Pelagic Trawl Research Articles

Redistribution of fisheries catch potential in Mediterranean and North European waters under climate change scenarios

The Mediterranean Sea is a hotspot of global warming where key commercial species, such as demersal and pelagic fishes, and cephalopods, could experience abrupt distribution shifts in the near future. However, the extent to which these range shifts may impact fisheries catch potential remains poorly understood at the scale of Exclusive Economic Zones (EEZs). Here, we evaluated the projected changes in Mediterranean fisheries catches potential, by target fishing gears, under different climate scenarios throughout the 21st century. We show that the future Mediterranean maximum catch potential may decrease considerably by the end of the century under high emission scenarios in South Eastern Mediterranean countries. These projected decreases range between −20 to −75 % for catch by pelagic trawl and seine, −50 to −75 % for fixed nets and traps and exceed −75 % for benthic trawl. In contrast, fixed nets and traps, and benthic trawl fisheries may experience an increase in their catch potential in the North and Celtic seas, while future catches by pelagic trawl and seine may decrease in the same areas. We show that a high emission scenario may considerably amplify the future redistribution of fisheries catch potential across European Seas, thus highlighting the need to limit global warming. Our projections at the manageable scale of EEZ and the quantification of climate-induced impacts on a large part of the Mediterranean and European fisheries is therefore a first, and considerable step toward the development of climate mitigation and adaptations strategies for the fisheries sector.

Lanternfishes of the genus Diaphus collected during cruises ESSCHA, NECTAlis, PUFFAlis and WALLAlis of RV Alis in the tropical southwestern Pacific

The present study contributes to update the checklist of Lanternfishes species of the genus Diaphus known to occur in the tropical southwestern Pacific. The findings are based on material collected from six recent oceanographic cruises of RV Alis in the Coral Sea, the Fiji Basin and the Wallis and Futuna Exclusive Economic Zone (EZZ). Diaphus spp. samples were obtained using pelagic trawl nets. We identified 20 species of the genus Diaphus. Specimens morphologically closest to D. termophilus and belonging to a possibly undescribed species were also sampled from the Wallis and Futuna waters, highlighting persisting gaps in our knowledge regarding this ecologically important group of fishes. Our collection of specimens, all preserved for DNA extraction, will be useful to complement the current Diaphus barcode database for the tropical southwestern Pacific. Dataset published through GBIF (Doi: 10.15470/ek0u3y)

Polar cod (Boreogadus saida) of the Siberian Arctic: Distribution and biology

Integrated pelagic trawl surveys were conducted in the eastern sector of the Russian Arctic (Laptev Sea, Chukchi Sea and East Siberian Sea) in August–September of 2003–2018. Data were used to further describe biology and spatial distribution of Polar cod (Boreogadus saida) in this region. Polar cod in surveyed areas are characterized by similar linear size and spatial distribution. In all surveyed seas, polar cod aggregations consisted of individuals 3–29 cm in length with the age of 0+ - 6+ years. Lower growth rates of polar cod were evident in the eastern sector compared to the Kara Sea (the western sector of Russian Arctic). The lower growth rates in the eastern sector are probably due to the significant difference in environmental conditions (mainly temperature) that directly affect polar cod metabolic rates.In the Chukchi and East Siberian seas, the main concentrations were observed within the near-bottom layer, while in the Laptev Sea they were recorded throughout the water column. The abundance and biomass of polar cod in the Chukchi Sea in different years ranged from 514 million inds. and 0.83 thousand tons (2008) to 8.26 billion inds. and 117.5 thousand tones (2003). Respective indices for the Laptev Sea amounted to 233 thousand tones and 12.75 billion individuals. The abundance and biomass of the East Siberian Sea polar cod were at a relatively low levels compared to other areas in the Russian Arctic (about 0.150 thousand tons and 20 million individuals).

First record of the Atlantic soft pout Melanostigma atlanticum (Teleostei, Zoarcidae) in the eastern Mediterranean Sea

Abstract This paper reports the first record of the Atlantic soft pout Melanostigma atlanticum Koefoed, 1952, from the eastern Mediterranean Sea. The specimen was caught in a pelagic trawl during a research trip carried out north of the island of Crete (Greece) in December 2019. The fish measured 66.1 mm in total length and weighed 0.810 g. The presence of M. atlanticum in the eastern Mediterranean Sea indicates that the geographical distribution of the species is not restricted only to the western part of it but spreads throughout the basin. Melanostigma atlanticum is typically found in the deep sea, where limited surveys and research have resulted in major data gaps. The lack of recording of the species until recently in the eastern Mediterranean Sea is attributed to the species' small size and slender body shape that allow it to escape traditional fishing gears, as well as the low trawling activity in depths greater than 400 m and the lack of surveys targeting the mesopelagic fish communities.

Modifying a pelagic trawl to better retain small Arctic fishes

Pelagic trawls are one of the primary methods of sampling midwater fishes. However, these trawls are species- and size-selective, and small fish can escape through trawl meshes. This can introduce uncertainty and bias into survey abundance estimates if not accounted for. The small, abundant pelagic fishes of the Alaska Arctic are challenging to sample with trawls as they are sufficiently motile to avoid small fine-mesh trawls but are also small enough to escape through the meshes of trawls designed to capture larger fishes. A pelagic herring trawl equipped with a fine-mesh codend liner was used to quantify the size and species composition of pelagic fishes during a baseline acoustic-trawl survey of the Chukchi Shelf. Subsequent experiments with recapture nets attached to the outside of the trawl netting suggested that escapement of small fishes was substantial, particularly in the aft net section. Thus, the trawl was further modified by reducing the taper in the aft net section and adding a small-mesh section in front of the codend to potentially reduce escapement. Further use of recapture nets during two subsequent acoustic-trawl surveys confirmed that this trawl modification substantially increased retention of small fishes and resulted in less size selectivity. These improvements will reduce biases in estimates of abundance, size, and species composition of pelagic Arctic fishes. This work highlights the importance of quantifying escapement from survey trawls and demonstrates that escapement estimates can guide successful trawl modifications.

DISTRIBUTION PATTERNS OF METACERCARIAE OF THE TREMATODA <i>APOPHALLUS </i><i>MUEHLINGI</i> (JÄGERSKIÖLD, 1899) IN UNDERYEARLINGS IN AN INVASIVE POPULATION OF <i>CLUPEONELLA CULTRIVENTRIS</i> (NORDMANN, 1840) FROM THE GORKY RESERVOIR (UPPER VOLGA BASIN)

After the successful naturalization of the prosobranch mollusk Lithoglyphus naticoides (C. Pfeiffer, 1828) and a number of associated trematodes in the Gorky Reservoir (in 2005-2015) an intensive spread of apophallesis in fish of this water body has been observed. As one of the second intermediate hosts of the trematode causing this disease, Apophallus muehlingi (Jägerskiöld, 1899), a freshwater form of the Black Sea-Caspian kilka Clupeonella cultriventris (Nordmann, 1840) was recorded. The aim of the work is to study the consequences of dispersal of C. cultriventris for the formation of large permanent foci of apophallesis in the Upper Volga. For comparison, data on the spread of this type of "black-spot" disease in the populations of C. cultriventris from the Gorky Reservoir and an unregulated area of the Lower Volga (downstream the cascade of Volga reservoirs, pelagic trawl coordinates from 47°08ʹN, 47°17ʹE to 46°51ʹN, 47°41ʹE) were used. The high rates of occurrence of A. muehlingi metacercariae (the infection prevalence P, %) are recorded in the fall along the entire area of the Gorky Reservoir: from the northernmost site near Rybinsk (58°01ʹN, 39°06ʹE) to the dam area (56°41ʹN, 43°21ʹE). It is found that the distribution pattern of A. muehling metacercariae varies in the sections of the reservoir differing in hydrological characteristics. In the middle (transitional type) section of the reservoir the prevalence of A. muehlingi metacercariae in groups of the smallest Black Sea-Caspian kilka fingerlings (with a body length of up to 45 mm), is close to the maximally possible (30.00-94.49%). In the upper (river-type) section of the reservoir, the prevalence of metacercariae in this group of fish does not exceed 24.39%. The minimum values of this indicator are found in the lower (lake-type) section of the reservoir (6.76-14.84%). Judging by the values of the abundance index and the coefficient of variation in the infection intensity, the aggregation of metacercariae is more pronounced in the groups of faster growing underyearlings and the Black Sea-Caspian kilka yearlings as compared to the groups of the smallest fingerlings. In the Black Sea-Caspian kilka fingerlings samples from the Lower Volga in 2020 reveals no statistically significant differences between the infection prevalence values (13.33-18.11%) in the different size groups. Thus, although the main second intermediate hosts of A. muehlingi are various fish species of the Cyprinidae family, in some cases the presence of C. cultriventris in the water body ecosystem can significantly increase the likelihood of apophallesis spread. In conditions of the Upper Volga, due to the high migration activity of large individuals of the Black Sea-Caspian kilka, a continuous zone of apophallesis can form without clearly defined boundaries between the individual foci of disease.

JC2-1 Joint cruise part 1 2021

The Nansen Legacy Joint Cruise 2, part 1 (JC2-1) 12-29 July 2021, continued the investigation of the interannual variability during the late summer season. At the same time will the cruise provide a late summer reference for the seasonal investigation that was separated to late summer and polar night 2019, and winter and spring 2021. The transect represents an environmental gradient going through the northern Barents Sea, and included 7 process stations (P1-P7) lasting 10-39 hrs. Additional CTD stations (NLEG) were taken between the process stations to increase the hydrographic resolution on the transect. The work started at 76°N at the open Atlantic Water dominated station P1, was sea ice covered from station P4 at 79 45.00 °N and included deep water stations at the P7 station at 82°N in the Nansen Basin.
 
 The program included measurements and sampling from the atmosphere, sea ice, ocean and sea floor. Data collected includes several disciplines to map the physical environment, the chemical characterization and biological communities. Key parameters from the Nansen Legacy joint cruises were selected and included in this reduced sampling program, compared to the other joint cruises. An important aim was to characterize the northern Barents Sea to map the interannual variability, but also to see how the proceeding winter and spring conditions has impacted the environment and conditions this year. A third task is to carry out a shelf investigation that can complement the investigations in the deep Arctic Basin starting in late August. Tests and improvements of a modified pelagic trawl (Harstad) were carried out as preparations for the Arctic Basin cruise in late August 2021.

A catch limitation device to avoid excessive catches in the blue whiting (Micromesistius poutassou) Northeast Atlantic pelagic trawl fishery

Blue whiting (Micromesistius poutassou) is harvested in the Northeast Atlantic by a multinational fleet of pelagic trawlers. Occasionally, vessels take catches which exceed their remaining holding capacity and in extreme cases large catches cause codends to burst, resulting in spill of catch. To control catch quantity, a catch limitation system was developed and tested. The system consists of three components: 1) escape opening(s) in front of the codend to release excess fish, 2) a fish lock to prevent loss of fish through the escape opening(s) during haulback and at the surface, and 3) a choking unit to match codend capacity to the desired size of catch. Blue whiting escaped through both longitudinal slots and large (≥ 2 m) meshes in front of the codend. However, video observations showed that with large meshes in the upper panel, large amounts of blue whiting escaped long before the codend was full. Therefore, a design with large openings in the bottom was combined with longitudinal slots in the side and top panels. Two fish locks were tested: an oblique netting panel designed to seal off the codend when vessel speed reduce during haulback, and a cylinder of netting with a choking rope that closed it after the codend was filled. Both fish lock designs inhibited release of fish during haulback and at the surface, but the attachment of the constricting rope in the cylinder frequently broke. The choking unit consisted of a depth triggered releaser connected to a strap of rope wrapped around the codend. Mechanical releasers with factory-set depth trigger and electronic versions were tested. Both freed the choke point as intended, but occasionally at unpredictable depth. A reliable relationship (r2 = 0.94) was attained between codend choking position and catch amount, demonstrating that codend capacity could be adjusted to achieve target catch quantities. Our work shows that controlling catch quantity in the blue whiting pelagic trawl fishery can be achieved effectively through relatively simple modifications to the codend section Future work is needed to optimize the fish lock design and ensure the codend choking rope releasers trigger reliably and at the proper depth.

Evaluating the stock status of 10 croaker species landed along the north-eastern Arabian Sea using the length-based Bayesian biomass approach

India accounts for nearly 60% of the croakers caught in the Indian Ocean. The north-west (NW) coast of India is the most productive fishing ground for croakers and contributes almost half of the nation’s croaker catch. Lesser sciaenids (small- and medium-sized croakers) are the multi-species complex landed by commercial trawlers along the NW coast of India. Despite several notable changes in the fishing pattern in the region, such as the emergence of multi-day fishing and increasing dominance of pelagic trawling, there is no recent assessment of this major demersal fishery group. The present study evaluates the stock status of 10 species of lesser sciaenids forming the commercial fishery in the region using length frequency data collected during 2020–2021. The assessment was made using the length-based Bayesian biomass (LBB) estimation method. The indicators of relative biomass (B/B0 and B/BMSY) showed that most of the species (seven) are fully exploited, whereas two and one species were found under- and over-exploited, respectively. Excessive juveniles (Lmean/Lopt and Lc/Lc_opt< 0.90) in catches were observed in the case of Paranibea semiluctuosa. A sufficient number of larger individuals (L95th/Linf< 0.90) in the population were lacking in the case of Johnius belangerii and Otoithes ruber. However, the study indicated a gradual improvement in stock status for most of the species over previous estimates, which can be attributed to the diversion of trawl fishing efforts towards the pelagic realm.

Pelagic and demersal fish diversity of the Saya de Malha and Nazareth Banks, Mascarene Plateau

The Saya de Malha (SMB) and Nazareth Banks (NB) are the main offshore locations where fishing activities are carried out by the Republic of Mauritius, targeting mainly shallow water Lethrinids, deep-water snappers and groupers. A multi-disciplinary survey was carried out on the two banks in May 2018 on-board the R/V Dr. Fridtjof Nansen with the objective of studying the diversity of fish on both banks using pelagic trawls, bottom trawls, basket traps and video using a Remotely Operated Vehicle (ROV). Analysis of data showed that the main fish family recorded in the pelagic waters of SMB, using pelagic trawl, was Myctophidae while the bottom trawls on NB showed the presence of fishes from the families Gobiidae, Triglidae and Synodontidae, mainly at depths between 200 and 300 m. The ROV video analysis highlighted principally the presence of demersal fishes of the family Lethrinidae and other reef-associated and commercial families recorded between 20 and 50 m. The main catch from the basket traps set at the SMB was Lethrinus mahsena, caught at a depth of 21 m. While previous studies focussed mainly on commercial fishes, this study brings forth new information on other fish families, contributing to the knowledge of the fish community that exists at these two banks.

Recruitment variability of fish stocks in the Barents Sea: Spatial and temporal variation in 0-group fish length of six commercial species during recent decades of warming (1980–2017)

Young-of-the-year (0-group) fish in the Barents Sea have been investigated in an annual joint Norwegian-Russian pelagic trawl survey in autumn, using a standardized procedure since 1980. We use a conceptual framework of ‘upstream’ spawning areas and ‘downstream’ nursery areas, recorded as 0-group distribution in the Barents Sea, to address spatial (geographical) and temporal (1980–2017) variation in 0-group length. Four boreal species (cod Gadus morhua, haddock Melanogrammus aeglefinus, herring Clupea harengus, and deepwater redfish Sebastes mentella) tended to have smaller 0-group individuals in the northern and eastern parts of the Barents Sea, with the largest individuals found in the central part where they were also most abundant. We interpret this to reflect slower growth as the ‘fore-runners’ of the seasonal cohort of juveniles are transported into colder waters (through lateral mixing). The Arctic species (capelin Mallotus villosus and polar cod Boreogadus saida) showed a different pattern with increasing 0-group length with increasing distance away from the spawning areas, seen most clearly for capelin. The longer juveniles in northern areas are probably older and stemming from early spawning.There was temporal covariation in 0-group length between the six species over the 38-year time series, with highest correlation between cod and haddock. The covariation reflected similar fluctuations in four decadal ‘waves’, with maxima in 0-group length in the early/mid 1980s, 1990s, 2000s, and 2010s. There was a high degree of spatial consistency in the temporal patterns of variation in 0-group length, with synchronous variations in different geographical areas. There were also increasing linear trends over the time series for cod, haddock, and polar cod, which represented increase of about 20%, 40%, and 15% of the initial length for the three species, respectively. The fluctuations and trends in 0-group length were positively correlated with seawater temperature, which suggests a strong effect of climate variability and warming (by 1.5–2.0 °C since 1980) on 0-group length. The clear differences among the species, and the limited fraction of variance explained by temperature, suggest that other factors such as food play additional roles. Zooplankton biomass integrated over the water column had low explanatory power, but this may reflect intrinsic limitations in the data (e.g., depth-integrated, end of season) in providing an adequate representation of feeding conditions, rather than suggesting that food was not important.

Reducing the Fuel Use Intensity of Fisheries: Through Efficient Fishing Techniques and Recovered Fish Stocks

Understanding the drivers of greenhouse gas emissions in food production systems is becoming urgent. For wild capture fisheries, fuel use during the fishing phase generally dominates emissions and is highly variable between fisheries. Fuel use is also essential for the economy of the fisheries, but fuel-intensive fisheries can still be profitable due to fuel subsidies, in particular, if the target species is of high value. Developing an innovative bottom-up approach based on detailed catch and spatial fishing effort data, in the absence of direct fuel data, we analysed the fuel use intensity (fuel use per kg landed) and economic efficiency (landing value per litre fuel used) of Danish capture fisheries for the period 2005-2019. An overall decline in fishing effort did not significantly affect the overall fuel use intensity and efficiency, which was stable for most of the fleet segments and marine species. Robust differences in fuel use intensity among individual fisheries, reflected differential spatial accessibility and vulnerability of target species to fishing. In addition, different fishing techniques targeting the same set of species showed differences in fuel use per unit landed. Danish seining and gillnets had a lower fuel use intensity and higher economic efficiency than demersal trawling; and purse seining than pelagic trawling. The variability between stocks and fleets also indicates that there is generally potential for improvement in overall efficiency from improved stock status. Short-term management actions to promote the best available fuel-efficient fishing techniques combined with additional long-term actions to secure the recovery of stocks have the potential to reduce fishery greenhouse gas emissions. Sustainable fisheries and normative environmental management are crucial to developing incentives towards reducing fuel use whenever the fishing sector industry and science work jointly at implementing solutions, as incentives for the industry to reduce fuel use are limited as long as the fishing activity is profitable.

Length–weight relationships for six elasmobranch species from the Adriatic Sea

Length–weight relationships were observed for six elasmobranch species from the Adriatic Sea. Between 2006 and 2019, data on weight and total length were collected for three shark species Alopias vulpinus, Mustelus mustelus, Mustelus punctulatus; and data on weight and disk width were collected for three batoid species Aetomylaeus bovinus, Myliobatis aquila, Pteroplatytrygon violacea. Data collection comes from monthly observations as part of a monitoring program targeting specifically bycatch on pelagic pair trawlers involved in anchovy and sardine fishing. This fishery operates using pelagic trawls with a minimum mesh size opening of 20 mm. All elasmobranchs were measured to the nearest cm using a measuring board and weighed to the nearest gram using an electronic scale or a dynamometer for the largest specimens. A linear regression analysis performed on log-transformed data was used to estimate intercept and slope, and to describe the length–weight relationship for each species.

Distribution, diet and relationships of the invasive ctenophore Mnemiopsis leidyi with anchovies and zooplankton, in the northeastern Adriatic Sea

Blooms of invasive ctenophore Mnemiopsis leidyi can have massive consequences on fish stocks and marine food webs. The distribution, abundance and diet of this ctenophore were investigated in the northeastern (NE) Adriatic between 2016 and 2019. The abundance of M. leidyi was determined daily along the coast of Rovinj (Croatia), and its spatial distribution monitored by visual census from research vessels and by pelagic trawl during acoustic surveys in September of each year. Mesozooplankton samples were collected along the western coast of Istria by vertical tows from the bottom to the surface. Spatial distribution and abundance of anchovy (Engraulis encrasicolus) assemblages were determined by geo-referenced hydro-acoustic sampling using a scientific echosounder. Large swarms of M. leidyi covering several km2 were regularly reported between July and November extending up to 25 NM from the western coast of the Istrian peninsula and reaching maximum offshore densities of 270 individuals per m2. The abundance of anchovy in the areas where M. leidyi was present evidently decreased. The content of M. leidyi’s digestive tract and plankton samples consisted both mainly of cladocerans, copepods, pteropods, echinodermata and bivalvia larvae. Results indicate that M. leidyi may accumulate and increase its abundance in the stagnant and trophically rich areas of the northern Adriatic gyres, spreading to the surrounding larger areas with currents. We assume that M. leidyi presence correlates with a decrease in anchovy population due to competition for food (zooplankton). Our findings support the importance of implementing an international monitoring program throughout the Adriatic Sea and demonstrate the ability of current MEDIAS surveys to detect changes in the pelagic ecosystem throughout surveyed areas.

Temperature strongly correlates with regional patterns of body size variation in Mediterranean small pelagic fish species

In this study, we consider the applicability of Bergmann’s rule to the populations of small pelagic fish species in the Mediterranean Sea. Under Bergmann’s rule, body size increases with decreasing temperature and increasing latitude. Although this macroecological pattern in body sizes is well established for many taxa of endotherms and ectotherms, it remains not universal and the proposed mechanisms underlying it are multiple and still lack consensus. We explored here the occurrence of geographical body size clines using measurements of average body sizes of 10 species collected in pelagic trawl hauls carried out during acoustic surveys in the Mediterranean Sea. Bergmann’s rule was evaluated by correlating body sizes with latitude and temperature for each species while accounting for potential confounding variables and sampling bias. For 5 species, namely anchovy, sardine, Atlantic chub mackerel, bogue, and blue jack mackerel, we demonstrate that they follow a Bergmann’s rule, with a decline in average body size by about 3.01, 3.43, 3.67, 3.82, and 3.76 % per 1°C of warming respectively, although this did not translate with an increase in size with latitude. The adherence of these 5 pelagic fish to Bergmann’s rules strongly suggests that temperature is a major determinant of their body sizes and enables them to act as sentinel species for identifying the drivers and consequences of warming in the Mediterranean ecosystems.

An Acoustic Study on the Overwintering Black Sea Anchovy in 2020

The Black Sea anchovy (Engraulis encrasicolus ponticus) is not only the top commercial species with around 250 thousand tonnes of annual catch but a key species of the Black Sea ecosystem facilitating the flow of energy within the food chain. The General Fisheries Commission for the Mediterranean has assessed the status of its stock for the Mediterranean since 2013. Underlining the shortcomings in the assessments, the commission has recommended diversifying and strengthening the data used and promote methods that provide biomass and abundance indices, such as hydroacoustics. This study aims to help fulfill the underlined deficiency by pursuing the implementation of the hydro-acoustic research surveys in the Turkish Black Sea EEZ. The survey was carried in November/December 2020, when the anchovies were accumulated within the Turkish EEZ, and cruise tracks were designed to cover the distribution areas of juvenile (0-year-old) and adult (Age 1 and over) anchovies displaying different distribution patterns within the Turkish EEZ in winter. The results show that the stock size is noticeably smaller than in previous years. Pelagic trawl sampling conducted alongside the acoustic data collection to estimate the size composition of anchovies indicated that the juvenile fish constitute an alarmingly large part of the overwintering stock.

The use of the contribution margin on the valorisation of polish fisheries for maritime spatial planning

One of the primary goals of spatial planning is to provide decision makers with documents that will allow them to optimize the use of marine space. The function of such an optimization strategy is to maximize the usability of the sea surface. This article focuses on the pragmatic aspects of marine spatial planning. The authors presuppose a tool for planners that (i) is based on readily available information, is comparable for various countries (ii) and for which the economic interpretation is straightforward and allows for the comparison of fisheries with other sectors. The analysis is based on two pan-European surveys collected under the Common Fisheries Policy. The distribution and catch information is sourced from the Vessel Monitoring System and logbooks, and the economic data come from the national data submissions for the Scientific, Technical and Economic Committee for Fisheries. A contribution margin consisting of the difference between the revenue and variable costs at a spatial unit with a 0.05-degree resolution was chosen as the most appropriate indicator for these purposes. A variable costing method can be used to determine the efficiency of maritime sectors in specific spatial units without artificially assigning costs that are unrelated to a given sea area. The analysis covers the period of 2013–2017. Three key areas for Polish fisheries have been identified: the Gulf of Gdansk, the Bornholm Basin, and the Słupsk Furrow; the average contribution margins in these regions were 1133, 651 and 580 EUR/km2, respectively. The variance analysis revealed that the high indicator values were mostly influenced by high catches of sprat and herring fished with pelagic trawls as well as high sprat prices. Fishing with passive gear (gillnets, hooks) and in the 3rd and 4th quarters proved to result in deficits in a large Polish maritime area. The indicators may have been influenced by the lack of data on the individual steaming times, as well as by variations among fuel consumptions and salary costs within fleet segments. Despite these limitations, the method used in this study allows a first attempt at the estimation of the contribution margin and its spatial variation over time in the context of Maritime Spatial Planning needs. The calculation undertaken in this paper yields the monetary interpretation of private spatial rents and future comparisons among various maritime sectors and various countries.

Productive efficiency of the pelagic trawl fisheries in the Southern Black Sea

This study aimed to reveal the need for efficient catching activity by comparing the efficiency of pelagic trawl fisheries in Turkey with Stochastic frontier analysis (SFA). For this purpose, data were obtained through face-to-face interviews with 19 vessels randomly selected among 82 fishing vessels during the period. Variables used for technical inefficiency (ui) were determined as professional trawling experience, the total crew, pelagic trawling subsidy rates, and the use of pelagic trawling credits. It was used the FRONTIER 4.1. for Stochastic efficiency frontier calculations developed by Coelli (2007). As a result of the study, it was revealed that an improvement of 26% was required for trawlers to become efficient. Technical efficiency in the sampled vessels ranged from 0.413 to 0.998, with an average of 0.739. According to the results, it was concluded that the efficiency of pelagic trawl fisheries could be increased due to the improvements in the existing structural conditions and the revisions to be made in the policies implemented and the subsidies provided. However, the factors affecting inefficiency seem to be influenced by internal factors such as experience in pelagic trawling, the total crew, and the most critical issue to eliminate inefficiency seems to be increasing the subsidy rate in pelagic trawlers.In this study, it was found that the effects of engine power, total length, fuel consumption and active fishing day reduce the effect of fish catching pressure to a low level. However, other factors affecting this pressure were also included in the model. Especially when it was considered that the use of credit did not affect the efficiency, it was revealed that the increase in the subsidy rates rather than the fuel subsidy would make the trawlers more efficient.

Acoustic evidences of the beginning of anchovy (Engraulis encrasicolus) schooling in the Northern Alboran Sea (Mediterranean Sea)

During the MEDiterranean International Acoustic Survey (MEDIAS) carried out in 2016 and 2017 in the Northern Alboran Sea in July, a benthic scattering layer located mainly in Malaga Bay was acoustically detected at multiple frequencies and biologically identified using different sampling devices (plankton net and pelagic trawl). This layer mainly corresponded to an anchovy larvae aggregation ranged 2 and 40 mm standard length. Our results pointed out that anchovy larvae massively migrate from the surface to the bottom near the coast, until the 70 m isobath, forming large aggregations acoustically detected as a scattering benthic layer, in which small schools form and emerge.This work has highlighted the potential of acoustic surveys such as MEDIAS to generate anchovy recruitment success indicators complementary and simultaneously to the traditional ones (biomass of the reproductive stock) and their great utility as a fisheries management tool in areas such as the Alboran Sea where the fishing resource is scarce.

A new look on the morphometric characteristics of Congridae leptocephali from the southern Adriatic Sea

AbstractAnguillid leptocephali of three Congridae species (Conger conger, Ariosoma balearicum and Gnathophis mistax) were caught as bycatch of pelagic trawls during acoustic surveys targeting small pelagic fish species in the southern Adriatic Sea, carried out under the framework of the Italian MEDIAS project (western side) and its extension in the ambit of the FAO AdriaMed project (eastern side). Results refer to the findings of Congridae leptocephali during surveys conducted in 2011, 2014, 2015 and 2016. A total of 25 specimens were caught and analysed (morphological features and pigmentation patterns). Leptocephali of Conger conger were found in the range of 8.4–13.1 cm total length (TL) (between 50 and 132 m depth), Ariosoma balearicum from 9.7–12.2 cm TL (between 50 and 128 m depth) and for Gnathophis mystax in the range from 6.4–11.7 cm TL (between 40 and 79 m depth). The results indicate that the southern Adriatic Pit could be the spawning area of these species in the Adriatic Sea. Present data represent a contribution to existing knowledge about the ecology of leptocephali from the Congridae family in the southern Adriatic Sea, and also indicate the existence of differences in morphometric parameters between different areas, that is, the possibility of the existence of new geographic lines within the genus Ariosoma in the Adriatic Sea.