Remove derelict fishing gear from mammals found entangled
Overall effectiveness category Beneficial
Number of studies: 2
Background information and definitions
Abandoned, lost or otherwise discarded fishing gear (or ‘ghost’ gear) is a major threat to marine and freshwater mammals. Mammals may become entangled in ‘ghost’ gear, such as nets, lines and ropes resulting in injury or death (Stelfox et al. 2016). Attempts may be made to remove derelict gear from mammals found entangled to improve survival. This may require specialist techniques, tools and training. Injuries or wounds caused by entanglement may also require treatment. Evidence is summarised below for studies that removed derelict gear from mammals in the wild. For studies that removed fishing gear from mammals in captivity as part of rehabilitation, see Rehabilitate and release injured, sick or weak marine and freshwater mammals.
Stelfox M., Hudgins J. & Sweet M. (2016) A review of ghost gear entanglement amongst marine mammals, reptiles and elasmobranchs. Marine Pollution Bulletin, 111, 6–17.
Supporting evidence from individual studies
A review of interventions in 1980–2012 for Hawaiian monk seals Monachus schauinslandi in the North Pacific Ocean, Hawaii, USA (Harting et al. 2014) found that removing derelict fishing gear from seals, along with at least seven other interventions to enhance survival, resulted in 139 of 532 (26%) seals surviving and reproducing. The study did not distinguish between the effects of removing derelict fishing gear and the other interventions carried out. The 139 surviving seals (including 71 females) produced at least 147 pups, which also went on to reproduce (15 pups). In 2012, the number of surviving seals and their offspring were estimated to make up 17–24% of the seal population (198–271 of 1,153 seals). In 1980–2012, a total of 885 intervention events of seven types were carried out: removal of derelict fishing gear from seals (275 events); translocation (284 events); rescue of stranded or trapped seals (37 events); pups reunited with mothers (113 events); umbilical cord removed or other medical treatment (84 events); other actions, such as deterring aggressive male seals (120 events). Field biologists monitored the seal population in 1980–2012. Data were analysed for 532 individual seals facing severe mortality risks and involved in 698 of the 885 intervention events.Study and other actions tested
A review of three case studies in 2003–2010 in the North Atlantic Ocean, USA (Wells et al. 2013) found that three common bottlenose dolphins Tursiops truncatus entangled in derelict fishing gear that were rescued and released survived for at least 1–4 years. All of three rescued and disentangled dolphins (including one calf) were successfully tracked for 365–1,541 days after release. The dolphins (two males, one female calf) were found entangled in derelict fishing gear in 2003, 2006 and 2008. They were disentangled, treated, transported to appropriate habitats, and released immediately. All three dolphins were radio-tracked after release. Details of monitoring methods were not reported. Data were from published and unpublished studies.Study and other actions tested