Article

Trawl disturbance on benthic communities: Chronic effects and experimental predictions

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Abstract

Bottom trawling has widespread impacts on benthic communities and habitats. While the direct impacts of trawl disturbances on benthic communities have been extensively studied, the consequences from long-term chronic disturbances are less well understood. The response of benthic macrofauna to chronic otter-trawl disturbance from a Nephrops norvegicus (Norway lobster) fishery was investigated along a gradient of fishing intensity over a muddy fishing ground in the northeastern Irish Sea. Chronic otter trawling had a significant, negative effect on benthic infauna abundance, biomass, and species richness. Benthic epifauna abundance and species richness also showed a significant, negative response, while no such effect was evident for epibenthic biomass. Furthermore, chronic trawl disturbance led to clear changes in community composition of benthic infauna and epifauna. The results presented indicate that otter-trawl impacts are cumulative and can lead to profound changes in benthic communities, which may have far-reaching implications for the integrity of marine food webs. Studies investigating the short-term effects of fishing manipulations previously concluded that otter trawling on muddy substrates had only modest effects on the benthic biota. Hence, the results presented by this study highlight that data from experimental studies can not be readily extrapolated to an ecosystem level and that subtle cumulative effects may only become apparent when fishing disturbances are examined over larger spatial and temporal scales. Furthermore, this study shows that data on chronic effects of bottom trawling on the benthos will be vital in informing the recently advocated move toward an ecosystem approach in fisheries management. As bottom-trawl fisheries are expanding into ever deeper muddy habitats, the results presented here are an important step toward understanding the global ecosystem effects of bottom trawling.

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... This index can on the one hand be used as a standalone index to attain a measure of the vulnerability or resilience of a community to trawling, on the other hand it can be used to explore the link between vulnerability and ecosystem functions. Besides introducing the RRI and its sub-indices, the present study aimed to validate and demonstrate the mulitple uses of the index by applying it to benthic data from the north-eastern Irish Sea Nephrops fishing ground (Hinz et al., 2009) and linking it to a well-established functional index, the bioturbation potential index (BPI) developed by Queirós et al. (2013). ...
... To validate the developed indices, we used macrofauna data collected over an active fishing ground for Norway lobster (Nephrops norvegicus, Linnaeus) and gadoid fish in the north-eastern Irish Sea. This data was previously published investigating the effects of trawling on a taxonomic level by Hinz et al. (2009). For more detailed information about the sampling design, as well as the fishing effort calculation, refer to Hinz et al. (2009). ...
... This data was previously published investigating the effects of trawling on a taxonomic level by Hinz et al. (2009). For more detailed information about the sampling design, as well as the fishing effort calculation, refer to Hinz et al. (2009). Macrofauna data was collected at 15 sites over a gradient of fishing intensity varying from 1.3 times trawled/year to 18.2 times trawled/year. ...
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The vulnerability to trawling on a species level is determined by a species' individual combination of biological traits that is related to the ecosystem functions. Trait-based indices of physical resistance RI and reproductive potential RPI were developed and combined into an overall vulnerability index on a species level, the RRI or Resistance and Reproductive Potential Index. The indices are used to explore how resistance and reproductive potentia change over a trawling gradient. The RRI allows for dividing the benthic community into groups expressing different levels of vulnerability that can be linked to ecosystem functions. The RRI index opens up the possibility of scenario modelling by simulating the extinction or loss of vulnerable species and its effects on functions. The validity of the trait-based RRI index was explored by comparing individual species' RRI scores to empirically observed responses over a trawling gradient based on a previously published data. RRI score and observed responses (regression slopes) were significantly correlated providing support for the rationality of the approach taken. Data analyses evidenced increases of resistance and resilience indices over the trawling gradient, demonstrating that communities lost vulnerable species with increasing trawling. When exploring the effects of trawling on the bioturbation, we found it to be disproportionately affected though the loss of vulnerable species. The proposed indices provide new insights into the link of species vulnerability and function.
... This has come about due to the increased availability of spatially resolved information on fishing vessel activities, and the development of open source methods to estimate fishing effort (Bastardie et al., 2010;Hintzen et al., 2012). As a result, there is an improved understanding of the distribution of commercial trawling effort Eigaard et al., 2017;Puig et al., 2012), and how gradients of trawling intensity alter the structure and ecological functioning of benthic macrofaunal communities (Bolam et al., 2017;Hinz et al., 2009;Tillin et al., 2006). Growing societal concern regarding fisheries effects has prompted the adoption of an 'Ecosystem Approach to Fisheries Management' (EAFM) (FAO, 2003) in the European Union. ...
... In general, declines in these indicators will occur when the fishery exerts mortality rates higher than what can be replaced by the wider population, either through recruitment or potentially immigration. Although this rate may vary between location, the efficacy of N as indicator of trawling impacts in gradient studies has been demonstrated in a number of regions, including in the Kattegat (Gislason et al., 2017), Irish Sea (Hinz et al., 2009), Mediterranean (Mangano et al., 2014), and New Zealand (Thrush et al., 1998). Equally, biomass has been shown to be an effective indicator of trawling disturbance. ...
... Nephrops grounds in the Irish Sea have conversely shown A. filiformis to be highly sensitive to trawling Hinz et al., 2009). While the exact reasons for these discrepancies are unclear, it is possible that local sedimentary and hydrodynamic conditions may affect the relationship between some taxa and trawling. ...
Article
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Bottom trawling alters the abundance, diversity, size-composition, and function of benthic communities. However, the ability to detect these impacts over large spatial scales can be obscured by various complicating factors, such as community adaptation to disturbance and co-varying environmental conditions. An ecosystem-based approach to fisheries management therefore requires ecological indicators which can ‘disentangle’ trawling effects from other natural and human drivers, and respond effectively to shifts in ecological quality. We collected benthic macrofaunal samples at 21 sites across a Norway lobster Nephrops norvegicus fishing ground in the Kattegat, and separated the benthic community into small (1-4mm) and large (>4mm) size fractions. Four taxonomic indicators (total density, species density, Shannon diversity, and biomass) and four functional indicators (functional diversity, functional richness, functional evenness, and functional dispersion) were calculated based on each size fraction, and the two fractions combined (pooled community). Here, we compare the ability of these indicators to detect trawling impacts across size categories. We show that indicators derived from large macrofauna were highly effective in this regard, and were less influenced by other environmental drivers, such as depth, sediment grain size, bottom current velocity, salinity, and temperature. This suggests that the taxonomic and functional characteristics of benthic communities display a size-dependent sensitivity to trawling disturbance, and therefore community metrics based on large benthic macrofauna may provide useful indicators. By contrast, indicators derived from the small fraction performed poorly, and those based on the pooled community demonstrated a varied ability to detect trawling. Small macrofauna are typically characterised by high density, diversity, and population growth rates, and their relative resilience to trawling may mask the response of the more sensitive macrofauna. This highlights an underlying issue with calculating indicators based on the whole benthic community. The approach outline here is easily applied, improves indicator performance, and has the potential to reduce laboratory workloads due to the fewer taxa and individuals required for analyses.
... Our a priori expectation was that the biological mediation of carbon and nutrient cycling would differ with sediment type, irrespective of species composition, and that projections of the ecosystem consequences of altered biodiversity within these environments would not follow the same trajectory pattern. Further, we anticipated that the average body-size of the community would decrease with increased levels of trawling pressure [51,52] and, because of the importance of body size in determining a species functional contribution [53,54], would lead to an accelerating decline in seabed functions as trawling pressure increases. Realisation of these expectations would emphasize the importance of context in determining the ecological consequences of altered biodiversity. ...
... Our projections suggest that compensation following bottom trawling is primarily undertaken by taxa belonging to the same functional groups (slow biodiffusers, Mi/Ri 3-4; surficial modifiers, Mi/Ri 3-2; and conveyor belt feeders, Mi/Ri, 2-3, sensu [9]). This is broadly in agreement with expectations that sessile or low mobility taxa living at and/or around the sediment-water interface (Mi and Ri lower than 2) are predominantly impacted by bottom trawling [57,106] and is consistent with previous findings [52,57] that emphasise the importance of functional redundancy exercised by smallersized species. Nevertheless, functioning does not appear to be as sensitive to extinction per se as it does to the loss of specific taxonomic groups because high levels of functioning have been reported for low levels of species richness [17,97,107]. ...
... #Creating the data frame output <expand.grid(Simulation = 1:nsims, Nsp = nsp:1, ExtSp=NA, CompSp=NA, AbnComp=NA, BioExt=NA) # Sort the output dataframe for clarity output <-output[order(output$Simulation),] ###Simulations for (sim_count in 1:nsims){ #browser() cat("sim_count: ", sim_count, "\n") # Reset parameters to their respective starting value after each simulation start$AiSim <-start$Aavg #Abundance start$BiSim <-start$Bavg #Biomass start$EPSimTheo <-start$ExtProb #Extinction probability start$EPSim <-start$ExtProb #Extinction probability start$EPSim[start$AiSim ==0] <-0 #Only present taxa can go extinct start$EPSim<-start$EPSim / sum(start$EPSim) # Normalise start$CPSim <-start$CompProb output[output$Simulation == sim_count & output$Nsp==sp_count, "sNOx_L_BPc"] <-sNOx_L_BPc #********************************************************************************** ****** # if sand chosen -run the below********************************************* #CHLA_BPc <-exp ( #********************************************************************************** ****** # Randomly pick a taxa to go extinct based on probability Extinct <which(cumsum(start$EPSim)>=runif(1)) [1] # How much biomass will be lost with the doomed taxa 52 BiomassLost <-start[Extinct,"BiSim"] # Picking the compensatory taxa # Taxa going extinct cannot compensate start[Extinct,"CPSim"] <-0 start$CPSim<-start$CPSim / sum(start$CPSim) # Normalise Compensate <which(cumsum(start$CPSim)>=runif(1)) [ 5.53,],aes(x=Nsp,y=BPc))+ geom_point(colour="grey",alpha=0.1)+ stat_density2d(aes(fill=..level.., alpha=..level..), size=3, bins=20, geom='polygon') + theme_bw()+ theme(legend.position="none") ...
Article
A research agenda is currently developing around predicting the functional response of ecosystems to local alterations of biodiversity associated with anthropogenic activity, but existing conceptual and empirical frameworks do not serve this area well as most lack ecological realism. Here, in order to advance credible projections of future ecosystems, we use a trait-based model for marine benthic communities to inform how increasing trawling pressure changes the biological-mediation of seabed functioning. Our simulations reveal that local loss of species, and the associated compensatory community response, lead to multiple and disparate biogeochemical alterations that are contingent on relative vulnerabilities to extinction, environmental and biological context, and the level of functional redundancy within replacement taxa. Consequently, we find that small changes in faunal mediation caused by community re-organisation can disproportionately affect some biogeochemical components (macronutrients), whilst having less effect on others (carbon, pigments). Our observations indicate that the vulnerability of communities to future human-induced change is better established by identifying the relative magnitude and direction of covariance between community response and effect traits. Hence, projections that primarily focus on the most common or most productive species are unlikely to prove reliable in identifying the most likely ecological outcome necessary to support management strategies.
... To validate the developed indices, we used macrofauna data previously collected over an active fishing ground for Norway lobster (Nephrops norvegicus, Linnaeus) and gadoid fish in the north-eastern Irish Sea in 2007. This data was previously published by Hinz et al. (2009) to investigating the effects of chronic trawling on benthic communities. For more detailed information about the sampling design, as well as the fishing effort calculation, refer to Hinz et al. (2009). ...
... This data was previously published by Hinz et al. (2009) to investigating the effects of chronic trawling on benthic communities. For more detailed information about the sampling design, as well as the fishing effort calculation, refer to Hinz et al. (2009). In short, macrofauna data was collected at 15 sites over a gradient of fishing intensity varying from 1.3 times trawled/year to 18.2 times trawled/year. ...
... The effectivity of the indices to represent the overall vulnerability of species to trawling was validated by comparing the calculated RRI scores of individual species to observed responses of those same species over a gradient of trawling intensity (as recorded by Hinz et al., 2009), using linear regression slopes. Prior to analysis, the individual species biomass data was normalized. ...
Article
Full-text available
The physical impact of bottom towed fishing gears does not only reduce the abundance and biomass of species, but also alter the overall species composition and, through this, the functioning of benthic communities. The vulnerability of a species is determined by its individual combination of morphological, behavioural and life history traits. In turn, ecosystem functions are most affected when those species identified as vulnerable, contribute disproportionately to that function. On the basis of this paradigm, trait-based indices of physical resistance (RI) and recovery potential (RPI) were developed and combined into an overall vulnerability index on a species level, the RRI or Resistance and Recovery Potential Index. The developed indices can be used to explore how resistance and recovery potential of benthic communities change over different levels of trawling. Furthermore, the RRI allows for dividing the benthic community into groups expressing different levels of vulnerability that can be linked to ecosystem functions to explore functional vulnerability to trawling. The RRI index futher opens up the possibility for scenario modelling by simulating the extinction or loss of vulnerable species and its effects on functions. This may be of particular interest in data poor case studies that lack trawling gradient data, or to explore the consequences of potential increases in fishing effort. The validity of the trait-based RRI index was tested by comparing individual species' RRI scores to empirically observed responses over a trawling gradient. RRI score and observed responses (regression slopes) were significantly correlated providing support for the rationality of the approach. Moreover, further analysis of the data evidenced clear increases of resistance and resilience indices over the trawling gradient, demonstrating that communities lost vulnerable species with increasing trawling. When exploring the effects of trawling on the bioturbation, as a chosen ecosystem function, we found it to be disproportionately affected though the loss of vulnerable species. The proposed indices provide new insights into the link of species vulnerability and function. Such information is of vital interest to environmental managers focused on preserving ecosystem functions and services in the face of anthropogenic global change.
... Together, these studies demonstrate high sensitivity of epifaunal communities to fishing, which can affect population size structure (Hinz et al. 2009), alter community composition (Hinz et al. 2009) and reduce the maximum size of organisms within the community (e.g. 17% reduction in mean size, Lambert et al. 2011), overall epifaunal biomass (Hinz et al. 2009, Lambert et al. 2011) and species richness. ...
... Together, these studies demonstrate high sensitivity of epifaunal communities to fishing, which can affect population size structure (Hinz et al. 2009), alter community composition (Hinz et al. 2009) and reduce the maximum size of organisms within the community (e.g. 17% reduction in mean size, Lambert et al. 2011), overall epifaunal biomass (Hinz et al. 2009, Lambert et al. 2011) and species richness. ...
... Together, these studies demonstrate high sensitivity of epifaunal communities to fishing, which can affect population size structure (Hinz et al. 2009), alter community composition (Hinz et al. 2009) and reduce the maximum size of organisms within the community (e.g. 17% reduction in mean size, Lambert et al. 2011), overall epifaunal biomass (Hinz et al. 2009, Lambert et al. 2011) and species richness. The focus on benthic habitat degradation via fishing methods continues to the present (e.g. ...
... Another anthropogenic factor which is known to cause widespread changes in benthic ecosystems is bottom trawling (Jennings and Kaiser, 1998;Frid et al., 2000;Kaiser et al., 2002). The physical disturbance caused directly by bottom trawling causes alteration in seabed morphology, damage or destruction of biota etc., which ultimately lead to substantial, long-term changes in benthic community structure and food webs (Kaiser et al., 2002;Zhou et al., 2007;Hinz et al., 2009). High trawling intensity over long periods of time is known to reduce the abundance of larger and more common but vulnerable species (e. g. echinoderms), and lead to increased abundance of small-sized, burrowing opportunists (e. g. ...
... High trawling intensity over long periods of time is known to reduce the abundance of larger and more common but vulnerable species (e. g. echinoderms), and lead to increased abundance of small-sized, burrowing opportunists (e. g. Prionospio spp.) (Zhou et al., 2007;Hinz et al., 2009;De Juan et al., 2011;Jørgensen et al., 2016). The continental shelf off the west coast of India, particularly between ~30-100 m depths, is an area with intense fishing activity, particularly bottom trawling for crustaceans and demersal finfishes. ...
... The silty sand sediments of the study area prove ideal for bottom trawl operations. While studies have shown that short-term impacts of trawling may be modest in such sediments (Hinz et al., 2009), the changes could potentially accumulate over longer periods of time (e. g. on decadal scales). ...
Article
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Changes in macrozoobenthic standing stock and composition along the south-eastern Arabian Sea continental shelf (30–200 m) are investigated, based on data collected from the same sites during the same season 14 years apart (winter monsoon, 1998 and 2012), using the same platform, sampling gear, methods etc. During both surveys, polychaetes dominated among the macrozoobenthos, followed by crustaceans and molluscs. A decline in macrozoobenthic density and biomass with increasing depth was noted in both surveys. Macrozoobenthic density increased significantly between 1998 and 2012, especially in the inner and mid shelf (30–50 m), due to the increase in density of polychaetes and molluscs, while the density of crustaceans decreased. The mean individual body weight of polychaetes decreased between 1998 and 2012, most notably in the inner and mid shelf (30–50 m). This reflected an overall increased dominance of small-sized opportunists such as spionids, magelonids, paraonids, cirratulids and pilargids in 2012 across the entire shelf. Such an increase in dominance of opportunists and decline in abundance of sensitive taxa is indicative of long-term environmental stress and anthropogenic pressure. However, no significant changes were noted in the measured environmental variables which are known to influence benthic faunal distribution in the region, such as sediment nature and oxygen availability. The observed changes may rather be indicative of the long-term effect of intense bottom trawling, which is practiced in the study area year-round. This is the first study of its kind for soft-sediment shelf benthos from the tropical belt.
... The effect of bottom trawling on sediment infauna is well studied (Hinz et al. 2009;Hiddink et al. 2017). Much less in known about the effect of bottom trawling on benthic biogeochemical processes (ecosystem function) (e.g., Olsgard et al. 2008;Pusceddu et al. 2015;Sciberras et al. 2016); there has only been one study on the critical ecosystem process of denitrification, and it showed no effect of trawling (Trimmer et al. 2005). ...
... However, based on the inspection of 5 years of trawl effort data supplied by the trawler employed for this study, it is likely that effort is considerably higher in adjacent areas along the trawl exclusion boundary for periods of the year. As such, chronic impacts on benthic denitrification may still occur under higher trawl intensities or from trawling over a longer period (see Hinz et al. 2009). This will particularly be the case if, under higher trawl intensities, there is a long-term negative effect on benthic infauna abundance, biomass and/or diversity, as has previously been reported (Collie et al. 2000;Kaiser et al. 2006;Sköld et al. 2018). ...
Article
Full-text available
Bottom trawling and eutrophication are large stressors that are critically coupled. Here we show, using a before‐after control‐effect design, the significant reduction in denitrification as a result of experimental bottom trawling in a shallow coastal system. Trawl disturbance destroys the complex three‐dimensional redox structures in surface sediments that maximize denitrification potential, resulting in up to a 50% reduction in net denitrification. The decrease in net denitrification also increased after each trawling event suggesting a declining resilience to trawling and eutrophication. Bottom trawling occurs at such a large scale that it could result in significant amounts of nitrogen being retained on the continental shelf. As such, impacts on the global ocean nitrogen cycle and associated eutrophication should be counted among the many negative consequences of extensive seafloor trawling.
... These pressures are pervasive and long-lasting, with improved technologies over the last two centuries, and in particular since the 1950s, increasing the spread of mobile fishing gears to deeper waters and much of the global ocean (Kroodsma et al., 2018;Morato et al., 2006;Roberts, 2007;Watson & Morato, 2013). Compared to many other types of stressors, in intensively fished areas, trawling and dredging can also occur on the same area of seabed numerous times in a year (Eigaard et al., 2017;Hinz et al., 2009;Oberle, Storlazzi, & Hanebuth, 2016;Tillin et al., 2006). ...
... The largest impacts follow initial experimental trawling events or are seen when comparisons are made to an area of long-standing protection (Cook et al., 2013;Thrush & Dayton, 2002). Many studies may underestimate the damage done by mobile fishing gears and overestimate the speed of recovery because they measure the recovery of areas already impacted (Collie et al., 2000;Cook et al., 2013;Hiddink et al., 2017;Hinz et al., 2009;Kaiser et al., 2002Kaiser et al., , 2006Sciberras et al., 2018). ...
Article
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Subtidal marine sediments are one of the planet's primary carbon stores and strongly influence the oceanic sink for atmospheric CO2. By far the most widespread human activity occurring on the seabed is bottom trawling/dredging for fish and shellfish. A global first‐order estimate suggested mobile demersal fishing activities may cause 0.16–0.4 Gt of organic carbon (OC) to be remineralized annually from seabed sediment carbon stores (Sala et al., 2021). There are, however, many uncertainties in this calculation. Here, we discuss the potential drivers of change in seabed sediment OC stores due to mobile demersal fishing activities and conduct a literature review, synthesizing studies where this interaction has been directly investigated. Under certain environmental settings, we hypothesize that mobile demersal fishing would reduce OC in seabed stores due to lower production of flora and fauna, the loss of fine flocculent material, increased sediment resuspension, mixing and transport and increased oxygen exposure. Reductions would be offset to varying extents by reduced faunal bioturbation and community respiration, increased off‐shelf transport and increases in primary production from the resuspension of nutrients. Studies which directly investigated the impact of demersal fishing on OC stocks had mixed results. A finding of no significant effect was reported in 61% of 49 investigations; 29% reported lower OC due to fishing activities, with 10% reporting higher OC. In relation to remineralization rates within the seabed, four investigations reported that demersal fishing activities decreased remineralization, with three reporting higher remineralization rates. Patterns in the environmental and experimental characteristics between different outcomes were largely indistinct. More evidence is urgently needed to accurately quantify the impact of anthropogenic physical disturbance on seabed carbon in different environmental settings and to incorporate full evidence‐based carbon considerations into global seabed management. Subtidal marine sediments are one of the planet's primary carbon stores and strongly influence the oceanic sink for atmospheric CO2. Considering basic principles, we hypothesize that under certain environmental settings, trawling/dredging for fish and shellfish would reduce seabed sediment carbon storage; however, this may be offset by positive feedback mechanisms in some circumstances. A review of studies which directly investigated this impact in situ also highlighted mixed results. More evidence is urgently needed to accurately quantify this impact in different environmental settings, and incorporate full evidence‐based carbon considerations into global seabed management.
... Measuring the impacts of trawling 2.2.1.1. extrapolate findings to the ecosystem scale at which fisheries operate (Hinz et al., 2009). Most studies are of the 'compare and contrast type', examining the benthic ecosystem in areas that have been subject to differing levels of fishing intensity. ...
... In shallow water, the impacts of fishing disturbance on infauna have been well studied (Collie et al., 2000, Kaiser et al., 2002, Hinz et al., 2009. However, in the deep sea there is limited knowledge on the impacts on infauna (Leduc and Pilditch, 2013), even less than for epifauna, presumably due to the challenges of sampling and the costs of conducting experiments. ...
Thesis
The deep sea (>200 m) is the world’s least explored and largest biome, covering ~65% of the earth’s surface, it is increasingly subject to anthropogenic disturbance from fishing. The offshore Greenland halibut (Reinhardtius hippoglossoides) fishery, west Greenland, employs demersal trawl gear at depths of 800-1,400 m. Recent Marine Stewardship Council (MSC) certification of this fishery highlighted the paucity of knowledge of benthic habitats and trawling impacts. This interdisciplinary thesis employs a benthic video sled to investigate deep-sea habitats and trawling impacts and conducts a critical analysis of the fishery’s governance, with reference to the role of the MSC certification. The results provide new insights into this poorly known region of the Northwest Atlantic, including identifying four candidate vulnerable marine ecosystems (VMEs). Imagery obtained demonstrates that chronic trawling has had extensive impacts on the seafloor, which are significantly associated with the benthic communities observed. Further, trawling effort is shown to have a significant negative association with the abundance of some VME indicator taxa. The governance case study finds an effective system of state-led governance, supported by scientific, certification and industry actors. Outcomes directly attributable to engagement with the MSC certification include the introduction of a management plan and new benthic research programmes. However, questions are raised about the MSC certification, providing case study examples of existing criticisms. Assessments are weak with respect to benthic habitats and overreliant on the definitive, expert judgement of Conformity Assessment Bodies (CABs), whose independence is questioned. The assurance offered by the MSC certification in terms of the sustainability of trawling impacts on benthic ecosystems is found to seriously lack credibility. Findings are of direct relevance to the management of deep-sea fisheries in Greenland and elsewhere. Widely applicable critical insights into deep-sea fishery governance are presented, including into the role of eco-labels as a market-mechanism to promote sustainable fishery management.
... Comparing the spatiotemporal effects of bottom trawling on the benthic community may reveal a negative cumulative effect in areas with a long history of fishing. These potential effects can cause the biota to recover slowly, especially sessile organisms, and consequently affect the entire trophic network (Hiddink et al. 2006;Hinz et al. 2009;Jørgensen et al. 2016). In the present study, the interannual variability detected by the models in the probability of occurrence of the assemblages identified could be a signal of the effects of the intensity of the fishing efforts. ...
Article
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In Chile, bottom trawling for squat lobsters is one of the most important crustacean fisheries. The fishery has been monitored for the last 15 years to assess the resource status, spatial distribution, and effects on benthic species. It is of critical importance to understand the interactions of fishing and non-fishing activities with the benthic communities to estimate the potential bycatch of important economic species from fishing operations and to determine adequate spatial and temporal fishing bans. In this study, we characterized the community of the main non-target species caught during historical squat lobster biomass surveys from 2000 to 2015 and interpreted the included species as potential bycatch of the fishery. We found 4 ecological assemblages, which differed in abundance but not in species richness, which suggested that the community structures did not differ among the areas but rather in the relative abundances of the species. We also created habitat suitability maps for the identified groups and discussed the effect of the environment and the survey method on the distribution of the groups. Managers can use this information to detect regions with high bycatch risk for demersal trawl fisheries and to understand the potential interaction of fishing operations with the environment.
... Larger-sized taxa can dilute trawl-induced impacts on community biomass (Hinz et al., 2009) and likely led to the inconsistent patterns in biomass found between treatments in this study. C. subterranea, was observed in higher densities in trawled shallow cores where it significantly contributed to the community biomass, (Figure 6). ...
Thesis
SUMMARY SECTION. Bottom trawling can cause severe alterations on benthic ecosystems, however, we are just beginning to understand how these disturbances can affect biogeochemical functioning and benthic pelagic coupling. The cycling of carbon, oxygen and nutrients regulate the existence of Earth’s ecosystems but can also be significantly affected by the organisms living in these habitats. As trawling has a direct impact on both biogeochemical and organismal parameters, the net effect on benthic pelagic coupling can be complex and difficult to predict. European waters exhibit some of the highest levels of trawling on Earth (Amoroso et al., 2018). Bottom trawling in the North Sea, as well as opposition against it, has been occurring for well over 600 years (Collins, 1887). In recent times, novel ‘electric pulse’ fishing methods, occurring in the North Sea, have been steeped in controversy concerning their unstudied ecosystem effects (Kraan et al., 2020). This PhD aims to uncover some of the mysteries behind bottom trawl-induced effects on benthic pelagic coupling and to discover the potential effects of electric pulse trawls on biogeochemistry and ecosystem functioning. The research in this thesis begins with a large-scale field study conducted to compare the in situ impacts of electric pulse and traditionally used tickler chain beam trawl techniques (Chapter 2). This study was conducted in the Frisian Front region of the North Sea in collaboration with professional fishermen to produce intensively trawled areas. Here, we discovered that acute trawling could significantly reduce the benthic mineralization of organic matter (OM) while reallocating some of the metabolic activity into the water column. This was accompanied with a deepening of the sedimentary oxic layer suggesting lower levels of biological activity for these sediments due to decreased OM content and possibly reduced microbial densities caused by the trawl-induced removal of surficial sediment. Reduced benthic metabolism after trawling was attributed to a steep decline in labile OM on surface sediments, also implying lower food availability for benthic organisms. Although both fishing methods caused significant biogeochemical alterations, an overall reduced impact could been seen in pulse trawls versus traditional methods. Chapter 3 takes data from the same field campaign as chapter 2, this time investigating the effects of bottom trawls on benthic ecological communities and physical changes. Acoustic and optical techniques revealed a flattening of the seabed and a reduction of burrow holes made by benthic organisms. A severe decline in epibenthos and juvenile taxa after trawling was accompanied with increases of the deep burrowing mud shrimps, Callianassa subterranea. These results suggest that while organisms residing near the sediment surface were removed by bottom trawling, fauna that had escaped trawling in deep burrows will spend more time close to the sediment surface, possibly fixing damaged/buried burrow entrances, after trawling impact. Historical information shows a regime shift occurring in the Frisian Front, which was once home to high abundances of shallow burrowing brittle stars (Amphiura filiformis) but is now a C. subterranea dominated habitat (Amaro, 2005). Our results suggest that trawling may have facilitated this shift in species. Unlike the previous study (chapter 2), here our results did not detect a differential effect of pulse or conventional beam trawls implying that they can have similar effects on benthic communities in soft sediments. To better understand the biogeochemical effects from mechanical-induced sediment resuspension and potential electrolysis, Chapter 4 simulated these disturbances in controlled mesocosms. Sediments were taken from 9 North Sea and 2 Easter Scheldt locations and received either mechanical mixing perturbations in the surface layers (to represent physical disturbances from trawling), or electrical exposures of 3 or 120 seconds from pulsed bipolar currents (PBC) or pulsed direct currents (PDC). Mechanical disturbances released the equivalent of 90+ hours of natural nutrient effluxes in some sediments, while rapidly depleting water column oxygen. Electrolysis was only detected in sediments exposed to 120 seconds of PDC. This treatment caused the electric-induced movement of porewater ions creating the formation of iron oxides on the sediment surface, subsequently binding to phosphorus in the water column. Mechanical and PDC-induced alterations to solute concentrations were linked with labile OM content, sediment grain size, and time of year when sediments were collected. These results suggest that PBC employed by the pulse trawling used for flatfish is not likely to generate biogeochemical effects while direct currents, which have been employed in Ensis electrofishing, may affect marine phosphorus dynamics. Furthermore, our findings show that mechanical disturbance will have a higher biogeochemical impact in the late summer/early autumn, in soft sediments rich with labile OM. Chapter 5 documents a study, which combined physical, biogeochemical and ecological data collection techniques, resulting in one of the most comprehensive acute effects focused bottom trawling studies to date. We worked with professional fishermen to create multiple trawled treatment areas in the dynamic coastal waters ofthe Vlakte van de Raan, in habitats dominated by Lanice conchilega reefs. Here we detected significant declines of 46% and 57% in sediment oxygen consumption from pulse and tickler chain beam trawls respectively, which was attributed to a decrease in faunal-mediated biogeochemical functioning. Trawling also decoupled relationships between L. conchilega and abundances of other macrofauna, oxygen consumption, sediment characteristics, and nitrate fluxes. Our study shows that biogenic habitats are vulnerable to ecological and biogeochemical changes from trawling, even in dynamic sandy areas where disturbance effects are expected to be lower. Pulse trawls showed more inconsistent effects compared to beam trawls, leading to a lower average impact, though these methods can sometimes create equal levels of disturbance. The research in this thesis concludes with a discussion on the applied and fundamental implications of the research carried out during this PhD (Chapter 6). Our findings show a slightly reduced direct impact from pulse versus beam trawls, though significant effects can be expected from both gear types. We found that pulse trawls do not elicit a significant electrochemical response and have a slightly lower effect on biogeochemical parameters compared to conventional methods due to less mechanical disturbance. In light of other research, however, the main benefit of pulse trawls compared to tickler chain beam trawls has less to do with any decreased direct environmental impact but rather with the efficiency of pulse trawl gears, which leads to less time at sea and a reduced ecological footprint (Rijnsdorp et al., 2020). While we can ascertain if certain gears produce greater biogeochemical effects than others, we still have only a limited understanding of the larger scale (fundamental) implications of these effects. Our findings of lower mineralization may create consequences related to reduced nutrient cycling of sedimentary habitats. More research is necessary to understand the consequences of bottom trawling on holistic ecosystem processes including benthic pelagic coupling, but the work conducted during this PhD was able to uncover some important information that contributes to a more complete understanding of this topic.
... Moreover, the formation of reserves aids to restore the structure and complexity of the ecosystem in those MPAs that have been under overexploitation pressure previous to reserve formation (Sala and Giakoumi 2017). A bulk of the research has demonstrated that after intense fishing activities, ecosystems usually undergo drastic changes in fish assemblage structure and composition (Hinz et al. 2009). For example, fish biomass in marine reserves is, on average, 670% greater than in adjacent unprotected areas, and approximately 343% greater than in partially-protected MPAs (Sala and Giakoumi 2017). ...
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The first non-coastal Sub-Antarctic Marine Protected Area (Namuncurá) in Argentina was created in 2013, at Burdwood Bank (MPAN-BB), an undersea plateau located about 200 km south from Malvinas/Falkland Islands, SW Atlantic Ocean. The main contribution of this work was to explore fish species composition and the structure of fish assemblages in three different zones of the MPAN-BB with different conservation strategies and different surrounding areas. Twenty-two fishing trawls were performed using a demersal bottom trawl pilot net at depths between 71 and 608 m. A total of 667 fish belonging to 30 species were collected in the surveyed area. The richest family in terms of species number was Nototheniidae (seven species), followed by Macrouridae, Myxinidae and Zoarcidae (four species each), then Moridae and Arhynchobatidae (three species each), and finally Muraenolepididae and Psychrolutidae (two species each). The remaining families were represented by a single species. Three significantly different fish assemblages were detected. These distinct assemblages were largely circumscribed at the plateau, the shelf-break slope, and the area west of the BB. The results showed that fish diversity in the MPAN-BB is relatively high constituting ~ 10% of the fish composition reported for the Atlantic sector of the Magel-lanic Province. The present data suggest that fishes are an important component of the benthic community planned to be protected by the implementation of the MPAN-BB. These findings have important implications for habitat preservation and threatened species conservation.
... Industrial trawlers which registered as the highest cause of the reduction in the stock of fish can be seen as a globally used fishing gear that physically disturb the seabed and kill non-target organisms, including those that are food for the targeted. This is also consistent with, the work of Hinz et al. (2009). However, other causes for the reduction in the stock of fish identified were an increase in the number of fishermen at sea, and dynamite fishing also contribute to these declines. ...
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This study assessed the vulnerability and coping livelihood strategies of fishermen within the context of declining marine fisheries in Elmina, Ghana. One hundred and fifty-five (155) fishermen were purposively selected for questionnaire interviews from January to March 2017. The results showed that most of the fishermen depended heavily on fishing as a major source of livelihood. Nonetheless, their income levels were trifled due to declining fisheries. The vulnerability index of the community proved to be significantly high. The coping livelihood strategies were largely informal, comprising farming and trading, among others. A little over half of the fishermen were willing to leave the fishing sector for different livelihoods, given other prospects. It is concluded that improving livelihoods in the community will require strengthening supplementary livelihood occupations, and educating fishers on the dangers of using illicit fishing methods are required for the growth of the sector and enhancement of income levels of fishermen.
... While the benefits of the batwing otter board are clear, it might be possible to retroactively modify conventional otter boards to similarly reduce habitat impacts. As one example, reducing the bottom contact of a conventional otter board to two points via sleds angled to the tow direction or rollers on articulated joints (proposed by Kennelly and Broadhurst 2002) might allow some habitat to pass beneath the main length of the otter board unimpeded and reduce the impacts to various sessile organisms, including bivalves (Gilkinson et al. 1998;Hinz et al. 2009). Such alternatives warrant investigation, considering that replacing conventional otter boards with completely new designs would be expensive in some fisheries. ...
Article
A benthic trawl’s substrate contact (e.g. spreading mechanisms (i.e. otter boards) and ground gears) determines both its catching efficiency and the extent of perceived habitat impacts. The potential for mitigating habitat impacts was investigated here via the novel ‘batwing’ otter board and ‘soft-brush’ ground gear. A purpose-built testing assembly towed treatments across three artificial habitat types with incrementally greater detachment thresholds (~ 8, 32 and 56 N), and the batwing and soft-brush were alternately compared against a conventional flat-rectangular otter board and three chain ground gears (6-, 8- and 10-mm diameter link), respectively. Overall, during 48 alternate deployments, the batwing removed up to 61% fewer of all habitats than the flat-rectangular otter board. By comparison, during 42 alternate replicates, the soft-brush ground gear failed to displace any habitat, while all three chain ground gears similarly removed between 3 and 5% of the two least resistant habitats (irrespective of position). The results imply the perceived impacts of penaeid trawls across sensitive areas can be reduced via simple modifications to spreading mechanisms and ground gears, along with appropriate spatio-temporal regulation. This study represents a unique approach to understanding the relative differences in impacts between ground gears and commercial-sized otter boards under controlled conditions.
... Trawling is known to impact the structure and functioning of benthic ecosystems (Alverson et al. 1994;Collie et al. 2000;Hinz et al. 2009;Hiddink et al. 2017). The pressure of constant extraction can damage the maintenance of populations as it impacts recruitment, reproduction and growth of specimens (Stanski et al. 2016). ...
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Studies of the bycatch associated to the shrimp trawling fishery in the Pacific coast of Costa Rica do not assess small organisms (< 10 cm TL) and non-dominant species (< 0.1% of total catch). There is a void in assessing the maintenance of the ecology and ecosystem on which the fishery depends. Furthermore, the Constitutional Court of Costa Rica prohibited the renewal of existing and the issuing of new shrimp bottom-trawl licenses, indicating the necessity of more scientific information on the impacts of this fishery. We present the results of a 23-month study of the shrimp bottom-trawl fishery performed between 50 and 350 m deep in the Pacific coast of Costa Rica. A total of 109 hermit crabs were collected (six species and two families). Paguristes cf. holmesi was the most common species. Zone II presented the highest species richness and abundance. Most specimens (81.8 %) were caught in shallower waters (50-149 m). More than 45% of the trawls presented hermit crabs. It is imperative to further assess the trawling effects on non-commercial benthic fauna and changes on predator-prey relationships before issuing new shrimp licenses
... Con respecto al efecto del arrastre en esta comunidad, se observó la disminución de organismos sésiles y frágiles, y el aumento de organismos depredadores y/o detritívoros al compararse con áreas de exclusión pesquera ; Escolar en evaluación), tal como sucede en la mayoría de las comunidades bentónicas sujetas a arrastres de fondo (Kaiser et al. 2000;Hinz et al. 2009). Este aumento se relacionó con el incremento en la disponibilidad de alimento, producto del descarte de los buques comerciales de vieira y de los organismos dañados por el paso de la red (Jennings et al. 2001). ...
Article
La vieira patagónica Zygochlamys patagonica (King 1832) es un molusco bivalvo que se distribuye alrededor de América del Sur en el área comprendida entre los 36° S en el Océano Atlántico y los 42° S en el Océano Pacífico. Las agregaciones más importantes a nivel comercial se encuentran en el Océano Atlántico a lo largo del frente de talud asociadas a la isobata de 100 m. La pesquería de esta especie en la Argentina se inició formalmente en 1996 con el esfuerzo pesquero de cuatro buques factoría arrastreros. En los últimos años el promedio de desembarques anuales se situó alrededor de las 5.000 t con un valor medio de USD 9.300 la tonelada de callo, cifra que la ubicaron entre las cuatro pesquerías más importantes del país. En el presente trabajo se describen los avances recientes en materia de investigación científica a 22 años de su inicio. Se detallan, además, los aspectos más relevantes en lo que respecta a biología, explotación comercial y evolución de las medidas de administración que llevaron a establecer un sistema de manejo adaptable.
... Collie et al., 2000;Kaiser et al., 2006;Clark et al., 2016a;Hiddink et al., 2017;Sciberras et al., 2018). Contact of trawl gear with the seabed directly impacts the benthos by crushing, damaging, and removing benthic biota (Fig. 2), and reducing species abundance and biomass (Koslow et al., 2001;Fosså et al., 2002;Hall-Spencer et al., 2002;Hinz et al., 2009). Trawling impacts vary across habitats, and it is probable that they are more severe on isolated topographical features such as seamounts due to the aggregation of fishing effort over small areas (O'Driscoll and Clark, 2005). ...
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Despite bottom trawling being the most widespread, severe disturbance affecting deep-sea environments, it remains uncertain whether recovery is possible once trawling has ceased. Here, we review information regarding the resilience of seamount benthic communities to trawling. We focus on seamounts because benthic communities associated with these features are especially vulnerable to trawling as they are often dominated by emergent, sessile epifauna, and trawling on seamounts can be highly concentrated. We perform a meta-analysis to investigate whether any taxa demonstrate potential for recovery once trawling has ceased. Our findings indicate that mean total abundance can gradually increase after protection measures are placed, although taxa exhibit various responses, from no recovery to intermediate/high recovery, resistance, or signs of early colonisation. We use our results to recommend directions for future research to improve our understanding of the resilience of seamount benthic communities, and thereby inform the management of trawling impacts on these ecosystems.
... Finally, activities that result in bottom disturbance, such as the installation and operation of renewable energy or the extraction of aggregates, can lead to the destruction of benthic habitats (Gill 2005, Foden et al. 2010). Many benthic invertebrates are sensitive to habitat disturbance and often suffer high mortality leading to reduced biomass, production, and species richness (Hinz et al. 2009). ...
Article
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The Maritime Spatial Planning (MSP) Challenge simulation platform helps planners and stakeholders understand and manage the complexity of MSP. In the interactive simulation, different data layers covering an entire sea region can be viewed to make an assessment of the current status. Users can create scenarios for future uses of the marine space over a period of several decades. Changes in energy infrastructure, shipping, and the marine environment are then simulated, and the effects are visualized using indicators and heat maps. The platform is built with advanced game technology and uses aspects of role-play to create interactive sessions; it can thus be referred to as serious gaming. To calculate and visualize the effects of planning decisions on the marine ecology, we integrated the Ecopath with Ecosim (EwE) food web modeling approach into the platform. We demonstrate how EwE was connected to MSP, considering the range of constraints imposed by running scientific software in interactive serious gaming sessions while still providing cascading ecological feedback in response to planning actions. We explored the connection by adapting two published ecological models for use in MSP sessions. We conclude with lessons learned and identify future developments of the simulation platform.
... Larger-sized taxa can dilute trawl-induced impacts on community biomass (Hinz et al., 2009) and likely led to the inconsistent patterns in biomass found between treatments in this study. C. subterranea, was observed in higher densities in trawled shallow cores where it significantly contributed to the community biomass (Fig. 6). ...
Article
In this study, we analysed the benthic effects of two in situ fisheries disturbance experiments using a combination of side-scan sonar, high definition underwater video, sediment profile imagery, and box core sampling techniques after conventional beam trawling and box core sampling after electric pulse trawling in a southern North Sea habitat. Acoustic and optical methods visualised the morphological changes induced by experimental beam trawling, showing the flattening and homogenisation of surface sediments. Video transects found a 94% decrease in epibenthos in beam trawled sediments compared to an untrawled control site and a 74% decrease in untrawled sediments of the same transect. Box core samples taken 5.5 h, 29 h and 75 h after trawling detected a downward trend in infaunal densities and species richness that continued after the initial impact with small-bodied and juvenile taxa being especially prone to depletion. Data from shallow sediment samples showed trawl resilience in large mud shrimps and evidence of their upward movement towards the sediment surface after disturbance. Both trawl gears induced significant changes to infaunal communities, with no differential effect between the two gears. Our results suggest that in the Frisian Front, trawling may favour the survival of deep burrowers while removing surficial macrofauna.
... Comparing the spatiotemporal effects of bottom trawling on the benthic community may reveal a negative cumulative effect in areas with a long history of fishing. These potential effects can cause the biota to recover slowly, especially sessile organisms, and consequently affect the entire trophic network (Hiddink et al. 2006;Hinz et al. 2009;Jørgensen et al. 2016). In the present study, the interannual variability detected by the models in the probability of occurrence of the assemblages identified could be a signal of the effects of the intensity of the fishing efforts. ...
Article
In Chile, bottom trawling for squat lobsters is one of the most important crustacean fisheries. The fishery has been monitored for the past 15 years to assess the resource status, spatial distribution and effects on benthic species. Understanding the interactions of fishing and non-fishing activities with the benthic communities is of critical importance to estimate the potential bycatch of important economic species from fishing operations and to determine adequate spatial and temporal fishing bans. In this study we characterised the community of the main non-target species caught during historical squat lobster biomass surveys from 2000 to 2015 and interpreted the species included as potential bycatch of the fishery. Four ecological assemblages were found that differed in abundance but not in species richness, which suggests that the community structures did not differ among the areas, but rather in the relative abundances of the species. In addition, we created habitat suitability maps for the groups identified and discuss the effects of the environment and the survey method on the distribution of the groups. Managers can use this information to detect regions with high bycatch risk for demersal trawl fisheries and understand the potential interaction of fishing operations with the environment.
... Collectively, the commercial fishing of these species is lucrative (e.g. M. challengeri is valued at US $40 kg −1 ; Seafood New Zealand 2019), resulting in their habitats being exposed to continuous bottom trawling over decades, which may influence their diet, and has likely altered benthic food web dynamics (Jones 1992, Thrush & Dayton 2002, Hinz et al. 2009, Ogilvie et al. 2018, Hiddink et al. 2019. Catchpole et al. (2006) identified that discards from the Norway lob ster Nephrops norvegicus (a close relative of Metane phrops) fisheries create a positive feedback loop, with the energy gained from the discards potentially providing more than 30% of their energetic requirements during the fishing seasons. ...
Article
Deep-sea benthic ecosystems are difficult to study, particularly when trying to clarify diet and trophic relationships. New Zealand scampi Metanephrops challengeri are endemic, commercially prized deep-sea lobsters that are bottom trawled. These lobsters are typically the dominant mobile megafaunal species in the deep-sea benthic habitat, and their burrowing behaviour plays an important role in bioturbation of seafloor habitats. DNA metabarcoding was undertaken on the gut contents of 66 scampi from 4 fishery management areas using COI and 18S rRNA markers to better understand their feeding habits and trophic role. Scampi were confirmed to be opportunistic benthic scavengers, with the gut samples containing over 150 species, ranging from small (e.g. alveolates) to large eukaryotes (e.g. fish). The main dietary components consisted of crabs and prawns, but also included macroalgae and fish. Significant differences were found among scampi gut contents when comparing season and geographic region, but not when comparing sex and size. Due to their generalist scavenging nature, scampi play an important role in the deep-sea benthic ecosystems and are natural benthic samplers that are well suited to being used as deep-sea ecosystem/biodiversity monitors.
... Bottom-fishing activities involving mobile fishing gears have a direct physical interaction with the seabed and its biota, and the levels of disturbance vary among habitats as a result of fishing frequency and intensity. Bottom trawling impacts on benthic communities causing the re-suspension of sediment, modifying the fluxes of nutrients, reducing the structural complexity of the benthic communities and leading, eventually, to their complete elimination (Olsgard et al., 2008;Hinz et al., 2009). Also, the direct effect of abandoned long-line fishing lines entangled in cold-water coral communities has been reported (Madurell et al. 2012). ...
... Since the beginning of the 19 th century, the seafloor is continuously affected due to dredging and dumping activities or bottom trawl fishery [84,85]. Thus, benthic communities of the whole study area are exposed to a continuous disturbance, which might have led to an adapted community structure, which has the ability of a fast recovery and thus stable diversity patterns [86][87][88]. Another indicator is the high occurrence of opportunistic species with a high reproduction rate such as Phoronis spp., Spiophanes bombyx, or Kurtiella bidentata. ...
Article
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Current research revealed distinct changes in ecosystem functions, and thus in ecosystem stability and resilience, caused by changes in community structure and diversity loss. Benthic species play an important role in benthic-pelagic coupling, such as through the remineralization of deposited organic material, and changes to benthic community structure and diversity have associated with changes in ecosystem functioning, ecosystem stability and resilience. However, the long-term variability of traits and functions in benthic communities is largely unknown. By using abundance and bioturbation potential of macrofauna samples, taken along a transect from the German Bight towards the Dogger Bank in May 1990 and annually from 1995 to 2017, we analysed the taxonomic and trait-based macrofauna long-term community variability and diversity. Taxonomic and trait-based diversity remained stable over time, while three different regimes were found, characterised by changes in taxonomic and trait-based community structure. Min/max autocorrelation factor analysis revealed the climatic variables sea surface temperature (SST) and North Atlantic Oscillation Index (NAOI), nitrite, and epibenthic abundance as most important environmental drivers for taxonomic and trait-based community changes.
... We detected significant management implications for the small-scale beam trawl of the Ria de Arousa. This novel hypothesis (to our knowledge, the first time this has been addressed) is important to understand impacts of aquaculture activities in the ecological realm (Hinz et al., 2009) and the likely implications of this on socio-economic issues (Natale et al., 2013b). The second is of great importance to adequately manage and plan coastal ecosystem services and effectively use efforts to alleviate pressure on ecosystems with tools such as Marine Spatial Planning (Stelzenmüller et al., 2013). ...
Article
Marine ecosystems have been traditionally exploited by coastal communities in several ways, especially by fishing. More recently, aquaculture has emerged as an activity through which coastal communities have diversified their economies. Thus, many regions of the world face the challenge of allowing both activities to maximise their yields while complying with conservation objectives. Our study area represents a paradigm of this reality as intensive mussel aquaculture has expanded in the region since the 1950's, forcing small-scale fisheries to adapt to the new scenario. Using a cross-disciplinary approach, we identified two métiers in the studied fleet: a) one composed mostly of queen scallop catches (Queen Scallop Métier - QSM), and b) a more heterogeneous one with a varied composition of Crustacea, Cephalopoda and Fishes (Mixed Composition Métier - MCM). The MCM is strongly spatio-temporally correlated with mussel raft locations, which indicates how the bottom trawl small-scale fleet has adapted its strategies to the presence of aquaculture. Moreover, the rich community associated with mussel rafts is reflected in the heterogeneous catch composition (of valuable species) of the fishing operations carried out near mussel rafts. However, accumulated biodeposits have attracted detritus feeding non-commercial species, creating a new ecological paradigm and posing operational difficulties for the fleet and higher discards.
... Studies focussing on the impact of bottom trawling on the benthic community, such as Frid et al. (2000), Hiddink et al. (2006), andHinz et al. (2009), show the importance of quantifying bottom trawl activity to the fine spatial scale at which it causes a disturbance. With the framework developed here, the cumulative fishing intensity of local patches can be predicted and reconstructed for years in which effort data are available on the scale of, for instance, the ICES rectangle, but not on the more precise VMS level. ...
Article
High-resolution vessel monitoring (VMS) data have led to detailed estimates of the distribution of fishing in both time and space. While several studies have documented large-scale changes in fishing distribution, fine-scale patterns are still poorly documented, despite VMS data allowing for such analyses. We apply a methodology that can explain and predict effort allocation at fine spatial scales; a scale relevant to assess impact on the benthic ecosystem. This study uses VMS data to quantify the stability of fishing grounds (i.e. aggregated fishing effort) at a microscale (tens of meters). The model links effort registered at a large scale (ICES rectangle; 1° longitude × 0.5° latitude, ˜3600 km2) to fine spatial trawling intensities at a local scale (i.e. scale matching gear width, here 24 m). For the first time in the literature, the method estimates the part of an ICES rectangle that is unfavourable or inaccessible for fisheries, which is shown to be highly stable over time and suggests higher proportions of inaccessible grounds for either extremely muddy or courser substrates. The study furthermore shows high stability in aggregation of fishing, where aggregation shows a positive relationship with depth heterogeneity and a negative relationship with year-on-year variability in fishing intensity.
... Synthetic aperture sonars would allow higher resolution seafloor images compared to SSS and MBES [15], but its application, especially in turbid shallow waters, is not routinely possible at the present time. Several case studies have demonstrated that standard SSS can image bottom fishing activity [16][17][18]. SSS combines the advantages to survey large areas with high spatial resolution. However, it is still challenging to digitize trawl tracks from SSS mosaics for quantitative interpretation. ...
Article
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Bottom trawling is one of the most significant anthropogenic pressures on physical seafloor integrity. The objective classification of physical impact is important to monitor ongoing fishing activities and to assess the regeneration of seafloor integrity in Marine Protected Areas. We use high-resolution bathymetric data recorded by multibeam echo sounders to parameterize the morphology of trawl mark incisions and associated mounds in the Fehmarn Belt, SW Baltic Sea. Trawl marks are recognized by continuous incisions or isolated depressions with depths up to about 25 cm. Elevated mounds fringe a subset of the trawl marks incisions. A net resuspension of sediment takes place based on the volumetric difference between trawl mark incisions and mounds. While not universally applicable, the volume of the trawl mark incisions is suggested as an indicator for the future monitoring of the physical impact of bottom trawling in the Baltic Sea basins.
... However, the area being shallow (as discussed earlier) and characterized with a bottom substrate comprising mostly coarse grained sand, susceptibility to bottom trawling induced severe seabed scraping is very high (Sivalingam, 2005;Bhagirathan et al., 2014;Kularatne, 2014). Bottom trawling in its path homogenizes habitats, reduces habitat complexity and reduces species diversity (which could lead to dominance by detrimental predatory scavenger species in the long-term) (Jones, 1992;Dayton et al., 1995;Moran and Stephenson, 2000;Hinz et al., 2009;Bhagirathan et al., 2014;Dannheim et al., 2014;Sosai, 2015;Wijesundara and Amunugama, 2017). 6 Gulf of Mannar and Palk Bay is a shallow area (as discussed earlier) and water mixing between the Gulf of Mannar and Palk Bay is restricted by the Adam's Bridge (which is a shoal between India and Sri Lanka) leading to relatively calmer conditions with a flushing period between 30 days and 45 days (Kularatne, 2014). ...
Article
Sri Lankan and South Indian fishermen have been using the Palk Bay and Gulf of Mannar waters for a long period. Nevertheless, after signing the maritime agreements in 1974 and 1976, Indian fishermen encroaching Sri Lankan waters with the usage of bottom trawlers (banned in Sri Lanka) has been a serious issue (which worsened since the cessation of the ethnic conflict in 2009). This article reviews the legal framework in Sri Lanka addressing illegal fishing methods and operation of foreign fishing boats with suggestions for law reformations. Fisheries and Aquatic Resources Act No. 2 of 1996 (as amended) enacted by the Department of Fisheries and Aquatic Resources (DFAR) describes the types of fishing gear (including bottom trawling), fishing methods and harmful material (e.g., usage of explosives) that are prohibited, while describing the penalties for any violations. Fisheries (Regulation of Foreign Fishing Boats) Act No. 59 of 1979 (as amended) also enacted by the DFAR prohibits fishing by foreign boats in Sri Lankan waters (without a permit from the DFAR) with provisions to impose penalties for violations. However, in the Fisheries (Regulations of Foreign Fishing Boats) Act it is not indicated regarding the type of fishing gear, methods and harmful material that are prohibited (with or without any permits), while there is no specific penalty system for usage of banned fishing gear, materials and methods. Hence there is a requirement to reform the existing laws with proper law enforcement and regular monitoring of illegal fishing.
... Trawling on soft bottom habitats will not only remove non-target species, but also resuspend sediments and change the sediment composition in ways that could affect future invertebrate recruitment (Tudela, 2004;Kiparissis et al., 2011). This has already been shown by otter trawling from a Norway lobster fishery in the Irish Sea, where infauna abundance, biomass, and species richness were reduced 72, 77, and 40%, respectively (Hinz et al., 2009). Largescale degradation of valuable habitats such as illegal trawling on deep Posidonia oceanica seagrass meadows reduces the ecological integrity and the associated invertebrate assemblages (Guillén et al., 1994;Sánchez-Jerez et al., 2000;González-Correa et al., 2005). ...
Article
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Making up over 92% of life in our oceans, marine invertebrates inhabit every zone in the water column, with contributions ranging from ecosystem functioning to socioeconomic development. Compared to charismatic species, marine invertebrates are often underrepresented in IUCN reports and national conservation efforts. Because of this, as climate change intensifies in conjunction with increasing anthropogenic pressures such as habitat destruction, many marine invertebrates are at risk of silently heading toward extinction. However, public perception has shifted in recent years due to the growing awareness of the important roles these invertebrates play in marine and human life. This change may promote greater support for future research and conservation campaigns of key species. This review highlights the importance of marine invertebrates, the environmental and anthropogenic stressors they are currently facing, and the inherent challenges in their successful conservation. Potential solutions to fill the gaps in current knowledge will be also explored in the context of recent globalization and technological advancements. The loss of marine invertebrate biodiversity will have cascading ecological, economic, and sociological repercussions, so compiling key information into a holistic review will add to the conversation of the importance of global marine invertebrate conservation.
... Overfishing has, however, played its part with larger bodied bottom-living fish being particularly vulnerable, but with smaller bodied fish following climate (Genner et al. 2010). Overfishing has no doubt influenced the benthos by the disturbance caused by bottom trawling (Holme 1960(Holme , 1966Hinz, Prieto and Kaiser 2009), but there is evidence of recovery when fishing gears are excluded from marine protected areas (Sheehan et al. 2013). In recent years, there has been a realisation that the Russell Cycle is really an expression of the Atlantic Multidecadal Oscillation (AMO) (Edwards et al. 2013), a larger scale North Atlantic phenomenon. ...
Chapter
Estuarine and coastal waters are acknowledged centres for anthropogenic impacts. Superimposed on the complex natural interactions between land, rivers and sea are the myriad consequences of human activity – a spectrum ranging from locally polluting effluents to some of the severest consequences of global climate change. For practitioners, academics and students in the field of coastal science and policy, this book examines and exemplifies current and future challenges: from upper estuaries to open coasts and adjacent seas; from tropical to temperate latitudes; from Europe to Australia. This authoritative volume marks the 50th anniversary of the Estuarine and Coastal Sciences Association, and contains a prologue by founding member Professor Richard Barnes and a short history of the Association. Individual chapters then address coastal erosion and deposition; open shores to estuaries and deltas; marine plastics; coastal squeeze and habitat loss; tidal freshwaters – saline incursion and estuarine squeeze; restoration management using remote data collection; carbon storage; species distribution and non-natives; shorebirds; modelling environmental change; physical processes such as sediments and modelling; sea level rise and estuarine tidal dynamics; estuaries as fish nurseries; policy versus reality in coastal conservation; developments in estuarine, coastal and marine management.
... Demersal trawling modifies epibenthic habitat (Collie et al., 2000;Hiddink et al., 2017), which can lead to changes in fish communities (Sainsbury et al., 1993). Otter-trawling can have cumulative impacts on benthic communities (Hinz et al., 2009), and large epifauna such as sponges can take many years to recover following disturbance (Kaiser et al., 2006). Currie et al. (2011) found lower abundances of sponges and bryozoans and lower biomass of fish on more heavily trawled grounds in Spencer Gulf in South Australia, although environmental gradients were the dominant driver of overall community composition. ...
Article
We examined spatial and temporal variations in the demersal fish assemblage on the continental shelf of the central Great Australian Bight to understand how the assemblage is affected by both fishing and environmental gradients. Data from the Great Australian Bight Trawl Sector (1988–2018) and fishery-independent trawl surveys (2005–2009, 2011, 2015, 2018) were used for the analyses. The independent survey data were used to analyse trends in overall species composition and abundances, while the commercial fishery data were used to extend the time series for the key commercial species, Deepwater Flathead (Platycephalus conatus) and Bight Redfish (Centroberyx gerrardi). The demersal fish assemblage was dominated by four commercial species: Deepwater Flathead, Bight Redfish, Ocean Jacket (Nelusetta ayraud), and Latchet (Pterygotrigla polyommata); and one by-catch species: Wide Stingaree (Urolophus expansus). Assemblage composition varied between day/night and along an east-west gradient. Survey abundance and commercial catch-per-unit-effort of several species declined at the end of the time series. Survey abundance was low in 2011, 2015, and 2018 for Bight Redfish and in 2015 and 2018 for Deepwater Flathead. Assemblage composition and catch rates of some species recorded in 2011, 2015, and 2018 were distinct from previous years, but the differences appear to reflect the longer gaps between these surveys and the combined effects of historical fishing pressure and environmental variability. Recent downward trends in the abundance indices of target species, as well as long-term changes in the assemblage, demonstrate the need for continued fishery-independent monitoring. The relative importance of fishing pressure, environmental variability, and other human activities in driving these changes warrant further investigation.
... Our study confirmed an even higher contribution of the discard composed of non-commercial benthic organisms. Although a single experimental tow does not produce a significant effect on long-lived surface taxa (Pranovi et al., 2000), commercial exploitation implies multiple trawling in the same area and therefore produces a cumulative disturbance on those species (Hinz et al., 2009). Our study detected differences in the benthic community between beam trawl fishing and non-fishing areas. ...
Article
Beam trawl fishery is highly important in the Croatian part of the northern Adriatic wherein 116 vessels have a licence for this type of fishing gear. A sharp decrease in the beam trawl catch observed since 2015 has raised concern about not only socio-economic issues but also ecological issues and the effect that beam trawl fisheries have had on exploited stocks. Besides the effect that beam trawl fisheries can have on targeted economically important species, intensive dredging can cause long-term changes in the benthic community. Therefore, this study aimed to detect the effect that this type of fishing gear has on target and by-catch species. Furthermore, survey data were compared with the official beam trawl fishery data gathered through Vessel Monitoring System data together with fishermen’s logbooks. Our research targeted two adjacent areas: an area where beam trawl fishing is allowed and an area where it is forbidden. The results demonstrate that the commercially important catch represented a minor share of the total beam trawl catch in both survey areas, while discard made up more than 93% of the total catch. The main beam trawl commercially important species in the Croatian part of the northern Adriatic Sea was Pecten jacobaeus, followed by Solea solea and Ostrea edulis. Our results suggest that beam trawl fisheries mostly affect target bivalve species and some non-commercial benthic species (e.g. sponges). The differences recorded between areas could suggest that beam trawl fisheries cause changes mostly in the P. jacobaeus population.
... Trawled sediments show higher degrees of mixing, erosion and grain-size sorting as well as organic carbon impoverishment as a consequence of the removal of surficial sediments (Mayer et al., 1991;Watling et al., 2001;Sánchez et al., 2009;Martín et al., 2014a). Since sediment properties and organic matter have an important role in the distribution of benthos (Sanders, 1958;Harkantra et al., 1982;Jayaraj et al., 2007;Gogina et al., 2017), species complexity, diversity, abundance, size and the productivity of benthic communities are also indirectly affected by trawling (Bergman and Hup, 1992;Ball et al., 2000;Collie et al., 2000;Frid et al., 2000;Duplisea et al., 2002;Jennings et al., 2002;Hinz et al., 2009;Thrush et al., 2015;Buhl-Mortensen et al., 2016;Sköld et al., 2018). Trawled areas are often dominated by small-bodied, opportunistic species with fast life histories to the detriment of large, long-lived organisms (Pitcher et al., 2000;Tillin et al., 2006;Olsgard et al., 2008;van Denderen et al., 2015). ...
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Experimental benthic dredging was conducted in an unfished area in the Baltic Proper to mimic the impact of trawling, with a focus on benthic biogeochemical processes. Sediment cores were taken on the track where the surface sediment had been scraped away and compared to undisturbed controls. Benthic fluxes were immediately affected and pore water DIC profiles were truncated. The time needed for the sediment to readjust to a new steady state seemed to be nutrient-specific. Sediment properties (profiles of chlorophyll, organic carbon and water content) were found to change significantly. Macrofauna was removed completely by the dredge pointing out the potential loss of highly valuable functions that are associated with them. In the Baltic Sea, in areas which were previously the most heavily fished, the frequency of trawling may have left little time for recovery and potentially kept the seabed in a permanent state of transient biogeochemical cycling.
... Apart from these slow and fast emerging variables, there are also continuous harmful variables such as fishing pressure. The damaging impacts of demersal trawls on demersal communities and habitats have been studied by many researchers (Auster and Langton, 1999;Bergman and van Santbrink, 2000;Hinz et al., 2009) Since deep water trawling is a common fishing method, well established scientific knowledge has been obtained from the seas of Turkey (Zengin et al., 2004;Knudsen et al., 2010;Ceylan et al., 2013;Yemişken et al., 2014;Keskin et al., 2014;Çiçek et al., 2014;Yıldız and Karakulak, 2017;Dalyan, 2020). These researches were conducted mostly western part of the Black Sea, North Aegean Sea and northeastern part of the Mediterranean Sea. ...
Article
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Demersal fish fauna of the Sea of Marmara, Turkey was determined by bottom trawl surveys between March 2017-December 2018 at 34 stations with the monthly samplings. During the study, a total of 61 teleost and 12 cartilaginous fish species belonging to 42 families were sampled. The target, bycatch and discard rates of CPUE were determined as 13.40%, 69.64% and 16.95%, respectively. In total, 53.9% of the CPUE was stemmed from Trachurus trachurus. Mustelus mustelus, Raja clavata, Merluccius merluccius and Merlangius merlangius had the highest CPUE with a mean of 77.63, 71.86, 71.72 and 72.68 kg/km2, respectively. The highest biodiversity was observed in the southwestern part of the Marmara Sea. With increasing depth, the species number of the teleost fish decreased, whereas the species number of the cartilaginous fish increased. The mean CPUE values of the economical demersal fish species were lower in comparison to those reported from other regions in Turkey. Evidence suggests fish stocks with shallower distribution is under heavier threat against fishing pressure. Since commercial trawling is banned in the Sea of Marmara, beam trawl fishery can be considered as the major threat to demersal fish stocks in the region.
... Burial and reduction of live rhodoliths increase in substrates with a high proportion of fine sediment [62,63]. On the other hand, the effects of bottom trawling on epibenthic communities lead to changes in community structure and biodiversity [20,[64][65][66][67], also changing the composition and morphology of rhodoliths beds [20][21][22]. The comparison of all the areas between them could mask the effect of bottom trawling, due to the strong variability that causes the environmental conditions on the epibenthic communities analyzed. ...
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One of the objectives of the LIFE IP INTEMARES project is to assess the impact of bottom trawling on the vulnerable benthic habitats of the circalittoral bottoms of the Menorca Channel (western Mediterranean), designated a Site of Community Importance (SCI) within the Natura 2000 network. The present study compares the epibenthic communities of four areas, subjected to different bottom trawl fishing intensity levels. The assignment of fishing effort levels was based on the fishing effort distribution in the area calculated from Vessel Monitoring System (VMS) data and the existence of two Fishing Protected Zones in the Menorca Channel. Biological samples were collected from 39 beam trawl stations, sampled during a scientific survey on April 2019. We compare the diversity, composition, and density of the epibenthic flora and fauna, together with the rhodoliths coverage and the morphology of the main species of rhodoliths of four areas subjected to different levels of bottom trawl fishing effort, including one that has never been impacted by trawling. Our results have shown negative impacts of bottom trawling on rhodoliths beds and the first signals of their recovery in areas recently closed to this fishery, which indicate that this is an effective measure for the conservation of this habitat of special interest and must be included in the management plan required to declare the Menorca Channel as a Special Area of Conservation.
... Such fishing activities can also reduce the biomass and diversity of the demersal biological community (Hiddink et al., 2011;Collie et al., 2017), as well as altering the trophic structure and functioning of the marine ecosystem (Jennings et al., 2001). Apart from direct harvesting of demersal fishes and crustaceans, trawling can also reduce availability of prey via direct removal and habitat destruction, resulting in dietary shifts and reduced energy intake and body size of predatory fishes in frequently trawled areas (Hinz et al., 2009;Hiddink et al., 2011). Thus, benthic trawling, if not regulated properly, could seriously deteriorate the marine biological communities and ecosystem functions. ...
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Trawl fisheries have been shown to cause overfishing and destruction of benthic habitats in the seabed. To mitigate these impacts, a trawling ban has been enforced in Hong Kong waters since December 31, 2012 to rehabilitate the ecosystem and enhance fisheries resources. Previous studies demonstrated that reduced trawling activities would increase the heterogeneity of benthic habitats, thereby enhancing species richness and abundance of benthic fauna and providing more prey resources for predatory fishes. This study aimed to test a hypothesis that the population and trophic dynamics of the Bartail flathead Platycephalus indicus, a heavily fished benthic predatory fish, at inner and outer Tolo Channel of Hong Kong (i.e., EI and EO) improved with increases in their body size, abundance, biomass, trophic niche, and trophic position after the trawl ban. Samples were collected from trawl surveys before and after the trawl ban to compare the pre-ban and post-ban populations of P. indicus from EI and EO. Body size, abundance, and biomass were assessed in 2004, 2013–2014, and 2015–2016, whereas trophic niche and trophic position were analyzed based on stable isotopes of fish samples collected in dry season of 2012, 2015, and 2018. Following the trawl ban, the abundance and biomass of P. indicus increased in EO, with body size increased in EI. Furthermore, as indicated by the results of stable isotope analysis (SIA) on their tissues and prey items, trophic niche, and trophic position of P. indicus increased in EI and EO, respectively. Our study demonstrated that the trawl ban had promoted the recovery of a predatory fish population through restoring size structure and trophic dynamics.
... The distinct geomorphology facilitated the development of an extensive inshore trawl fishery, resulting in one of the most intensively trawled areas in New Zealand waters since the expansion of industrialized fishing, measured on Catch Effort Landing Returns (CELRs) (Baird et al. 2011). Since the start of industrialized fisheries, the removal of species and the physical disturbance on the seafloor caused by trawling may have impacted the structure of benthic communities, with possible effects in whole ecosystems (Jennings et al. 2001;Hinz et al. 2009). ...
Article
Composition and length-frequency are important attributes considered in the management of fish communities and can be affected by both exploitation and environmental forces. Vulnerability to these effects varies among species depending on environmental tolerance, ecological traits, and life-history strategies. In the present study, data from scientific bottom trawl surveys conducted between 1991 and 2018 were analysed to identify long-term changes in community structure and length frequency of demersal fish species of the east coast of the South Island, New Zealand. Analysis of variance, hierarchical clustering analysis and multidimensional scaling relationships demonstrated that community composition has changed significantly over the last three decades, with a tendency towards greater spatial overlap among species in the most recent periods. Changes in depth distribution were identified but were mainly correlated with shifts in relative biomass. Total catch rate (kg km−2) of the whole community has increased significantly over time, while the average trophic level decreased, primarily explained by an increase in relative biomass of intermediate trophic level species. Fishing activity was significantly related to the variation in length frequency of species at intermediate trophic levels, confirming that the impacts of fisheries are heterogeneous throughout the community, providing vital information to support multi-species management of fishery resources.
... Among fishing practices, bottom trawling is widely used and profoundly disrupts benthic habitats and communities (Hiddink et al., 2019;Olsgard et al., 2008;Van Denderen et al., 2015). Indeed, the direct footprint of bottom trawling on the seafloor is thoroughly documented (Amoroso et al., 2018;de Juan et al., 2011;Hinz et al., 2009;Rijnsdorp et al., 2016), as well as its direct and indirect impacts on targeted commercial species (Hiddink et al., 2011;Thurstan et al., 2010). The resources harvested by bottom trawling fisheries are economically important, and understanding the ecosystem-level footprint of the latter is necessary to provide efficient management (Pikitch et al., 2004). ...
Article
The impacts of bottom trawling in coastal ecosystems are significant, not only for targeted species but also for non-commercial ones. However, the critical gaps in scientific knowledge associated with these impacts on untargeted but functionally important species remain to be filled. This is notably the case for a great proportion of discarded invertebrates, for which only a handful of studies have investigated their survival. In this study, 600 individuals from six different benthic invertebrate species were collected in commercial conditions in the Bay of Biscay for short-term survival experiments. Overall, the observed survival after 100–130 h and the predicted survival via mixture models were very high (>93%) for Asterias rubens, Aphrodita aculeata, Buccinum undatum and Pagurus sp. Survival of Maja brachydactyla was lower though still high (>80% overall) and Atelecyclus undecimdentatus was more vulnerable to trawling and handling, with 50% of survival. Both showed 100% mortality when presenting carapace cracks and survival of M. brachydactyla was lower when missing appendages. No biotic nor abiotic parameters were correlated to survival, except injury class for M. brachydactyla and A. undecimdentatus. This study shows an overall high survival but highlights the fact that otter trawl fisheries may differentially affect discarded benthic invertebrates, therefore bringing light for future studies on longer-term impacts on benthic communities and coastal ecosystems. Furthermore, we recommend incorporating survival rates of discarded invertebrates in ecosystem-level modelling studies and encourage the use of detailed information and biomass reports of benthic invertebrates for a better management of natural populations and fisheries resources.
... From a functional perspective, filter feeders play an important role in benthic-pelagic coupling (Griffiths et al. 2017), nutrient cycling, and the transfer of organic material into the sediment matrix (Rosenberg 2001, Lohrer et al. 2004. Although mobile fishing gears are known to negatively impact populations of tube-dwelling benthos (Collie et al. 1997, Kenchington et al. 2006, Hinz et al. 2009), few trait-based studies have highlighted tube-dwelling as a sensitive trait at the community level. In our study, unfished sites were characterised by a high biomass of maldanid (e.g. ...
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Bottom trawling results in widespread impacts to the structure and composition of benthic communities. Although an ecosystem approach to fisheries management aims to conserve marine biodiversity and ecosystem function, there remains a lack of empirical evidence regarding the effects of trawling on benthic functional properties. Here, we examine the sensitivity of benthic macrofauna communities to trawling using their biological traits, and compare trait responses across size-categories and survey types. 84 benthic soft-sediment samples were collected by Van Veen grab (0.1m2) in the Kattegat in 2016, and complemented with 827 Haps cores (0.0143m2) gathered over a long-term monitoring programme between 2006 and 2013. By analysing trait response in three size categories (small: 1-4 mm fraction, large: ≥4 mm fraction, and full community: all individuals combined), we demonstrate a size-dependent effect of trawling on benthic trait composition, where the traits of large-bodied fauna (≥4mm) were more sensitive. Specifically, larger sessile, deep-living, suspension-feeding, tube-dwelling, subsurface deposit feeding, burrow-dwelling, and long-lived (≥10 years) individuals were among the most affected. Our results based on large fauna were largely in agreement with trait responses observed in the multi-year monitoring data. This would suggest that trait data gathered from a targeted one-off sampling event can convey information on both acute (short-term) and chronic (long-term) trawling impacts. Given that most trawling impact assessment do not consider size-based effects, we outline how size-separating the community can be used to improve the detectability of trawling impacts, and provide new insights into the functional impacts of fishing on the seabed.
... Studies focussing on the impact of bottom trawling on the benthic community, such as Frid et al. (2000), , and Hinz et al. (2009), show the importance of quantifying bottom trawl activity to the fine spatial scale at which it causes a disturbance. With the framework developed here, the cumulative fishing intensity of local patches can be predicted and reconstructed for years in which effort data are available on the scale of, for instance, the ICES rectangle, but not on the more precise VMS level. ...
Article
The spatial–temporal distribution of cetacean species often overlaps with fishing practices in the Mediterranean, having direct and indirect consequences. This is the first long‐term study focusing on the effects of fisheries on the behavior of T. truncatus in Montenegro. Focal group scan sampling was used during surveys between September 2016 and August 2020 to create transition probability matrices using first‐order Markov chains for behavioral states in both control (absence of fishery practices) and impact chains (presence of fishery practices). Despite the low number of dolphin‐fishery interactions in Montenegro, results revealed that the behavioral budgets of T. truncatus were significantly altered both for commercial and artisanal fisheries. However, the magnitude of the threat differed between practices, with commercial fisheries altering three out of the four behaviors in the behavioral budget while artisanal fisheries altered just one. Significant behavioral changes due to disturbance can have negative consequences on the energy budget of individuals and while the Montenegrin fishing fleet is currently limited to 224 vessels, the significant effects already witnessed are concerning for Montenegrin bottlenose dolphins. To develop in‐situ mitigation strategies, there is a clear need to better understand the impact that fisheries interactions have on these individuals.
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Habitat loss, fragmentation and alteration are frequently identified as important threats to biodiversity, inducing major changes in the structure and composition of species communities and the resulting interspecific interactions. North American woodland caribou (Rangifer tarandus caribou) populations suffer from habitat modifications and most are currently in decline. It has been suggested that the conversion of old-growth coniferous forests into early-seral stages has increased cervid abundances, which have, in turn, stimulated a numerical response of predator populations, ultimately threatening caribou populations via a habitat-mediated apparent competition mechanism. Using a long-term dataset (1984–2012) of the Atlantic-Gaspésie caribou population, we quantified changes in interspecific interactions triggered by apparent competition between moose (Alces americanus) and caribou via the responses of two incidental predators, coyote (Canis latrans) and black bear (Ursus americanus). We also documented calf recruitment rates and analysed temporal trends (last three decades) in this vital rate. Inter-annual variations in autumn calf recruitment were mostly affected by the proxy of regional abundance of coyotes, which was highly correlated with moose and black bear proxies of abundance. The increase in coyote abundance proxy in the Gaspésie Peninsula following anthropogenic habitat modifications seems to be the main mechanism responsible for the current decline in the Atlantic-Gaspésie caribou population. Our analyses revealed some impacts of habitat alteration and the complexity of the resulting trophic cascades.
Article
We describe the first application of eDNA‐Metabarcoding for the assessment of fish species diversity in two Marine Protected Areas of the North Sea: the Doggerbank and the Sylt Outer Reef. We collected 64 water samples and detected a total of 24 fish species. We discuss qualitative differences between MPAs, and we compare our results with those obtained from bottom‐trawl surveys in the same areas. We found 3 additional species to those documented in the same year with trawls, including the critically endangered European Eel. This article is protected by copyright. All rights reserved.
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Bottom‐trawl fisheries are the most‐widespread source of anthropogenic physical disturbance to seabed habitats. Development of fisheries‐, conservation‐ and ecosystem‐based management strategies requires the selection of indicators of the impact of bottom trawling on the state of benthic biota. Many indicators have been proposed, but no rigorous test of a range of candidate indicators against 9 commonly‐agreed criteria (concreteness, theoretical basis, public awareness, cost, measurement, historical data, sensitivity, responsiveness, specificity) has been performed. Here, we collated data from 41 studies that compared the benthic biota in trawled areas with those in control locations (that were either not trawled or trawled infrequently), examining 7 potential indicators (numbers and biomass for individual taxa and whole communities, evenness, Shannon‐Wiener diversity and species richness) to assess their performance against the set of 9 criteria. The effects of trawling were stronger on whole‐community numbers and biomass than for individual taxa. Species richness was also negatively affected by trawling but other measures of diversity were not. Community numbers and biomass met all criteria, taxa numbers and biomass and species richness satisfied most criteria, but evenness and Shannon‐Wiener diversity did not respond to trawling and only met few criteria, and hence are not suitable state indicators of the effect of bottom trawling. Synthesis and applications. An evaluation of each candidate indicator against a commonly agreed suite of desirable properties coupled with the outputs of our meta‐analysis showed that whole‐community numbers of individuals and biomass are the most suitable indicators of bottom trawling impacts as they performed well on all criteria. Strengths of these indicators are that they respond strongly to trawling, relate directly to ecosystem functioning, and are straightforward to measure. Evenness and Shannon‐Wiener diversity are not responsive to trawling and unsuitable for the monitoring and assessment of bottom trawl impacts.
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The aim was to examine which characteristics of benthic communities are most sensitive to bottom trawling. This was done using two intensive trawl fisheries in Denmark as case studies; shellfish dredging in shallow coastal waters, and otter trawling for Norway lobster in the Kattegat. Detailed benthic sampling programmes were undertaken to survey and analyse the response of benthic communities along spatially accurate gradients of trawling intensity. A particular focus was to develop and test a range of benthic indicators. The results are presented in three research papers, which form the basis of the thesis.
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The benthic fauna of European continental shelves is a severely impacted community, mostly due to intense bottom trawling activity. Trawling effect may be dependent on the spatial and temporal distribution of abrasion, the habitat type including natural perturbation intensity and the fishing gear used. Nonetheless, there is an urgent need to identify or develop indices likely to measure the effect of trawling. For this purpose benthic fauna by-catch monitored in scientific trawl surveys carried out in all European waters in the frame of the Common Fishery Policy Data Collection Multiannual Program may be used. Benthic invertebrates data used in this study were collected during scientific bottom trawl surveys covering the English Channel, the North Sea and the North-West Mediterranean. Swept area ratios derived from VMS data were used to quantify the intensity of fishery induced abrasion on the seabed. Fifteen indices were investigated: taxonomic diversity metrics, functional diversity indices and functional indices, the two later based on sensitivity traits to physical abrasion. Their properties, such as their capacity to detect trawling effect, their statistical behavior or their ability to inform on community structure, were investigated. Among them, fours indices specific to fishery effect detection based on biological traits appeared to be the best performing benthic indices regarding these requirements: Trawling Disturbance Index (TDI), modified-Trawling Disturbance Index (mTDI), partial-Trawling Disturbance Index (pTDI), modified sensitivity index (mT). Maps of the distribution pattern of seabed sensitivity captured through each of these four indices were produced. This work has highlighted the need to use specific indices to monitor the effect of trawling on benthic communities but also that the use of different indices may be necessary to carry out this monitoring in all European waters.
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Subtidal marine sediments are one of the planet's primary carbon stores and strongly influence the oceanic sink for atmospheric CO2. By far the most pervasive human activity occurring on the seabed is bottom trawling and dredging for fish and shellfish. A global first-order estimate suggested mobile demersal fishing activities may cause 160-400 Mt of organic carbon (OC) to be remineralised annually from seabed sediment carbon stores. There are, however, many uncertainties in this calculation. Here, we discuss the potential drivers of change in seabed OC stores due to mobile demersal fishing activities and conduct a systematic review, synthesising studies where this interaction has been directly investigated. Mobile demersal fishing would be expected to reduce OC in seabed stores, albeit with site-specific variability. Reductions would occur due to lower production of flora and fauna, the loss of fine flocculent material, increased sediment resuspension, mixing and transport, and increased oxygen exposure. This would be offset to some extent by reduced faunal bioturbation and respiration, increased off-shelf transport and increases in primary production from the resuspension of nutrients. Studies which directly investigated the impact of demersal fishing on OC stocks had mixed results. A finding of no significant effect was reported in 51% of 59 experimental contrasts; 41% reported lower OC due to fishing activities, with 8% reporting higher OC. In relation to remineralisation rates within the seabed, 14 experimental contrasts reported that demersal fishing activities decreased remineralisation, with four reporting higher remineralisation rates. The direction of effects was related to sediment type, impact duration, study design and local hydrography. More evidence is urgently needed to accurately quantify the impact of anthropogenic physical disturbance on seabed carbon in different environmental settings, and incorporate full evidence-based carbon considerations into global seabed management.
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To incorporate ecosystem-based approaches into fisheries management, an understanding of patterns of habitat use during the key life stages of commercial species is fundamental. The main aim of this study was to provide a baseline survey of the benthic habitats in Baie ny Carrickey closed area, Isle of Man and to investigate habitat associations of commercially fished lobster, Homarus gammarus and brown crab, Cancer pagurus. Seabed habitats were sampled using non-destructive video techniques and benthic assemblages classified using the Marine Habitat Classification for Britain and Ireland in addition to multivariate approaches. Catch per unit effort data was calculated from fishermen’s logbooks, and used to compare the abundance of juvenile and adult crustaceans across different habitats. The resultant habitat maps indicated that benthic assemblages were diverse across the study area, with large extents characterised by rocky reefs. Two habitats of conservation interest, maerl beds and seagrass patches (Zostera marina), were identified inside the marine protected area. It was found that adult H. gammarus and adult C. pagurus did not exhibit any habitat preferences. In contrast, juvenile lobster abundance was revealed to be positively associated with habitats dominated by kelp forests or macroalgae. In addition, juvenile crabs also indicated preferences to similar biotopes in coastal areas. These structurally complex biotopes are likely to serve as nursery areas for juvenile crustaceans and fish, providing shelter and refuge from predators. Overall, this study demonstrates the effectiveness of an integrated approach to fisheries management, combining conventional and ecosystem-based approaches. However, robust monitoring programmes are essential in achieving sustainable fisheries.
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We used complementary stable isotope (SIA) and stomach content (SCA) analyses to investigate feeding relationships among species of the nektobenthic communities and the potential ecological effects of the bottom trawling of a coastal ecosystem in northeastern Brazil. Carbon (δ13C) and nitrogen (δ15N) compositions were determined for five basal sources and 28 consumers, from zooplankton to shrimp and fish species. Fishes and basal sources showed a broad range of δ15N (fishes: 6.49–14.94‰; sources: 2.58–6.79‰) and δ13C values (fishes: -23.86 to -13.71‰; sources: -24.32 to -13.53‰), while shrimps and crabs exhibited similar nitrogen and carbon ratios. Six trophic consumer groups were deter- mined among zooplankton, crustaceans and fishes by SIA, with trophic pathways associ- ated mostly with benthic sources. SCA results indicated a preference for benthic invertebrates, mainly worms, crabs and shrimps, as prey for the fish fauna, highlighting their importance in the food web. In overall, differences between SCA and the SIA approaches were observed, except for groups composed mainly for shrimps and some species of high δ15N values, mostly piscivorous and zoobenthivores. Given the absence of regulation for bottom trawling activities in the area, the cumulative effects of trawling on population param- eters, species composition, potentially decreasing the abundance of benthic preys (e.g., shrimps, worms and crabs) may lead to changes in the trophic structure potentially affect the food web and the sustainability of the fishery.
Article
This paper describes the impact of dredging on populations of the wedge clam (Donax trunculus) at two sites along the northern Alboran coast. Damage was assessed by quantifying shell and foot damage on commercial clams caught with mechanical dredges. Survival experiments were carried out to assess their survival capacity after 24 h purification treatment and 72 h cold storage, which represents an issue of great interest for fisheries research, management and marketing. Overall, 2.4% of wedge clams suffered any type of damage, including chipped edges and scratched valves. Higher proportions of shell-damaged individuals were positively correlated to bottom features (e.g. gravel content in sediment). Moreover, higher towing speed significantly increased shell damage. Analyses of shell damage areas revealed that the anterior dorsal and ventral parts of the shell are the most vulnerable to dredging. A total of 15.9% of individuals showed damage on the foot, which seems not to affect their survival. The incidence of foot damage was mostly linked to sublethal predation, reflected in a positive correlation between the proportion of foot-damaged individuals and biomass of decapod crustaceans in the fishing ground. Finally, D. trunculus exhibited very low mortality rates after 24 h purification treatment (0.2–0.4%) and 72 h cold storage (0.3–3.2%). The survival rate at the end of the experiment was high (>96%), with the highest mortality observed 96 h after the fishing day. No correlations were found between mortality rates and bottom type or towing speed.
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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.
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