Lost at sea: Genetic, oceanographic and meteorological evidence for storm-forced dispersal

Department of Biosciences, College of Science, Swansea University, Swansea SA2 8PP, UK.
Journal of The Royal Society Interface (Impact Factor: 3.92). 02/2012; 9(73):1725-32. DOI: 10.1098/rsif.2011.0788
Source: PubMed


For many species, there is broad-scale dispersal of juvenile stages and/or long-distance migration of individuals and hence the processes that drive these various wide-ranging movements have important life-history consequences. Sea turtles are one of these paradigmatic long-distance travellers, with hatchlings thought to be dispersed by ocean currents and adults often shuttling between distant breeding and foraging grounds. Here, we use multi-disciplinary oceanographic, atmospheric and genetic mixed stock analyses to show that juvenile turtles are encountered 'downstream' at sites predicted by currents. However, in some cases, unusual occurrences of juveniles are more readily explained by storm events and we show that juvenile turtles may be displaced thousands of kilometres from their expected dispersal based on prevailing ocean currents. As such, storms may be a route by which unexpected areas are encountered by juveniles which may in turn shape adult migrations. Increased stormy weather predicted under climate change scenarios suggests an increasing role of storms in dispersal of sea turtles and other marine groups with life-stages near the ocean surface.

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    • "Sea turtles are among the most studied of marine vertebrates, with all seven species having been tracked from multiple sites (Godley et al. 2008, Pendoley et al. 2014); many studies have identified and described hitherto unrecognised foraging patterns, migratory routes and habitat use. Loggerhead sea turtles (Caretta caretta Linnaeus, 1758) are perhaps the best studied species, having been comprehensively studied over several decades through multi-disciplinary approaches including, tagging (Arendt et al. 2012a, Rees et al. 2013), tracking (Rees et al. 2010, Hawkes et al. 2011, Arendt et al. 2012b), genetic (Carreras et al. 2011, Monzón-Argüello et al. 2012) and stable isotope (Eder et al. 2012, Pajuelo et al. 2012, Thomson et al. 2012) studies. A neritic, coastal model for adult loggerhead sea turtle post-nesting migratory behaviour was established some decades ago (Bolten & Witherington 2003); however, recent tracking (Hatase et al. 2002, Hawkes et al. 2006, McClellan & Read 2007, Mansfield et al. 2009, Rees et al. 2010) has demonstrated that there is considerably more plasticity than previously thought and some loggerhead turtles remain in the oceanic zone as adults, only returning to coastal waters during the breeding season. "
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    ABSTRACT: The integration of satellite telemetry, remotely sensed environmental data, and habitat/environmental modelling has provided for a growing understanding of spatial and temporal ecology of species of conservation concern. The Republic of Cape Verde comprises the only substantial rookery for the loggerhead turtle Caretta caretta in the eastern Atlantic. A size related dichotomy in adult foraging patterns has previously been revealed for adult sea turtles from this population with a proportion of adults foraging neritically, whilst the majority forage oceanically. Here we describe observed habitat use and employ ecological niche modelling to identify suitable foraging habitats for animals utilising these two distinct behavioural strategies. We also investigate how these predicted habitat niches may alter under the influence of climate change induced oceanic temperature rises. We further contextualise our niche models with fisheries catch data and knowledge of fisheries ‘hotspots’ to infer threat from fisheries interaction to this population, for animals employing both strategies.Our analysis revealed repeated use of coincident oceanic habitat, over multiple seasons, by all smaller loggerhead turtles, whilst larger neritic foraging turtles occupied continental shelf waters. Modelled habitat niches were spatially distinct, and under the influence of predicted sea surface temperature rises, there was further spatial divergence of suitable habitats. Analysis of fisheries catch data highlighted that the observed and modelled habitats for oceanic and neritic loggerhead turtles could extensively interact with intensive fisheries activity within oceanic and continental shelf waters of northwest Africa. We suggest that the development and enforcement of sustainable management strategies, specifically multi-national fisheries policy, may begin to address some of these issues; however, these must be flexible and adaptive to accommodate potential range shift for this species.
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    • "This contraposition could be related to the different ecophysiological response of both species during their migration cycle. Recent studies suggest an important role of currents and storms in dispersal of loggerhead turtles [39]. Thus, the arrival of juvenile loggerhead turtles into the Mediterranean through the Strait of Gibraltar seems to be motivated by a combination of favourable currents and storms, rather than preestablished migration routes. "
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    ABSTRACT: Recent studies showed that regional abundance of loggerhead and leatherback turtles could oscillate interannually according to oceanographic and climatic conditions. The Western Mediterranean is an important fishing area for the Spanish drifting longline fleet, which mainly targets swordfish, bluefin tuna, and albacore. Due to the spatial overlapping in fishing activity and turtle distribution, there is an increasing sea turtle conservation concern. The main goal of this study is to analyse the interannual bycatch of loggerhead and leatherback turtles by the Spanish Mediterranean longline fishery and to test the relationship between the total turtle by-catch of this fishery and the North Atlantic Oscillation (NAO). During the 14 years covered in this study, the number of sea turtle bycatches was 3,940 loggerhead turtles and 8 leatherback turtles, 0.499 loggerhead turtles/1000 hooks and 0.001014 leatherback turtles/1000 hooks. In the case of the loggerhead turtle the positive phase of the NAO favours an increase of loggerhead turtles in the Western Mediterranean Sea. However, in the case of leatherback turtle the negative phase of the NAO favours the presence of leatherback turtle. This contraposition could be related to the different ecophysiological response of both species during their migration cycle.
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