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Deep-sea fish species are targeted globally by bottom trawling. The species captured are often characterized by longevity, low fecundity and slow growth making them vulnerable to overfishing. In addition, bottom trawling is known to remove vast amounts of non-target species, including habitat forming deep-sea corals and sponges. Therefore, bottom trawling poses a serious risk to deep-sea ecosystems, but the true extent of deep-sea fishery landings through history remains unknown. Here, we present catches for global bottom trawling fisheries between years 1950-2015. This study gives new insight into the history of bottom trawled deep-sea fisheries through its use of FAO capture data combined with reconstructed landings data provided by the Sea Around Us Project, which are the only records containing bycatches, discards and unreported landings for deep-sea species. We illustrate the trends and shifts of the fishing nations and discuss the life-history and catch patterns of the most prominent target species over this time period. Our results show that the landings from deep-sea fisheries are miniscule, contributing less than 0.5 % to global fisheries landings. The fisheries were also found to be overall under-reported by as much as 43 %, leading to the removal of an estimated 25 million tonnes of deep-sea fish. The highest catches were of Greenland halibut in the NE Atlantic, Longfin codling from the NW Pacific and Grenadiers and Orange roughy from the SW Pacific. The results also show a diversification through the years in the species caught and reported. This historical perspective reveals that the extent and amount of deep-sea fish removed from the deep ocean exceeds previous estimates. This has significant implications for management, conservation and policy, as the economic importance of global bottom trawling is trivial, but the environmental damage imposed by this practice, is not.

Introduction: Chondrichthyans (sharks, batoids and chimaeras) play key roles in the regulation of marine food webs dynamics. However, more than half of the assessed species in the Mediterranean are threatened, primarily by fishing pressure and compounded by habitat degradation and climate change. Nevertheless, there is an important knowledge gap in identifying the underlying drivers of their community structure and spatial distribution. Methods and Results: We provide insights into the current bycatch rates of chondrichthyans in the western Mediterranean commercial bottom trawling fishery by accurately depicting the unaltered practices of the local fleet. A total of 17 species were recorded in the studied fishing grounds (ranging from 50 to 800 m deep), including 7 sharks, 9 batoids, and 1 chimaera, although the total catch was dominated by few species. Furthermore, we tested the effect of environmental and fishing-related factors on multiple community descriptors by using analysis of community structure (multidimensional scaling and analysis of similitude) and generalized linear mixed models to further understand the drivers of the chondrichthyan community distribution and structure. This study revealed the importance of combining environmental and anthropogenic drivers to further understand the spatial distribution patterns of chondrichthyan communities. Our results indicate that depth was the main driver of the community structure, with deeper areas within the fishing grounds hosting a higher diversity. Sea bottom temperature and substrate type also influenced the distribution of the community, with substrate effects changing depending on the intensity of fishing pressure. In all cases, density, biomass, and diversity of chondrichthyans were negatively impacted by increasing fishing effort. Discussion: Understanding the drivers of the structure and distribution of the chondrichthyan community is crucial to understand the potential impacts that increased fishing pressure, habitat loss and global change may entail. The ongoing challenges that the Mediterranean chondrichthyans and their ecosystems are facing highlights the need for continued monitoring and improved chondrichthyan-focused fisheries management.

To inform ecosystem-based fisheries management in line with the EU legislation objectives for marine fisheries, we evaluated the ecological outcomes of alternative spatial management scenarios to fisheries that consider the ecological impact of bottom trawling on the benthic ecosystem in the Eastern Ionian Sea. Trawling intensity in terms of swept area ratio (SAR) and benthic community sensitivity were combined to estimate the relative benthic status (RBS). Then, five management scenarios were tested. The scenarios include four static closure scenarios (below 800 m, below 600 m, the least-trawled 10% of fishing grounds, and areas shallower than 150 m), where trawling is completely excluded without fishing effort redistribution, and one with a trawl ban in all marine protected areas, where fishing effort displacement is modelled dynamically. Baseline RBS was high (>0.9 on a scale of 0 to 1 where 1 is unaffected benthic community) in all habitats, reflecting relatively low benthic degradation due to bottom trawling. Excluding bottom trawling from areas shallower than 150 m in depth produced the greatest improvements, while thresholds at 600 or 800 m depth, and the closure of the 10% least-trawled grounds, had no significant effects on benthic ecological status. Closure of trawling in the marine protected areas produced mixed outcomes, with improvements in some habitats but localized declines due to displaced effort in others. Our study demonstrates the value of including benthic indicators in spatial management strategies to guide adaptive, evidence-based fisheries governance, balancing conservation objectives with socio-economic sustainability.

Chondrichthyans are a very important taxon that plays a top predator role in the trophic level of the food web, and species are particularly vulnerable to exploitation in the marine ecosystem. The deep waters of the eastern Mediterranean Sea have been less studied than the continental shelf, especially for the chondrichthyans. Therefore, the present study was conducted to investigate the spatio-temporal distribution of chondrichthyans collected monthly in eight different (200–900 m) depth strata during different periods (2010–2011 and 2019–2021) using an otter bottom trawl. A total of 17 species were identified in upper bathyal, composed of 6 batoids, 10 sharks, and one chimaera. The constant species (dominance: DO% > 50) in the study area were Galeus melastomus , Scyliorhinus canicula , Etmopterus spinax , and Raja clavata . The most abundant species was E. spinax , followed by G. melastomus . Fourteen and 15 species were caught during the first and the second survey, respectively. Biodiversity characteristics (number of species, abundance, and diversity indices) varied only with bottom depth. Two different depthwise assemblages were estimated along the bottom depth gradient; ≤ 500 m and > 500 m. The discriminator species were R. clavata , S. canicula , G. melastomus , Dipturus oxyrinchus , and Squalus blainville found on the upper slope and E. spinax , G. melastomus , and Centrophorus cf. uyato found on the lower slope. With our results, total number of demersal chondrichthyan species found in the bottom (bathyal and continental shelf) of Antalya Bay was reached to 26 species.

Many studies have been conducted with the aim of reducing fuel consumption by the fishing industry. We examined whether drag can be reduced by changing the arrangement of gears without requiring the development of new parts for the conventional float and ground gear. Ten differently shaped floats and ground gears were measured in a water flume tank. The float and ground gear were fixed to a steel rod to measure fluid drag according to attack angle, using a multi-component load cell. To estimate the frictional drag of ground gear on the seabed, five types of large ground gear were towed on flat land while changing attack angle using the load cell to measure tension. The fluid drag of the float and ground gear was highest at an attack angle of 60°, regardless of shape, size, and flow velocity. The resistance coefficients of the float and ground gear varied depending on the attack angle and tended to be lower at small attack angles. The frictional drag of the ground gear was greater when the axis of rotation had a small attack angle in the towing direction compared to other attack angles. We then investigated a method for designing bottom-towed gear that reduces drag while maintaining the size, buoyancy, and sinking force of conventional fishing gear parts. This gear design showed 1.2% drag reduction and an estimated 0.8% improvement in fuel efficiency per haul.

Greiner, B.E.; Marrone, A.; Mifsud, J.; Camilleri, K.; Camilleri, L.; Gauci, A.; Zammit, A.; Kossari-Tarnik, E., and Deidun, A., 2024. Exploring the spatial distribution, composition, and depth-related patterns of marine litter in Maltese waters: Insights from the MEDITS survey data. In: Phillips, M.R.; Al-Naemi, S., and Duarte, C.M. (eds.), Coastlines under Global Change: Proceedings from the International Coastal Symposium (ICS) 2024 (Doha, Qatar). Journal of Coastal Research, Special Issue No. 113, pp. 396-401. Charlotte (North Carolina), ISSN 0749-0208. Marine litter is one of the most serious anthropogenic challenges to the integrity of global marine ecosystems. Public awareness is often limited to the visible litter that washes up on beaches or floats on the ocean surface. Less attention is paid to marine litter that is deposited and accumulates on the seafloor, due to operational constraints. The Mediterranean Bottom Trawl Survey (MEDITS) can provide insights into the state of seabed litter distribution and composition collaterally with the primary fish shock assessment. This study analyses the MEDITS 2020/2021 marine litter dataset in terms of a spatial, temporal and depth distribution in the Geographical Subarea (GSA) 15, i.e. off the coast of Malta. The composition of the litter and its potential major sources were determined. For these analyses, a two-sided independent t-test was applied using SPSS. Visualization was done by creating maps and bar charts using QGIS and MATLAB. Results revealed tourism and household items as primary contributors to marine litter, with plastics comprising the majority. Surprisingly, the onset of the COVID-19 pandemic appears correlated with a significant reduction in seafloor litter accumulation. Spatial distribution dynamics suggest that subsurface currents influence the transport of light litter items like plastic, while heavy litter, such as metals, tends to remain localised. Compared to other Mediterranean regions, the seabed off Malta shows a relatively clean status. This study not only provides valuable insights into the local marine environment but also underscores the need for novel global strategies to address the marine litter issue. These findings prompt considerations for future environmental management practices and highlight potential areas for further research in the broader context of marine environmental monitoring.

Bottom trawl fishing has widespread impacts on benthic habitats and communities. The benthic response to trawling seems to be smaller or absent in areas exposed to high natural disturbance, leading to the hypothesis that natural and trawl disturbance affect benthic communities in a similar way. However, systematic tests of this hypothesis at large spatial scales and with data from sites spanning a large range of natural disturbance do not exist. Here, we examine the effects of trawl and natural (tidal-bed shear stress) disturbance on benthic communities over gradients of commercial bottom trawling effort in 8 areas in the North and Irish Seas. Using a trait-based approach, that classified species by life-history strategies or by characteristics that provide a proxy for their role in community function, we found support for the hypothesis that trawl and natural disturbance affect benthic communities in similar ways. Both sources of disturbance caused declines in long-living, hard-bodied (exoskeleton) and suspension-feeding organisms. Given these similar impacts, there was no detectable trawling effect on communities exposed to high natural disturbance. Conversely, in 3 out of 5 areas with low bed shear stress, responses to trawling were detected and resulted in community compositions comparable with those in areas subject to high natural disturbance, with communities being composed of either small-sized, deposit-feeding animals or mobile scavengers and predators. The findings highlight that knowledge of the interacting effects of trawl and natural disturbance will help to identify areas that are more or less resilient to trawling and support the development of management plans that account for the environmental effects of fishing.

Bottom trawling represents the most widespread anthropogenic physical disturbance to seafloor sediments on continental shelves. While trawling-induced changes to benthic ecology have been widely recognized, the impacts on long-term organic carbon storage in marine sediments remains uncertain. Here we combined datasets of sediment and bottom trawling for a heavily trawled region, the North Sea, to explore their potential mutual dependency. A pattern emerges when comparing the surface sediment organic carbon-to-mud ratio with the trawling intensity represented by the multi-year averaged swept area ratio. The organic carbon-to-mud ratio exhibits a systematic response to trawling where the swept area ratio is larger than 1 yr −1 . Three-dimensional physical–biogeochemical simulation results suggest that the observed pattern is attributed to the correlated dynamics of mud and organic carbon during transport and redeposition in response to trawling. Both gain and loss of sedimentary organic carbon may occur in weakly trawled areas, whereas a net reduction of sedimentary organic carbon is found in intensely trawled grounds. Cessation of trawling allows restoration of sedimentary carbon stock and benthic biomass, but their recovery occurs at different timescales. Our results point out a need for management of intensely trawled grounds to enhance the CO 2 sequestration capacity in shelf seas. Intensive bottom trawling causes a long-term reduction of organic carbon stored in seafloor sediments, suggesting a need for more effective management, according to observations and biogeochemical modelling.

The climate regime in the eastern Bering Sea has recently been dominated by a pattern of multi-year stanzas, in which several successive years of minimal sea-ice formation and warm summer temperatures (e.g., 2002–2005, 2014–2017) alternate with several years of relatively extensive sea-ice formation and cold summer temperatures (e.g., 2006–2013). This emerging climate pattern may be forcing long-term changes in the spatial distributions of the Bering Sea’s marine fauna. The National Marine Fisheries Service’s Alaska Fisheries Science Center recently conducted two bottom trawl surveys covering the entire Bering Sea shelf from the Alaska Peninsula to the Bering Strait. The first, in the summer of 2010, was conducted during a cold year when the majority of the continental shelf was covered by a pool of cold (< 2 °C) water. The second, in the summer of 2017, was during a warmer year with water temperatures above the long-term survey mean. These two surveys recorded significantly different spatial distributions for populations of several commercially important fish species, including walleye pollock (Gadus chalcogrammus), Pacific cod (Gadus macrocephalus), and several flatfish species, as well as jellyfishes. Population shifts included latitudinal displacement as well as variable recruitment success. The large-scale distributional shifts reported here for high-biomass species raise questions about long-term ecosystem impacts, and highlight the need for continued monitoring. They also raise questions about our management strategies for these and other species in Alaska’s large marine ecosystems.

Day-night variations in catch of demersal species were examined by a six-day trawl survey carried out in September 2017 on the shelf-break (125–155 m depth) off the southwestern coast of Sicily. A total of seven hauls per day were performed, distributed between full daylight and complete darkness. Two main assemblages separating nocturnal and diurnal hauls were identified using ANOSIM and PERMANOVA analysis. The diurnal assemblage was characterised by higher species richness, dominance, and low diversity, with the main species consisting of visual bentho-pelagic predators, such as Illex coindetii and Merluccius merluccius, whereas lower richness but higher evenness and diversity were observed during the night, with species such as Chlorotocus crassicornis, Alloteuthis spp., and Lesueurigobius suerii characterising the assemblage. Among the main commercial species caught by bottom trawling in the area, Parapenaeus longirostris showed high CPUE values during daylight hours, while Trachurus trachurus displayed a clear diel pattern with a peak around midday and a minimum at night. In contrast, M. merluccius did not exhibit any significant variation in catch rates over the daily cycle. Understanding diel variations in shelf-break assemblages and commercial species may contribute to the regulation of fishing activities by guiding the implementation of technical measures to minimize unwanted catch and promote more sustainable demersal fisheries.