Stranding records and cumulative pressures for sea turtles as tools to delineate risk hot spots across different marine habitats

Dimitriadis, Charalampos; Mazaris, Antonios D.; Katsanevakis, Stelios; Iosifakis, Andreas; Spinos, Efthimios; Kalli, Elpiniki; Sourbès, Laurent; Ghinis, Stamatis; Kapellaki, Kadiani; Mpeka, Evangelia; Evagelopoulos, Athanasios; Koutsoubas, Drosos

doi:10.1016/j.ocecoaman.2021.106017

Cited by 11 publications

(12 citation statements)

References 70 publications

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“…It would be interesting to explore in greater detail such year-to-year variability once a more prolonged time series will become available, a step that will allow us to better understand sea turtles strandings in relation to parameters such as sea surface temperature, chlorophyll concentration and fishing effort, an approach recently exploited in the Adriatic Sea for fishery by-caught individuals (Pulcinella et al, 2019;Bonanomi et al, 2022). The number of stranded sea turtles•km -1 as well as absolute numbers of strandings during three years, clearly confirmed that the area south of the Po River delta is the most impacted in Italy (Casale et al, 2010) and perhaps in the whole Mediterranean Sea (Tomás et al, 2008;Türkozan et al, 2013;Belmahi et al, 2020;Hama et al, 2020;Dimitriadis et al, 2022). Indeed, it is important to highlight that monitoring activities spanned only about 18 km of coastline and the numbers presented herein represented underestimates as we are aware of other and partly overlapping monitoring programs for which data could not be accessed.…”

Section: Data Collectionmentioning

confidence: 62%

“…The number of stranded sea turtles•km -1 as well as absolute numbers of strandings during three years, clearly confirmed that the area south of the Po River delta is the most impacted in Italy (Casale et al ., 2010) and perhaps in the whole Mediterranean Sea (Tomás et al ., 2008; Türkozan et al ., 2013; Belmahi et al ., 2020; Hama et al ., 2020; Dimitriadis et al ., 2022). Indeed, it is important to highlight that monitoring activities spanned only about 18 km of coastline and the numbers presented herein represented underestimates as we are aware of other and partly overlapping monitoring programs for which data could not be accessed.…”

Section: Discussionmentioning

confidence: 99%

“…Whilst quantifying and describing the effects of such threats at sea is rather difficult to achieve for logistical constraints, monitoring coastal strandings represents a more feasible approach and a cost-effective solution. Accordingly, a proper monitoring program of stranded sea turtles can provide a fair picture of the situation at sea, delivering useful information about interaction with marine debris (Domènech et al ., 2019), migration patterns (Tolve et al ., 2018) as well as delineate areas of high risk (Dimitriadis et al ., 2022). Therefore, developing a regular monitoring program of strandings is a useful approach that contributes to improving conservation plans.…”

Section: Introductionmentioning

confidence: 99%

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Strandings of loggerhead sea turtles south of the Po River delta: insights from a highly impacted area

Marisaldi¹,

Torresan²,

Ferrari³

2022

Preprint

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The northern Adriatic Sea is an important foraging ground for the loggerhead sea turtle Caretta caretta within the Mediterranean Sea. Here, spatial-temporal patterns of loggerhead sea turtles strandings along a short portion (~18 km) of the coast south of the Po River delta (Italy) during a three-year period (2019-2021) were investigated. A total of 244 records (alive, n=7; dead, n=237) were analysed and the curved carapace lengths (CCL, notch to tip, cm) mainly reflected sub-adults (average CCL=55.2 cm; 95% CI= 53.3-57). The month of July was identified as the critical month with the highest number of strandings, mirroring migratory processes toward this area during warmer months. Interaction with the trawl fishery was hypothesized as the main cause of mortality and a small fraction of deaths (6%; n=16) could be linked to boat strikes and net entanglement. The number of stranded turtles*km-1 as well as the absolute number of strandings along the short portion of monitored coast confirmed this area as the most impacted in Italy and perhaps in the whole Mediterranean Sea. This study provides valuable information to improve conservation efforts for this species and highlight that, with all due caution, monitoring stranding events can offer useful insights into the geographic ranges, seasonal distribution, and life history of marine species of conservation interest such as the loggerhead sea turtle.

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Section: Data Collectionmentioning

confidence: 62%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Strandings of loggerhead sea turtles south of the Po River delta: insights from a highly impacted area

Marisaldi¹,

Torresan²,

Ferrari³

2022

Preprint

View full text Add to dashboard Cite

show abstract

“…However, stranding data are potentially biased. The probability that a dead or distressed sea turtle will drift ashore and become reported is influenced by several factors such as decomposition and scavenging rates, carcass buoyancy, oceanographic and atmospheric conditions, shoreline characteristics, and detection probability, which are highly variable by location and time of year (Cook et al, 2021;Dimitriadis et al, 2022). In this respect, the number of reported onshore strandings may only represent a minimum measure of the overall mortality and, most importantly, may not reflect events occurring in oceanic areas (Hart et al, 2006), where fatal collisions likely go unnoticed due to the sinking of the carcasses.…”

Section: Introductionmentioning

confidence: 99%

“…In summary, given the intrinsic difficulty of quantifying the mortality rate due to vessel collisions on turtles, especially in oceanic environments, the extent of this human pressure on sea turtles likely goes underestimated. Risk assessment approaches, such as those already implemented in the study of collision events between vessels and large cetaceans (Williams and O'Hara, 2010;Nichol et al, 2017;Pennino et al, 2017;Blondin et al, 2020;Smith et al, 2020;Grossi et al, 2021;Silber et al, 2021;Awbery et al, 2022), or more recently on the study of multiple anthropogenic pressures that potentially impact sea turtles (Dimitriadis et al, 2022), may improve our understanding of maritime traffic consequences in oceanic areas. However, the assessment of collision risk requires preliminary information on animal and vessel distribution patterns and vessel-and animal-related factors, which in the case of Mediterranean sea turtles are still unknown and require targeted research.…”

Section: Introductionmentioning

confidence: 99%

Ocean highways in the Western Mediterranean: Which are the areas with increased exposure to maritime traffic for loggerhead turtles?

et al. 2022

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Many marine megafauna taxa are tied to the sea surface for breathing which makes them vulnerable to vessel collisions. Sea turtles have developed efficient mechanisms to reduce surface time for breathing to a few seconds, but they can extend their surface periods to rest or to rewarm after diving into deep and colder waters. However, knowledge of collision occurrences is limited to data of turtles stranded along the coastline worldwide, whereas events occurring offshore go likely underestimated due to the sinking of carcasses. Here we performed a spatially explicit assessment to identify, for the first time, oceanic areas of higher exposure for sea turtles from maritime traffic in the Tyrrhenian Sea, Western Mediterranean. Satellite-tracking data were used to estimate utilization distributions of loggerhead turtles using Brownian bridge kernel density estimation. Maritime traffic density maps based on Automatic Identification System (AIS) data were extracted from open-access data layers, provided by the European Maritime Safety Agency, summarized, and used for the exposure analysis. Turtle occurrences were also investigated in response to vessel densities and seasonal patterns by fitting a generalized additive model to the data. Our results demonstrated that loggerhead turtles are potentially exposed to maritime traffic across the entire basin, especially in the easternmost part. The exposure varies among spring/summer and autumn/winter months. Highest turtle occurrences were found in regions primarily subjected to cargo, tanker, and passenger transportation. This study represents the first-ever effort to characterize the exposure of oceanic loggerhead turtles to maritime traffic and highlights oceanic areas of higher exposure where research and conservation efforts should be directed to understand the effective impact of this stressor on the species.

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Speaking Deads: Sea Turtle Mortality Areas and Fisheries Overlaps Identified Through Backtracking of Stranded Carcasses in the Adriatic Sea

Agabiti,

Zanetti,

Quattrocchi

et al. 2024

Aquatic Conservation

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Interaction with fishing gears represents the main anthropogenic threat at sea for sea turtles worldwide, and identifying the hotspots of turtle bycatch is a priority knowledge gap. Turtle stranding data represent a source of information about mortality areas at sea that are not fully exploited. This study aims to infer turtle mortality areas of turtles stranded along the Italian Adriatic Coast in the period 2019–2021 (1432 records), through backtrack modelling of carcasses. Specifically, the decomposition process of eight loggerhead carcasses was monitored, and the relationship between floating period (FP), turtle size and sea temperature was modelled through a generalized additive model. Oceanographic information was then used to track the routes of floating carcasses back, knowing their size and decomposition stage, and finally estimate the likely area of mortality. A complementary numerical experiment of connectivity between coastal and offshore areas gave indication that areas of potential mortality are relatively close to the coast, particularly in the northern Adriatic. Stranded turtles probably represent just a small fraction (17%–25%) of total at‐sea mortalities in the study area (Italian Adriatic waters), with decomposition rates, season and distance from shore influencing their stranding likelihood. Hence, strandings can inform only about spatio‐temporal variability of coastal mortality hotspots. Inferred areas of turtle mortality were most likely located in the North and Central Adriatic all over the year and overlap with heatmaps of fishing effort, obtained from vessel monitoring system (VMS) and automatic identification system (AIS) data, in the Gulf of Manfredonia and in the North‐West Adriatic in the cold (September–December) and warm (May–August) periods, respectively.

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Stranding records and cumulative pressures for sea turtles as tools to delineate risk hot spots across different marine habitats

Cited by 11 publications

References 70 publications

Strandings of loggerhead sea turtles south of the Po River delta: insights from a highly impacted area

Strandings of loggerhead sea turtles south of the Po River delta: insights from a highly impacted area

Ocean highways in the Western Mediterranean: Which are the areas with increased exposure to maritime traffic for loggerhead turtles?

Speaking Deads: Sea Turtle Mortality Areas and Fisheries Overlaps Identified Through Backtracking of Stranded Carcasses in the Adriatic Sea

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