Sublittoral meiobenthic assemblages from disturbed and non-disturbed sediments in the Balearics

Publicación online disponible en: http://www.icm.csic.es/scimar/index.phpQualitative and quantitative differences in species composition of meiobenthic communities illustrate the differences among various taxonomic assemblages in the Balearic Islands (Western Mediterranean) analysed by means of multivariate analysis. Average densities ranged between 1000 and 4000 ind⋅10cm-2, and are in the same range as previously reported from other shallow Mediterranean areas. The dominant meiofaunal taxa were Nematoda (range 40 to 75%), Turbellaria (5-47%) and Copepoda (2-14%), while other meiofaunal groups (Tardigrada and Rotifera) were only represented by approximately 5% of the total abundance. The dominant nematode families were Desmodoridae, Chromadoridae and Xyalidae. The meiofaunal communities showed little variation among locations. Moreover, small-scale heterogeneity does not seem to affect nematode distribution as shown by the high similarity between replicates in the multivariate analysis.This work was supported by a grant from the Ministerie van de Vlaamse Gemeenschap (Belgium) to S. Deudero.Peer reviewe

Interspecific trophic relationships among pelagic fish species underneath FADs

Fortnightly experimental purse-seine hauls at fish aggregation devices (FADs) and open water control sites, over a 2-year period in oceanic waters off the eastern coast of Majorca revealed that carangid, coryphaenid, serranid, balistid and centrolophid fishes caught there were mostly planktivores. Most of the species had a high food intake. The dominance of neustonic and holoplanktonic epipelagic prey could indicate a direct link between FADs, invertebrates (biofouling) and fish. Polyprion and Schedophilus were more generalist predators than the more specialized Naucrates and Trachurus spp. There was low variation in feeding intake and the types of prey categories important for each species. Naucrates, Coryphaena and Schedophilus characterized the autumn community under FADs, while Trachurus, Seriola and Balistes were present throughout the summer. There was little diet overlap among the species suggesting only limited competition for the food resources among Trachurus spp, Naucrates and Seriola, and among Seriola and Coryphaena. © 2001 The Fisheries Society of the British Isles.This study was funded by EC and Consejo Superior de Investigaciones Cient´fiı cas (Spanish Government) in the framework of the projects: Biology and Fishery of dolphin-fish in the western Mediterranean and Canary island area Project no 94/031, and Dolphin-fish biological and fishing data in the western Mediterranean Project no 95/73Peer Reviewe

Fish fauna associated with floating objects sampled by experimental and commercial purse nets

Publicación online disponible en: http://www.icm.csic.es/scimar/index.phpBased on the commercial surrounding nets traditionally used in the Coryphaena hippurus fishery, we designed an experimental purse seine (64 m long and 14 m high, with a purse line and a central codend of 2 mm mesh) for sampling fish fauna associated with flotsam. Taxa, number, biomass and sizes of fishes caught with both types of gear around fish aggregation devices were compared. From 63 hauls with the experimental net, we caught 11370 fishes belonging to 17 families and 26 species. In contrast, 816 fishes belonging to 7 species and 5 families were collected from 39 commercial hauls. Despite differences in number of hauls for each net, the curves of cumulative species richness showed that additional hauls could not increase the number of species collected with the commercial net. The most abundant species from experimental net catches were Trachurus picturatus, which represented over 80% of the specimens caught in spring and summer, Naucrates ductor, which represented about 50% of autumn catches, both in terms of abundance and biomass, and Seriola dumerili, which represented 46% and 21% of the samples taken in summer and autumn respectively. Seriola dumeril was also frequent in commercial net catches, in which T. picturatus did not appear, while Coryphaena hippurus and N. ductor represented more than 85% of both abundance and biomass. Large differences between the two types of net were also obtained in the mean fish weight and length frequency distributions of the catches by season. Fish caught with the experimental net ranged from 6 to 570 mm length, while fish collected from commercial hauls had a size range of 35 to 700 mm. The effectiveness of the experimental net in catching small fishes showed that it can be an optimal sampling method not only in the study of fish fauna associated with flotsam, but also in studies to catch early life stages.This paper is a result of the research project “Dolphin-fish biological and fishing data in the Western Mediterranean”, funded by Directorate General XIV of the European Commission (Ref. 95/73).Peer reviewe

A large scale survey of trace metal levels in coastal waters of the Western Mediterranean basin using caged mussels (Mytilus galloprovincialis)

Autores: Benedicto, José ... [et al.]. -- 11 páginas, 3 figuras, 1 tablaA large scale study of trace metal contamination (Hg, Cd, Pb and Ni) by means of caged mussels Mytilus galloprovincialis was undertaken along the coastal waters of the Western Mediterranean Sea within the context of the MYTILOS project. Individual mussels from an homogeneous population (shell size 50 ± 5 mm) obtained from an aquaculture farm were consecutively caged and deployed at 123 sites located in the Alborán, North-Western, South-Western and Tyrrhenian sub-basins for 12 weeks (April–July) in 2004, 2005 and 2006. After cage recoveries, both the metal content in the whole mussel tissue and the allometric parameters were measured. Statistical analysis of the datasets showed significant differences in concentrations between sub-basins for some metals and mussel condition index (CI). Linear regression models coupled to the CI were revisited for the data adjustment of certain trace metals (Hg, Cd and Ni), and four level categories were statistically derived to facilitate interregional comparison. Seawater masses surrounding coastal areas impacted by run-off from land mineralised coasts and industrial activities displayed the highest concentration ranges (Hg: 0.15–0.31 mg kg−1 dw; Cd: 1.97–2.11; Ni: 2.18–3.20 and Pb: 3.1–3.8), although the levels obtained in most of the sites fitted within moderate or low categories, and they could be considered as baseline concentrations. However, few sites considered little-influenced by human activities, at present, showed high concentrations of Cd, Ni and Pb, which constitute new areas of concern. Overall, the use of active biomonitoring (ABM) approach allowed to investigate trace metal contamination in order to support policy makers in establishing regional strategies (particularly, with regard to the European Marine Strategy Directive).Esta investigación ha sido financiada por el EEC (Proyecto Interreg/MedoccIIIB/MYTILOS). El Programa UNEP MEDPOL ha subvencionado a: INRH (Marruecos), ESSMAL (Algeria) e INSTM (Túnez).Peer reviewe

Population size structure, age and growth of Naucrates ductor in the small scale FADs fishery of Mallorca Island (western-Mediterranean)

Publicación online disponible en: http://www.icm.csic.es/scimar/index.phpThe pilotfish (Naucrates ductor) is mainly caught as a by-catch of the dolphinfish fishery using FADs deployed around Mallorca (western-Mediterranean) from the end of August to December. The age and growth parameters of this species were estimated by length frequency analysis and daily growth increments observed in the otoliths. To validate the daily formation of the ring observed in the sagittae otoliths, a marking otoliths experiment with SrCl2 was carried out with juvenile specimens kept in laboratory conditions. The growth parameters obtained from otolith interpretation were based on age at length of 99 specimens ranging between 15 and 31.2 cm FL. Length frequency analyses were based on the monthly length distribution obtained in 1990, 1991, 1995 and 1996. The results obtained from the two methods were similar and showed rapid growth during the first 6 months of life. The von Bertalanffy growth equation from otoliths was FL= 28.97 (1-e (-6.87(t - 0.055)). Positive allometric growth was observed in the length-weight relationship, with no differences existing between sexes: W (g)= 0.0147*FL3.040 (cm).Peer reviewe

Occurrence of Polyprion americanus under floating objects in western Mediterranean oceanic waters, inference from stomach contents analysis

Catches of 11 juvenile specimens of Polyprion americanus (Osteichthyes: Polyprionidae) are reported under fish aggregation devices (FADs) in waters off Mallorca (western Mediterranean). Sampling was carried out fortnightly by surrounding artificial FADs with a purse seine from April 1995 till February 1997. Juveniles were present from June-August. Specimens were mostly solitary during the period of association to the FADs, with a length interval of 25.8 and 34.2 cm total length. The trophic spectrum was analysed to explain a possible food link with the FAD. The diet of Polyprion was mainly based on juvenile fish Trachurus and the eunestonic isopod Idotea metallica that were associated with the objects providing evidence for a trophic relation to the artificial structures.UE 94/031 and 95/73Peer Reviewe

Surface mesozooplankton in open waters of the Western Mediterranean

The seasonal abundance and distribution of mesozooplankton were studied in relation to the presence of floating objects, physical and biological variables from 1995 to 1997 in the epipelagic waters off Majorca. Zooplankton were sampled fortnightly using a vertically hauled WP-2 net (330 μm). Comparisons between zooplankton abundance at four fixed stations with Fish Aggregating Devices (FADs) and four open water control stations were conducted to 1) describe the seasonal succession of mesozooplankton organisms in relation to physical parameters and 2) to test for any attraction phenomena of zooplankton towards floating objects. Mean zooplankton densities were low and ranged from 4 ind·m-3 to 659 ind·m-3. Species composition showed no significant inter-annual variations and a dominance of copepods. Average dry weight biomass was 3 mg·m-3. Environmental factors did not directly determine the total zooplankton community structure but influenced the seasonal patterns of the individual taxa. Although, in the past, floating structures have been shown to increase spatial heterogeneity in the pelagic environment and enhance the aggregation of several fish species, the present study found no evidence of mesozooplankton aggregation below FADs. No significant differences were found in the abundance or biomass of zooplankton at sites with FADs, suggesting that the intrinsic variability in zooplankton overrides any possible FAD effect on plankton aggregation. We hypothesise that at the mesoscale level FADs do not provide a microhabitat with sufficiently different physical conditions, although they could locally induce patchiness in resource availability and predation linked with the presence of shoals of juvenile fishes aggregated underneath the floating device.Peer Reviewe

Fish communities associated with FADs

Publicación online disponible en: http://www.icm.csic.es/scimar/index.phpTwo groups of six fish aggregating devices (FADs) were deployed at two locations off the eastern coast of Majorca (Western Mediterranean). Samples were obtained fortnightly throughout a two-year period by means of hauls performed with an experimental purse seine. Two control areas were established to check the aggregation efficiency of the FADs. A total of 16 families and 26 species of fishes were recorded beneath FADs. Pelagic fishes, largely Trachurus picturatus, T. mediterraneus, T. trachurus, Naucrates ductor, Seriola dumerili and Coryphaena hippurus, dominated the fauna. The total fish abundance, number of species and length range of the species confirmed that the FAD community was significantly related to season (recruitment period), resulting in a sequential fish colonisation of the FADs during the study period. Some of the species were present only during a particular period, such as Trachurus spp. in spring and summer. Other species, although evident for a longer period, were more occasional in catches (Schedophilus ovalis, Balistes carolinensis and Polyprion americanus), and some others were also present in small quantities. Diversity and equitability of the fish community associated with FADs were higher in summer than in winter. Many species were more abundant around FADs than in open water controls. The species that showed the most distinct recruitment phase beneath the FADs were N. ductor, S. ovalis, Trachurus spp., P. americanus, S. dumerili, C. hippurus and B. carolinensis. FADs can be considered nursery structures for many pelagic and demersal species, thus having an effect on the redistribution of juveniles. In the deployment of artificial structures as aggregators for fishing purposes one should consider the patchiness and seasonal characteristics of these communities as well as the redistribution aspect for fishery management.This work has been financed by the Directorate General for Fisheries (Project UE 94/031 and 95/73) and was supported by grants from I.M.E.D.E.A. to the first author.Peer reviewe

Population dynamics and fishery of dolphinfish (Coryphaena hippurus) in the western Mediterranean

Publicación online disponible en: http://www.icm.csic.es/scimar/index.phpThe dolphinfish (Coryphaena hippurus) fishery based on the island of Majorca (western Mediterranean) and the population dynamics of the species were studied between 1995 and 1996. Fishing effort, landings and length composition of the catches during the sampling period, as well as the historic catch data series and fleet were analysed. Virtual Population Analysis (VPA), taking as the time unit the week in 1995 and the fortnight in 1996, were also carried out. Dolphinfish is fished from August to December, with main catches in September-October, using anchored fish aggregation devices (FADs) and surrounding net. The mooring areas, placed from 70 to 1200 m depth, are distributed among the boats registered for the year´s fishery. A total of 46 boats took part in this fishery in 1995 and 37 in 1996, with a catch of 128 and 52 metric tons respectively. These wide fluctuations are also shown in the annual catches of the 16year series, which ranged from 2 to more than 120 metric tons, showing a slightly increasing trend (4 tons per year). The comparison of different measures of effort (FADs, days and hours) showed similar values of CPUE, although the number of FADs showed the lowest variation, with normal variances and average values not significantly different between harbours. The length composition of the catches ranged from 20 to 64 cm fork length, which corresponds to juveniles between 2 and 6 months of age. The main results of the VPA, which must be regarded in relative rather than absolute values, showed that the available population and the recruitment in 1995 are greater (around one order of magnitude) than in 1996. For both years, the number of individuals declined in the course of the fishing season, while biomass increased during the first 5 weeks. The fact that the exploited fraction of the dolphinfish population is composed of 0-age class suggests that catch fluctuations might be related to environmental parameters and to the migratory behaviour pattern of the species. These two interrelated factors can produce failures of its annual spawning in the western Mediterranean, and/or of the recruitment of the species to the fishery.This paper is a result of the research projects “Biology and fishery of dolphinfish in the western Mediterranean and Canary Islands area” and “Dolphinfish biological and fishing data in the western Mediterranean”, funded by Directorate General XIV of the European Commission (Refs. 94/031 and 95/73 respectively).Peer reviewe

Distribution and densities of the decapod crab Percnon gibbesi, an invasive Grapsidae, in western Mediterranean waters

Density, population structure and spatial distribution of the invasive crab Percnon gibbesi in western Mediterranean waters were investigated. Densities appeared highest within pebble substrates, reaching up to 3 ind. m-2. Modal length was 20 mm carapace length (CL), with the presence of ovigerous females from 18 mm CL. Maximum densities were observed at 1 m depth. There were significant differences in habitat preference toward boulders of variable size with algal cover not higher than 0.5 cm. Although individuals were highly active during the daytime, activity patterns were highest at sunset. Further studies are required on the biology and ecology of this grapsid crab to better understand the reasons for its population growth along Mediterranean coasts and to ascertain the means of colonization.Thanks to the Societat d’Història Natural de les Illes Balears for supporting our research. This research was funded by the Departament de Medi Ambient i Natura del Consell Insular de Mallorca and the Fundació Sa Nostra de BalearsPeer Reviewe