Trawl fishing impacts on the status of seabed fauna in diverse regions of the globe

Bottom trawl fishing is a controversial activity. It yields about a quarter of the world's wild seafood, but also has impacts on the marine environment. Recent advances have quantified and improved understanding of large-scale impacts of trawling on the seabed. However, such information needs to be coupled with distributions of benthic invertebrates (benthos) to assess whether these populations are being sustained under current trawling regimes. This study collated data from 13 diverse regions of the globe spanning four continents. Within each region, we combined trawl intensity distributions and predicted abundance distributions of benthos groups with impact and recovery parameters for taxonomic classes in a risk assessment model to estimate benthos status. The exposure of 220 predicted benthos-group distributions to trawling intensity (as swept area ratio) ranged between 0% and 210% (mean = 37%) of abundance. However, benthos status, an indicator of the depleted abundance under chronic trawling pressure as a proportion of untrawled state, ranged between 0.86 and 1 (mean = 0.99), with 78% of benthos groups > 0.95. Mean benthos status was lowest in regions of Europe and Africa, and for taxonomic classes Bivalvia and Gastropoda. Our results demonstrate that while spatial overlap studies can help infer general patterns of potential risk, actual risks cannot be evaluated without using an assessment model that incorporates trawl impact and recovery metrics. These quantitative outputs are essential for sustainability assessments, and together with reference points and thresholds, can help managers ensure use of the marine environment is sustainable under the ecosystem approach to management

Biomass and trait biogeography of cephalopods on the European and North American continental shelves

Aim: We evaluate whether the biomass and trait biogeography of cephalopods follow the distribution expected by metabolic theory for ectotherms with rapid growth and high metabolic rate. Location: Continental shelves of the North Atlantic and Northeast Pacific oceans; global marine ecoregions. Time Period: 1968–2020. Major Taxa Studied: Cephalopods and fishes (Chondrichthyes and Osteichthyes). Methods: We map the biomass of cephalopods and their traits across marine shelves using scientific bottom trawl survey data from the North Atlantic and Northeast Pacific. We further map global fisheries catch. We apply statistical methods to evaluate how temperature, zooplankton productivity and depth drive these patterns. Results: Cephalopods represent a small fraction (1%) of the combined fish and cephalopod biomass on continental shelves. However, their distribution displays a high regional heterogeneity, with some areas being virtually absent of cephalopods and other areas accounting for up to 24% of total biomass. Higher temperatures and zooplankton productivity are associated with increased cephalopod biomass and proportional biomass relative to fish. The largest cephalopods are found in the Northeast Pacific. Growth rates are highest in warmer waters with fastest growth rates found in lower latitudes of the North Atlantic. Cephalopods constitute 5% of the combined fish and cephalopod global fisheries catch. This proportion varies across regions. Higher temperature and zooplankton productivity are associated with increased cephalopod catch relative to fish. Main Conclusions: Temperature and productivity shape the large‐scale biogeography of cephalopods and their traits on marine shelves. The relations with temperature suggest that future warming could lead to a proliferation of fast‐growing cephalopods in cold and temperate systems, with implications for ecosystem dynamics and fisheries. Despite a relatively low observed biomass, cephalopods hold substantial potential to change ecosystem structure and functioning given their high energy lifestyle

Impact of increased fishing on long-term sequestration of carbon by cephalopods

Fish and other metazoans play a major role in long-term sequestration of carbon in the oceans through the biological carbon pump1. Recent studies estimate that fish can release about 1,200 to 1,500 million metric tons of carbon per year (MtC year-1) in the oceans through feces production, respiration, and deadfalls, with mesopelagic fish playing a major role1,2. This carbon remains sequestered (stored) in the ocean for a period that largely depends on the depth at which it is released. Cephalopods (squid, octopus, and cuttlefish) have the potential to sequester carbon more effectively than fish because they grow on average five times faster than fish3,4 and they die after reproducing at an early age4,5 (usually 1–2 years), after which their carcasses sink rapidly to the sea floor6. Deadfall of carcasses is particularly important for long-term sequestration because it rapidly transports carbon to depths where residence times are longest1,6. We estimate that cephalopod carcasses transfer 11–22 MtC to the seafloor globally. While cephalopods represent less than 5% of global fisheries catch7, fishing extirpates about 0.36 MtC year-1 of cephalopod carbon that could otherwise have sunk to the seafloor, about half as much as that of fishing large fish8

Large Pelagic Fish Are Most Sensitive to Climate Change Despite Pelagification of Ocean Food Webs

Global climate change is expected to impact ocean ecosystems through increases in temperature, decreases in pH and oxygen, increased stratification, with subsequent declines in primary productivity. These impacts propagate through the food chain leading to amplified effects on secondary producers and higher trophic levels. Similarly, climate change may disproportionately affect different species, with impacts depending on their ecological niche. To investigate how global environmental change will alter fish assemblages and productivity, we used a spatially explicit mechanistic model of the three main fish functional types reflected in fisheries catches (FEISTY) coupled to an Earth system model (GFDL-ESM2M) to make projections out to 2100. We additionally explored the sensitivity of projections to uncertainties in widely used metabolic allometries and their temperature dependence. When integrated globally, the biomass and production of all types of fish decreased under a high emissions scenario (RCP 8.5) compared to mean contemporary conditions. Projections also revealed strong increases in the ratio of pelagic zooplankton production to benthic production, a dominant driver of the abundance of large pelagic fish vs. demersal fish under historical conditions. Increases in this ratio led to a “pelagification” of ecosystems exemplified by shifts from benthic-based food webs toward pelagic-based ones. The resulting pelagic systems, however, were dominated by forage fish, as large pelagic fish suffered from increasing metabolic demands in a warming ocean and from declines in zooplankton productivity that were amplified at higher trophic levels. Patterns of relative change between functional types were robust to uncertainty in metabolic allometries and temperature dependence, though projections of the large pelagic fish had the greatest uncertainty. The same accumulation of trophic impacts that underlies the amplification of productivity trends at higher trophic levels propagates to the projection spread, creating an acutely uncertain future for the ocean’s largest predatory fish

Data from: Estimating sensitivity of seabed habitats to disturbance by bottom trawling based on the longevity of benthic fauna

Bottom fishing such as trawling and dredging may pose serious risks to the seabed and benthic habitats, calling for a quantitative assessment method to evaluate the impact and guide management to develop mitigation measures. We provide a method to estimate the sensitivity of benthic habitats based on the longevity composition of the invertebrate community. We hypothesize that long-lived species are more sensitive to trawling mortality due to their lower pace of life (i.e. slower growth, late maturation). We analyse data from box-core and grab samples taken from 401 stations in the English Channel and southern North Sea to estimate the habitat-specific longevity composition of the benthic invertebrate community and of specific functional groups (i.e. suspension feeders and bioturbators), and examine how bottom trawling affects the longevity biomass composition. The longevity biomass composition differed between habitats governed by differences in sediment composition (gravel and mud content) and tidal bed-shear stress. The biomass proportion of long-lived species increased with gravel content and decreased with mud content and shear stress. Bioturbators had a higher median longevity than suspension feeders. Trawling, in particular by gears that penetrate the seabed >2cm, shifted the community towards shorter-lived species. Changes from bottom trawling were highest in habitats with many long-lived species (hence increasing with gravel content, decreasing with mud content). Benthic communities in high shear stress habitats were less affected by bottom trawling. Using these relationships, we predicted the sensitivity of the benthic community from bottom trawling impact at large spatial scale (the North Sea). We derived different benthic sensitivity metrics that provide a basis to estimate indicators of trawling impact on a continuous scale for the total community and specific functional groups. In combination with high resolution data of trawling pressure, our approach can be used to monitor and assess trawling impact and seabed status at the scale of the region or broadscale habitat and to compare the environmental impact of bottom-contacting fishing gears across fisheries

CumulativeBiomass_by_LongevityClass_Data_Dryad

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Relating benthic sensitivity and status to spatial distribution and intensity of trawling in the Eastern Mediterranean

The ecosystem approach to fisheries management needs information of not just where bottom trawlers operate but also on their impact on the seabed, which is also highly relevant to the EU Marine Strategy Framework Directive (MSFD) Descriptor D6, seafloor integrity. In this study, we assess the benthic impact of bottom trawling in the Eastern Mediterranean in areas primarily fished by the Greek fleet. Seabed habitat sensitivity was modelled using macrofaunal longevity and biomass relationship based on data from more than 800 locations, representing 9 MSFD benthic habitats, and benthic status was assessed using the relative benthic status indicator. The pressure of seabed trawling was higher in circalittoral mud and circalittoral sand habitats showing a heterogeneous distribution pattern with intensive trawling in localized areas mainly coastal. Benthic status was high for all habitats reflecting the low trawling intensity and impact in most of the study area compared to other regions of Mediterranean or European waters. The results constitute the benchmark for benthic status in relation to trawling intensity in Eastern Mediterranean allowing to identify regions that are most at risk, and to prioritize management actions

FISHGLOB_data: an integrated dataset of fish biodiversity sampled with scientific bottom-trawl surveys.

Scientific bottom-trawl surveys are ecological observation programs conducted along continental shelves and slopes of seas and oceans that sample marine communities associated with the seafloor. These surveys report taxa occurrence, abundance and/or weight in space and time, and contribute to fisheries management as well as population and biodiversity research. Bottom-trawl surveys are conducted all over the world and represent a unique opportunity to understand ocean biogeography, macroecology, and global change. However, combining these data together for cross-ecosystem analyses remains challenging. Here, we present an integrated dataset of 29 publicly available bottom-trawl surveys conducted in national waters of 18 countries that are standardized and pre-processed, covering a total of 2,170 sampled fish taxa and 216,548 hauls collected from 1963 to 2021. We describe the processing steps to create the dataset, flags, and standardization methods that we developed to assist users in conducting spatio-temporal analyses with stable regional survey footprints. The aim of this dataset is to support research, marine conservation, and management in the context of global change