Longline Fishing Research Articles

Bias in spatiotemporal index standardization models caused by unbalanced sampling designs and allocation schemes

Abstract Relative indices of abundance are key to providing science advice for the management of many fish stocks. Historical focus has been on design-based estimation, wherein mathematical formulae for aggregating data into a single index are directly informed by the underlying sampling design. Recent efforts have moved toward using index standardization models instead. However, the impacts sampling designs and allocation schemes have on these index standardization models have not been fully examined. Using a spatio-temporal multinomial index standardization model developed for survey data obtained with longline fishing gear, we develop a simulation framework to analyze the effects of five different combinations of sampling designs and allocation schemes under various conditions. These simulations expose bias in model-based indices caused by non-proportional-to-area designs, which are common in surveys that have historically utilized design-based estimation. We explore the impact of robust statistical alternatives on this bias. This effort highlights an important source of bias and the importance of periodically reassessing allocation schemes and sampling designs for scientific surveys.

A Crusade Throughout the World’s Oceans: Genetic Evidence of the Southern Bluefin Tuna Thunnus maccoyii and the Pacific Bluefin Tuna Thunnus orientalis in Brazilian Waters

The large pelagic species play an important role in transferring energy in vast distant marine ecoregions. Results obtained report on extraordinary findings of important commercial species in southeast–south Brazilian waters, including the Southern bluefin tuna Thunnus maccoyii and the Pacific bluefin tuna Thunnus orientalis, an endemic species from the Pacific Ocean. These specimens were identified within the genomic description of 10 individuals randomly selected from the catch to evaluate the catch composition of pelagic longline fisheries off Brazilian waters. Most of the records were from T. maccoyii (6), followed by the Bigeye tuna T. obesus (2), Yellowfin tuna T. albacares (1), and T. orientalis (1). Yellowfin and Bigeye tuna are expected to be captured in the vicinity of the longline fishing areas. However, the unlikely presence of the cold-water T. maccoyii and the warm-water T. orientalis suggests a long migration from common species ranges that could be influenced by climate change. These results imply a readjustment of spatial management structures for these species.

Understanding the Risks to Artisanal Fishers on Lake Victoria Using Design Methods

ABSTRACT Objectives The purpose of this study was to document, understand, and communicate the daily activities and associated risks faced by artisanal fishers working on Lake Victoria, Tanzania, in order to identify opportunities for intervention design. Methods Established human-centered design techniques were combined with drowning risk analysis to create a process that visually captured and analyzed the risks to fishers in two lakeside communities engaged in long-line fishing (mostly by day) and net fishing at night. Results Two visual journey risk maps were developed. One map detailed the long-line fishing process for larger fish like Tilapia and Nile Perch, while the other focused on seine net fishing for dagaa at night. Each journey map covered the “before,” “during,” and “after” stages of fishing activities. For long-line fishers, preparation began early in the morning, including food and equipment collection, launching the boat, and setting long lines at the fishing site. Risk scenarios, such as storms or boat capsizing, were identified, with fishers often relying on makeshift flotation devices. For seine net fishers, the journey began in the afternoon with preparatory tasks at the fishing camp. Night fishing required the deployment of solar lamps to attract fish, followed by net casting. Risk factors like boat collisions, crew fatigue, and engine failure were noted. Both groups identified common risks and discussions around these journey risk maps emphasized the need for holistic safety interventions, including access to accurate weather forecasts, buoyancy devices, and formal safety training. The participatory mapping approach enabled fishers to provide valuable insights into how risks can be mitigated. Conclusion Small-scale artisanal fishers working on Lake Victoria face significant drowning risks. The design-led co-creation of visual journey risk maps with fishers and drowning prevention experts allows a deep understanding of livelihood journeys and associated risks. Opportunities for risk mitigation and intervention design are presented visually. Further research combining other design tools with scientific analysis could highlight points where control measures can be most effectively implemented, but this must be documented, and its impact and effectiveness evaluated. Interventions suggested by the process will be co-created and evaluated for effectiveness.

Development of Artificial fish bait incorporated with Surimi and fatty acid bioattractant derived from seafood processing wastes for longline fishing

Development of Artificial fish bait incorporated with Surimi and fatty acid bioattractant derived from seafood processing wastes for longline fishing

Discovery of a potential open ocean nursery for the endangered shortfin mako shark in a global fishing hotspot

Populations of large pelagic sharks are declining worldwide due to overfishing. Determining the overlap between shark populations and fishing activities is important to inform conservation measures. However, for many threatened sharks the whereabouts of particularly vulnerable life-history stages – such as pregnant females and juveniles – are poorly known. Here, we investigated the spatial distribution of size classes, energy transfer and reproductive states of pregnant females of the endangered shortfin mako, Isurus oxyrinchus, using spatially resolved catch data from a Spanish surface longline vessel (1996 − 2009) in the South-east Pacific Ocean. Our results suggest a general eastward gradient of occurrence of pregnant females of thousands of kilometers from western oceanic feeding grounds towards the eastern Pacific, where we observed an aggregation area of small juveniles. Moreover, the potential nursery likely overlapped a longline fishing hotspot, increasing the vulnerability of juveniles from fisheries. Our results suggest that limiting fishing pressure in this area could reduce mortality of early life stages and contribute to the conservation of this endangered shark species.

Composition of pelagic fish in commercial landings of the longline fishery in the Costa Rica Pacific during 2015-2021

Longline fishing in the Pacific of Costa Rica targets multiple species of large pelagic fishes and faces challenges in assessment due to lack of data. This study analyzes landing data of pelagic fish in this fishery using unconventional statistical methods, to better understand the dynamics and provide recommendations for improving data collection and analysis. Landing data reported during 2015-2021 were examined. A descriptive and comparative analysis of landings was conducted using Spearman correlation tests and Non-Metric Multidimensional Scaling (NMDS) to visualize patterns in catch composition. Permutational Multivariate Analysis of Variance (PERMANOVA) and Similarity Percentage Analysis (SIMPER) were employed to identify significant differences between fleet types, landing ports, months, and years, as well as species contribution to these differences. The annual mean total landing of large pelagic fish was 7531.01 tons, with 39.14% corresponding to sharks, 24.34% to billfish (Istiophoridae and Xiphiidae), 18.05% to mahi-mahi, and 14.94% to tuna. Statistically significant differences were found between fleet types, landing ports, months, and years. Shark landings were the least correlated (rho=0.36) and had the greatest influence on variation by fleet type. An increase in the similarity of catch composition by port since 2015 was observed. In addition, a shift towards increasingly less selective fishing over the study period was evident. Our findings highlight the urgent need for advanced research methodologies to address gaps in data collection for commercial fisheries in Costa Rica. Improving these methods is crucial to ensure that management policies are based on accurate and comprehensive information. Results highlight the need for a comprehensive strategy involving diverse stakeholders to improve our understanding and ensure the sustainability of fisheries and the preservation of marine ecosystems in Costa Rica.

Artisanal Longline Fishing for Greenland Halibut (Reinhardtius hippoglossoides) Operated Under Sea Ice Using a Metal Plate Kite in Northwest Greenland

Artisanal Longline Fishing for Greenland Halibut (Reinhardtius hippoglossoides) Operated Under Sea Ice Using a Metal Plate Kite in Northwest Greenland

Enhancing model robustness to imbalanced species abundance distributions: Eliminating misclassified records via a model-agnostic approach, exemplified by tuna fisheries datasets

Enhancing model robustness to imbalanced species abundance distributions: Eliminating misclassified records via a model-agnostic approach, exemplified by tuna fisheries datasets

The Financial Feasibility Analysis of Freshwater Fishing Business in Tempe Lake Waters After Revitalization

The freshwater fishing business in Lake Tempe is the main livelihood for the coastal societies around Lake Tempe. In recent years, there have been floods due to the overflow of Lake Tempe, which caused losses to fishermen. One of the causes is the high sedimentation every year. The lake revitalization program is the way to solve this problem. The revitalization process provides social and economic changes to the society in the Lake Tempe area It has an impact on improving the economy of fishermen's households. This research aimed to analyze the financial feasibility of freshwater fishing based on the fishing gear used, namely gill nets, longlines, and traps. This research was carried out on the coast of Lake Tempe, namely Tempe, Sabbangparu, Tanasitolo, and Belawa Districts in Wajo Regency from March to June 2022. The researchers chose the location in a purposive way. This research is survey research. Data analysis used financial analysis by looking at the net present value (NPV), Net Benefit Cost (net B/C), Internal Rate of Return (IRR), and Payback Period (PP). The results showed that the large profits obtained from the catching freshwater fish business in Lake Tempe using gill nets were 13,526,859 (IRD) per year, then the longline fishing gear gains a profit of 10,557,023 (IRD), and for fishing traps gear, the profit is7,548,808 (IRD). The acquisition of each financial analysis obtained by NPV>0, net B/C>1, IRR>the applicable interest rate is 5%, and the payback period is less than 5 years. Therefore, it concluded that these three types of fishing gear are feasible to be developed.

Contributions of small‐scale and longline fishing to sea turtle mortality in the Solomon Islands

AbstractA focus of sea turtle management has been reducing bycatch in commercial fisheries, but sustainable harvest for consumption is also an important objective in many nations. Identifying how much different fisheries contribute to turtle mortality could help focus limited management resources. We estimated national scale turtle catches for two fisheries in the Solomon Islands: a small‐scale reef fishery where turtles are caught for food and sale, and an offshore longline fishery where turtles are bycatch. The footprint of the longline fishery spanned the entire exclusive economic zone of the Solomon Islands and was 67 times bigger than the footprint of the small‐scale fishery. The median catch summed across both fisheries was ∼12,000 turtles in 2018, with 85%–97% of that catch in the small‐scale fishery. We suggest that turtle management in the Solomon Islands, a nation with globally significant turtle breeding populations, should focus on sustainable management of small‐scale coastal fisheries.

Physiological assessment of the effects of experimental capture and transport in Pacific spiny dogfish

Sharks are collected from the wild as live specimens for display in aquariums and use in research. The methods by which live sharks are captured and transported can be associated with sub-lethal physiological outcomes or even mortality, which requires evaluation to determine optimal collection and transport methods for a given species. The present study evaluated the primary (i.e., endocrine) and secondary (i.e., biochemical) stress responses and mortality in Pacific spiny dogfish ( Squalus suckleyi) following capture and subsequent transport between experimental rod-and-reel angling and longline fishing. Dogfish were resilient to transport following capture by either method, exhibiting no at-vessel mortality and 0.03% delayed mortality. Longline captured dogfish exhibited signs of primary (i.e., elevated corticosterone) and secondary (i.e., elevated plasma potassium, osmolality, glucose, and lactate; decreased blood pH) stress responses, whereas dogfish that experienced rod-and-reel capture and transport only exhibited a secondary stress response (i.e., elevated plasma potassium, osmolality, and lactate; decreased blood pH). Together, these data demonstrate that Pacific spiny dogfish are robust to capture and transport using experimental hook-and-line fishing techniques.

Blue shark vertical movement patterns in the Central Mediterranean: bycatch mitigation windows revealed from pop-up satellite archival tag data

In the Mediterranean Sea, pelagic longline fisheries, targeting tuna and swordfish, have contributed significantly to the bycatch of threatened chondrichthyan species, such as blue shark (Prionace glauca). The Mediterranean blue shark population is assessed as critically endangered, making a timely implementation of mitigation measures crucial. A comprehensive understanding of blue shark habitat use dynamics is essential for deriving appropriate mitigation measures. This study aimed at evaluating vertical movement behaviour and investigating factors potentially influencing the movements of blue sharks in the Mediterranean Sea. Twenty-six blue sharks, bycaught in a longline fishery in the southern Adriatic, were tagged with pop-up satellite archival tags. Analysis of data from thirteen recovered tags revealed a distinctive diel movement pattern. Blue sharks used shallower waters during the night and deeper waters during the day, characterised by steep ascents and descents during sunset and sunrise, respectively. In addition, lunar phases were also influencing the depth of blue shark movements, with sharks using deeper waters right before and during full-moon. Shark size, salinity, currents, spatial location and time of the year were additional factors influencing blue shark depth use. The observed tendency of blue sharks to use deeper areas at daytime and prior and during the full moon period offers possibilities to develop and test bycatch mitigation strategies. Aligning longline fishing schedules and fishing depths with blue shark behaviour during the fishing seasons could hold promise to effectively reduce spatio-temporal overlap between fishing and blue shark distribution and may ultimately decrease the bycatch impact of the fishery.

Addressing illegal longlining and ghost fishing in the Galapagos marine reserve: an overview of challenges and potential solutions

Despite regulations aimed at curbing shark finning and bycatch, shark fishing mortality rates continue to escalate, partly due to unintended consequences of these policies which, along with illegal, unreported, and unregulated fishing and ghost fishing, undermine conservation efforts. The ineffectiveness of current regulations to curb shark mortality highlights the pressing need for reevaluating shark conservation strategies, especially in ecologically sensitive areas. In this context, the debate on enforcing longlining bans in multiple-use marine protected areas, including shark sanctuaries, is intensifying. Some argue for total bans to minimize incidental shark mortalities, while others highlight the socioeconomic importance of longlining, advocating for alternative conservation measures. In 2000, longline fishing was banned in the Galapagos Marine Reserve (GMR) as a precautionary measure to prevent illegal fishing of sharks and bycatch of endangered, threatened, and protected species. After 24 years of enforcement, official and anecdotal evidence indicate that illegal small-scale tuna longlining and ghost fishing are increasing threats across the reserve. This paper provides an overview of the longline fishing controversy within the GMR, incorporating scientific evidence, legal and socioeconomic considerations, and perceptions from the Galapagos small-scale fishing community. We offer novel insights and recommendations for the development of the Galapagos small-scale tuna fishery within an ecosystem approach to fisheries. This approach aims to reconcile conservation goals with the needs of local communities, while also proposing innovative solutions to address the longstanding debate surrounding longlining in the GMR.

Feature Selection for Explaining Yellowfin Tuna Catch per Unit Effort Using Least Absolute Shrinkage and Selection Operator Regression

To accurately identify the key features influencing the fisheries distribution of Pacific yellowfin tuna, this study analyzed data from 43 longline fishing vessels operated from 2008 to 2019. These vessels operated in the Pacific Ocean region (0° to 30° S; 110° E to 170° W), with a specific focus on 25 features of yellowfin tuna derived from marine environment data. For this purpose, this study opted for the Lasso regression analysis method to select features to predict Pacific yellowfin tuna fishing grounds, exploring the relationship between the catch per unit effort (CPUE) of yellowfin tuna and multiple features. This study reveals that latitude and water temperature at various depths, particularly the sea surface temperature of the preceding and subsequent months and the temperature at depths between 300 and 450 m, are the most significant features influencing CPUE. Additionally, chlorophyll concentration and large-scale climate indices (ONI and NPGIO) also have a notable impact on the distribution of CPUE for yellowfin tuna. Lasso regression effectively identifies features that are significantly correlated with the CPUE of yellowfin tuna, thereby demonstrating superior fit and predictive accuracy in comparison with other models. It provides a suitable methodological approach for selecting fishing ground features of yellowfin tuna in the Pacific Ocean.

Enjoy the darkness: Forsake partially nocturnal sets provides a good opportunity to improve profits and sustainability in the southern Brazil longline fishery

Enjoy the darkness: Forsake partially nocturnal sets provides a good opportunity to improve profits and sustainability in the southern Brazil longline fishery

Factors influencing the at‐haulback mortality of striped marlin Tetrapturus audax caught by tuna longline fishery in the western Indian Ocean

Abstract Striped marlin (Tetrapturus audax) is an oceanic pelagic migratory fish. The stock status of striped marlin in the Indian Ocean is now considered to be overfished and subject to overfishing. Quantifying the level of at‐haulback mortality caused by longline fisheries for tuna and tuna‐like species is critical to reducing fishing pressure and protecting the fate of billfish stocks. This study was based on data from 2482 longline fishing operations recorded by Chinese observers in the western Indian Ocean from 2012 to 2019. The dataset includes information on the survival status of 774 striped marlin and their corresponding details. We used a generalized linear model (GLM) to analyse the level of at‐haulback mortality and its potential influencing factors. The results indicate that the distribution of 774 striped marlin had a lower jaw‐fork length (LJFL) range from 130 to 220 cm, and 51.5% of the specimens died at the time of haul‐back. The GLM model revealed that quarter, sea‐surface temperature (SST), hook type, LJFL, chlorophyll (CHL) and longitude had significant effects on at‐haulback condition when the fish were retrieved on board, with the quarter and sea surface temperature having the most significant effects. The interaction term between hook type and LJFL also had a significant effect on at‐haulback mortality, with the model predictions showing that mortality increased with LJFL when using circle hooks but decreased when using Japanese tuna hooks. There has been limited observational analysis of hooking mortality rates for striped marlin, and the present study may provide an important reference for the conservation and management of striped marlin stocks in the Indian Ocean.

Spatiotemporal Analysis of Stranded Loggerhead Sea Turtles on the Croatian Adriatic Coast.

This study investigates the spatiotemporal trends of loggerhead turtles along the Croatian Adriatic coast by using stranding data and post-mortem analyses. Information on 620 loggerhead turtles (Caretta caretta), collected in the period between 2010 and 2022, has been analysed. Seasonal stranding variations reveal distinct patterns, indicating season-specific abundance and age-specific mortality in different areas, particularly in the key neritic habitat of the northern Adriatic. The analysis identifies four critical areas in the northeast and central Adriatic showing high stranding densities and provides regional managers with a tool with which to effectively conserve and manage this species. Fishing-induced mortality, collision with vessels, and potential cold stunning are identified as major threats to loggerhead turtles. Post-mortem investigations reveal that longline fishing gear and collisions with vessels are significant age-specific mortality contributors, underscoring the need for targeted conservation efforts in high-risk areas. The study acknowledges potential biases in strandings records but highlights the importance of post-mortem investigations in understanding mortality causes. The findings provide valuable insights for improving conservation strategies, emphasizing the importance of focused surveillance and conservation efforts in identified high-risk locations to mitigate human-turtle interactions.

Abudance of demersal fish by longline fishing gear in Sentang Waters, Serdang Bedagai Regency, Sumatera Utara

Demersal fish is the main catch for traditional fishermen using longline fishing gear in Sentang Beach waters located in Serdang Bedagai Regency, North Sumatra Province. The high economic value of demersal fish is the focus of traditional fishermen to make it the main catch. This study aims to determine the composition of the catch and the abundance index of demersal fish caught by longline in the waters of Sentang Beach. The method used in this research is to use a random sampling method with the mechanism of joining fishermen to go to sea for one month every time fishermen go to sea in November 2022. The data analysis technique uses abundance index value analysis and multiple linear regression analysis. The results showed that the composition of demersal fish caught using longline fishing gear consisted of 5 species of fish namely Snapper (Lates calcarife), Threadfins (Eleutheronema tetradactylum), Pomfret (Pampus argenteus), Sagor catfish (Hexanematichthys sagor) and Mullet (Valamugil saheli) with the highest abundance index obtained by the mullet species. Obtained the highest relative relative abudance of fish found in Senangin species which is 100% and the lowest relative relative abudance of fish in the species of Snapper which is 1.14%.

Monitoring threats to Australian threatened birds: climate change was the biggest threat in 2020 with minimal progress on its management

ABSTRACT Most biodiversity monitoring globally tends to concentrate on trends in species’ populations and ranges rather than on threats and their management. Here we review the estimated impact of threats and the extent to which their management is understood and implemented for all threats to all Australian threatened bird taxa. The assessment reports the situation in 2020 and how this differs from 2010. The most marked finding was that the impact of climate change has increased greatly over the last decade, and now surpasses invasive species as the threat imposing the heaviest threat load. Climate change has driven recent massive population declines from increased temperatures in tropical montane rainforests and from fire. For both direct climate change impacts and fire management, progress in understanding how to relieve the threats has been slow and patchy. Consequently, little effective management has occurred. By comparison, our analysis showed that the single successful campaign to eradicate introduced mammals from Macquarie Island relieved the total threat load on Australian threatened birds by 5%, and more than halved the load on the birds from oceanic islands. Protection or rehabilitation of habitat, particularly on islands, has also delivered measurable benefit as have, in the longer term, controls on longline fishing. Our approach can be used with other taxonomic groups to understand progress in research and management and to allow quantification of potential benefits from proposed actions, such as the national threatened species plan.

НАХОДКИ ЛАМИНАРИЕВЫХ И ДРУГИХ ВОДОРОСЛЕЙ В УЛОВАХ ДОННЫМ ТРАЛОМ И ЯРУСОМ У ЗАПАДНОГО ПОБЕРЕЖЬЯ КАМЧАТКИ В 2018–2023 гг.

Data are provided on findings of marine macroalgae during bottom trawls and longline fishing on the Western Kamchatka shelf in 2018-2023. During the study period, algae were noted at 65 stations in the depth range from 20 to 350 m. Most of the algae findings were found in the Kamchatka-Kuril fishing subzone, within the South Kamchatka Nature Reserve. Among the macrophytes, representatives of the order Laminariales predominated: Agarum pertusum, A. clathratum, Alaria esculenta, Arthrothamnus bifidus, Eualaria fistulosa, Hedophyllum bongardianum, H. dentigerum, Laminaria yezoensis, Laminaria inclinatoriza and Thalassiophyllum clathrus. For southwestern Kamchatka, only 9 out of 13 species of kelp algae indicated in the literature were discovered. Brown algae Fucus distichus, Desmarestia intermedia, red algae – Ptilota asplenioides, Turnerella mertensiana and lamellar green algae – Ulva fenestrata were found sporadically. A comparative analysis of aerial photography data of coastal areas from Cape Sivuchy to Cape Lopatka in 2002 and modern satellite images did not reveal significant changes in the distribution of littoral and sublittoral algae beds. In the coastal line of capes Sivuchy, Kambalny and Maria that we studied, the kelp belt with an average width of 100-130 m reached in the summer of 2018–2023 the total coverage area is 1.92 km2. The use of accompanying data when conducting bottom surveys of commercial invertebrates and fish, longline cod fisheries, together with the analysis of satellite images, allows for an expert assessment of changes in the species composition and distribution of kelp algae, and is also a promising tool for monitoring the state of macrophyte communities in the Far Eastern seas of Russia.