ArticlePDF Available

Abstract and Figures

Bottom trawling causes chronic and widespread disturbance to the seabed in shallow shelf seas and could lead to changes in the trophic structure and function of benthic communities, with important implications for the processing of primary production and the wider functioning of the marine ecosystem. We studied the effects of bottom trawling on the trophic structure of infaunal and epifaunal benthic communities in 2 regions (Silver Pit and Hills) of the central North Sea. Within each region, we quantified long-term (over 5 yr) differences in trawling disturbance at a series of sites (using sightings data from fishery protection flights), and related this to differences in the biomass and trophic structure of the benthic community. There were 27- and 10-fold differences in levels of beam trawl disturbance among the Silver Pit and Hills sites respectively, and we estimated that the frequency with which the entire area of the sites was trawled ranged from 0.2 to 6.5 times yr(-1) in the Silver Pit and 0.2 to 2.3 times yr(-1) in the Hills. The impacts of fishing were most pronounced in the Silver Pit region, where the range of trawling disturbance was greater. Infaunal and epifaunal biomass decreased significantly with trawling disturbance. Within the infauna, there were highly significant decreases in the biomass of bivalves and spatangoids (burrowing sea-urchins) but no significant change in polychaetes. Relationships between trophic level (estimated using nitrogen stable isotope composition, delta N-15) and body mass (as log(2) size classes) were rarely significant, implying that the larger individuals in this community did not consistently prey on the smaller ones. For epifauna, the relationships were significant, but the slopes or intercepts of the fitted linear regressions were not significantly related to trawling disturbance. Moreover, mean delta N-15 Of the sampled infaunal and epifaunal communities were remarkably consistent across sites and not significantly related to trawling disturbance. Our results suggest that chronic trawling disturbance led to dramatic reductions in the biomass of infauna and epifauna, but these reductions were not reflected in changes to the mean trophic level of the community, or the relationships between the trophic levels of different sizes of epifauna. The trophic structure of intensively trawled benthic invertebrate communities may be a robust feature of this marine ecosystem, thus ensuring the efficient processing of production within those animals that have sufficiently high intrinsic rates of population increase to withstand the levels of mortality imposed by trawling.
Content may be subject to copyright.
A preview of the PDF is not available
... This pattern was similar to that of the biomass variation along the ISEP grades. Sea urchin habitats, which convey a higher biomass and better functional value on ISEP grades I and II, are susceptible to and impacted by anthropogenic disturbance activities, such as bottom trawling and dredging [74,77,78]. This habitat requires long-term recovery when disturbed because the life span of sea urchins occasionally exceeds 100 years [79]. ...
Article
Full-text available
We tested the performance of an ecological index, ISEP in the west coast of Korea. The ISEP responded effectively to bottom-water SS, a key impact source in this area. ISEP was found robust to habitat condition variability like salinity and sediment. The variation in the SAB curves along the ISEP grade corresponded well with that of the P-R model. Conformity to the P-R model indicated the potential applicability to other areas.
... This pattern was similar to that of the biomass variation along the ISEP grades. Sea urchin habitats, which convey a higher biomass and better functional value on ISEP grades I and II, are susceptible to and impacted by anthropogenic disturbance activities, such as bottom trawling and dredging [74,77,78]. This habitat requires long-term recovery when disturbed because the life span of sea urchins occasionally exceeds 100 years [79]. ...
Article
Full-text available
An ecological index of macrobenthic communities is an important tool for assessing the biological quality of habitats and ecosystems. We tested the performance of the inverse function of the Shannon–Wiener evenness proportion (ISEP) with data from the entire west coast of Korea, seasonally sampled from 2006 to 2008. Two validations were performed: (1) examination of the relationship between ISEP and environmental factors and (2) correspondence between the ISEP and the Pearson–Rosenberg (P-R) model for the species-abundance-biomass (SAB) patterns and taxonomical variations. The ISEP was significantly correlated with suspended solids but independent of other natural habitat conditions due to their low to moderate contamination levels. From this, ISEP performed as expected in transitional zones of low salinity and applications across habitats of various sediments. The SAB patterns and taxonomic variations along the ISEP grades showed marked similarities to the P-R model. The only departure was biomass, which increased after the normal status. The increase was interpreted as reflecting a healthier and more mature status. Taxonomic variation patterns and the taxa composition that characterized either poor or healthy status corresponded well with the P-R model. The conformity to the P-R model indicates the capability and potential applicability of the ISEP to other coastal systems.
... This was supported by the absence of sponges in PIII and the reduction in abundance and biomass values between cruises (60.6% and 78.7%, respectively) (Table II). This is altogether a pattern consistent with documented trends for these communities in the trawl areas (Jennings et al. 2001;Schroeder 2003;Jones 2005). ...
Article
Various ecosystems of the Gulf of Mexico (GoM) may be impacted by the present increase in offshore oil exploitation. To identify future changes caused by this activity, we assessed the structure of the megabenthos community in the Perdido Fold Belt (PFB) and its relationships with environmental variables, hydrocarbons, and heavy metals. To achieve this, biological and sediment samples were obtained during the surveys Perdido II (PII) and Perdido III (PIII). 325.75 10³ ind km⁻² and 582.34 kg AFDW km⁻² were collected, distributed in 110 species. Crustaceans and echinoderms comprised more than 70% of the total abundance and biomass. The most abundant species were Astropecten cingulatus Sladen, 1883, Callinectes sapidus Rathbun, 1896, Astropecten duplicatus Gray, 1840, and Penaeus aztecus (Ives, 1891) (12.2 10³ ≤ ind Km⁻² ≤ 59.4 10³). They also had the greatest biomass contribution (16.8 ≤ kg AFDW km⁻² ≤ 192.2). BIOENV test showed the influence of depth (Z), salinity, dissolved oxygen (DO), Acenaphthylene (Acy), Fluoranthene (Flu), n-C12, n-C37, and nickel (Ni) on the community structure. Recruitment and trawling also influenced the abundance and biomass values. Despite Z defines the environmental gradient, the hydrocarbon concentration gradient within the shelf areas makes it a good candidate for developing monitoring programmes.
... L'assemblage III semble constituer un faciès appauvri de l'assemblage II caractérisé par (1) une plus faible abondance, occurrence et diversité, et (2) l'absence de raies et de Syngnathidae. Sturbois et al. (2021a) ont montré une dégradation des habitats benthiques dans la zone d'étude, avec des changements taxonomiques et fonctionnels significatifs, et suggèrent que le dragage des coquilles Saint-Jacques était le principal moteur de ces changements, comme cela a été démontré dans d'autres systèmes fortement exploités (Bradshaw et al., 2001 ;Craven et al., 2013 ;Fanelli et al., 2009 ;Jennings et al., 2001 ;Jennings et Kaiser, 1998 ;Pinnegar et al : Rosenberg et al., 2000). ...
Technical Report
Full-text available
L'évaluation des flux de matière et des interactions inter- et intra-spécifiques dans les réseaux trophiques est importante pour comprendre le fonctionnement écologique des baies et des estuaires caractérisés par une grande diversité de producteurs et de consommateurs primaires, y compris de prédateurs. Les espèces de poissons et de céphalopodes et leur réseau alimentaire ont été étudiés à travers un réseau de 24 stations subtidales peu profondes dans la baie de Saint-Brieuc en utilisant des analyses d’assemblages, d'isotopes stables et de contenu stomacaux. La communauté était composée de 21 taxons, huit espèces représentant 94,4% de l'abondance totale. Des variations de compositions et d'abondances ont été observées parmi les trois assemblages identifiés : l'un principalement limité aux stations les moins profondes, les deux autres plus profonds dont un caractérisant un faciès appauvri. La POM marine et la SOM étaient les bases les plus probables du réseau trophique en ce qui concerne la gamme δ13C chez les poissons et céphalopodes sans différence entre les assemblages. Les amphipodes étaient la principale proie dans les estomacs, ce qui a conduit à des chevauchements de régime significatifs entre les espèces de poissons, avec quelques variations liées à des proies moins dominantes. Sepia officinalis était caractérisé par un régime unique et des valeurs très faibles de chevauchement alimentaire. Des contrastes dans les compositions isotopiques et des chevauchements de niche entre les espèces ont été mis en évidence dans l'espace δ13C / δ15N. Callionymus lyra et Buglossidium luteum, caractérisés par les niches les plus grandes dans l’espace isotopique, englobaient la niche des autres espèces, à l'exception de la singulière Spondyliosoma cantharus appauvrie en 13C. L’association d’analyses d’assemblages taxonomiques, de contenus stomacaux et d’isotopes stables a permis de mettre en évidence l’utilisation des ressources et les voies de transfert trophiques. Les contrastes taxonomiques des assemblages démersaux de poissons et de céphalopodes présents à différentes profondeurs n'impliquent pas de différences dans l'utilisation des ressources trophiques dans cet écosystème côtier peu profond sous influence anthropique.
... This monitoring is achieved by observing and then estimating the diversity and abundance of fish species to understand the structure and dynamics of the coral reef community [7]. Traditional techniques used to observe ecosystems and monitor biodiversity, such as techniques (fishing [8], anesthesia [9]) and underwater visual census (UVC) [10], are destructive and/or do not ensure continuous monitoring of underwater biodiversity. It is important to adopt more advanced techniques that are non-destructive and provide continuity in ecosystem monitoring. ...
Article
Full-text available
Nowadays, underwater video systems are largely used by marine ecologists to study the biodiversity in underwater environments. These systems are non-destructive, do not perturb the environment and generate a large amount of visual data usable at any time. However, automatic video analysis requires efficient techniques of image processing due to the poor quality of underwater images and the challenging underwater environment. In this paper, we address live reef fish species classification in an unconstrained underwater environment. We propose using a deep Convolutional Neural Network (CNN) and training this network by using a new strategy based on incremental learning. This training strategy consists of training the CNN progressively by focusing at first on learning the difficult species well and then gradually learning the new species incrementally using knowledge distillation loss while keeping the high performances of the old species already learned. The proposed approach yields an accuracy of 81.83% on the LifeClef 2015 Fish benchmark dataset.
... Trawling is known to reduce the biomass and biological diversity of benthic ecosystems, with demersal trawling, in particular, causing mechanical damage to the seabed (Jones 1992;Dayton et al. 1995;Hall-Spencer et al. 1999;Jennings et al. 2001;Chuenpagdee et al. 2003;Puig et al. 2012;Oberle et al. 2016;Eigaard et al. 2017) and dramatic chemical alterations . Bottom trawls may alter the substrate substantially, e.g. by mowing down corals, sponges, and seagrass meadows. ...
Article
Full-text available
Several populations of odontocete cetaceans, including at least 19 species, have modified their behavior and adapted to foraging in association with trawlers. We review information on odontocete interactions with different types of trawlers across 13 Food and Agriculture Organization fishing areas around the world. We also review knowledge gaps, the effects on odontocete ecology, distribution, behavior and social organization, the main mitigation options, and some management avenues that could help reduce incidental mortality. Trawlers involved in the interactions varied greatly in gear and target species, implying odontocetes have developed behavioral specializations to forage under a variety of conditions. Specialized behavior included venturing into a moving trawl net to feed on the organisms trapped in the net, feeding on fish stirred up by the net, extracting fish from the outer mesh, feeding on catch lost during hauling, and scavenging on discarded catch. Foraging behind trawlers facilitates access to prey, and in some instances may compensate for scarcity of natural prey within areas exposed to intensive fishing or environmental degradation. This opportunistic foraging strategy, however, exposes the animals to potential harm and mortality in trawl gear. The combined effect of facilitated foraging and bycatch on the status and trends of odontocete populations is unknown. The economic damage caused by odontocetes, e.g. in terms of loss of marketable catch and gear damage, remains largely conjectural. Attempts to reduce depredation and/or bycatch in trawl gear have included acoustic deterrents and exclusion devices installed in nets, although neither technique has proven to be consistently effective. --- https://doi.org/10.1007/s11160-022-09712-z
... Changes in the trophic structure and function of benthic communities have important implications on primary production and the wider functioning of the marine ecosystem [8,9]. Ecological studies on bottom trawling have focused on ecosystem impacts through widespread physical disturbance of the bottom substrate, excessive removal of juveniles, and the potential of modifying ecosystems' trophic structure [10,11]. ...
Article
Full-text available
Bottom trawling is a common fishing method that targets bottom-dwelling fisheries resources. It is non-selective and large amounts of by-catch are discarded, raising serious sustainability and ecosystem conservation concerns. In this study, a shallow-water bottom-trawl fishery was evaluated using logbook catch data between 2011 and 2019 and the species composition data collected by fisheries observers between 2016 and 2019. The logbook data showed a twenty-fold increase in the annual catches with a ten-fold increase in fishing effort and an increase in the proportion of retained catch from 2011 to 2019. The observer data showed that for prawn, the by-catch ratio ranged from 1:3 to 1:9 during the four years. Multivariate analysis revealed significant differences between the compositions of retained and discarded catches mainly attributed to Pellona ditchela, Nematopalaemon tenuipes, and Secutor insidiator. There was no significant decline in species diversity and the trophic level of the catches over the 4-year observer period indicating no marked impact of trawling on the stock at the current level of fishing effort. This study provides baseline information on the prawn trawl fishery against which the performance of the management regulations may be evaluated towards the Ecosystem Approach to Fisheries management.
Article
Pollution status and benthic ecological quality of the two types of ports were assessed based on heavy metals and macrofaunal assemblages. Macrofaunal abundance and biomass in the industrial port were significantly higher than those in the fishing port. The dominant species of the two ports were Echinocardium cordatum and Nephtys oligobranchia. The AZTI marine biotic index (AMBI), multivariate AMBI, and Shannon-Wiener diversity index demonstrated that the benthic ecological quality of the two ports was moderate to good. The benthic ecological quality of the distant port sites was better than those of the nearby port sites. The geoaccumulation index and the Hakanson potential ecological risk index indicated that mercury posed a serious threat to port sediment pollution. AMBI, multivariate AMBI, and Shannon-Wiener diversity index were not good indicators for heavy metal pollution. The dominant species and Pielou’s evenness index were significantly correlated with heavy metal pollution and were good biological indicators.
Thesis
Full-text available
Les progrès réalisés dans l’imagerie optique sous-marine conduisent de plus en plus à l’utilisation de ces systèmes dans des applications de surveillance, d’observation et/ou d’exploration. En effet, la vidéo sous-marine dispose d’atouts notables comme une haute résolution, une facilité d’interprétation et surtout une forte miniaturisation à faible coût. Malgré ces développements, le traitement automatique des enregistrements vidéos est encore très rare du fait de la complexité de l’information sous-marine' est pourtant une technologie pleine de promesses, en particulier pour le déploiement de robots et des observatoires sous-marins, dans un contexte de suivis pérennes des écosystèmes côtiers. Localiser, recenser et exploiter les populations marines nécessitent de recueillir en continu de la connaissance sur le milieu marin. L’objectif essentiel de cette thèse est la mise au point d’une chaîne de traitement et d’analyses d’images vidéo sous-marines pour la reconnaissance et le comptage automatique d’espèces de poissons. Cet outil est destiné à des aquariums grand public et à des stations d’observation pour le suivi des aires marines protégées (AMP) et des dispositifs de concentration de poissons (DCP). Dans ce travail de thèse nous voulons en particulier tester l’apport de l’apprentissage profond pour la représentation de l’environnement sous-marin et pour la classification des espèces.
Article
Full-text available
In Kiel Bay (Western Baltic), benthos samples were taken at 20 m water depth using rectangular botanical dredges fixed to the otter boards of an 80 ft Sonderborg standard trawl to document possible effects of trawl fishery on the benthic fauna. Thin-shelled bivalves like Syndosmya (Abra) alba, Mya spp. and Macoma calcarea, as well as the starfish Asterias rubens were damaged by otter-boards to a high extent. Thick-shelled bivalves such as Astarte borealis and Corbula gibba, however, seem to be more resistant to mechanical stress of bottom-trawl fishery. Musculus niger, an epibenthic species, is probably only resuspended and dislocated. The rate of damage to Arctica islandica, Macoma baltica and Macoma calcarea is related to their body size. Large specimens are more affected than smaller specimens due to the unfavourable relationship between shell surface and shell thickness. The size distribution of Arctica islandica in heavily trawled areas of Kiel Bay shows reductions in the upper size class in these areas.
Article
Full-text available
The diets of gurnards Aspitrigla cuculus and Eutrigla gurnardus, lesser-spotted dogfish Scyliorhinus canicula and whiting Merlangius merlangus were examined to determine whether they migrated into recently trawled areas to feed on animals that may be damaged or dislodged by the action of a 4 m beam trawl. Gurnards and whiting increased their intake of prey after an area had been fished. In particular, they increased the proportion of the amphipod Ampelisca spinipes in their diets. Beam trawling damaged the purple burrowing heart urchin Spatanguspurpureus, scallop Aequipecten operculans, Ensisspp. and Laevocardium sp., exposing internal tissues which were then eaten by whit- ing. Some mobile invertebrate scavengers, such as Pandalusspp., only occurred in diets after the area had been fished, suggesting that these animals were also scavenging over the trawl tracks. Observa- tions of the seabed using a side-scan sonar revealed a greater concentration of fish marks around the trawl tracks than in adjacent unfished areas. Our results indicate that fish rapidly migrate into beam trawled areas to feed on benthic animals whlch have been either damaged or disturbed by fishing or on scavenging invertebrates. In areas where certain benthic communities occur, beam trawling inten- sity may be such that it creates a significant food resource for opportunistic fish species. This is a possi- ble mechanism whereby long-term community structure could be altered by fishing activity.
Article
Full-text available
Stable nitrogen isotope ratios (δ15N) are commonly used to represent the trophic structure of aquatic systems, yet the ability of δ15N to indicate the trophic position of aquatic consumers remains untested using traditional dietary methods. Interpreting the δ15N of aquatic consumers relative to large, long-lived primary consumers such as unionid mussels provides a continuous measure of an organismís trophic position that adjusts for among-system variation in baseline δ15N. We used this method to estimate the trophic position of eight littoral fish species from 36 lakes in Ontario and Quebec. We validated these δ15N measures of trophic position by compiling literature dietary data from 342 populations of these same fish species and calculated a continuous measure of trophic position for each population. Mean dietary trophic position estimates corresponded closely to 15N estimates, with mean trophic position ranging from 3.3 for pumpkinseed (Lepomis gobbosus) to 4.4 for walleye (Stizostedion vitreum). Both methods indicated approximately one trophic level of variation among populations of a species. This study confirms the ability of baseline-adjusted δ15N to represent the trophic position of aquatic consumers. Résumé : Les rapports díun isotope stable de líazote (δ15N) sont couramment utilisØs pour reprØsenter la structure trophique des systmes aquatiques; pourtant, la capacitØ du δ15N díindiquer la position trophique des consommateurs aquatiques nía pas encore ØtØ testØe employant des mØthodes alimentaires traditionnels. LíinterprØtation de δ15N des consommateurs aquatiques
Article
Full-text available
The effects of trawling disturbance on a benthic community were investigated with a manipulative field experiment in a fine muddy habitat that has been closed to fishing for over 25 yr. We examined the effects of extensive and repeated experimental trawl disturbance over an 18 mo period on benthic community structure and also followed the subsequent patterns of recovery over a further 18 mo. During the period of trawl disturbance the number of species and individuals increased and measures of diversity (Shannon's exponential H' and Simpson's reciprocal D) and evenness decreased in the trawled area relative to the reference site. The cirratulid polychaetes Chaetozone setosa and Caulleriella zetlandica were found to be most resistant to disturbance, whilst the bivalve Nucula nitidosa and polychaetes Scolopolos armiger and Nephtys cirrosa were identified as sensitive species. Multivariate analysis and abundance biomass comparison plots confirmed that community changes occurred following disturbance, with some differences between treatment and reference sites still apparent after 18 mo of recovery. Physical effects, examined with Side-scan and RoxAnn, were identifiable immediately after disturbance, but were almost indistinguishable after 18 mo of recovery. Such long recovery times suggest that even fishing during a restricted period of the year may be sufficient to maintain communities occupying fine muddy sediment habitats in an altered state.
Article
Full-text available
This study addresses ongoing concerns over the effects of mobile fishing gear on benthic communities. Using side-scan sonar, bottom photographs and fishing records, we identified a set of disturbed and undisturbed sites on the gravel pavement area of northern Georges Bank in the northwest Atlantic. Replicate samples of the megafauna were collected with a 1 m Naturalists' dredge on 2 cruises in 1994. Compared with the disturbed sites, the undisturbed sites had higher numbers of organisms, biomass, species richness and species diversity; evenness was higher at the disturbed sites. Undisturbed sites were characterized by an abundance of busby epifaunal taxa (bryozoans, hydroids, worm tubes) that provide a complex habitat for shrimps, polychaetes, brittle stars, mussels and small fish. Disturbed sites were dominated by larger, hard-shelled molluscs, and scavenging crabs and echinoderms. Many of the megafaunal species in our samples have also been identified in stomach contents of demersal fish on Georges Bank; the abundances of at least some of these species were reduced at the disturbed sites.
Chapter
Study of natural variation in 15N can provide information on biogeochemical, physical, physiological and biochemical investigations. Following considerations of measurement, isotope effects and fractionation, comments are made on 15N in the atmospheric, terrestrial, freshwater, estuarine and marine compartments; sources; and food chain dynamics. -P.J.Jarvis
Article
Annual length increments of female North Sea plaice were back-calculated from distances between rings in otoliths. Growth of the smaller size classes (<25 cm) increased from the mid-1950s and decreased in the 1980s. Length increments of intermediate size classes varied more or less randomly, and those of the larger size classes (>35 cm) increased from 1970. Growth changes of the smaller size classes were significantly correlated with indices of plaice density, eutrophication, and seabed disturbance by beam trawling. Moreover, they could be related to spatial and temporal patterns in variations in eutrophication and beam trawling. No correlation was observed with temperature. The analysis led to a consistent interpretation suggesting that eutrophication and beam trawling have both affected the growth rate of plaice. The contributions of these factors differed in space. Effects of eutrophication dominated in the shallow coastal waters, whereas beam trawling dominated in the waters further offshore.