal benthic invertebrates. The study was in the Irish Sea (Isle of Man). COMMUNITY RESPONSE (1 STUDY)

221Unwanted catch overall composition (1 study): One replicated, controlled, study in the Irish Sea found that an otter trawl caught a different species composition of unwanted invertebrate and fish species (combined) compared to two scallop dredges.

222POPULATION RESPONSE (1 STUDY)

223Overall abundance (1 study): One replicated, controlled, study in the Irish Sea found no difference in total invertebrate abundance and biomass living in or on the sediment of the trawl tracks following fishing with either an otter trawl or two scallop dredges.

224Unwanted catch overall abundance (1 study): One replicated, controlled, study in the Irish Sea found that an otter trawl caught fewer unwanted invertebrates and fish (combined) compared to two scallop dredges.

225OTHER (1 STUDY)

226Commercial catch abundance (1 study): One replicated, controlled, study in the Irish Sea found that an otter trawl caught similar number of commercially targeted queen scallops compared to two scallop dredges.

227Assessment: unknown effectiveness (effectiveness 45 %; certainty 35 %; harms 0 %).

https://www.conservationevidence.com/actions/2123

Use different bait species in traps

228One study examined the effects of using different bait species in traps on subtidal benthic invertebrates. The study took place in the South Pacific Ocean (New Zealand).

229COMMUNITY RESPONSE (0 STUDIES)

230POPULATION RESPONSE (1 STUDY)

231Unwanted catch abundance (1 study): One replicated, controlled study in the South Pacific Ocean found that the type of bait used in fishing pots did not change the amount of unwanted invertebrates caught.

232Assessment: unknown effectiveness (effectiveness 1 %; certainty 37 %; harms 0 %).

https://www.conservationevidence.com/actions/2145

Use traps instead of fishing nets

233One study examined the effects of using traps instead of fishing nets on subtidal benthic invertebrates. The study took place in the Mediterranean Sea (Spain).

234COMMUNITY RESPONSE (0 STUDIES)

235POPULATION RESPONSE (1 STUDY)

236Unwanted catch abundance (1 study): One replicated, controlled study in the Mediterranean Sea found that the combined amount of unwanted catch of invertebrates and fish appeared lower using plastic traps than trammel nets, but higher using collapsible traps.

237OTHER (1 STUDY)

238Commercial catch abundance (1 study): One replicated, controlled study in the Mediterranean Sea found that the catch of commercially targeted lobsters was lower using traps than in trammel nets.

239Assessment: unknown effectiveness (effectiveness 40 %; certainty 32 %; harms 20 %).

https://www.conservationevidence.com/actions/2142

No evidence found (no assessment)

240We have captured no evidence for the following interventions:

  • Fit one or more mesh escape panels/windows on pots and traps

  • Limit the maximum weight and/or size of bobbins on the footrope

  • Modify harvest methods of macroalgae

  • Modify trawl doors to reduce sediment penetration

  • Outfit trawls with a raised footrope

  • Release live unwanted catch first before handling commercial species

  • Set unwanted catch quotas

  • Use alternative means of getting mussel seeds rather than dredging from natural mussel beds

  • Use hook and line fishing instead of other fishing methods

  • Use lower water pressure during hydraulic dredging

  • Use more than one net on otter trawls.

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