Use catch and hook protection devices on fishing gear
Overall effectiveness category Likely to be beneficial
Number of studies: 5
Background information and definitions
Catch and hook protection devices may be used to cover caught fish and hooks during hauling to reduce predation by marine and freshwater mammals and the subsequent capture of mammals. This may include ‘net sleeves’ which cover caught fish and hooks with the downward pressure of hauling, or triggered devices (e.g. chains, cages, cones etc.) that automatically release when a fish is hooked. This may prevent mammal injury or death due to hooking. A reduction in mammal predation on fish catches may also reduce human-wildlife conflict at wild fisheries. However, there are reports of automated protection devices failing to trigger or becoming tangled in fishing gear (Hamer et al. 2015, Rabearisoa et al. 2015).
Hamer D.J., Childerhouse S.J., McKinlay J.P., Double M.C. & Gales N.J. (2015) Two devices for mitigating odontocete bycatch and depredation at the hook in tropical pelagic longline fisheries. ICES Journal of Marine Science, 72, 1691–1705.
Rabearisoa N., Bach P. & Marsac F. (2015) Assessing interactions between dolphins and small pelagic fish on branchline to design a depredation mitigation device in pelagic longline fisheries. ICES Journal of Marine Science, 72, 1682–1690.
Supporting evidence from individual studies
A before-and-after study in 2002 and 2006 of a pelagic area in the South Pacific Ocean, Chile (Moreno et al. 2008) reported that using net sleeves on fishing hooks resulted in less sperm whale Physeter macrocephalus and killer whale Orcinus orca damage to catches of Patagonian toothfish Dissostichus eleginoides. Results are not based on assessments of statistical significance. The average percentage of fish damaged/haul by sperm or killer whales was lower when net sleeves were used on fishing hooks (0.4%) than when conventional fishing gear without net sleeves were used (3%). Eleven industrial vessels targeting Patagonian toothfish each deployed 99–120 ‘long line’ fishing lines. Each deployment consisted of a main line with vertical branch lines (15–20 m long) and hooks at 40 m intervals. A cone-shaped net sleeve (1–1.2 m long) on each branch line covered caught fish during hauling. Fish damaged by whales were recorded by fishers and onboard observers as each line was hauled in September–December 2006. Data for 2002 were taken from a previous study in which the same area was fished with conventional ‘long line’ fishing gear without net sleeves (see original paper for details).Study and other actions tested
A replicated, controlled study in 2007–2008 of two pelagic areas in the Southwest Atlantic Ocean (Goetz et al. 2011) found that using ‘umbrella’ devices on fishing hooks did not reduce sperm whale Physeter macrocephalus predation or damage to catches of Patagonian toothfish Dissostichus eleginoides. The proportion of hauls in which toothfish were taken or damaged by sperm whales did not differ significantly between fishing lines with all hooks covered by ‘umbrella’ devices (0–17% of hauls) and fishing lines with two-thirds or half of the hooks covered (0% and 8–16% respectively). Fewer toothfish were caught on hooks with ‘umbrella’ devices than on those without (data not reported). A total of 297 ‘long line’ fishing lines (each with 900–3,000 hooks) were deployed across two fishing areas with different proportions of hooks (all, two-thirds or half) covered by ‘umbrella’ devices. ‘Umbrella’ devices were cone-shaped net sleeves (1.5–2 m long) that covered caught fish during hauling. An observer on board the fishing vessel recorded catches and whale-damaged fish or hooks during each of the 297 hauls in November–April 2007/2008.Study and other actions tested
Referenced paperGoetz S., Laporta M., Martinez Portela J., Begona Santos M. & Pierce G.J. (2011) Experimental fishing with an “umbrella-and-stones” system to reduce interactions of sperm whales (Physeter macrocephalus) and seabirds with bottom-set longlines for Patagonian toothfish (Dissostichus eleginoides) in the Southwest Atlantic. ICES Journal of Marine Science, 68, 228-238.
A controlled study in 2007 of a pelagic area in the Indian Ocean off the Seychelles (Rabearisoa et al. 2012) reported that using ‘spider’ devices on fishing hooks did not reduce toothed whale (Odontoceti) predation and damage to fish catches. Results are not based on assessments of statistical significance. The proportion of fish damaged by toothed whales was higher on hooks protected with ‘spider’ devices (4 of 6 fish, 67%) than on unprotected hooks (8 of 15 fish, 53%). Fishing trials were carried out by a ‘long line’ fishery targeting tuna Thunnus spp. and swordfish Xiphias gladius. On each of 13 days, two fishing line sections were deployed, each with 480 hooks and 27–126 ‘spider’ devices (one device on every 2–4 hooks). Devices (8 x 120 cm polyester strands attached to a plastic disc on the branch line) were designed to automatically trigger and cover hooked fish. Fish damage by toothed whales (ragged wounds, torn flesh, conical tooth marks) were recorded during each of the 26 hauls in November–December 2007.Study and other actions tested
A controlled study in 2010–2013 of two pelagic areas in the South Pacific Ocean, Australia, and Fiji (Hamer et al. 2015) reported that using cage or chain devices on fishing hooks resulted in fewer catches of toothed whales (Odontoceti) and fewer whale-damaged fish. Results are not based on assessments of statistical significance. Overall, fewer whales were caught on hooks with cage or chain devices (0 whales) than on hooks without devices (4 whales). Whale-damaged fish were recorded on fewer hooks with cage or chain devices (3 hooks) than on those without (24 hooks). Catch rates of the five most abundant target fish species did not differ significantly between hooks with or without the devices (see original paper for data). Seven fishing vessels deployed a total of 94 ‘long line’ fishing lines (34–42 km long) across two areas during eight trips. Each fishing line consisted of a treatment section (<1,000 branch lines with cage or chain devices attached to alternate hooks, each separated by a hook without a device) and a control section (<1,000 branch lines without devices). Devices were set to automatically trigger and cover caught fish with two steel chains or a cone-shaped nylon and aluminium cage. An observer on board each fishing vessel recorded catches and entangled whales during each of 94 hauls in 2010–2013.Study and other actions tested
A controlled study in 2011 in coastal waters in the Indian Ocean, off Reunion Island, near Madagascar (Rabearisoa et al. 2015) found that attaching catch protection devices made from streamers to fishing lines reduced Indo-Pacific bottlenose dolphin Tursiops aduncus and spinner dolphin Stenella longirostris predation on fish bait, but only during the first two hauls. Fishing lines with streamers attached had a lower proportion of fish partly or fully removed by bottlenose dolphins (15–26%) or spinner dolphins (3–15%) than lines without streamers (bottlenose dolphins: 50–68%; spinner dolphins: 24–65%) during the first two hauls. The proportion of partly or fully removed fish on lines with and without streamers did not differ significantly for four subsequent hauls with bottlenose dolphins present (with: 8–40%; without: 10–24%) and one subsequent haul with spinner dolphins present (with: 3%; without: 18%). Twenty ‘long line’ fishing lines (500 m long) baited with small fish were deployed in coastal waters. Each had 40 branch lines with streamers attached and 40 without. Streamers were 8 x 1 m lengths of tarpaulin (four of which were weighted) attached to the branch line above the fish. Fish status (intact, partly, or fully removed) on each branch line was recorded during six hauls with bottlenose dolphins present and three hauls with spinner dolphins present in March–June 2011.Study and other actions tested