Rehabilitate and release injured, sick or weak marine and freshwater mammals

How is the evidence assessed?
  • Effectiveness
    60%
  • Certainty
    70%
  • Harms
    10%

Study locations

Key messages

COMMUNITY RESPONSE (0 STUDIES)

POPULATION RESPONSE (26 STUDIES)

  • Reproductive success (1 study): One replicated study in the North Pacific Ocean found that more than a quarter of rehabilitated and released Hawaiian monk seals reproduced.
  • Survival (26 studies): Twenty-one studies (including two controlled studies, four replicated studies and one review) in the North Atlantic Ocean, the Gulf of Maine, the Gulf of Mexico, the North Pacific Ocean, the Indian River Lagoon, The Wash estuary, water bodies in Florida, El Dorado Lake, and the Gulf of California found that 10–100% of dolphins, porpoises, whales, seals, sea lions and manatees released after rehabilitation in captivity survived during post-release monitoring periods, which ranged in length from three days to five years. Five studies (including one replicated study) in the North Sea, the North Atlantic Ocean, Bohai Bay and the North Pacific Ocean found that two of three harbour porpoises, 152 of 188 grey seal pups, a common seal, a west Pacific finless porpoise and 14 of 35 California sea lions were successfully rehabilitated and released but survival after release was not reported. One controlled study in the North Pacific Ocean found that at least a quarter of California sea lions treated for toxic algae poisoning and released back into the wild died or had to be euthanized.

BEHAVIOUR (3 STUDIES)

  • Behaviour change (3 studies): Two of three controlled studies in the North Atlantic Ocean, the North Pacific Ocean and The Wash estuary found that a harbour porpoise and six harbour seals that were rehabilitated and released had similar movements and/or behaviours to wild mammals. The other study found that California sea lions treated for toxic algae poisoning and released travelled further from the shore, spent less time diving or hauled out and made shorter, shallower dives than wild sea lions without poisoning.

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

  1. A study in 1988 of a pelagic area in the North Sea, the Netherlands (Kastelein et al. 1990) found that two of three stranded harbour porpoises Phocoena phocoena were successfully rehabilitated and released back into the wild. Two stranded harbour porpoises (a young female and an adult male) were successfully rescued and released back into the wild after eight months of rehabilitation. Survival after release was not reported. The other porpoise (an adult male) was rescued and rehabilitated but died of an infection seven months after capture. The three porpoises were found stranded on a beach in March 1988 in poor condition (wounded, dehydrated and underweight) and taken to a rehabilitation facility. They were kept in a rectangular pool (8 x 3 m, 1 m deep), had wounds treated, were given antibiotics, parasite and hormone treatments, oral rehydration salts and vitamins, and fed fish (3–4 times/day). Two of the three porpoises were released back into the wild in November 1988.

    Study and other actions tested
  2. A study in 1991 of a pelagic area in the Gulf of Maine, USA (Mate et al. 1994) found that a stranded Atlantic white-sided dolphin Lagenorhynchus acutus that was rehabilitated and released back into the wild survived for at least six days. The rehabilitated male dolphin was successfully tracked for six days before contact was lost with the transmitter following a storm. The dolphin travelled at least 309 km during that time at an average speed of 5.7 km/h and was recorded diving regularly (>4,000 dives during 45 h). The dolphin was rescued after stranding on an island and taken to a rehabilitation facility. After eight months of rehabilitation, the dolphin was satellite-tagged and released offshore in an area with known sightings of Atlantic white-sided dolphins. The dolphin was tracked to 53 locations during six days in October 1991.

    Study and other actions tested
  3. A study in 1995 of a pelagic area in the Gulf of Mexico, USA (Davis et al. 1996) found that a stranded Atlantic spotted dolphin Stenella frontalis that was rehabilitated and released back into the wild survived for at least one month. The adult male dolphin was successfully tracked for 28 days after release before the transmitter detached. During that time, the dolphin travelled at least 1,711 km at an average rate of 72 km/day. He moved along 300 km of coast at an average distance of 52 km from the shore and made regular dives (average 698 dives/day). The dolphin was found stranded on an island on 10 February 1995 and transported to a rehabilitation facility. He was housed in a pool (7 m wide, 1.5 m deep) and fed fish (10 kg/day). On 17 March 1995, the dolphin was satellite-tagged and released 16 km offshore. He was tracked to 124 locations during 28 days in March–April 1995.

    Study and other actions tested
  4. A controlled study in 1995–1996 of a pelagic area in the North Atlantic Ocean, off the coast of Maryland, USA (Westgate et al. 1998) found that a stranded harbour porpoise Phocoena phocoena that was rehabilitated and released back into the wild survived for at least 50 days and had similar movements and behaviour to wild porpoises. The rehabilitated female porpoise was successfully tracked for 50 days after release before contact was lost with the transmitter. The average distance of the released porpoise from the shore (31 km), average daily distance travelled (33 km), average rate of travel (1.4 km/h) and proportion of time spent at the water surface (3%) were within the ranges of seven wild porpoises tracked by the authors in a previous study (see original paper for details). In April 1995, the porpoise was found stranded and underweight, and taken to a rehabilitation facility. The porpoise was kept in a 4-m deep, 370,000-l pool, treated for parasites and bacterial infections, and fed fish and squid at 11% of its body mass/day. After 13 months of rehabilitation, the porpoise (aged approximately two years old) was satellite-tagged and released offshore. The porpoise was tracked to 142 locations in April–June 1996.

    Study and other actions tested
  5. A replicated study in 1996–1997 of two pelagic areas in the Gulf of Mexico and the North Atlantic Ocean, USA (Wells et al. 1999) found that two stranded common bottlenose dolphins Tursiops truncatus that were rehabilitated and released back into the wild survived for at least 1.5 months. The two adult male dolphins were successfully tracked for 43 and 47 days after release back into the wild. The dolphins travelled a total of 2,050 and 4,200 km at average rates of 48 and 89 km/day respectively, along the coast and into deeper offshore waters. The dolphins were found stranded in December 1996 and January 1997 and transported to rehabilitation facilities. They were housed in pools (200,000–800,000 l), given antibiotics and fed fish. After 39–85 days of rehabilitation, the dolphins were satellite-tagged and released at sites 46–70 km offshore. The dolphins were tracked to 10–69 locations in March–April and May–July 1997.

    Study and other actions tested
  6. A study in 1998 of a pelagic area in the North Pacific Ocean, off the coast of California, USA (Lander et al. 2000) found that a stranded and underweight Guadalupe fur seal Arctocephalus townsendi that was rehabilitated and released back into the wild survived for at least seven weeks. The rehabilitated female seal was successfully tracked for seven weeks after release before contact was lost with the transmitter. During that time, the seal travelled at least 2,890 km at an average rate of 3 km/h. The adult seal was found stranded and underweight in January 1998 and taken to a rehabilitation facility. After eight weeks of rehabilitation, the seal was released at a peninsula with a satellite transmitter attached. The seal was recorded at 25 locations during seven weeks in March–April 1998.

    Study and other actions tested
  7. A replicated study in 1992–1998 at multiple sites in the North Atlantic Ocean, off the coast of southwest England, UK (Barnett & Westcott 2001) found that 152 of 188 (81%) sick or injured grey seal Halichoerus grypus pups were successfully rehabilitated and released. Eighty-one percent of rescued grey seal pups (152 of 188) were successfully rehabilitated and released back into the wild. Survival of the pups after release was not reported. The other 36 seal pups died during rehabilitation due to their original illness or injury (28 pups) or complications during rescue and rehabilitation (e.g. accidental drowning, reaction to treatment, hyperthermia; 8 pups). All of 188 sick or injured seal pups (aged <5 days to 10 months old) were rescued between August 1992 and February 1998 along the coast of southwest England, UK and taken to a rehabilitation facility by experienced handlers or members of the public. Following rehabilitation, 152 pups were released back into the wild (number of release sites not reported).

    Study and other actions tested
  8. A study in 1993–1994 of a pelagic area in the North Atlantic Ocean, off the coast of Florida, USA (Scott et al. 2001) found that a stranded pygmy sperm whale Kogia breviceps that was rehabilitated and released back into the wild survived for at least four days. The female pygmy sperm whale was successfully tracked for four days after release before contact was lost with the transmitter. During that time, the whale travelled at least 425 km at an average speed of 5.5 km/h and made regular dives. In November 1993, the whale (aged 12–18 months old) was found stranded and in poor health and taken to a rehabilitation facility. Pieces of plastic were removed from the whale’s stomach. In May 1994, the whale was transferred to an outdoor tank close to the release site for 25 days before being radio-tagged and released 65 km offshore. The whale was tracked every 30 minutes and observed daily from a vessel during four days in May–June 1994.

    Study and other actions tested
  9. A study in 1989–1999 of multiple sites in the North Atlantic Ocean, off the coast of Brittany, France (Vincent et al. 2002) found that at least a quarter of stranded grey seal pups Halichoerus grypus that were rehabilitated and released back into the wild survived and were re-sighted alive. Twenty-five of 92 (27%) rehabilitated seal pups were re-sighted alive 1–49 times up to five years after release. Nineteen pups (21%) were re-sighted dead. Survival was not known for the other 48 pups, which were not seen again. Seventeen of the seals re-sighted alive settled at two grey seal haul-out sites close to release sites or along the coast. Eight seals dispersed across the English Channel. In 1989–1999, ninety-two seal pups (aged a few days to a few months old) were found stranded and underweight and taken to a rehabilitation facility. They were released at sea after one month of rehabilitation (in 1989–1990) or after they reached a weight of 40–45 kg (in 1991–1999). All 92 pups were marked with flipper tags. Some were additionally marked with coloured markings (40 pups) or head tags (28 seals) or were photographed for identification (25 seals) or satellite-tagged (four seals). Opportunistic observations were made of released seals both on shore and at sea (dates not reported). The four satellite-tagged seals were tracked for 14–80 days in June–September 1997.

    Study and other actions tested
  10. A study in 1999–2000 of a pelagic area in the Gulf of Maine, USA (Nawojchik et al. 2003) found that two stranded juvenile long-finned pilot whales Globicephala melas that were rehabilitated and released back into the wild survived for at least four months. The two rehabilitated male whales were successfully tracked for 127–132 days after release back into the wild. During that time, they travelled at least 3,790 km at average speeds of 23–66 km/day. Tracking positions suggest that the two whales remained together after release. The two juvenile whales (220 and 313 cm long) were found stranded on a beach in June 1999 and taken to a rehabilitation facility. They were housed in a pool and fed herring (average 25 kg/day). After four months of rehabilitation, both whales were fitted with satellite-linked time-depth recorders and released at sea in October 1999. They were recorded at 329–386 locations during 127–132 days between October 1999 and February 2000.

    Study and other actions tested
  11. A study in 1986–1987 of a pelagic area in the North Atlantic Ocean, near Cape Cod, USA (Mate et al. 2005) found that a stranded juvenile long-finned pilot whale Globicephala melas that was rehabilitated and released back into the wild survived for at least three months. The rehabilitated male whale was successfully tracked for 95 days after release and travelled at least 3,144 km during that time. The whale was observed with a group of wild long-finned pilot whales 20 days after release. The juvenile whale (aged two years old) was rescued after a mass stranding event in December 1986 and taken to an aquarium. After seven months of rehabilitation, the whale was fitted with a satellite tag and released in the ocean 160 km southeast of the stranding site. Two other juvenile whales rescued from the same site were also released but were not fitted with tags. The tagged whale was tracked to 204 locations during 95 days in June–September 1987.

    Study and other actions tested
  12. A study in 1999 on an island in the North Sea, off the Netherlands (Osinga & t'Hart 2006) found that an injured common seal Phoca vitulina that had ingested a fishing hook was successfully rehabilitated and released back into the wild. The fishing hook was successfully removed from the female seal, and she was released back into the wild four months after capture. Survival after release was not reported. The seal was found stranded and in poor condition on the coast of an island on 9 April 1999. An x-ray showed an ingested fishing hook within the seal’s stomach. The seal was fed small bits of loose cotton wool through a tube and given oral rehydration salts. On 30 May 1999, the seal defecated the remains of the hook and the cotton wool. The seal was released back into the wild on 6 August 1999. In 2005, a male common seal that had ingested a fishing hook and given the same treatment was also reported to have survived but the authors did not state whether the seal was successfully released.

    Study and other actions tested
  13. A replicated study in 1977–2002 at multiple pelagic sites in the North Pacific Ocean, off the coast of California, USA (Zagzebski et al. 2006) found that seven of 70 (10%) stranded toothed whales (Odontoceti) were successfully rescued, rehabilitated and released back into the wild, and three were known to survive for at least three days to five months after release. Seven of 70 (10%) stranded toothed whales were successfully rescued and released back into the wild. Two common dolphins Delphinus delphis and one harbour porpoise Phocoena phocoena were tracked after release for 3 days, 31 days and five months respectively. Survival of the other four released animals (two bottlenose dolphins Tursiops truncatus, two common dolphins Delphinus spp.) was not reported. The other 63 stranded animals either died during rescue (21), transport (five) or rehabilitation (34) or were kept in captivity (three). Seventy toothed whales of 13 species were found stranded alive in 1977–2002 (see original paper for details). Thirty-seven animals were given medical treatment at rehabilitation facilities. Two common dolphins and one harbour porpoise were satellite-tagged and tracked after release in 1994, 1995 and 2001–2002 respectively. Two bottlenose dolphins and two common dolphins were released but not tracked (dates not reported).

    Study and other actions tested
  14. A study in 2003–2004 of a pelagic area in the North Atlantic Ocean, off the coast of Maryland, USA (Schofield et al. 2008) found that a stranded juvenile harbour porpoise Phocoena phocoena that was rehabilitated and released back into the wild survived for at least two months. After release, the rehabilitated male porpoise was successfully tracked for 63 days before contact was lost with the transmitter due to battery failure. During that time, the porpoise travelled at least 2,880 km and returned to an area close to the original stranding site. In March 2003, the 10-month old harbour porpoise was found stranded and underweight with injuries from birds and fishing nets. After 10 months of rehabilitation at an aquarium, the porpoise was satellite-tagged and released offshore at a site >1,200 km north of the stranding location. Prior to release, the porpoise was gradually acclimatized to local sea water and ambient temperatures. The porpoise was tracked to >300 locations during six days in January–March 2004.

    Study and other actions tested
  15. A study in 2000–2001 in an estuary in the Indian River Lagoon, Florida, USA (Mazzoil et al. 2008) found that a stranded common bottlenose dolphin Tursiops truncatus that was rehabilitated and released back into the wild survived for three months. The adult male dolphin (aged 24 years) survived for 100 days after release but subsequently died after an invasive species of fish (black chin tilapia Sarotherodon melanotheron) became lodged in his larynx. The dolphin travelled 67 km from the release site and was observed socializing with other dolphins after release. In August 2000, the dolphin was found stranded on a boat ramp with severe shark bite wounds and transported to a rehabilitation facility. After six months of rehabilitation, the dolphin was radio-tagged and released back into the estuary. He was tracked twice weekly until June 2001 when his body was recovered 35 km from the release site.

    Study and other actions tested
  16. A study in 2005 of a pelagic area in the North Atlantic Ocean, off the coast of Florida, USA (Wells et al. 2008) found that five stranded rough-toothed dolphins Steno bredanensis that were rehabilitated and released back into the wild survived for at least 2–7 weeks. The five dolphins were tracked for 12–49 days after release before contact was lost with their transmitters. They travelled a total of 687–3,488 km, at average rates of 4–6 km/h and 55–99 km/day, in both coastal and offshore waters. In March 2005, ten dolphins were rescued during a mass stranding event and taken to rehabilitation facilities. The dolphins were released in April, May and September 2005, five (one male, four females) with satellite-tags attached. The five satellite-tagged dolphins were tracked to 45–289 locations each in April–June or September 2005.

    Study and other actions tested
  17. A study in 2005–2006 of a pelagic area in the Gulf of Mexico, USA (Wells et al. 2009) found that a stranded Risso’s dolphin Grampus griseus that was rehabilitated and released back into the wild survived for at least three weeks. The released male dolphin was successfully tracked for 23 days before contact was lost with the transmitter. The dolphin travelled more than 3,300 km at an average speed of 7.2 km/h and occupied appropriate habitats (warm water over steep slopes) in areas known to be used by the species. The adult dolphin was taken to a rehabilitation facility after a mass stranding event in July 2005. He was treated with antibiotics, anti-fungal and anti-ulcer medications, and fed 18 kg squid/day. After seven months of rehabilitation, the dolphin was satellite-tagged and released 159 km offshore. The dolphin was tracked for 23 days in February–March 2006. A female adult Risso’s dolphin rescued at the same time died during rehabilitation.

    Study and other actions tested
  18. A study in 2008 of a pelagic area in Bohai Bay, China (Yu et al. 2009) found that a stranded west Pacific finless porpoise Neophocaena phocaenoides sunameri was successfully rehabilitated and released back into the wild. The stranded female porpoise was successfully released back into the wild after two months of rehabilitation. Survival after release was not reported. The porpoise was found stranded, dehydrated and infected with parasitic flatworms (Nasilrema spp. and Zalophotrema hepaticum) in March 2008.  She was transported to an aquarium and placed in a medical pool (6 x 3 x 1 m, 1,500 l artificial saltwater) and given minced herring and shrimp (0.5–1.5 kg/day), vitamin powders, fluids, electrolytes and antibiotics. Water quality parameters (temperature, pH, dissolved oxygen, ammonia and nitrite) were monitored daily within the pool. After two months of rehabilitation, the porpoise was released 18.5 km offshore in shallow waters in June 2008.

    Study and other actions tested
  19. A controlled study in 2003–2006 of multiple coastal and pelagic sites in the North Pacific Ocean, California, USA (Thomas et al. 2010) found that at least a quarter of stranded California sea lions Zalophus californianus treated for toxic algae poisoning and released back into the wild died or had to be euthanized, and released sea lions travelled further from the shore, spent less time diving or hauled out and made shorter, shallower dives than wild sea lions without poisoning. Nine of 34 stranded sea lions treated for toxic algae poisoning died or were euthanized within 7–43 days of release. The fate of the other 25 sea lions was not known. Compared to wild sea lions without poisoning, treated sea lions on average travelled greater maximum distances from the shore (163–186 vs. 35 km), spent a lower percentage of time diving (20% vs. 22%) or hauled out (33% vs. 39%) and made shorter, shallower dives (9 vs. 15 minutes, maximum 203 vs 286 m). In 2003–2006, thirty-four stranded sea lions with toxic algae poisoning (domoic acid toxicosis; 12 acute, 22 chronic) were taken to a rehabilitation facility. Drugs were given to control seizures and reduce brain swelling (dexamethasone). All 34 sea lions were satellite-tagged and released. Nineteen sea lions with chronic poisoning were fitted with tags to record dive behaviour. Released sea lions were tracked for <1–129 days in 2003–2006. Sixty-seven wild sea lions without poisoning were captured, tagged and tracked in 2003–2006.

    Study and other actions tested
  20. A replicated study in 1984–2005 of multiple sites on islands in the North Pacific Ocean, Hawaii, USA (Gilmartin et al. 2011) found that approximately half of Hawaiian monk seal Monachus schauinslandi young that were rehabilitated, translocated, and released back into the wild survived for at least one year, and half of those produced offspring. The study did not distinguish between the effects of rehabilitation and translocation. Thirty-five of 68 monk seal young (52%) that were rehabilitated, translocated, and released back into the wild survived for at least one year after release. By 2005, eighteen of the 35 surviving seals (51%) had produced offspring in the wild (at least 68 pups). Thirty other monk seal young captured for rehabilitation either died in captivity (17 seals) or were kept permanently in captivity for health or behavioural reasons (13 seals). In 1984–1985, a total of 98 weaned, female seals (aged <3 years old) that were underweight, sick or threatened (by human disturbance, shark predation or aggressive adult male seals) were collected from islands (the French Frigate Shoals) and brought into captivity. The seals were transported by plane or ship and kept at care facilities or in beach enclosures. Captive seals were given medical treatment and fed milk formula or fish with multivitamins. After 3–14 months of rehabilitation, the 68 seals were fitted with tags, released at different islands (Kure Atoll and Midway Islands), and observed annually in 1984–2005.

    Study and other actions tested
  21. A controlled study in 2003–2004 in an estuary, The Wash, Norfolk, UK (Morrison et al. 2012) found that six sick or injured harbour seal Phoca vitulina pups that were rehabilitated and released back into the wild survived for at least three months, were tracked for similar durations and had similar dive behaviour to wild seals. Six rehabilitated harbour seal pups were tracked for 100–175 days after release. On average, the six rehabilitated seals were tracked for similar durations (122 days) to five wild seals (150 days), indicating similar short-term survival. Average dive durations and percentage of time at-sea spent diving were also similar for rehabilitated seals (4.0 minutes; 81.6%) and wild seals (4.1 minutes; 81.5%). In September–October 2003, six juvenile seals (aged 2–3 months; four males, two females) were rescued with wounds and/or respiratory problems. After 134–169 days of rehabilitation, the six seals were satellite-tagged and released in an estuary in February 2004. Five wild adult harbour seals (one male, four females) were caught in the estuary and satellite-tagged in February 2004. Data were collected for each of the 11 seals during 100–170 days in February–August 2004. Average dive durations were adjusted according to body mass.

    Study and other actions tested
  22. A review of 56 case studies in 1986–2008 in the North Atlantic Ocean and North Pacific Ocean, USA (Wells et al. 2013) found that approximately one third of rehabilitated common bottlenose dolphins Tursiops truncatus and other small cetacean species that were released back into the wild survived for at least six weeks and had normal behaviour. For common bottlenose dolphins, seven of 20 releases (35%) were considered successful (the dolphin was tracked for at least six weeks after release with normal behaviour for the species). Eight releases (40%) had unknown success, and five (25%) failed (the dolphin died, re-stranded or had abnormal behaviour). For other small cetaceans (including other dolphin species, porpoises and whales; see original paper for details), 13 of 36 releases (36%) were considered successful, 22 releases (61%) had unknown success, and one (3%) failed. The common bottlenose dolphins were found stranded (13 dolphins), trapped out of their natural habitats (three), entangled in fishing gear (three) or orphaned (one) in 1992–2008 and rehabilitated for 37–225 days before release. Thirty-six other small cetaceans were found stranded in 1986–2007 and rehabilitated for 35–394 days before release. Data were from published and unpublished studies. Eleven studies have also been summarized individually. Details of monitoring methods were not reported.

    Study and other actions tested
  23. A study in 2010–2012 of coastal sites in the North Pacific Ocean, California, USA (Prager et al. 2015) found that less than one half of stranded California sea lions Zalophus californianus were successfully rehabilitated and released back into the wild. Fourteen of 35 sea lions were rehabilitated and released back into the wild, although survival after release was not reported. The other 21 sea lions died shortly after admission to the rehabilitation facility. Antibiotic treatments eliminated a bacterial infection (leptospirosis) within 1–7 weeks for four of the 14 surviving sea lions. The other 10 sea lions tested positive for leptospirosis during final tests before their release (4–12 weeks after admission to the facility). In 2010–2011, thirty-five stranded sea lions were admitted to a rehabilitation facility and diagnosed with the bacterial infection leptospirosis. Fourteen surviving sea lions were treated with antibiotics, fluids, parasite treatments and anti-inflammatory drugs (see original paper for details). Urine and blood samples were collected approximately every 14 days from admission until release in 2010–2012. DNA analysis, urine cultures and tests for antibodies were used to detect leptospirosis infections.

    Study and other actions tested
  24. A replicated study in 1988–2013 at multiple freshwater, marine and brackish water sites in Florida, USA (Adimey et al. 2016) found that 41 of 51 (80%) sick or injured Florida manatees Trichechus manatus latirostris that were rehabilitated and released back into the wild survived for at least one year. Twenty-two of 25 sick manatees (88%) and 19 of 26 injured manatees (73%) that were rescued and rehabilitated survived for at least one year in the wild after release, occupied appropriate habitats, did not require additional rescue and were in good condition. Three sick and seven injured manatees required intervention or died within the first year (number for each not reported). Twenty-five rescued manatees were sick (exposed to toxic algae or severe cold weather) and 26 were injured (by boat collisions, fishing gear or entrapment). All 51 manatees were rehabilitated in captivity for between <1 and >10 years before being released back into the wild. Release sites were warm freshwater, marine or brackish water near rescue locations or alternative locations used by wild manatees (number of sites for each not reported). Each of 51 released manatees was monitored with radio-tracking and visual observations once or twice/week for at least one year in 1988–2013.

    Study and other actions tested
  25. A study in 2011 at a freshwater site in El Dorado Lake, Pacaya Samiria National Reserve, Peru (Landeo-Yauri et al. 2017) found that three rehabilitated female Amazonian manatees Trichechus inunguis that were released into the wild survived for at least 3–5 months, and two rehabilitated male manatees dispersed away from the release site. Three rehabilitated female manatees were tracked for 91–161 days after release and were found to use appropriate habitats at the release site (areas with floating vegetation). Contact was lost with the two rehabilitated male manatees 1–11 days after release when they dispersed to other areas. Five rescued manatees that were either pets (two males, two females) or illegally traded (one female) were rehabilitated with veterinary treatment and a diet of water lettuce Pistia stratiotes. After 13–31 months of rehabilitation, each of the five manatees (aged 32–79 months) was transported by seaplane, fitted with a radio-tag and placed in a floating cage (10 x 10 x 3 m) within a lake for an acclimatization period of three months before being released in July 2011. Radio-tracking was carried out between 0600 and 1800 h during 161 days in July–November 2011.

    Study and other actions tested
  26. A study in 2017 at a coastal site in the southern Gulf of California, Mexico (Elorriaga-Verplancken et al. 2018) found that a rehabilitated blind California sea lion Zalophus californianus that was released back into the wild survived for at least 53 days after release. The male sea lion was observed 53 days after release at a beach located 1,500 km from the release site on a known migration route for the species. In February 2017, the blind sea lion (aged 5–6 years) was found stranded in poor condition and was transported to an aquarium for medical care. The sea lion was fed >11 kg of fish/day and increased in body mass by 74 kg during 106 days of rehabilitation. In May 2017, the sea lion was tagged and released at a known California sea lion colony in the southern Gulf of California. The sea lion was observed on an island in the North Pacific Ocean off the coast of Mexico in July 2017 during a field expedition.

    Study and other actions tested
  27. A study in 2015–2016 of a pelagic area in the Gulf of Mexico, USA (Pulis et al. 2018) found that one of two stranded pygmy killer whales Feresa attenuata that were rehabilitated and released back into the wild survived for at least three months. One of two rehabilitated male pygmy killer whales survived for at least 88 days after release, after which contact was lost with the transmitter. The pygmy killer whale used a 250-km span of continental shelf and travelled an average of 24 km/day. The other pygmy killer whale was tracked for 15 days before contact was lost and is likely to have died (diving behaviour was reduced before loss of contact). Two adult pygmy killer whales were found stranded in an estuary on 1 September 2015 and transported to a rehabilitation facility. On 11 July 2016, both pygmy killer whales were satellite-tagged and released offshore in water >200 m deep with known sightings of other pygmy killer whales. The whales were tracked to 129–947 locations during 15–88 days in July–October 2016.

    Study and other actions tested
Please cite as:

Berthinussen, A., Smith, R.K. and Sutherland, W.J. (2021) Marine and Freshwater Mammal Conservation: Global Evidence for the Effects of Interventions. Conservation Evidence Series Synopses. University of Cambridge, Cambridge, UK.

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