ISRA FACTSHEETS
ISRA FACTSHEETS
MEDITERRANEAN AND BLACK SEAS REGION
Balearic Islands
Summary
Balearic Islands is located east of Spain in the central Balearic Sea. The area consists of continental shelf and deeper waters around the two main islands of the archipelago and is characterised by the lowest productivity levels of the Western Mediterranean Basin. Habitats in the area include rhodolite and maërl beds, seagrass meadows, sandy substrates, and pelagic waters. Within this area there are: threatened species (e.g., Rough Skate Raja radula); range-restricted species (e.g., Speckled Skate Raja polystigma); reproductive areas (e.g., Spinetail Devil Ray Mobula mobular); feeding areas (Blackmouth Catshark Galeus melastomus); undefined aggregations (Common Smoothhound Mustelus mustelus); and the area sustains a high diversity of sharks (22 species).
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Balearic Islands
DESCRIPTION OF HABITAT
Balearic Islands is located in the Western Mediterranean Basin, ~175 km from the Iberian Peninsula coastline of Spain. The continental shelf is in general narrow except on the southern coast of Mallorca Island (~35 km width) and between Mallorca and Menorca (the Menorca Channel). The continental slope is gradual on the western and southern sides, while the northern and eastern sides display an abrupt shelf-break (Serrat et al. 2023).
Balearic Islands act as an oceanographic barrier between the Balearic sub-basin to the north and the Algerian sub-basin to the south. The Ibiza and Mallorca channels play an important role in the highly dynamic water exchange between the northern basin (cooler and more saline with a mean sea surface temperature [SST] of 13.46ºC and salinity of 38.0 in the boreal winter; and mean SST of 23.2ºC and salinity of 37.9 in summer) and the Algerian basin (warmer and less saline; mean SST of 14.08ºC and salinity of 37.81 in winter and mean SST of 24.9ºC and salinity of 37.5 in summer). A southward current predominates through the Ibiza Channel and a northward current through the Mallorca Channel (Vargas-Yañez et al. 2017; Pinot et al. 2022).
Waters around Balearic Islands are oligotrophic, presenting the lowest productivity values in the Western Mediterranean Basin (Bosc et al. 2004; Basterretxea et al. 2018). The high transparency of the water column enables algal growth down to 90–100 m depth (Ballesteros 1994). Maërl and rhodolites characterise the benthic habitats together with detrital substrates (Julià et al. 2019).
Balearic Islands is included in two Ecologically and Biologically Significant Marine Areas (EBSAs): North-west Mediterranean Pelagic Ecosystems and North-west Mediterranean Benthic Ecosystems (CBD 2023a, 2023b). The area partially overlaps with six Key Biodiversity Areas: Archipélago de Cabrera; Aguas del Sur de Mallorca y Cabrera; Aguas del Poniente de Mallorca; Aguas del Norte de Mallorca; Aguas del Norte y Oeste de Menorca; and Aguas del Sureste de Menorca (KBA 2023). It also partially overlaps with 14 Natura 2000 sites and four Marine Protected Areas.
This Important Shark and Ray Area is delineated from surface waters (0 m) to a depth of 1,700 m based on the bathymetry of the area and the depth distribution of the Qualifying Species.
CRITERION A
VULNERABILITY
Twenty Qualifying Species considered threatened with extinction according to IUCN Red List of Threatened Species™ regularly occur in the area. Threatened sharks comprise two Critically Endangered, four Endangered, and three Vulnerable species; threatened rays comprise two Critically Endangered, five Endangered, and three Vulnerable species; and threatened chimaeras comprise one Vulnerable species (IUCN 2023).
CRITERION B
RANGE RESTRICTED
This area holds the regular presence of the Rough Skate and Speckled Skate as resident range-restricted species. These two species occur year-round in the area in high abundance (Morey et al. 2006; Mancusi et al. 2016; Follesa et al. 2019; Ramírez-Amaro et al. 2020; Ferragut-Perello et al. 2022). The Speckled Skate is mostly caught by benthic trawlers, whereas the Rough Skate is mostly captured by the small-scale fleet (Morey & Navarro 2010; G Morey unpubl. data 2023). This is related to habitat and depth preferences of both species, with the Speckled Skate preferring deep shelf sandy-mud substrates, and the Rough Skate being more abundant on shallow shelf substrates over sand or maërl (Ramírez-Amaro 2017). Rough Skates and Speckled Skates are restricted to the Mediterranean Sea Large Marine Ecosystem.
CRITERION C
SUB-CRITERION C1 – REPRODUCTIVE AREAS
Balearic Islands is an important reproductive area for two ray species.
The Speckled Skate is widely distributed around the Balearic Islands. Based on catches (n = 236 individuals) from the Mediterranean International Trawl Surveys (MEDITS) carried out between 2003 and 2018 in Geographical Subarea (GSA) 5 (corresponding to the Balearic Islands) at depths of 46–375 m, the species reproduces throughout the year in the Balearic Islands. However, a spawning peak was identified in the boreal winter when the highest number of egg capsules are recorded (~4% of females) followed by a spring cohort of individuals 16–25 cm TL (~9% of the catch in spring, n = 62) (Ferragut-Perelló et al. 2022). This is greater than the size-at-birth (11.5 cm TL and 11.8 cm TL for males and females, respectively) but overlapping with young-of-the-year size estimates (~20 cm TL) in Sardinia, Italy (Porcu et al. 2020). The spatial distribution of the catches revealed a hotspot off the northwest coast of Mallorca, in the Menorca Channel and off the east coast of Menorca.
Balearic Islands is an important mating ground for the Spinetail Devil Ray. Fishers and researchers have collected 82 opportunistic records with >350 sightings of Spinetail Devil Rays around the Balearic Islands since 2018 (Save the Med Foundation unpubl. data 2023). Seasonality in sightings, size of individuals, and population structure were uniform across the archipelago. Most individuals have been reported from late May to mid-August, with a peak in June and July. Most (70%) of the Spinetail Devil Ray sightings (n = 239) were reported from the area, with the main sighting hotspots located along the Tramuntana coast, around Cabrera Island, and along the north coast of Menorca (Save the Med Foundation unpubl. data 2023). Almost half of the observations (42%) corresponded to aggregations of two or more individuals (range 2–30 individuals) and courtship behaviour has been recorded multiple times. Females with mating scars have also been reported in the area (Morey et al. 2022a). Most of the individuals (75%) in the area were adults, based on visual estimations of their size (~200–300 cm disc width [DW]; male size-at-maturity, 206 cm DW; female size-at-maturity, 218 cm DW; Rambahiniarison et al. 2018).
CRITERION C
SUB-CRITERION C2 – FEEDING AREAS
Balearic Islands is an important feeding area for one shark species.
The Blackmouth Catshark is one of the two most common shark species in the upper and middle slopes of the western Mediterranean Sea (Ramírez-Amaro et al. 2020) where they segregate bathymetrically by size, with juveniles being most abundant on the upper slope between 300–500 m (Ordines et al. 2021, Massutí and Morata 2003). Juvenile Blackmouth Catsharks have higher nourishment in the Balearic Islands compared to the Alboran Sea, despite the Balearic Islands having lower productivity levels overall. Nourishment was evaluated based on condition indicators (Le Cren’s relative condition factor, heptosomatic index, and digestivosomatic index) and stomach contents (Ordines et al. 2021). Blackmouth Catshark juveniles showed better condition indicators and higher food ingestion in the Balearic Islands (Ordines et al. 2021). In the Balearic Islands, juvenile Blackmouth Catsharks inhabit a relatively narrow bathymetric range (~300–500 m) with little overlap with adult populations compared to the Alboran Sea, but also with fewer other demersal small shark species. Therefore, they benefit from low intra- and inter- competition for food resources (Ordines et al. 2021). In the area, Blackmouth Catsharks display specialist feeding behaviour whereby they predate mainly on euphausiids (Valls et al. 2011). This prey resource in this bathymetric range is only shared with adult Smallspotted Catshark; this competition may be mitigated by the size selection of prey (Valls et al. 2011). Therefore, the upper slope of the Balearic Islands provides and exclusive niche for juvenile Blackmouth Catsharks. Furthermore, a modelling study based on MEDITS data also supports that statement since it identified a persistent hotspot for recruits in northern Menorca and southern Mallorca (Giannoulaki et al. 2013).
CRITERION C
SUB-CRITERION C5 – UNDEFINED AGGREGATIONS
Balearic Islands is an important area for undefined aggregations of one shark species.
Local Ecological Knowledge and fisher interviews showed that Common Smoothhounds are regularly caught by fishers operating benthic trawls at ~150 m depth off the southern coast of Mallorca (G Morey unpubl. data 2023). Daily catches of >20 individuals recorded from a single vessel have been reported. Additionally, small-scale vessels operating at shallower depths in the same area also catch them although they catch fewer individuals. Sizes commonly range 47–65 cm TL. The size-at-birth of Common Smoothhounds is 34–42 cm TL (Saïdi et al. 2008), suggesting that these individuals were young-of-the-year, and this area could be important in the early stages of their lives although further research is needed to examine if this is a nursery area for the species. Multiple large, mature individuals (130–192 cm TL; male size-at-maturity, 108 cm TL; female size-at-maturity, 121 cm TL; Riginella et al. 2020) have also been caught in the same net within the area, suggesting potential aggregations of adults, although further research is needed to examine whether these represent mating aggregations.
CRITERION D
SUB-CRITERION D2 – DIVERSITY
Balearic Islands sustains a high diversity of Qualifying Species (22 species). This exceeds the regional diversity threshold (19 species) for the Mediterranean and Black Seas region. The regular presence of Qualifying Species has been documented through published and unpublished sources (Carbonell et al. 2003; Massuti & Morata 2003; Mancusi et al. 2005, 2020; FAO Fisheries and Aquaculture 2008; Morey & Navarro 2010; Gouraguine et al. 2011; Valls et al. 2011; Grau et al. 2015; Abril et al. 2020; Morey et al. 2022a, 2022b; Prat-Varela et al. 2023; Serrat et al. 2023; G Morey unpubl. data 2023).
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