Bottom Trawl Research Articles (Page 1)

Pb, Cd, and Cu concentrations in Scyliorhinus canicula (Linnaeus, 1758) and M. merluccius (Linnaeus, 1758): Accumulation trends and interspecific biomonitor potential.

Shift in demersal marine communities at the edge of two biogeographic areas between 1996 and 2021.

The seafloor under study: analysis of substrate and habitat influence on the distribution of benthic litter.

The sustainable management of water bodies with hydropower plants (HPPs) and protected rheophilic fish species is challenging. The key question is whether impounded rivers can still provide habitat for protected rheophilic fish species, including Natura 2000 species. We investigated hydro-morphological conditions and fish communities, focusing on the bottom-dwelling Danube longbarbel gudgeon (Romanogobio uranoscopus) and the medium-distance migrating cactus roach (Rutilus virgo) in the Brežice HPP system on the Sava River in Slovenia. Fish sampling using an electric bottom trawl in the HPP impoundment, electrofishing in the nearshore, and video surveillance in the fish pass revealed a diverse and distinctive fish community. This community reflected rheophilic conditions in the upper impoundment and fish pass, and lentic conditions in the lower impoundment. These findings provide evidence that impounded rivers, when complemented by well-designed mitigation measures, can sustain rheophilic fish species, including the Danube longbarbel gudgeon and cactus roach. Maintaining rheophilic habitat within the impoundment, combined with a functioning river-like side channel, is crucial. However, at Brežice HPP, changes in the management of the fish pass water inflow are necessary to ensure adequate and consistent hydraulic conditions and water temperatures. Applying a knowledge co-creation approach, which requires productive interaction among scientists, managers and policy makers, could help to find the best solutions for sustainable water ecosystem management.

Seasonal dynamics and driving factors of habitat for two small-size shark species in the northern South China Sea.

Abstract. Continental shelves are critical for the global carbon cycle as they store substantial amounts of organic carbon (OC). Shelf sediments can also be subject to considerable anthropogenic pressures, offshore construction and bottom trawling for example, potentially releasing OC that has been sequestered into sediments. As a result, these sediments have attracted attention from policy makers regarding how their management can be leveraged to meet national emissions reduction targets. Spatial models offer solutions to identifying organic carbon storage hotspots; however, regional predictions of OC often rely on global scale predictors which may have biases on smaller scales, reducing their utility for practical management decisions. In addition, estimates of dry bulk density (DBD), an important factor in calculating OC stock from sediment OC content, are typically derived from an empirical relationship developed in one region and applied elsewhere, rather than from local in situ data, leading considerable uncertainty in regional OC stock estimates. We compared the performance of two spatial models of OC stock. The first used unadjusted predictors and a commonly used empirical relationship to estimate DBD. The second spatial model incorporated bias-adjusted predictors and a machine learning DBD model, trained on in situ DBD data. The adjusted model predicted a total OC reservoir of 46.6 ± 43.6 Tg in the top 10 cm of sediment in the Irish Sea, which was 31.4 % lower compared to unadjusted estimates. 70.1 % of the difference between adjusted and unadjusted OC stock estimates was due to the approach for estimating DBD. These findings suggest that previous models may have overestimated OC reservoirs and highlight the influence of accurate DBD and predictor adjustments on stock estimates. These findings highlight the need for increased in situ DBD measurements and refined modelling approaches to enhance the reliability of OC stock predictions. This study provides a framework for refining spatial models and underscores the importance of reducing uncertainties in key parameters to better understand and manage OC storage potential of marine sediments.

For the best part of the nineteenth century, sail trawlers used for sea fishing were the most important issue the Greek state had to deal with. The ‘Neapolitan trawlers’, as they are termed in the sources, were identified, from the very beginning of their intrusion, as a problem requiring a solution. The very presence of foreign fishing boats, as well as the specific methods employed by them, introduced in the most urgent manner the issue of marine ecosystem protection into the public debate. The Greek state, in its efforts to remove foreign fishing vessels from the coast, used a variety of provisions from the Law of Nations and imposed prohibitive measures, thus establishing the first legislative framework for fisheries. Despite the restrictions on the use of trawlers and the pressures exerted to enforce them, their use did not decrease but, on the contrary, was adopted by Greek fishermen.

The Underwater Noise Footprint of Bottom Trawling in the National Marine Park of Alonnisos, Greece

The starry ray, Raja asterias (Delaroche 1809), is a demersal Mediterranean skate often caught as bycatch in bottom trawls and set nets. Due to high fishing pressure in the Adriatic Sea, key life history traits were investigated to support effective conservation and fishery management. Specimens were collected from 2019 to 2023 through both fishery-dependent and independent sampling in the mid-western Adriatic. Age was estimated for the first time in cartilaginous fish using burnt and dissected vertebrae. The reproductive cycle was assessed through macroscopic gonad examination, while spatial distribution was analyzed in relation to sex and maturity (mature vs immature). Trends in relative abundance and biomass (2007–2024) were evaluated using standardized survey data. Results revealed significant sexual dimorphism in biological traits. Females showed a broader size range (170–590 mm vs 160–505 mm), greater disc width (115–410 mm vs 105–342 mm), and positive allometric growth, compared to isometric growth in males. Growth patterns also differed: Von Bertalanffy parameters were L∞ = 724, k = 0.28 for females and L∞ = 574, k = 0.44 for males. Females reached greater maximum age (4.5 vs 4.0 years), and achieved sexual maturity at larger sizes (425 vs 360 mm) and older ages (approx. 3.0 vs 2.0 years). Spatial analysis showed that immature individuals are concentrated nearshore (<50 m depth), while mature ones inhabit deeper waters (up to 80 m). During the reproductive season, adults migrate inshore, overlapping with immature habitats. Abundance and biomass indices significantly increased over time, particularly after 2020. These findings underscore the need for sex-specific biological parameters in management strategies. Conservation measures should avoid using population-wide averages and instead adopt the most precautionary approach. Additionally, limiting fishing in shallow waters could reduce bycatch of immature or egg-laying individuals for much of the year, positively impacting population recovery.

The Polar areas of the Arctic and Antarctic are the coolers of the world. In the Arctic there is floating sea ice covering the more than 4,000 m deep central Arctic Ocean surrounded by islands like Greenland with a thick ice sheet, and Svalbard and other high-Arctic Islands with glaciers. Antarctica is a large continent (about 14.2 mill. km2) with a huge ice sheet, and seasonal sea ice in the surrounding, more than 4,000 m deep, Southern Ocean. The shallow marginal seas like the Barents Sea and the Bering Sea, are influenced by relatively warm, nutrient-rich sea currents, with associated plankton, from lower latitudes and therefore very productive. In the European Arctic there are rich fisheries in salmonids, clupeoids, gadoids, and crustaceans. The circulation of the Southern Ocean is dominated by the strong Antarctic Circumpolar Current, and there is a high abundance of plankton, krill, fish, seabirds, penguins, seals, and whales. The large Antarctic krill resources are subject to a fishery limited to about 600,000 tons annually. Through the working groups PAME and CAFF of the Arctic Council there are ongoing processes for area-based management in Arctic waters. In the territorial waters of the Arctic nations, many examples exist of different categories of Marine Protected Areas (MPA) with different degrees of protection. For the central Arctic Ocean there is an agreement from 2021 of no fishing for the next 15 years until the potential resources in the area has been properly mapped and assessed scientifically. In the Barents Sea, there is a system of temporary real-time closures of large areas for Danish seining and bottom trawling to protect juvenile fishes. The Antarctic Treaty, the Environment Protection Committee, and the Convention of Conservation of Living Marine Resources have been backdrops for ongoing processes to further develop area-based management in the Southern Ocean. Just two marine protected areas are established, but there are several Antarctic Specially Protected Areas (ASPA) and Antarctic Specially Managed Areas (ASMA), both which may have marine components. There are also proposals for several new MPAs. Recently, large areas in the Weddell Sea were discovered to be spawning habitats for icefish (Neopagetopsis ionah). This species lay fertilized eggs in a nest on the bottom substrate, and guard them until hatching. Any kind of active bottom fishing gears or other bottom gears would easily disturb and destroy their habitats. Thus, such areas need protection to conserve vulnerable biodiversity.

Fishery-independent surveys are vital for marine resource management, offering unbiased assessments of species abundance. Consistent trawl gear performance, however, is challenging across diverse geographic ranges or with multiple vessels. A trawl modification that has repeatedly been shown to improve consistency across a large depth range is the use of a restrictor rope to limit the width of trawl gear. While its stabilizing impact on gear performance is established, its effect on catch rates is less understood. We assessed the utility of this gear component in a collaborative experiment conducted in southern New England, USA, focusing on the impact of a restrictor rope on catches of the region's commercially important species in a common trawl survey net. Drawing input from regional stakeholders, this experiment utilized a commercial fishing vessel to conduct alternate tows, with and without a restrictor rope attached to the trawl doors. Results suggest few or subtle impacts of the restrictor rope treatment on total catches or catch-at-length for the examined species. This research offers valuable insights for standardizing gear performance using restrictor ropes.

Bottom trawling affects trophic niche diversity of red mullet in muddy bottoms of the Mediterranean continental shelf.

Habitat suitability and ecological corridors for cuttlefish Sepiella japonica: Informing conservation and release strategies.

Drivers of microplastic accumulation in a densely canyoned continental margin: Insights from blackmouth catsharks (Galeus melastomus).

Seamounts host some of the most biodiverse and vulnerable deep-sea ecosystems, as epitomised by the elevated diversity and biomass of fauna associated with extensive reefs of the frame-work forming coral Solenosmilia variabilis. In places, these vulnerable marine ecosystems (VMEs) have been substantially impacted by commercial bottom trawl fishing and face increasing threats from climate variability. Understanding both the current and historical distribution of coral reefs enables naturalness and recovery to be considered in conservation planning. Our study on the Tasmanian seamounts, an area characterised by extensive deep-sea coral reefs and historical trawling impacts, employed fine-scale Species Distribution Modelling (SDM) using acoustically derived bathymetry and backscatter data resolved to 15 m resolution to capture fine-scale habitat heterogeneity. We used a two-model methodology to predict VME habitat distributions before and after trawling impacts across a broad region (>480 km2) containing multiple seamounts with peak depths ranging from 720–2,073 m and varied substrates, as indicated by a spectrum backscatter intensity values. Bathymetry, relative slope position, backscatter and trawling history were most influential among a suite of predictor variables. Comparison of before and after models showed a reduction in both total area and patch sizes of coral habitat consistent with areas classified as historically impacted by trawling. The reduction in extent of coral VME area was dependent on the probability threshold of habitat suitability used in the model, decreasing by 20.44%–26.07% following trawling across a range of thresholds from 0.5–0.85. Our study highlights the benefits to future spatially based biodiversity management initiatives that will stem from using high-resolution bathymetry and backscatter data, and information on anthropogenic impacts, in SDM predictions.

A comprehensive understanding of a species life history is fundamental for effective fisheries management. This study contributes crucial, up-to-date information by analyzing the age structure and key biological parameters of southern blue whiting (Micromesistius australis) in the area defined by the 52° S-56° S parallels, based on data collected in 2019. It determined the population structure, growth parameters, and natural mortality using data from 2019 commercial bottom trawls and one research cruise. Analyzed specimens ranged from 26 to 59 cm total length (TL) in males and 26 to 64 cm TL in females. Length-frequency distributions were similar between sexes, with a main mode between 45 and 47 cm TL. Age analysis of 2,378 otoliths indicated a minimum age of two years and maximum ages of 20 years old. Significant differences in growth parameters were observed between sexes, primarily due to females having a larger asymptotic length. Von Bertalanffy growth function parameters were: females L¥ = 63.93 cm, K = 0.18 year-1, and t0 = -1.41 years; and males, L¥ = 57.43 cm, K = 0.21 year-1, and t0 = -1.39 years. The length-weight relationship also showed a significant sex difference. Length and age at 50% maturity were estimated at 35.25 cm TL and 2.93 years, respectively, with no significant differences between sexes. Estimates of instantaneous natural mortality ranged from 0.27 to 0.33 year-1. These findings provide valuable insights into M. australis life history in the region, relevant for future stock assessments and sustainable management strategies. The inclusion of Malvinas Islands data significantly enhances the robustness and applicability of these findings across the Southwest Atlantic.

Two goby species, Egglestonichthys melanoptera (Visweswara Rao, 1971) and Obliquogobius yamadai Shibukawa & Aonuma, 2007, are recorded for the first time from southwestern Taiwan based on specimens collected by bottom trawl. The former is represented by four specimens, representing its northernmost distributed range. The latter is represented by a single specimen, marking the first record of the genus and species from Taiwan. This finding fills the distribution gap between Japan and the region spanning southern Indonesia to northwestern Australia. Detailed descriptions and photographs are presented, with comparisons to previously documented specimens and notes on morphological variation.

The waters surrounding the Five West Sea Islands of South Korea are ecologically important but challenging to survey due to their location within a strategic military zone, strong tidal currents, and significant tidal variation. To assess the fish community in this region, we conducted Korea's first parallel investigation combining traditional bottom trawl surveys with environmental DNA (eDNA) metabarcoding. Sampling was performed at 10 stations in March, May, and August 2023, and the relationship between fish species occurrence and environmental variables (water temperature, salinity, and depth) was examined. Dominant trawl-caught species included Engraulis japonicus, Johnius grypotus, Coilia nasus, and Okamejei kenojei, each showing seasonal migration and spawning patterns associated with temperature changes. eDNA analysis detected nine additional species absent from trawl catches, such as Ilisha elongata and Thamnaconus modestus, demonstrating its sensitivity in identifying both migratory and sedentary taxa. Our findings confirm that eDNA surveys can complement traditional sampling, improving biodiversity assessment in regions with limited accessibility and complex oceanographic conditions.

Biogeographical partitioning of ecological communities has been renewed in recent decades to illustrate broad distributional patterns. In the oceans, observational datasets have grown substantially and open new access to test bioregional patterns beyond classically fixed thresholds of endemism to differentiate regions. This work combines a recently collated dataset of 29 different scientific bottom trawl surveys spanning 21 years with network‐based clustering to illustrate biogeographical partitions of vast tracts of the Northern Hemisphere's continental shelf seas. Our work contributes to testing bioregionalization patterns in demersal fishes using observational data, totaling 138 227 trawls and > 1700 species, with bipartite network clustering weighted by species occurrence frequencies. We propose eight major biogeographical partitions of marine demersal fish communities across shelf seas in the Northern Hemisphere. These patterns capture known biogeographical boundaries (e.g. North Sea–Baltic Sea, Cape Hatteras) alongside potential transition areas deduced from uncertainty estimates based on shared network nodes between bioregions. The most species‐rich areas include the Southeast US Shelf, Temperate Pacific, Northeast Atlantic Shelf, and the Outer European Shelf – corresponding to relatively high endemicity. However, the relatively species‐poor partitions including the Baltic Sea and the North and Celtic Seas display comparatively low endemicity (~10%), illustrating apparent statistical differences in partitions captured by bipartite networks and occurrence frequencies that would otherwise be missed using a fixed endemic criterion. Our proposed bioregionalization can be compared against the growing availability of species occurrence data, dispersal limitations, or other quantitative observations of ecological communities.

Fisheries management faces challenges due to political, spatial, and ecological complexities, which are further exacerbated by variation or shifts in species distributions. Effective management depends on the ability to integrate fisheries data across political and geographic boundaries. However, such efforts may be hindered by inconsistent data formats, limited data sharing, methodological differences in sampling, and regional governance differences. To address these issues, we introduce the surveyjoin R package, which combines and provides public access to bottom trawl survey data collected in the Northeast Pacific Ocean by NOAA Fisheries and Fisheries and Oceans Canada. This initial database integrates over 3.3 million observations from 14 bottom trawl surveys spanning Alaska, British Columbia, Washington, Oregon, and California from the 1980s to present. This database standardizes variables such as catch-per-unit-effort (CPUE), haul data, and in-situ measurements of bottom temperature. We demonstrate the utility of this database through three case studies. Our first case study develops a coastwide biomass index for Pacific hake (Merluccius productus) using geostatistical index standardization, comparing results to independent acoustic survey estimates. The second case study examines spatial patterns in groundfish community structure, highlighting breakpoints between assemblages in their mixture of life histories and trophic compositions. Our third example applies spatially varying coefficient models to assess sablefish (Anoplopoma fimbria) biomass trends, identifying regional variability in increases in occurrence and biomass. Together, these case studies demonstrate how the surveyjoin R package and database may improve species and ecosystem assessments by providing insights into population trends across geopolitical boundaries. This database and package represent an important step toward offering a scalable framework that can be extended to include additional data types, surveys, and species. By fostering collaboration, transparency, and data-driven decision making, surveyjoin supports international efforts to sustainably manage shared marine resources under dynamic environmental conditions.