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The offshore Northern shrimp (Pandalus borealis) bottom trawl fishery in eastern Canada currently uses 22 and 28 mm bar spacing Nordmøre grids to limit bycatch from using small mesh codends. However, a recent rebound of juvenile redfish (Sebastes spp.), that can pass through the grids, has greatly increased bycatch. To address this concern, this study investigated the effectiveness of 17 and 15 mm bar spacing Nordmøre grids in a twin-trawl (paired) configuration against the traditional 22 mm bar spacing grid. Size selectivity analyses showed that the 17 and 15 mm grids resulted in no significant reduction in shrimp catch across all length classes. The 17 mm grid significantly reduced redfish bycatch for all length classes and the 15 mm grid significantly reduced redfish bycatch for individuals larger than 95 mm total length. Less redfish entered the codend with the experimental grids, however, the overlap in width between redfish and Northern shrimp limits the overall sorting efficiency of the grids, leaving some redfish still vulnerable to capture.

The offshore Northern shrimp (Pandalus borealis) bottom trawl fishery in eastern Canada currently uses 22 and 28 mm bar spacing Nordmøre grids to limit bycatch from using small mesh codends. However, a recent rebound of juvenile redfish (Sebastes spp.), that can pass through the grids, has greatly increased bycatch. To address this concern, this study investigated the effectiveness of 17 and 15 mm bar spacing Nordmøre grids in a twin-trawl (paired) configuration against the traditional 22 mm bar spacing grid. Size selectivity analyses showed that the 17 and 15 mm grids resulted in no significant reduction in shrimp catch across all length classes. The 17 mm grid significantly reduced redfish bycatch for all length classes and the 15 mm grid significantly reduced redfish bycatch for individuals larger than 95 mm total length. Less redfish entered the codend with the experimental grids, however, the overlap in width between redfish and Northern shrimp limits the overall sorting efficiency of the grids, leaving some redfish still vulnerable to capture. [ABSTRACT FROM AUTHOR]

A new gillnet made from multiple mesh sizes ranging from 125 to 180 mm of stretched mesh (experimental gillnet) was tested under commercial fishing conditions to compare the fishing performance with that of conventional gillnets with a 125 mm mesh opening (control gillnet). Catch efficiency and size selectivity between the two gillnet types were evaluated throughout one year of fishing in three different locations in the waters of Vietnam. Experimental gillnets caught narrow-barred Spanish mackerel (Scomberomorus commerson), spotted mackerel (Scomberomorus guttatus), and wahoo (Acanthocybium solandri) in comparable amounts to the control gillnets, with the moon phase, month, and depth explaining some of the variation in the catch per unit effort (CPUE). An analysis of the size-dependent catch comparison rates and selectivity parameters showed that the experimental gillnets captured a wider range of narrow-barred Spanish mackerel sizes, but with a substantial proportion of individuals larger than those caught by the control gillnets. This is of higher weight per unit effort, and fishing enterprises therefore could improve their economic benefits by using modified gillnets with multiple mesh sizes. Our findings also support the biological and environmental benefits of the modified gillnet size selection, which might also extend to other species. [ABSTRACT FROM AUTHOR]

In this study, we used escape location underneath the trawl to understand groundfish herding behaviour at the trawl mouth. Three collecting bags (port, center, starboard) were mounted under the trawl and behind the footgear to collect escapees. The escape-at-length of species that escaped into the center bag were compared to the two wing bags to infer fish response behaviour, herding behaviour, and swimming capacity at the trawl mouth. For roundfish, smaller-sized individuals escaped more in the center for both Atlantic cod (Gadus morhua) and haddock (Melanogrammus aeglefinus), <20 and 11 cm, respectively, indicating that larger-sized fish were to a greater extent seeking to escape under the trawl at the wings, vs small fish being herded to the center and likely overrun due to reduced swimming capacity. For flatfish and monkfish (Lophius piscatorius), results varied. European plaice (Pleuronectes platessa), American plaice (Hippoglossoides platessoides), and monkfish were caught most often in the wings, though not significantly for American plaice. Catches of dab (Limanda limanda) between 18 and 27 cm were significantly higher in the center, with no difference for smaller and larger individuals. The differences between fish escape location likely result from a combination of varying herding behaviour, size, and swimming capacity. Here, we were able to show how these size-dependent behaviours relate to fish response behaviour, escape behaviour, size, and likely swimming capacity. [ABSTRACT FROM AUTHOR]

In the last decade, there has been increasing interest in the use of artificial illumination as a bycatch reduction device. In the U.S. West Coast groundfish bottom trawl fishery, research has found that the addition of green light-emitting diode (LED) lights to the upper bridles of low-rise cutback trawls significantly reduced Pacific halibut (Hippoglossus stenolepis) bycatch. Recent regulation changes in this fishery now permit high-rise trawls, a gear configuration with a higher vertical opening, in areas where only low-rise trawls were previously permitted. This study conducted catch comparison and catch ratio analyses to determine if catches of Pacific halibut and three commercially important groundfishes (e.g., petrale sole [ Eopsetta jordani ], Dover sole [ Microstomus pacificus ], and sablefish [ Anoplopoma fimbria ]) differ between illuminated and non-illuminated tows for a high-rise bottom trawl. Illuminated tows caught fewer individuals than the non-illuminated tows across all species, including Pacific halibut; however, the difference in catch efficiency was not significant. Total catch volume did have a significant positive effect on levels of glucose and lactate for Pacific halibut. However, no statistically significant differences between illuminated and non-illuminated tows were exhibited across all of the physiological parameters assessed. The results from our study provide valuable information to fishers and managers that can be used for future decision-making and identifying research priorities. [ABSTRACT FROM AUTHOR]

Reducing the impacts of bottom trawling on seafloor habitats is a management priority in the U.S. West Coast groundfish bottom trawl fishery as well as other trawl fisheries internationally. Modifications to conventional bottom trawls, such as semi-pelagic trawl technology, are commonly used in demersal fisheries to reduce trawl-seafloor interactions by elevating the doors and portions of the sweeps off the seafloor. This study evaluated changes in catch efficiency and trawl geometry between a conventional bottom trawl outfitted with bottom-tending doors and the same trawl modified with midwater doors to fish semi-pelagically. We observed the seafloor interactions using Dual-frequency IDentification SONar (DIDSON) and quantified the reduction in trawl-seafloor interactions by periodically placing an altimeter on the semi-pelagic trawl door to measure height off bottom. Across the tows where the altimeter was used, results showed that the midwater doors fished off bottom >96% of all tow durations at a minimum height of 0.6 m. The midwater doors also spread 43 m wider on average than the conventional doors, which was significant (p < 0.001). Catch comparison results showed no significant difference in catch efficiency between the two gear types for any target groundfish species, however, the mean catch per unit effort for sablefish (Anoplopoma fimbria) did substantially increase when switching from the conventional to semi-pelagic trawl. Mean door spread did not significantly affect the catch efficiency of any species. DIDSON and altimeter data showed the midwater doors and raised sweeps provide clearance for low profile and infaunal benthic organisms to pass beneath without contact. This study demonstrates semi-pelagic trawl gear can effectively harvest demersal groundfishes in this fishery while substantially reducing trawl interactions with the seafloor. While our study has direct management implications for the U.S. West Coast groundfish bottom trawl fishery, our findings are also likely to apply to other demersal trawl fisheries internationally where reducing the impacts of bottom trawling on seafloor habitats is a management priority. • Developed a semi-pelagic trawl with off-bottom doors for harvesting demersal fishes. • The doors of the semi-pelagic trawl fished off bottom >96% of all tow durations. • DIDSON imaging sonar was used to examine trawl-seafloor interactions. • Results show the semi-pelagic trawl can effectively harvest demersal groundfishes. • Trawl-seafloor interactions can be considerably reduced using a semi-pelagic trawl. [ABSTRACT FROM AUTHOR]

The use of high-power lights during night-time purse seining is common in Vietnam. Typically, metal halide (MH) lamps are used in the commercial fishery to attract fish, however these lights require more energy, have a shorter lifespan, and lower chromatic performance than light emitting diode (LED) lamps. This study examined catch efficiency and fuel consumption when using LED lamps in combination with reduced numbers of MH lamps (10.24 kW), compared to conventional lighting (28.6 kW), used during purse seining off the coast of Ninh Thuan province, Vietnam. The economic performance associated with using LED lamps in this fishery was also assessed. We found no significant differences in catch rates between the different light treatments, however fuel consumption was significantly reduced. Fuel consumption per nightly trip using LED with MH lamps was 70.8 l (11.1 l/h) compared to114 l (17.45 l/hr) using MH lamps alone, an estimated 37.9% reduction in fuel consumption. An investment in LED lamps by a fishing enterprise will require additional initial costs, however our analysis revealed the financial break-event point can be reached after approximately 101 nightly trips when the fuel price is at the 2015 level of USD $0.74 per l. Fishing enterprises can increase their profitability, and reduce CO2 emissions, by using LED lamps in the Vietnamese purse seine fishery.

A new gillnet made from multiple mesh sizes ranging from 125 to 180 mm of stretched mesh (experimental gillnet) was tested under commercial fishing conditions to compare the fishing performance with that of conventional gillnets with a 125 mm mesh opening (control gillnet). Catch efficiency and size selectivity between the two gillnet types were evaluated throughout one year of fishing in three different locations in the waters of Vietnam. Experimental gillnets caught narrow-barred Spanish mackerel (Scomberomorus commerson), spotted mackerel (Scomberomorus guttatus), and wahoo (Acanthocybium solandri) in comparable amounts to the control gillnets, with the moon phase, month, and depth explaining some of the variation in the catch per unit effort (CPUE). An analysis of the size-dependent catch comparison rates and selectivity parameters showed that the experimental gillnets captured a wider range of narrow-barred Spanish mackerel sizes, but with a substantial proportion of individuals larger than those caught by the control gillnets. This is of higher weight per unit effort, and fishing enterprises therefore could improve their economic benefits by using modified gillnets with multiple mesh sizes. Our findings also support the biological and environmental benefits of the modified gillnet size selection, which might also extend to other species.

We studied the relative catch performance of a modified trawl fitted with an extension piece using a 90º turned mesh (T90) in comparison with a standard trawl net used in NW Mediterranean bottom trawl fisheries employing a diamond mesh net. The comparison was made by means of paired experimental hauls using the same fishing vessel with alternate deployments of the standard net (control) and the experimental net. We used the catch comparison approach for three target species of the fishery: European hake, red mullet and striped red mullet. Our results show that the experimental net significantly reduces the catches of small-size hake and red mullet (though there was no discernible difference for striped red mullet), reducing unwanted catches of regulated species under the Landings Obligation. The overall catch rates of hake, pooled over all sizes, also increased by an estimated 50%, while the catch rates of red mullet and striped red mullet were significantly lower. However, considering all commercial species, the experimental net produced losses of commercial catch and income estimated at 17% and 18%, respectively, which may pose a barrier to the adoption of this relatively simple, inexpensive solution.

Passive bottom-set nets are the most widely used fishing gears in Mediterranean small-scale fisheries (SSFs). Trammel nets, in particular, have key advantages such as their ease of use and handling and high capture efficiency for numerous commercial species. However, they entail high discard rates (5–44% of the total catch) connected to high mortality, thus exerting an adverse impact on benthic communities, besides catching individuals of commercial species under the minimum conservation reference size (MCRS) and specimens of protected species. Fish pots are seen as alternative and a more sustainable gear type that allow reducing discards in SSFs. In this study, a collapsible pot was tested at three coastal sites in the north-western Adriatic Sea (GFCM GSA 17) to compare its catch efficiency with that of the local traditional trammel nets. Data analysis demonstrated a similar catch efficiency for the commercial species, both among sites and as a whole. Moreover, the trammel net caught a larger amount of discards, both in terms of species number and of CPUEW. The catch comparison study involved the two most abundant landed species, common cuttlefish Sepia officinalis and annular sea bream Diplodus annularis. The pots were more effective for S. officinalis, whereas the trammel net was more effective for the shorter length classes for D. annularis, which were mostly under the MCRS (12 cm). The innovative pots could provide a valuable alternative to the trammel nets traditionally used in the Adriatic Sea, at least in certain areas and periods. Their main advantages include that they do not require a different rigging and they can be used without bait, while their foldable design allows large numbers to be easily loaded on board SSF vessels. The results of this pilot study indicate that pots can achieve the objectives of reducing discards and bycatch in SSFs without penalizing the catch of commercial species.

In the present study, the commercial (16 mm nominal mesh size) and experimental deep water cast nets with different mesh sizes (20 mm, 24 mm, 28 mm and 32 mm nominal mesh size) were tested to compare the captured fish lengths and catch amounts for whiting (Merlangius merlangus euxinus). Experiments were carried out between July, 11 and August, 29, 2018 in Rize province of the south-eastern Black Sea Region. A commercial fishing boat was chartered for 20-day sea trials and in total, 66 set operations were done for all nets. Generalized Linear Mixed Models (GLMM) was used to compare fish sizes caught with experimental and commercial deep water cast nets. Results showed that more than 70 percent of the individuals caught in cast nets with 16 mm, 20 mm and 24 mm size were below the minimum landing size of whiting (13 cm). Among tested nets, only cast net with 32 mm size caught significantly less individuals under the minimum landing size. Finally, the results obtained from this study are discussed in terms of sustainable fisheries of whiting in the Black Sea. [ABSTRACT FROM AUTHOR]

Passive bottom-set nets are the most widely used fishing gears in Mediterranean small-scale fisheries (SSFs). Trammel nets, in particular, have key advantages such as their ease of use and handling and high capture efficiency for numerous commercial species. However, they entail high discard rates (5-44% of the total catch) connected to high mortality, thus exerting an adverse impact on benthic communities, besides catching individuals of commercial species under the minimum conservation reference size (MCRS) and specimens of protected species. Fish pots are seen as alternative and a more sustainable gear type that allow reducing discards in SSFs. In this study, a collapsible pot was tested at three coastal sites in the north-western Adriatic Sea (GFCM GSA 17) to compare its catch efficiency with that of the local traditional trammel nets. Data analysis demonstrated a similar catch efficiency for the commercial species, both among sites and as a whole. Moreover, the trammel net caught a larger amount of discards, both in terms of species number and of CPUEW. The catch comparison study involved the two most abundant landed species, common cuttlefish Sepia officinalis and annular sea bream Diplodus annularis. The pots were more effective for S. officinalis, whereas the trammel net was more effective for the shorter length classes for D. annularis, which were mostly under the MCRS (12 cm). The innovative pots could provide a valuable alternative to the trammel nets traditionally used in the Adriatic Sea, at least in certain areas and periods. Their main advantages include that they do not require a different rigging and they can be used without bait, while their foldable design allows large numbers to be easily loaded on board SSF vessels. The results of this pilot study indicate that pots can achieve the objectives of reducing discards and bycatch in SSFs without penalizing the catch of commercial species. [ABSTRACT FROM AUTHOR]

Installing artificial lights on fishing gear is increasingly being explored to alter the behaviour of fish during the capture process and modify selectivity. We investigated the effect of introducing artificial light on a commercial trawler operating in the English southwest mixed demersal fishery. Total catch and species vertical separation were compared and analysed in two identical separator trawls towed simultaneously. One trawl was equipped with blue LEDs along its headline, the other trawl served as a control to allow for pairwise catch comparison. Fishing trials were conducted at night and during the day. In the presence of lights, catches-at-length of haddock (Melanogrammus aeglefinus) were lower during the night and marginally higher during the day. Catches of grey gurnard (Eutrigla gurnardus), megrim (Lepidorhombus whiffiagonis) and whiting (Merlangius merlangus) were unaffected by lights. In terms of vertical separation, in the presence of lights, more haddock were retained in the lower codend during the day and night. Lights also increased the proportion of catches in the lower codend for grey gurnard, whiting and Northern squid (Loligo forbesii), but only during the day. This study shows there are species-specific reactions to artificial light during the trawl capture process and these reactions can be different between day and night. When reviewed with other studies, some common observations are identified, indicating that lights can change the behaviour of some species which normally rise inside the trawl during the capture process, such as haddock. The use of artificial lights offers an alternative method to modify trawl selectivity, by utilising species-specific reactions to light, and the ability to change the position and characteristics of the light, offers many avenues to investigate. [ABSTRACT FROM AUTHOR]

Abstract In the U.S. West Coast groundfish bottom trawl fishery, lengthy sweeps (>85 m) that maintain seafloor contact are traditionally used. While these sweeps are effective at herding groundfishes, their bottom tending characteristics increase the potential to cause seafloor disturbances, and injury and unobserved mortality to benthic organisms. In this study, we examined if changing from conventional to modified sweeps (with sections elevated 6.5 cm off bottom) would affect catch efficiency of target groundfishes and seafloor interactions. We used a DIDSON imaging sonar to observe how each sweep configuration interacted with the seafloor. An altimeter was periodically placed on the modified sweep to measure height off bottom. Results detected no significant catch efficiency effect of changing from conventional to modified sweeps. The DIDSON and altimeter data showed the modified sweeps exhibit elevated sections where infaunal and lower-profile epifaunal organisms can pass under without disturbance. Results demonstrate that seafloor interactions can be substantially reduced using elevated sweeps in this fishery without impacting catch efficiency. Further, findings from this research could be potentially applicable to other fisheries nationally and internationally. [ABSTRACT FROM AUTHOR]

Soak duration in the gillnet fisheries can vary from a few hours to several days. The industry reports a variation of soak tactics between target species, but also between seasons for the same species. These are determined by the robustness of the target species and the catch of unwanted species. Different soak tactics were compared to estimate the role that the choice of a soak tactic plays in the catch efficiency of both target and unwanted species. In the Danish summer gillnet fishery targeting plaice (Pleuronectes platessa) , nets are deployed approximately 12 h (h) during day. Unwanted species are common dab ( Limanda limanda ) and edible crab ( Cancer pagurus ). The commercially used 12 h deployment during day was compared to 12 h deployment during night and 24 h deployment. On average, there were about 1.5 more catches of commercial size plaice (above 27 cm), and 2 and 4 times less catches of the unwanted dab and edible crab, respectively, for 12 h at day compared to the other soak tactics (12 h at night or 24 h). Gillnetters participating in the coastal summer fishery for plaice follow the theoretical optimal soak tactic. The commercially used 12 h deployment during day maximises the catch of commercial sized plaice and limits handling time by catching less unwanted dab and crabs. [ABSTRACT FROM AUTHOR]

In Pacific halibut (Hippoglossus stenolepis) longline fisheries in the eastern North Pacific Ocean bycatch of yelloweye rockfish (Sebastes ruberrimus) is a concern as their stock status along the U.S. West Coast is "rebuilding" from being "overfished", the southeast Alaska stock has shown a ∼60% decline since at least 1994 and through 2015 where it stabilized, and the Canadian stock has been recently declared "threatened". In this study, we evaluated how size 16/0 and 18/0 circle hooks affect the catch efficiency of Pacific halibut and yelloweye rockfish. Further, we examined the catch efficiency of these hooks modified with a 3.1 mm stainless-steel wire appendage extending 7.6 cm from their shank at either a 45° or 90° angle. We estimated hooking location probabilities for Pacific halibut and yelloweye rockfish for the hooks tested, and tested for a difference in the time of capture between Pacific halibut and yelloweye rockfish. Results showed that hook size did not significantly affect the catch efficiency of Pacific halibut or yelloweye rockfish. However, hooks with a 45° appendage angle caught significantly fewer yelloweye rockfish than hooks without an appendage, irrespective of hook size. Appendage angle did not affect the catch efficiency of Pacific halibut. For both Pacific halibut and yelloweye rockfish, the most frequent hooking location was hook through cheek , both with and without an appendage. Time of capture of Pacific halibut and yelloweye rockfish did not differ over the duration of a set; however, the majority (75%) of individuals were caught within 2.5 h of gear deployment. Results from our study suggest that hook appendages could have potential use in reducing catch rates on yelloweye rockfish in Pacific halibut longline fisheries, which could lead to increased fishing opportunities, more efficient Pacific halibut fisheries and less effect of fluctuations in the more productive Pacific halibut stock on fisheries that may be constrained by yelloweye rockfish. • We tested how hook appendages affect the catch rate of halibut and yelloweye rockfish. • Hooking location probabilities were modeled for halibut and yelloweye rockfish. • Hook timers showed most fish were caught within 2.5 h of gear deployment. • Hooks with a 45° appendage significantly reduced yelloweye rockfish catches. • Hook appendages did not affect the catch rate of halibut. [ABSTRACT FROM AUTHOR]

In the English Channel and Southern Bight, French demersal trawlers target a mix of demersal species including whiting ( Merlangius merlangus ). The discard ban to be implemented in January 2016 motivated fishermen to look for technical measures to reduce unwanted catches of undersized individuals (<27 cm). From 2008–2014, 18 different gear configurations were tested for bycatch reduction on board fleets of vessels of 16–20 m and 20–24 m. Selective devices tested included grids, square mesh panels (SMP), square mesh cylinders (SMC), various combinations of these devices and large mesh trawls. Using the catch comparison method, our results focus on six devices that proved efficient to reduce catches of undersized whiting, equally divided between the two vessel size groups. Large mesh trawls are not adequate to improve whiting size selectivity with losses of commercial size fish. The mandatory 80-mm SMP was efficient at letting undersized whiting escape from the trawl for both vessel length classes. Its efficiency was enhanced when it was positioned 6–9 m ahead of the codline compared with that placed at 12–15 m. The most appropriate bar spacing for whiting size-selectivity was found in a flexigrid with 23 mm bar spacing, but this required a large portion of square mesh netting to be installed ahead of it (SMP and SMC) to limit catches of undersized individuals. The most promising device tested was an 80 mm SMC, either 2 m long and used alone or 1 m long and used in association with the mandatory SMP; these setups allowed significant escapes of fish up to 25 cm in length. For both SMP and SMC, a mesh size equal to or larger than 100 mm led to losses of commercial size whiting. [ABSTRACT FROM AUTHOR]

Selectivity studies have found applications in a wide range of topics within fishery science, such as fishery management, stock assessment, and ecological process studies. However, obtaining selectivity functions can often be a difficult and costly endeavor. Because of this difficulty, many studies are limited to the comparison of catch from two fishing gears, where relative differences in catch efficiency are often presented in the form of catch comparison rate or catch ratio. Studies of these rates are well known to often improve commercial fisheries, which benefit from highly selective gears. However, utility of these statistics for the purposes of fisheries surveys and stock assessment is not very well understood. In this study we adapted methods previously used for catch ratio to obtain length-dependent selectivity ratio function for two survey gears. Selectivity ratio can be obtained when area-swept or volume-swept fish density estimates are available from both gears. In other cases it is possible to obtain relative selectivity ratio. We present a general approach to obtain selectivity ratio in survey gear comparison studies and model it using three alternative techniques (linear and smooth mixed effect, and beta-regression). We use crossvalidation to choose between alternative models. We present examples of practical application of selectivity ratio with three case studies: a comparison of fine-and large mesh bottom trawls used in Arctic surveys, a study testing an assumption of non-selectivity of the Nephrops bottom trawl for snow crab in the Bering Sea, and a comparison of two survey midwater trawls for pollock in the Bering Sea. We show that selectivity ratio statistics can be used as a generalization of selectivity studies, where one gear is non-selective, as well as in catch comparison studies where selectivity of both gears is unknown. [ABSTRACT FROM AUTHOR]

Expeditious uptake of quad-rig trawling in the economically important Irish fishery for Nephrops norvegicus outpaced technical understanding of this newly introduced gear. The main driver for its introduction is increased catch rates of Nephrops. Higher Nephrops discard rates associated with quad-rig trawling are likely to be problematic under the landing obligation unless size selectivity can be improved. Catch comparison methods are suitable for assessing the performance of fishing gear modifications to reduce discards. Utilizing a quadrig potentially increases the number of gears that can be included in a catch comparison study to four but current modeling methods are limited to two gears. Our study provides a new general multinomial mixed effects modeling framework that can be applied to two or more gears, elucidates how case-specific and choice-specific covariates may influence catch at length, and facilitates discussion on appropriate gear based management measures. Application of the method to catches from four different cod-end mesh sizes revealed significant effects of carapace length, catch weight and net position, on the numbers of Nephrops retained in each cod-end. Results suggest that management measures which specifically address different catch profiles associated with different numbers of trawling rigs are required to optimize Nephrops size selectivity. [ABSTRACT FROM AUTHOR]

On January 1st, 2016, the French mixed Nephrops and hake fishery of the Grande Vasière , an area located in the Bay of Biscay, fell under the discard ban implemented as part of the new European Common Fisheries Policy. The fleet records historically high levels of discard despite numerous gear selectivity studies. Together with high discards survival, new technological solutions to minimize catches of undersized individuals could justify local exemptions from the discard ban. Our study focuses on the effects of two selective devices, a square mesh cylinder (SMC) and a grid, on the escapement of undersized individuals and discard reduction. Relative catch probability of the modified gear compared with the traditional gear was modelled using the catch comparison method. Potential losses from the commercial fraction of the catch were taken into account to assess their influence on the economic viability of fishing with the modified gears. The two devices had similar effects on undersized Nephrops escapement and on discard reduction, with median values of 26.5% and 23.6% for the SMC and of 30.4% and 21.4% for the grid, respectively. Only the grid was efficient for undersized hake, recording median values of escapement and discard reduction equal to 25.0% and 20.6%, respectively. Some loss from the commercial fraction of the catch was to be expected with both devices, which could be compensated for in the long term by the contribution of undersized individuals to the stock biomass. Our results support the use of selective gears technology as part of an integrated framework including control and management measures to mitigate the effect of the discard ban both for fishers and for the ecosystem. Further work is needed to quantify the effect of additional escapement from the gear on stock dynamics. [ABSTRACT FROM AUTHOR]

This paper describes a method to estimate the relative catch efficiency of different fishing gear designs based on comparison of catch data. This method does not require an equal number of deployments or alternation between gears, but it accounts for multiple competing models describing the data by using multi-model inference. By applying a double bootstrapping procedure, this method also accounts for the uncertainty in the estimation resulting from between-deployment variation in catch efficiency and availability of fish as well as uncertainty about the size structure of the catch for the individual deployments. Finally, by incorporating the multi-model inference into each bootstrap iteration, the method also accounts for the uncertainty due to uncertainty in model selection. Using the described method, we investigated the effect of gear design changes on catch efficiency for a Spanish longline fishery targeting hake ( Merluccius merluccius ). We tested and compared four different designs against the traditional design used in the fishery. The first was a design compatible with automation that differed from the traditional one in hook size, snood line length, and snood line diameter (new automatized design). In the other three designs, only one of the parameters was changed. The results demonstrated that the new automatized design resulted in a significant decrease in catch efficiency due to its thicker snood line. The hook type and snood line length used had no effect on the efficiency of the fishery. [ABSTRACT FROM AUTHOR]

This paper illustrates the importance of length, angle and bottom contact of the sweep that connects the trawl and the otterboard for haddock ( Melanogrammus aeglefinus ) in Barents Sea. We compared the fishing efficiency of two different trawl setups over two cruises. During cruise 1, the sweep angle was 22.3° and the difference in sweep length with actual bottom contact was 30 m. During cruise 2, the average sweep angle was 12.0°, and the difference in length with actual bottom contact was 45 m. Setup 1 had less sweep bottom contact for both cruises. We estimated the relative change in length dependent catch efficiency of haddock between the two setups for each of the two cruises using catch comparison and catch ratio analyses. The results showed the importance of the length of sweep that actually contacted with the seabed for catching haddock. The differences between the two setups were significant for a limited range of length classes in both cruises, indicating that effect of the sweep bottom contact for this species is length dependent. The results also demonstrate that lack of control over the position of the doors in the water column when fishing semi-pelagic may cause loss of contact of the sweep with the seabed, reducing fishing efficiency for haddock. [ABSTRACT FROM AUTHOR]

In Skagerrak and the North Sea, coastal vessels harvest deep-water shrimp (Pandalus borealis) in a mixed fishery, in which catches of Nephrops (Nephrops norvegicus) are of economic importance for the fleet. Fishermen targeting shrimp in this area must use a sorting grid with a maximum bar spacing of 19 mm, which means that only the smallest Nephrops can pass through the grid to be retained in the main codend. Although fish collection bags may be mounted to the grid's fish outlet, most Nephrops escape through the large meshes in these bags. Using data from 70 hauls collected during three different commercial cruises, we investigated whether inserting a 15 cm gap in the lower part of the compulsory sorting grid could help retain a higher fraction of the commercial sizes of Nephrops. We also evaluated whether this lower gap in the grid would change the catch pattern for the most relevant fish bycatch species in the fishery. The results showed that the gap in the grid significantly increased the catches of Nephrops above the minimum legal size and increased the catches of commercial-size shrimp. However, absolute catch rates of Nephrops were still low and, from a management point of view, the modest catch increase does not justify the significant increase in the catch of juveniles of a range of fish species as well as undersized Nephrops. [ABSTRACT FROM AUTHOR]

Commercial fishing vessels can be a cost-effective alternative to research vessels for performing towed gear fishery-independent surveys, if catch rates are comparable among commercial vessels and with research vessels. A parallel fishing experiment was conducted off the coast of Wales, United Kingdom, to compare the king scallop (Pecten maximus) catch rates of three commercial vessels using commercial dredges and a research vessel using two types of scientifically modified dredges. The scientific dredges are currently used in the fishery-independent survey of local scallop populations. Size-structured scallop catch-per-unit-effort (CPUE) was compared among vessel-gear combinations. Two similarly sized commercial vessels had generally similar CPUEs, however there were some significant differences with scallop size. A smaller commercial vessel had significantly lower CPUEs for a broad range of scallop sizes. The research vessel dredges had significantly higher CPUE for smaller scallops than the commercial vessels. Vessel size is likely to be driving the differences among commercial vessels and belly ring size is likely to be driving differences among research and commercial dredges. These findings highlight commercial vessel CPUE should not be assumed the same, whilst also showing that vessel size may be the best indicator of catch rate similarity. These results also highlight that changing the fishery-independent vessel and gear to the commercial options trialled here would result in a considerable loss of information about the smaller scallops in the population. These findings will be of interest to fishery scientists or managers using multiple vessels, or considering a change of vessels, for fishery-independent surveys. • Research vessel caught significantly more small scallops than commercial vessels. • Smallest commercial vessel caught significantly less scallops at greater depths. • Two commercial vessels of similar size and engine power had similar catch rates. • Differences in catch rates likely driven by belly ring size and vessel size. • Vessel catch rates should not be assumed to be directly comparable. [ABSTRACT FROM AUTHOR]

Fuel consumption and environmental concerns have led bottom trawlers fishing for cod ( Gadus morhua ) in the Barents Sea to use semi-pelagic doors. However, this change may affect fish herding and consequently the catch efficiency of the gear. In this study we compared the catch efficiency of two different setups where the sweep length with bottom contact was different. This setup also enabled us to estimate the herding efficiency of the sweeps on the seabed. The data for this study were collected using the alternate haul method and analyzed using a new method for unpaired data. We estimated that the setup with the lifted sweeps captured on average 33% fewer cod than the setup that kept the sweeps at the seabed. The loss of catch for cod was length independent and significant for a length span between 41 and 104 cm. When sweeps were lifted above the seabed, herding was negatively impacted and fish were lost; in contrast, when on the seabed, the sweeps were able to herd (on average) 45% of the cod into the catch zone of the gear. Lifting the trawl doors from the seabed is touted as a positive development for this fishery. However, our results show that lifting the doors and consequently the sweeps can lead to substantial catch losses. Finally, the study highlights the importance of carefully evaluating the positive and negative potential consequences of introducing changes in a fishing gear. [ABSTRACT FROM AUTHOR]

Abstract: Pulse trawling is used to a growing extent in the Dutch flatfish beam trawl fleet, and deemed as a promising alternative to tickler chain beam trawling. A comparative fishing experiment was carried out with one vessel using conventional beam trawls, and the other two using flatfish pulse trawls supplied by two different companies. Pulse trawl landings were lower both expressed in kgh−1 (67% based on auction data) or baskets per hectare (81%). The pulse trawls had fewer fish discards (57%, p <0.0001), including 62% undersized plaice (Pleuronectes platessa L.) (p <0.0001), and 80% discarded weight of benthic invertebrates (p =0.0198) per hectare. The pulse fishing technique resulted in a lower fuel consumption (37–49%), and consequently in spite of lower landings net revenues were higher. A downside of using pulse trawls is the possible spinal damage of marketable cod (Gadus morhua L.), but because total cod landings by beam trawls are low (4–5%), the implication will likely be limited. [Copyright &y& Elsevier]

Bycatch of rays and skates in towed fishing gears represents one of the major threats to these relatively slow-growing marine species. The objective of this study was to modify ground gear in a bottom trawl fishery to increase the escape of these species during towing without associated loss of target catch. Sea trials were carried out with a research vessel in Mersin Bay, North-eastern Mediterranean. Experimental ground gear was modified by cutting the rigging twine between the fishing line and the footrope in the central part of the ground gear. Capture of three unwanted bycatch species were estimated. The probability of capture of guitarfish (Rhinobatos sp.) and common stingray (Dasyatis pastinaca) was significantly reduced to 8% and 20% for guitarfish and stingray, respectively compared to standard ground gear. The results for spiny butterfly ray (Gymnura altavela) were inconclusive due to the wide confidence intervals. Further, the catch comparison results for five out of six target species investigated did not show significant reduction in catch efficiency when using experimental gear compared to the standard trawl. Only for common sole (Solea solea) the modified trawl had significantly lower catch efficiency than the standard trawl. We believe that this technical measure for reducing unwanted bycatch in bottom trawls has a potential to be adopted by the fishery due to being an efficient, low-cost measure which does not create additional challenges during handling of the gear. [ABSTRACT FROM AUTHOR]

Management measures to facilitate the recovery of fish stocks can lead to shifts in traditional fishing patterns and target species. In the Baltic Sea, drastic reductions in catch quota for cod (Gadus morhua) force mixed demersal trawl fisheries to avoid cod bycatch and focus on flatfish species. This study developed and tested a simple selection concept that aims to avoid cod bycatch in flatfish-directed trawl fisheries by removing a section of the top panel from the extension piece of the trawl (roofless concept). Sea trials testing the performance of a baseline roofless design, and two designs intended to enhance escape reactions of cod were conducted during two sea cruises. Analysis of the resulting catch data revealed that applying the baseline roofless design consistently reduced cod bycatch by ∼75%. Catches of the target species plaice (Pleuronectes platessa) and flounder (Platichthys flesus) were reduced by less than 15%; however, we estimated that catch losses of the two flatfish species could be balanced by increasing fishing effort to ∼8% and ∼12%, respectively. None of the two roofless designs, intended to enhance escape reactions on cod, improved the performance of the baseline design. Under the scenario of fishery choke caused by limited cod quotas, we estimated that the use of the baseline roofless concept could increase fishing possibilities for flatfish by more than 300%. [ABSTRACT FROM AUTHOR]

Favaro, B., Duff, S. D., and Côté, I. M. 2013. A trap with a twist: evaluating a bycatch reduction device to prevent rockfish capture in crustacean traps. – ICES Journal of Marine Science, 70:114–122.Bycatch, or the incidental capture of non-target species, occurs in fisheries around the world, with often detrimental ecological consequences. Bycatch reduction devices (BRDs) that increase catch specificity have been used successfully in some fisheries, and the development of such devices remains an important component of the global effort to reduce bycatch rates. We tested novel devices designed to exclude juvenile rockfish (Sebastes spp.) from traps used to catch spot prawns (Pandalus platyceros), a commercially important species in British Columbia, Canada. The devices included reductions in trap opening sizes and novel bent-tunnel openings. Reducing trap opening size did not affect bycatch rates of rockfish or other non-target fish species. In contrast, bent-tunnel BRDs eliminated rockfish bycatch, and two of the bent-tunnel variants also excluded other fish species. However, prawn catch rates were reduced in all modified gear, and large prawns were often excluded more than small prawns. Videos recorded in situ revealed that prawn attempts to enter traps took longer and were more likely to fail in BRD-equipped than in unmodified traps. We conclude that bent-tunnel BRDs have the potential to be useful, but improvements are needed to increase prawn catch to levels similar to that of unmodified traps. [ABSTRACT FROM PUBLISHER]

Abstract: Comparative fishing trials investigated the effect of increasing the mesh size in the forward sections of a trawl from 120 and 160mm to (i) 300mm and (ii) 600mm on the catches in the Shetland mixed whitefish fishery. The 300 and 600mm trawls respectively caught an estimated 49 and 75% fewer Atlantic cod (Gadus morhua), 79 and 93% fewer megrim (Lepidorhombus whiffiagonis), 36 and 68% fewer ling (Molva molva), and 28 and 53% fewer hake (Merluccius merluccius) than the control trawl at all lengths. The 300mm trawl caught ∼40% more haddock (Melanogrammus aeglefinus) than the 600mm and control trawls which had similar catch rates. The catch rates for monkfish (Lophius piscatorius) were length dependent and the 300mm trawl caught ∼50% fewer monkfish at 30cm with no significant difference>76cm. The 600mm trawl caught ∼90% fewer monkfish at 30cm with no significant difference>83cm. Both the 300mm and 600mm trawls caught significantly fewer saithe (Pollachius virens) above 53cm. [Copyright &y& Elsevier]

Abstract: In an attempt to reduce catches of juvenile fish in the Icelandic Nephrops norvegicus fisheries, the mesh sizes in the upper part of a commercial Nephrops trawl were increased and the netting hung to force wide mesh opening. Two different designs, each with 135mm nominal mesh upper panel were compared to an unmodified commercial trawl in June 2009. Design A had a 23.2m long panel and design B had a 16.1m long panel, extending respectively to 9.7 and 15.0m from the cod-line. The panels in both designs were one third narrower and longer than the matching lower panel. With design A, about half of Nephrops, haddock (Melanogrammus aeglefinus) and whiting (Merlangius merlangus) catches were lost, while with design B, the losses were restricted to smaller specimen of fish and Nephrops, i.e. a marked size selection was observed. These trials demonstrate the potential for size selection by a simple manipulation of a Nephrops trawl to reduce discarding. [Copyright &y& Elsevier]

Abstract: The results of catch comparison trials of a trawl gear, where the 160mm mesh size netting in the forward sections of the gear is replaced with 300mm mesh size netting, are presented. This gear, which has become known as the ‘Orkney gear’, was designed to reduce, but not eliminate, catches of Atlantic cod in the North Sea mixed whitefish fishery. The results show that the modified gear retains significantly fewer cod smaller than 78cm while, above 78cm, there is no significant difference in the amount of cod caught. Catches of monkfish were 16% less, however, there was no significant difference in the numbers of monkfish caught above 55cm. There was about a 43% loss of megrim across all length classes and there were no losses of haddock and whiting. [Copyright &y& Elsevier]

Abstract: The survival of fish discarded after being caught can be improved by simple gear-based technical measures aimed at reducing discards. We look at the effects of three different codends on the initial health and short-term survival of trawl-caught skate (Rajidae), using a control codend (80mm diamond mesh used as standard in the fishery) and two experimental codends (100mm diamond mesh and 100mm diamond mesh turned on the square). Both experimental nets reduced discarded numbers of fish by ∼70%, with no commercial loss. This reduction in discards had an effect in reducing the total weight of the experimental codends by as much as 80%. We also placed 278 skate in onboard holding tanks for 48h and evaluated the survival rates of fish caught in the different codends. Visual inspection of “health” at time zero was a good indicator of survival, because 86% of skate with a good health score survived (p <0.01). From a further 1539 skate assessed for health, we show that fish caught in the control codend have the lowest proportional good health score (25%), followed by the 100mm diamond mesh codend (34%) and the 100mm square mesh codend (47%). The health of the fish caught is related to codend weight (p =0.01). We conclude that technical measures aimed at reducing discards have an additional benefit; they indirectly increase discard survival, and the benefits of mitigating discards through by-catch reduction devices may be a more powerful tool in fisheries management than previously thought. [Copyright &y& Elsevier]

Abstract: For analysing catch comparison data, we propose a simple method based on Generalised Linear Mixed Models (GLMM) and use polynomial approximations to fit the proportions caught in the test codend. The method provides comparisons of fish catch at length by the two gears through a continuous curve with a realistic confidence band. We demonstrate the versatility of this method, on field data obtained from the first known testing in European waters of the Rhode Island (USA) ‘Eliminator’ trawl. These data are interesting as they include a range of species with different selective patterns. [Copyright &y& Elsevier]

The effect of artificial lights mounted on the headrope trawl net on the catch of deep water rose shrimp (Parapenaeus longirostris), European hake (Merluccius merluccius), and Atlantic horse mackerel (Trachurus trachurus) was tested in a survey carried out on-board a commercial trawler off the SW Sicilian coast. A total of 18 repeated nocturnal hauls, alternating without (control) and with (test) LED lights (10 green and 10 white) according to the fishers' setup, were conducted. Overall, the test net catch rates were not significantly higher than those of the control net (Kruskal-Wallis test, p > 0.05), except for P. longirostris (p < 0.05). Conversely, the two-tailed Kolmogorov–Smirnov test revealed statistical differences in the size structure of P. longirostris , M. merluccius , and T. trachurus between the test and control nets (p < 0.05). Using generalised linear mixed models, the test net was found to yield higher catches of undersized individuals of the three species and adults of P. longirostris than the control net. Our study results are discussed in the context of the exploitation and management of Mediterranean trawl fisheries. [Display omitted] [ABSTRACT FROM AUTHOR]

Catchpole, T. L., Revill, A. S., Innes, J., and Pascoe, S. 2008. Evaluating the efficacy of technical measures: a case study of selection device legislation in the UK Crangon crangon (brown shrimp) fishery. – ICES Journal of Marine Science, 65: 267–275.Bycatch reduction devices are being introduced into a wide range of fisheries, with shrimp and prawn fisheries particularly targeted owing to the heavy discarding common in these fisheries. Although studies are often undertaken to estimate the impact of a technical measure on the fishery before implementation, rarely have the impacts been assessed ex post. Here, the efficacy of the UK legislation pertaining to the use of sievenets in the North Sea Crangon crangon fishery is assessed. Three impacts were evaluated: on fisher behaviour (social), on the level of bycatch (biological), and on vessel profitability (economic). An apparent high level of compliance by skippers was identified despite a low level of enforcement. The estimated reduction in fleet productivity following the introduction of the legislation was 14%, equalling the mean loss of Crangon landings when using sievenets calculated from catch comparison trawls. Sievenets did reduce the unnecessary capture of unwanted marine organisms, but were least effective at reducing 0-group plaice, which make up the largest component of the bycatch. Clearly the legislation has had an effect in the desired direction, but it does not address sufficiently the bycatch issue in the Crangon fishery. [ABSTRACT FROM PUBLISHER]

Abstract: Discarding of roundfish species in many European Nephrops fisheries remains at relatively high levels, despite the existence of mandatory gear-based technical measures specifically aimed at mitigating this phenomenon. This work reports on a new design of Nephrops trawl (the cutaway trawl), tested in the Farne Deeps fishery of the North Sea, and which reduced by-catches of whiting by 50% (across the length range), without any loss of Nephrops. The cutaway trawl could therefore potentially be used to reduce discarding of this species in certain fisheries. Several comparisons are made between the cutaway trawl and three designs of commercial trawl in existing use in Nephrops fisheries. Comparisons are made from both a biological and economic standpoint. Vessel size (length and engine power) did not affect the selectivity parameters obtained with the cutaway trawl, when the sea trials were repeated on vessels ranging from 9.9m LOA (150hp) to 21m LOA (650hp). [Copyright &y& Elsevier]

The discarding of small (non-marketable) brown shrimp (Crangon crangon) in the North Sea brown shrimp fisheries is substantial in magnitude (circa 27,000 t/75 billion individuals annually). This work assessed the efficacy of various trawl modifications aimed at reducing small shrimp discarding. Changes to the mesh size of the codend (i.e. 16, 22, 24 and 26 mm) and also forward parts of the net were evaluated (multi-mesh trawl).Of all the trawl modifications investigated, the fitting of a 26 mm codend to a shrimp trawl was shown to be the most effective and reduced the catches of small shrimp by 13%. Such a trawl modification is however less effective than fitting a sieve net inside a shrimp trawl, which can reduce such shrimp catches of small shrimp by 16–26%. [Copyright &y& Elsevier]

In the U.S. West Coast groundfish bottom trawl fishery, Pacific halibut (Hippoglossus stenolepis) bycatch can impact some fishers' ability to fully utilize their quota shares of groundfishes. In this study, we compared the catch efficiency for Pacific halibut and four commercially important groundfish species between an illuminated and non-illuminated trawl. The illuminated trawl caught significantly fewer Pacific halibut and sablefish than the non-illuminated trawl. For Dover sole (Microstomus pacificus), petrale sole (Eopsetta jordani), and lingcod (Ophiodon elongatus), the illuminated trawl caught fewer individuals than the non-illuminated trawl. However, this catch difference was not statistically significant. Physiological data collected on Pacific halibut caught in illuminated and non-illuminated trawls show blood levels of cortisol, a stress hormone, were significantly higher in fish caught in the illuminated trawl than in the non-illuminated trawl in the absence of differences in condition factor or fat content. While our results have obvious implications for the West Coast groundfish bottom trawl fishery, our findings could also have potential applications in Alaska and British Columbia, Canada trawl fisheries where Pacific halibut bycatch occurs. [ABSTRACT FROM AUTHOR]