Marine Litter ingested by Sea Turtles

A first protocol for monitoring litter ingestion by sea turtles, based on the Fulmar approach, was proposed by Matiddi et al., (2011) and published in the MSFD guidance (Galganiet al., 2013). It consisted in quantifying the litter found in the digestive tract extracted during necropsy of dead individuals. It also proposed the collection of the litter in the excrements of live individuals in rescue centres. The protocol has been adapted (Matiddi et al., 2019), then completed by the project INDICIT (INDICIT, 2018) and is part of the updated MSFD guidance under revision.

After the work done by the EU projects INDICIT I and II, coordinated  measurements are now performed  by  rescue centres, stranding networks, research or veterinarian laboratories, all now using a harmonised procedure to collect sea turtle individuals in the field and extract ingested litter in the laboratory. The quality and quantity of standardised data acquired by this network highlight the collective capacity for a global and continuous monitoring of litter impact on sea turtles through ingestion. While a precise definition of a threshold is to be completed, the data collected provides a first assessment and important knowledge for reinforcing measures related to the conservation of sea turtles.

Based on the protocol elaborated within the MSFD and updated in the framework of the EU project INDICIT, the indicator “Litter ingestion by sea turtles” is focusing on the loggerhead turtle Caretta caretta –although the evaluation of litter impacts on other species is also recommended. It consists in quantifying the litter found in the digestive tract extracted during necropsy of dead individuals (mostly found stranded or by-caught by fishermen) or excreted by live animals in rescue centres after one to two months, the digestive transit time being evaluated as a maximum of four to six weeks (INDICIT, 2019). This protocol aims to target especially the plastic categories (MSFD compatible categories), the litter most often found ingested by sea turtles. The monitoring of litter ingested by sea turtles targets all size items, including micro-litter between 1 and 5 mm, meso-litter from 5 to 25 mm and macro-litter larger than 25 mm.

For this first assessment, the prevalence of litter ingestion in sea turtles was calculated as the percentage of dead turtles found with ingested litter, based on the occurrence (or incidence) reported as presence or absence. The quantity of ingested litter was measured as dry mass (grams) and number of pieces per plastic category. The precision of the measurements was two decimals.

According to the distribution of sea turtles, the monitoring is applicable to OSPAR Regions IV and V, as well as in Macaronesia.

While a precise definition of a threshold value is under review, the data collected provides the first assessment and important knowledge for measuring the impact of actions from the first OSPAR marine litter Regional Action Plan on the ban of plastic bags. More generally it also contributes to reinforcing the measures related to the conservation of sea turtles.

The assessment was performed by the EU INDICIT project, using checked, classified and standardised data from each partner from OSPAR Regions IV and V and Macaronesia (France/Biscay, Portugal/Azores, Spain/Canaries).

References methods

• Guideline for Monitoring Marine Litter ingested by sea turtle (MSFD TG ML, 2013)
• INDICIT protocol, (INDICIT, 2018), to be integrated in MSFD TG ML’s guideline
• Matiddi, M., deLucia, G.A., Silvestri, C., Darmon, G., Tomás, J., Pham, C.K., Camedda, A., Vandeperre, F., Claro, F., Kaska, Y., Kaberi, H., Revuelta, O., Piermarini, R., Daffina, R., Pisapia, M., Genta, D., Sözbilen, D., Bradai, M.N., Rodríguez, Y., Gambaiani, D., Tsangaris, C., Chaieb, O., Moussier, J., Loza, A.L., Miaud, C., 2019. Data Collection on Marine Litter Ingestion in Sea Turtles and Thresholds for Good Environmental Status. JoVE J. Vis. Exp. e59466. https://doi.org/10.3791/59466 (including a video tutorial)

For this first assessment, 182 loggerhead turtles obtained from 1988 to the end of 2019 in the southern OSPAR area [mean straight carapace length of 37,94 ± 1,34 (standard error) cm] were necropsied to measure the prevalence of ingestion (% of individuals affected) and amount of litter ingested (dry mass and abundance of litter in the digestive tract).

The assessment was performed by the EU INDICIT project, using data from each partner from the area (France/Biscay, Portugal/Azores, Spain/Canaries), collected before or during the project, standardised according to common criteria developed for the INDICIT database, thus being comparable.  Data was checked, classified and standardised, e.g., to minimize the number of factors for qualitative parameters (e.g., circumstances of discovery or causes of death).

The prevalence of litter ingestion in sea turtles was calculated as the percentage of dead turtles found with ingested litter, based on the occurrence (or incidence) reported as presence or absence. The quantity of ingested litter was measured as dry mass (grams) and number of pieces. The precision of the measurements was 1 decimal.

A total of 52,5% of the turtles have been found with ingested litter (plastics) in their digestive tract, and on the average 0,6 ± 0,1 g, equivalent to 13,1 ± 2,0 pieces were found per individual’s digestive tract. By considering data collected from 2013 to 2019 included, which could testify a more standardised collection of data in line with the MSFD protocol, the occurrence of litter ingestion increased to 68,1%, while the mean dry mass and the mean abundance of ingested plastics reached respectively 0,7 ± 0,2 g and 14,3 ± 6,7 pieces.

Considering data from 2013 to 2019, there was a significant difference in occurrence among the three areas for ingested dry mass but not for number of items. The occurrence of plastic ingestion was the lowest in the Bay of Biscay 47,6% (N=21), while it reached 71,1% in Azores (N=38) and was 100% in Canary Islands (N=10). The mean dry mass of ingested plastic was respectively of 0,2 ± 0,1 g in Bay of Biscay, 1,0 ± 0,3 g in Azores, and 0,2 ± 0,1 g in Canary Islands). The mean abundance of ingested plastics was of 9,6 ± 4,1 pieces, 16,3 ± 4,3 pieces and 16,3 ± 3,1 pieces respectively for these 3 Regions.

As it stands, this initial assessment provides consistent data and the technical and scientific basis for future implementation of monitoring. Further implementation of sampling will also enable a larger coverage of sampling, to record all stranded animals in all parts of Regions IV, V, and Macaronesia. A long-term management of sampling and data collection will also enable the evaluation of trends. Alignments of data with the threshold value, as defined by the EU project INDICIT and to be agreed by OSPAR, indicate that the population of sea turtles is strongly affected by marine litter in the OSPAR Maritime area, requiring reinforced actions.

As it stands, this initial assessment provides consistent but partial data when considering the geographic scale of assessment. Three critical points will have to be considered during the next cycle to improve the process:

1. A larger coverage of sampling to record all stranded animals in all parts of OSPAR Regions IV, V, and Macaronesia. More specifically, data on dead animals (stranded or by-caught) from the coasts from mainland Portugal and Spain will be required for a complete assessment.
2. While a long-term management of sampling and data collection is possible by relying on both existing infrastructures and skills (rescue centres, stranded networks, scientific institutions, NGOs, Aquaria, etc.), coordination and optimisation will have to be better formalised to enable the use of other data than those provided only by scientific projects.
3. Evaluation of the data against the threshold value will normally be possible during the present cycle (definition of thresholds under way within the INDICIT and MSFD work plans), but will have to be finalised through an OSPAR formal agreement.

Galgani, F., Hanke, G., Werner, S., et al. (2013). Guidance on Monitoring of Marine Litter in European Seas (EUR - Scientific and Technical Research Reports). Publications Office of the European Union, 128 pages. https://doi.org/10.2788/99475 (pdf)

Darmon, INDICIT Consortium, Miaud (2019); Implementation of indicators of marine litter impacts on sea turtles and biota. INDICIT Final report, Project number: 11.0661/2016/748064/SUB/ENV.C2, 82 pages.

INDICIT, 2018. Monitoring marine litter impact on sea turtles. Protocol for the collection of data on ingestion and entanglement in the loggerhead turtle (Caretta caretta Linneaus, 1758). Version 1.0 - 2018.04.15 Project number: 11.0661/2016/748064/SUB/ENV.C2, 20 pages. https://indicit-europa.eu/cms/wp-content/uploads/2018/09/Protocole_v8.pdf

INDICIT Consortium (2021) Implementation of the Indicator of marine litter on Sea turtles and biota in Regional Sea Conventions and Marine Strategy Framework Directive (MSFD) areas, 82 pages. https://indicit-europa.eu/cms/wp-content/uploads/2019/09/INDICIT-Final-report_Final.pdf

Matiddi, M., van Franeker, J.A., Sammarini, V. (2011). Monitoring litter by sea turtles: an experimental protocol in the Mediterranean. Proceedings of the 4th Mediterranean Conference on Sea Turtles.

Matiddi, M., Hochsheid, S., Camedda, A., et al., (2017). Loggerhead sea turtles (Caretta caretta): A target species for monitoring litter ingested by marine organisms in the Mediterranean Sea. Environmental Pollution 230, 199–209.
https://doi.org/10.1016/j.envpol.2017.06.054

Matiddi, M., deLucia, G. A., Silvestri, C., et al., (2019). Data Collection on Marine Litter Ingestion in Sea Turtles and Thresholds for Good Environmental Status. J. Vis. Exp. (147), e59466, doi: https://doi.org/10.3791/59466 (2019).

OSPAR- EIHA 16/5/13, (2016). Marine litter in sea turtles: A risk assessment as a scientific background for including ingestion of debris by sea turtles as a candidate indicator for impact of marine litter on biota in the southern OSPAR area (Region IV)., in: Agenda Item 5 Document EIHA 16/5/13 Presented by France. OSPAR Convention for the Protection of the Marine Environment of the North-East Atlantic. Presented at the Meeting of the Environmental Impact of Human Activities Committee (EIHA), Berlin (Germany).

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