Weight Of Bycatch Research Articles

Integrating research and fishing extension approaches to engage small-scale fishers in the participatory evaluation and voluntary use of bycatch reduction devices

The main strategy for reducing discards in shrimp trawl fisheries has been the development and use of bycatch reduction devices (BRDs). Research has focused on the performance of BRD in biological and technological terms, undermining the importance of the human dimensions, such as fishers’ perceptions. On the other hand, a better comprehension of which methodological approach enables fishers volunteer adoption of BRDs is required. This paper analyzed the performance of BRD through a combination of interaction activities and conventional scientific experiments. Four interaction activities were conducted with shrimp trawlers from 12 fishing sites at the coast of Paraná, South Brazil. Adapted from previous research and after fishers’ suggestion in the interaction activities, a Nordmore grid was tested against a control net to evaluate differences in shrimp (Xiphopenaeus kroyeri) and bycatch weight, and total length of X. Kroyeri. Interaction activities stressed the importance of dialogue and participation and showed that fishers perceived a high diversity of parameters, expanding the understanding of BRD performance. Also, the methodological approach provided room for collective learning and fishers’ engagement, with reports of voluntary initiatives to reduce bycatch. The results showed that the dialog is improved with diversification and integration of communication methods, as well as timing is crucial for fishers to process information and to build knowledge. An analysis of the methodological approach used in this paper provide insights on how to increase voluntary BRD adoption as well as to engage fishers more consistently in being stewards for the responsible fishing.

Juvenile and Trash Fish Excluder Device (JTED) for Taiwanese Bottom Trawl

Juvenile and trash fish excluder devices (JTEDs) are used to mitigate the ecological impact of trawling. Trawling has a large ecological footprint in Taiwan. Thus, this study designed three JTEDs, which differed only in grid interval, for single boat bottom otter trawls that are commonly used in Taiwan. The designed JTEDs were tested in the waters off of Kaohsiung on a Kaohsiung-based bottom trawler, and the results were as follows. (1) At least 300 species were caught, and 189 of these species had little commercial value; their weight accounted for 52.5% of the total catch. (2) The three JTEDs had good exclusion performance. (3) The ratios of the weight of bycatch excluded to the weight of total catch were 7.9%, 29.1%, and 36.2%, for grid intervals of 10, 15, and 20 mm, respectively. (4) JTEDs with grid intervals of 10, 15, and 20 mm were associated with a 0.4%, 11.5%, and 19.0% loss in revenue, respectively. (5) Mature (and thus commercially valuable) Loliginidae tended to be excluded when the grid interval was 20 or (especially) 15 mm. In general, the designed JTEDs should be used at a grid size of 15 mm because this strikes the best balance between profitability and sustainability.

Bycatch in the California halibut (Paralichthys californicus) Trawl Fishery

Bycatch rates within the California halibut trawl fishery were calculated using landed catch data from 1997–2020 fishery logbooks and estimated using landed and discarded catches from 2002–2019 fishery observer data. Average bycatch rates were significantly different between the two datasets. The average bycatch ratio estimated from fishery logbooks was 0.36 ± 0.17 while the average bycatch ratio estimated from the observer data was 4.61 ± 1.29, based on the weight of bycatch to weight of California halibut catch. Additionally, the most frequently caught bycatch species were estimated for each dataset. Bycatch rates calculated from the observer data were closely aligned with fishery-independent surveys conducted by the California Department of Fish and Wildlife, signaling the importance of using fishery observers to obtain estimates of bycatch within the California halibut fishery. Spatial patterns of bycatch revealed that fishing effort was highest near Monterey, San Luis Obispo and Ventura. Our results suggest that data from logbooks alone are not sufficient to adequately estimate bycatch within the California halibut trawl fishery.

Spatiotemporal modeling of bycatch data: methods and a practical guide through a case study in a Canadian Arctic fishery

Excess bycatch of marine species during commercial fishing trips is a challenging problem in fishery management worldwide. The aims of this paper are twofold: to introduce methods and provide a practical guide for spatiotemporal modelling of bycatch data, as well as to apply these methods and present a thorough examination of Greenland shark (Somniosus microcephalus) bycatch weight in a Canadian Arctic fishery. We introduce the spatially explicit two-part model and offer a step by step guide for applying the model to any form of bycatch data, from data cleaning, exploratory data analysis, variable and model selection, model checking, to results interpretation. We address various problems encountered in decision making and suggest that researchers proceed cautiously and always keep in mind the aims of the analysis when fitting a spatiotemporal model. Results identified spatiotemporal hotspots and indicated month and gear type were key drivers of high bycatch. The importance of onboard observers in providing robust bycatch data was also evident. These findings will help to inform conservation strategies and management decisions, such as limiting access to spatial hotspots, seasonal closures and gear restrictions.

Application of association analysis for identifing indicator taxa of vulnerable marine ecosystems in the Emperor Seamounts area, North Pacific Ocean

Reflecting the growing interest in ecosystem-based fishery management, deep sea bottom fisheries are being called upon to minimize adverse impacts on vulnerable marine ecosystems (VMEs), communities of marine organisms susceptible to anthropogenic disturbance. Many fishery management organizations have introduced indicator-based management measures for VME conservation, such as encounter protocols, in which VME indicator species and bycatch weight thresholds are assigned. If the bycatch amount of the indicator species in a fishing operation exceeds the predetermined threshold, the fishing vessel halts the fishing operation and moves a certain distance away from the encounter point. However, the representativeness of VME indicator taxa has not been evaluated quantitatively. In this study, we analyzed the co-occurrence of benthic animals collected by scientific bottom tow-net surveys in the Emperor Seamounts area, North Pacific Ocean, to characterize benthic communities in the area and to examine the ability of six candidate indicator taxa (gorgonians, Alcyonacea excluding gorgonians, Antipatharia, Scleractinia, Stylasterina, and Porifera) to represent the local benthic communities. Cluster analysis revealed four clusters of benthic communities, each of which includes both sessile and mobile benthos: (1) gorgonians-Scleractinia community with many mobile benthic taxa and Pisces; (2) Porifera-Stylasterina community with Polychaeta and Bivalvia; (3) Antipatharia-Alcyonacea (excluding gorgonians) community with Cephalopoda; and (4) Zoanthidea-Pennatulacea community with Crinoidae and Holothuroidea. The first cluster included the largest number of taxa and showed strong tendencies of co-occurrence, possibly reflecting the habitat-providing function of gorgonians and Scleractinia as well as the common environmental preferences of filter feeders, which constitute major components of the cluster. We used association analysis to identify VME indicator species in the study area. Association analysis reveals relationships between items in the form of association rules, where the occurrence of an “antecedent” {A} implies the co-occurrence of a “consequent” {B}; {A} and {B} contain items, in this case, taxa. Association analysis applied to the co-occurrence data extracted many effective association rules that include gorgonians or Scleractinia as the consequent and many benthic taxa as antecedents. These results demonstrate that gorgonians and Scleractinia are effective VME indicators in the study area because they co-occur with many other benthic animals and represent VME characteristics such as functional significance as habitat and structural complexity as well as fragility and slow recovery from physical damage.

Analysis of body size selectivity of by-catch using the cover net method for a shrimp beam trawl

Selectivity and by-catch are the main features used to define fish catch for fisheries management or to determine fishing gear efficiency. A fish girth distribution analysis was carried out to determine the retention rate of juveniles discarded and to establish common selectivity for a multispecies catch. Total body length, body weight, and girth of juvenile fish retained in the cod-end and cover net separately were collected using an 18-mm mesh cover net during 12 fishing trials with a 41-mm cod-end beam trawl. The by-catch weight ratio in the cod-end was twice that of the by-catch ratio in number. The 50% selectivity of body length and 50% girth of redfin velvet fish were not significantly different between the cod-end and cover net, whereas those of other fish species were significantly different between the cod-end and cover net. The difference in 50% selectivity girth of other fish between the cod-end and cover net was similar between cod-end mesh size and cover net mesh size. Furthermore, the difference in 50% body length selectivity of other fish between the cod-end and cover net was almost double the difference in girth. Girth selectivity in a multispecies catch using towed fishing gear was effectively used to determine fish and net mesh size.

Evolving and devolving bycatch reduction devices in an Australian penaeid-trawl fishery

Since bycatch reduction devices (BRDs) were first tested in Australian penaeid-trawl fisheries almost 20 years ago, there have been ongoing refinements to a discrete range of legislated designs; mostly in response to dynamic fishery-specific operational requirements. This study assesses the relative utility of the latest versions of two generic BRDs that have evolved/devolved in an estuarine fishery. Compared with a codend containing no BRD, a simplified Nordmøre-grid and radial escape section significantly reduced the total weight of bycatch by 74 and 36%, respectively. Catches of the targeted school prawns ( Metapenaeus macleayi) were also reduced by 4 and 11%, respectively, although, at least for the Nordmøre-grid, these losses were apparently offset by the practicality of the revised design in terms of a simpler and cheaper construction. The presence of large quantities of displaced submerged plants (e.g. Egeria densa and Hydrilla verticillata) on the trawl grounds at certain times (which preclude using the Nordmøre-grid) may similarly compensate for the reduced efficiency of the radial escape section. In addition to quantifying the performance of the revised BRDs, the results provide direction for their future refinement in this and other similar fisheries.

Bycatch in a tropical schooling – penaeid fishery and comparisons with a related, specialised trawl regime

Abstract The bycatch in a tropical Australian banana prawn, Penaeus merguiensis (de Man), fishery is described and contrasted with the closely related tiger prawn, Penaeus semisulcatus De Haan and Penaeus esculentus Haswell, fishery. Most of the similarity between banana prawn fishery catches was accounted for by three teleost species constituting 51.4% of the total bycatch weight. The bycatch assemblage structure of this fishery was significantly different (P < 0.05) from the adjoining tiger prawn fishery. The banana prawn fishery had a higher mean bycatch catch rate from shorter duration trawls, but lower estimated total annual bycatch (1502 t yr−1) than the longer duration trawls of the tiger prawn fishery (20 073 t yr−1). This study provides new data for quantifying bycatch and improving the accuracy of quantitative risk assessments currently being used to demonstrate sustainability of bycatch populations. The information will be incorporated into collaborative development of a long‐term monitoring programme.

Effect of catch size and shape on the selectivity of diamond mesh cod-ends

Abstract A series of computer simulations were carried out to predict how the selectivity of haddock in a diamond mesh cod-end varies according to total catch, by-catch, entry time of by-catch and the shape of the catch build-up in the cod-end. Results were compared to those from sea trials. I also investigated the predicted selectivity on the assumption that the shape of the cod-end does not change as the catch accumulates. The latter investigations were carried out for various shapes of the cod-end. The simulations indicated that the 50% retention length (L50) increases with both the total catch and the by-catch weight. They also indicated that the entry time of the by-catch may have an important influence on both the 50% retention length and selection range (SR). The shape of the catch in the cod-end had a similar effect, for the cases analyzed. Different cod-end shapes showed very large differences in the values for L50 as well as more narrow SRs, assuming that the shape of the cod-end remained constant during the tow. The simulations strongly indicate that the change of shape of the diamond mesh cod-end as the catch builds up during towing is a major contribution to the SR.

Low levels of bycatch from estuarine prawn seining in New South Wales, Australia

We present estimates of the composition, catch rates and quantities of bycatches taken in the seine fishery for school prawns ( Metapenaeus macleayi) in coastal rivers in New South Wales, Australia. Observers sampled 91 fishing trips throughout the Richmond, Manning, Wallamba and Shoalhaven Rivers between September 1998 and June 1999 and identified a total of 43 finfish and 5 invertebrate taxa in bycatches. Multivariate analyses indicated that the composition and structure of bycatches varied little between locations within each estuary, but differed significantly between estuaries. Small fishes (<15 cm TL) of little economic value primarily dominated bycatches in all estuaries, except the Shoalhaven River. Dominant species in bycatches included Herklotsichthys castelnaui, Arius graeffei and Zebrias scalaris in the Richmond River, H. castelnaui, Siphamia sp., Ambassis spp., Gerres subfasciatus, Cnidoglanis macrocephalus and Acanthopagrus australis in the Manning and Wallamba Rivers and Pomatomus saltatrix, G. subfasciatus and A. australis in the Shoalhaven River. Several species important in other commercial and recreational fisheries were recorded in bycatches, but generally in low numbers, the notable exception being G. subfasciatus. Mean prawn catch-to-bycatch ratios by weight for each estuary ranged from 1:0.07 to 1:0.52, which are considerably less than those reported for other net-based prawn fisheries. The estimated total weight of bycatch from seining in each estuary ranged from 1.7 to 17.6 t during the 10-month fishing season. Across all four estuaries, in catching an estimated 131 t of prawns the fleet took an estimated 27 t of bycatch throughout the survey. The relatively low levels of observed bycatches in the seine fishery were attributed to a combination of the small size of nets (40 m headline length) and the relatively short time (3–15 min) it took to operate each individual seine. The latter also led to observations that bycaught fish were in particularly good condition when discarded. The data indicate that discarding in this fishery probably has minimal impact on other interacting finfish fisheries in the region.

Analysis of bycatch in the fishery for orange roughy, Hoplostethus atlanticus, on the South Tasman Rise

Government fisheries observers made detailed records of the catch weights of all species caught on 545 trawls between October 1997 and August 2000 in the South Tasman Rise orange roughy (Hoplostethus atlanticus) fishery. Bycatch ratios, the ratio of bycatch weight to tow duration, were derived from these data and used to make estimates of total annual bycatch for several species groups. Bycatch ratios based on tow duration were chosen over ratios based on orange roughy catch weights after comparing the coefficients of variation (c.v.) of sets of trial data. Bycatch ratios and total bycatch were estimated for three species of oreos (Oreosomatidae), corals and all other bycatch species combined, for the fishing years from 1997–1998 to 2000–2001. Total oreo bycatch dropped from about 7400 t to less than 350 t during this time. These estimates agreed well with recorded oreo landings data for three of the four years. There was a considerable bycatch of corals, with both the bycatch ratio and the total bycatch reducing during the period examined, the latter from about 1750 t to 100 t per year. The coral bycatch comprised a large number of species, but was dominated by the reef-forming stony coral Solenosmilia variabilis. Annual bycatch of all other species combined, mainly rattails (Macrouridae) and dogfishes (Squalidae), was low (13–120 t). Bycatch of this group dropped sharply in each year as the result of a combination of decreasing bycatch ratio and decreasing fishing effort.

Using composite square-mesh panels and the Nordmøre-grid to reduce bycatch in the Shark Bay prawn-trawl fishery, Western Australia

An industry-modified Nordmøre-grid was tested on its own and with a composite square-mesh panel as a secondary bycatch reduction device (BRD) at two different positions (aft and forward) in codends. Compared to the control codend (which had no BRDs), all three combinations (Nordmøre-grid only, Nordmøre-grid and aft composite square-mesh panel and Nordmøre-grid and forward composite square-mesh panel) reduced catches of prawns (mostly western king prawns, Penaeus latisulcatus). However, prawns were found to escape out of the Nordmøre-grid—not through the composite square-mesh panels. The Nordmøre-grid with the aft composite square-mesh panel significantly reduced the weight of bycatch (by 49%) and the numbers and weights of several commercially and non-commercially important bycatch species (by up to 75.7%). No other significant differences were detected. The results are discussed in terms of the likely factors influencing the performance of the various designs, including the behaviour of fish in codends, influences of hydrodynamics on their escape and the importance of the positioning of BRDs in codends.

Bycatch diversity and variation in a tropical Australian penaeid fishery; the implications for monitoring

The composition of teleost and elasmobranch bycatch in two tropical Australian penaeid prawn fisheries was examined using scientific surveys. These covered the major fishing grounds in February and October 1997. On average 82% of the bycatch was teleosts and elasmobranchs, resulting in a high proportion of the bycatch which is unlikely to survive capture. The bycatch is highly diverse (over 350 species of teleosts and elasmobranchs) and dominated by species which occur rarely (75% of species occurred in <10% of trawls) and in low abundance (<10 n h −1) and biomass (<1 kg h −1). Eight families, including 83 species had to be included to account for 66% of the bycatch weight. Overall the general catch characteristics (e.g. total bycatch weight, catch rate of teleosts and elasmobranchs), bycatch composition and individual species abundances showed significant variation among the regions and between February and October. The variation due to regional differences was much greater than between the two times of year. The inclusion of covariates (depth, acoustic measures of seabed roughness and hardness, commercial prawn catch and commercial fishing effort) explained some of the observed variation but there was still significant regional variation present. The primary implication of the results is the clear need for future monitoring strategies to be stratified with respect to region. Monitoring from a single region or time is unlikely to be representative of the fishery.