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Leatherback turtles are seldom observed along the Moroccan Atlantic coast; only stranded sub-adult and adult individuals have been observed and no nesting has been confirmed there (Tiwari et al. 2001; Casale & Margaritoulis 2010). Along the coastline of Casablanca, rare cases have been recorded in the past by the National Institute of Fisheries Research (INRH). During 2015, we documented 10 stranded leatherback turtles, and we conducted a survey along the shoreline of Casablanca to make sure that all stranding events were recorded. We synthesise here the information of these stranding cases, as well as available historical data on leatherback turtle stranding events along the entire Atlantic and Mediterranean Moroccan coasts, with complementary data from southern peninsular Spain and the Canary Islands. 

The INRH is the Moroccan government authority that manages data on stranded sea turtles and provides scientific advice in managing stranding events. For all reported stranding events, we recorded standardized stranding information, including species identification, location, and biometric and biological parameters, and we collect tissue samples, primarily skin and muscle. We obtained data for 2015 from field operations for the Casablanca region, complemented with data from the Royal Gendarmerie of Morocco, who respond to stranding events throughout the Moroccan coast. Historical data for Morocco were extracted from a reconstructed stranding database (Masski & De Stéphanis 2015). Data for Spain (1980 to 2012) were gathered from an online biodiversity database (<http://siare.herpetologica.es/>). For all databases, images were used when available to collect supplementary information and measurements using ImageJ (Schneider et al. 2012). 

We conducted a beach survey on foot along 105 km of shoreline around Casablanca, to search for stranded sea turtles, and to interview local coastal inhabitants. The people we spoke to were asked if they could identify leatherback turtles on photographs and they were questioned on how frequently they observed this species during their lives. The 22 respondents, ranging in age from 19 to 56 years old, had all participated in fishing activities for fish, shellfish or urchins.

Figure 1. Leatherback sea turtle strandings 1. In the Moroccan coast for 2015, 2. historical records in Morocco (1990-2014) and Spain (1980-2012 from: <http://siare.herpetologica.es/>).

Between 14 November and 12 December 2015, we observed five stranded dead leatherback sea turtles along 25 km of the coastline in the area of Casablanca (Fig. 1). The stranded individuals were all female and had a mean curved carapace length (CCL) of 130 cm ± 18 SD (range: 118 - 162 cm). Two individuals were in early stages of decomposition and the three others were freshly stranded. None of them was thin or showed injuries or signs of interaction with fishing gear and one of them seemed to have arrived alive on the sandy beach. Two of them were necropsied and no anomalies were observed in the lung, liver, heart or kidney. The intestines were full of digesta, but the single stomach that was analysed was empty. Furthermore, no obstructing material (e.g., plastic bags) was observed in the trachea after dissection. On 23 January 2016, a decomposing individual with 120 cm CCL was observed stranded in the same area. Its death may have occurred in December 2015.

Earlier during the 2015, five other stranded leatherback turtles were recorded in a 120 km area around Casablanca in February, May, July, September and November. The first turtle was decomposed and had lost its internal organs (98 cm CCL), while the others were between 103-144 cm CCL and were in the first stages of decomposition. One of them was female, and the others were not examined due to being buried before the INRH was alerted.

The survey conducted around Casablanca did not lead to the discovery of any other stranded leatherback sea turtles. During the interviews, only two fishermen recognised the leatherback sea turtle. One of these fishermen described a stranding a few months earlier and the other fisherman recounted that a large turtle had been caught 15 years ago by a fishing boat. The lack of recognition of the leatherback turtle by the local population supports the apparent scarcity of stranded leatherbacks in this area.

The review of historical leatherback stranding records prior to 2015 showed that four out of 21 records occurred in the Casablanca area and dated back to December 1990, July and December 2004, and December 2005. Most stranding events were recorded in the last two decades, which may reflect increased survey effort of the least surveyed areas (Casale et al. 2003). Four cases were recorded in the Saharan area, a coastline of more than 1000 km long where the detection probability of stranded turtles is low. The fourteen other cases occurred in the Mediterranean, of which 10 were recorded in three weeks in October and November 1995 on 8 km of coast on the Mediterranean coast close to the strait of Gibraltar. 

Although rare, the leatherback turtle appears to be present all months of the year in Moroccan waters, as indicated by stranding events. This is concordant with what is observed in the Alboran sea (Rojo-Nieto et al. 2011), Portuguese waters (Nicolau et al. 2016) and in the Bay of Biscay (Morinière & Dell’amico 2011). Few leatherback stranding events were documented along the entire Moroccan coast, which may be due in part to underreporting. The shoreline of Casablanca is a highly populated region and stranding events are nearly always reported by local and law enforcement authorities. The multiple reports of stranded leatherbacks during 2015 in this area were unusual. Two mass stranding events occurred in winter in the western Mediterranean coast of Morocco in 2004 and during the 1980s (De Los Rios Y Los Huertos & Ocaña 2009), close to the strait of Gibraltar. These events probably occurred during the migration of leatherbacks into the Mediterranean of groups of sub-adults and adults, but females seem to be more common. Wind and current patterns influence where dead or debilitated sea turtles end up on land (Hart et al. 2006), and stranding probability decreases with increased distance from the shore (near zero for >100 km). The Casablanca coastline receives yearly stranded cetaceans (Masski & De Stéphanis 2015) and 2015 was not different in this regard from other years, suggesting that there were no exceptional environmental circumstances that led to the leatherback stranding event. We suspect that the death of these observed stranded leatherback turtles in 2015 may have occurred in an area close to Casablanca. The stranded leatherback turtles did not have signs of interaction with fishing gear and none of the other data collected pointed to a specific cause of the stranding events. Indeed, the cause(s) of stranded leatherback sea turtles remain to a large extent unknown (Nicolau et al. 2016). More consistent and standardized reporting of stranded sea turtles in Morocco may help better characterize the occurrence of leatherbacks in Moroccan waters, and the threats they face.

Acknowledgements. The Royal Gendarmerie of the Kingdom of Morocco graciously offered us the opportunity to use their stranding database. We are grateful to Dewez A. from GEFMA (Groupe d’étude de la faune marine Atlantique) gave us advice for the analysis of stranding causes. We also thank anonymous reviewers for their comments and suggestions. 

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