Bathymetric Strata Research Articles

Preliminary records of abundance and morphometry of the tiger crab, Aegla concepcionensis (Schmitt, 1942) (Anomura, Aeglidae) in a lake of southern Chile

Abstract The tiger crab, Aegla concepcionensis, is a threatened endemic freshwater decapod of Chile, distributed throughout small areas of the Mediterranean region of Central Chile (37°30′-38°00′S). Its habitat includes streams and lakes with riparian areas dominated by native plants, with little or null human intervention. To our knowledge, the tiger crab’s distribution is limited and human stressors (e.g., water withdrawal, exotic tree plantations and climate change) have led to degradation of its habitat. Based on the presence of these stressors and the virtual lack of knowledge of its ecology, the tiger crab has been categorized as Endangered (EN). This study presents a preliminary description of the species’ ecology based on its abundance and its morphometrics, as well as on its feeding habits in Caburgua lake, South Central Chile. We established 16 sampling points, half of which in the shallow bathymetric stratum (0-10 m depth) of the lake itself, and half in the Lumaco stream, one of the lake’s tributaries. We used baited traps to capture specimens. A. concepcionensis appeared to be found in the lake’s shallow bathymetric stratum, but not in the stream. Individuals showed negative allometric growth, males were larger than females, and they showed scavenger feeding behaviour. Our findings provide useful information to help with tiger crab conservation, although more extensive surveys will be required to collect sufficient data for establishing a robust conservation program for the species in the study area.

Decapods Associated with the Southern King Crab (Lithodes santolla) Fishery in Central Patagonia (44° S, Chile)

The southern king crab, Lithodes santolla, is an important fishery resource in the inner seas of Chilean Patagonia. The fishing gear used to catch southern king crab (bait trap) and its operation at different depths over several months provide the opportunity to gather information about relative abundance. The aim of the present study was to analyze the information collected from the catches of southern king crab and its associated fauna in the Magdalena Fjord to study the biodiversity and ecology of scavenging decapod crustaceans. Specifically, the study aimed to determine the bathymetric patterns of abundance by species, to model the abundance by season (winter and spring) and to determine the structuring pattern of scavenging decapods assemblage. Samples were collected between June and November 2019 by deploying traps in four bathymetric strata: 1 = 0–50 m; 2 = 51–100 m; 3 =101–150 m; 4 = 151–200 m. We registered a total of 673 decapod specimens associated with the southern king crab fishery, representing five species: Lithodes santolla (n = 96), Libidoclaea smithii (n = 10), Metacarcinus edwardsii (n = 58), Munida gregaria (n = 507) and Peltarion spinulosum (n = 2). The abundance of decapod species varied by month and bathymetric strata. We found bathymetric patterns for L. santolla abundance, M. gregaria, M. edwardsii, and total species abundance. The most informative model to explain scavenging decapod abundance by generalized linear model (GLM) included species and season. The null model of species co-occurrence analysis revealed that all species associations during the sampled months were random. Our study is the first that provides evidence about patterns of bathymetrical and temporal variation of scavenging decapod abundance and expands the body of knowledge regarding the biodiversity of scavenger decapods in the Magdalena Sound.

The demersal bathyal fish assemblage of the Central-Western Mediterranean: Depth distribution, sexual maturation and reproduction

This study compiles information on the size distribution and reproductive patterns of five chondrichthyans and 10 bony species dwelling on the continental slope of the Central-Western Mediterranean (south-eastern Sardinian waters, depth 720–1890 m). The abundance of the relatively less numerous chondrichthyans was found to decrease with depth. Almost all chondrichthyan species had a long reproductive period throughout the year at all depths. In bony fishes, the upper bathymetric stratum (<1100 m) was dominated by species with continuous and seasonal (autumn-winter) spawning cycles. At intermediate and lower depths (>1100 m), continuous reproduction was the most common pattern. Both chondrichthyans and bony fishes exhibited large sizes at maturity and at first maturity (>75% and >60% of their maximum body length, respectively), supporting the hypothesis that most deep-sea fish populations are characterized by a delayed maturity, which makes them highly vulnerable to fishing pressure and over-exploitation. In some sharks, population partitioning was observed, according to life stage as a function of depth: adult/mature females occupied deeper habitats than males and juveniles. Conversely, Dipturus nidarosiensis female and male juveniles (>1100 m) were segregated from the adult/mature population, dwelling between 1000 and 1100 m. In four of the 10 bony fishes examined, we found a clear and significant predominance of females, particularly pronounced in Alepocephalus rostratus, which is clearly related to their K-reproductive strategy. The four key-selected species (Galeus melastomus, A. rostratus, Bathypterois mediterraneus and Trachyrincus scabrus), characterized by different reproductive strategies/modalities and feeding behaviours, were differently affected by depth and fluxes of organic matter (Particulate Organic Carbon concentration) from the photic zone towards the sea-bottom as a function of sex and life -stage.

Scavenging crustacean fauna in the Chilean Patagonian Sea

The marine ecosystem of the Chilean Patagonia is considered structurally and functionally unique, because it is the transition area between the Antarctic climate and the more temperate Pacific region. However, due to its remoteness, there is little information about Patagonian marine biodiversity, which is a problem in the face of the increasing anthropogenic activity in the area. The aim of this study was to analyze community patterns and environmental characteristics of scavenging crustaceans in the Chilean Patagonian Sea, as a basis for comparison with future situations where these organisms may be affected by anthropogenic activities. These organisms play a key ecological role in marine ecosystems and constitute a main food for fish and dolphins, which are recognized as one of the main tourist attractions in the study area. We sampled two sites (Puerto Cisnes bay and Magdalena sound) at four different bathymetric strata, recording a total of 14 taxa that included 7 Decapoda, 5 Amphipoda, 1 Isopoda and 1 Leptostraca. Taxon richness was low, compared to other areas, but similar to other records in the Patagonian region. The crustacean community presented an evident differentiation between the first stratum (0–50 m) and the deepest area in Magdalena sound, mostly influenced by Pseudorchomene sp. and a marked environmental stratification. This species and Isaeopsis sp. are two new records for science. The discovery of undescribed species evidences that this region needs further studies exploring its biodiversity, which is most likely being already impacted by anthropogenic pressure.

Spatial and temporal distribution of marine litter on the seafloor of the Balearic Islands (western Mediterranean Sea)

Marine litter, and more specifically the plastic fraction, have been studied in the seafloor around the Balearic Islands. A total of 806 scientific bottom trawl hauls from 15 years of surveys (2001–2015) were analyzed covering a depth range from 38 to 800 m. Marine litter was detected in 88% of the hauls sampled, with a mean value of 1.39 ± 0.13 kg/km2. For the plastic fraction, the mean value obtained was 2.73 ± 0.26 kg/km2, with its presence in 66% of the sampled hauls. Amongst a series of analyzed factors, that may explain the distribution of seafloor plastics in the study area, sampling area, bathymetric strata and distance to the coastline were identified as significant. High quantities of seafloor plastics were observed along the northwestern coast of Mallorca, which could be related to oceanographic features, and in the continental shelf, close to the coastline, as well as in the upper slope. However, no increasing or decreasing temporal trend in abundance of seafloor plastics was seen throughout the 15 years of scientific surveys.

Seasonal and depth related variation of parasite communities of Notacanthus bonaparte Risso, 1840 (Notacanthiformes: Notacanthidae) over the northwest Mediterranean slope

In the last decades fishing activities have spread from coastal to deeper waters with serious effects on the deep-sea ecosystems and its fauna, which are considered to be highly susceptible to these impacts. The implementation of protection measures is necessary, but the knowledge on this biome is scant, and often limited to species of commercial value. To the best of our knowledge, this study is the first survey to describe and analyse parasite infracommunities of the deep-sea fish Notacanthus bonaparte sampled from three bathymetric strata between the upper and lower slope in the western Mediterranean Sea (Balearic Sea, Spain). The aim of this work was to assess the effect of host specific parameters as well as environmental conditions and spatial and temporal variation on the composition and structure of the parasite communities. We have found poor parasite infracommunities, usually described rather for bathypelagic fishes than observed in fishes with benthic feeding habits such as N. bonaparte, in which two out of five species are considered as accidental infections. The infracommunity composition is determined by the factors, depth and maturity status (size). The dominating taxon, cucullanid larvae, seem to be accumulated throughout the life of the host showing higher abundances in larger fish in deeper waters on the middle and lower slope. The prevalence and abundance of this parasite could be linked to increased water turbidity and it is supposed that these larvae are free-living in the sediment being ingested by N. bonaparte when feeding on benthic organisms. The results suggest that N. bonaparte acts as important intermediate host for this taxon though, the final host is still unknown. The single monogenean species Tinrovia mamaevi was mainly recorded in the upper slope and its higher prevalence in this depth range could be related to higher host densities observed in these depths. The prevalence and abundance of this parasite species could be linked to temperature and salinity, and although measured variations for these parameters were marginal it is supposed that these and probably further additional abiotic factors may influence its distribution pattern. Considering previously published diet data this study indicates potential pathways other than those expected for parasites transmitted via the food web using N. bonaparte as intermediate and definitive host.

Spatio-temporal distribution of demersal fish species in the northern Alboran sea and Gulf of Vera

Spatio-temporal distribution of demersal fish species in the northern Alboran sea and Gulf of Vera

Size‐spectra across geographical and bathymetric gradients reveal contrasting resilient mechanisms of recovery between Atlantic and Mediterranean fish communities

AbstractAimMarine conservation often prioritizes measures based on ecosystem diversity, missing important information on the size and structure of communities such as that provided by body size‐spectra (SS). While most studies have focussed on temporal or spatial patterns of SS, there is no research investigating their spatial heterogeneity, which is a key community trait revealing mechanisms of resilience. We aimed to comparatively determine the main patterns of variation of fish SS and their spatial heterogeneity across geographic and bathymetric gradients.LocationShelf and slope Atlantic and Mediterranean demersal ecosystems.MethodsUsing the information obtained from the experimental surveys, we calculated fish SS at four bathymetric strata and investigated the influence of the biomass of small‐sized and large‐sized fish on their temporal and spatial variation. We also assessed the functional relationship between the mean pattern and the spatial heterogeneity of SS as a characteristic structural trait of a community.ResultsThe variation in SS demonstrates that Atlantic communities were geographically and bathymetrically more connected, while those in the Mediterranean were more fragmented. The relationship between mean SS and its spatial heterogeneity was a community fingerprint differentiating two contrasting pathways of community recovery between Atlantic and Mediterranean ecosystems. Atlantic communities were recovering because of the temporal increasing contribution of large fish and a ‘rescue effect’ of neighbouring areas, which have spatially homogenized size structure. Mediterranean communities were, by contrast, spatially clustered and highly dependent on small‐sized fish variability that hampers the capacity of ecosystems to recover after a chronic degradation.Main conclusionsPatterns of SS variation depend on the spatial complexity of communities, which contrasts between Atlantic and Mediterranean systems. Integrative analyses of size‐based indicators (mean and variance) provide a complete assessment of the structural properties of communities and characterize the resilience mechanisms of recovery against perturbations under contrasting ecological contexts.

Hydrozoan diversity from Western Sahara and Atlantic coast of Morocco.

Hydrozoan diversity from Western Sahara and Atlantic coast of Morocco.

Biogeography of continental shelf and upper slope fishes off El Salvador, Central America

The present research provides detailed information on the geographic and bathymetric distributional patterns of fishes and describes the main species assemblages of the continental shelf and upper slope off El Salvador. The sampling was based on 673 bottom-trawl tows taken during research surveys from April to November 2003. The data analysis was based on presence-absence matrixes and was conducted with PRIMER 6 software. A total of 148 fish species were recorded during the study period: the families with the highest number of species were Sciaenidae (13) and Carangidae (10), and the highest percentages of occurrence were registered for Porichthys margaritatus (40.6%), Pontinus sp. (34.8%) and Monolene dubiosa (33.1%). The cluster analysis by depth showed three faunistic associations: (1) on the inner and part of the mid continental shelf (20–60 m), (2) one bathymetric stratum on the mid continental shelf (80–100 m), and (3) on the outer continental shelf and upper slope (120–240 m). The cluster analysis by geographic zones showed separation between three zones: Western, Central and Eastern Zones off El Salvador. The Central zone is characterized by a different fish community of mixed habitat, while the main factor that determined the fish assemblages on the continental shelf and upper slope was depth.

Preliminary evaluation of landings and discards of the Turkish bottom trawl fishery in the northeastern Aegean Sea (eastern Mediterranean)

Summary: This short-term study on commercial discards was carried out in fishing grounds around Gokceada Island in the northeastern Aegean Sea, a geographic area where fisheries information is rather limited. A total of 28 bottom trawls were performed between 70 and 410 m depth from December 2009 to February 2010. All the samples were collected on board a commercial trawler under commercial fishing conditions. A total of 3143 kg of biomass was caught in 28 valid hauls. Landings accounted for about 67% of the total catch while the remaining 33% was discarded. Fish species comprised 85% of the total catch and their composition could be divided into four main groups related to depth: shallow shelf (70 to 88 m), deep shelf (155 to 180 m), shelf break (196 to 276 m), and upper slope (307 to 410 m). Fish dominated the abundance and biomass of both landings and discards in all bathymetric strata. Echinoderms also accounted for a large proportion of the discards. Mean total catches varied between 78.4 kg/h on the shallow shelf and 38.1 kg/h on the shelf break with no differences in the landing biomass between groups, but with slightly higher discards over the shallow shelf. Taking into account the preliminary nature of the findings, based on a short-term analysis, the minimum mesh size and minimum landing size currently applied in the Turkish bottom trawl fishery are not sufficient to reduce discards and to protect juveniles of commercially important species in the northeastern Aegean Sea.

Geographical variation in metazoan parasites of the deep-sea fish Bathypterois mediterraneus Bauchot, 1962 (Osteichthyes: Ipnopidae) from the Western Mediterranean

This study examines the parasite fauna of Bathypterois mediterraneus, the most common fish below 1500m in Western Mediterranean waters. Samples were obtained during July 2010 from the continental slope of two different areas (off Catalonia and Balearic Islands) in three different bathymetric strata at depths between 1000 and 2200m. The parasite fauna of B. mediterraneus included a narrow range of species: Steringophorus cf. dorsolineatum, Scolex pleuronectis, Hysterothylacium aduncum, Anisakis sp. larva 3 type II and Sarcotretes sp. Steringophorus cf. dorsolineatum and H. aduncum were the most predominant parasites. H. aduncum showed significant differences in abundance between depths of 2000–2200m with 1000–1400m and 1400–2000m, irrespective of locality, whereas S. cf. dorsolineatum showed significant differences between the two localities at all depths except for 2000–2200m. We suggest the possible usefulness of these two parasites as geographical indicators for discriminating discrete stocks of B. mediterraneus in Western Mediterranean waters.

Structure and dynamics of cephalopod assemblages in the water column on shelf-break and slope grounds of the western Mediterranean

The structure and dynamics of cephalopod assemblages in different bathymetric strata from the surface to bottom grounds, down to a depth of 900m, in the western Mediterranean, were analysed. Data were collected both on the shelf-break and slope during the summer and early autumn surveys, using a midwater trawl and a bottom trawl gear, to catch pelagic and nektobenthic species, respectively. The pelagic tows were not random, but targeted at the strongest and widest acoustic sound layers. A total of 26 cephalopod species belonging to 12 families were collected. With regard to the abundance, biomass and frequency of occurrence, we did not find a common seasonal trend for all the species, suggesting that their population dynamics are not governed by major environmental drivers. Most assemblage metrics (e.g., diversity, species richness, abundance and biomass) showed similar, low values in the pelagic layers compared to the bottom grounds. In general, assemblage metrics were lower in summer than in autumn on the shelf-break, while showing an inverse seasonal trend on the slope. There was a clear general increase in all metrics during the night compared to the day. Cluster results revealed differences in diel migratory strategies by stratum, vertical movements being scarce in the shelf-break species, but intense in the slope species.

Reproductive biology and recruitment of the deep-sea fish community from the NW Mediterranean continental margin

Temporal patterns in deep-sea fish reproduction are presently unknown for the majority of deep continental margins. A series of seasonal trawling surveys between depths of 300 to 1750m in the Blanes submarine canyon and its adjacent open slope (NW Mediterranean) were conducted. The bathymetric size distributions and reproductive cycles of the most abundant species along the NW Mediterranean margin were analyzed to assess the occurrence of (i) temporal patterns in reproduction (i.e., spawning season) along a bathymetric gradient and (ii) preferential depth strata for recruitment. The fish assemblages were grouped in relation to their bathymetric distribution: upper slope, middle slope and lower slope species. Middle-slope species (i.e., 800–1350m) showed short (i.e., highly seasonal) reproductive activity compared to the upper (300–800m) and lower (1350–1750m) ones. Our results, together with those previously published for megabenthic crustacean decapods in the area, suggest a cross-phyla depth-related trend of seasonality in reproduction. In the middle and lower slope species, the reproductive activity reached a maximum in the autumn–winter months and decreased in the spring. The observed seasonal spawning patterns appear to be ultimately correlated with changes in the downward transport of organic particles and with seasonal changes in the physicochemical characteristics of the surrounding water masses. The distribution of juveniles was associated with the bathymetric stratum where intermediate nepheloid layers interact with the continental margins, indicating that this stratum acts as a deep-sea fish nursery area.

Variability in the Growth Patterns of &lt;I&gt;Loxechinus Albus &lt;/I&gt; Along a Bathymetric Gradient Associated with a Fishing Ground

Here we assess the growth pattern variability of the urchin Lochechinus albus (Molina, 1782) in a fishing ground where it was distributed between 0 and 100 m depth. The bathymetric gradient was divided into four strata, and urchin samples were collected for growth estimations. Images were used to characterize the urchin population along this bathymetric gradient, and historical records for the urchin fishery at this fishing ground were examined. four algorithms were used to model growth, and the Akaike's Information Criteria was used to determine the best model fit. Among the four bathymetric strata, both size and age composition, and the growth patterns of L. albus differed significantly. In the shallowest stratum, urchins were smaller and younger than in the deeper strata. Urchins from 5 to 15 m depth displayed greater initial growth rates compared with urchins from 25 to 100 m depth; however, growth decelerated faster at 5-15 m depth than at deeper habitats. Based on results, we hypothesize that the growth pattern of L. albus observed in the shallowest stratum represents a case of age (size) truncation due to fishing, which requires further study.

Population biology of the shark, Squalus megalops, harvested in the central-east Atlantic Ocean

This is the first study to analyse the structure and biological characteristics of Squalus megalops and the impact of fishing on its population in the Northern Hemisphere (central-east Atlantic). The sex ratio (1:2.59) diverged significantly from 1:1 in favour of females. The length at maturity for males and females was 490 and between 634 and 659 mm total length, respectively. The lengths at pregnancy and maternity were 661 and 681 mm, respectively. S. megalops is an asynchronous breeder in which ovulation, parturition and pregnancy do not take place at a specific time of year. The maximum litter size was six, and the ovulation–gestation period was two years, which is equal to a maximum productivity of 36 offspring per lifetime. The sex ratio of near-term embryos (1:1.15) did not show any significant differences. The mean growth rate of the embryos was 179 mm/year in the first year and 47 mm/year in the second, indicating a period of gestation of two years. Age estimates ranged between 4 and 26 years for males and 4 and 32 years for females. Males and females of all total lengths were found in the same area and bathymetric strata in different seasons of the year. The estimate of total mortality for females was 0.22 year −1 and 0.19 year −1 for males. Natural mortality was 0.107 years −1 and 0.12 years −1 for females and males, respectively. The values for fishing mortality and the exploitation ratio were 0.113 years −1 and 0.51 for females and 0.07 years −1 and 0.38 for males, respectively. The estimated biological parameters indicate that S. megalops is highly susceptible to overfishing, given the high fishing pressure this species experiences in the central-east Atlantic.

Cephalopod Species in Mozambican Waters Caught in the “Mozambique 0307” Survey: Distribution, Abundance and Assemblages

—The present paper reports for the first time for Mozambique waters the distribution, abundance and species assemblages of cephalopods in the outer shelf and upper/middle slope (100 – 700 m depth) from data collected in spring of 2007 during the “Mozambique 0307” bottom-trawl survey. A total of 129 hauls were performed following a random stratified sampling scheme in the different sectors and bathymetric strata. The biomass estimates were computed by the sweptarea method. Cephalopod species accounted for 8.4% of the total biomass captured, with a total of 50 species belonging to 13 families. The most important families in terms of species richness were Octopodidae and Sepiidae with 10 representatives each. The most abundant species was theomastrephid Nototodarus hawaiiensis, present in all sectors. The second most abundant species in terms of biomass was Sepia acuminata, followed by the Veladona togata (Octopodidae) mainly between 400 and 600 m depth. The highest biomass estimates were recorded in the sectors named Bazaruto B and Boa Paz, between 200 and 400 m depth. Species assemblages were analysed with the Bray-Curtis similarity index and the group average clustering method was applied, revealing three cephalopod assemblages : the shelf community (100-200m), a wide transitional zone between shelf edge-upper slope (200-600 m) and the middle slope (600-700 m), mainly characterised by Sepia species, Nototodarus hawaiiensis, and Histioteuthis species, respectively. The diversity indices showed a higher diversity in Sofala, in the north of the study area, and inthe shelf community in all sectors. Keywords: Mozambican waters, assemblages cephalopods, shelf community, upper-middle slope

Spatio-temporal variations in deep-sea demersal communities off the Balearic Islands (western Mediterranean)

The spatial and temporal variations of deep-sea megafaunal assemblages from the western Mediterranean are analysed in the present paper. The assemblages from two locations of the Balearic Islands situated 120 km apart were compared using data collected seasonally on a bathymetric stratum covering the 150–750 m depth range during six bottom-trawl surveys. The assemblage structure, in terms of species composition, species dominance and population sizes, was differentially affected by the spatio-temporal variables analysed (depth, location and fishing period). Although depth was the main factor determining the assemblage composition, the differences obtained between the two locations were also relevant. On the upper slope these between-location differences in the dynamics of megafaunal assemblages were found to be related to the effect of fishing exploitation. Population size-based metrics and biomass spectra were good predictors of meso-scale fishing effects, and were mainly reflected by elasmobranchs and demersal teleosts. Nevertheless, the effects of fishing depended on the species considered. Two dominant large-sized fish species found on the upper slope in both localities, Galeus melastomus and Phycis blennoides, had higher biomass values associated with lower fishing effort. Although the mean body weight (MBW) of both species and also the mean maximum body weight (MMBW) of G. melastomus agreed with this pattern, the P. blennoides MMBW did not. This last case could be indicative of natural size-trends such as the bigger–deeper phenomenon which refers to the displacement of large individuals towards the deeper limit of their bathymetric distribution, beyond the maximum depth sampled in this study for this species. By contrast, the target species of the upper slope fishery, the red shrimp Aristeus antennatus, was not negatively affected by the direct impact of fishing activity and other environmental factors, such as the presence of specific water masses could also be important.

The multi-component structuration of the species diversity of groundfish assemblages of the east coast of Corsica (Mediterranean Sea): Variation according to the bathymetric strata

The multi-component aspect of species diversity of groundfish assemblages was examined on the basis of a set of experimental trawl surveys conducted on the east coast of Corsica. We analysed and compared the structuration of diversity within three different bathymetric strata: the continental shelf (60–120 m depth), the upper slope (250–400 m) and the lower slope (450–570 m). For each of these three bathymetric strata, we simultaneously analysed 12 indices that are theoretically complementary and relate to 4 diversity components: (1) the number of species, (2) rarity, (3) evenness and (4) taxonomic diversity. Principal component analysis based on Spearman's correlation coefficients was carried out to investigate empirical relationships between the selected indices. Our results showed not only that a single diversity index cannot provide a complete view of the groundfish diversity along the east coast of Corsica, but also that – in some cases – one index cannot even encapsulate a complete description of a specific diversity component. We also found that the nature and the number of independent diversity components slightly varied from one bathymetric stratum to another. The main differences – which mainly occurred in the deepest bathymetric stratum – might be associated with lower density of individuals and lower dominance of some species at deeper depths. Finally, this study is the first dealing with groundfish diversity in this area, which is currently characterized by one of the lowest fishing intensity rates in the northern Mediterranean Sea. It might be considered as a first “reference state” with a view to monitoring the spatio-temporal changes in species diversity patterns along the east coast of Corsica in the future.

Biology and fishery of Eledone cirrhosa in the Ligurian Sea

Biological information for Eledone cirrhosa has been reassessed through two series of trawls in the framework of the Research Projects MEDITS (summer) and GRUND (autumn) over a 10-year period of surveys in the Ligurian Sea. This information covers aspects such as life span and growth and mortality rates. The sum of samples obtained in the two different seasons allowed the analysis of consistent length frequency distributions and resulted in distinguishing recruits/juveniles from adults of two different ages, i.e. E. cirrhosa is a relatively long living cephalopod, whose reproduction occurs in the second or third year of life. By sampling in different bathymetric strata, different densities on shelf and slope fishing grounds were measured and their displacements with changing season were monitored. The most important stratum in terms of summer densities was in the range 100–200 m depth, which includes the shelf edge, at 150 m. In a relatively narrow strip of seabed, covered by the shelf-edge detritic assemblage and adjacent muddy bottom assemblage VTC (80–150 m), the recruitment of E. cirrhosa occurs from January onwards, while till recent times a specific trawling targeting juveniles used to be carried out in late spring and summer months. In autumn E. cirrhosa is mainly concentrated in shallower waters where trawling activity does not specifically target this species. Trends in numbers and biomass derived by the two series of surveys, and in particular those during autumn series have revealed a significant decrease over the studied time interval. Therefore, the possible relationship between large-scale environmental factors and/or exploitation, was investigated and a positive relationship between summer biomass and winter NAO index was found, even if the cause of such relationship remains unexplained. However, trends of E. cirrhosa landings reported in other studies of the north-western Mediterranean resulted in a similar relationship, thus reinforcing the hypothesis of climatic factors influencing the success of the fishery of this biological resource. A tentative stock assessment, based on relative yield-per-recruit functions, taking into account the two different lengths at first capture and corresponding to mesh sizes of 20 or 40 mm (juveniles and adults nets), showed overexploitation and underexploitation, respectively. A preliminary study of density indices by vital phase also demonstrated a correlation between summer spawners and autumn juveniles of the following year, thus providing evidence of a stock–recruitment relationship.