Captive Breeding of Marine Mammals: Challenges and Mitigating Measures
Introduction
The growing demand to sustain the current lifestyle of the human population puts an added strain to the natural resources of the world. The increase in the exploitation of tropical forests and marine communities leads to a series of habitat destruction thereby leaving thousands of species of both terrestrial and marine animal homeless (Soule et al., 1986). Since 1986, there are already about nineteen percent and nine percent of the world’s mammals and birds respectively that are bread by zoos as per the International Zoo Yearbook Census. Based on the International Species Inventory System, there are about 60,000 specimens of mammals and birds in the collection of North America. Of the 60,000 specimens of mammals and birds ninety percent of all mammals were bred in captivity while there are seventy five percent of all listed birds that were also under captive breeding programs. Species of reptiles, amphibians, fishes and invertebrates are not yet included in the said inventory. As the years go by, the list of endangered species is steadily growing in numbers (Soule et al., 1986). To date, there are about ten thousand species of animals with a total population of twenty six billion that are kept under the care of farms, zoos, conservation breeding center, laboratories and households (Mason, 2012).
Captive breeding is often considered as a last resort for the conservation of a critically endangered species. Some of the animals that are under breeding in captivity include the California condor (Gymnogyps californicus) and the Owens pupfish (Cyprinodon radiosus). The aim of this paper is to discuss the pros and cons of captive breeding focusing on the habitat, biology, and conservation status of marine mammals with special emphasis on cetaceans and sirenians. It is also the aim of this paper to discuss the viability of captive breeding in marine mammals, the emerging concerns and issues that confront conservation biologists with respect to the captive breeding in general and how conservation biologists attempt to address these challenges in captive breeding.
The Marine Mammals: Cetaceans and Sirenians
Marine mammals are subdivided into two major orders: Cetacea (composed of whales, dolphins and porpoises); and Sirenia (i.e. manatees and dugong, pinnipeds, sea lions, walrus, and sea otter). Other marine mammals also include polar bears.
Both sirenians and cetaceans are the only marine mammals that lived under water. Cetaceans have generally developed unique ways to adapt to their environment. Some of these manifestations of adaptations with the marine environment include blowholes, flippers and tail flukes. Cetaceans and Sirenians expend too much energy in maintaining their internal body temperature. Thus, they develop layers of fat in their body to keep them insulated and consume their diet in huge proportions. These marine mammals have a wide range of diet extending from phytoplankton, seagrasses and fishes. Because of the large amount of food and a specialized diet that Baleen whales consume, these species have rarely been kept for captivity (Anonymous, 2005; Anandharaj et al., 2013).
Marine mammals especially Cetaceans are very sensitive to acoustics since it is the main sense that these animals use to navigate (echolocate) and communicate. Cetaceans are also very sensitive to chemicals. The presence of chlorine in their aquatic environment disallows these mammals to detect pheromones. While dugongs are solitary in nature or travel in small groups, whales and dolphins are social in nature. Because dolphins and whales live in groups, these animals are able to maximize their foraging and defense units while increasing the efficiency of reproduction and calf-rearing. Compared to whales and dolphins, dugongs have low reproductive rates that contribute to a great decline in their population (Anonymous, 2005; Anandharaj et al., 2013).
Pros of Captive Breeding
Understanding the Status of Global Biodiversity and Coverage of Marine Mammals
Marine mammals are considered as top predators in the complex food web that exists in the marine environment. Predators put a strong influence on the community structure of every ecosystem. However, these predators are also affected by a wide range of anthropogenic activities such as excessive fishing activities, offshore wind farming, military sonar activities, and siltation. Such anthropogenic activities may affect the habitat of these marine mammals that could also implicate marine biodiversity (Kaschner et al., 2012). Over the past 40 years, conservation efforts have been made to study cetacean abundance and distribution. In the 430 surveys that were undertaken from 1975-2005, 47 species of Cetaceans were only identified. In total, only 25% of the world’s ocean surface was surveyed. Of this 25% only 6% were frequently surveyed focusing mostly on the Eastern Tropical Pacific. Sperm whales were the only Cetaceans where data is abundant for analysis. The Baltic Sea on the other hand supports 6,065 species of marine flora and fauna to include 3 species of seal—ringed seal (Phoca hispida), grey seal (Halichoerus grypus), and harbor seal (Phoca vitulina). The population size of ringed seals ranges from 180,000-200,000 in the early 1900s. However, the population of ringed seals dwindled by 5,000 in the early 1970s. Similarly, there were 90,000 grey seals during the same period, but the population was reduced to 3,000 in the early 1970s. Harbor seals are the only species that is widely distributed all over the Baltic Sea (Ojaveer, 2010). According Anandharaj and colleagues (2013) there were 250 dugongs found foraging in the Indian, Andaman Nicobar, and Sri Lankan and coasts that were killed in April 1983 to August 1984.
Attempts to predict the number of mammalian species that would require captive maintenance in 200 years past 1986 were also projected by Soule and colleagues. Of the 65 recognized species of toothed whales (SubOrder Odontocea), there would be 10 vulnerable species that may require captive breeding. On another note, all four recognized species of sirenians (Order Sirenia) would require captive breeding in the next 200 years.
Conservation of Endangered Marine Mammals: The Viability of Captive Breeding
Basic knowledge of the abundance and trends, as well as the distribution of marine mammals is among the most important keys toward conservation. The function of zoo and aquariums has changed significantly since the 1980s. In 1993, the first World Zoo and Aquarium Conservation Strategy are established. Indeed captive breeding has become a very essential tool in conservation programmes. Several molecular studies related to captive populations of several animals are published, especially those that are identified as an endangered species. In these published studies, there is a common pattern indicating the possibility of inbreeding that could be minimized through a thorough management of captive population. There are several problems that may arise in captive breeding that could affect the survival of the captive population as well as the success of reintroducing these captive animals. However, captive breeding helps conservation biologist to preserve the maximum genetic viability of animals (Witzenberger and Hochkirch, 2011).
In some studies, captive breeding has been made to perpetuate the existence of the endangered Hawaiian monk seal (Monachus schauin-slandi). The poor survival of these species is due to the limited number of prey that these seals could feed on. In 2006-2007, a captive care project was initiated to determine whether temporary nutrition supplements should and protection from predation would enhance the proliferation of the monk seals. At first, the captive seals were alive. However, they did not reached their 2-year old mark as compared to the 4-year old control group. Such results however, could be attributed to the suitability of release locations and the duration of the captive feeding program (Norris, Littnam, and Galland, 2011).
The reproductive success of Indo-Pacific bottlenose dolphins (Tursiops aduncus) at Ocean Park, Hongkong was monitored using technologies such as ultrasonographic monitoring of the process called folliculogenesis and ovulation. Through ultrasonography captive breeders could identify the reproductive state of female dolphins. The success rate of unassisted breeding and using ultrasonography alone is 91% better than using artificial insemination (Brook and Kinoshita, 2005). According to Brook and Kinoshita (2005), controlled captive breeding of dolphins allows all reproductively fit animals within a group to be able reproduce while minimizing the incident of inbreeding. Controlled captive breeding and ultrasonography further ensures the genetic health and sustainability of bottlenose dolphins in captivity.
Cons of Captive Breeding
Emerging Issues on Captive Breeding
It is not entirely true that captive animals are often healthier and more successful in reproduction as opposed to their wild counterparts. On the genetic level, Lynch and O’Hely (2001) contended that endangered species subject to a recurring process of introduction from a different environment that is opposite to the natural habitat can lead to having a deleterious allele. That is; in the case of captive breeding programs, the population of endangered species deleterious alleles could rise at high levels leading to a fixation in the current environment opposite to the direction of the wild. Lynch and O’Hely (2001) noted that the genetic response to enhancements can lead to a high risk of extinction for natural populations especially when associated to the gene pool dominated by captive populations. Such significant enhancement load may likely occur when captive breeders are taken from wild. Thus, the restriction of gene flow to the natural population may be severed requiring the reduction of load to a negligible or insignificant level. It is also contended that domestication promotes the fixation of deleterious alleles that may affect the wild instincts and behaviors of animals in general. Lest the captive environment closely resembles the selective pressure that is common in the wild, enhancement programs are expected to be underway where alterations in the genetic component of the wild animals that would always remain dependent to the captive breeding program.
Similarly, Araki and colleagues (2009) agrees to the previous contention that captive breeding lowers the reproductive fitness of wild populations, although it is the most common resort to the conservation of critically endangered wild species. Using an assigned genetic parentage to construct a pedigree and determine the reproductive fitness of the descendants of captive-bred parents, results showed a 37% reproductive fitness from the captive-bred parents and 87% from at least one wild parent of steelhead trout. The findings of their study indicate that the significant carry-over effect of captive breeding has also negative effect on the size of the wild population after supplementation or enhancements.
One of the many contentions about captive breeding is the impediment of the normal social behaviour of marine mammals. Geraci (1986b as cited by Anonymous, 2005) noted the disruption of the group of marine mammals and the harm in the younger ones during captivity. Aggression is often seen in adult male bottle nose dolphins towards the young ones reflecting the propensity of the adult males to guide the young ones when threatened. Such behaviour may even lead to obsessive hostility in captivity where the young ones may not be able to escape from the crowding of adult males. Some studies also emphasized that there are some cetaceans that find it difficult to adjust to tank conditions because they are more accustomed to open-ocean as opposed to those that are accustomed to shallow, coastal waters (Defran and Pryor, 1980 as cited by Anonymous, 2005).
Addressing the Challenges
The main goal of captive breeding programs is to maintain the highest level of genetic diversity, and increase the success rate of reintroducing captive populations to the wild.
Several attempts have been made to understand the problems involving dominance and compatibility of Cetaceans within a tank enclosure. Some surveyed facilities stressed the need to recreate enough social structure during captivity to avoid mixing adult males with juvenile males in the presence of females. It is also important to provide enough space to allow separation and escape from crowding. Some of the arrangements in hierarchy of dominance consider the priority of access to the surface. Based on swimming arrangements pantropical spotted dolphins, Pacific white-sided dolphins, and bottlenose dolphins are seen together along with spinner dolphins (Anonymous, 2005).
In the conservation case of manatees in Mexico, Nourisson and colleagues (2011) suggested that the two distinct genetic populations of the animal should be considered in order to produce a healthier stock of genes. This stock of genes may be used as a source for the potential mixture of the two primary genetic clusters of manatees—from the Caribbean coast and in the riverine system linked to Gulf of Mexico (GMx). Nourisson et al. (2011) also emphasized the maintenance of a natural migration routes of the manatees by conserving suitable habitats while reducing poaching activities and increasing public awareness.
On the other hand, Griffin et al. (2000) argues that most animals that are reintroduced and translocated via captive breeding programs are mostly unsuccessful because of predation. Griffin also agrees that animals that have been isolated from their natural predators losses the genes to express an antipredator behavior. Thus, one of the ways to look at addressing the issues of captive breeding is to include an antipredator training before preparing the animals to be released in the wild. Griffin et al. (2000) also noted that it would be easier for captive-bred animals to acquire antipredator skills if these animals experience ontogenic isolation as opposed to undergoing evolutionary isolation. Although there may be difficulties with respect to teaching how captive-bred animals should avoid predators, training techniques such as classical conditioning, may improve the expression of antipredator behavior.
Theodorou and Couvet (2010) proposed circular mating to conserve captive populations. Their study reveals that circular mating indicates the highest allelic diversity for all population sizes. The process is also efficient in purging deleterious alleles. To demonstrate the effectiveness of circular mating, a computer simulation was performed using the Gc/mc method. In this method, parental allelic contributions should produce minimum coancestry among the offsprings and lower the mean pairwise coancestry via mating. Results revealed that circular mating may increase the success rate of captive-bred populations that are released to the wild. Although there may be some drawbacks regarding circular mating, this drawbacks are offset when the captive population and litter size are high.
References
Araki, H., Cooper, B. & Blouin, M. S. (2009). Carry-over effect of captive breeding reduces reproductive fitness of wild-born descendants in the wild. Biology Letters, 5(5), 621-624.
Anandharaj, M., Sivakumar, S., Parveen Rani, M. R. (2013). Conservation of Dugong dugon (sea cow) in Gulf of Mannar. Current Science, 105(2), 149-150.
Anonymous. (2005). 2. whales, dolphins, and porpoises: Presentation of the cetaceans. Aquatic Mammals, 31(3), 288.
Brook, F. M., & Kinoshita, R. E. (2005). Controlled unassisted breeding of captive indo-pacific bottlenose dolphins, tursiops aduncus, using ultrasonography. Aquatic Mammals, 31(1), 89-95.
Griffin, A. S., Blumstein, D. T. & Evans, C. S. (2000). Training captive-bred or translocated animals to avoid predators. Conservation Biology, 14(5), 1317–1326.
Kaschner, K., Quick, N. J., Jewell, R., Williams, R., & Harris, C. M. (2012). Global coverage of cetacean line-transect surveys: Status quo, data gaps and future challenges. PLoS One, 7(9): e44075.
Lynch, M. & O’Hely, M. (2001). Captive breeding and the genetic fitness of natural populations. Conservation Genetics, 2, 363–378.
Mason, G. J. (2010). Species differences in responses to captivity: stress, welfare and the comparative method. Trends in Ecology and Evolution, 25(12), 713-721.
Norris, T. A., Littnan, C. L., & Gulland, F. M. D. (2011). Evaluation of the captive care and post-release behavior and survival of seven juvenile female hawaiian monk seals (monachus schauinslandi). Aquatic Mammals, 37(3), 342-353.
Nourisson, C., Morales-Vela, B., Padilla-Saldivar, J., Tucker, K. P., Clark, A. M. et al. (2011). Evidence of two genetic clusters of manatees with low genetic diversity in Mexico and implications for their conservation. Genetica, 139, 833–842.
Ojaveer, H., Jaanus, A., MacKenzie, B. R., Martin, G., Olenin, S., et al. (2010). Status of biodiversity in the baltic sea. PLoS One, 5(9): e12467.
Soule, M., Gilpin, M., Conway, W. and Foose, T. (1986). The millenium ark: How long a voyage, how many staterooms, how many passengers? Zoo Biology, 5, 101-113.
Theodorou, K. & Couvet, D. (2010). Genetic management of captive populations: the advantages of circular mating. Conservation Genetics, 11, 2289–2297.
Witzenberger, K. A., & Hochkirch, A. (2011). Ex situ conservation genetics: A review of molecular studies on the genetic consequences of captive breeding programmes for endangered animal species. Biodiversity & Conservation, 20(9), 1843-1861.
