Eastern Ionian Sea Research Articles

Metal concentrations in native and transplanted species in the Eastern Ionian Sea (Greece).

Metal concentrations (Cu, Cr, Ni, Zn, Fe, Mn, Cd, and Pb) in marine indicator species were assessed for the study of metal pollution in the Eastern Ionian Sea during the cold period of the year (December 2018 to February 2019). Limpets and sea urchins were collected from natural populations at seven coastal stations while mussels were transplanted at three near-shore stations in the study area. Mixed mesozooplankton samples were selected from a twelve-station offshore network. Additionally, fish, shrimp, and shortfin squid samples were collected by trawling. For the first time, metal concentrations in marine animals were measured in an extended variety of organisms in the area. Higher metal concentrations in limpets, sea urchins, and mussels were observed in the wider area of the two ports located at the sampling area's eastern and southern geographical borders. Levels in zooplankton also followed the same spatial variation. In general, metal concentrations in the investigated organisms were within the same range as those in other non-impacted Mediterranean areas. Accordingly, metal levels in the flesh of the fish, shrimps, and the mantle of shortfin squids did not reveal any risk for human consumption. Metal levels from the present study are proposed as a reference state for the area, while future deviations should be evaluated taking into account potential changes in the natural and anthropogenic pressures on the specific coastal marine ecosystem.

Biological Aspects of Sphyraena sphyraena (L., 1758) in the Central Mediterranean (E. Ionian Sea)

S. sphyraena is a widely distributed species with low commercial value and no sufficient scientific knowledge of its biology. In the present study, the age, growth, weight–length relationship, otolith morphometry, and reproduction of the species were investigated in the Eastern Ionian Sea for the first time. The von Bertalanffy growth function parameters were L∞ = 63.65 cm, k = 0.14 year−1 and t0 = −2.01 years and Φ′ = 2.75. The negative allometric growth in weight was found. Slope b of the weight–length relationship was 2.634. For the otolith moprhometry, the variables radius, length, width, area, perimeter, roundness, circularity, form factor, rectangularity, and ellipticity were examined, which showed that the otolith shape is elongated with an elliptical and rectangular form. Six otolith variables (radius, length, width, area, perimeter, and ellipticity) showed a significant relationship with size. The sex ratio (females/males) was 1:0.74 (no statistically significant difference from 1:1), and the spawning season extended from April to June with peak values of GSI in May for females and April for males. The results of this work improve our knowledge of the species life cycle and provide basic information for species stock identification and fisheries management.

Stable isotope ratios indicate trophic niche overlap in three sympatric delphinid species in the Eastern Ionian Sea

AbstractStudying the sympatric ecology of closely related marine top predator species is of interest both from an ecological and conservation standpoint, because it provides insights into ecosystem functioning, how such species avoid competitive exclusion, and how human stressors may impact these patterns. In this study, we examine the isotopic niche of three sympatric dolphin species that inhabit the eastern Ionian Sea: the common dolphin (Delphinus delphis), the striped dolphin (Stenella coeruleoalba), and the common bottlenose dolphin (Tursiops truncatus). We used carbon, nitrogen, and sulfur isotope ratios to construct three‐dimensional isotope niches and calculate niche sizes and their overlaps among the three species to study interspecific competition for resources. Common dolphin niche overlapped with that of the striped dolphin by 77%, suggesting potential resource competition between these two species. The niche overlap between striped/common dolphins and bottlenose dolphins was much lower (47%). Large differences in isotopic ratios were found between the bottlenose dolphins of the Ionian Sea and those of a largely isolated population in the adjacent semienclosed Gulf of Ambracia, further corroborating the previously documented isolation between the two populations.

Ecology and behaviour of the invasive lionfish Pterois miles colonizing coastal areas of the central Mediterranean

Biodiversity redistribution is occurring at an unprecedented pace, with one prominent example being the invasion of the lionfish (Pterois miles) in the Mediterranean Sea, altering the fish community composition by creating novel interspecific interactions and potentially threatening local biodiversity. Our study attempts to identify patterns in the lionfish distribution and behaviour in the coastal zone of the eastern Ionian Sea (central Mediterranean). Over a 14-month period, visual censuses were conducted along coastal strip transects at six stations, situated in three areas (Mani, Katakolo, Astakos) across a latitudinal gradient. Lionfish density was highest in Mani, the southernmost area. Higher densities were found at two stations experiencing direct anthropogenic pressures: one with structural modifications by port infrastructure, and the other in the vicinity of a fish farm, indicating a potential role of human interventions in facilitating the establishment of invasive populations. Lionfish group size was influenced by overall density, exhibiting variation between the two natural stations. Lionfish activity levels by microhabitat were site-specific, with more inactive individuals in crevices. Temporal activity patterns were similar in the natural stations, with increased activity during spring and summer months; however, temporal activity patterns were not identical in the two anthropogenic sites, suggesting that the specific nature of anthropogenic intervention might possibly influence lionfish activity. Finally, lionfish densities were not significantly different between early morning and late afternoon times of day, in agreement with the crepuscular behaviour already documented for this species.

Ten Years of Mediterranean Monk Seal Stranding Records in Greece under the Microscope: What Do the Data Suggest?

This paper presents the results of an analysis of stranding events of the Mediterranean monk seal Monachus monachus over a decade. The analysis involved categorization according to the cause of stranding and seasonality, the identification of hotspot stranding areas and an assessment of possible correlations between stranding events and environmental/climatic patterns using time series analysis. Moreover, Generalized Additive Models (GAMs) were applied to explore the effects of the size of small-scale fishing grounds, the number of species sightings, and the occurrence of reproduction sites on "human-related" strandings. Finally, special focus was put on the central part of the eastern Ionian Sea for the assessment of stranding hotspot areas by means of the Multi-Criteria Decision Analysis (MCDA) approach, based on different kinds of spatial information such as anthropogenic pressures and the location of breeding sites and feeding grounds. Time series analysis results revealed that oscillation indices, during the first half of the year, and sea surface temperature (SST) in the Mediterranean from October to December were positively correlated with monk seal stranding events. GAMs underlined that areas combining extended small-scale fishery grounds and a higher number of sightings were more likely to cause more strandings. Regarding spatial analyses, the central Aegean Sea was highlighted as a hotspot for "human-related strandings", while the MCDA approach emphasized that the southern coasts of Cephalonia and the gulf between Lefkada and mainland Greece were susceptible to subadult strandings.

Decline in Size-at-Maturity of European Hake in Relation to Environmental Regimes: A Case in the Eastern Ionian Sea.

European hake, Merluccius merluccius L. 1758, is a highly valuable demersal fish species exploited in both the east Atlantic and the Mediterranean Sea. Changes in the size-at-maturity of this species have been reported in various geographic areas. Size-at-maturity is a key parameter in fishery management. Our main goal was to study the trend of the size-at-maturity of European hake in the eastern Ionian Sea (Central Mediterranean) over the last five decades. Utilizing a multi-decadal series of data for various environmental variables, we employed multivariate analyses and non-additive modeling in an attempt to identify shifts in the climatic environment of the eastern Ionian Sea and whether the maturation of the hake population could be affected by these changes. The analyses used suggest a plausible environmental regime shift in the study area in the late 1990s/early 2000s. The decrease in size-at-maturity that was detected in the last two decades may, thus, be associated with environmental changes. However, as many fish stocks already experience fishery-induced evolution, further investigation is necessary to determine whether this environmental effect is an additional stressor on a possibly already fishery-impacted population. The outcomes of this study highlight the importance of investigating the relationship between fish reproductive traits and altered environmental conditions, as the latter are generally ignored during assessments, affecting the robustness of fishery management.

Plastic pollution in the deep-sea Giant red shrimp, Aristaeomorpha foliacea, in the Eastern Ionian Sea; an alarm point on stock and human health safety

Plastic litter, including microplastics, is an ever-growing threat adversely affecting a variety of marine organisms; however, their known effects on marine organisms are still lacking. Aristaeomorpha foliacea is a valuable commercial deep-sea species in the Mediterranean Sea. Hence, due to its importance to human consumption, the investigation of plastic impact on these animals is vitally necessary. In this study the occurrence of ingested plastics has been studied in the giant red shrimp for the first time in the eastern Ionian Sea, as well as any possible differences regarding the plastic ingestion per sex, size, year and its relation to shrimp's health condition. A total of 621 individuals were collected from the Essential Habitat of this species in the eastern Ionian Sea. Plastics were contained in the stomachs of 14.65 % of the examined individuals, with an average of 2.97 ± 0.3 items per stomach. The occurrence of plastics was higher in males than in females. The ingested plastics detected were exclusively fibers of different sizes, colors, and shapes (single form or tangled balls). Plastic items size ranged from 0.75 to 110.59 mm. Significant differences in the occurrence of plastic in the stomachs of A. foliacea were found among years, stations and sex, whereas no considerable effect on shrimp's health condition factors was found. The chemical analysis of plastics showed that 83.82 % of fibers were polyester (PET). Among the shrimps with ingested plastics, the immature individuals were predominant (85.18 %). The results of this study aspire to increase the knowledge on plastics ingestion in the Mediterranean, and highlight the various factors that may be involved in this process. This study demonstrates the obvious threats of plastics in commonly edible shrimps and emphasizes the role of this decapod at the trophic chain by transferring plastics to humans.

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

Sea turtles are highly mobile species that use oceanic, neritic, and coastal habitats as nursery, foraging, wintering, breeding and migration areas at distant locations throughout their lifetime. Due to their highly migratory nature and large-scale habitat use, they are subjected to multiple threats across marine and coastal ecosystems that can impact every stage of their life cycle and result in increased mortality rates. Here, we present new data on stranding events across the eastern Ionian Sea (central Mediterranean). Our analysis on stranding data, collected over a 6-year period, provided clear evidence of continuing and increased mortality events in the region (n = 413, Caretta caretta: 79%, Chelonia mydas: 4%, and unknown: 17%). Based on the alarming results of increased mortality, and taking into account the limitations posed by the nature of stranding data, we further identified potential risk hotspots within critical marine and coastal sea turtle habitats. To do so, we performed a spatially explicit cumulative pressure assessment at different spatial scales in an effort to identify, map, quantify, and synthesize the multiple anthropogenic pressures that are recognized to potentially impact sea turtles. Our results clearly demonstrated that the Ionian Sea is subjected to intense pressures (i.e. fisheries, marine traffic, and underwater noise). We identified three main hotspots of very high risk related to critical foraging grounds, nesting sites, and migration corridors for sea turtles regardless of the spatial scale of the analysis. We found high sea turtle mortality associated with locations characterized as high and very high risk areas. This study offers key information on mortality and spatial risk for sea turtles that can facilitate their effective conservation. Thus, our findings can be used in the light of marine spatial planning, allowing planners to more realistically assess where conservation resources should be directed to control harmful activities and to mitigate impacts on sea turtles.

Fishery spatial plans and effort displacement in the eastern Ionian Sea: A bioeconomic modelling

The management of fisheries requires well-planned approaches that consider the socio-ecological costs and benefits of management options while minimising conflicts among fishing practices. We developed a framework to anticipate the cost-effectiveness of several fisheries management options, including space-time closures, gear selectivity improvements, and fishing effort reduction of eastern Ionian Sea fisheries. We also examined to what extent these fisheries could be influenced by placing new aquaculture sites into specific areas. We used a dynamic space-time model considering the effect of possible fishing effort displacement on alternative marine areas. A fine-scale distribution of 6 species of high commercial importance, for the eastern Ionian fisheries (central Mediterranean), was used together with the fishing effort distribution of trawlers, purse-seines, and small-scale fisheries to track the implications on several bio-economic indicators. The study revealed that the stocks and the fisheries economics benefited from a 10% reduction in fishing effort for all fishery sectors, while the unwanted fish catch was slightly higher. Thus, although there are notable advantages, this management option is not sufficient to support an EU regulatory framework aiming to promote more selective fishing practices and mitigate unwanted catches. However, we showed that the protection of juveniles, by imposing selectivity improvements or space-time closures on trawlers, slightly reduced the unwanted catch. Nevertheless, the benefit for the majority of stocks and fisheries economics, during the five-year simulation period, was limited. In the case of space-time closures, this is attributed to the offset due to the fishing effort displacement towards other areas. While the benefit on fish populations by improving trawl selectivity, it depends on the species. Finally, the establishment of new aquaculture units could lead to a slight re-allocation of fishing effort along the border of the new sites without substantially affecting the profit of small-scale fisheries. Such findings are useful for fisheries management and broader spatial planning in the Ionian Sea. They will provide insight to policymakers and different fishing sectors, thus enabling a more transparent and participatory decision–making process.

Surface connection between the Ionian Sea and different areas of the Mediterranean derived from drifter data

The surface connection between the Ionian Sea (central Mediterranean Sea) and the surrounding areas is studied by looking at the statistical properties of 1632 near-surface Lagrangian trajectories. The choice of the area is due to the key role in the dynamics of the Mediterranean Sea and to the geographical distribution of data. The Lagrangian drifter data were taken from the OGS Mediterranean drifter database, which gathers drifter data collected in the Mediterranean Sea from various institutions and countries between 1986 and 2016. The database has proved to be sufficiently complete, but the spatial and temporal data coverage are less satisfactory in the case of selection of a specific study area and temporal range. The strategy used in this work aims to limiting the problem of data coverage by choosing many target boxes around the study area, choice based on drifter trajectories, current patterns and areas of interest. The pseudo-eulerian analysis obtained from all trajectories passing through the Ionian Sea show the main dynamic structure present in the central Mediterranean Sea (e.g. Atlantic Ionian Stream, Mid Ionian Jet, etc.).On the other hand, the data density decreases progressively toward the eastern and western sectors of the Mediterranean. The highest connection was observed with the Strait of Sicily, Eastern Ionian and Adriatic Sea, with connection percentages 30%, 25% and 16% respectively. The transit times between the Ionian Sea and these target boxes are about 20–50 days. The Ionian Sea is characterized by phenomena of inversion of the basin surface circulation, from cyclonic to anti-cyclonic, over a ten-year timescale, the so-called Adriatic-Ionian Bimodal Oscillating System (BiOS, e.g. Gačić et al., 2010; Gačić et al., 2011). An application of the “target box methodology” has been used to describe how the cyclic variability of the dynamic surface currents generates an equally cyclical fluctuation of the connectivity between the Ionian Sea and the surrounding areas during the BiOS phases.

Marine spatial closures as a supplementary tool to reduce discards in bottom trawl fisheries: Examples from southern European waters

Discards is an important issue in fisheries around the world. The spatial management of discards has attracted interest as a potential tool for minimizing the unwanted catch. The aim of the present work was to identify areas with high quantities of bottom trawl discarded catch regarding species subjected to MCRS, in six areas of southern European waters (southern Portuguese waters, Catalan Sea, Ligurian and northern Tyrrhenian Seas, Strait of Sicily, eastern Ionian Sea, and Aegean Sea). Analyses were based on two types of data: (a) the undersized catch of species subjected to MCRS from bottom trawl surveys and (b) the actual discarded catch (including undersized and non-undersized individuals) of species subjected to MCRS from commercial bottom trawling. Geostatistical analysis techniques were applied to the first type of data and Generalized Additive Models using environmental variables were applied to the second one. Subsequently, areas that persistently presented high quantities of discarded catch (i.e., “iDC grounds”) or undersized catch (i.e., “iUC grounds”) were identified and mapped. The “iDC grounds”/“iUC grounds” were located either over the slope or within the continental shelf and over marine plateaus, largely depending on the main target species of each fishery. Next, the overlap of “iDC grounds”/“iUC grounds” with the existing Fisheries Restricted Areas (FRAs) and the proposed Marine Protected Areas (MPAs) was estimated aiming to explore how spatial closures could contribute to the reduction of bottom trawl discarded catch/undersized catch. Certain spatial closures were more effective in the Central Mediterranean and others to the Eastern Mediterranean. The overlapping of existing FRAs with “iDC grounds”/“iUC grounds” did not exceed 24 % in any study area, whereas proposed MPAs, like the CIESM Marine Peace Parks, reached up to 90 % for the same study area.

New Records of Penaeus aztecus Ives, 1891 from the Eastern Ionian Sea

Brown shrimp Penaeus aztecus Ives, 1891 seems to be well adapted in the Ionian Sea since its first occurrence in the coastal zone of the island of Corfu during 2013. In the current work, we present additional new records from Argostoli Gulf (Cephalonia Island), Sagiada Bay (Therspotia, NW Greece) and Mesoggi (Corfu Island), which verify the wider distribution of the species. Moreover, direct contacts with shrimpers in the region, suggested that commercial exploitation of the species has been recently established. Although it poses potential threats to the lucrative caramote shrimp (Penaeus kerathurus) populations, which support the income of the fishing communities in the region, the presence of P. aztecus populations represents a new promising fisheries resource.

The 2018 Mw 6.8 Zakynthos, Greece, Earthquake: Dominant Strike-Slip Faulting near Subducting Slab

Abstract With different styles of faulting, the eastern Ionian Sea is an ideal natural laboratory to investigate interactions between adjacent faults during strong earthquakes. The 2018 Mw 6.8 Zakynthos earthquake, well recorded by broadband and strong-motion networks, provides an opportunity to resolve such faulting complexity. Here, we focus on waveform inversion and backprojection of strong-motion data, partly checked by coseismic Global Navigation Satellite System data. We show that the region is under subhorizontal southwest–northeast compression, enabling mixed thrust faulting and strike-slip (SS) faulting. The 2018 mainshock consisted of two fault segments: a low-dip thrust, and a dominant, moderate-dip, right-lateral SS, both in the crust. Slip vectors, oriented to southwest, are consistent with plate motion. The sequence can be explained in terms of trench-orthogonal fractures in the subducting plate and reactivated faults in the upper plate. The 2018 event, and an Mw 6.6 event of 1997, occurred near three localized swarms of 2016 and 2017. Future numerical models of the slab deformation and ocean-bottom seismometer observations may illuminate possible relations among earthquakes, swarms, and fluid paths in the region.

Spatial and temporal trend in the abundance and distribution of gurnards (Pisces: Triglidae) in the northern Mediterranean Sea

In this study we investigated the spatio-temporal distribution of gurnards (8 species of Triglidae and one species of Peristediidae) in the northern Mediterranean Sea using 22 years of MEDITS bottom trawl survey data (1994-2015). Gurnards showed significant differences in terms of abundance, dominance and composition among geographical sub-areas and ecoregions, with the highest relative biomass (BIy) being found in Malta, eastern Corsica, the Balearic Islands and the eastern Ionian Sea. The lowest gurnards BIy were observed in the highly exploited areas of the western Mediterranean and the Adriatic Sea, where the largest number of species with a negative linear trend in BIy was also found. The temporal trends in species abundances highlighted a general decrease for the coastal species (C. lucerna, C. lastoviza, C. obscurus) as compared with the species inhabiting the deep continental shelf and slope (T. lyra, P. cataphractum). The results provide for the first time an overview of the spatiotemporal trend in the abundance of gurnards over the wide spatial scale of the northern Mediterranean Sea, also suggesting the possible use of these species as indicators for monitoring the impact of fishing pressure on demersal fish assemblages.

Modeling of floating marine litter originated from the Eastern Ionian Sea: Transport, residence time and connectivity

A Lagrangian particle tracking model coupled to a circulation was used to explore the transport, residence time and connectivity of floating litter that originated from the Εastern Ionian Sea during 2011–2014. At the end of simulations, on average 26% of litter was retained within the coastal waters of the Eastern Ionian Sea, whereas 58% was washed into offshore waters without formulating permanent accumulation areas, as the basin-wide surface circulation was characterized by considerable interannual variability. The inflow of litter into the Adriatic and Eastern Mediterranean Seas was moderate, ranging between 9% and 20%, and the beached litter was on average 9.2%, mostly located in the northern subregions. The average residence time of litter particles ranged between 20 and 80 days, implying their temporary retention before drifting offshore. Connectivity patterns depicted an exchange of litter mainly between adjacent subareas and with a northward direction.

Modelling the spatiotemporal distribution of fisheries discards: A case study on eastern Ionian Sea trawl fishery

The mitigation and incorporation of fisheries discards into the spatial management perspective call for a well-planned approach considering their high spatiotemporal variability. This study describes an approach to map the spatiotemporal distribution of bottom trawl discards taking into account on-board observer data, environmental information and high-resolution estimates of fishing effort derived from Vessel Monitoring System data. Two were the main objectives: i) mapping the Discards Per Unit Effort (DPUE: kg/h) and ii) mapping the total discards quantities (in kg) in a predefined spatial unit (grid cell of 5 × 5 km). For this purpose, discards data from commercial bottom trawlers (seasonal basis, period 2003–2006, 2008) operating on the continental shelf of the eastern Ionian Sea were analyzed. The DPUE for a) all species with Minimum Landing Size (MLS), b) all species without MLS and c) all fish species, were modeled by means of Generalized Additive Models (GAMs) using satellite environmental parameters, bathymetry and season as independent covariates. Mapping discards quantities in a predefined spatial unit was based on the spatial overlapping between GAM estimates for the year 2010 and fishing effort distribution for the same year. Spatial clusters of high discard quantities (hot spots) and their spatiotemporal persistence were also investigated. Results revealed how the environmental and temporal factors influence the DPUE distribution of each discard group and indicated increased discards quantities in areas of high fishing effort. The potential implications of the resulting DPUE maps for advancing discards spatial mitigation are further discussed. Mapping discards quantities using both the DPUE and the fishing effort distribution provide valuable insights that can be useful to investigate the broader ecosystem consequences of the EU landing obligation and other potential fishery management policies.

Multilocus phylogeography of Patella caerulea (Linnaeus, 1758) reveals contrasting connectivity patterns across the Eastern–Western Mediterranean transition

AbstractAimThe Mediterranean Sea is a biodiversity hotspot, hosting a wide variety of habitats and organisms resulting from its complex past history and present‐day processes. Although several biogeographical areas are defined within the Mediterranean Sea, a comprehensive description of the main connectivity patterns among these areas is still lacking. In the present work, we describe the main features structuring the past and present genetic diversity and connectivity in a shallow subtidal limpet across the Mediterranean Sea.LocationMediterranean Sea.MethodsThe genetic diversity and structure of the common and widespread limpet Patella caerulea were analysed in 32 locations across the Mediterranean Sea using two mitochondrial markers (COI and 16S) and five nuclear microsatellite loci. Demographic history and phylogenetic analyses were carried out using mitochondrial markers, and assignment tests were performed on nuclear markers.ResultsTwo main evolutionary units were detected according to both mitochondrial markers. The most significant genetic differentiation was located between the southern tip of Sicily and the Calabria Peninsula. However, the full transition between the Western and Eastern basins is broadly located in the area between the Siculo–Tunisian Strait and the eastern Ionian Sea. Highly variable nuclear markers revealed further complexity related to current connectivity patterns, showing a genetic structure in the Sicily Channel and the Tyrrhenian–Ligurian transition and gene flow across the Messina Strait. The three markers showed a consistent pattern of isolation by distance only in the Eastern basin.Main conclusionsComplex connectivity patterns in the central Mediterranean confirm that this area represents a genetic diversity hotspot for limpets, reflecting the interplay of the past and present processes. For this crucial area, we propose to use the term “transition area,” which may better reflect its complexity and so avoid further debate on the location of a single “genetic barrier.”

First observations on diet and feeding strategy of boarfish, Capros aper (Actinopterygii: Perciformes: Caproidae), in the eastern Ionian Sea (central Mediterranean)

First observations on diet and feeding strategy of boarfish, Capros aper (Actinopterygii: Perciformes: Caproidae), in the eastern Ionian Sea (central Mediterranean)

Crustacean prey in the diet of fishes from deep waters of the Eastern Ionian Sea

The gut analysis of 26 fish species caught in the deep waters of the Eastern Ionian Sea showed that crustaceans were a substantial resource for fish found in deep- water environments, comprising 37 crustacean taxa. Among all species examined, 77% included crustaceans in their guts. Dendrobranchiata/Caridea shrimps were the most frequent crustacean prey found in the guts of almost all examined fishes, with high values of relative abundance (N%). Season (summer, autumn) and fish behaviour (demersal, benthic) were not found to affect the diet of the examined fish species. Galeus melastomus could be considered to be a separate case showing the most diverse diet comprising all the crustacean groups. Differences in the proportion of the main crustacean categories consumed by the examined fish species were observed. The low richness and preference towards specific crustacean taxa or different crustacean species could be considered as an indication of interspecific competition for the same food resource in the oligotrophic waters of the Eastern Mediterranean. The occurrence of different crustacean taxa in the gut of some species through the analysed seasons, could be related to differences in prey availability or to selective preference for certain prey which in turn could be linked to different energetic requirements for growth and reproduction of predators.

The challenge of habitat modelling for threatened low density species using heterogeneous data: The case of Cuvier’s beaked whales in the Mediterranean

The Mediterranean population of Cuvieŕs beaked whale (Ziphius cavirostris), a deep-diving cetacean, is genetically distinct from the Atlantic, and subject to a number of conservation threats, in particular underwater noise. It is also cryptic at the surface and relatively rare, so obtain robust knowledge on distribution and abundance presents unique challenges. Here we use multiplatform and multiyear survey data to analyse the distribution and abundance of this species across the Mediterranean Sea. We use a novel approach combining heterogeneous data gathered with different methods to obtain a single density index for the region. A total of 594,996km of survey effort and 507 sightings of Cuvier’s beaked whales, from 1990 to 2016, were pooled together from 24 different sources. Data were divided into twelve major groups according to platform height, speed and sea state. Both availability bias and effective strip width were calculated from the sightings with available perpendicular distance data. This was extrapolated to the rest of the sightings for each of the twelve groups. Habitat preference models were fitted into a GAM framework using counts of groups as a response variable with the effective searched area as an offset. Depth, coefficient of variation of depth, longitude and marine regions (as defined by the International Hydrographic Organization) were identified as important predictors. Predicted abundance of groups per grid cell were multiplied by mean group size to obtain a prediction of the abundance of animals. A total abundance of 5799 (CV=24.0%) animals was estimated for the whole Mediterranean basin. The Alborán Sea, Ligurian Sea, Hellenic Trench, southern Adriatic Sea and eastern Ionian Sea were identified as being the main hot spots in the region. It is important to urge that the relevant stakeholders incorporate this information in the planning and execution of high risk activities in these high-risk areas.