The spatio-temporal pattern of Argentine shortfin squid Illex argentinus abundance in the southwest Atlantic

The Argentine shortfin squid (Illex argentinus) is a common neritic species occurring in waters off Brazil, Uruguay, Argentina, and the Falkland/Malvinas Islands in the southwest Atlantic. Illex argentinus is the most important fished cephalopod species in the area and plays a significant role in the ecosystem. It is object of major fisheries using both trawlers (mostly from European countries) and jigging vessels (mainly from Asian countries) and estimated total annual average catch for the last 15 years (1988-2003) is about 700 000 tons. The present paper aims to develop predictive models of squid abundance in relation to physical and environmental conditions, models that could ultimately be applied to fishery forecasting. Fishery and biological data collected by scientific observers aboard commercial trawlers between 1988 and 2003 were analysed in relation to physical and environmental factors to establish the spatio-temporal pattern of the species’ distribution and quantify the influence of environmental variables (e.g. SST, depth) on local abundance. The data included 26 168 fishing haul records, of which 11 103 were positive for Illex. CPUE (Catch Per Unit Effort, kg h−1) was used as abundance index. The analyses were based on time-series maps created using Geographical Information Systems (GIS). GIS maps showed that highest CPUE values were recorded during the first four months of the year (the Austral summer-autumn), with peak values higher than 5000 kg h−1 mainly located within 42◦ S, 46◦ S and MN (North part of Malvinas/Falkland) areas. Generalised additive models (GAMs) were used to describe variation in Illex argentinus abundance in relation to geographical and environmental variables. The presence/absence (PA) of Illex and its abundance (CPUE) in areas of presence were modelled separately. Predictors retained in the optimal models included SST, latitude, longitude, month, average fishing depth and year. Both models suggest a clear seasonal effect: maximum catchability was found during March (PA model) and the maximum abundances were found during the first quarter of the year (CPUE model). GAM models also demonstrated that higher catches and maturity of squid were related, in general terms, to warmer and deeper water.Abondance spatio-temporelle du calmar Illex argentinus dans l’Atlantique Sud. L’encornet rouge argentin (Illex argentinus) est une espèce néritique commune de l’Atlantique Sud-Ouest présente dans les eaux du Brésil, de l’Uruguay de l’Argentine et des îles Malouines (Falklands). Illex argentinus est la principale espèce de céphalopode exploitée dans cette région où elle joue un rôle majeur dans l’écosystème. L’espèce est pêchée par d’importantes flottilles de chalutiers (principalement de pays européens) et aux turluttes industrielles (de pays asiatiques) pour une production annuelle de 700 000 t en moyenne sur les 15 dernières années (1988-2003). Cet article présente des modèles prédictifs de l’abondance en fonction des facteurs physiques et environnementaux ; modèles qui pourraient à terme être appliqués à la gestion des pêches. Les données de capture et les paramètres biologiques récoltés, grâce à des observateurs embarqués, de 1988 à 2003, ont été analysées en relation avec les facteurs physiques pour préciser les variations spatio-temporelles de répartition et quantifier l’effet de la température et de la profondeur sur l’abondance. Le jeu de données porte sur 26 168 traits de pêche dont 11 103 comportant des captures d’Illex. Les captures par unité d’effort (CPUE en kg h−1) sont utilisées comme indice d’abondance et les analyses utilisent des séries de cartes, créées avec un système d’information géographique (SIG). Les valeurs les plus élevées de CPUE sont enregistrées durant les quatre premiers mois de l’année (l’été et l’automne austral) avec un pic dépassant 5000 kg h−1 localisé entre 42◦ S et 46◦ S dans la partie Nord desMalouines. Les modèles additifs généralisés (GAM) ont servi à décrire les variations d’abondance en fonction des variables géographiques et environnementales. La présence ou l’absence de la ressource est modélisée séparément de l’abondance. Les modèles optimaux retiennent comme variables explicatives la température, la latitude, la longitude, le mois, la profondeur et l’année. Les deux modèles indiquent un effet saisonnier net: la capturabilité est maximale en mars (présence/absence) et l’abondance (CPUE) est la plus élevée durant le premier trimestre. Les modèles additifs généralisés montrent également que les captures les plus élevées d’animaux à maturité sont associées à des eaux plus tièdes et des secteurs plus profonds

Resource Quantity Affects Benthic Microbial Community Structure and Growth Efficiency in a Temperate Intertidal Mudflat

Estuaries cover <1% of marine habitats, but the carbon dioxide (CO2) effluxes from these net heterotrophic systems contribute significantly to the global carbon cycle. Anthropogenic eutrophication of estuarine waterways increases the supply of labile substrates to the underlying sediments. How such changes affect the form and functioning of the resident microbial communities remains unclear. We employed a carbon-13 pulse-chase experiment to investigate how a temperate estuarine benthic microbial community at 6.5°C responded to additions of marine diatom-derived organic carbon equivalent to 4.16, 41.60 and 416.00 mmol C m−2. The quantities of carbon mineralized and incorporated into bacterial biomass both increased significantly, albeit differentially, with resource supply. This resulted in bacterial growth efficiency increasing from 0.40±0.02 to 0.55±0.04 as substrates became more available. The proportions of diatom-derived carbon incorporated into individual microbial membrane fatty acids also varied with resource supply. Future increases in labile organic substrate supply have the potential to increase both the proportion of organic carbon being retained within the benthic compartment of estuaries and also the absolute quantity of CO2 outgassing from these environments

Landscape homogenization due to agricultural intensification disrupts the relationship between reproductive success and main prey abundance in an avian predator

Selecting high-quality habitat and the optimal time to reproduce can increase individual fitness and is a strong evolutionary factor shaping animal populations. However, few studies have investigated the interplay between land cover heterogeneity, limitation in food resources, individual quality and spatial variation in fitness parameters. Here, we explore how individuals of different quality respond to possible mismatches between a cue for prey availability (land cover heterogeneity) and the actual fluctuating prey abundance.Peer reviewe

A review of the spatial extent of fishery effects and species vulnerability of the deep-sea demersal fish assemblage of the Porcupine Seabight, Northeast Atlantic Ocean (ICES Subarea VII)

We review information from scientific trawl surveys carried out between 1977 and 2002 in the Porcupine Seabight and Abyssal Plain area of the Northeast Atlantic (240-4865 m water depth). Since the late 1980s, commercial bottom-trawl fisheries targeting mainly roundnose grenadier (Coryphaenoides rupestris), black scabbardfish (Aphanopus carbo), and orange roughy (Hoplostethus atlanticus) have been operating at depths of 500-1500 m, intersecting the depth ranges of 77 demersal fish species that would therefore be vulnerable to fishery effects. Comparisons of trawls pre-1989 and post-1997 indicate a significant decrease in total abundance of demersal fish down to 2500 m. Detailed analyses of the 15 most-abundant species showed that nine species with depth ranges within the commercial fishing depth have decreased in abundance. Other species were either not affected (Bathypterois dubius) or only affected at the shallow end of their range (Coryphaenoides guentheri). Species with a minimum depth of occurrence >1500 m (Coryphaenoides armatus and Coryphaenoides leptolepis) increased in abundance over part of their depth range. Decreases in abundance are probably caused by commercial fishing activities, an effect that is transmitted downslope by removal of fish at the shallow end of their depth range, resulting in declines at the deeper end of the depth range. The estimated fishery area is ca. 52 000 km(2), but the potential impact probably extends to ca. 142 000 km(2) and to many non-target species

A roadmap for analysis of overdispersed sandeel counts in seal scat

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WESTHER: A multidisciplinary approach to the identification of herring (Clupea harengus L.) stock components west of the British Isles using biological tags and genetic markers.

A considerable amount of research has been carried out on the complex of commercially important herring stocks to the west of the British Isles, from the south-west of Ireland and the Celtic Sea to the north-west of Scotland. Despite all this effort, the inter-stock mixing between components within this complex is still an unknown. The overall goal of WESTHER is to describe the population structure of herring stocks in this area through a large-scale analysis of the genetic, morphological, physiological and parasite faunal differences across spatial clines of herring stocks in these western European waters. All the different methods of stock discrimination employed have been applied to the same individual herring initially aiming to differentiate between spawning aggregations, thereby creating reference points to help describe juvenile and mixed adult aggregations. WESTHER's holistic approach allows apparent discrepancies implied by individual methods to be resolved and improves confidence in the results of stock identification. In this paper the data were analysed using various statistical techniques, for example discriminant analysis and classification trees, among others. These data analysis methods were used to predict a discrete outcome, as group membership, from the mix of variables (continuous, discrete and nominal) produced by the different techniques used to discriminate between stocks. The methods are being tested and refined using data from the first year's samples to give an assessment of the relative merits of the various phenotypic, chemical and genetic techniques for examining the stock structure of herring to the west of the British Isles. Keywords: herring, classification and discrimination techniques, multi-disciplinary approach, stock component

Resource quality affects carbon cycling in deep-sea sediments

Deep-sea sediments cover ~70% of Earth's surface and represent the largest interface between the biological and geological cycles of carbon. Diatoms and zooplankton faecal pellets naturally transport organic material from the upper ocean down to the deep seabed, but how these qualitatively different substrates affect the fate of carbon in this permanently cold environment remains unknown. We added equal quantities of 13C-labelled diatoms and faecal pellets to a cold water (?0.7?°C) sediment community retrieved from 1080?m in the Faroe-Shetland Channel, Northeast Atlantic, and quantified carbon mineralization and uptake by the resident bacteria and macrofauna over a 6-day period. High-quality, diatom-derived carbon was mineralized &gt;300% faster than that from low-quality faecal pellets, demonstrating that qualitative differences in organic matter drive major changes in the residence time of carbon at the deep seabed. Benthic bacteria dominated biological carbon processing in our experiments, yet showed no evidence of resource quality-limited growth; they displayed lower growth efficiencies when respiring diatoms. These effects were consistent in contrasting months. We contend that respiration and growth in the resident sediment microbial communities were substrate and temperature limited, respectively. Our study has important implications for how future changes in the biochemical makeup of exported organic matter will affect the balance between mineralization and sequestration of organic carbon in the largest ecosystem on Earth