Bycatch is one of the key threats to juvenile marine turtles in the Mediterranean Sea. As fishing methods are regional or habitat specific, the susceptibility of marine turtles may differ according ...to inter- and intra-population variations in foraging ecology. An understanding of these variations is necessary to assess bycatch susceptibility and to implement region-specific management. To determine if foraging ecology differs with region, sex, and size of juvenile loggerhead turtles (
Caretta caretta
), stable isotope analysis of carbon and nitrogen was performed on 171 juveniles from a range of foraging regions across the central and eastern Mediterranean Sea. Isotope ratios differed with geographical region, likely due to baseline variations in δ
13
C and δ
15
N values. The absence of sex-specific differences suggests that within an area, all comparably sized animals likely exploit similar foraging strategies, and therefore, their susceptibility to fisheries threats will likely be similar. The isotope ratios of juveniles occupying the North East Adriatic and North Levantine basin increased with size, potentially due to increased consumption of more prey items at higher trophic levels from a more neritic source. Isotope ratios of juveniles with access to both neritic and oceanic habitats did not differ with size which is consistent with them consuming prey items from both habitats interchangeably. With foraging habitats exploited differently among size classes in a population, the susceptibility to fisheries interactions will likely differ with size; therefore, region-specific management approaches will be needed.
Knowledge about migratory routes and highly frequented areas is a priority for sea turtle conservation, but the movement patterns of juveniles frequenting the Adriatic have not been investigated yet, ...although juveniles represent the bulk of populations. We tracked by satellite six juvenile and one adult female loggerhead from the north Adriatic. The results indicated that loggerhead juveniles (1) can either show a residential behaviour remaining in the Adriatic throughout the year or perform seasonal migrations to other areas, (2) can remain even in the coldest, northernmost area during winter, (3) can frequent relatively small foraging areas, (4) mostly frequent the eastern part of the Adriatic, and (5) follow preferred migratory routes along the western and eastern Adriatic coasts. The movements of the adult turtle also revealed (6) a behavioural polymorphism in Mediterranean adults, which included a lack of area fidelity and connection between distant neritic foraging grounds.
The Natura 2000 (N2k) network is an important site-based protection tool for the protection of biodiversity in Europe. However, for highly mobile and adaptable marine species, such a tool might not ...be the most effective way to achieve conservation objectives, unless this includes a broader consideration of the direct threats to these species throughout their range. Considering that the N2k network requires that a ‘significant proportion’ of 60% of the population be under protection, this creates a challenge for the conservation of these wide-ranging species. This paper reviews the efficacy of the N2k network as it is presently implemented within the Adriatic Sea for the conservation of two highly mobile marine species - the common bottlenose dolphin and the loggerhead turtle. In particular, it considers the appropriateness of the current Sites of Community Importance (SCIs) in the region and the relevance of the existing marine N2k network for the conservation of these species. It provides new insights on the approach used to evaluate SCI designations highlighting important weaknesses in the system, including threat identification after SCI designation, and the relevance of SCI size in relation to management commitments. Data from two basin-wide aerial surveys were used to define areas of relative high density of these species, in comparison to other areas in the basin. Given the ambitious 60% conservation target of the N2k network, analysis shows that site-based protection tools are unlikely to be sufficient to protect a ‘significant proportion’ of either species, unless very large areas are designated as SCIs. However, given that the main threats known to affect these species in this region (i.e. fishery bycatch and seismic surveys) are present throughout the basin, these large SCIs would still have limited conservation success without implementing other wide-scale mitigation measures. For these two species, the Member States and the European Union authorities should give higher priority to the implementation of another pillar of the Habitats Directive, mitigating accidental catches in fishing gear and other human-induced mortalities. This should take into consideration the full effects of these mortalities on the populations of these two species through regular transboundary monitoring programs.
In recent years, biofilm-forming diatoms have received increased attention as sea turtle epibionts. However, most of the research has focused on carapace-associated taxa and communities, while less ...is known about diatoms growing on sea turtle skin. The current study investigated diatom diversity on the skin of loggerhead sea turtle heads detached from the carcasses found along the Adriatic coast between 1995 and 2004 and stored frozen for a prolonged period of time. By using both light and scanning electron microscopy we have found diatom frustules in 7 out of 14 analysed sea turtle samples. Altogether, 113 diatom taxa were recorded, with a minimum of seven and a maximum of 35 taxa per sample. Eight taxa, Achnanthes elongata, Berkeleya cf. fennica, Chelonicola sp., Licmophora hyalina, Nagumoea sp., Navicula sp., Nitzschia cf. lanceolata, and Poulinea lepidochelicola exceeded 5% of relative abundance in any one sample. The presumably obligately epizoic diatom taxa, A. elongata, Chelonicola sp., and P. lepidochelicola, dominated in six loggerhead samples, contributing up to 97.1% of the total diatom abundance. These observations suggest that on the sea turtle skin highly specialised taxa gain even greater ecological advantage and dominance over the co-occurring benthic forms than in the carapace biofilms. The suitability of frozen sea turtle skin specimens for diatom analysis and limitations of this approach are discussed.
As a response to increasing human pressures on marine ecosystems, the legislation aimed at improving the conservation and management of marine coastal areas in European and Contiguous Seas (ECS) ...underwent crucial advances. ECS, however, still remain largely affected by increasing threats leading to biodiversity loss. Here, by using emblematic case studies and expert knowledge, we review current conservation tools, comparing their application in different areas to assess their effectiveness, potential for synergies, and contradictions. Despite regional differences in their application, the existing legislative frameworks have the potential to regulate human activities and to protect marine biodiversity. However, four challenges remain to be addressed to fully achieve environmental policy goals: 1) Lack of shared vision representing a limitation in transboundary collaboration. Although all EU countries are committed to fulfil EU Directives and other binding international legislative acts, a remarkable heterogeneity exists among countries in the compliance with the common legislation on conservation and in their degree of implementation. 2) Lack of systematic procedures for the selection of protected marine sites. Regional and national approaches in designating Natura 2000 sites and nationally designated Marine Protected Areas (MPAs) reflect varying conservation targets and importance of conservation issues in political agendas. 3) Lack of coherent ecological networks. Natura 2000 sites and other MPAs are still far from reaching the status of effective networks in all considered case studies. 4) Hotspot of conflicts with private economic interests prevailing over conservation aims. Recommendations are given to overcome the fragmented approach still characterizing the conservation and management of coastal marine environments. Holistic, integrated, ecosystem-based, cross-cutting approaches can avoid conflicts among institutions so as to provide effective and timely solutions to current and future challenges concerning the conservation and management of marine ecosystems and associated goods and services.
► Marine debris was ingested by 35.2% loggerheads foraging in neritic habitats of the Adriatic. ► Soft plastic was the most frequent type of debris found in digestive tract. ► Debris ingestion was ...not significantly affected by sex or body size of turtles. ► High occurrence of debris intake represents a factor of concern for loggerheads in the Adriatic Sea.
We examined the occurrence of marine debris in the gastrointestinal tract of 54 loggerhead sea turtles (Caretta caretta) found stranded or incidentally captured dead by fisheries in the Adriatic Sea, with a curved carapace length of 25.0–79.2cm. Marine debris was present in 35.2% of turtles and included soft plastic, ropes, Styrofoam and monofilament lines found in 68.4%, 42.1%, 15.8% and 5.3% of loggerheads that have ingested debris, respectively. The dry mass of debris per turtle was low, ranging from <0.01 to 0.71g, and the ingestion was not significantly affected by sex or body size (all p>0.05). Marine debris averaged 2.2±8.0% of dry mass of gut content, with a maximum of 35% found in a juvenile turtle that most likely died due to debris ingestion. Considering the relatively high occurrence of debris intake and possible sub-lethal effects of even small quantities of marine debris, this can be an additional factor of concern for loggerheads in the Adriatic Sea.
The available information regarding the 2 sea turtle species breeding in the Mediterranean (loggerhead turtle Caretta caretta and green turtle Chelonia mydas) is reviewed, including biometrics and ...morphology, identification of breeding and foraging areas, ecology and behaviour, abundance and trends, population structure and dynamics, anthropogenic threats and conservation measures. Although a large body of knowledge has been generated, research efforts have been inconsistently allocated across geographic areas, species and topics. Significant gaps still exist, ranging from the most fundamental aspects, such as the distribution of major nesting sites and the total number of clutches laid annually in the region, to more specific topics like age at maturity, survival rates and behavioural ecology, especially for certain areas (e.g. south-eastern Mediterranean). These gaps are particularly marked for the green turtle. The recent positive trends of nest counts at some nesting sites may be the result of the cessation of past exploitation and decades of conservation measures on land, both in the form of national regulations and of continued active protection of clutches. Therefore, the current status should be considered as dependent on such ongoing conservation efforts. Mitigation of incidental catch in fisheries, the main anthropogenic threat at sea, is still in its infancy. From the analysis of the present status a comprehensive list of research and conservation priorities is proposed.
In sea turtles, somatic growth rates and Age at Sexual Maturity (ASM) are important parameters for investigating population dynamics. Moreover, ASM informs on the time lag needed to observe the ...effects of past environmental variables, threats and conservation measures acting at nesting beaches on future numbers of clutches or nesting females, that are the most monitored indices. Assessing ASM of mixed populations that share the same foraging areas is difficult, as in the case of the Mediterranean Sea that is frequented by turtles originating from both the Mediterranean and the Atlantic. Here we investigated growth rates of loggerhead sea turtles (
Caretta caretta
) foraging in the Adriatic Sea, known to be frequented only by individuals of Mediterranean origin. Capture–mark–recapture records of 79 turtles provided growth rates ranging from – 1.1 to 9.6 cm yr
−1
which were analyzed through Generalized Additive Models. When integrated with previous data on growth rates in the first years of life, results indicate a non-monotonic growth curve, likely due to an ontogenetic shift from oceanic to neritic areas. Using an integration equation, we estimated mean ASM to be 29.5 or 25.0 year based on mean nester size in Greece (83.4 cm curved carapace length, CCL) or across the Mediterranean (79.7 cm CCL), respectively. Growth rates and size-at-age are similar to the Atlantic population, but Mediterranean turtles mature earlier at a smaller size. The heterogenous growth rates and ASM reported so far in the Mediterranean are probably due, at least in part, to different foraging areas.
Abstract
Assessing sea turtle movements and connectivity among different areas is pivotal to understanding their biology and implementing efficient conservation actions. In the Adriatic Sea, one of ...the most important sea turtle foraging areas in the Mediterranean, a total of 311 capture–mark–recapture (CMR) records (mostly bycatch) from 294 loggerhead turtles (Caretta caretta) in the period 1984–2021 were analysed. A general fidelity pattern to Adriatic subareas was indicated by a significantly shorter CMR distance than the potential dispersal distance and by the significantly higher proportion of re-encounters in the same area of release than expected. No seasonal pattern was detected between subareas, and shorter re-encounter distances were observed in turtles released and re-encountered in the same season, suggesting different winter and summer residential areas. Results suggest that turtles frequenting the Adriatic can go anywhere in the Mediterranean basin and may exhibit a wandering behaviour regardless of their size. A substantial connectivity with nesting sites in Greece was observed, confirming with empirical evidence that this is the most important breeding area for turtles foraging in the Adriatic Sea. This study highlights the value of cooperation among different groups and shows a main behavioural pattern of fidelity to neritic foraging grounds.
We analyzed 15 polychlorinated biphenyls (PCBs) and five organochlorine pesticides (OCPs) in fat tissue of 27 loggerhead sea turtles (
Caretta caretta) from eastern Adriatic Sea with the curved ...carapace length ranging from 25.0 to 84.5
cm. The PCB profile was dominated by hexa- and hepta-chlorinated congeners, with PCB-153 (median: 114.9
ng
g
−1 wet mass), PCB-138 (80.0
ng
g
−1 w.m.), and PCB-180 (26.7
ng
g
−1 w.m.) detected with the highest levels. Toxic mono-
ortho congeners PCB-118, PCB-105 and PCB-180 with dioxin-like toxicity were found in >70% samples. 4,4′-DDE (81.0
ng
g
−1 w.m.) prevailed the OCP signature, accounting for 80% of the total DDTs. A significant increasing trend in accumulation with size was found for PCB-52 (
r
s
=
0.512,
p
<
0.01) and PCB-114 (
r
s
=
0.421,
p
<
0.05). Comparison of our results with organochlorine contaminant (OC) pattern in some prey taxa suggest that contamination occurs primarily through the food web, with biomagnification factors of 0.14–6.99 which were positively correlated with the octanol–water partition coefficient (log
K
ow;
p
<
0.05). This study, based upon a fairly large sample size collected mostly from incidentally captured animals over a short time period (June 2001–November 2002), present a temporal snapshot of OC contamination in wild, free-ranging loggerheads from Adriatic feeding grounds and provide a baseline for monitoring the regional OC trends in this endangered species.
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