Population Dynamics of Marine Turtles Under Harvest

Natural Environment Research Council (NERC) CASE PhDUnderstanding the ecology and life history of marine turtle populations is fundamental for their effective conservation, especially for those that are harvested for food. This thesis presents a collection of six chapters that progress from the applied to the pure; conservation and management in the first chapters through to animal ecology in the latter. A variety of contemporary and multidisciplinary techniques are utilised to explore the structure, populations dynamics and ecology of two marine turtle species, the green turtle (Chelonia mydas) and the hawksbill turtle (Eretmochelys imbricata), under harvest in the Turks and Caicos Islands (TCI), Caribbean. The work first focuses on the structure of TCI’s small-scale fishery and the demographics of turtles landed and incorporates nesting seasonality, adult take, satellite tracking and genetic structure to suggest evidence-based legislative amendments. As part of the study of this fishery, this work reports on how the harvest might increase prevalence of disease in green turtles. As an exploration into the ecology of turtle stocks found in TCI, the work then describes and compares in- water immature and adult sex ratios, genetic differentiation and sex biased dispersal. Finally, stomach content and habitat matching, and stable isotope analyses provide insights into the foraging ecology and suggested keystone roles of sympatric green and hawksbill turtles.NERC / MC

Fisher choice may increase prevalence of green turtle fibropapillomatosis disease

This document is protected by copyright and was first published by Frontiers. All rights reserved. It is reproduced with permission.Open access journalDisease in wildlife populations is often controlled through culling. But when healthy individuals are removed and diseased individuals are left in the population, it is anticipated that prevalence of disease increases. Although this scenario is presumably common in exploited populations where infected individuals are less marketable, it is not widely reported in the literature. We describe this scenario in a marine turtle fishery in the Turks and Caicos Islands (TCI), where green turtles are harvested for local consumption. During a 2-year period, we recorded the occurrence of fibropapillomatosis (FP) disease in green turtles (Chelonia mydas) captured during in-water surveys and compared it with that of turtles landed in the fishery. 13.4% (n = 32) of turtles captured during in-water surveys showed externally visible signs of FP. FP occurred at specific geographic locations where fishing also occurred. Despite the disease being prevalent in the size classes selected by fishers, FP was not present in any animals landed by the fishery (n = 162). The majority (61%) of fishers interviewed expressed that they had caught turtles with FP. Yet, 82% of those that had caught turtles with the disease chose to return their catch to the sea, thereby selectively harvesting healthy turtles and leaving those with the disease in the population. Our study illustrates that fisher choice may increase the prevalence of FP disease and highlights the importance of this widely neglected driver in the disease dynamics of exploited wildlife populations.Natural Environment Research Council (NERC) CASE PhD studentshi

Marine turtle harvest in a mixed small-scale fishery: Evidence for revised management measures

Copyright © 2013 Elsevier. NOTICE: this is the author’s version of a work that was accepted for publication in Ocean and Coastal Management. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Ocean and Coastal Management, 2013, Vol. 82, pp. 34 – 42 DOI: http://dx.doi.org/10.1016/j.ocecoaman.2013.05.004Small-scale fisheries (SSF) account for around half of the world's marine and inland fisheries, but their impact on the marine environment is usually under-estimated owing to difficulties in monitoring and regulation. Successful management of mixed SSF requires holistic approaches that sustainably exploit target species, consider non-target species and maintain fisher livelihoods. For two years, we studied the marine turtle fishery in the Turks and Caicos Islands (TCI) in the Wider Caribbean Region, where the main export fisheries are queen conch (Strombus gigas) and the spiny lobster (Panulirus argus); with fin-fish, green turtles (Chelonia mydas) and hawksbill turtles (Eretmochelys imbricata) taken for domestic consumption. We evaluate the turtle harvest in relation to the other fisheries and recommend legislation and management alternatives. We demonstrate the connectivity between multi-species fisheries and artisanal turtle capture: with increasing lobster catch-per-unit-effort (CPUE), hawksbill catch increased whilst green turtle catch decreased. With increasing conch CPUE, hawksbill catch declined and there was no demonstrable effect on green turtle catch. We estimate 176–324 green and 114–277 hawksbill turtles are harvested annually in TCI: the largest documented legal hawksbill fishery in the western Atlantic. Of particular concern is the capture of adult turtles. Current legislation focuses take on larger individuals that are key to population maintenance. Considering these data we recommend the introduction of maximum size limits for both species and a closed season on hawksbill take during the lobster fishing season. Our results highlight the need to manage turtles as part of a broader approach to SSF management

Minimizing the impact of biologging devices: Using computational fluid dynamics for optimizing tag design and positioning

Biologging devices are used ubiquitously across vertebrate taxa in studies of movement and behavioural ecology to record data from organisms without the need for direct observation. Despite the dramatic increase in the sophistication of this technology, progress in reducing the impact of these devices to animals is less obvious, notwithstanding the implications for animal welfare. Existing guidelines focus on tag weight (e.g. the ‘5% rule'), ignoring aero/hydrodynamic forces in aerial and aquatic organisms, which can be considerable. Designing tags to minimize such impact for animals moving in fluid environments is not trivial, as the impact depends on the position of the tag on the animal, as well as its shape and dimensions. We demonstrate the capabilities of computational fluid dynamics (CFD) modelling to optimize the design and positioning of biologgers on marine animals, using the grey seal (Halichoerus grypus) as a model species. Specifically, we investigate the effects of (a) tag form, (b) tag size, and (c) tag position and quantify the impact under frontal hydrodynamic forces, as encountered by seals swimming at sea. By comparing a conventional versus a streamlined tag, we show that the former can induce up to 22% larger drag for a swimming seal; to match the drag of the streamlined tag, the conventional tag would have to be reduced in size by 50%. For the conventional tag, the drag induced can differ by up to 11% depending on the position along the seal's body, whereas for the streamlined tag this difference amounts to only 5%. We conclude by showing how the CFD simulation approach can be used to optimize tag design to reduce drag for aerial and aquatic species, including issues such as the impact of lateral currents (unexplored until now). We also provide a step-by-step guide to facilitate the implementation of CFD in biologging tag design

The Substantial First Impact of Bottom Fishing on Rare Biodiversity Hotspots: A Dilemma for Evidence-Based Conservation

<div><p>This study describes the impact of the first passage of two types of bottom-towed fishing gear on rare protected shellfish-reefs formed by the horse mussel <i>Modiolus modiolus</i> (L.). One of the study sites was trawled and the other was scallop-dredged. Divers collected HD video imagery of epifauna from quadrats at the two study sites and directed infaunal samples from one site.</p><p>The total number of epifaunal organisms was significantly reduced following a single pass of a trawl (90%) or scallop dredge (59%), as was the diversity of the associated community and the total number of <i>M. modiolus</i> at the trawled site. At both sites declines in anthozoans, hydrozoans, bivalves, echinoderms and ascidians accounted for most of the change. A year later, no recovery was evident at the trawled site and significantly fewer infaunal taxa (polychaetes, malacostracans, bivalves and ophuroids) were recorded in the trawl track.</p><p>The severity of the two types of impact reflected the undisturbed status of the habitats compared to previous studies. As a ‘priority habitat’ the nature of the impacts described on <i>M. modiolus</i> communities are important to the development of conservation management policy and indicators of condition in Marine Protected Areas (EU Habitats Directive) as well as indicators of ‘Good Environmental Status’ under the European Union Marine Strategy Framework Directive.</p><p>Conservation managers are under pressure to support decisions with good quality evidence. Elsewhere, indirect studies have shown declines of <i>M. modiolus</i> biogenic communities in fishing grounds. However, given the protected status of the rare habitat, premeditated demonstration of direct impact is unethical or illegal in Marine Protected Areas. This study therefore provides a unique opportunity to investigate the impact from fishing gear whilst at the same time reflecting on the dilemma of evidence-based conservation management.</p></div

GLMM coefficients for diversity measures for impacted and unimpacted <i>M. modiolus</i> communities from PoA.

<p>Fixed factor = physical impact; random factors = time (year) and quadrat position. Estimate includes ± standard deviation (sd). Significance at α = 0.05.</p><p><b>See also <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0069904#pone.0069904.s002" target="_blank">Table S1</a></b>.</p

Details of study sites.

<p>(A) Map of fixed quadrat locations (dotted squares) on raised ridges (grey polygons) at Point of Ayre study site. Dotted ellipses indicate infaunal sample areas for impacted and control treatments. Two trawl door marks in 2008 are indicated by dashed lines. One trawl door mark in (A) is visible in the video-grab image (B) where the more extreme impact (compared to the net) in the path of the trawl door is also illustrated with dashed lines. The numbers “7” and “3” in (A) are quadrat numbers refered to in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0069904#pone-0069904-g003" target="_blank">Figure 3</a> and <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0069904#s4" target="_blank">Discussion</a> (respectively). Metal waypoint pins enabled navigation around the site. (C) Side scan sonar image from 2012 at the study site off the north of the Lleyn Peninsula: marks from two gangs of scallop dredges are visible across the surface of the <i>Modiolus modiolus</i> ridges.</p

Reductions in epifauna and infauna following bottom-towed fishing gear.

<p>Total number of individuals (A), upright emergent epifauna (B) and numbers of <i>M. modiolus</i> (C) recorded on impacted and unimpacted 0.25×0.25 m video quadrats off Point of Ayre(PoA) and North Lleyn Peninsula (nLP). (D) Abundance of infaunal taxa contributing the most to the dissimilarities between impacted and unimpacted treatments at the PoA site (SIMPER). Box plots represent inter-quartile range, median, maximum and minimum values. The effect of physical impact was significant at α of 0.05 for all measures except <i>M. modiolus</i> abundance at nLP (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0069904#pone-0069904-t001" target="_blank">Table 1</a>).</p