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Although gear efficiency is an important parameter in stock assessments, estimating its value experimentally is often time-consuming and laborious. The effort required is huge, especially when the survey gear previously used for a stock assessment is changed for some reason. To address the problem, we built a state-space model that can be used to estimate the gear efficiency of any new equipment relative to the original one using a dataset obtained from comparative trawl surveys. This approach is much easier to use than the direct experimental estimation used to calculate absolute gear efficiency. Using this model, we successfully estimated the relative gear efficiency of a new surface trawl net (NST-660), employed in the Japanese survey for Pacific saury, relative to the reference one (NST-99), whose gear efficiency is already known. The estimated 2.5–50–97.5 percentiles of the relative gear efficiency of NST-660 to NST-99 was 0.873, 1.59, and 2.91, respectively. The plausibility of the model assumption was validated through model diagnostics.

When evaluating catching efficiency of trawl nets for snow crabs, assessing crab behavior around the footrope is crucial. Using two underwater video cameras, we captured footage at three sections of footrope with different thicknesses and attack angles in relation to the towing direction: the belly, the lower wing gusset, and the wing sections. Based on the footage, we calculated the entry ratio (ratio of snow crabs entering the trawl net to the overall number of snow crabs in contact with the footrope). Our results indicated that the entry ratio was 0.122 at both the belly and the lower wing gusset sections and 0.530 at the wing section, suggesting that footrope thickness and/or attack angle in relation to towing direction affects the entry ratio. The total number of crabs that entered was estimated using these entry ratios and corresponded well to the number of individuals captured at the cod end. Considering the variation among entry sections, the catching efficiency of the trawl net used was estimated to range from 0.311 to 0.361. These results demonstrate that calculating the entry ratio at each section of the footrope separately allows for a more accurate estimation of catching efficiency.

Fisheries bycatch is one of the biggest threats to marine mammal populations. A literature review was undertaken to provide a comprehensive assessment and synopsis of gear modifications and technical devices to reduce marine mammal bycatch in commercial trawl, purse seine, longline, gillnet and pot/trap fisheries. Successfully implemented mitigation measures include acoustic deterrent devices (pingers) which reduced the bycatch of some small cetacean species in gillnets, appropriately designed exclusion devices which reduced pinniped bycatch in some trawl fisheries, and various pot/trap guard designs that reduced marine mammal entrapment. However, substantial development and research of mitigation options is required to address the bycatch of a range of species in many fisheries. No reliably effective technical solutions to reduce small cetacean bycatch in trawl nets are available, although loud pingers have shown potential. There are currently no technical options that effectively reduce marine mammal interactions in longline fisheries, although development of catch and hook protection devices is promising. Solutions are also needed for species, particularly pinnipeds and small cetaceans, that are not deterred by pingers and continue to be caught in static gillnets. Large whale entanglements in static gear, particularly buoy lines for pots/traps, needs urgent attention although there is encouraging research on rope-less pot/trap systems and identification of rope colours that are more detectable to whale species. Future mitigation development and deployment requires rigorous scientific testing to determine if significant bycatch reduction has been achieved, as well as consideration of potentially conflicting mitigation outcomes if multiple species are impacted by a fishery.

Owing to the development and adoption of a variety of methods for sampling and identifying microplastics, there is now data showing the presence of microplastics in surface waters from all over the world. The difference between the methods, however, hampers comparisons, and to date, most studies are qualitative rather than quantitative. In order to allow for a quantitative comparison of microplastics abundance, it is crucial to understand the differences between sampling methods. Therefore, a manta trawl and an in situ filtering pump were compared during realistic, but controlled, field tests. Identical microplastic analyses of all replicates allowed the differences between the methods with respect to (1) precision, (2) concentrations, and (3) composition to be assessed. The results show that the pump gave higher accuracy with respect to volume than the trawl. The trawl, however, sampled higher concentrations, which appeared to be due to a more efficient sampling of particles on the sea surface microlayer, such as expanded polystyrene and air-filled microspheres. The trawl also sampled a higher volume, which decreased statistical counting uncertainties. A key finding in this study was that, regardless of sampling method, it is critical that a sufficiently high volume is sampled to provide enough particles for statistical evaluation. Due to the patchiness of this type of contaminant, our data indicate that a minimum of 26 particles per sample should be recorded to allow for concentration comparisons and to avoid false null values. The necessary amount of replicates to detect temporal or spatial differences is also discussed. For compositional differences and size distributions, even higher particle counts would be necessary. Quantitative measurements and comparisons would also require an unbiased approach towards both visual and spectroscopic identification. To facilitate the development of such methods, a visual protocol that can be further developed to fit different needs is introduced and discussed. Some of the challenges encountered while using FTIR microspectroscopic particle identification are also critically discussed in relation to specific compositions found.

A subadult female loggerhead sea turtle (Caretta caretta) was caught in a trawl net off the west coast of Florida with a spotted eagle ray (Aetobatus narinari) spine lodged in the left stifle. Surgical removal of the spine was performed and antibiotic treatment was initiated. Four weeks later, endoscopy revealed a second spine entering an intestinal lumen. The fistulous tract of the left prefemoral fossa was surgically excised and the intestinal perforation was repaired. Dehiscence occurred and a vacuum-assisted closure (VAC) system was used on the wound for approximately 18 days to help reduce infection and increase the rate of healing. The left stifle wound was treated to heal by second intention. The turtle remained in rehabilitation for 19 mo before being released off the west coast of Florida. This case describes stingray envenomation injuries as a complex and potentially life-threatening bycatch effect to sea turtles caught in trawl nets.

Marine biodiversity monitoring in the Mediterranean’s increasingly threatened ecosystems is crucial for effective ecosystem conservation and management. Here, we leveraged the Mediterranean International Trawl Survey program (MEDITS) to implement eDNA sampling through the recently tested ‘metaprobe’ procedure and characterize fish assemblages in three separate areas off the Italian coasts: Northern Adriatic Sea (NoAS), Ligurian and Northern Tyrrhenian Sea (LNTS), and Sardinian Sea (SaS). By combining the information from two homologous mitochondrial 12S metabarcodes––i.e., Elas02 and Tele02 targeting elasmobranchs and teleosts, respectively––we identified 108 species, over 60% of which overlapped with those caught by the trawl net. We produced an accurate reconstruction of fish community composition of the examined sites, reflecting differences in species assemblages linked with both geographic area and depth range. Metaprobe eDNA data consistently returned a biodiversity ‘bonus’ mostly consisting of pelagic taxa not captured through bottom trawl surveys, including rare and endangered taxa (e.g., elasmobranchs). Overall, the spatial characterisation of the assemblages across the surveyed areas was better delineated and more robust using eDNA metabarcoding than trawl data. Our results support the operationalisation of the metaprobe as a simple, inexpensive, versatile sampling tool, in association with pre-existing ship surveys, to overcome many of the limitations of marine data collection and strengthen marine management.

Citarum River is the largest natural stream in West Java, Indonesia, flowing across an area of 6614 km2. About 3000 industries discharge their wastewater into the stream, affecting almost 19 million people who live along the river. Considering the perseverance and the prospective toxicity of microplastics (MPs), investigating their concentrations in this river is critical to help illustrate the exposure of the risks to the residents of the area and beyond. This study was focused on identifying the MPs concentrations in the water, sediment, and milkfish (Chanos chanos). A volume-reduce method by using manta trawl was used to take water samples. Sediment and milkfish samples were taken using a grab sampling method. Digestion of fish was using Fenton oxidation method according to weighted ratio (1:5) and H2O2 30% (w/v). The average MPs concentration in the river was 0.0574 ± 0.025 particles/m3; in the seawater ponds 3.000 ± 2.645 particles/L; and in the mixed-water ponds, where the water from the river and the sea were mixed, 0.666 ± 0.577 particles/L. The average MPs concentration in the sediment of Citarum River was 16.666 ± 0.577 particles/100 g; in the seawater ponds 13.335 ± 1.527 particles/100 g; in the mixed-water ponds 11.665 ± 0.577 particles/100 g; and in the seawater 3.335 ± 0.331 particles/100 g. The average of MPs concentration in the gut and gills of milkfish in the seawater ponds was 2.666 ± 2.333 particles/fish, and in the mixed-water ponds was 1.166 ± 0.983 particles/fish. The average of MPs concentration in the milkfish tissues taken from the sea was 1.333 ± 0.577 particles/fish; and for the ones taken from the mixed-water ponds, the concentration was 1.111 ± 0.838 particles/fish. Using the Kruskal Wallis test to generate statistical analysis, there is a significant difference between the MPs concentrations in the water and sediment samples of Citarum River based on their locations (p value = 0.024 and 0.032 < 0.05). The most dominant plastic polymers in the samples were polyethylene (PE) and polypropylene (PP). There is no correlation between the level of MPs concentrations in water and sediments and the level of MPs concentrations in milkfish. However, the existence of microplastics in every sample that came from different points in the sampling area should sound an alarm, either to the local government or residents.

Microplastics in marine environments are of emerging concern due to their widespread distribution, their ingestion by various marine organisms, and their roles as a source and transfer vector of toxic chemicals. However, our understanding of their abundance and distribution characteristics in surface seawater (SSW) remains limited. We investigated microplastics in the surface microlayer (SML) and the SSW at 12 stations near-shore and offshore of the Korean west coast, Incheon/Kyeonggi region. Variation between stations, sampling media, and sampling methods were compared based on abundances, size distribution, and composition profiles of microsized synthetic polymer particles. The abundance of microplastics was greater in the SML (152,688 ± 92,384 particles/m 3 ) than in SSW and showed a significant difference based on the sampling method for SSWs collected using a hand net (1602 ± 1274 particles/m 3 ) and a zooplankton trawl net (0.19 ± 0.14 particles/m 3 ). Ship paint particles (mostly alkyd resin polymer) accounted for the majority of microplastics detected in both SML and SSWs, and increased levels were observed around the voyage routes of large vessels. This indicates that polymers with marine-based origins become an important contributor to microplastics in coastal SSWs of this coastal region.

The use of citizen science in the collection of surface water marine microplastics (MP) samples with manta trawl was tested in the Baltic Sea, where the collection of surface water samples is often hampered by environmental conditions. Sampling was carried out at 7 locations around the Baltic Sea with a custom-made manta trawl which was operated onboard a sailing boat. The total concentrations of ≥ 0.3 mm MP in the samples ranged from 0.45 to 1.98 MP m −3 . Based on the results and experiences from this study, citizen science could be introduced into the toolbox of monitoring large MP. When the common basic constraints of surface water sampling within a regional sea are defined and agreed upon, citizen science could be used for strengthening the power of assessments on the state of the marine environment by increasing the spatial coverage of the monitored area.

1. Bottom-trawl fisheries are widespread and cause mortality of benthic invertebrates, which in turn may lead to a decrease in the availability of prey for target fish species. Exploitation also reduces the abundance of the fish species themselves. Modelling studies have shown that bottom trawling could lead to both increases and decreases in fish production, but so far empirical evidence to test these ideas has been very limited. We hypothesize that the effect of bottom trawling on the food intake and condition of fish depends on how the ratio of prey to consumers changes with increasing fishing pressure. 2. We assessed the impact of bottom trawling on the food availability, condition and stomach contents of three flatfishes and the Norway lobster in an area in the Kattegat that is characterized by a steep commercial bottom-trawling gradient due to the establishment of an area closed to all fisheries, but otherwise has homogeneous environmental conditions. 3. For plaice, prey biomass initially decreased at a slower rate with trawling than the biomass of fish, and as a result, the amount of food available per plaice increased before decreasing at trawling frequencies > 5 times year⁻¹. This pattern was mirrored in both the condition and stomach contents of plaice and for long-rough dab. 4. No effect of trawling on dab prey and condition was found. Conversely, the condition of the main target species - Norway lobster - increased as its biomass decreased with increased trawling intensities. 5. Together, these results support the idea that when the abundance of the prey declines in response to exploitation, the ratio of the prey to consumer biomass will determine whether exploitation will result in an increase or a decrease in the food intake and condition of the predator. 6. Synthesis and applications. Our study indicates that fish production may be maximized by keeping bottom-trawling intensities relatively low, although this may negatively affect the economically more important Nephrops fishery. The effects of bottom trawls may be mitigated by switching to gears, which affect prey availability to a lesser extent, such as pots or creels.