Experimental Bottom Trawl Surveys Research Articles

Distribution and life strategy of the deep-sea crab Paromola cuvieri (Risso, 1816) (Brachyura, Homolidae) in the central Mediterranean Sea over twenty-five years

The present study represents a new contribution to the knowledge on the distribution and life strategy of P. cuvieri in the central Mediterranean. During 71 experimental bottom trawl surveys carried out in the Northern Ionian Sea from October 1994 to July 2019 a total of 457 specimens was sampled from 91 to 1118 m in depth. The highest frequency of occurrence and density was observed in the 600–800 m depth range. The relationship between carapace length and depth was statistically significant showing a significant decrease in size with depth. The length-frequency distribution was unimodal for both sexes and there was a low number of small individuals. The most represented size classes for both sexes were between 50 and 130 mm Carapace Length (CL), with males significantly larger than females. The sex ratio by size showed an increase of males with increasing length. Of the sampled females, 50 were in ovigerous condition and 92 females were non ovigerous. P. cuvieri appears to have continuous reproduction throughout the year, with ovigerous females observed in all seasons, with the highest abundance in spring and winter and between 400 and 800 m of depth. The fecundity ranged between 138165 and 374453 eggs with a mean value of 217237 eggs. The eggs show a spherical shape and their mean size increased with maturity stage. Egg development appears to not be completely synchronous, and two patterns can be observed simultaneously. The relationships between CL/brood size and weight/brood size were highly significant. The relationships between width and hand-length of both chelae and Carapace Width (CW) for both sexes were highly significant. Time-series data showed a scanty abundance of P. cuvieri in the studied area with no trend over the period 1995–2019 with no significant trend over. Its preferential distribution on the middle slope was confirmed. Time-series data (1995-2019) showed a scanty abundance of P. cuvieri in the studied area with no signficant trend. Its preferential distribution on the middle slope was confirmed.

Comparing life-history traits in two contiguous stocks of the deep-water rose shrimp Parapenaeus longirostris (H. Lucas, 1846) (Crustacea: Decapoda) in the Southern Tyrrhenian Sea (Central Mediterranean Sea)

Most Mediterranean fish and crustaceans’ stocks are overexploited, but they could increase if fishing intensity would be reduced for only a few years. Today exploited stocks are constituted of young and small fish that are mostly caught before they can reproduce. This paper, which is based on long-term data (1994–2010) obtained from experimental bottom trawl surveys, contributes to the Parapenaeus longirostris exploitation control in South Tyrrhenian Sea (SW Mediterranean; GSA 10). Stock dynamics parameters of rose shrimp were investigated and compared in two different locations along the North coasts of Sicily (South of GSA 10) characterized by different fishing patterns. A huge inter-annual biomass and density fluctuations of the investigated rose shrimp were recorded, although no significant trends over time were observed, in both sectors. It is worth highlighting that the mean year fishing indices (mean KW of the trawl fleet, as capacity index, and number of days at sea per month, as activity index), contrary to what is reported in literature, were significantly higher in the western part of the area, where the stock is surprisingly mainly composed of young specimens. The fishing / total mortality ratio F/Z showed an overfishing status of rose shrimp in the two sectors, but at a lower degree than the rose shrimp of the whole GSA 10. The present paper support two stocks conjecture for the rose shrimp. The different biological structures in the two studied sectors are mainly influenced by interactions among the typical high plasticity of the life history species in the Mediterranean Sea and several typologies and activities (including the illegal aspects) of fishing fleets harbored in the E and W sectors.

Diel Variability in the Bottom-Trawl Catch Rates of Sparid Fishes in İzmir Bay (Central-Eastern Aegean Sea)

Time of day may affect the availability, distribution and behaviour of many fishes, at least in the depths that the light penetrates. Changes in the activity and position of the demersal fish as a response to the changing light levels during a diel (24 h) cycle may affect their catchability or vulnerability to the bottom trawl. Diel variability in the bottom-trawl catch rates of five sparid fish species, namely Boops boops, Diplodus annularis, Diplodus vulgaris, Pagellus acarne and Pagellus erythrinus, were investigated during seven experimental bottom-trawl surveys conducted within the same locality in İzmir Bay. All trawl haulings were performed using the same operation and sampling procedure and carried out for each seasonal survey at different periods day, including the morning, noon, afternoon, dusk, early-night, midnight, late-night and dawn. Percentage contribution by weight of the sparid fishes to the total catch varied according to the sampling season between 23-79%. Catch rates of the sparid fishes usually did not show significant diel periodicity except D. vulgaris. Daylight catch rates of D. vulgaris were significantly higher than twilight and night periods (Daylight>Twilight>Night). Information on diel variations obtained in this study could be fundamental in understanding the distribution dynamics of the five sparid fishes and developing future management approaches.

Evidence on Otolith Structure and some Ecological Features of Three Small Foraging Species along the Southern Black Sea Coast

In this study, we aimed to describe otoliths to provide information about the stomach contents of three small foraging species and to contribute to the currently limited biological and ecological evidence about the species. Seasonal experimental bottom trawl surveys were conducted along the shelf areas of the Kızılırmak-Yeşilırmak and Melet Rivers to collect investigation materials which were abundant in the bycatch composition of the target catch. The information about body size measurements, abundance values, depth, season, and locality of samplings was recorded for further evaluations. Otolith shapes were defined as discoidal to ovate for the Aphia minuta, discoidal for the Pomatoschistus marmoratus, and square for the Arnoglossus kessleri. The mean length and weight values of the Aphia minuta, which was abundant along shallow coastal waters (0-30 m), were significantly different between localities and sampling season, but no difference was found between depth ranges. Pomatoschistus marmoratus, whose distribution varied significantly between depths and seasons had dense distributions along with the depth range of 30-60 m. Arnoglossus kessleri was most abundant along with the depth range of 0-30 m and had no samples in depths of over 60 m. It was found that the mean values of length and weight of this species were only significantly different among seasons but similar over the depth ranges and localities.

Spatial and temporal patterns in the Mediterranean populations of <em>Aristaeomorpha foliacea</em> and <em>Aristeus antennatus</em> (Crustacea: Decapoda: Aristeidae) based on the MEDITS surveys

The aristeids Aristaeomorpha foliacea and Aristeus antennatus are two species of great economic importance in the Mediterranean Sea, where they are exploited almost exclusively by bottom trawlers. We analysed their geographical and inter-annual patterns using data collected, following a standardized protocol, during the MEDITS international experimental bottom trawl surveys. The data used consisted of standardized abundance and biomass indices, size structure and individual biological information collected in the northern Mediterranean for more than two decades. Several univariate and multivariate methodologies were used to analyse the data. The current study confirms previous findings, such as the longitudinal gradient in the relative presence of the aristeids, but also offers additional information for a better understanding of the intrinsic variability of the data over the years and between areas. Moreover, geographical variability in the somatic condition index is discussed, taking into account the role of environmental conditions and fishing pressure. The large geographical variability found for both species in this regional approach reflects the importance of additional studies at a small-scale geographical level. Such studies could be particularly important for managing and ensuring the stability of these species, for which large regional approaches may be inadequate.

A trophic model of the benthopelagic fauna distributed in the Santa Maria di Leuca cold-water coral province (Mediterranean Sea)

The benthopelagic fauna distributed in and around the Santa Maria di Leuca (SML) cold-water coral (CWC) province (Northern Ionian Sea–Central Mediterranean Sea) was analyzed through the development of a mass-balanced ecosystem model. A total of nine balanced simulations were provided taking into account the biomass data collected during several experimental bottom trawl surveys carried out from 2005 to 2010 in a depth range between 101 and 541 m. A total of 100 species were included in the analysis corresponding to 15 cephalopods, 25 crustaceans, 7 chondrichthyes and 54 osteichthyes. Simulations were developed maintaining the species-level detail. The total system throughput estimated in the SML CWC province trophic web resulted mainly due to consumption and about 80% of it was maintained by species with trophic level between 2 and 4. Results highlighted important features in terms of the structure and functioning of the system, such as the high level of activity maintained by intermediate trophic levels and the important role of top-down control in the faunal assemblage due to both vertebrate and invertebrate species.

Investigating gear and seasonal effects in experimental trawl surveys: The case of Galeus melastomus Rafinesque, 1810 (Chondrichthyes, Scyliorhinidae) in the South of Sicily (Central Mediterranean)

Mediterranean young-fish oriented experimental bottom trawl surveys represent a precious source of information on both past and current standing stocks and their life history traits and exploitation state. In the present note, taking the occasion of the same vessel employed in the South of Sicily (Central Mediterranean), an indirect approach has been implemented to compare MEDITS (Mediterranean International Bottom Trawl Survey) and GRUND (Gruppo Nazionale Demersali) abundance and biological features of the blackmouth catshark Galeus melastomus Rafinesque, 1810 to highlight gear and season effects if any. Data were gathered between 1994 and 2006, in spring-summer (MEDITS) and autumn (GRUND). The density and biomass indexes and occurrences were substantially lower in spring than in autumn. On the contrary, the biological traits were more similar, although significant differences were detected in the length frequency distribution. The homogeneity of life traits between seasons and the critical features showed in this study demonstrate that an annual experimental trawl survey can be enough to monitor G. melastomus. Similar analysis could be useful to highlight seasonal and gear effects on the other demersal stocks to better figure out limits and possibility of Mediterranean young-fish oriented experimental bottom trawl surveys data.

N90 index: A new approach to biodiversity based on similarity and sensitive to direct and indirect fishing impact

An important effort has been made to develop diversity indices suitable to monitor the loss of biodiversity due to anthropogenic impacts in an accurate and comprehensible way. Here, N90, a diversity index based on the species’ contribution to the similarity between samples in a group, is presented. N90 uses the results of the classic Similarity Percentage analysis and a jack-knife routine to calculate the average and a dispersion value of the number of species contributing up to the ninety percent of the similarity in a group of samples. N90 is applied to two groups of samples subjected to contrasting levels of bottom trawl fishing pressure using time series of experimental bottom trawl surveys of the Balearic Islands. The results are compared to those obtained using more ‘traditional’ diversity indices such as species richness, Shannon–Wienner, Simpson, Pielou, and Margalef diversity indices. The N90 diversity index displayed a clear response to fishing pressure with significantly lower values in impacted communities, while the ‘traditional’ diversity indices showed almost null sensitivity to fishing pressure. In addition, N90 also detects indirect fishing impacts by fluctuating in response to environmental variation in impacted areas, making this index sensitive to the synergies between climate and fishing impact at community level. The application of the N90 diversity index to the case study shows that it may be an alternative to ‘traditional’ diversity indices when trying to monitor fishing impacts and the effects of environmental changes. Its units, number of species, and the corresponding summary list of species facilitate the interpretability of the results, improving the communication to managers and stakeholders.

Distribution and biological features of the common pandora, Pagellus erythrinus (Linnaeus, 1758), in the southern Tyrrhenian Sea (Central Mediterranean)

A synthetic analysis of the distribution, abundance and some biological traits of the common pandora (Pagellus erythrinus) was performed. Data were gathered in 15 experimental bottom trawl surveys carried out off the southern Tyrrhenian Sea from 1994 to 2008. A total of 2,166 P. erythrinus were found in the investigated area, with a preference for the upper continental shelf (10–100 m). The highest persistence was recorded in the trawl-banned areas. The sex ratio Sr = F/(F + M) ranged between 0.60 and 0.96 (overall 0.78). The size at which 50 % of the individuals were mature was 157 and 170 mm total length for females and males, respectively. The length–weight relationship for all individuals was described by the following parameters: a = 0.016 and b = 2.905. Growth was evaluated (sexes combined) by applying length-based methods; up to eight significant modal components were evidenced. The von Bertalanffy growth parameters for the whole population were estimated at L ∞ = 454 mm, K = 0.08 and t 0 = −2.57. The present results are in agreement with the information available for the other Mediterranean stocks suggesting common biological features.

Species composition, distribution patterns and population structure of penaeid shrimps in Malindi-Ungwana Bay, Kenya, based on experimental bottom trawl surveys

The species composition, distribution patterns and abundance of penaeid shrimps in Malindi-Ungwana Bay, Kenya, were investigated after six years of no bottom trawling in the area. Two surveys undertaken during the dry Northeast Monsoon (NEM) and wet Southeast Monsoon (SEM) seasons in 2011 identified areas with abundant shrimps near the outflows of the Sabaki and Tana rivers. Distinct species composition and abundance patterns were found at the two areas, attributed mainly to depth, turbidity and season. Penaeus semisulcatus was more abundant at the Sabaki area, where it was deeper with a muddy bottom and less turbid waters. Fenneropenaeus indicus was more abundant in the Tana area, a shallower, more turbid area with sandy-mud sediments. Penaeus monodon, Penaeus japonicus and Metapenaeus monoceros were found in both areas, suggesting wider tolerance to environmental conditions. Shrimp total biomass and catch rates were significantly greater during the SEM survey, and decreased as depth increased beyond 10m. Small-sized M. monoceros and P. monodon individuals were abundant during the SEM survey, whereas large ones with ripe and spent gonads were more common during the NEM survey, suggesting that spawning took place between the two surveys. Seasonal patterns in gonad maturity were less clear for F. indicus and P. semisulcatus. The length at first maturity (L50) varied among species, suggesting that different species in the bay start spawning at different sizes, an important biological reference for sustainable resource exploitation. This study confirms the importance of the Sabaki and Tana areas as important habitats for penaeid shrimps in Malindi-Ungwana Bay.

Small-scale differences in the distribution and population dynamics of pandalid shrimps in the western Mediterranean in relation to environmental factors

Pandalidae is one of the most diverse families of marine shrimps. Most studies on pandalid shrimps focus on their vertical zonation, and there are few studies on their horizontal distribution and their relation to environmental factors. The aim of this paper was to study the small-scale spatial and temporal patterns of pandalid shrimps in two nearby areas off the Balearic Islands that have different environmental regimes, and determine the relationship between these patterns and the environmental conditions. Information was obtained from seasonal and annual experimental surveys. The abundance and biomass of all the pandalid shrimps caught as well as the length, weight, sex and maturity stage of the most abundant species were recorded. Environmental parameters were obtained from seasonal experimental surveys and included data on hydrography, trophic resources and sediment characteristics. Information about the trawl fleet was obtained through onboard sampling, and daily landings data were obtained from sales records. Eight pandalid species were found during the annual and seasonal experimental bottom trawl surveys carried out around the Balearic Islands. These species showed clear spatial differences in their population dynamics at the two study sites, the Algerian sub-basin (AsB) and the Balearic sub-basin (BsB), which could be related to the different environmental conditions of the two sub-basins. The relative importance of pandalid shrimps of the genus Plesionika in the slope crustacean communities was higher in the Algerian sub-basin. The abundances of Plesionika martia, Plesionika acanthonotus, Plesionika giglioli and Plesionika antigai were higher in the Algerian sub-basin, and only Plesionika heterocarpus, the most benthic species among those analysed, was more abundant in the Balearic sub-basin, where trophic webs are supported largely by suprabenthos rather than zooplankton biomass. The influence of water masses depends on the specific bathymetric distribution, and the shallowest species (P. antigai) was related to the Western Mediterranean Intermediate Waters, while the deepest species (P. martia and P. acanthonotus) were related to the warmer and more saline Levantine Intermediate Waters and Western Mediterranean Deep Waters. The two species found in intermediate waters (P. heterocarpus and P. giglioli) had a deeper distribution in the Algerian sub-basin, where the layer of Levantine Intermediate Waters is wider. The mean length of P. heterocarpus was higher in the Balearic sub-basin, and that of P. martia was higher in the Algerian sub-basin. The condition index was higher in the BsB than in the AsB for both P. heterocarpus and P. martia. This could be because the BsB is influenced to a greater extent by slope fronts that increase the primary production in the area, and thus enrich the trophic chain. The condition index also showed seasonal differences, which could be related to the reproductive cycle and to the availability of potential food resources. The strong relations found between the geographical distribution of the pandalid shrimps in the Balearic Islands and the environmental variables imply that there are important differences between populations of nearby areas when the environmental conditions in which they live differ.

Assessment of the deep water trawl fishery off the Balearic Islands (western Mediterranean): from single to multi-species approach

The bottom trawl fishery developed on the slope off Balearic Islands (western Mediterranean) has been analysed from different sources of information: (i) data obtained during experimental bottom trawl surveys developed annually since 2001; (ii) daily sale bills from the bottom trawl fleet, available since 2000. Considering both hydrographical and geomorphologic conditions, the study area was divided in four geographical sectors. Multivariate techniques were applied to identify assemblages and their main species, and to investigate the influence of environmental variables in the slope communities. Fishery-independent and fishery-dependent indicators were calculated, both at specific and community level, for the assemblages identified. In all cases, they were summarised using the Traffic Light approach. Three assemblages have been identified in the slope trawl fishing grounds off the Balearic Islands: (1) the almost unexploited shelf break, where teleosts predominate; (2) the upper slope, where teleosts still predominate but crustaceans are also very important (with Nephrops norvegicus as target species); (3) and the middle slope, where crustaceans predominate (with Aristeus antennatus as target species). Depth was the main factor affecting the species composition of the assemblages, although other factors such as area, year and effort level also affect. Indicators estimated from both sets of data suggested an improvement in the state of N. norvegicus, although the results suggest the influence of other factors than fishing impact in the state of this resource. For A. antennatus, marked differences have been found depending on the data source. In the upper slope, indicators suggested an improvement in the state of this assemblage, which can be related to a decreasing trend found in the fishing effort exerted in this depth range. Indicators from the middle slope showed differences for both sets of data. The characteristics of both data sources and of the species analysed are discussed as responsible of these differences.

Distribution and Biological Features of the African Armoured Searobin,<I> Peristedion Cataphractum</I> (Actinopterygii: Scorpaeniformes: Peristediidae), Off the Southern Coasts of Sicily (Mediterranean Sea)

Background. The African armoured searobin, Peristedion cataphractum, is a medium sized, gregarious, demersal fish distributed in the Eastern Atlantic and the Mediterranean Sea. Once considered abundant in all the Mediterranean basins, nowadays the species represents an appreciable by-catch of bottom trawlers only in limited areas. The aim of the present was to perform a synthetic analysis of the distribution, abundance, and biological traits of this poorly investigated species. Materials and methods. This paper is based on theinformation recovered from the available “grey” data sources as well as on new original data gathered in 13 experimental bottom trawl surveys carried out off the southern coasts of Sicily from 1994 to 2005.  Data recovering and processing regarded distribution, abundance, sex ratio, maturity condition, length structure, and its evolution in time, and growth estimation. Results. Thespecimens of P. cataphractum were present in all investigated areas, with highest abundance in the eastern grounds, between 50 and 800 m, showing a preference for the upper slope (201–500 m). Sexed specimens were almost equally distributed between females and males (overall sex ratio, Sr, between 0.49 and 0.54). Recruits (80–130 mm total length, TL) occurred continuously from September to March, with a peak from late December thru March. The size at onset of sexual maturity (Lm at 50%) was achieved at 191 and 212 mm for females and males, respectively. Growth was evaluated (sex combined) by applying length based methods (LBMs); up five significant modal components were evidenced, the first 2–3 well distinguished. Two sets of the special von Bertalanffy function were derived reflecting juveniles/adult (L∞ = 380 mm, Ky–1 = 0.34 and t0y = –0.76) and adults (L∞ = 313 mm, Ky–1 = 0.28 and t0y = –0.99) growth trajectories. Conclusion. The review performed in the frames of the presently reported study helped to propopse a plausible life history of the investigated stock was proposed.

Seasonal abundance of non-commercial demersal fish in the eastern Mediterranean Sea in relation to hydrographic and sediment characteristics

Fish-habitat associations were investigated for twenty-five non-commercial demersal species in the Aegean Sea (eastern Mediterranean) using Generalized Additive Modeling techniques. Fishery related abundance indices, derived from experimental bottom trawl surveys, were linked to various habitat variables: substrate characteristics, area, season, depth, temperature and salinity. Depth was the most important factor for all species. Eleven species showed decreasing abundance with depth, while the remaining species were more abundant in specific depth zones either on the continental shelf or in the upper continental slope. Most species were associated with specific substratum characteristics such as the dry weight percentage of sand-gravel and the carbonate content. The dry weight percentage of sand-gravel in the sediments was selected as a predictor of the relative abundance of most (twenty three) species. Seasonal patterns in the relative abundance of species were observed, related in most cases to the seasonal differentiation of temperature. The effect of temperature was more pronounced in summer and autumn, when a marked thermocline is observed, while it was much less intense in winter. For most of the species, the preferable habitat was identified, that contributes valuable information for the successful implementation of an ecosystem approach to fisheries management.

Bathymetric and longitudinal distribution analyysis of the rockfish Helicolenus Dactylopterus (Delaroche, 1809) in the southern Tyrrhenian Sea (central Mediterranean)

This study provides information on bathymetric and longitudinal distribution heterogeneity of the rockfish Helicolenus dactylopterus in the southern Tyrrhenian Sea. Data were drawn from experimental bottom trawl (1996-2002) plus bottom trap (2001-02) surveys. The frequency of occurrence and mean relative density (N/km2) and biomass (kg/km2) indexes were calculated for two survey seasons (spring and autumn), four geographic sectors and three depth strata. MANOVA was used to test fish abundance among years, sectors and strata. Analysis of the length-frequency distributions was carried out by two-way (gears and depths) ANOVA, post hoc multiple comparisons for testing differences among depths and Student’s t test for testing differences between gears. Length-weight relationship was also estimated and the allometric coefficient was tested with the Student’s t test. The results showed a significant positive bathymetric gradient of sizes both for trawl and trap surveys; at same depths, fish caught by traps were significantly longer than those caught by trawl. In spring surveys, significant differences were found among strata for both abundance indexes; in autumn surveys, significant differences between depth strata were found only for density indices. The distribution and abundance patterns of H. dactylopterus along the southern Tyrrhenian Sea was homogeneous among sectors. Length-weight relationship showed a significant positive allometric growth.

Distribution and biology of the Blackmouth catshark Galeus melastomus in the Strait of Sicily (Central Mediterranean Sea)

The Blackmouth catshark, Galeus melastomus, Rafinesque, 1810 (Carcharhiniformes; Scyliorhinidae), is a common, although at present discarded, by- catch of the bottom trawl fisheries in the Strait of Sicily. Given its ecological interest, data gathered in experimental bottom trawl surveys were analysed in order to describe its distribution and main biological traits. The Blackmouth catshark was sampled almost exclusively on the upper slope (200-800), showing the highest frequency of occurrence (69-100%), biomass (BI; 10-85 kg*km-2) and density (DI; 54-506 N*km-2) indexes in the deeper (501-800m) grounds. Individual size (total length, TL, mm) were between 70-590 and 90-510 in females and males, respectively. The sex ratio (SR) was around 0.5. The SR by size showed a gradual decrease till 450 mm class size, followed by an increase up 1 after 500 mm. Virginal/immature specimens represented the bulk of the samples in both females (77%) and males (65%); the length at 50% of sexual maturity (Lm50%) and corresponding maturity range (Lm25% - Lm75% ) was 433 (423-443) and 380 (366-394) mm, respectively.

Relationships between macro‐epibenthic communities and fish on the shelf grounds of the western Mediterranean

Abstract The present study characterizes the macro‐epibenthic assemblages, and the relationships between demersal species and benthic habitats on the shelf trawl fishing grounds off the Balearic Islands (western Mediterranean). The data used were collected during experimental bottom trawl surveys from 2002 to 2005. A total of 157 samples from 38–255 m depth were analysed. Three macro‐epibenthic assemblages were identified in both the shallow (at 38–91 m) and deep shelf (90–255 m). Macroalgae bathymetric distribution was identified as the main factor explaining the segregation between shallow and deep shelf assemblages. Two especially sensitive habitats were identified: maërl and crinoid beds; a third habitat was identified as Peyssonnelia beds, which represented the highest biomass on the whole shelf, with a similar species richness to the maërl beds. On the deep shelf, crinoid beds represented the highest biomass. Habitat type had a significant effect on the distribution of demersal commercial species, most of them being more abundant in the two sensitive habitats mentioned and in the Peyssonnelia beds. Some species showed size‐specific habitat preferences. Fisheries management in the area should take into account the resilience of these benthic habitats, and their importance from both ecological and sustainable fisheries management perspectives. Copyright © 2008 John Wiley & Sons, Ltd.

A bio-economic indicators suite for the appraisal of the demersal trawl fishery in the Southern Adriatic Sea (Central Mediterranean)

The state of demersal fishery in the Southern Adriatic Sea (GFCM-GSA 18, Central Mediterranean), years 1996–2003, from a biological, social and economic point of view was analysed using 47 indicators: 22 biological indicators obtained from fishery-independent data through yearly experimental bottom trawl surveys (“Medits” Programme), and 25 socio-economic indicators estimated from fishery-dependent data, available from the monitoring system of the Italian Institute for Economic Research on Fisheries and Aquaculture (IREPA). Biological indicators were applied for “single-species” ( Eledone cirrhosa, E. moschata, Illex coindetti, Merluccius merluccius, Mullus barbatus, Nephrops norvegicus, Parapenaeus longirostris, Raja clavata, Zeus faber) and for “multi-species” analysis. Economic indicators describing economic performance, productivity, costs and prices, and the overall economic sustainability of fishery were estimated. Social indicators and a general indicator summarising social sustainability were also considered. Indicators’ values were displayed using the Traffic Light system. Both fishery-independent and fishery-dependent indicators highlighted a progressive decline of the trawl fishery system in the GSA 18. This decline was mainly related to the ongoing depletion of the traditional fishery target species (mostly long-living, late-maturing species) partially replaced by the increase of traditional accessory species (generally short-living species), as well as to the reduction of productivity and increasing costs. The whole procedure was proposed as a contribution to the identification and applicability of bio-economic indicators for fishery management purposes.

Some information on the biology of Illex coindetii Verany, 1839 (Cephalopoda, Ommastrephidae) in the South-Western Adriatic Sea (Central Mediterranean)

Distribution, length frequency structure, sex-ratio, maturity and dorsal mantle length–total weight relationship for Illex coindetii (Verany, 1839) were described for the first time in the South-Western Adriatic Sea (Central Mediterranean). Samples came from six experimental bottom trawl surveys carried out within the framework of the Medits programme from 1997 to 2002. Although specimens have been collected at a wide depth range, I. coindetii concentrates between 50 and 200 m. The population had a smaller squid size and length at first maturity with respect to other Mediterranean and Atlantic regions, probably due to the interaction of some environmental factors (sea temperature and fishing pressure) and the biological characteristics of the species. There was no difference in males/females ratio by year, but there was a general dominance of females over males at larger sizes and of males over females at smaller sizes. The different proportion of juveniles and mature individuals in the catch suggested the possibility of a prolonged spawning season with a spring spawning peak. There was a pronounced sexual dimorphism, females mature at larger mantle length attaining larger size in respect of males. Length–weight relationship revealed a difference between sexes in maturing and mature individuals only, with males resulting heavier and more robust than females at the same size. There were no differences in body proportions between unsexed and immature individuals of both sexes, which were considerably slimmer than maturing and mature counterparts.