Bycatch Estimates Research Articles

Assessing seabird bycatch in gillnet fisheries using electronic monitoring

The unintentional capture (bycatch) of seabirds in gillnet fisheries kills hundreds of thousands of individuals annually and is thought to threaten the conservation of entire populations. However, data from commercial fisheries is often lacking to confirm these suspicions. In Denmark, sparse or incomplete catch data from small-scale gillnetters prevent managers from gaining a comprehensive overview of the importance of seabird bycatch in coastal waters. In this study, electronic monitoring (EM) with video is used to identify and quantify seabird bycatch in a Danish coastal gillnet fishery. Three gillnetters were monitored over a period of 9 years, resulting in 2118 fishing trips and 10,964 hauls; 700 birds from six families were identified. Three species composed >90% of the incidental captures, the common eider (Somateria mollissima), the great cormorant (Phalacrocorax carbo) and the common guillemot (Uria aalge), respectively qualifying regionally as endangered, least concerned and near threatened. There was a clear species-specific spatial and seasonal variability in bycatch per unit effort (BPUE) estimates, highlighting areas of high risk of seabird bycatch. Approximately 40% of all bycatch events were observed in 0.2% of the hauls, suggesting that the full fishing activity should be analysed to obtain accurate seabird bycatch estimates.

ObsCovgTools: Assessing observer coverage needed to document and estimate rare event bycatch

Observer program design and evaluation often overlook the challenges of documenting rare-event bycatch. To support and facilitate consideration of threatened, endangered, and protected species bycatch in evaluating observer programs and assessing fisheries impacts, we developed a software tool to assess observer coverage with respect to several objectives for documenting or estimating rare-event bycatch. The ObsCovgTools package for the R programming language, also available as an online application, predicts observer coverage performance for a given total fishery effort in relation to three metrics: (1) the conditional probability of observing any bycatch given that bycatch occurred in the fishery and the probability of any bycatch in the total fishery effort, (2) the upper confidence limit for total bycatch when none is observed, and (3) precision (coefficient of variation) of the bycatch estimate. We describe the tool; explore how specific observer coverage targets for these metrics vary with total effort, BPUE, and dispersion index; and apply it to evaluate observer coverage in the California drift gillnet fishery. Our results underscore the importance of considering effort as well as percentage in assessing how well an observer program documents bycatch. We caution that rare species interactions may not be documented in many observer programs, and should be anticipated through a complementary risk assessment approach. The tool’s modular design and open source programming approach encourage adaptation and augmentation to address additional objectives or complexities in sampling design or estimation.

Cetacean bycatch in Indian Ocean tuna gillnet fisheries

Pelagic gillnet (driftnet) fisheries account for some 34% of Indian Ocean tuna catches. We combined published results from 10 bycatch sampling programmes (1981−2016) in Australia, Sri Lanka, India and Pakistan to estimate bycatch rates for cetaceans across all Indian Ocean tuna gillnet fisheries. Estimated cetacean bycatch peaked at almost 100 000 ind. yr−1 during 2004−2006, but has declined by over 15% since then, despite an increase in tuna gillnet fishing effort. These fisheries caught an estimated cumulative total of 4.1 million small cetaceans between 1950 and 2018. These bycatch estimates take little or no account of cetaceans caught by gillnet but not landed, of delayed mortality or sub-lethal impacts on cetaceans (especially whales) that escape from gillnets, of mortality associated with ghost nets, of harpoon catches made from gillnetters, or of mortality from other tuna fisheries. Total cetacean mortality from Indian Ocean tuna fisheries may therefore be substantially higher than estimated here. Declining cetacean bycatch rates suggest that such levels of mortality are not sustainable. Indeed, mean small cetacean abundance may currently be 13% of pre-fishery levels. None of these estimates are precise, but they do demonstrate the likely order of magnitude of the issue. Countries with the largest current gillnet catches of tuna, and thus the ones likely to have the largest cetacean bycatch are (in order): Iran, Indonesia, India, Sri Lanka, Pakistan, Oman, Yemen, UAE and Tanzania. These 9 countries together may account for roughly 96% of all cetacean bycatch from tuna gillnet fisheries across the Indian Ocean.

Intra-gear variation in sea turtle bycatch: Implications for fisheries management

In the Mediterranean Sea, bottom trawl, bottom longline and set nets are the fishing gears with the highest impact on marine turtle populations. These demersal gear types are characterised by a variety of métiers (fishing operations targeting a specific assemblage of species, using specific gear, during a precise period of the year and/or within a specific area). Data on fishing methods, target species and turtle bycatch were collected through interviews in three different study areas in the central Mediterranean. The results show that, even in the same fishing area, different métiers of the same gear can have a different impact on turtles. These findings have several implications. First, traditional turtle bycatch estimations and comparisons based on a fishing gear as a whole may be spatially or temporally biased by spatial and temporal differences in métier composition, respectively. Second, the efficiency of conservation measures may be different according to the métiers involved and caution is needed when measures developed in small areas with certain métiers are exported to a wider scale with possibly very different métiers. Third, conservation measures may induce shifts among métiers that may have an impact on other species, but such shifts are difficult to detect. All this suggests that, in the Mediterranean, a métier-based approach is needed to provide realistic estimates of turtle bycatch, to increase the efficiency of conservation measures by targeting only the most relevant métiers and to predict the changes in target species and effort distribution that can be driven by conservation measures. The variability of fishing methods and métiers implies that the most effective management strategies should be identified at relatively small geographical scales.

How much do we know about seabird bycatch in pelagic longline fisheries? A simulation study on the potential bias caused by the usually unobserved portion of seabird bycatch.

Not much is known about the fleet level total seabird bycatch from pelagic longlines of United States vessels in the western North Atlantic or other fleets of the Atlantic or other oceans. Onboard observers generally only record seabird bycatch during line hauling. Seabirds are predominantly caught during the line setting stage, and, due to predation or mechanical action, those caught prior to the haul can drop off the hook and be lost to the onboard observer. We developed a model to gauge the size of this bycatch loss problem and provide a first approximation of its impact on estimates of total fleet bycatch. We started with a traditional loss-free bycatch model, which assumes that birds recorded were the only birds captured, and integrated into it two crucial components of the bycatch process: capture origin (set or haul) and bycatch loss of set-captures. We extracted count data on seabird bycatch loss and bycatch mortality from the literature on other longline fisheries and used these data to simulate potential total seabird bycatch in the western North Atlantic. Simulations revealed the shortcomings of both the traditional bycatch model and the current haul-only observer protocol, each of which contributed to biologically significant underestimation of total bycatch and estimation uncertainty. Based on our results, we recommend a loss-corrected modeling approach to provide a more accurate estimate of seabird mortalities in pelagic longline fisheries. Where possible, fishery-specific seabird bycatch loss rates need to be ascertained via specific set and haul observing protocols. But, even where fishery-specific estimates for a region are not available, the methodology developed here is applicable to other pelagic longline fisheries to approximate fleet-level loss-corrected bycatch.

Seabird bycatch vulnerability to pelagic longline fisheries: Ecological traits matter

Abstract Fisheries bycatch of seabirds presents a serious management problem, and relatively little is known about this problem. In the Western North Atlantic, the issue is complicated by the relatively low effort and coverage of the observer programme and the high uncertainty in species identification. The Western North Atlantic is home to many endemic and endangered seabird populations, and the impact of fishery‐caused seabird bycatch has been of high interest, especially for those species with a low population size; however, species‐specific bycatch estimates have been difficult. From 1992 to 2016, 158 seabirds were observed caught by the US Atlantic pelagic longline fleet; among them, only 80 were identified to species, 25 were identified to family, and the rest – mainly in the older records – were unidentified. In this study, ecological traits of seabirds were used to improve bycatch estimation and provide species‐specific risk analysis to all the potentially affected seabird species in this region. Bayesian state–space modelling was used to accommodate the high level of uncertainty in the species identification process. Seabird bycatch risk was found to be highly dependent on population size. The group of large seabird species was estimated to be two times as vulnerable as the group of mid‐to‐small seabird species, scavenging and plunge‐diving feeding modes were identified as imposing high bycatch risks, and spatial and temporal distribution patterns were also good indicators of bycatch risk. Based on these ecological traits, shearwaters, gulls, gannets, and petrels were identified to potentially suffer from high bycatch in this region. These species, especially those that have not been identified historically, deserve extra attention in the observer programme, and for the implementation of conservation measures of seabirds in this region.

Population growth of an endangered pinniped—the New Zealand sea lion (Phocarctos hookeri)—is limited more by high pup mortality than fisheries bycatch

AbstractThe endangered New Zealand sea lion, Phocarctos hookeri is killed as incidental bycatch in a trawl fishery operating near their second largest population on Campbell Island in New Zealand’s sub-Antarctic. Using the Potential Biological Removal (PBR) procedure to assess the sustainability of this bycatch for the sea lion population on Campbell Island indicated that annual bycatch estimates, particularly following the implementation of bycatch mitigation measures, are below the PBR threshold of 25 (derived using a precautionary approach). Preliminary Population Viability Analysis (PVA) modelling supported the finding that current bycatch levels, especially given a strong male bias (98%) in bycatch, are sustainable for this population. Models showed that reducing pup mortality through management actions, such as installing ramps in wallows where large numbers of pups drown, would lead to increased population growth. While obtaining more accurate data on population status and demographic parameters for the Campbell Island population should be a priority, this will take many years of research. The PBR and PVA tools demonstrate that contemporary conservation management should continue to focus on increasing pup survival while maintaining mitigation approaches that have reduced bycatch to low levels, together with high observer coverage to sustain confidence in annual bycatch estimates.

Spatial and temporal variations in seabird bycatch: Incidental bycatch in the Norwegian coastal gillnet-fishery.

The general decline of seabird populations worldwide raises large concerns. Although multiple factors are interacting to cause the observed trends, increased mortality from incidental bycatch in fisheries has proven to be important for many species. However, the bulk of published knowledge is derived from longline fisheries, whereas bycatch in gillnet fisheries is less studied and even overlooked in some areas. We present seabird bycatch data from a 10-year time-series of fishery data from the large fleet of small-vessels fishing with gillnets along the Norwegian coast—a large area and fishery with no prior estimates of seabird bycatch. In general, we document high rates of incidental bycatch (averaging 0.0023 seabirds/net, or approximately 0.08 seabirds/fishing trip). This results in an estimated annual bycatch between 1580 and 11500 (95% CI) birds in this fishery. There was a surprisingly high percentage (43%) of surface-feeding seabirds in the bycatch, with northern fulmar being the most common species. Among the diving seabirds caught, common guillemot was most numerous. Our findings suggest that coastal gillnet fisheries represent a more general threat to a wider range of seabird populations, as opposed to longline fisheries where surface-feeding seabird species seem to dominate the bycatch. The bycatch estimates for the Norwegian gillnet-fishery varied in time, between areas, and with fishing depth and distance from the coast, but we found no clear trends in relation to the type of gillnets used. The results enabled us to identify important spatio-temporal trends in the seabird bycatch, which can allow for the development and implementation of more specific mitigation measures. While specific time closures might be an efficient option to reduce bycatch for diving seabirds, measures such as gear modification and reduction in release of wastewater during fishing operation are probably a more effective mitigation approach for reducing bycatch of surface-feeding seabirds.

Marine mammal bycatch by the industrial bottom trawl fishery at the Rio de la Plata Estuary and the adjacent Atlantic Ocean

Fisheries interactions with non-target marine vertebrates are a worldwide problem. The impact of coastal bottom trawl fisheries on marine mammals has never been evaluated before in the Rio de la Plata Estuary and the adjacent Atlantic Ocean. Our aim was estimating the bycatch per unit effort (BcPUE) and incidental mortality rates of marine mammals caused by the industrial coastal bottom trawl fisheries fleet. We evaluated the mortality of three species ( i.e ., franciscana dolphin Pontoporia blainvillei , South American sea lion Otaria flavescens , and the South American fur seal Arctocephalus australis ); these species are facing conservation problems either at the regional or local scale. We conducted an onboard data collection program of marine mammals' bycatch involving crew members of 10 vessels (30%) of the Uruguayan coastal bottom trawl fleet between January 2009 and April 2012. A total of 102 marine mammal individuals were bycaught during 490 fishing trips involving 2,398 fishing days. Mortalities estimated for franciscana dolphin were the highest among the species affected, with values adding up to ~100 individuals for year (with scenarios of population decline in the area), followed by South American sea lion with ~77 individuals by year (0.8% of local population) and the South American fur seal with an annual mortality estimate of ~25 individuals (~0.02% of local population). BcPUE showed significant temporal variation, with franciscana dolphin BcPUE varying seasonally and those of otariids according to their breeding season. Our estimates of marine mammal bycatch by bottom trawl fisheries should constitute an important input for the sustainable management of fisheries and the conservation of marine biodiversity in the southwestern Atlantic Ocean.

Sustainable Fisheries Management and the Welfare of Bycaught and Entangled Cetaceans.

The incidental capture of cetaceans and other protected marine wildlife in fishing gear has significant welfare implications. Many thousands of cetaceans are bycaught in fishing gear in European waters and hundreds of thousands die globally. We can expect many more to survive, but suffer from such interactions. As marine policy focuses on “population level” impact assessments and “sustainability” of fishing to preserve fish populations, the impacts to the bycaught individual, and their wider social group, are often largely underestimated, despite the large numbers affected. The wide range of recorded injuries, including abrasions, cuts, bruising, and broken bones, along with the potential for panic associated with forced submersion, indicate that the welfare of bycaught cetaceans is, individually and collectively, very poor. Commercial fishing is the last human activity targeting wildlife (fish) on a grand scale where slaughter includes incidental killing of other large sapient wildlife on such a regular basis. Here, we review the compelling evidence of the short and long term welfare impacts of bycatch, and the progress made toward implementation of measures to understand and solve this significant welfare issue. We argue that policy decisions surrounding fishing do not adequately consider cetacean bycatch, including welfare impacts. Ultimately, there are welfare issues in all bycatch situations and suffering cannot plausibly be reduced without preventing bycatch. The well-documented welfare implications provide a strong argument for zero tolerance of cetacean bycatch and provide a compelling case for immediate action in fisheries where bycatch is taking place. The only way to reduce the suffering of bycaught cetaceans is to decrease, or ideally eliminate, the number of animals caught in fishing gear. Uncertainties around the scale of bycatch should not delay management, even where individual bycatch estimates are considered “sustainable.” Lack of monitoring of sub-lethal impacts on populations may result in flawed impact assessments. We urge that animal welfare considerations should become an integral part of management decision-making in relation to bycatch globally. Enhanced, robust and transparent management systems are urgently required for the range of fisheries within which cetacean bycatch occurs, with the aim to better document and most importantly, work toward eliminating cetacean bycatch altogether.

The utility of spatial model-based estimators of unobserved bycatch

Abstract Quantifying effects of fishing on non-targeted (bycatch) species is an important management and conservation issue. Bycatch estimates are typically calculated using data collected by on-board observers, but observer programmes are costly and therefore often only cover a small percentage of the fishery. The challenge is then to estimate bycatch for the unobserved fishing activity. The status quo for most fisheries is to assume the ratio of bycatch to effort is constant and multiply this ratio by the effort in the unobserved activity (ratio estimator). We used a dataset with 100% observer coverage, 35 440 hauls from the US west coast groundfish trawl fishery, to evaluate the ratio estimator against methods that utilize fine-scale spatial information: generalized additive models (GAMs) and random forests. Applied to 15 species representing a range of bycatch rates, including spatial locations improved model predictive ability, whereas including effort-associated covariates generally did not. Random forests performed best for all species (lower root mean square error), but were slightly biased (overpredicting total bycatch). Thus, the choice of bycatch estimation method involves a tradeoff between bias and precision, and which method is optimal may depend on the species bycatch rate and how the estimates are to be used.

Conserving and recovering vulnerable marine species: a comprehensive evaluation of the US approach for marine mammals

AbstractHuman-caused mortality due primarily to bycatch in fisheries is considered a major threat to some long-lived, slow-growing, and otherwise vulnerable marine species. Under many jurisdictions these species are designated as “protected”, and fisheries are subject to a management system that includes monitoring and assessment of bycatch impacts relative to management objectives. The US management system for marine mammals is one of the most sophisticated in the world, with a limit on human-caused mortality computed using the potential biological removal (PBR), formula. Fisheries are categorized according to their impact relative to PBR, and take reduction teams established to develop take reduction plans (TRPs) when bycatch exceeds PBR. The default values of the parameters of the PBR formula were selected in the late 1990s using management strategy evaluation (MSE), but the system, in particular the classification of fisheries, has yet to be evaluated in its entirety. A MSE framework is developed that includes the PBR formula, as well as the processes for evaluating whether a stock is “strategic”, assigning fisheries to categories, and implementing TRPs. The level of error associated with fisheries classification was found not to impact the ability to achieve the conservation objective established for a stock under the US Marine Mammal Protection Act (i.e. maintain or recover the stock to/at optimum sustainable population). However, this ability is highly dependent on the life history and absolute abundance of the species being managed, as well as on the premise that bycatch is reduced if bycatch is estimated to exceed the PBR. The probability of correctly classifying fisheries depends on both the coefficient of variations (CVs) of the estimates of bycatch and the marine mammal stock’s abundance because classification depends on the ratio of the estimate of bycatch by fishery-type to the stock’s PBR, and the precision of the former depends on the bycatch CV and the latter on the abundance estimate CV. Moreover, the probability of correctly classifying a fishery decreases for smaller populations, particularly when a fishery has low to moderate impact.

Uncertainty associated with total bycatch estimates for rarely-encountered species varies substantially with observer coverage levels: Informing minimum requirements for statutory logbook validation

Concerns regarding quantifying fishing impacts on rarely-encountered bycatch species in a demersal fish trawl fishery in north-western Australia have raised issues with, 1) uncertainty associated with extrapolated estimates from low levels of coverage by human observers, and 2) appropriate minimum levels of observer coverage. This study used data collected from a very high level of independent observations (85% coverage, n = 2127 trawls) using electronic monitoring (EM) to determine the uncertainty of extrapolated estimates of chondrichthyan, cetacean and reptile bycatch at different levels of observer coverage. The distribution of extrapolated estimates of total numbers for rarely-encountered bycatch (i.e. dolphins and hammerhead sharks) was asymmetric, with a higher tendency for overestimation at lower levels of observer coverage (≤ 25%). Conversely, the minimum level of observer coverage required to achieve a reasonable level of precision (± 30% or lower) for rarely-encountered species would need to be very high (≥90%). Combining the interaction rates of rarely-encountered species (i.e. via statutory logbook validation) reduces the minimum level of observer coverage required to an achievable level (~64%), whilst maintaining relatively accurate (± 25%) quantitative bycatch estimates for management purposes. Future programs need to consider that, in contrast to the infrequent presence of human observers, EM with cameras installed to monitor all fishing activity will effectively negate the need to assume that fishing practices are equivalent between observed and unobserved events. Hence, analysis of data collected by human observers may need to account for additional biases and/or imprecision along with the marked increase in uncertainty associated with lower levels of observer coverage.

Untangling the impacts of nets in the southeastern Pacific: Rapid assessment of marine turtle bycatch to set conservation priorities in small-scale fisheries

Bycatch of marine megafauna by small-scale fisheries is of growing global concern. The southeastern Pacific sustains extensive fisheries that are important sources of food and employment for millions of people. Mismanagement, however, jeopardizes the sustainability of ecosystems and vulnerable species. We used survey questionnaires to assess the impact of small-scale gillnet fisheries on sea turtles across 3 nations (Ecuador, Peru and Chile), designed to fill data gaps and identify priority areas for future conservation work. A total of 765 surveys from 43 small-scale fishing ports were obtained (Ecuador: n = 379 fishers, 7 ports; Peru: n = 342 fishers, 30 ports; Chile: n = 44 fishers, 6 ports). The survey coverage in study harbors was 28% for Ecuador, 37.0% for Peru, and 62.7% for Chile. When these survey data are scaled up across the fleets within surveyed ports, the resulting estimate of total annual bycatch across the study harbors is 46 478 turtles; where Ecuador is 40 480, Peru 5 828 and Chile 170 turtles. Estimated mortality rates vary markedly between countries (Ecuador: 32.5%; Peru 50.8%; Chile 3.2%), leading to estimated lethal takes of 13 225, 2 927, and 6 turtles for Ecuador, Peru, and Chile, respectively. These estimates are remarkably large given that the ports surveyed constitute only 16.4, 41, and 22% of the national gillnet fleets in Ecuador, Peru, and Chile, respectively. Limited data from observer-based surveys in Peru suggest that information from surveys are reliable and still informative. Information from surveys clearly highlight Ecuador and Peru as priority areas for future work to reduce turtle bycatch, particularly given the status of regional populations such as leatherback and hawksbill turtles.

Estimating common dolphin bycatch in the pole-and-line tuna fishery in the Azores.

Small-scale artisanal fisheries can have a significant negative impact in cetacean populations. Cetacean bycatch has been documented in the pole-and-line tuna fishery in the Azores with common dolphins being the species more frequently taken. Based on data collected by observers on ∼50% of vessels operating from 1998 to 2012, we investigate the influence of various environmental and fisheries-related factors in common dolphin bycatch and calculate fleet-wide estimates of total bycatch using design-based and model-based methods. Over the 15-year study dolphin bycatch occurred in less than 0.4% of the observed fishing events. Generalized additive modelling results suggest a significant relationship between common dolphin bycatch and duration of fishing events, sea surface temperature and location. Total bycatch calculated from the traditional stratified ratio estimation approach was 196 (95% CI: 186–205), while the negative binomial GAM estimated 262 (95% CI: 249–274) dolphins. Bycatch estimates of common dolphin were similar using statistical approaches suggesting that either of these methods may be used in future bycatch assessments for this fishery. Our work shows that rates of common dolphin bycatch in the pole-and-line tuna fishery in the Azores are low, despite considerable variations between years. Dolphins caught were released alive although the fate of these individuals is unknown. Continued monitoring will provide a better understanding of dolphin bycatch and more accurate estimates essential in the development of potential mitigation measures.

Quasi‐Stationary Atlantic Cod Bycatch Estimation in the Maine American Lobster Homarus americanus Trap Fishery

AbstractThe Atlantic Cod Gadus morhua population in the Gulf of Maine (GOM) is currently near historically low levels of abundance. Reliable estimates of incidental Atlantic Cod bycatch from Maine's American lobster Homarus americanus fishery, which are unavailable and not included in the current stock assessment, are potentially critical for understanding complete catch dynamics and are thus essential for rebuilding the stock. Available fishery‐dependent data cannot be used directly in estimating Atlantic Cod bycatch because of nonrandom spatial and temporal sampling efforts. We developed a standardized framework for estimating Atlantic Cod bycatch in Maine's inshore lobster fishery for the years 2006–2013. We employed environmental covariates in a bootstrapped generalized additive model framework to standardize monthly zonal Atlantic Cod bycatch per unit effort (BCPUE) and lobster CPUE. Bootstrapped distributions of standardized CPUE and BCPUE were combined with landings data to estimate spatiotemporally explicit confidence intervals of Atlantic Cod discards in the Maine lobster fishery. Modeling results remained consistent throughout the study years, suggesting robustness in our approach. The estimates of Atlantic Cod discards in the lobster fishery improve the understanding of the total GOM Atlantic Cod bycatch and help to address current stock assessment deficiencies.

Analysis of bycatch in the South African midwater trawl fishery for horse mackerel Trachurus capensis based on observer data

The South African midwater trawl fishery targets adult horse mackerel Trachurus capensis. The bulk of the catch is taken by a single freezer-trawler, the biggest fishing vessel operating in South African waters. As fishing takes place off the south coast in ecologically sensitive areas, there are concerns about the potential impacts of this fishing operation on non-target species. Fishing behaviour and bycatch of this fishery from 2004 to 2014 were investigated by analysing observer records with regard to catch composition, volume and temporal and spatial patterns. The midwater trawl fishery was estimated to have caught 25 415 tonnes annually, with a bycatch of 6.9% of the total catch, by weight. There are species overlaps with various fisheries, namely the demersal trawl, small-pelagic, line, shark longline and squid fisheries, yet the total bycatch estimates from this fishery are generally small relative to catches taken in the target fisheries. Bycatch species with the highest average annual catches were chub mackerel Scomber japonicus, redeye roundherring Etrumeus whiteheadi, ribbonfish Lepidopus caudatus and hake Merluccius spp. Large-fauna bycatch species included sunfish Mola mola as well as a number of CITES II- and IUCN-listed species, such as Cape fur seal Arctocephalus pusillus, dusky shark Carcharhinus obscurus, smooth hammerhead shark Sphyrna zygaena and thresher sharks Alopias spp. The 97.9% observer coverage is high and the 6.9% bycatch rate low compared to other South African fisheries; however, due to the large size of the individual hauls (average of 46.3 t), the average sampling rate of 1.56% is low. Our analyses suggest that bycatch in the South African midwater trawl fishery has been lower than in other South African fisheries and similar fisheries elsewhere, but due to the combination of high catch volumes and low sampling rates, estimation errors for rare species are high and there is a substantial risk of incidental unmonitored bycatch of rare large fauna and aggregations of small fauna. This could be mitigated by spatio-temporal management of this fishery, to avoid fishing in high-risk areas, and the introduction of an electronic monitoring programme.

Comprehensive estimates of seabird–fishery interactions for the US Northeast and mid‐Atlantic

Abstract Relatively little is known about seabird–fishery interactions (i.e. bycatch) for the U.S. North‐east and mid‐Atlantic, despite concerted efforts to document observed interactions since 1989. Fisheries observer data were used to estimate seabird–fishery interactions for 10 species and six gear types that operated within the US Northeast and mid‐Atlantic from 1996 to 2014. Hierarchical Bayes estimation was used and accounted for temporal, spatial, and operational considerations inherent in the data through post‐stratification. Over the 19‐year study period, 48 821 (coefficient of variation [CV] = 0.03) seabirds were estimated to have interacted with commercial fishing gear, resulting in an average of 2570 interactions per year. Trends in estimated interactions were explored using the marginal posterior distributions, with the majority of interactions pertaining to gillnets and shearwaters/fulmars. Comparison with previous work highlighted the need for consistency in data preparation, making it easier to compare relative trends in seabird bycatch estimates for the region. Future assessments should focus on providing context for the interaction estimates, so that population‐level impacts can be inferred and the necessary conservation measures enacted.

A first estimate of sea turtle bycatch in the industrial trawling fishery of Gabon

Gabon hosts nesting grounds for several sea turtle species, including the world’s largest rookery for the leatherback turtle (Dermochelys coriacea), Africa’s largest rookery for the olive ridley turtle (Lepidochelys olivacea) and smaller aggregations of the hawksbill turtle (Eretmochelys imbricata) and green turtle (Chelonia mydas). To assess the level of incidental captures of turtles by the Gabonese trawl fishery, an onboard observer program was conducted in the period 2012–2013. A total of 143 turtles were captured by 15 trawlers during 271 fishing days. The olive ridley turtle was the main species captured (80% of bycaught turtles), with mostly adult-sized individuals. The remaining 20% included green turtles, hawksbill turtles, leatherback turtles and undetermined species. Bycatch per unit of effort (BPUE) of olive ridley turtles varied greatly depending on the period of the year (range of means: 0.261–2.270). Dead and comatose turtles were 6.2 and 24.6% respectively (n = 65). By applying the available fishing effort to two BPUE scenarios (excluding or considering a seasonal peak), the total annual number of captures was estimated as ranging between 1026 (CI 95% 746–1343) and 2581 (CI 95% 1641–3788) olive ridley turtles, with a mortality ranging from 63 (CI 95% 13–135) to 794 (CI 95% 415–1282) turtles per year depending on the scenario and on the fate of comatose turtles. Such a potential mortality may be reason for concern for the local breeding population of olive ridley turtles and recommendations in terms of possible conservation measures and further research are given.

Incidental bycatch of northern fulmars in the small-vessel demersal longline fishery for Greenland halibut in coastal Norway 2012–2014

With seabird populations in rapid decline, understanding and reducing anthropogenic mortality factors is essential. One such factor is incidental bycatch in fisheries. Here we analyze bycatch in the small-vessel demersal longline fishery for Greenland halibut outside the coast of Northern Norway in 2012–2014, by means of self-reporting from fishers and independent observers. A sample of killed birds were analysed for sex, age, reproductive status and condition. Nearly all were northern fulmars. Estimated total bycatch for this fishery for the 3-year period was about 312 birds (SE ≈ 133) using a stratified estimator. Bycatch rate per 1000 hooks was estimated to approximately 0.031 (SE ≈ 0.012). Exploring per trip bycatch rates utilizing generalized linear mixed models, we found no convincing trends of environmental, spatial and temporal variables in explaining bycatch. However, trips using longlines with non-swivel hooks had a more than 100-fold larger bycatch rate (mean ≈ 0.760, SE ≈ 0.160) than those using swivel hooks (mean ≈ 0.008, SE ≈ 0.002). Further, trips with external observers had higher bycatch estimates (mean ≈ 0.75, SE ≈ 0.16) compared with trips where bycatch was registered by the fishers (mean ≈ 0.02, SE < 0.01). Of the analysed birds, about two-thirds were adult birds and males dominated (71.1%). A majority were in good or moderate condition. The findings suggest that the incidental bycatch in the Greenland halibut fishery along the Norwegian coast is more limited than previous studies indicated, and that the use of swivel hooks can significantly reduce such bycatch. However, the impacts on the red-listed, diminishing population of fulmars breeding in mainland Norway should be assessed further and requires a method to assign killed birds to regions/colonies. Also, gaining a better understanding of what triggers events with extreme bycatch numbers is important to reduce the problem further and to improve bycatch modelling.