Conservation importance of previously undescribed abundance trends: increase in loggerhead turtle numbers nesting on an Atlantic island
J AC Q U E S-OLI VIER L ALOË ,J AC Q U I E COZE N S,BERT A RENOM ALB ERT TAXONERA and GRAEME C. HAY S
Abstract For many species abundance data from across their entire range are incomplete, and therefore it is difficult to accurately assess their conservation status. Even for spe- cies that are large, charismatic and relatively easy to study, conservation assessments are often hampered by lack of data. Here we report a marked, previously undescribed, increase in numbers at a breeding colony of the logger- head turtle Caretta caretta, a species that is Critically Endangered in several parts of its range, and place this report in the global context for this species. We present a 10-year (2008–2017) dataset of nesting activities for this spe- cies on the island of Sal, one of the CapeVerde islands in the Atlantic Ocean. Foot patrols recorded 21,938 nests during the study period. We estimate that the annual number of nests on Sal increased from 506 in 2008 to 7,771 in 2017. Taking into account that there are only two known loggerhead turtle rookeries (on Masirah Island, Oman, and in Florida, USA) with .50,000 nests reported annually, and few with .1,000 nests per year, our results suggest that Sal is one of the 10 largest loggerhead turtle rookeries globally. Our work highlights the conservation significance of reporting trends in abundance at breeding sites for marine turtles and other taxa.
Keywords Conservation policy, extinction, global assess- ments, IUCN Red List, loggerhead turtle, marine turtles, Regional Management Unit, threatened species
Supplementary material for this article is available at
https://doi.org/10.1017/S0030605318001497
Introduction F
or many plant and animal species key ecological information such as their distribution or abundance
JACQUES-OLIVIER LALOË (Corresponding author,
orcid.org/0000-0002-1437-
1959) and GRAEME C. HAYS Centre for Integrative Ecology, Deakin University, Geelong, Australia. E-mail
j.laloe@
deakin.edu.au
JACQUIE COZENS,BERTA RENOM* and ALBERT TAXONERA* SOS Tartarugas, Santa Maria, Sal, Republic of Cape Verde
*Also at: Project Biodiversity, Santa Maria, Sal, Republic of Cape Verde
Received 8 August 2018. Revision requested 6 November 2018. Accepted 30 November 2018. First published online 16 September 2019. Oryx, 2020, 54(3), 315–322 © 2019 Fauna & Flora International doi:10.1017/S0030605318001497
is lacking. For instance, one in six species assessed by the International Union for Conservation of Nature and Natural Resources (IUCN) is categorized as Data Deficient (IUCN, 2018). Assessing the global status of a species often relies on the collation of disparate datasets (e.g. Mazaris et al., 2017). In addition, species may be increasing in abun- dance in part of their range but decreasing elsewhere, driv- ing regional conservation status assessments (e.g. Wallace et al., 2010). However, at both global and regional scales as- sessment quality is limited by the accuracy and complete- ness of the data available, and abundance estimates can be incomplete even for well-studied taxa (Mazaris et al., 2017). Lack of data can have profound conservation implications. Firstly, the conservation outlook for species with hitherto undescribed large and/or increasing populations can be more optimistic than previously believed. For example, a recently discovered breeding population of the Indochinese tiger Panthera tigris corbetti in eastern Thailand brought the total known number of breeding populations of this Critically Endangered subspecies to two (Reid, 2017). Secondly, negative population trends may be undescribed and the species’ conservation outlook may be worse than previously suspected. For example, it was recently estimated that although there are more western lowland gorillas Gorilla gorilla gorilla than previously thought, their num- bers are declining (Strindberg et al., 2018). Population abun- dance and trend data are essential for making informed conservation assessments at both local and global scales, and for guiding conservation management and policy. Marine turtles are amongst the taxa of conservation concern for which recent information on population trends is lack- ing for many parts of their global range. For example, in a review of published time series of global nesting trends Mazaris et al. (2017) identified time series for 299 rookeries, but data for 118 had not been updated since 2009. Even for areas where marine turtles are well-studied, there are few recent estimates of population trends. For example, although fivemarine turtle species nest in Australia in large numbers, time series extending beyond 2010 are only available for one species, the flatback turtle Natator depressus (Mazaris et al., 2017). In addition to a lack of recent datasets, the use of global assessments to establish the conservation status of individual marine turtle species has been widely debated in the scientific community because of regional variations in population trends (e.g. Mrosovsky, 2003; Godfrey &
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