Study Notes on Population Restoration for Marine Conservation

Population Restoration as a Tool for Marine Conservation

Population Enhancement in Threatened Birds and Mammals

1. Captive Breeding and Reintroduction

  • Captive breeding is a method aimed at restoring endangered species through the breeding of individuals in controlled environments and their eventual reintroduction into their natural habitats.

  • There have been 42 pandas born this year as a specific example of successful captive breeding efforts.

2. Translocation

  • Translocation refers to relocating individuals from one site to another, often to restore a population to its former range or to create a new population.

  • Refuge areas such as islands can serve as suitable translocation sites.

  • Key concepts:

    • Remnant Population: Remaining individuals of a species in a specific area.

    • Previously Occupied Area: Regions where a species existed but is now extinct.

Examples of Successful Captive Breeding

  • Golden Lion Tamarin (Leontopithecus rosalia): A notable success story where captive breeding led to an increase in wild populations.

  • Andean Condor (Vultur gryphus) and Red Wolf (Canis rufus) also highlight species that have benefited from such strategies.

  • Approximately 20% of mammals and 10% of birds have been bred in captivity.

  • Benefits include:

    1. Provides protection from extinction.

    2. Increases reproductive success through environmental control.

  • Overall success rate remains less than 40% due to various challenges:

    • Ongoing factors contributing to the decline of species.

    • Offspring may lack skills for survival in the wild.

    • Genetic issues and diseases stemming from reduced genetic diversity.

Case Studies

  • Lord Howe Island Woodhen (Hypotaenidia sylvestris):

    • 1969: Population ~25 individuals.

    • 1980: Declined to 15 individuals due to threats such as feral pigs.

    • 2008: Population rebounded to ~250 after controlling feral threats.

    • 2022: Population reached 779 individuals.

  • Hawaiian Goose (Branta sandvicensis):

    • Once over 25,000 individuals, population drastically reduced due to introduced predators, leading to < 30 in the wild by 1951.

    • Intensive conservation efforts raised numbers to 3,862 individuals.

Translocations vs. Captive Breeding

Advantages of Translocations

  • Translocations can prove more successful than captive breeding, particularly when individuals are moved to ideal habitats that resemble their former ranges or to islands free from predators.

  • A study by Griffith et al. (1989), published in Science, indicates:

    • Wild-caught birds that are translocated are twice as likely to succeed compared to those reared in captivity.

  • Example: Palila (Loxioides bailleui) has shown complex movement patterns upon translocation, with a portion returning to their original locations.

Success Story: New Zealand Saddleback

  • The New Zealand saddleback was driven to extinction on the mainland due to introduced predators, declared extinct in 1910.

  • Successful translocations to predator-free islands and fenced nature reserves occurred starting in 1983 on Tiritiri Matangi.

  • The population is now estimated at 17,000 birds and serves as a model for successful recovery efforts.

Captive Breeding of Marine Mammals, Birds, and Reptiles

  • Captive breeding efforts for marine species have been controversial and have seen limited success for conservation purposes.

Methods for Enhancing Threatened Marine Populations

  1. Captive Breeding and Reintroduction of Juveniles

    • Goal: Close the life cycle of marine species to exploit high fecundity and combat high mortality rates among egg and larval stages.

    • Hatchery production has become routine for various species:

      • Salmonids

      • Cod (Norway)

      • Red Drum (America)

      • Flounder and Snappers (Japan)

      • Lobster (Europe and America)

      • Molluscs (scallops, mussels)

      • Echinoderms and some coral reef fishes.

    • Assumptions for conservation benefit:

    1. Higher reproductive success in captivity than in the wild.

    2. Releases do not harm natural populations.

    3. Released juveniles contribute to breeding populations.

  2. Release of Hatchery-Reared Juveniles

    • Survival rates for released hatchery juveniles vary based on several factors:

      • Developmental stage at release.

      • Size at release.

      • Specific release locations.

Challenges in the Release of Hatchery-Reared Populations

  • Survival is often poor, highlighting the necessity for understanding the developmental biology and ecology of species being reintroduced.

Community Engagement and Ethical Considerations

  • Release efforts and conservation strategies must be evaluated for ethical implications, especially related to habitat degradation and interactions with natural populations.

  • Concerns include:

    • Potential dominance by hatchery fish over natural populations.

    • Modification of local genetic diversity through hatchery practices.

Summary of Arguments Against Marine Captive Breeding and Reintroduction

  1. Loss of natural spawners replaced by hatchery fish leading to dominance of non-native genetics.

  2. Potential reduction in local genetic diversity.

  3. Every strategy should carefully assess long-term ecological impacts.