The European lobster, Homarus gammarus (Linnaeus), is a decapod crustacean species of great ecological and economic importance found in the northeastern Atlantic. Its distribution ranges from northern Norway to Morocco, but it is not present in the Baltic Sea (Holthuis 1991). It also inhabits the Mediterranean and the western Black Sea, including the Istanbul Strait (Gönülal 2015).

The species is listed in the Mediterranean in Appendix 3 (Protected fauna species) of the Berne convention on the Conservation of European Wildlife and Natural Habitats (e.g. Lloret and Riera 2008). This benthic animal is a nocturnal and territorial species found mainly on rocky substrates which feeds on a wide range of prey such as blue mussels, hermit crabs and Polychaeta (Bertran and Le Calvez 1988, Prodöhl et al. 2006). Individuals can weigh more than 7 kg and the largest males and females may live up to 42 and 72 years, respectively (Sheehy et al. 1999). H. gammarus and the American lobster H. americanus (Milne Edwards), found on the northwest coast of the Atlantic, are the only two species representing their genus within the family Nephropidae, and are anatomically very similar (Wahle et al. 2013).

With 5194 t of total landings in 2014 (FAO 2017), the European lobster is a significant fishery resource throughout its range. It is an important source of income and employment for artisanal and coastal fisheries considering its high commercial value. It is targeted by trap fisheries in northern Europe, mainly in the United Kingdom, Ireland, and northern France (Bennett and Lovewell 1977, Bennet et al. 1993, Browne et al. 2001). The traps have various designs, shapes, and sizes, and they can capture singly (one buoy for one trap) or in a gang (several buoys for several tens of traps) (Cobb and Castro 2006). Trap fishing is primarily performed inshore, often less than 5 km from the coast.

Genetic analyses using different molecular markers (mitochondrial DNA and allozymes) were conducted to look for genetic differentiation across the entire range of H. gammarus (Jørstad et al. 2005, Triantafyllidis et al. 2005). They indicated the presence of genetic subpopulations, broadly defined as Mediterranean, Atlantic, northern Norway, and the Netherlands (Triantafyllidis et al. 2005). This information, coupled with studies showing limited movement of adult lobsters (Moland et al. 2011), a short larval stage (Bennet et al. 1993), and possibly small-scale larval dispersal (Schmalenbach and Buchholz 2010), suggests that the Mediterranean subpopulation of the European lobster population should be considered separately.

Artisanal fisheries or small-scale coastal fisheries are particularly important in the Mediterranean (Farrugio et al. 1993, Guyader et al. 2013), where they constitute about 80% of the fishing fleet (European Commission 2004). Fishermen operate with small boats near the coast (0-200 m depth) and adapt their practices to resource availability: a wide variety of gear is used, targeting a diversity of species that change in space and time (Colloca et al. 2004, Leleu et al. 2014). Along the Mediterranean coast, the European lobster is not a target species and is more often a by-catch that occurs in trammel nets targeting the common spiny lobster Palinurus elephas (Fabricius) (Marin 1987, Quetglas et al. 2004) or in gillnets targeting fish (Gönülal 2015). Spiny lobster fishing in the Mediterranean accounts for a large part of the income generated during the fishing season, but it is showing increasing signs of overexploitation (Goñi and Latrouite 2005, Pere 2012). Given the equivalent high commercial value of H. gammarus, this species is of potential interest for fishermen wishing to diversify crustacean-fishing activities in the Mediterranean. In Corsica (NW Mediterranean), the overall fleet can be described as artisanal, which makes it fully representative of Mediterranean small-scale fisheries (Marengo et al. 2016).

While the literature on the ecology and fishing of H. gammarus in the Atlantic is abundant, no single study provides comprehensive information regarding its exploitation in the Mediterranean Sea and its potential for the development of specific fisheries. The aim of this study was therefore to obtain a better understanding of the exploitation pattern and to collect initial biological information on the European lobster population around Corsica. More specifically, we analysed (1) the catch per unit of effort (CPUE), including the dynamics of the catches in space, time, and water depth; (2) the total annual production of the island; (3) the distribution; and (4) the potential abundance of the species.

Marin (1987) estimated European lobster and European spider crab Maja squinado (Herbst) production at 5 to 10 t per year in Corsica. This result is consistent with average annual catches estimated at 6.7 t in this study. Based on FAO data for the period (2006-2013), production in France was estimated at 550 t per year (Atlantic and Mediterranean coasts, FAO 2017), so Corsica represents about 1.2% of total captures of this species at the national level. The European lobster is an accessory catch in Corsica, but it can constitute a significant part of landings, especially in the south of the island. Production on the French Mediterranean coast is estimated at 5.5 t, confirming the general underestimates of FAO data in the Mediterranean in general and also in Corsica (Le Manach et al. 2011).

Historical records of the Mediterranean show catastrophic declines in the landings of clawed lobster in the 20th century (Dow et al. 1980). According to Cobb and Castro (2006), this trend persists today. Statistics of this type should be considered with caution, since it is difficult to evaluate the landings of artisanal small-scale fisheries and they are often underestimated. However, it has been clearly demonstrated that specific lobster stocks in the Mediterranean have suffered from overexploitation, with significant declines in catches, e.g. in Spain (Lloret and Riera 2008) and in the Adriatic (Lotze et al. 2011).

In addition to overexploitation, a pattern of low abundance is evident throughout the Mediterranean compared with Atlantic fisheries. Temperature changes might play a major role for the H. gammarus population in its southern distribution, with excessively high temperatures leading to reduced population abundance (Triantafyllidis et al. 2005). High temperature could especially affect fragile, newly settled European lobsters. Although specific observation of the early benthic phase of the European lobster in the wild is still lacking (Linnane et al. 2001), H. gammarus post larvae are assumed to settle and remain cryptic in shelter-providing rocky substrata and to emerge from their shelters only once they have reached between 25 and 40 mm CL (Linnane et al. 2000a,b, Ball et al. 2001). Hence, high temperatures in shallow coastal waters during the summer period in the Mediterranean could play a major role in juvenile survival and recruitment success. Moreover, the European lobster may be sensitive to climate change, as rising temperature is the most important factor driving shifts in its range of distribution, and increased abundance is found at higher latitudes and decreased abundance at lower latitudes (Caputi et al. 2013, Green et al. 2014).

Catchability of the European lobster is affected by numerous factors, including feeding behaviour and moulting status (Wahle et al. 2013). Thus, high catches in April could be the consequence of an increase in lobster feeding activity with increasing temperature (Bennett and Lovewell 1977, Lizárraga-Cubedo et al. 2015). The decline in catch rates from May to June may be attributable to moulting activity (Miller 1990, Sheehy et al. 1999), and the following peak in CPUE in July is consistent with the increased feeding activity observed during the post-moult period.

The size structures of Corsican catches (range 61-200 mm CL; mean size 127 mm CL) seem to shift towards larger individuals compared with those coming from east Britain (range 78-115 mm CL; mean size 94 mm CL), South Wales (range 90-146 mm CL; mean size 109 mm CL), Scotland (range 62-140 mm CL; modal size 95 mm CL), and Brittany (range 60-160 mm CL) (Howard 1987, Lizárraga-Cubedo et al. 2003, Laurans et al. 2009). The minimum conservation reference size (MCRS), which is usually broadly equivalent to the mean size at first maturity, was imposed under EU fisheries legislation at 87 mm CL for the Atlantic (EC Reg., 850/98) and 105 mm CL for the Mediterranean (EC Reg., 1967/2006). In this study, 80% of the lobsters sampled were above the MCRS, indicating that the individuals were mostly mature.

No individual smaller than 60 mm CL was caught, and similar observations were made by Latrouite (2001) and Prodöhl et al. (2006) in the Atlantic. This result could be linked to gear selectivity, because many European lobsters in the Mediterranean are caught in trammel nets with a large-mesh size (62-83 mm) for the inner panel (Campillo and Amadei 1978). Finally, the cryptic behaviour and limited movement of juveniles could better explain the absence of small and young European lobsters.

In the Atlantic, H. gammarus primarily occurs from low intertidal zones to depths usually no greater than 50 m (Holthuis 1991). For example, the mean water depth of the lobster catches was 37.5 m on the Basque continental shelf (Galparsoro et al. 2009). In Corsica, bathymetric analysis revealed that the highest abundance was between 40 and 80 m. This deeper distribution is potentially due to the high surface temperature in the Mediterranean Sea, which can affect this cold-water species.

In this study, 65% of the animals were encountered in “spiny lobster nets”, which are gears defined by the target species P. elephas and by their use (soak time ≥2 d and depth ≥50 m) (Pere 2012). Other Mediterranean small-scale fisheries display the same trend. In Languedoc-Roussillon (northwestern Mediterranean, France), H. gammarus is mainly found in gillnets for various finfish and in trammel nets for crustaceans (Guillou et al. 2002). Around the Tabarca Marine Reserve (southwestern Mediterranean, Spain), H. gammarus and Scorpaena scrofa Linnaeus are accessory species caught in trammel nets for Palinurus (mean water depth=64 m; mean soak time=46 h) (Forcada et al. 2009).

The bathymetric distribution of European lobsters and the nature of the fishing net in which it is caught provide information on adult habitats, which essentially consist of rocky and coralligenous substrates where natural protective structures (micro-caves, holes and crevices) are numerous. It has been reported that the most suitable habitats for the European lobster are locations at the boundary between sedimentary and rocky bottoms (Galparsoro et al. 2009). In Corsica, these kinds of substrates are widely distributed around the island (except on the east side, Martin et al. 2014) and are particularly common in the Strait of Bonifacio, where the continental shelf has the particularity of being very large (Buron et al. 2012).

The spatial approach identified an area of high abundance in the south, precisely in the Strait of Bonifacio. In the south of the island, potentially suitable habitats for adults coupled with (i) a considerable larval pool from the Bonifacio Strait Natural Reserve (Santoni et al. 2008), (ii) favourable early life history traits such as short pelagic larval duration (Bennet et al. 1993, Goñi and Latrouite 2005, Øresland and Ulmestrand 2013) and (iii) advantageous hydrological features such as eddies (Gérigny et al. 2015) could explain the high abundance of the European lobster. For H. gammarus, larval self-recruitment mechanisms have already been discussed (Schmalenbach and Buchholz 2010, Øresland and Ulmestrand 2013). Elsewhere, several spots around the island also show high European lobster abundance. Despite the lack of favourable habitats on the eastern coast, several wrecks known by fishermen provide shelters for lobsters (Reveche 1979). The north of the island is marked by low yields. This result is somewhat surprising because the northern grounds are potentially suitable for the European lobster, with the occurrence of rocky bottoms and coralligenous assemblages (Pluquet 2006, Bonacorsi 2012). However, this low European lobster catch rate is corroborated by the fishery-independent data from the scientific survey performed in west Cap Corse. By contrast, spiny lobsters are abundant in these areas, which is consistent with their preference for such grounds (Marin 1987, Pere 2012).

Various habitats and depths were covered seasonally by the spatially randomly stratified sampling scheme, but only one lobster was caught out of 540 traps. It is generally expected for experimental fishing to achieve lower catch rates that follow a randomly stratified sampling scheme than fishery-dependent data obtained by fishing effort concentrated on specific areas. Experimental Atlantic fishing surveys had a mean catch rate of between 0.8 and 3 lobsters per trap in Norway (Moland et al. 2013) and between 0.29 and 1.32 lobster per trap in England (Addison 1995). A relatively low abundance of 0.09 lobsters per trap was observed in the south of the Bay of Biscay (Galparsoro et al. 2009). The low abundance in west Cap Corse corroborates the low catch rates obtained with fishery-dependent data for the same area. Unfortunately, to our knowledge no single survey using specific lobster traps has been performed in the Mediterranean, thus making it impossible to make such a comparison.

Onboard monitoring of small-scale fisheries is an important tool that contributes to the suitable exploitation of various key species from the perspective of the island’s fishery management (Le Manach et al. 2011, Marengo et al. 2016). Despite the reporting of greater landings in Fishstat statistics since 2006, the abundance of H. gammarus seems to remain low and stable (Wahle et al. 2013). In Corsica, the lack of historical landing datasets prevents us from concluding on the evolution of the stock and on the current population’s health status. However, the occurrence of this non-target species in selective (trap) and non-selective (trammel net) fishing gear around the island is low. In this context, we cannot reasonably expect that the targeting of European lobster would be an efficient solution for diversification of the artisanal fishery at the scale of the whole island.