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What Works in Conservation 2021

 | 
William Junior Sutherland
, 
Lynn V. Dicks
, 
Silviu O. Petrovan
, 
et al.

14. Marine and freshwater mammal conservation

14.12 Species management

Texte intégral

14.12.1 Species recovery

Beneficial

Rescue and release stranded or trapped marine and freshwater mammals

1Eleven studies evaluated the effects of rescuing and releasing stranded or trapped marine and freshwater mammals. Five studies were in the North Atlantic Ocean (USA), two studies were in the Indian Ocean (Tasmania, South Africa), and one study was in each of the South Atlantic Ocean (Brazil), the Cachoeira River estuary (Brazil), the North Pacific Ocean (USA) and the Shannon Estuary (Ireland).

2COMMUNITY RESPONSE (0 STUDIES)

3POPULATION RESPONSE (11 STUDIES)

4Reproductive success (2 studies): One review in the North Pacific Ocean found that after rescuing and releasing stranded or trapped Hawaiian monk seals, along with at least seven other interventions to enhance survival, more than a quarter of the seals reproduced. One study in the Shannon Estuary found that a stranded common bottlenose dolphin that was rescued and released was observed with a calf a year later.

5Survival (11 studies): Seven studies (including one review) in the North Atlantic Ocean, Indian Ocean and the Shannon Estuary found that 17–100 % of rescued and released Atlantic white-sided dolphins, short-beaked common dolphins, common bottlenose dolphins, long-finned pilot whales, short-finned pilot whales, and Cape fur seals survived during post-release monitoring periods, which ranged in length from three weeks to three years. Three studies in the South Atlantic Ocean, the Cachoeira estuary and the Indian Ocean found that a trapped rough-toothed dolphin, two stranded tucuxi dolphins and seven stranded sperm whales were successfully rescued and released, although long-term survival was not reported. One review in the North Pacific Ocean found that rescuing and releasing stranded or trapped Hawaiian monk seals, along with at least seven other interventions to enhance survival, resulted in more than a quarter of the seals surviving.

6BEHAVIOUR (0 STUDIES)

7Assessment: beneficial (effectiveness 70 %; certainty 64 %; harms 10 %).

https://www.conservationevidence.com/​actions/​2924

Likely to be beneficial

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

8Twenty-seven studies evaluated the effects of rehabilitating and releasing injured, sick or weak marine and freshwater mammals. Nine studies were in the North Atlantic Ocean (USA, UK, France), six studies were in the North Pacific Ocean (USA), four studies were in the Gulf of Mexico (USA), two studies were in each of the North Sea (the Netherlands) and the Gulf of Maine (USA), and one study was in each of the Indian River Lagoon (USA), Bohai Bay (China), The Wash estuary (UK), water bodies in Florida (USA), El Dorado Lake (Peru), and the Gulf of California (Mexico).

9COMMUNITY RESPONSE (0 STUDIES)

10POPULATION RESPONSE (26 STUDIES)

11Reproductive 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.

12Survival (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.

13BEHAVIOUR (3 STUDIES)

14Behaviour 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. Assessment: likely to be beneficial (effectiveness 60 %; certainty 70 %; harms 10 %).

https://www.conservationevidence.com/​actions/​2925

Trade-off between benefit and harms

Hand-rear orphaned or abandoned marine and freshwater mammal young

15Twelve studies evaluated the effects of hand-rearing orphaned or abandoned marine and freshwater mammal young. Four studies were in the North Pacific Ocean (USA), two studies were in captive facilities (USA), and one study was in each of the North Atlantic Ocean (USA), the Indian River Lagoon (USA), the Salish Sea (USA), the Guerrero Lagoon (USA), the South Atlantic Ocean (Brazil) and water bodies in Florida (USA).

16COMMUNITY RESPONSE (0 STUDIES)

17POPULATION RESPONSE (11 STUDIES)

18Reproductive success (1 study): One replicated study in the South Atlantic Ocean found that most captive-reared Antillean manatees released back into the wild reproduced.

19Survival (11 studies): Three studies (including one replicated and controlled study) in the North Pacific Ocean, and the Indian River Lagoon found that a gray whale calf, three Steller sea lion pups, and a common bottlenose dolphin calf that were released after being reared in captivity survived during post-release monitoring periods of between three days to three months. Two replicated studies in the South Atlantic Ocean and water bodies in Florida found that approximately three-quarters of Antillean manatees and two-thirds of Florida manatees that were captive-reared and released were known to survive for at least one year, and some survived for more than seven years. Three studies in the North Atlantic Ocean, the North Pacific Ocean and the Guerrero Lagoon found that three West Indian manatee calves, seven Hawaiian monk seal pups and one Antillean manatee calf that were captive-reared either died before or after release, had to be returned to captivity after release, or survived in the wild only with supplemental feeding. Two studies at captive facilities found that a captive-reared grey whale calf and five pygmy and dwarf sperm whale calves increased in body weight but were either not released or died in captivity. One controlled study in the North Pacific Ocean found that captive-reared, released Pacific harbour seal pups had similar survival estimates to wild pups.

20BEHAVIOUR (3 STUDIES)

21Behaviour change (3 studies): Two controlled studies (including one replicated study) in the North Pacific Ocean found that captive-reared and released Pacific harbour seal pups and Steller sea lion pups had similar diving behaviour to wild pups. One controlled study in the Salish Sea found that captive-reared and released harbour seal pups travelled greater distances and further from the release site than wild pups born at the same site and in the same season. Assessment: trade-off between benefit and harms (effectiveness 60 %; certainty 50 %; harms 20 %).

http://www.conservationevidence.com/​actions/​2926

Remove individual marine and freshwater mammals exhibiting aggressive behaviours that may limit population recovery

22One study evaluated the effects of removing individual marine mammals exhibiting aggressive behaviours that may limit population recovery. The study was in the North Pacific Ocean (USA).

23COMMUNITY RESPONSE (0 STUDIES)

24POPULATION RESPONSE (1 STUDY)

25Survival (1 study): One before-and-after study in the North Pacific Ocean found that after removing aggressive male Hawaiian monk seals, the survival of adult female Hawaiian monk seals increased.

26Condition (1 study): One before-and-after study in the North Pacific Ocean found that fewer female Hawaiian monk seals were injured after aggressive male Hawaiian monk seals were removed.

27BEHAVIOUR (0 STUDIES)

28Assessment: trade-off between benefit and harms (effectiveness 60 %; certainty 40 %; harms 20 %).

https://www.conservationevidence.com/​actions/​2929

Unknown effectiveness

Reunite abandoned marine and freshwater mammal young with parents

29One study evaluated the effects of reuniting abandoned marine and freshwater mammal young with parents. The study was in the North Pacific Ocean (USA). COMMUNITY RESPONSE (0 STUDIES)

30POPULATION RESPONSE (1 STUDY)

31Reproductive success (1 study): One review in the North Pacific Ocean found that after reuniting Hawaiian monk seal pups with their mothers, along with at least seven other interventions to enhance survival, more than a quarter of the seals reproduced.

32Survival (1 study): One review in the North Pacific Ocean found that after reuniting Hawaiian monk seal pups with their mothers, along with at least seven other interventions to enhance survival, more than a quarter of the seals survived.

33BEHAVIOUR (0 STUDIES)

34Assessment: unknown effectiveness (effectiveness 50 %; certainty 25 %; harms 0 %).

http://www.conservationevidence.com/​actions/​2927

No evidence found (no assessment)

35We have captured no evidence for the following interventions:

  • Legally protect marine and freshwater mammal species

  • Place orphaned or abandoned marine and freshwater mammal young with foster parents.

14.12.2 Translocation

Likely to be beneficial

Translocate marine and freshwater mammals to re-establish or boost native populations

36Four studies evaluated the effects of translocating marine mammals to re-establish or boost native populations. The four studies were in the North Pacific Ocean (USA).

37COMMUNITY RESPONSE (0 STUDIES)

38POPULATION RESPONSE (4 STUDIES)

39Reproductive success (2 studies): One replicated study and one review in the North Pacific Ocean found that after translocating Hawaiian monk seals, along with rehabilitation or at least seven other interventions to enhance survival, more than a quarter of the seals reproduced.

40Survival (4 studies): Two studies (including one replicated and one controlled study) in the North Pacific Ocean found that 50–83 % of translocated, and 52 % of rehabilitated and translocated, Hawaiian monk seal pups survived for at least one year. One of the studies and one review in the North Pacific Ocean found that translocated seal pups had similar survival rates to non-translocated pups born at release sites or greater survival rates than non-translocated pups remaining at the original site. One review in the North Pacific Ocean found that translocating Hawaiian monk seals, along with at least seven other interventions to enhance survival, resulted in more than a quarter of the seals surviving.

41BEHAVIOUR (1 STUDY)

42Behaviour change (1 study): One review in the North Pacific Ocean found that translocated Hawaiian monk seal pups had similar dispersal times to non-translocated seal pups born at release sites.

43Assessment: likely to be beneficial (effectiveness 50 %; certainty 50 %; harms 15 %).

https://www.conservationevidence.com/​actions/​2930

No evidence found (no assessment)

44We have captured no evidence for the following interventions:

  • Translocate marine and freshwater mammal species before onset of impactful activities.

14.12.3 Captive breeding, rearing and releases (ex-situ conservation)

Trade-off between benefit and harms

Breed marine and freshwater mammals in captivity

45Six studies evaluated the effects of breeding marine and freshwater mammals in captivity. Three studies were in the USA, one study was also in China, Indonesia and Venezuela, and one study was in each of South Africa, Hong Kong and China.

46COMMUNITY RESPONSE (0 STUDIES)

47POPULATION RESPONSE (6 STUDIES)

48Reproductive success (2 studies): One study in Hong Kong found that four of six female Indo-Pacific dolphins successfully conceived during a controlled captive breeding programme and gave birth to a total of nine calves. One study in China found that wild-caught Yangtze finless porpoises successfully reproduced in semi-captive conditions.

49Survival (4 studies): Two studies in South Africa and the USA found that a captive-born common bottlenose dolphin, and a captive-born and hand-reared common bottlenose dolphin, survived in captivity for at least two and a half years and four years respectively. One review in the USA found that 80 % of common bottlenose dolphins born in captivity over two decades survived, and survival increased with improved husbandry techniques. One review in the USA, China, Indonesia and Venezuela found that most captive-born Amazon river dolphins, narrow-ridged finless porpoises and Irrawaddy dolphins did not survive in captivity.

50Condition (1 study): One study in China found that a population of Yangtze finless porpoises breeding in semi-captive conditions had low genetic diversity. BEHAVIOUR (1 STUDY)

51Behaviour change (1 study): One study in the USA found that a captive-born and hand-reared common bottlenose dolphin displayed normal behaviour for the species and joined a dolphin social group in captivity.

52Assessment: trade-off between benefit and harms (effectiveness 40 %; certainty 40 %; harms 20 %).

https://www.conservationevidence.com/​actions/​2932

Unknown effectiveness

Release captive-bred marine and freshwater mammals to re-establish or boost native populations

53Two studies evaluated the effects of releasing captive-bred marine and freshwater mammals to re-establish or boost native populations. One study was in the Porto de Pedras estuary (Brazil) and one in water bodies in Florida (USA).

54COMMUNITY RESPONSE (0 STUDIES)

55POPULATION RESPONSE (2 STUDIES)

56Survival (2 studies): Two studies in the Porto de Pedras estuary and water bodies in Florida found that two of three Antillean manatees and two of 14 Florida manatees born in captivity and released into the wild survived for at least one year without further intervention.

57BEHAVIOUR (0 STUDIES)

58Assessment: unknown effectiveness (effectiveness 30 %; certainty 30 %; harms 20 %).

http://www.conservationevidence.com/​actions/​2933

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