scholarly journals Combining in-trawl video with observer coverage improves understanding of protected and vulnerable species by-catch in trawl fisheries

2014 ◽  
Vol 65 (9) ◽  
pp. 830 ◽  
Author(s):  
Vanessa F. Jaiteh ◽  
Simon J. Allen ◽  
Jessica J. Meeuwig ◽  
Neil R. Loneragan
Keyword(s):  
Video Camera ◽  
Fishing Effort ◽  
Vulnerable Species ◽  
Independent Observer ◽  
Video Footage ◽  
Trawl Fishery ◽  
Scalloped Hammerhead ◽  
Sea Snakes ◽  
By Catch ◽  
Trawl Fisheries

Assessments of incidental wildlife mortality resulting from fishing rarely account for unobserved by-catch. We assessed by-catch of protected and vulnerable wildlife species in an Australian trawl fishery by comparing in-trawl video footage with data collected by an on-board observer. Data were obtained from 44 commercial trawls with two different by-catch reduction devices (BRDs). Eighty-six individuals from six major taxa (dolphins, sharks, rays, sea snakes, turtles and sygnathids) were documented from video analysis, including the endangered scalloped hammerhead shark (Sphyrna lewini) and the critically endangered green sawfish (Pristis zijsron). On the basis of the 2008–2009 fishing effort of 4149 trawls and scaling from these results, we estimated the annual catch of protected and vulnerable species (± 1 s.e.) at 8109 ± 910 individuals. Only 34% of by-catch was expelled through the BRDs. Independent observer data for the 44 trawls showed that 77% of the landed by-catch from these taxa were dead when discarded. The results indicate that unaccounted by-catch in trawl fisheries can be substantial, and that current methods of recording by-catch on-board vessels are likely to underestimate total fishing mortality. We recommend gear modifications and their validation through dedicated observer coverage, combined with in-trawl video camera deployments to improve current approaches to by-catch mitigation.

scholarly journals Biology and population dynamics of by-catch fish species of the bottom trawl fishery in the western Mediterranean

2014 ◽  
Vol 15 (3) ◽  
pp. 613 ◽  
Author(s):  
F. ORDINES ◽  
M.T. FARRIOLS ◽  
J. LLEONART ◽  
B. GUIJARRO ◽  
A. QUETGLAS ◽  
...  
Keyword(s):  
Population Analysis ◽  
Conservation Status ◽  
Fishing Effort ◽  
Western Mediterranean ◽  
Distribution Range ◽  
Bottom Trawl ◽  
Trawl Fishery ◽  
Virtual Population ◽  
Trawl Fishing ◽  
By Catch

The teleosts Chelidonichthys cuculus, Trigloporus lastoviza, Serranus cabrilla and Trachinus draco, are important by-catch species, in terms of landed biomass and commercial value, from the continental shelf bottom trawl fishery off the Balearic Islands (western Mediterranean). The main biological parameters of these species were calculated from monthly biological samplings, and were used along with three years pseudo-cohorts (2008-2010) obtained from monitoring on-board of the bottom trawl fleet, to assess their exploitation level through Virtual Population Analysis (VPA) and Yield per Recruit (Y/R) analysis. Time series of fishery independent indicators based on MEDITS surveys data such as the evolution of the abundance and biomass, the distribution range, and the Conservation Status of Fish b (CSFb), were also analyzed. All four species analyzed showed growth overfishing. The reductions of the fishing effort required to reach the Y/RF0,1 reference point were lower, 66-73% depending on the species, to those reported for the target species M. merluccius (87%), but higher than that reported for M. surmuletus (53%), in the study area in the period 2000-2010. The abundance and biomass, and the distribution range did not show any trend for the period 2001-2011, whereas the CSFb showed signs of recovery that may be due to the displacement of the trawl fishing effort from the shelf to the slope during the last decade. Our results underline the necessary incorporation of monitoring and assessment of by-catch species to the management of fisheries as their populations can show a more pronounced overexploitation than target ones.

scholarly journals Metodologia para a monitorização e gestão da pesca de arrasto em Portugal. O exemplo do SIG GEOCRUST 1.0

Finisterra ◽  
2012 ◽  
Vol 38 (76) ◽  
Author(s):  
Joana Simões ◽  
Carlos Pinto ◽  
Manuel Afonso-Dias
Keyword(s):  
Fishing Effort ◽  
Geographical Information ◽  
Catch Per Unit Effort ◽  
Trawl Fishery ◽  
Single Vessel ◽  
External Software ◽  
Directorate General ◽  
Exploratory Data ◽  
The University ◽  
Trawl Fisheries

A METHODOLOGY FOR THE MONITORING AND MANAGEMENT OF TRAWL FISHERIES IN PORTUGAL. THE SIG EXAMPLE OF GEOCRUST 1.0. This paper aims to present the Geographical Information System GEOCRUST 1.0, a computer programme developed within the fishery research project DGXIV 99/059, Use of Satellite GPS data to map effort and landings of the Portuguese crustacean fleet (GEOCRUST), in the University of Algarve. This stand-alone application was developed essentially to map fishing effort and catch per unit effort (CPUE) information for the Portuguese crustacean trawl fleet, operating off the Southwest and South coasts of Portugal. The data available for this study included GPS vessels’ geographical positions and speed, transmitted via satellite to the Portuguese fisheries inspection authorities, and their catch reported to the Portuguese Directorate-General of Fisheries. GEOCRUST 1.0 was developed in ®VISUAL BASIC 6.0 using two ActiveX control: ADODB, to connect with the ®MSACCESS 2000 database and ®MAPOBJECTS 2.0 PRO, to communicate with the maps and provide GIS facilities. The application includes seven modules with the following objectives: Module 1 – to map and edit the original VMS data for a single vessel or group of vessels, for different periods of time; Module 2 – to analyse the trawl speed of each vessel; Module 3 – to define the boundaries of all fishing trips performed by vessel along the year; Module 4 – to identify and define the trawl hauls, within each fishing trip; Module 5 – to issue maps of fishing effort and CPUE; Module 6 – for exploratory data analysis and to extract data from the DB for further use in other computer packages and Module 7 – to recreate the activity of a single vessel, group of vessels or the total fleet, for a fixed period of time. This GIS application, fully developed by programming, has the advantage of being able to be used on its own without any need for external software support. The system developed is a methodological proposal to implement in Portugal, to monitor and manage the trawl fisheries, in particular, the crustacean trawl fishery.

scholarly journals Comparison of beam trawl catch, by-catch and discard in fishing and non-fishing areas – a case study from the northern Adriatic Sea

2021 ◽  
Vol 22 (1) ◽  
pp. 108
Author(s):  
DARIA EZGETA -BALIĆ ◽  
NEDO VRGOČ ◽  
IGOR ISAJLOVIĆ ◽  
DAMIR MEDVEŠEK ◽  
ANTE VUJEVIĆ ◽  
...  
Keyword(s):  
Adriatic Sea ◽  
Beam Trawl ◽  
Northern Adriatic Sea ◽  
Important Species ◽  
Northern Adriatic ◽  
Trawl Fishery ◽  
Trawl Catch ◽  
Commercially Important ◽  
By Catch ◽  
Trawl Fisheries

Beam trawl fishery is highly important in the Croatian part of the northern Adriatic wherein 116 vessels have a licence for this type of fishing gear. A sharp decrease in the beam trawl catch observed since 2015 has raised concern about not only socio-economic issues but also ecological issues and the effect that beam trawl fisheries have had on exploited stocks. Besides the effect that beam trawl fisheries can have on targeted economically important species, intensive dredging can cause long-term changes in the benthic community. Therefore, this study aimed to detect the effect that this type of fishing gear has on target and by-catch species. Furthermore, survey data were compared with the official beam trawl fishery data gathered through Vessel Monitoring System data together with fishermen’s logbooks. Our research targeted two adjacent areas: an area where beam trawl fishing is allowed and an area where it is forbidden. The results demonstrate that the commercially important catch represented a minor share of the total beam trawl catch in both survey areas, while discard made up more than 93% of the total catch. The main beam trawl commercially important species in the Croatian part of the northern Adriatic Sea was Pecten jacobaeus, followed by Solea solea and Ostrea edulis. Our results suggest that beam trawl fisheries mostly affect target bivalve species and some non-commercial benthic species (e.g. sponges). The differences recorded between areas could suggest that beam trawl fisheries cause changes mostly in the P. jacobaeus population.

scholarly journals Round scallops and square meshes: a comparison of four codend types on the catch rates of target species and by-catch in the Queensland (Australia) saucer scallop (Amusium balloti) trawl fishery

2008 ◽  
Vol 59 (10) ◽  
pp. 849 ◽  
Author(s):  
Anthony J. Courtney ◽  
Matthew J. Campbell ◽  
Darren P. Roy ◽  
Mark L. Tonks ◽  
Keith E. Chilcott ◽  
...  
Keyword(s):  
Sea Urchins ◽  
Catch Rate ◽  
Target Species ◽  
Bivalve Molluscs ◽  
Sea Stars ◽  
Incidental Capture ◽  
Trawl Fishery ◽  
By Catch ◽  
Catch Rates ◽  
Trawl Fisheries

Concern over the amount of by-catch from benthic trawl fisheries and research into the problem have increased in recent years. The present paper demonstrated that by-catch rates in the Queensland (Australia) saucer scallop (Amusium balloti) trawl fishery can be reduced by 77% (by weight) using nets fitted with a turtle excluder device (TED) and a square-mesh codend, compared with a standard diamond-mesh codend with no TED. This large reduction was achieved with no significant effect on the legal size scallop catch rate and 39% fewer undersize scallops were caught. In total, 382 taxa were recorded in the by-catch, which was dominated by sponges, portunid crabs, small demersal and benthic fish (e.g. leatherjackets, stingerfish, bearded ghouls, nemipterids, longspine emperors, lizard fish, triggerfish, flounders and rabbitfish), elasmobranchs (e.g. mainly rays) and invertebrates (e.g. sea stars, sea urchins, sea cucumbers and bivalve molluscs). Extremely high reductions in catch rate (i.e. ≥85%) were demonstrated for several by-catch species owing to the square-mesh codend. Square-mesh codends show potential as a means of greatly reducing by-catch and lowering the incidental capture and mortality of undersize scallops and Moreton Bay bugs (Thenus australiensis) in this fishery.

scholarly journals A Deep Learning Approach to Assist Sustainability of Demersal Trawling Operations

2021 ◽  
Vol 13 (22) ◽  
pp. 12362
Author(s):  
Maria Sokolova ◽  
Adrià Mompó Alepuz ◽  
Fletcher Thompson ◽  
Patrizio Mariani ◽  
Roberto Galeazzi ◽  
...  
Keyword(s):  
Absolute Error ◽  
Monitoring Tool ◽  
Video Footage ◽  
Trawl Fishery ◽  
Augmentation Techniques ◽  
Image Acquisition System ◽  
Catch Composition ◽  
First Time ◽  
Trawl Fisheries ◽  
Resolution Dataset

Bycatch in demersal trawl fisheries challenges their sustainability despite the implementation of the various gear technical regulations. A step towards extended control over the catch process can be established through a real-time catch monitoring tool that will allow fishers to react to unwanted catch compositions. In this study, for the first time in the commercial demersal trawl fishery sector, we introduce an automated catch description that leverages state-of-the-art region based convolutional neural network (Mask R-CNN) architecture and builds upon an in-trawl novel image acquisition system. The system is optimized for applications in Nephrops fishery and enables the classification and count of catch items during fishing operation. The detector robustness was improved with augmentation techniques applied during training on a custom high-resolution dataset obtained during extensive demersal trawling. The resulting algorithms were tested on video footage representing both the normal towing process and haul-back conditions. The algorithm obtained an F-score of 0.79. The resulting automated catch description was compared with the manual catch count showing low absolute error during towing. Current practices in demersal trawl fisheries are carried out without any indications of catch composition nor whether the catch enters the fishing gear. Hence, the proposed solution provides a substantial technical contribution to making this type of fishery more targeted, paving the way to further optimization of fishing activities aiming at increasing target catch while reducing unwanted bycatch.

scholarly journals Effect of Cutting Ratio and Catch on Drag Characteristics and Fluttering Motions of Midwater Trawl Codend

2021 ◽  
Vol 9 (3) ◽  
pp. 256
Author(s):  
Wei Liu ◽  
Hao Tang ◽  
Xinxing You ◽  
Shuchuang Dong ◽  
Liuxiong Xu ◽  
...  
Keyword(s):  
Drag Force ◽  
Mesh Size ◽  
Current Speed ◽  
Midwater Trawl ◽  
Minimum Drag ◽  
Fish Catch ◽  
Spatial Geometry ◽  
By Catch ◽  
Trawl Fisheries ◽  
Crucial Part

The codend of a trawl net is the rearmost and crucial part of the net for selective fish catch and juvenile escape. To ensure efficient and sustainable midwater trawl fisheries, it is essential to better understand the drag characteristics and fluttering motions of a midwater trawl codend. These are generally affected by catch, cutting ratio, mesh size, and twine diameter. In this study, six nylon codend models with different cutting ratios (no cutting, 6:1, 5:1, 4:1, 7:2, and 3:1) were designed and tested in a professional flume tank under two conditions (empty codends and codends with catch) and five current speeds to obtain the drag force, spatial geometry, and movement trend. As the cutting ratio of empty codends decreased, the drag force decreased, and the drag coefficient increased. The unfolding degree of codend netting and the height of empty codends were found to be directly proportional to the current speed and inversely proportional to the cutting ratio. The positional amplitude of codend with cutting ratio 4:1 was the smallest for catch. The drag force of codends with catch increased as the current speed increased, and first decreased and then increased as the cutting ratio decreased. To ensure the best stability and minimum drag force of the codend, it is recommended to use the 4:1 cutting ratio codend.

scholarly journals Actual conditions of discards of by-catch from small-scale trawl fishery in Ariake Sea

2003 ◽  
Vol 69 (3) ◽  
pp. 330-336 ◽  
Author(s):  
YOSHIO HIRAI ◽  
HIDEYUKI NISHINOKUBI
Keyword(s):  
Small Scale ◽  
Ariake Sea ◽  
Trawl Fishery ◽  
By Catch

Hydrophis donaldi (Elapidae, Hydrophiinae), a highly distinctive new species of sea snake from northern Australia

Zootaxa ◽  
2012 ◽  
Vol 3201 (1) ◽  
pp. 45 ◽  
Author(s):  
KANISHKA D.B. UKUWELA ◽  
KATE L. SANDERS ◽  
BRYAN G. FRY
Keyword(s):  
New Species ◽  
Habitat Preferences ◽  
The Body ◽  
Colour Pattern ◽  
Northern Australia ◽  
Nucleotide Substitutions ◽  
Sea Snake ◽  
Sea Snakes ◽  
Morphological Diagnosis ◽  
By Catch

A new species of viviparous sea snake, Hydrophis donaldi sp. nov. (Hydrophiinae), is described from the Gulf of Carpen-taria, northern Australia. Molecular analyses reveal this species as a deeply divergent lineage within the Hydrophis sub-group, and separate it from all other sampled taxa by fixed nucleotide substitutions at three independent mitochondrial andnuclear loci. The new species is assigned to Hydrophis based on the current morphological diagnosis of this large but pa-raphyletic genus, and is distinguished from all other Hydrophis species and closely allied genera by a combination of mor-phological characters relating to scalation, colour pattern and osteology. Using current keys for sea snakes, H. donaldi sp.nov. might be mistaken for H. coggeri, H. sibauensis or H. torquatus diadema but it is readily distinguished from thesespecies by a higher number of bands on the body and tail, lower ventral count, strongly spinous body scales, and a wider,more rounded head. Sea snakes have been sampled intensively in the Gulf of Carpentaria due to their vulnerability to by-catch in the region’s commercial prawn-trawl fisheries. That this highly distinctive new species has evaded discovery inthe region until now is surprising, but might be explained by its habitat preferences. All known specimens of H. donaldi sp. nov. were found in estuarine habitats that are relatively poorly surveyed and are not targeted by commercial fisheries.

scholarly journals Use of avoidance behaviours to reduce the economic impacts of the EU Landing Obligation: the case study of a mixed trawl fishery

2019 ◽  
Vol 76 (6) ◽  
pp. 1554-1566
Author(s):  
Fabien Pointin ◽  
Fabienne Daurès ◽  
Marie-Joëlle Rochet
Keyword(s):  
Temporal Distribution ◽  
Grid Method ◽  
Fishing Effort ◽  
Economic Losses ◽  
Otter Trawl ◽  
Trawl Fishery ◽  
Nested Grid ◽  
Fishing Practices ◽  
The Eu

Abstract The EU Landing Obligation (LO) is designed to reduce bycatch (i.e. unwanted catch) through more selective fishing practices, such as avoidance behaviours which consist in allocating fishing effort to other species, fishing grounds or seasons. Incentives for fishers to change their behaviours depend on their economic performances as well as their ability to avoid bycatch. Changes in economic performances under the LO are evaluated based on cost and revenue equations. The nested grid method is then used to explore the spatial and temporal distribution of landings and discards, and to suggest alternative effort allocation to avoid bycatch. This article is focussed specifically on the French otter trawl fishery in the eastern English Channel and southern North Sea. Results suggest that under the LO the choke species problem will curtail fishing activities earlier in the year, leading to significant economic losses. In the absence of significant quota top-ups (at least 75%), a change in fishing practices consisting in reducing overall bycatch by 30% is insufficient to reduce losses. With a particular attention to choke species, more economically efficient avoidance strategies can be found thanks to the nested grid method.

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