A scientific study of Eastern Pacific hawksbill turtles has discovered genetic differences between hawksbills that nest in mangrove estuaries and those that nest along open-coast beaches. Fauna & Flora International’s (FFI) Velkiss Gadea and Eduardo Altamirano, and Alexander Gaos from ICAPO (the Eastern Pacific Hawksbill Initiative, a partnership that includes FFI) were among the authors of the paper, published in the scientific journal Ecology and Evolution.

Hawksbill turtles were considered almost completely absent from the Eastern Pacific until 2008, when several nesting colonies were discovered along the coast between Mexico and Ecuador.

Since then it has been discovered that the majority of Eastern Pacific hawksbills use mangrove estuaries for nesting and foraging – unlike Atlantic and Indo-Pacific hawksbills, which are predominantly found in coral reefs. This behaviour is completely unique to hawksbills in this region and the researchers were keen to find out more.

Releasing turtles on the Nicaraguan Coast. Credit: Marvin Torres.

Releasing turtles on the Nicaraguan coast. Credit: Marvin Torres.

In the genes

Through genetic testing, the study found that hawksbills in the Eastern Pacific have low genetic diversity and very small reproductive populations. For example, the largest of the four main hawksbill sites, Estero Padre Ramos, is estimated to support no more than 210 nesting females.

However, while this might be cause for conservation concern, the hawksbill populations were also found to have strong genetic structures – this means there is high genetic variability between the four main populations, which previously had been grouped together as one.

This genetic diversity increases the species’ ability to survive threats such as climate change. The genetic differences between hawksbills nesting in mangrove estuaries and those nesting along open-coasts are particularly important as they suggest mangrove estuaries may serve as critical habitat refuges for the species as the world’s coral reefs continue to decline.

Further monitoring of Estero Padre Ramos and the other large nesting rookery located in nearby Bahía de Jiquilisco in El Salvador, found that females return to the same nesting beaches every year and do not switch between the two sites. This behaviour separates nesting populations and explains the strong genetic differences between the two sites despite their close proximity. The genetic results of this study provide a more complete picture of the life history of hawksbill turtles on a regional and global scale.

The results suggest that each site and population should be treated as separate units, with corresponding implications for the conservation management of these Eastern Pacific hawksbills.

Estero Padre Ramos. Credit: Velkiss/FFI.

The largest of the four main hawksbill sites is Estero Padre Ramos. Credit: Velkiss/FFI.

Hawksbill conservation

Once abundant, hawksbills are now one of the world’s most endangered marine turtle populations; they are threatened primarily by the collection of their eggs and meat for consumption and sale and also by the trade in their shells which are used to make jewellery and other decorative items.

FFI works at two important hawksbill nesting sites in Nicaragua – Estero Padre Ramos and a recently discovered site, Aserradores – which account for over 50% of nesting hawksbills in the region.

“The unique trait of these hawksbills, to nest in small pocket beaches throughout large mangrove estuaries, meant that this population only came to the attention of the conservation community relatively recently” said Eduardo Altamirano, FFI Field Biologist in Estero Padre Ramos.

“Studies like this illustrate how fascinating and valuable this hawksbill population is and help to fill gaps in our knowledge. There is still a long way to go and further studies on feeding behaviour, habitat selection, and population dynamics will help us to better understand these hawksbill turtles and design appropriate conservation strategies for this Critically Endangered reptile.”

For more information read ‘Hawksbill turtle terra incognita: conservation genetics of eastern Pacific rookeries’ in full.