Seabird Bycatch Research Articles

Synthesising a network of evidence on a seabird bycatch mitigation measure

AbstractRobust estimates of the relative efficacies of alternative management interventions are essential for developing evidence‐informed fisheries bycatch policy. Bycatch is a major threat to the conservation of albatrosses and other pelagic seabirds. Branchline weighting is one approach prescribed by regional fisheries management organisations and the Agreement on the Conservation of Albatrosses and Petrels to reduce seabird bycatch in pelagic longline fisheries. We used a Bayesian multilevel network meta‐regression modelling approach to conduct the first synthesis of available evidence to assess the relative efficacies at mitigating seabird bycatch of alternative pelagic longline weighting designs. Unlike conventional pairwise meta‐analysis, network meta‐analysis enables the simultaneous comparison of multiple interventions within a coherent modelling framework. There was a > 97% probability that all weighting designs significantly reduced seabird bycatch compared to a reference design with no weight within 5 m of the hook. Nonetheless, some weighting designs were significantly more effective at reducing seabird bycatch than others—for instance, the 2 designs with weights >60 g and >1 m from the hook performed the best with >93% probability that those 2 designs performed significantly better than 2 more commonly used designs with less weight but attached closer to the hook. These two best performing designs reduced seabird bycatch by ca 89% relative to the reference design. These relative efficacies and rankings, when combined with other performance criteria such as costs to commercial viability and crew safety, support robust evaluations of alternative bycatch management strategies.

Correction: Feasibility and knowledge gaps to modeling circumpolar seabird bycatch in the Arctic

Correction: Feasibility and knowledge gaps to modeling circumpolar seabird bycatch in the Arctic

A probabilistic time geographic approach to quantifying seabird‐vessel interactions

AbstractAccounting for uncertainty is essential for precautionary approaches to managing seabird bycatch in commercial fisheries. However, there is no existing mechanism to explicitly quantify the uncertainty of seabird‐vessel interactions (i.e. co‐occurrence in space and time). Here we develop a time geographic method to measure the probability of individual birds encountering (co‐occurring within 30 km) and attending (within 5 km) individual fishing vessels. The approach involves creating voxel‐based probabilistic space–time prisms (PSTPs) to model the movements of individual birds and vessels, with trajectory data from bird‐borne GPS devices and vessel Automatic Identification Systems (AIS). We intersected these PSTPs to quantify the probability of interaction between bird‐vessel pairs over time and space. We demonstrate the approach with a case study of interactions of Endangered Toroa (Antipodean Albatross; Diomedea antipodensis antipodensis) with pelagic longline vessels in part of the South Pacific high seas. We found 15 vessels within 150 km and 3 h of two birds, yet interaction occurred with only two of those vessels. We visualised the probability of encounter and attendance over time and space and determined that interactions lasted several hours each (up to 6.2–14.1 h attendance, 20.8–26.1 h encounter for one bird‐vessel pair). Our time geographic approach adds to existing tools to quantify seabird bycatch risk by providing an explicit measure of uncertainty of seabird‐vessel interactions. We provide a flexible methodological pathway and R scripts, the application of which would allow managers to estimate interaction probability for multiple marine species and fisheries, including those with lower‐resolution positional datasets.

Seabird bycatch in European waters

AbstractThe incidental capture (bycatch) of seabirds is a global conservation issue and a top threat to European species that demands urgent conservation and management action. Here, we present the first European review of seabird bycatch data, considering all fishing gears and data collection methods available in the region. We calculate seabird bycatch numbers per species, family, country and European marine region and assess the reliability of the data available. The cumulative bycatch estimate extracted from this review suggests that about 195,000 seabirds (ranging from around 130,000 to 380,000) are bycaught in European waters annually. The most affected seabird species is the Common Guillemot Uria aalge with over 31,000 birds killed per year. The marine region with the highest bycatch estimate is the Northeast Atlantic (over 115,000 seabirds year−1). Gillnet fisheries are responsible for the highest bycatch levels, with over 95,000 seabirds year−1, followed by longline fisheries. The families most affected by bycatch are Anatidae and Alcidae. These numbers are likely an underestimation since we were unable to find bycatch estimates, or to extrapolate estimates from available bycatch data for 12 (out of 34) European coastal states. Our assessment also identified significant data gaps in key areas such as Gran Sol (in the north‐east Atlantic), the central and Eastern Mediterranean and the Black Sea. Combining systematic data collection with immediate implementation of mitigation measures will be crucial to fill in knowledge gaps, reduce current mortality levels and meet international conservation commitments such as those of the European Union and the Convention on Migratory Species.

Can depth-based restrictions avoid seabird bycatch while maintaining catch in the Icelandic lumpfish fishery? A reply to Kennedy & Sigurðsson (2024).

Can depth-based restrictions avoid seabird bycatch while maintaining catch in the Icelandic lumpfish fishery? A reply to Kennedy & Sigurðsson (2024).

Feasibility and knowledge gaps to modeling circumpolar seabird bycatch in the Arctic

Feasibility and knowledge gaps to modeling circumpolar seabird bycatch in the Arctic

Test of light emitting diodes (LED) as a possible bycatch mitigation measure in a gillnet fishery

Substantial seabird bycatch occurs in North Atlantic lumpfish fisheries, potentially impacting seabird populations and raising concerns about the fisheries’ sustainability. Despite increased efforts to address this issue, existing approaches have yielded inconclusive and mixed results. In this study, we explored an alternative approach by comparing bycatch levels between conventional gillnets and LED-illuminated gillnets during the 2023 Greenland lumpfish fishing season. Results indicated that LED-illuminated nets showed almost no difference in bycatch compared to no-LED nets for the three main bird species (common eider, king eider, and long-tailed duck), with no statistically significant differences observed. Additionally, the LED-illuminated nets exhibited a slightly lower, but insignificant, catch rate of the targeted female lumpfish. In conclusion, our findings suggest that using LED as a bird deterrent in this fishery is not an optimal solution to bycatch mitigation.

The implementation of ACAP Best Practice Advice to mitigate seabird bycatch in fisheries: Issues and options

The Agreement on the Conservation of Albatrosses and Petrels (ACAP) is a multilateral agreement which strives to conserve albatrosses and petrels by coordinating international activities to mitigate threats to their populations. One of the major threats that seabirds face is fisheries-induced mortality, or bycatch. In recognition of the serious nature of this problem, ACAP established a Seabird Bycatch Working Group (SBWG) to advise on actions that will assist in the mitigation and reduction of seabird interactions with fisheries. The SBWG regularly examines the range of measures available that can minimise bycatch and has developed “best practice advice” (BPA), a suite of tools and methods for trawl and longline fisheries. This BPA has been widely promoted by ACAP Parties and others within jurisdictions and at Regional Fisheries Management Organisations (RFMOs) and CCAMLR other over the last 10 years. To assess the levels of implementation of ACAP’s BPA for industrial fisheries we employed both a qualitative and semi-quantitative multiple method research design that comprised content analysis of documents and meeting reports from ACAP meetings, a review of current seabird conservation measures of all tRFMOs that had members which were also ACAP parties, and by conducting a survey that asked 13 questions in relation to the uptake and adoption of ACAP BPA. We confined our analysis to pelagic longline and trawl fisheries within the jurisdictions of both ACAP parties and non-parties. Our research identified a number of key gaps in the uptake of the BPA guidelines in these fisheries. Complete uptake of BPA was poor by ACAP Parties both within their jurisdictions, and in high seas fisheries managed through RFMOs. For Parties, the level of uptake was difficult to assess accurately because reporting to the Agreement has thus far been inadequate for this purpose. Uptake of BPA in high seas fisheries by non-parties and RFMos was also poor and unlikely to improve while ACAP Parties are unable to demonstrate commitment to their use in all national fisheries. The study findings provided advice and recommendations on addressing impediments to uptake that could lead to improved management of seabird bycatch in commercial fisheries.

Looming-eyes buoys fail to reduce seabird bycatch in the Icelandic lumpfish fishery: depth-based fishing restrictions are an alternative.

Bycatch in gillnets from lumpfish (Cyclopterus lumpus) fisheries is an important conservation issue in the north Atlantic, with up to 30 000 seabirds potentially killed each year. To date, no technical solutions exist to reduce the bycatch of seabirds in gillnet fisheries, but research on above-water bird deterrents as a form of bycatch mitigation has shown promising results. Here, we tested whether a floating device called 'looming-eyes buoy' (LEB) would consistently reduce the bycatch of seabirds in the Icelandic lumpfish fishery. We conducted 61 controlled trials with sets of normal gillnets and experimental nets equipped with LEBs. We compared both fish catch and bycatch between net types while accounting for exposure time, water depth and season, and found no effect of LEBs on both target lumpfish catch and bycatch. Our analysis indicated however a strong correlation between bycatch rates and fishing depths, suggesting that depth-based fishing restrictions could virtually eliminate the bycatch of seabirds in this fishery. We estimated that limiting fishing to waters more than 50 m deep could save between 5000 and 9300 seabirds every year, arrest the population decline of endangered black guillemots in Iceland, while having only a marginal effect on target fish catch.

Ecological risk assessment in the southern Indian Ocean: Towards better seabird bycatch mitigation

Abstract Fisheries bycatch has been identified as the most serious threat to many seabird species and there is an increasing awareness of the responsibility of fisheries management bodies to include the impact on non‐target species in their management and regulatory frameworks. In 2022, an ecological risk assessment (ERA) for seabirds and fisheries was presented to the Scientific Committee of the Southern Indian Ocean Fisheries Agreement (SIOFA). This ERA identified 32 seabird species that regularly occurred in the SIOFA Area, of which 11 were determined as being at high risk. This high‐risk group included 10 albatross species that have the greatest likelihood of interacting with SIOFA managed fisheries in Subareas 1, 2 and 3b (west of 40° E) where they overlap with the pelagic longline fishery. Although the pelagic longline fishery for Ruvettus pretiosus is the largest fishery under the auspices of SIOFA, in terms of catch and number of vessels, the existing management measures of SIOFA focused on demersal fisheries and did not include any mitigation requirements for pelagic longlines. In response to the outcomes of the ERA, a proposed amendment to SIOFA's management measures was presented by France to the Meeting of Parties of SIOFA and led to the revision of SIOFA's seabird bycatch mitigation measures in respect of pelagic longlines, making them consistent with those agreed by the Indian Ocean Tuna Commission. Regulatory diffusion, the increased likelihood of adoption of regulation by one agency if that regulation has been adopted by another agency, contributed to the relatively rapid transition from the identification of the risk posed by pelagic longline vessels to the change in regulations to address those risks in SIOFA.

Bird scaring lines reduce seabird mortality in mid-water and bottom trawlers in Argentina

Abstract Seabird bycatch in fisheries, and the development of effective mitigation to minimize this, have been subject to increasing research attention over the past three to four decades. Trawl fisheries represent a particular challenge, as bird mortalities (especially highly threatened albatrosses and large petrels, Procellariforms) occur primarily through difficult-to-detect collisions with warp and net monitoring cables. Effectiveness of bird-scaring lines (BSLs) as a mitigation measure can be fleet-specific, and studies relating specifically to reducing collisions with the net monitoring cable are rare. To support improved assessment and mitigation of seabird bycatch in trawl fisheries, we studied the mortality associated with mid-water and bottom factory trawl vessels along the southern tip of the Argentine Patagonian shelf, across 2144 trawls from 2012 to 2019, with three specific objectives: (i) inform improved bycatch management in this (and other) trawl fisheries by analysing differences in seabird collision rates and outcomes between net monitoring and warp cables, as well as the effect of mitigation measures in reducing collisions; (ii) explore the effects of key fishing operation variables on seabird impact outcomes; and (iii) estimate the annual seabird mortality in the study fleet. We tested the efficacy of BSLs as a mitigation measure to reduce seabird mortality, on warps and net monitoring cables. Our results show that seabird mortality increases in the presence of a net monitoring cable. Our estimation of fishery-wide mortality without the use of BSLs includes 108 [31–186] Southern royal albatross (Diomedea epomophora) and 279 [108–465] Black-browed albatross (Thalassarche melanophris) killed annually by the collisions with the net monitoring cable. We demonstrate the efficacy of BSLs in reducing the number of collisions and in combination with no discarding of fishes, seabird interactions fell to c. zero. Our study builds the case for better bycatch data collection in trawl fisheries, the strong influence of discarding, and the feasibility of simple mitigation measures to reduce seabird bycatch, including on the net monitoring cable.

Advances in Scale Assessment of Seabird Bycatch: A New Methodological Framework

This paper presents a methodology for indirectly estimating the scale of seabird bycatch using existing data. The study focuses on five key species of ducks that winter in the Polish waters of the Baltic Sea and are highly susceptible to bycatch: Long-tailed Duck, Velvet Scoter, Common Scoter, Greater Scaup, and Tufted Duck. The evaluation units used are divided into the Bornholm (BS) and Gotland Subdivisions (GS) within the Polish Exclusive Economic Zone (PEEZ). The analysis acknowledges the lack of bycatch data for certain areas known to have high concentrations of diving birds and fishing activity. The population sizes of waterbirds were assessed using ship-based surveys and a distance sampling approach. Fishing effort data from the five winter seasons between 2015/2016 and 2019/2020 were analyzed. Bycatch rates were estimated based on surveys conducted in previous seasons, and threshold values for bycatch were established using the concept of “small numbers” defined in EU directives. The results show that within the GS of the PEEZ, the estimated average abundance of all diving waterbirds was 174,800 individuals, with an average annual bycatch of 7921 birds (4.5% of the total). The Velvet Scoter was the most abundant species, followed by the Long-tailed Duck. In the BS, the estimated average abundance of diving waterbirds was 624,600 individuals, with an average annual bycatch of 5056 birds (0.8% of the total). The Long-tailed Duck was the most numerous species, followed by the Velvet Scoter. Acceptable bycatch thresholds were exceeded for all species in both subdivisions despite a much smaller scale of bycatch in the BS. The findings highlight the need for effective management and conservation measures to address the high mortality of seabirds due to bycatch. The methodology presented in this study offers a valuable approach for estimating bycatch scale and can support efforts to minimize the impact on seabird populations.

Mitigation of seabird bycatch in New Zealand squid trawl fisheries provides hope for ongoing solutions

ABSTRACT Although there is an increasing awareness of the high rates of seabird bycatch in trawl fisheries globally, there is relatively limited implementation of effective mitigation measures. Seabirds that are attracted to the stern of the trawl vessel to feed on fish-waste can be drowned or injured when they collide with warps/cables or when they become entangled in nets. Managing fish-waste discharge (processing offal and discards) and limiting access to it by scaring birds have been identified as the most effective measures to reduce seabird mortality from collisions with warps. New Zealand’s arrow squid (Nototodarus spp.) trawl fishery occurs during the austral summer and autumn when there is significant overlap with large numbers of foraging seabirds due to the proximity of breeding areas. Regulations introduced by the New Zealand government in 2007 requiring the use of devices to reduce warp strikes and operational procedures to manage fish-waste were independently implemented by the fishing industry in 2007 with the support of fishery regulators. The rate of capture of albatrosses by warps decreased from a mean of 2.9 birds per 100 tows during the period 2003 to 2006 to a mean of 0.7 birds per 100 tows after 2007. Long-term ownership of squid fishery quota catalysed the proactive engagement of the industry and has been reflected in a positive cultural shift in the attitude of fishers towards managing the risk of the capture of seabirds. Multi-sector collaboration and engagement allowed for the translation of experimental mitigation results into long-term, industrial-scale operational practices.

Cetacean bycatch management in regional fisheries management organizations: Current progress, gaps, and looking ahead

Bycatch is the leading global threat to cetaceans, with at least 300,000 cetaceans estimated to be killed each year in fisheries. Regional fisheries management organizations (RFMOs) are key actors in global fisheries management, including bycatch reduction, but their role in cetacean bycatch management is often overlooked. The primary mandate of RFMOs is to manage fisheries of target stocks, but many of their Convention Agreements call for addressing bycatch of threatened and protected species in their fisheries, including cetaceans. We reviewed 14 RFMOs to understand their current cetacean bycatch management efforts. We developed twenty-five criteria for best practices in cetacean bycatch management to understand efforts made by each RFMO, grouped into five categories: 1) general bycatch governance; 2) observer coverage; 3) quantitative bycatch limits; 4) data analysis and transparency; and 5) mitigation efforts. Collectively, based on our application of these criteria, RFMOs scored highest in “data analysis and transparency” (average=0.74) and lowest in setting “quantitative bycatch limits” (average=0.15). Overall, RFMOs have passed few binding conservation and management measures focused on cetacean bycatch, particularly compared to those addressing the bycatch of seabirds and sea turtles; the few existing measures are primarily focused on bycatch in purse seines. Notwithstanding the United Nations (UN) large-scale drift gillnet ban (46/215) on the high seas, only one RFMO has passed a management measure specifically focused on cetaceans and gillnets, widely recognized as the gear type posing the highest risk to cetaceans. No measure in any RFMO specifically addresses cetacean bycatch in longlines. We provide recommendations to the RFMO community to encourage progress on this critical issue, including leveraging other recent policy developments such as the adoption of the 2021 UN Food and Agriculture Organization Guidelines to prevent and reduce bycatch of marine mammals in capture fisheries and implementation of the U.S. Marine Mammal Protection Act Import Provisions.

Adjusting time-of-day and depth of fishing provides an economically viable solution to seabird bycatch in an albacore tuna longline fishery

Marine megafauna exposed to fisheries bycatch belong to some of the most threatened taxonomic groups and include apex and mesopredators that contribute to ecosystem regulation. Fisheries bycatch is a major threat to the conservation of albatrosses, large petrels and other pelagic seabirds. Using data sourced from a fisheries electronic monitoring system, we assessed the effects of the time-of-day and relative depth of fishing on seabird and target species catch rates for a Pacific Ocean pelagic longline fishery that targets albacore tuna with an apparently high albatross bycatch rate. Using a Bayesian inference workflow with a spatially-explicit generalized additive mixed model for albacore tuna and generalized linear mixed regression models both for combined albatrosses and combined seabirds, we found that time-of-day and fishing depth did not significantly affect the target species catch rate while night-time deep setting had > 99% lower albatross and total seabird catch rates compared to both deep and shallow partial day-time sets. This provides the first evidence that night-time setting in combination with fishing deep reduces seabird catch risk and may be commercially viable in this and similar albacore tuna longline fisheries. Findings support evidence-informed interventions to reduce the mortality of threatened seabird bycatch species in pelagic longline fisheries.

Avoiding grey seal depredation in the Baltic Sea while increasing catch rates of cod

The escalating conflict between gillnet fisheries and the growing seal populations in Baltic Sea has increased the need to reduce direct effects in form of reduced or damaged catches. This study describes the design and catch rates of 20 different seal safe cod (Gadus morhua) pot designs suitable for the Baltic Sea. Catches in numbers of individuals and total catch weight were recorded in 2762 pot hauls with pots varying in terms of size, shape, number of entrances, entrance length, pot placement in relation to the sea floor and catch holding chamber. The aim was to investigate the how the different designs and soak times affected the catch rates under similar conditions. Volume and soak time was significantly positively correlated with catch rates and round bottom-standing pots with a fish holding chamber, funnels and 5 entrances had the highest catch rates. The findings are important for the development of cod pots, which can allow the fishers to continue fishing in areas of high seal density with static gear and hence low-carbon emission and minimum bycatch of marine mammals and sea birds.

Increase in bycatch rates of plunge- and surface-feeding seabirds observed while setting and hauling bottom set gillnets equipped with LED lights

Seabird bycatch in gillnets is a worldwide problem with few if any available mitigation tools. LED lights attached to the gillnets have been suggested as a potential solution, and a study in Peru showed promising results where bycatch of diving seabirds was reduced by adding LED lights to bottom set gillnets. In this study the potential bycatch reduction of LED lights was tested in a set gillnet fishery that targets Atlantic cod Gadus morhua in Iceland. A variety of seabirds such as common guillemots, cormorants, eiders, northern gannets, northern fulmars, and gulls have been observed as bycatch in that fishery. In a paired trial, nets with and without LEDs were fished off a commercial gillnetter in western Iceland. The LED-equipped net sets caught significantly more seabirds while a slight but statistically insignificant reduction in fish catches was also observed. The seabirds caught in the LED-equipped nets were mainly northern gannets and northern fulmars, plunge- and surface-feeding birds, which seemed to be attracted to the lights while hauling and setting the nets. Caution should be taken when implementing the use of LED lights on gillnets or trawls as while they might reduce bycatch of some taxa of diving seabirds or sea turtles, it is possible that some bird species or groups of bird species are attracted to the lights, in particular during hauling and setting of the nets.

Identifying social practices to inform fisheries management—the case of bycatch practices of marine mammals and seabirds of German gillnet fishers

AbstractGillnets are one of the most common fishing gears globally and provide a fundamental contribution towards the income of millions of people as well as to the supply of protein. At the same time, bycatch from gillnet fisheries is one of the biggest threats to seabirds and marine mammals worldwide, because their habitats coincide spatially and temporally with gillnet fisheries. There has been research on technical solutions to unwanted bycatch, yet the social-science perspective is rather understudied. Little is known about fishers’ bycatch behaviour, which can be researched as a social practice. Against the background of Anthony Giddens’ structuration theory, this study used social sciences methods to analyse the bycatch practices of gillnet fishers in the German Baltic Sea. The results show that fishers normalize bycatch of seabirds as part of their fishing routine, while bycatch of marine mammals is experienced as a crisis. Underlying mechanisms for different bycatch practices are identified, and their meaning for management as well as further research questions are discussed. The perspective of normalizing and non-normalizing bycatch practices as well as fishers’ own mitigation strategies should be considered by fisheries management when addressing bycatch mitigation measures as they could be designed more effectively.

Assessing the Uncertainty of Total Seabird Bycatch Estimates Synthesized from Multiple Sources with a Scenario Analysis from the Western and Central Pacific

Each year, billions of seabirds undertake migrations, connecting remote regions of the world, potentially synchronizing population fluctuations among distant areas. This connectedness has implications for the uncertainty calculations of the total seabird bycatch estimate at a regional/global scale. Globally, fisheries bycatch poses a major problem in fishery management, and estimating the uncertainty associated with a regional/global seabird bycatch estimate is important because it characterizes the accuracy and reliability of the fisheries’ impact on the seabird populations. In this study, we evaluate different assumptions underlying the estimation of the variability of the total seabird bycatch at a regional/global scale based on local assessment reports. In addition to theoretical analysis, we also simulate multiple spatially distant separately managed areas with relatively low levels of observer coverage, based on bycatch data from the Western and Central Pacific Fisheries Commission convention area. The results show that assuming a completely synchronized variation produced the most conservative uncertainty estimate and it also missed an opportunity to improve the precision. Simplified correlation structures also failed to capture the complex dynamics of bycatch rates among spatially distant areas. It is recommended to empirically estimate the correlation of bycatch rates between each pair of sources based on bycatch rate time series.

Slow sink rate in floated-demersal longline and implications for seabird bycatch risk.

Bycatch of birds in longline fisheries is a global conservation issue, with between 160,000-320,000 seabirds killed each year, primarily through being caught and drowned as they attempt to snatch baits off hooks as they are set. This conservation issue has received significant recognition in southern hemisphere longline fisheries over the past several decades, largely due to the impact on highly charismatic and highly threatened birds, notably Albatrosses. As a result, the use of effective mitigation measures has been subject to fisheries regulations to reduce seabird bycatch from longliners in a number of national jurisdictions and in several Regional Fisheries Management Organisations (RMFOs). While mitigation measures have been mandated in a number of north Pacific longline fisheries, this is largely not the case in north Atlantic longline fisheries. This includes vessels using floated-demersal longlines in the North-East Atlantic longline fishery targeting European Hake Merluccius merluccius, in which high levels of seabird bycatch are estimated. In this paper, we analysed the sinking speed of a floated-demersal longline used to target European Hake in the offshore waters of Scotland, to determine potential bycatch risks to seabirds. We deployed Time Depth Recorder devices at different points of the gear. We assessed how this gear performed in comparison to the best practice minimum sink rate of 0.3 m/s recommended by the Agreement on the Conservation of Albatrosses and Petrels (ACAP) to limit bird access to baited hooks. We found that the average sinking speed of the floated-demersal longline was substantially slower than the ACAP recommendation, between two and nine times slower in non-weighted parts of the gear down to 10m water depth. Our work also found that the sink rate is particularly slow in the top 2m of the water column, increasing with depth and stabilizing at depths over 10m, presumably a consequence of propeller wash behind the vessel. We calculated that the distance astern of the vessel for hooks to sink beyond susceptible seabirds' reach largely exceeds optimum coverage of best practice design Bird Scaring Lines (100 m). Our results indicate that hooks from floated-demersal longlines are therefore readily open to seabird attacks, and as a result, present a clear bycatch risk. Research is needed to adapt existing mitigation measures to floated-longlines and to develop novel mitigation approaches to improve the sink rate of the gear without impacting target fish catch.