Protecting our Critically Endangered Hawksbill Turtles from Invasive Species
Hawksbill turtles are complex marine reptiles that are widely distributed across tropical and subtropical oceans. They rely on a variety of environments throughout their life cycle including beaches, open seas, and coastal waters and may disperse and travel long distances between these environments throughout their lifetime.
Hawksbills play a key role in maintaining the balance of coral reef ecosystems by feeding predominantly on sea sponges and in so doing they reduce the pressure that sponges place on the slower-growing corals. In spite of their value to the ecosystem, hawksbills are constantly threatened, and the species has experienced significant declines in population. As a result, they are at risk of extinction and are listed as Critically Endangered on the IUCN Red List.
Hawksbills currently have a well-established nesting population on the shores of Barbados, with the island recording the second-largest number of individuals in the Wider Caribbean. Through the long-term conservation efforts of the Barbados Sea Turtle Project, more than 600 females are documented nesting on our shores annually. These adult females migrate to nesting beaches every two or three years laying between three to five nests, each nest containing, on average, 150 eggs.
Observe the hawksbill sea turtle nesting process in the following video.
While this appears to be a significant number, sea turtle hatchlings have a high mortality rate due to various threats, including predators on land and in the sea. Tragically, it is estimated that less than 1 in 1000 hatchlings actually reach sexual maturity. Bath Beach, St John is the nesting site for a population of hawksbill turtles that are genetically distinct from those nesting elsewhere on the island. Unfortunately, for them, the site is also home to invasive species including mongooses and rats. Mongooses and rats are known to prey on sea turtle nests, attacking developing eggs and hatchlings. Mongooses in particular have a keen sense of smell and can detect nests and will dig into them to access the eggs; while rats will capture hatchlings that are emerging from the nest.
Observe the following video to see predatory mongooses in action.
Mongooses and rats are considered invasive because they are not native to the island and their presence contributes to environmental harm through direct impact on populations of native species as well as doing potential harm to human health.
Mongooses are considered to be in the top 10 most serious invasive species globally. They were first introduced to Barbados in the late 1870s as a biological control agent against rats. However, mongooses and rats are active at different times of the day, and the true impact of mongooses on the rodent population is unknown. Mongooses were also introduced to control rats in many other territories with little to no reported success. Instead, they have contributed to the declines and local extinctions of a large number of native and endemic species. In Barbados, mongooses likely contributed to the sharp decline and likely extinction of one of Barbados’ few endemic species, the harmless Barbados racer or grass snake. Mongooses also pose a constant threat to poultry (chickens and ducks) and are vectors of diseases harmful to humans including leptospirosis and murine typhus. Within the Caribbean region, in nearby Puerto Rico, mongooses are carriers of rabies. Since they pose a threat to agriculture, human health and biodiversity, mongooses fulfil all criteria of an invasive species.
In 2010 Patrick Leighton reported that the annual predation rate of turtle nests by mongooses at Bath Beach ranged from 17.9 – 38.9%. This is a major concern considering the already low survival rate of turtle hatchlings. Because of the Critically Endangered status of the hawksbill turtle, intervention is necessary to help protect this species on the island.
As part of the GEF-funded project “Preventing Costs of Invasive Alien Species (IAS) in Barbados and Countries of the OECS”, the Ministry of Environment and National Beautification, Green and Blue Economy in Barbados has collaborated with local consultancy firm, Mosaic Eco Consult, to undertake a mongoose and rat control pilot programme at Bath Beach, St John.
The aim of this pilot is to establish an effective mongoose and rat removal strategy that can be implemented to control these predatory species at Bath, and at other at-risk turtle nesting beaches. This programme has three main phases.
- Phase 1) To document nest predation at Bath beach in 2021,
- Phase 2) To remove mongooses and rats from the beach and surrounding area in 2022, and
- Phase 3) To reassess nest predation after mongooses and rats have been removed in the 2022 nesting season.
Phase 1 entails beach patrols to record new turtle nests and monitor rat and mongoose activity at these nests. In Phase 2, live and kill traps will be set to capture and remove mongooses and rats from the area. Finally, nest monitoring will resume in Phase 3 to document the predation rate on turtle nests after the removal of mongooses and rats. This approach provides an experimental study to determine whether the strategies employed were effective in their goal to reduce turtle nest predation.
Phase 1 occurred in July to August 2021 and revealed similar trends to those in 2010. Mongooses were pervasive at the site, spending most time along the beach area with the greatest density of sea turtle nests. Many mongooses were observed moving in groups or presumed family units. Rodents were present but not in high numbers, and rodent activity was not recorded at turtle nests. Of 63 hawksbill turtle nests documented on the beach, 25 were predated by mongooses, which represented almost 40% of turtle nests on the beach. Monitoring indicated that when a mongoose discovered a nest, it would revisit the nest every 10 – 20 minutes and quickly raid the entire nest. If that mongoose had a family unit, they would raid the nest collectively. Also, it seemed to be possible that mongooses learned how to locate eggs by watching others do it.
In March 2022, the project entered Phase 2, which involves the trapping and removal of mongooses and rats. Intense trapping is being conducted from April to June, after which turtle nest predation monitoring will begin. It is envisaged that as the mongoose and rat population on-site are controlled, there should be a significant reduction in predation of turtle nests.
The lessons learned and protocols established during this pilot project can be replicated at other sites to control problematic invasive predator species. The approach taken has a deliberately low environmental impact such that it can be replicated in other natural habitats to protect threatened species.