Reduce 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.

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.

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.

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.

Buoys with looming eyes deter seaducks and could potentially reduce seabird bycatch in gillnets.

Bycatch of seabirds in gillnet fisheries is a global conservation issue with an estimated 400 000 seabirds killed each year. To date, no underwater deterrents trialled have consistently reduced seabird bycatch across operational fisheries. Using a combination of insights from land-based strategies, seabirds' diving behaviours and their cognitive abilities, we developed a floating device exploring the effect of large eyespots and looming movement to prevent vulnerable seabirds from diving into gillnets. Here, we tested whether this novel above-water device called ‘Looming eyes buoy' (LEB) would consistently deter vulnerable seaducks from a focal area. We counted the number of birds present in areas with and without LEBs in a controlled experimental setting. We show that long-tailed duck Clangula hyemalis abundance declined by approximately 20–30% within a 50 m radius of the LEB and that the presence of LEBs was the most important variable explaining this decline. We found no evidence for a memory effect on long-tailed ducks but found some habituation to the LEB within the time frame of the project (62 days). While further research is needed, our preliminary trials indicate that above-water visual devices could potentially contribute to reduce seabird bycatch if appropriately deployed in coordination with other management measures.

Commercial viability of locating pelagic longline branchline weights at the hook to reduce seabird bycatch

Bycatch in pelagic longline fisheries threatens the viability of some seabird populations and reduces fishing efficiency. The mass of a branchline fishing weight and its distance from the hook significantly explain seabird catch risk during setting and hauling. We surveyed Hawaii tuna longline fishers to obtain their perspectives on the practicality, safety and economic viability of alternative designs which place weights adjacent to hooks instead of conventional designs with weighted swivels attached 0.6 m from the hook. We conducted experimental fishing to explore the commercial viability of a combination weighted swivel attached to the eye of the hook. We used a Bayesian random effects meta-analytic regression modeling approach to estimate pooled expected species-specific log relative risk of capture on conventional, as opposed to experimental, branchlines. There were significant decreases in catch rates on experimental branchlines of 54% (95% highest posterior density interval [HDI]: 34.3 to 73.8) for retained species and 28% (95% HDI: -7.5 to 93.3) for discarded species. For about 10% of experimental weighted hooks, the point of the hook tangled on the swivel, likely contributing to lower catch rates and making it more difficult for crew to coil branchlines. We identify possible factors explaining why the experimental gear reduced catch rates. The study demonstrates the benefits of stakeholder scoping to determine bycatch mitigation options with the highest promise for practicality, economic viability and safety, as well as benefits of conducting a pilot study to assess commercial viability to determine if a full experiment to assess bycatch mitigation efficacy is warranted.

A contribution to reducing bycatch in a high priority area for seabird conservation in Portugal

SummaryBycatch is one of the main threats to marine biodiversity, affecting ocean ecosystems at a worldwide scale. The main focus of bycatch studies has been on the impact of larger vessels, with few studies assessing the impact of artisanal fisheries. Moreover, bycatch studies are often limited to a small number of marine regions, and significant gaps still exist in our knowledge of the spatial and temporal patterns of seabird bycatch. Here we present a multi-approach method to accurately quantify seabird bycatch driven by small- and medium-sized fishing fleets operating in a high priority area for seabird conservation on the Portuguese mainland. Results of three mitigation measures to reduce seabird bycatch on fishing gear where seabird bycatch is most likely to occur were also tested: high contrast panels in bottom gillnets, black hooks in demersal longlines and a bird scaring device in purse seines. The efficacy, acceptance, and economic viability were tested for each mitigation measure. Sixty-seven individuals of seven seabird species were bycaught during 295 monitored fishing trips between 2015 and 2018. Bycatch occurred mainly in demersal longlines (0.07 birds fishing event-1), followed by purse seines (0.02 birds fishing event-1) and bottom gillnets (0.01 birds fishing event-1). Nevertheless, the bird scaring device caused birds to interact less with the vessel (the presence of gulls was reduced by 11%), thus decreasing the likelihood of bycatch. This device has proved to be low-cost (representing less than 5% income of a single day’s landings) and easy to implement, being also well accepted by purse seine fishermen. It was not possible to evaluate the efficacy of high contrast panels and black hooks, as no bycatch events were recorded during trials.

National Plans of Action (NPOAs) for reducing seabird bycatch: Developing best practice for assessing and managing fisheries impacts

Fisheries bycatch is one of the biggest threats to seabird populations. Managers need to identify where and when bycatch occurs and ensure effective action. In 1999, the Food and Agriculture Organization of the United Nations released the International Plan of Action for Reducing Incidental Catch of Seabirds in Longline Fisheries (IPOA-s) encouraging states to voluntarily assess potential seabird bycatch problems and implement a National Plan of Action (NPOA) if needed. However, the IPOA-s is ambiguous about the steps and objectives, diminishing its value as a conservation tool.We reviewed NPOAs to identify approaches taken to determine whether seabird bycatch is problematic, how bycatch minimisation and population objectives are set, and if thresholds are specified for managing impacts. Our aim was to recommend measures for improving consistency and effectiveness in future NPOAs and other management frameworks for seabirds, with relevance for other threatened marine vertebrates including sharks, turtles, pinnipeds and cetaceans. Globally, 16 NPOAs have been published, but few effectively linked seabird bycatch risk, objectives and management. However, we identified the following best-practice elements that could improve NPOA design: (1) defining explicit risk criteria and methods to assess bycatch problems; (2) setting specific and measurable objectives for minimising bycatch and achieving desired population status; and (3) defining fishery-specific thresholds to trigger management action linked to the population objective. Consistent adoption of NPOA best practice, particularly in states that have not already developed an NPOA, would help to mitigate bycatch threats and ensure fisheries do not reduce the viability of seabird populations.

Effects of best practices to reduce seabird bycatch in pelagic longline fisheries on other threatened, protected and bycaught megafauna species

Fisheries bycatch is one of main conservation problems for many threatened seabirds. Currently, it is unknown whether existing best practices to mitigate seabird bycatch in pelagic longline fisheries influence the capture of other vulnerable taxa. We assessed the effect of two seabird mitigation measures for pelagic longline fisheries on 13 threatened, protected and/or bycaught species, including elasmobranchs, teleosts, sea turtles and fur seals. Analyses were from two experimental studies in Uruguay assessing the effect of a bird scaring line (BSL) and branch lines with weights close to the hooks (weighted branch lines) on these taxa. One hundred longline sets with randomized use of a BSL were deployed. In turn, 224 paired longline sections, with control branch lines versus weighted branch lines, were deployed. BSL use did not increase the capture of any of the species addressed. No detectable differences in capture rate were recorded in our branch line weighting study. However, the effect of branch line weighting in the capture of Porbeagle shark (Lamna nasus) remains unclear and requires further research. Our study suggests that effective measures to reduce seabird bycatch in pelagic longline have no negative connotations for other vulnerable species. Caution should be exercised when interpreting our results as analyses were underpowered to detect small and subtle differences in the catch rates. We strongly encourage researchers to conduct similar studies to elucidate potential regional and across fisheries differences in the effect of seabird mitigation measures in other vulnerable taxa, as well as the effect that mitigation measures for other taxa may have on seabirds.

Hookpod-mini: a smaller potential solution to mitigate seabird bycatch in pelagic longline fisheries

ESR Endangered Species Research Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials ESR 39:1-8 (2019) - DOI: https://doi.org/10.3354/esr00953 ESR Special: Marine vertebrate bycatch: problems and solutions Hookpod-mini: a smaller potential solution to mitigate seabird bycatch in pelagic longline fisheries David Goad1,*, Igor Debski2, Joanne Potts3 1Vita Maris Limited, Papamoa, 3118, New Zealand 2Department of Conservation, Wellington, 6011, New Zealand 3The Analytical Edge Statistical Consulting, Tasmania, 7052, Australia *Corresponding author: goad.dave@gmail.com ABSTRACT: Hookpods are an emerging technology designed to reduce seabird bycatch in pelagic longline fisheries. Hookpod-minis were trialled in the New Zealand surface longline fishery in 2016-2017 during short-term experimental (20 longline sets) and longer-term operational (110 longline sets) trials. Two sets of experimental trials were conducted. The first compared snoods fitted with Hookpod-minis with a tori line to unweighted snoods with a tori line. The second compared snoods fitted with Hookpod-minis as a stand-alone mitigation measure to weighted snoods in combination with a tori line. All gear, across both trials, was set at night. Operational trials compared snoods fitted with Hookpod-minis and tori lines to standard mitigation requirements for unweighted gear and tori lines, with all gear set at night. Both sets of trials demonstrated that Hookpod-minis fit easily into fishing operations, do not reduce target species catch rate, and may reduce seabird bycatch to low levels. Our findings suggest that Hookpod-minis as a stand-alone mitigation measure are as effective, or more effective, than current bycatch mitigation measures including the combination of line weighting and tori lines. KEY WORDS: Mitigation · Pelagic longline · Seabird bycatch · Tori line Full text in pdf format NextCite this article as: Goad D, Debski I, Potts J (2019) Hookpod-mini: a smaller potential solution to mitigate seabird bycatch in pelagic longline fisheries. Endang Species Res 39:1-8. https://doi.org/10.3354/esr00953 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in ESR Vol. 39. Online publication date: May 02, 2019 Print ISSN: 1863-5407; Online ISSN: 1613-4796 Copyright © 2019 Inter-Research.

Improved line weighting reduces seabird bycatch without affecting fish catch in the Brazilian pelagic longline fishery

Abstract Increasing the sink rate of baited hooks by adding weights in close proximity to the hook is crucial to reduce seabird mortality in pelagic longline fisheries. However, weights placed next to the hook are a cause for concern for fishing crew because they can fly back in the event of a line break, injuring deck crew. Lumo Leads, an alternative weight system designed to slide in the event of a line break, and therefore prevent accidents, were trialled in pelagic longline fisheries off southern Brazil. Four fishing trips were conducted and 26,377 hooks sampled to compare sink rates, seabird bycatch rates and catch rates of target species between three treatments: (1) 60 g Lumo Lead attached at 1.0 m from the hook; (2) 60 g Lumo Lead at 3.5 m; and (3) 60 g leaded swivels at 3.5 m from the hook. A Lumo Lead placed at 1.0 m from the hook resulted in a faster sink rate and caught fewer seabirds (0.11 birds per unit of effort [BPUE]) when compared with a Lumo Lead (0.33 BPUE) or weighted swivel (0.85 BPUE) placed at 3.5 m. The bycatch with Lumo Lead placed at 1.0 m from the hook was 90% lower than the bycatch of Lumo Lead or weighted swivel placed at 3.5 m combined. There was no difference in the catch rates of target species between the three treatments. These findings support a growing body of evidence that placing weights close to the hook reduces seabird bycatch without affecting the catchability of the target species. The high seabird bycatch rates recorded despite night setting and recommended line weighting regimes reinforces the need of simultaneous deployment of a toriline with these other two mitigation measures to reduce seabird bycatch to negligible levels in the south‐west Atlantic.

Mitigating bycatch of threatened seabirds: the effectiveness of branch line weighting in pelagic longline fisheries

AbstractSubstantial numbers of seabirds are bycaught each year in pelagic longline fisheries. Increasing the sink rate of baited hooks by reducing the distance between the hook and the weight of the branch lines (leader length) has enormous potential to mitigate this bycatch. Here, we test the effect of reducing the leader length on seabird attacks on baited hooks and bycatch rates plus the effect on fish catch rates on the Uruguayan slope. Two branch line configurations were tested: a control treatment (CT) of the standard branch lines used in the Uruguayan fishery, with 75 g swivels on 4.5 m leaders; and two experimental treatments (ET) consisting of branch lines with either a 60 g or 65 g weight on 1 m leaders. Seabird attacks were assessed during 34 daylight longline sets (100–150 hooks each) without a bird scaring line (BSL) comparing two treatments: CT versus 65 g ET. The fish catch was assessed during 224 paired sections (75 vs. 75 hooks) from 109 fishing sets deployed mostly during the night and with a BSL, comprising 77 pairs of CT versus 60 g ET and 147 pairs of CT versus 65 g ET. The number of primary (231 vs. 91) and multiple (50 vs. 14) attacks were significantly higher in the CT compared with the 65 g ET respectively. The seabird bycatch rate was 42.5% lower in the 65 g ET than in the CT. The use of branch lines with short leaders did not affect the catch of target species. This study conducted in an area of high bycatch risk provides strong experimental support for the use of branch line weighting to reduce seabird bycatch. Based on the observed bycatch rates, this measure should be implemented in combination with other mitigation measures. The simultaneous use of branch line weighting, a BSL and night setting resulted in zero seabird bycatch.

At‐sea trialling of the Hookpod: a ‘one‐stop’ mitigation solution for seabird bycatch in pelagic longline fisheries

AbstractBycatch of pelagic seabird species in longline fisheries is recognized as one of the most important and pervasive sources of mortality, contributing to an increased risk of their extinction. Uptake of mitigation measures to reduce seabird bycatch has not been widespread by the industry. Here, we present the results of 18 at‐sea trials conducted between 2011–2015 onboard pelagic longliners targeting tuna (Thunnus spp) and swordfish (Xiphias gladius) in South African, Brazilian and Australian waters, using a recently designed seabird bycatch mitigation device. The ‘Hookpod’ is a polycarbonate capsule that encases the point and barb of baited pelagic longline hooks to prevent seabirds from becoming hooked and drowning during line‐setting operations. The assessment was based on efficacy (i.e. reducing rates of seabird bycatch without impacting target catch rate) and practicality (i.e. how the Hookpod fitted into fishing operations). We observed 59 130 experimental branchlines over 129 sets and recorded a single seabird mortality on the Hookpod branchlines compared to 24 on the control branchlines, a bycatch rate of 0.04 birds/1000 hooks and 0.8 birds/1000 hooks, respectively. No difference in catch rate of target fish species between Hookpod and control treatments was detected. These findings demonstrate that Hookpods do not negatively affect catch rate of target species and could make an important contribution to halting the decline of many seabird populations if adopted as a mitigation measure by the pelagic longline fishing industry.

Effectiveness of tori line use to reduce seabird bycatch in pelagic longline fishing.

Industrial longline fisheries cause the death of large numbers of seabirds annually. Various mitigation measures have been proposed, including the use of tori lines. In this study the efficiency of a single tori line to reduce seabird bycatch was tested on pelagic longline vessels (25-37m length). Thirteen fishing trips were carried out in the area and season of the highest bycatch rates recorded in the southwest Atlantic (2009–2011). We deployed two treatments in random order: sets with a tori line and without a tori line (control treatment). The use of a tori line significantly reduced seabird bycatch rates. Forty three and seven birds were captured in the control (0.85 birds/1,000 hooks, n = 49 sets) and in the tori line treatment (0.13 birds/1,000 hooks, n = 51 sets), respectively. In 47% of the latter sets the tori line broke either because of entanglement with the longline gear or by tension. This diminished the tori line effectiveness; five of the seven captures during sets where a tori line was deployed were following ruptures. Nine additional trips were conducted with a tori line that was modified to reduce entanglements (2012–2016). Seven entanglements were recorded in 73 longline sets. The chance of a rupture on these trips was 4% (95% c.l. = 1–18%) of that during 2009–2011. This work shows that the use of a tori line reduces seabird bycatch in pelagic longline fisheries and is a practice suitable for medium size vessels (~25-40m length). Because the study area has historically very high bycatch rates at global level, this tori line design is potentially useful to reduce seabird bycatch in many medium size pelagic longline vessel fishing in the southern hemisphere.

Influence of electric fishing lights on sink rates of baited hooks in Brazilian pelagic longline fisheries: implications for seabird bycatch

The incidental mortality of seabirds in longline fisheries is the major cause of the population declines threatening most albatross and large petrel species (LEWISON; CROWDER, 2003; ANDERSON et al., 2011). Currently there is a large and growing number of solutions for reducing seabird mortality on longlines. The combination of certain mitigation measures can greatly reduce seabird bycatch, although no single mitigation measure can reliably prevent seabird mortality. The combination of night setting, bird scaring lines and well-weighted branch lines are the best practice for the mitigation of seabird bycatch in pelagic longline fisheries (ACAP, 2014).The sink rate of baited hooks is arguably the major issue to be addressed to reduce seabird-longline interactions. Even when scaring lines are used, to make them effective the baited hooks must attain safe depths (i.e. deeper than the diving range of most petrel species) within the area protected by a scaring line. Many factors are known to affect the sink rate of baited hooks on pelagic longlines, such as the bait type (e.g. squid, mackerel, sardine, skipjack flash) and its state (e.g. dead or alive, frozen or thawed); the mainline tension during deployment; and line weight regimes (the use or not of leaded swivels, as well as their mass and distance from the hooks) (ANDERSON; MCARDLE, 2002; PETERSON et al., 2008, ROBERTSON et al., 2010; ROBERTSON et al., 2013).The best weighting regimes recommended are those that reach a depth of 10 m while under the protection of a scaring line with ~100 m aerial coverage (PETERSEN et al., 2008, MELVIN et al., 2009a). Experiments have indicated that ≥ 60 g placed no more than 3 m from the hooks is likely to achieve satisfactory sink rates under most operational conditions (MELVIN et al., 2009b; ROBERTSON et al., 2010; GIANUCA et al., 2011). Accordingly, among the best practices to reduce seabird mortality in pelagic longline fisheries recommended by the Agreement on the Conservation of Albatrosses and Petrels (ACAP, 2014) and the International Commission for the Conservation of Atlantic Tunas (ICCAT, 2011), is to use specific line-weighting regimes that ensure appropriate sink rates. The three recommended configurations are: weight greater than 45 g attached within 1 m of the hook or greater than 60 g attached within 3.5 m of the hook or greater than 98 g attached within 4 m of the hook. Positioning the weight farther than 4 m from the hook is not recommended.The use of chemical light sticks and more recently battery powered electric fishing lights (EFL), increases catch rates by attracting target species directly or by attracting their prey (BERKELEY et al., 1981; FREEMAN, 1989; ORTIZ; SCOTT, 2001; HAZIN et al., 2005). Despite the addition of this kind of device (usually ~2 m from the hooks) alters the surface/volume ratio of the terminal portion of the branch lines and potentially the sink rate of baited hooks, no investigation has yet been undertaken on this issue.EFL have recently been adopted by the southern Brazilian pelagic longline fleet, and their use and popularity are growing among fishermen and ship owners. Each EFL carries two AA batteries and, given its weight out of the water (~160 g), some fishermen argue that the use of this kind of device increases the sink rate of baited hooks, and using this untested premise as justification for not adopting the required line-weighting regimes.In the light of this scenario, the aim of the present

An integrated assessment model of seabird population dynamics: can individual heterogeneity in susceptibility to fishing explain abundance trends in Crozet wandering albatross?

SummarySeabirds have been incidentally caught in distant‐water longline fleets operating in the Southern Ocean since at least the 1970s, and breeding numbers for some populations have shown marked trends of decline and recovery concomitant with longline fishing effort within their distributions. However, lacking is an understanding of how forms of among‐individual heterogeneity may interact with fisheries bycatch and influence population dynamics.We develop a model that uses comprehensive data on the spatial and temporal distributions of fishing effort and seabird foraging to estimate temporal overlaps, fishery catchability and consequent bycatch. We apply a population model that is structured by age, sex, life stage and spatially to Crozet Island wandering albatross and explore how heterogeneity in susceptibility to capture may have influenced the population's demography over time.A model where some birds were assumed to be more susceptible to fisheries bycatch was able to successfully replicate the observed trend in breeding pairs. Considerably poorer fits were found without this assumption. Results suggested that the more susceptible birds may have been removed from the population by the 1990s.The model was also able to highlight areas, times and fleets prone to increased bycatch. Knowledge of these factors should assist fisheries and conservation management bodies to quantify and reduce seabird bycatch through spatial management and fleet‐specific mitigation efforts.Synthesis and application. Many seabirds show complex life histories that make them highly susceptible to additional incidental mortality from fishing vessels. By applying a population model that integrates key aspects of seabird and fishery dynamics, we were able to explain the observed trends in the breeding population of Crozet wandering albatross and identify key areas and fleets where further mitigation may be required. In addition, the potential removal of a category of birds that shows increased susceptibility to capture has important implications for the conservation management of this population and other iconic species incidentally caught by large‐scale commercial fisheries.

Tori‐lines with weighted branch lines reduce seabird bycatch in eastern South Pacific longline fishery

Abstract The effectiveness of tori‐lines combined with double‐weighted branch lines in reducing seabird bycatch was evaluated in a pelagic longline fishery. Seabird bait attack behaviour, bycatch number, and sinking rate of baited hooks were examined on double‐weighted and unweighted branch lines deployed on the same longline with a single tori‐line. Comparisons were conducted from July to October in 2011 during two cruises on a chartered longline vessel in the eastern South Pacific Ocean outside the Chilean and Peruvian exclusive economic zones. Cape petrels (Daption capense), white‐chinned petrels (Procellaria aequinoctialis) and Westland petrels (Procellaria westlandica) were abundant during line setting. There were 275 primary bait‐taking attacks by these species, but there were only eight primary attacks by albatrosses. Nevertheless, six albatrosses and six diving seabirds were incidentally caught as bycatch. Of the primary attacks by Cape petrels, white‐chinned petrels and Westland petrels, 153 led to secondary attacks. These results suggest that off Chile and Peru there is frequent secondary bycatch of albatrosses as a result of their stealing bait from Cape petrels and diving seabirds. Best‐fit models for the number of primary attacks and of bycatch included the weighted branch line; the use of weighted branch lines resulted in a lower number of primary attacks. Hooks on unweighted branch lines did not reach any of the benchmark depths (3, 5, and 10 m) within the aerial extent of the tori‐lines (the tori‐line remaining above the water surface), hooks on weighted branch lines reached 5 m depth within the aerial extent. These results suggest that, for the pelagic longline fishery off Chile and Peru, combining double‐weighted branch lines and tori‐lines reduces the bycatch more effectively than tori‐lines with unweighted branch lines. Copyright © 2014 John Wiley & Sons, Ltd.

Diving behaviour of white-chinned petrels and its relevance for mitigating longline bycatch

The white-chinned petrel (Procellaria aequinoctialis) is the seabird species most commonly killed by Southern Hemisphere longline fisheries. Despite the importance of diving ability for mitigating longline bycatch, little is known of this species’ diving behaviour. We obtained data from temperature–depth recorders from nine white-chinned petrels breeding on Marion Island, southwestern Indian Ocean, during the late incubation and chick-rearing period. Maximum dive depth (16 m) was slightly deeper than the previous estimate (13 m), but varied considerably among individuals (range 2–16 m). Males dived deeper than females, and birds feeding chicks dived deeper than incubating birds, but dive rate did not differ between the sexes. Time of day had no significant effect on dive depth or rate. Our findings will help to improve the design and performance of mitigation measures aimed at reducing seabird bycatch in longline fisheries, such as the calculation of minimum line sink rates and optimum aerial coverage of bird-scaring lines.

Cory’s shearwater by-catch in the Mediterranean Spanish commercial longline fishery: implications for management

Cory’s shearwater Calonectris diomedea is the main seabird species by-caught by the Spanish longline fleet operating in the western Mediterranean Sea. Identification of the principal factors that determine this by-catch and understanding how they could be controlled is fundamental for improving the management of fisheries and so carry out a better conservation of Cory’s shearwater populations in the Mediterranean. The aim of this paper was to model the longline by-catch of Mediterranean Cory’s shearwater in the Spanish Mediterranean longline fishery as a function of time of the year, technical characteristics of the fishing operation, and geographical location. We used data recorded by an onboard observer program monitoring commercial longline fisheries. During the 10 years covered in this study, 80 birds were captured in 30 fishing operations out of a total of 2,587 observed fishing sets. We used favourability functions and Random Forest analyses to relate the presence of Cory’s shearwater in the by-catch with the explanatory factors. The most explanatory factor in relation to incidence of by-catch was the geographical location (longitude and fishing over the continental shelf) and then the technical characteristics of the fishing operation (number of hooks and fishing during non-working days). Our conclusion is clear, because seabirds are more likely to approach longline vessels when trawlers are not allowed to operate (i.e. non-working days), activity of longliners should be limited to working days, and closing longliners activity during the month of October could reduce greatly reducing seabird bycatch.

Reducing seabird bycatch in the South African joint venture tuna fishery using bird-scaring lines, branch line weighting and nighttime setting of hooks

We compared the performance of two bird-scaring line designs (light lines with short streamers vs. hybrid lines with a mix of long and short streamers) deployed in pairs with unweighted branch lines on two joint venture tuna vessels typical of distant-water tuna fisheries in the South Africa Exclusive Economic Zone (EEZ). We also added weight to a subset of branch lines, and compared the effects of line weighting and night vs. day setting in combination with bird-scaring lines on bird and fish catch rates. White-chinned petrels (Procellaria aequinoctialis), a diving seabird, dominated the seabird assemblage; they were the most numerous seabird and they attacked baited hooks and were killed at the highest rates. Secondary attacks – surface foraging albatrosses stealing baits from white-chinned petrels – drove albatross mortality. With hybrid scaring lines deployed, both diving and surface foraging seabirds made fewer attacks (1.5 and 2 times, respectively) within the lines’ 100m aerial extent, where hooks are closest to the surface and birds are most vulnerable to hooking, than with light lines. However, all metrics of comparison between hybrid and light lines were not statistically conclusive, primarily because birds could access baited hooks in areas beyond the protection afforded by bird-scaring lines (aft and to port of their aerial extent). Seabird bycatch rates were 4.6 times higher during daylight hours (2.00 birds/1000 hooks; 52 birds) than at night (0.439 birds/1000 hooks; 28 birds) and night catch rates near the full moon doubled. Bird catch rates were 18 times higher on unweighted branch lines (1.07/1000 hooks; 79 birds) than on weighted branch lines (0.06/1000 hooks; 1 bird) with no detectable effect on fish catch. With respect to streamer lines, our results suggest that in Procellaria petrel dominated systems the aerial extent of bird-scaring lines (of any design) should span the distance that baited hooks are within 10m of the surface to effectively prevent bird attacks on baits. Overall, results suggest that night setting, adequate branch line weighting, and proper deployment of two bird-scaring lines have the potential to reduce seabird bycatch in pelagic longline fisheries without reducing the catch rates of target fishes. Further development of safe, fast-sinking branch line weighting configurations and bird-scaring lines less prone to tangling on fishing gear is critical to this effort.