Detecting green shoots of recovery: the importance of long‐term individual‐based monitoring of marine turtles

Abstract

Population monitoring is an essential part of evaluating the effectiveness of management interventions for conservation. Coastal breeding aggregations of marine vertebrate species that come ashore to pup or nest provide an opportunistic window of observation into otherwise widely dispersed populations. Green turtle (Chelonia mydas) nesting on the north and west coasts of northern Cyprus has been monitored consistently and exhaustively since 1993, with an intensive saturation tagging programme running at one key site for the same duration. This historically depleted nesting population is showing signs of recovery, possibly in response to nest protection approaching two decades, with increasing nest numbers and rising levels of recruitment. Strong correlation between year-to-year magnitude of nesting and the proportion of new breeders in the nesting cohort implies that recruitment of new individuals to the breeding population is an important driver of this recovery trend. Recent changes in fishing activities may be impacting the local juvenile neritic stage, however, which may hinder this potential recovery. Individuals returning to breed after two years laid fewer clutches than those returning after three or four years, demonstrating a trade-off between remigration interval and breeding output. Average clutch frequencies have remained stable around a median of three clutches a year per female despite the demographic shift towards new nesters, which typically lay fewer clutches in their first season. We show that where local fecundity has been adequately assessed, the use of average clutch frequencies can be a reliable method for deriving nester abundance from nest counts. Index sites where individual-based monitoring is possible will be important in monitoring long-term climate driven changes in reproductive rates.bs_bs_banner Animal Conservation. Print

Satellite tracking and stable isotope analysis highlight differential recruitment among foraging areas in green turtles

“…Tissue samples comprising of a small epidermal biopsy (< 0.5 cm 2 ) were taken from the trailing edge of the fore flipper and stored in 96% ethanol until sample preparation. All turtles were individually marked using both external flipper tags and Passive Integrated Transponder (PIT) tags (Stokes et al 2014).…”

“…If foraging site fidelity is typical within the Alagadi population, then the individually based nesting data collected at Alagadi since 1992 (Stokes et al 2014) can be used to retrospectively evaluate the foraging area-specific contributions to each breeding cohort based on the turtle's unique identification. Although the analysis is limited to nesting females that were satellite tracked, or had their foraging area inferred through SIA, some of these females have nested consistently since 1992, and their unique identity can therefore be used to gain an insight into foraging area dynamics prior to the initiation of the tissue sampling regime.…”

“…However, this turtle appeared to remain faithful to Bomba for the subsequent 2 interbreeding intervals. Evaluating foraging area-specific annual contributions to the breeding cohort Foraging site fidelity being typical within this population, we were able to utilise the individuallybased nesting data collected at the breeding study site since 1992 (Stokes et al 2014) retrospectively to evaluate foraging area specific contributions to each breeding cohort. We found that the contributions to the annual breeding cohort from each foraging area were unequal among years (generalised linear model, GLM, F 3, 84 = 8.91, p < 0.001) with a general biannual variation characteristic among foraging areas (Fig.…”

“…At present, the conservation efforts undertaken on the beaches of northern Cyprus have been effective in increasing the number of hatchlings reaching the water (Stokes et al 2014) with a possible rise in the number of juveniles reaching a reproductive age. However, ensuring that the current trends in recruitment continue may largely depend on the adequate protection of the turtles foraging within Lake Barda wil, although this might be challenging as some humanturtle conflict has been reported as turtle abundance increases (Nada et al 2013).…”

“…Here, we set out to fully categorise the foraging areas utilised by a green turtle Chelonia mydas population that has been the subject of long-term individual-based research (Stokes et al 2014). Extensive satellite tracking has identified several key foraging sites for this population (Godley et al 2002, Stokes et al 2015, and repeat tracking of a small sample suggested that they exhibit fidelity to these sites (Broderick et al 2007).…”