Breed marine and freshwater mammals in captivity
Overall effectiveness category Trade-off between benefit and harms
Number of studies: 6
Background information and definitions
Captive breeding involves taking wild animals into captivity and establishing and maintaining breeding populations. For conservation purposes, it tends to be undertaken when wild populations become very small or fragmented or when they are declining rapidly. Captive populations can be maintained while threats in the wild are reduced or removed and can provide an insurance policy against catastrophe in the wild. Captive breeding also potentially provides a method of increasing reproductive output beyond what would be possible in the wild. However, captive breeding can result in problems associated with inbreeding depression, removal of natural selection, adaptation to captive conditions and familiarity with humans.
The aim is usually to release captive-bred animals back to natural habitats, either to original sites once conditions are suitable, to reintroduce a species to sites that were previously occupied, or to introduce species to new sites. The studies summarised below evaluated the effects of captive-breeding only. For evidence related to the release of captive-bred mammals, see Release captive-bred marine and freshwater mammals.
Supporting evidence from individual studies
A study (year not stated) at an aquarium in Durban, South Africa (Peddemors et al. 1992) found that a captive-born common bottlenose dolphin Tursiops truncatus successfully suckled from its mother, weaned onto fish and survived for at least two and a half years. The male calf successfully suckled from its mother and began eating fish at 11 months of age. The calf survived for at least 30 months and grew in length (1.2–2.7 m) and body mass (50–240 kg) during that time. The calf was born in captivity from a wild-born mother (aged 6.5 years) captured three months earlier from the South Atlantic Ocean, Namibia. The mother and calf were kept in a pool and observed from an underwater window for a total of 1,149 h over 18 months (dates not reported). The length and weight of the calf were estimated at birth. The calf was measured directly from 2–30 months of age and weighed from 16–30 months of age on regular occasions.Study and other actions tested
A study in 1993–2003 at a marine park in Hong Kong (Brook & Kinoshita 2005) found that during a controlled captive-breeding programme, four of six female Indo-Pacific dolphins Tursiops aduncus successfully conceived and gave birth to nine calves, seven of which survived. Four of six female dolphins successfully conceived in captivity and gave birth to a total of nine live-born calves (1–3 calves each). One other female mated but did not conceive, and one female conceived but the calf was stillborn. Seven of the nine live-born calves survived (length of time not reported) and were considered healthy. The other two calves died within 1–3 days due to lung infections or trauma caused by the mother. On 11 occasions in 1993–2003, one of six ovulating female dolphins (aged 10–25 years) was placed in a pool with one of five male dolphins (aged 10–31 years). Male and female dolphins were housed separately at all other times. Ultrasound was used to predict the timing of ovulation and to monitor each of the 10 pregnancies during gestation periods of 349–382 days.Study and other actions tested
A study in 1990–2002 at the Tian-e-Zhou Oxbow in China (Xia et al. 2005) found that wild-caught Yangtze finless porpoises Neophocaena phocaenoides asiaeorientalis successfully reproduced in semi-captive conditions, but genetic diversity within the population was low. Between 1990 and 2002, wild-caught Yangtze finless porpoises introduced to an oxbow successfully gave birth to 1–3 calves/year. However, measures of genetic diversity within the population in 2002 were reported to be low (see original paper for details). Wild Yangtze finless porpoises captured from the Yangtze river (number not reported) were originally introduced to the oxbow in 1990. The naturally formed oxbow (21 km long, 1–1.5 m wide, average depth 4.5 m) was cut off from the main channel of the Yangtze River in 1972 and designated as a reserve in 1992. Following the escape and release of some individuals, four porpoises remained in the oxbow in 1997. A further nine wild-caught individuals were introduced in 1998–1999. In 2002, DNA samples were extracted from all 22 porpoises within the oxbow population (seven females, 15 males) and an additional female that was transferred to a captive facility in 1999.Study and other actions tested
A review of case studies in 1990–2009 at three captive facilities in the USA (Sweeney et al. 2010) reported that most common bottlenose dolphins Tursiops truncatus born in captivity survived for at least one year, and survival increased with improved husbandry techniques. Results are not based on assessments of statistical significance. A total of 249 common bottlenose dolphins were born in captivity over 20 years. Of those, 201 calves (80%) survived to at least one year of age. Calf survival within 30 days of birth was higher during the second decade of the study with improved husbandry techniques (126 of 139 calves; 91%) than during the first decade of the study (86 of 110; 78%). Data on live-births and survival of common bottlenose dolphin calves in captivity were collected from three public display/research facilities for 10 years before (1990–1999) and 10 years after (2000–2009) improvements to husbandry techniques. This included standardized monitoring of mothers and calves and interventions (medical treatments, nutritional supplements etc.; see original paper for details).Study and other actions tested
A review of case studies in 1970–2011 at five captive facilities in the USA, China, Indonesia and Venezuela (Curry et al. 2013) found that small numbers of Amazon river dolphins Inia geoffrensis, narrow-ridged finless porpoises Neophocaena asiaeorientalis and Irrawaddy dolphins Orcaella brevirostris were born in captivity but most did not survive. Two Amazon river dolphin calves born in captivity in the 1970s died within 15 days of birth, and two of three calves born in 2000–2009 died within 1.5–5 years. The other calf survived for at least six years. Two of three narrow-ridged finless porpoises born in captivity in 2005–2008 died within 5–39 days of birth. The other calf survived for at least six years. Two Irrawaddy dolphins born in captivity in 1979 were known to survive for at least five years. Live births and the survival of calves in captivity were recorded for each of the three dolphin or porpoise species at five facilities between 1970 and 2011.Study and other actions tested
A study in 2013–2017 at a captive facility in the USA (Flower et al. 2018) found that a common bottlenose dolphin Tursiops truncatus calf that was born in captivity and hand-reared survived for at least four years, displayed normal behaviour for the species and successfully joined a dolphin social group at the facility. In 2015, the hand-reared male dolphin (aged 15 months) had fully integrated into a mixed social group at the facility consisting of seven other bottlenose dolphins. In 2017, the hand-reared dolphin (aged four years) was observed to be healthy and displaying normal behaviours (feeding, social interactions). The calf was born in captivity in October 2013, housed in a nursery pool and given intensive medical care after being rejected and injured by its mother. The calf was fed milk and serum from the mother followed by formula via a gastric tube before being weaned onto herring at 4–6 months. At four months old, the calf was gradually reintroduced to other dolphins.Study and other actions tested