Fisheries Observer Research Articles

Commercial fishing vessels as marine-based sources of plastic pollution: The Namibian perspective

Plastic pollution in the marine ecosystem and their sources have been widely investigated, however some parts of the world remain under studied. Herein, we report on plastic pollution in the Namibian marine ecosystem, based on data collected by fisheries observers between 2003 and 2020 during commercial fishing activities. A total of 79 plastic pollution incidents were reported between 2003 and 2020, which consisted of unspecified non-biodegradable objects (55.7%), unspecified plastic items (25.3%), fishing gear (8.9%), plastic bottles (5.0%), plastic gloves (1.3%) and single-use plastic bags (3.8%). We found no significant Pearson correlation between the number of disposal incidents and the fisheries observer coverage (r = 0.3254, df = 14, p = 0.2187). The spatial analysis in the disposal of non-biodegradable objects show a fair distribution along the Namibian coast with more concentrations around latitude 18⁰S, 22⁰S, and 26⁰S. We conclude that fishing vessels are important marine-based sources of plastic pollution, highlighting a continuous need to raise awareness over the fishing industry, in particular seafarers, on plastic use and management. The study expands the plastic pollution knowledge by quantifying incidents of plastic pollution, plastic litter composition, and identifying spatial distribution in the Namibian waters, thus, to the best of our knowledge, represents a baseline for studies on marine plastic pollution in this oceanic region. Identifying sources of marine plastic litter and providing a spatial picture is a step closer to develop and implement specific regulatory tools to combat marine pollution.

Adaptive spatiotemporal management to reduce shark bycatch in tuna fisheries.

Purse-seine tropical tuna fishing in the eastern tropical Pacific Ocean (EPO) results in the bycatch of several sensitive species groups, including elasmobranchs. Effective ecosystem management balances conservation and resource use and requires considering trade-offs and synergies. Seasonal and adaptive spatial measures can reduce fisheries impacts on nontarget species while maintaining or increasing target catches. Identifying persistently high-risk areas in the open ocean, where dynamic environmental conditions drive changes in species' distributions, is essential for exploring the impact of fisheries closures. We used fisheries observer data collected from 1995 to 2021 to explore the spatiotemporal persistence of areas of high bycatch risk for 2 species of oceanic sharks, silky shark (Carcharhinus falciformis) and oceanic whitetip shark (Carcharhinus longimanus), and of low tuna catch rates. We analyzed data collected by fisheries scientific observers onboard approximately 200 large purse-seine vessels operating in the EPO under 10 different flags. Fishing effort, catch, and bycatch data were aggregated spatially and temporally at 1°×1° cells and monthly, respectively. When areas of high fishing inefficiency were closed the entire study period and effort was reallocated proportionally to reflect historical effort patterns, yearly tuna catch appeared to increase by 1-11%, whereas bycatch of silky and oceanic whitetip sharks decreased by 10-19% and 9%, respectively. Prior to fishing effort redistribution, bycatch reductions accrued to 21-41% and 14% for silky and oceanic whitetip sharks, respectively. Our results are consistent with previous findings and demonstrate the high potential for reducing elasmobranch bycatch in the EPO without compromising catch rates of target tuna species. They also highlight the need to consider new dynamic and adaptive management measures to more efficiently fulfill conservation and sustainability objectives for exploited resources in the EPO.

Fisheries observers: An overlooked vulnerability for crime and corruption within the global fishing industry

Human fishery observers play an important role in monitoring fish stocks, providing scientific data upon which management organizations set applicable fishing limits and quotas to maintain sustainable populations. At-sea observers, however, sometimes sustain harassment from crews that object to being monitored, and at least one observer has disappeared or died under suspicious circumstances while underway every year since 2009. This exploratory paper examines inherent vulnerabilities within the monitoring, control, and surveillance (MCS) framework that nations and regional fisheries management organizations (RFMO) have adopted to support sustainable fish stocks. As rational actors, perpetrators of observer harassment, assault, and murder likely do so to manipulate observers’ monitoring role in the MCS framework to conceal illegal, unreported, and unregulated (IUU) fishing and other criminal activities. Qualitative analysis of reporting on observer harassment and suspicious disappearances over the past 15 years indicates the following institutional, situational, jurisdictional, and physical conditions appear to contribute to observer safety issues—privatization of fishery observer programs, crime convergence on fishing vessels, conflicting maritime jurisdictional considerations, and harsh conditions endemic to the remote maritime environment. While recorded suspicious observer deaths are too few to draw general conclusions, most occurrences befell observers working for tuna RFMOs in the Pacific Ocean, and a disproportionate number of deaths were observers from Kiribati and Papua New Guinea. Alternative surveillance approaches such as Remote Electronic Monitoring (REM) produce limited results without human observers. Future policies that could contribute to observer safety include applying lessons learned from international efforts to address maritime transnational organized crime and providing observers personal communications and safety equipment to directly connect with search and rescue entities if under duress.

Modeling the importance of subsurface environmental variables in driving swordfish (Xiphias gladius) catchability in the Western Indian Ocean

AbstractMany oceanic species in pelagic habitats move vertically through the water column, highlighting the ecological importance of that spatial environment for modeling habitats of marine species. The role and importance of multiple oceanic subsurface environmental variables in modeling the habitat suitability of swordfish (Xiphias gladius), a highly migratory large pelagic fish, is poorly understood. In this study, we analyzed adult swordfish data from the 2017–2019 Chinese Indian Ocean tuna longline fishery observer. We used the maximum entropy model (MaxEnt) and random forest model (RF) to compare modeling schemes that included multiple subsurface environmental datasets. The area under receiver operating characteristic curve (AUC) from training and test sets was evaluated to investigate whether the inclusion of subsurface variables could enhance model performance and affect the simulation results. This analysis showed that model performance was significantly enhanced after addition of subsurface environmental variables, and the best model fit was achieved at 200–300 m depth. Sea water temperature, dissolved oxygen, net primary production, and ocean mixed layer depth were the critical environmental factors constituting catchability for swordfish in the Western Indian Ocean. As the depth increased, dissolved oxygen became the most important environmental factor, replacing surface temperature. Compared with the surface model, the location and extent of areas of high catchability in certain months changed significantly after the addition of subsurface variables. The results of this study provide evidence for a better understanding of the selection of critical environmental variables and improvement of model performance in 3D habitat modeling of pelagic fish.

Impact of fishery observer protocol on estimated bycatch rates of marine mammals

Abstract Managing fishing operations’ threat to marine mammal populations hinges on accurate bycatch estimates, often derived from fishery observer or monitoring programmes. Much global marine mammal bycatch occurs in gillnets, and observer protocols that do not include watching the haulback of gillnets may miss animals that drop out of the net. We investigated whether trips using a fish-focused observer protocol (no requirement to watch the haulback) in US northwestern Atlantic gillnet fisheries from 1994 to 2019 had different observed bycatch rates from trips under a mammal-focused observer protocol (watching the haulbacks) for grey seals (Halichoerus grypus atlantica), harbour seals (Phoca vitulina vitulina), and harbour porpoise (Phocoena phocoena phocoena). We found that observer protocol was likely to affect observed drop-out and bycatch rates. Under the fish-focused protocol, the ratio of animals removed from the net to those that fell from the net was generally higher than under the mammal-focused protocol, suggesting fish-focused observers missed bycatch that fell. Bycatch rates of animals removed from the net by fishers differed significantly between observer protocols for seals, but not for harbour porpoise, perhaps because of differences in entanglement and manner of decomposition. We estimate bycatch was underreported by 3–25% because of unobserved drop-outs on fish-focused observer protocols.

Fisheries observers as enforcement assets: 21 Years of lessons from the North Pacific

Fisheries sustainability through governance is achieved through enforcement of marine resource laws and regulations, and that enforcement depends upon accurate reporting of potential crimes. These potential crimes are reported by fisheries observers in regions where observers have a dual role as scientist and enforcement asset. Trends in reported violations from a large observer program were examined to increase accountability and transparency, identify how compliance has changed over time, and illustrate the complexities that come with the analysis of these data. Large increases in the rate of potential violations reported by observers were due to the passing of new regulations, a delayed response to a major event, or the efforts of few individual change agents. A much smaller proportion of reported violations have resulted in penalties in recent years when compared to a prior study conducted early in the time series. These differences likely reflect the cumulative effect of gradual increases in regulatory burdens put on observers to report relatively minor offenses for which there are inadequate resources to address.

Time of death: behavioral responses of an oceanic whitetip shark, Carcharhinus longimanus, to capture by a longline fishing vessel

BackgroundBycatch mortality in longline fisheries is a major contributor to global declines in shark populations. The duration of time that an animal is hooked and the impacts of hooking on behavior affect the likelihood of mortality. However, limited information exists on the behavior of sharks to longline capture because of difficulties observing hooking events. Using a fortuitous recovery of an archival satellite tag, we describe the movement of an oceanic whitetip shark (Carcharhinus longimanus) and examine the behavior prior to its mortality in response to hooking on a longline.ResultsA 1.5 m (fork length) C.longimanus was tagged and released in good condition by a fisheries observer following initial capture on a US longline fishing vessel. After release, the shark resumed normal vertical behavior within 5 h. Over 198 days, the shark undertook wide-ranging movements throughout the Pacific between Samoa, Niue, and Tonga. The shark was hooked by a second longline vessel while conducting routine yo-yo diving between 0 and 120 m depth. For the first hour after being hooked the shark exhibited high swimming activity with rapid vertical movements between 20 and 40 m indicative of an initial struggle against the line. After this, the shark struggled at the surface for approximately 5 h, until it succumbed to exhaustion and died on the line.ConclusionFight time has a strong influence on the mortality rates of sharks captured in commercial longline fishing operations. Data obtained from this shark offers further understanding of capture behavior and time to mortality on a longline for C.longimanus which may assist managers as they work on options to reduce mortality rates for this threatened species.

Harassment and obstruction of observers in U.S. fisheries

Fishery observers play a crucial role in the management and conservation of fish stocks, but the treatment they receive aboard fishing vessels can affect their ability to perform their duties. Using law enforcement data from the Northeast and Alaska regions, home to the most important commercial fisheries in the United States, we explore the extent of observer harassment, assault, interference, and obstruction (OHAIO). We find that 16% of 10,346 fishery violations reported in the Northeast and Alaska regions from 2014-2018 are observer-related, and over 80% of those involve OHAIO. We trace how OHAIO incidents are reported and processed and propose steps to mitigate the issue.

Addressing data-deficiency of threatened sharks and rays in a highly dynamic coastal ecosystem using environmental DNA

Marine biodiversity loss is accelerating, leading to the elevated extinction risks of many species, including sharks and rays. To mitigate these losses, information on their distribution and community composition is needed. Monitoring these (often) mobile species is challenging, especially in remote, highly dynamic and turbid coastal areas. Here, we use an environmental DNA (eDNA) approach to: (1) establish the presence and distribution of elasmobranch species, (2) compare this to a conventional fisheries-dependent approach, and (3) determine the influence of season, area-based protection and habitat on elasmobranch community composition in the highly dynamic Bijagós Archipelago in Guinea-Bissau (West Africa). We collected 127 seawater samples and detected elasmobranch DNA in 58 (45.7%) of these samples, confirming the presence of 13 different elasmobranch species (2 sharks, 11 rays), including seven threatened species. Eight of the species detected by the eDNA-approach were also recorded in a fisheries observer program, which recorded another eight species not detected by the eDNA approach. The most commonly occurring species, based on the number of eDNA sampling locations were the pearl whipray (Fontitrygon margaritella), smalltooth stingray (Hypanus rudis), scalloped hammerhead shark (Sphyrna lewini), and the blackchin guitarfish (Glaucostegus cemiculus). Species composition and richness differed significantly before (January-March) and after the rainy season (November-December). Furthermore, we showed that community composition and species richness did not differ between protected (MPA) and non-protected areas of the archipelago. Thus, we confirm that eDNA approaches are a valuable and non-invasive tool to study threatened shark and ray species in data-deficient and dynamic coastal areas, especially when combined with conventional monitoring methods such as fisheries-dependent information.

Building use-inspired species distribution models: Using multiple data types to examine and improve model performance.

Species distribution models (SDMs) are becoming an important tool for marine conservation and management. Yet while there is an increasing diversity and volume of marine biodiversity data for training SDMs, little practical guidance is available on how to leverage distinct data types to build robust models. We explored the effect of different data types on the fit, performance and predictive ability of SDMs by comparing models trained with four data types for a heavily exploited pelagic fish, the blue shark (Prionace glauca), in the Northwest Atlantic: two fishery dependent (conventional mark-recapture tags, fisheries observer records) and two fishery independent (satellite-linked electronic tags, pop-up archival tags). We found that all four data types can result in robust models, but differences among spatial predictions highlighted the need to consider ecological realism in model selection and interpretation regardless of data type. Differences among models were primarily attributed to biases in how each data type, and the associated representation of absences, sampled the environment and summarized the resulting species distributions. Outputs from model ensembles and a model trained on all pooled data both proved effective for combining inferences across data types and provided more ecologically realistic predictions than individual models. Our results provide valuable guidance for practitioners developing SDMs. With increasing access to diverse data sources, future work should further develop truly integrative modeling approaches that can explicitly leverage the strengths of individual data types while statistically accounting for limitations, such as sampling biases.

Observed fishery regulatory violations in Namibia and their possible implications for the sustainable management of fishery resources

Fisheries management of the Namibian fishery resources has been based on the best available scientific and socioeconomic information. Monitoring control and surveillance (MCS) ensures compliance with regulations and management measures during the harvesting, handling, and processing of marine resources. While much research focus has been given to the scientific aspects of fisheries management, little has been done concerning the MCS. This study, therefore, aimed at providing an understanding of the fishery regulatory violations and their implications for the sustainable management of fishery resources. The above was achieved by determining the type and frequency of fisheries violations and assessing deterrence’s relevance of the monetary sanction given their present values. The marine resource regulations in place were found to be comprehensive and regulate the harvesting, processing, and handling of marine resources. The most frequent violations reported include discarding of marine resources, dumping of gear or non-biodegradable objects, and intimidating, threatening, and obstructing fisheries observers. A decreasing temporal trend in violations has been observed, which may indicate that compliance with regulations has improved over time (2003–2022). The fines prescribed were found to have potentially lost their ability to act as deterrence because of the time value of money, hence needing revision. The findings of this study offer potential grounds for Namibian fishery management authorities to revise and enhance fishery regulations and policies to prevent fishery regulatory violations. If these violations are not addressed adequately, they hold the potential to substantially undermine the sustainable management of fishery resources.

Indications of habitat use patterns among small cetaceans in the central North Pacific based on fisheries observer data

Biological specimens and environmental data collected by observers monitoring Japanese squid driftnet fishing operations during the summers of 1990 and 1991 in the central North Pacific (37°N-46°N, and 170°E-150°W) were used to explore habitat use patterns among three small cetacean species common to that area: the Dall’s porpoise (Phocoenoides dalli), Pacific white-sided dolphin (Lagenorhynchus obliquidens) and northern right whale dolphin (Lissodelphis borealis). Sex and maturity status were determined for 805 northern right whale dolphins, 421 Pacific white-sided dolphins and 206 Dall’s porpoises incidentally taken in 800 observed gillnet sets, allowing sub-taxon comparisons of habitat use patterns. Habitat variables were based on observer records of sea surface temperature (SST), wind velocity and direction, and swell height. Current velocity and direction and SST gradients were also derived. Canonical Correspondence Analysis (CCA) was used to relate the species categories to the habitat conditions recorded for the gillnet operations in which entanglements occurred. The samples collected from the southern, middle and northern latitudes within the overall study area were examined separately to account for northward movement of the fishing fleets across the summer months. SST was the most dominant and consistent feature; northern right whale dolphins occupied the warmest waters, Dall’s porpoises the coldest; Pacific white-sided dolphins were found in-between, but more similar to the latter. Wind velocity and swell height also reflected potentially important habitat features. Young-of-the-year northern right whale dolphin showed a preference for the warmest waters observed in the middle latitude band, coincident with that species summer calving mode.

Blue Shark (Prionace glauca) Distribution in the Pacific Ocean: A Look at Continuity and Size Differences

Blue shark (Prionace glauca) is a major bycatch species in the long-line and gill-net Pacific Ocean tuna fisheries, and the population structure is critical for fishery management. We employed generalized additive models to analyze the fork lengths of blue sharks and biological data (i.e., feeding level, sex, and genetic data), as well as environmental and spatial variables (i.e., sea surface temperature, month, longitude, and latitude) collected from 2011 to 2014 by the Chinese Thunnus alalunga long-line tuna fishery observer program. Fork length was significantly affected (p < 0.05) with location (latitude and longitude) and sex, and positively effected with sea surface temperature. No relationships were found between fork length and feeding level, month, and genetic data. We detected fork length differences among blue sharks over the range of the observed data, but the genetic data implied a panmictic population. Thus, we hypothesize that the genetic similarity was so close that it could not be well separated. Based on the precautionary principle, we recommend that the blue shark in the Pacific Ocean should be managed as two independent populations to ensure its sustainable use.

Gillnet size selectivity of shark and ray species from Queensland, Australia

AbstractGillnets are size‐selective fishing gears commonly used by industrial and small‐scale fishers, so understanding selectivity can aid fisheries management by identifying suitable mesh sizes to optimize catches of target species while reducing bycatch. Few size selectivity parameters have been estimated for sharks, with even fewer for rays. Size selection parameters were estimated for seven species of sharks and two species of rays from the Queensland East Coast Inshore Finfish Fishery (ECIFF). Size frequency data from a fishery observer program on ECIFF vessels was used to fit a standard size selection model. Mesh size independent parameters, θ1 and θ2, were estimated for each species to define selectivity curves for different mesh sizes for each species. Parameter values were compared with previous studies that used the same method. Estimates of θ1 were similar among species within the same genus, such as Carcharhinus, Rhizoprionodon, and Sphyrna. Anoxypristis cuspidata had the largest θ1 and θ2 values, likely because of its toothed rostrum that affected catchability in gillnets. Our findings can be used for the ECIFF and other gillnet fisheries to aid in mesh size recommendations and risk mitigation.

Incidental capture of sea turtles in the Northeast Atlantic Portuguese pelagic longline fishery

Incidental catch or bycatch of sea turtles by pelagic longline fisheries is a major concern worldwide. The Northeast Atlantic hosts key foraging and developmental areas for oceanic juvenile loggerhead sea turtles (Caretta caretta) originating mainly from the Southeastern USA and Cape Verde. This region may be one of the most heavily fished areas by pelagic longline for which no recent assessments of fisheries interactions exist. We analysed fishery observer data collected between 2015 and 2020 to assess sea turtle bycatch by Portuguese commercial longliners targeting swordfish (Xiphias gladius) and blue shark (Prionace glauca) in the Northeast Atlantic. A total of 177 sea turtles interacted with the gear during the 896 fishing sets (887,641 hooks) monitored. Loggerheads (n = 139) ranging between 32 and 78 cm curved carapace length (CCL) were caught at a rate of 0.152 turtles per 1000 hooks, and leatherbacks (Dermochelys coriacea; n = 38) between 100 and 210 cm estimated length at a rate of 0.043 turtles per 1000 hooks. Loggerhead and leatherback bycatch shows a clear seasonal pattern in the region. At haul-back mortality rates of oceanic-stage juvenile loggerheads was estimated at 26% whereas no at haul-back mortality was registered for leatherback turtles. Model estimates, based on AIS derived fishing effort from Global Fishing Watch, indicate a total of 1439 interactions (552–3069 BCI) for loggerhead, and 604 interactions (262–1129 BCI) for leatherback turtles between 2016 and 2020. Information from this study is essential to support effective management strategies for sea turtle conservation in the Northeast Atlantic.

Sea turtle (Reptilia, Testudines) diversity and occurrence in the Azores Archipelago (NE Atlantic).

Six species of marine turtles occur in the Azores Archipelago. The loggerhead, Carettacaretta (Linnaeus, 1758), is by far the most common species and is being constantly monitored and tagged by a joint project between the University of the Azores and the University of Florida since 1989. With the implementation of the tuna fishery observers (for dolphin safe seals), an increment of sea turtle reports has been verified as expected. The leather back turtle, Dermochelyscoriacea (Vandelli, 1761) is the second most observed species in the Azores' EEZ, a fact probably also linked to the tuna fishery observation programme. All other species are occasional/vagrant albeit the green turtle, Cheloniamydas (Linnaeus, 1758) is more commonly seen than the others. Historically, sea turtles were occasionally taken for food in specific fishing villages and ports. Since 1986, sea turtles, as well as all marine mammals, are fully protected in the Azores although human-related activities (e.g. plastics, discarded fishing gear) do generate serious injuries and deaths. In this paper, we update sea turtle species' checklist for the Azores and give detailed geographic coordinates on their known occurrences.

Effect of pingers on harbour porpoise (Phocoena phocoena) bycatch in the US Northeast gillnet fishery

Harbour porpoise (Phocoena phocoena) bycatch in the US Northeast gillnet fishery is managed under the Harbour Porpoise Take Reduction Plan (HPTRP), which was implemented on 1 January 1999. The HPTRP divides this fishery into management areas that are either completely closed to all gillnets or closed only to gillnets that do not use pingers. Questions about pingers that have arisen include: (1) would pingers be as effective in an operational fishery as in controlled scientific experiments; (2) would the fishery comply with these regulations; and (3) would harbour porpoises habituate to pingers? To investigate these questions, data from over 25,000 gillnet hauls observed by the Northeast Fisheries Observer Program after the implementation of the HPTRP, 1999-2007, were examined. In a 1994 controlled scientific experiment conducted in part of this fishery that used 15cm mesh gillnets, the bycatch rate in pingered nets was 92% less than that in nets without pingers. In contrast, in the operational fishery, the bycatch reduction in pingered nets was 50-70%, depending on the time, area and mesh size. In particular, there was no observed bycatch in pingered nets that used the same mesh size as used in the experiment. Thus, it seem that the apparent decrease in pinger effectiveness in the operational fishery was partially due to the type of gillnet used and lack of compliance. Pinger usage started out high in 1999 (the first year required), dropped substantially during 2003-05 and perhaps due to outreach activities increased beginning in 2006. During years of high pinger usage, 87% of the tested pingers were functional, while only 36% of the tested pingers were functional during years of low pinger usage. In general, as expected, observed bycatch rates in hauls without pingers were greater than bycatch rates in hauls with the required number of pingers. Unexpectedly, bycatch rates of observed hauls with an incomplete set of pingers were higher that in observed hauls without pingers. Confounding factors that could partially explain this apparently contrary result are discussed. There was no evidence for temporal trends in the bycatch rates, suggesting that harbour porpoises had not habituated to the pingers. In conclusion, in the US Northeast gillnet fishery, harbour porpoises do not appear to have habituated to pingers, and pingers appear to have reduced the bycatch rate, particularly when the required number of pingers were used and in nets using mesh sizes of 15cm or less.

Towards non-entangling and biodegradable drifting fish aggregating devices – Baselines and transition in the world’s largest tuna purse seine fishery

Drifting Fish Aggregating Devices (dFAD) are widely used in purse seine tuna fisheries globally. DFADs are often lost or abandoned by the fishing industry which can lead to marine pollution, entanglement of sensitive species and habitat damage. They are considered as a high-risk lost or abandoned fishing gear due to their common construction with long-lasting synthetic materials, including netting. This study used data collected by fishery observers to investigate materials and designs used in dFAD construction over the last 10 years in the Western and Central Pacific Ocean (WCPO). Results indicated that apart from bamboo, which is commonly used in dFAD rafts with other synthetic materials for buoyancy, very few natural materials are used. The depth of dFAD appendages varied, with a median of 50 m. Most dFADs used netting of various mesh sizes in some aspect of their construction. There is limited information to assess the uptake of lower entanglement risk dFAD designs. Transition towards more environmentally friendly dFAD designs is being promoted by management measures imposed by the Western and Central Pacific Fisheries Commission that include banning of netting by 2024 and encouraging the use of natural materials. Scientific trials are underway to support industry adoption of biodegradable dFAD materials. This paper provides important baseline data to detect and monitor future changes in dFAD construction and materials in response to management measures, and also highlights limitations to data collected by observers that will need to be improved to better monitor these changes.

Modelling the distribution of rare and data-poor diadromous fish at sea for protected area management

Anthropogenic pressures have resulted in declines in diadromous fish. Many diadromous fish which were commercially important are now threatened and protected. Little is known about their marine life history phases, and no observation-based Species Distribution Model exists for this group of species at sea. Yet, fisheries dependent and independent data could provide new insights into the distribution of diadromous fish at sea.We collated a database of 168 904 hauls from fisheries observer bycatch data and scientific fisheries surveys, from eastern Atlantic and Mediterranean waters. The distribution of eleven rare and data-poor diadromous fish (shads, lampreys, salmonids, the European eel, the thinlip mullet, smelt and the European flounder) were modelled. A Bayesian site occupancy model, that incorporates imperfect detection to account for repeat detections and non-detections, the non-random nature of fishing gear type and spatial autocorrelation was used. From the model outputs, we explored bycatch risk and the role of MPAs, required under the Marine Strategy Framework Directive and Habitat Directive and assessed.Diadromous fish were observed within relatively shallow coastal areas. Species specific gear bycatch trends were observed. Core distribution areas corresponded to their known water basin presence, indicating connectivity with their freshwater habitats. Numerous Habitat Directive Marine Protected Areas were found to be of relevance.Given the coastal distribution of these species, they are exposed to higher anthropogenic pressures from both terrestrial and marine environments. Risk of bycatch at sea for most species appears to be low. Nonetheless, for threatened individuals, even a small amount of bycatch may impact their populations, especially since misreporting is likely to be high. Differences in catchability between gears highlight potential benefits of limiting access of certain gears within protected areas to reduce bycatch.

Spillover benefits from the world's largest fully protected MPA.

Previous research has cast doubt on the potential for marine protected areas (MPAs) to provide refuge and fishery spillover benefits for migratory species as most MPAs are small relative to the geographic range of these species. We test for evidence of spillover benefits accruing from the world's largest fully protected MPA, Papahānaumokuākea Marine National Monument. Using species-specific data collected by independent fishery observers, we examine changes in catch rates for individual vessels near to and far from the MPA before and after its expansion in 2016. We find evidence of spillover benefits for yellowfin (Thunnus albacares) and bigeye tuna (Thunnus obesus).