Yellowfin Tuna Fishery Research Articles

Deep learning-based fishing ground prediction for albacore and yellowfin tuna in the Western and Central Pacific Ocean

Tuna is a crucial economic fish species in the ocean, and the research on predicting the location of tuna fishing grounds has always been a key issue in deep-sea fisheries. Tuna, being a highly active fish that moves vertically in the ocean, is extremely sensitive to changes in marine environmental factors. This study aimed to investigate the impact of environmental factors and water depth changes on the accuracy of tuna fishing ground prediction. To achieve this, convolutional neural networks (CNNs) were utilized to train datasets using four key environmental factors - concentration of chlorophyll-a (CHLa), seawater temperature (ST), concentration of dissolved molecular oxygen (Oxy), and seawater salinity (SS) - at various depths ranging from 0 to 300 meters. A binary classification fishing ground prediction model for high and low yield areas of albacore and yellowfin tuna in the Western and Central Pacific Ocean was constructed. The goal was to identify the optimal fishing ground prediction model trained under these conditions and to explore the potential impact of environmental factors and water depth on the prediction accuracy of the model. The data used in this study included information from the Western and Central Pacific Ocean albacore and yellowfin tuna fisheries from 2003 to 2016, along with corresponding environmental data, which were used as the training and validation sets. The fishing data and environmental data from 2017 were then utilized as the test set to develop fishing ground prediction models for the two fish species. The results indicate that using convolutional neural networks to construct fishing ground prediction models is indeed feasible, and spatio-temporal information plays a significant role in optimizing predicting models for tuna fishing ground. Among the models developed for the same fish species using the four marine environmental factors at different depths, the model based on CHLa at each depth was found to be the most effective, while the model constructed using Oxy at the same depth performed the worst. Furthermore, the albacore fishing ground prediction model demonstrated significantly higher efficacy compared to the yellowfin tuna fishing ground prediction model when using the same marine environmental factors. It was also observed that the accuracy of fishing ground prediction models for the same species varied depending on water depth, even when based on the same marine environmental factors. These findings highlight the importance of considering both environmental factors and water depth in predicting tuna fishing grounds accurately.

Multiple lines of evidence highlight the dire straits of yellowfin tuna in the Indian Ocean.

Yellowfin tuna (Thunnus albacares) are highly valued pelagic fisheries target species. Regional fisheries management organizations (RFMOs) are the principal mechanism that manage yellowfin tuna fisheries. Determining changes in population abundances is crucial for effective conservation and management. We use multiple methods for monitoring biomass trends and evaluating the status of yellowfin tuna in each ocean basin and show how additional, multiple lines of evidence can enhance our understanding of the conservation and exploitation status of this species. Our analysis of regional biomass trajectories and Catch-MSY++ assessments corroborate the findings of the most recent RFMO stock assessments suggesting yellowfin tuna in the Indian Ocean are in critical condition, while the Eastern Pacific yellowfin tuna population shows the lowest levels of exploitation. These results are supported by fisheries-independent data from baited remote underwater video systems (BRUVS), showing that the Indian Ocean yellowfin tuna population is the least common, least abundant, and smallest across all oceans. Our findings support previous claims of systematic and widespread overfishing of yellowfin tuna in the Indian Ocean and thus confirm calls to reduce current fishing levels to ensure the long-term viability of the species.

UPAYA MENJAGA KESINAMBUNGAN PERIKANAN TUNA MADIDIHANG DI DESA TULEHU, KABUPATEN MALUKU TENGAH

Yellowfin tuna is the leading prima donna in the capture fisheries sector in Maluku Province with a total national contribution of the two foreign exchange earners. The increase in production volume has not been able to meet the increasing demand for regional and global markets. This has led to an increase in fishing intensity in almost all Indonesian waters. Especially in Maluku. The increasing intensity of fishing causes yellowfin tuna to experience fishing pressure which can result in a decrease in stock size, both individual size and population size. The method used is the delivery of theoretical material and interactive discussions to fishermen. The results of the counseling on efforts to maintain the sustainability of the yellowfin tuna fisheries show that the community understands the importance of the availability of catch data both in the number and size of fish caught. The community must also participate in efforts to limit the number of fish caught because it is a wise thing to provide opportunities for fish to reproduce. This counseling is a very relevant suggestion to the condition of the available yellowfin tuna fishery resources

Preliminary information for the small-scale yellowfin tuna fishery management in Nayarit, Mexico

The small-scale tuna longline fishery operating on the coast of Nayarit started recently in 2013. We provide the first detailed report on some biological parameters for the yellowfin tuna (YFT) in Nayarit (Mexico). We sampled 584 YFT, representing a catch of 25.5 t. We fit the length–weight relationship, used the t-test to determine the type of growth, and estimated the selectivity curve. The total length data varied from 73.0 to 228.0 cm, with a mean of 153.0 ± 23.5 cm (mean ± SD). Weight ranged from 5.8 to 128.0 kg, with a mean of 43.7 ± 19.4 kg. Length–weight fitting results and the t-test suggested negative allometric growth. Selectivity fitting results suggested that selectivity follows an asymptotic pattern. Our results represent the first step into gathering information to establish research and monitoring programs for the YFT on the Pacific coast of Mexico. The information provided in this study could help develop proper regulations to assure a well-managed fishery and the sustainable exploitation of YFT in Nayarit.

Analisis Bioekonomi Perikanan Tuna Sirip Kuning (Thunnus albacares) di Pelabuhan Benoa, Bali

The fisheries sector survived economic, financial, and monetary crises. Tuna fisheries currently face several challenges: decreased productivity, smaller size, and fishing areas that tend to go to the high seas. This study aimed to analyze the biological and economic aspects of yellowfin tuna fishery resources in the landing area of ??Benoa Harbor, Bali. Data is taken from PSDKP, Benoa-Bali, in the form of a time series from 2015 to 2019, which includes information on ship departures, data on fishing or production results, data on efforts, and data on fish species. The data analysis used the Gordon Schaefer model approach to calculate the CPUE, MSY, MEY, and OAE capture effort. The average CPUE value for yellowfin tuna fisheries for 2015-2019 is around 13.0 tons/gear. In MEY conditions, production (h) is 5.593 tons with an effort (E) of 1.082 trips per year. In MSY conditions, production (h) is 5.754 tons per year, and effort (E) is 1.300 trips per year. In OAE conditions, production (h) is 3.207 tons per year, and effort (E) is 2.165 trips per year. The gain obtained in the MEY condition has a more excellent value than in the MSY condition. MEY's profit earned (?) Rp327.101.497.889 per year, and MSY's (?) Rp313.880.136.037 per year.

Data requirements for operating model of harvest strategy for yellowfin tuna fisheries in North Maluku Waters

This Study focused on tuna handline fisheries in Morotai Island, North Maluku. Yellowfin tuna fisheries have great potential economic value. However, the high level of exploitation by small-scale fisheries in coastal waters is feared to disrupt the sustainability of tuna resources therefore, a better management approach is needed, known as a harvest strategy, based on the use of appropriate data and a strong operating model. Indonesia’s government initiated to development of the harvest strategies to manage tuna resources within Indonesia’s archipelagic waters (FMAs 713, 714, dan 715) as a priority action of the National Tuna Management Plan (NTMP). The implementation of the strategy requires adequate data and completeness of instruments. This research tried to identify the adequacy and availability of harvest strategy data and determine yellowfin resource status with LB-SPR. The case studies demonstrate the utility of scientific monitoring data to track trends in the abundance of adult fish without requiring complex stock assessment models through gap analysis. The adequate data harvest strategy was used to condition prototype operating models for testing preliminary harvest strategies through better OMs and MSE. The results showed that the adequacy of the HS data had a gap of 1.56 with an adjustable rate of 63% or not up to standard. The level of utilization of yellowfin tuna resources using the SPR method leads to overfishing.

Ocean Futures for the World’s Largest Yellowfin Tuna Population Under the Combined Effects of Ocean Warming and Acidification

The impacts of climate change are expected to have profound effects on the fisheries of the Pacific Ocean, including its tuna fisheries, the largest globally. This study examined the combined effects of climate change on the yellowfin tuna population using the ecosystem model SEAPODYM. Yellowfin tuna fisheries in the Pacific contribute significantly to the economies and food security of Pacific Island Countries and Territories and Oceania. We use an ensemble of earth climate models to project yellowfin populations under a high greenhouse gas emissions (IPCC RCP8.5) scenario, which includes, the combined effects of a warming ocean, increasing acidification and changing ocean chemistry. Our results suggest that the acidification impact will be smaller in comparison to the ocean warming impact, even in the most extreme ensemble member scenario explored, but will have additional influences on yellowfin tuna population dynamics. An eastward shift in the distribution of yellowfin tuna was observed in the projections in the model ensemble in the absence of explicitly accounting for changes in acidification. The extent of this shift did not substantially differ when the three-acidification induced larval mortality scenarios were included in the ensemble; however, acidification was projected to weaken the magnitude of the increase in abundance in the eastern Pacific. Together with intensive fishing, these potential changes are likely to challenge the global fishing industry as well as the economies and food systems of many small Pacific Island Countries and Territories. The modelling framework applied in this study provides a tool for evaluating such effects and informing policy development.

VULNERABILITY ANALYSIS OF YELLOWFIN TUNA (THUNNUS ALBACARES) BASED ON THE SEA SURFACE TEMPERATURE DYNAMICS

The vulnerability of fisheries to climatic variability can be measured through the capacity of species to adapt to environmental change. It was also analyzed based on the analysis of fish production and susceptibility. Yellowfin tuna is one of the main commodities in the Palabuhanratu fishing port of Indonesia. The condition of yellowfin tuna fisheries needs to be studied due to the vulnerability of existing fishing activities and climate change parameters. This research was conducted at the Palabuhanratu fishing port, Sukabumi, West Java, Indonesia. Productivity and susceptibility analysis was used to determine the value of species vulnerability to fishing activities and based on the climatic variability. This study aims to analyze the vulnerability level of capture fisheries, especially for yellowfin tuna, to the Sea Surface Temperature dynamics through the analysis of productivity and susceptibility. The research will support capture fisheries management based on vulnerability analysis by providing a novel integrated analysis between productivity, susceptibility, and oceanographic data. The result of the productivity score was 2.11, and the susceptibility score was 2.17. It means that yellowfin tuna landed at the Palabuhanratu fishing port was threatened by vulnerability, but yellowfin tuna can recover and survive properly against fishing activities. The vulnerability score of yellowfin tuna was 1.6, which was classified as low vulnerability. The relationship between climate change parameters, namely sea surface temperature, and yellowfin tuna parameter, has a low-medium correlation and has an inverse relationship. Sea surface temperature can affect the development of larvae and eggs and the availability of yellowfin tuna food. By knowing the vulnerability of the yellowfin tuna fishery, sustainable fisheries management can be carried out both based on the regulation of the fishing season and the level of utilization.

Analysis of sizes and state of ovarian maturity in yellowfin tuna (Thunnus albacares) captured in the Gulf of Mexico

The yellowfin tuna Thunnus albacares is the second most important fishery in Mexico, due to its production costs and commercial value” The species is fished on both coast of the country, with the Pacific Ocean presenting productions lightly higher than that of the Gulf of Mexico where, in spite of the above statement, tuna catches have recently shown a downward trend. For this reason, analysis is required of the size and stage of ovarian maturity and it is necessary to determine whether capture size is the primary reason behind the decline in the yellowfin tuna fishery Three tuna fishing trips were conducted in the Gulf of Mexico in order to gather data pertaining to fork length (Lf) and gonads Histological sections were obtained from the latter for analysis and determination of maturity stage. The results showed that males were predominant (40%) among the individuals for which the sex could be differentiated in the catches of T. albacares. The Lf values in the catch, were between 75 and 162 cm. However, variations in this parameter were found between sexes. The relationship between length and weight showed that the males are larger than the females, however, the equationgiven by the parameters of a=0.9406 and b= 3.4504, demonstrated growth of positive allometric type in both sexes. There was progressive development in the state of ovarian maturity over the months of capture. Chromatin nuclear (CN) was the most frequent phase within primary ovarian development (November, February, March), stages were present, although these did not present a direct relationship to fork length.

Status of yellowfin tuna (Thunnus albacares) handlines fisheries based on length of maturity

Yellowfin tuna (Thunnus albacares) is one of large pelagic potential and economical species from the family of Scombridae. Production of yellowfin tuna from several potential fisheries areas (WPP) in Maluku was reported in the condition of overfishing. Meanwhile, tuna fisheries have been the potential resource for export demand. It is therefore, the status of yellowfin tuna fisheries should be monitored regularly following the regulation of PERMEN KP no 4 year 2017. The aims of this study were to measure the size of maturity of yellowfin tuna during October to December 2018 and utilize the empirical relationship to estimate optimum length and maximum length reached during this period. Observation on yellowfin tuna was conducted by joining local fishers from Kawa village, West Seram Regency. Handlines were occupied to catch yellowfin tuna around Banda Sea. From the catch sizes ranged from was 34cm to 168cm, the length maturity (Lm) of yellowfin tuna is 107.2cm of total length for female and 112.9cm for male. From the empirical relationship, the optimum length (Lopt) of yellowfin tuna during October-December 2018 was 120.5cm and maximum length (Lmax) was 181.4cm. This study showed that 90% of yellowfin catch was immature which indicated a recruitment overfishing. Only 2.4% of mega-spawners were caught during this study and indicated growth overfishing. Indication of an overfishing of the yellowfin tuna fishery contradicted to larger size of first maturity found. This contrary is discussed and balance fishing strategy is proposed as the idea to maintain the population of yellowfin tuna.

Shifting demand to sustainable fishing practices in Darwin's Archipelago: a discrete choice experiment application for Galapagos' certified Yellow-fin tuna

In spite of several policies to promote fisheries management in the Galapagos Marine Reserve (GMR), in the past there has been a collapse or near collapse of the two most important fisheries: the sea cucumber and the lobster fishery respectively. Currently, there is particular concern for the Galapagos Sailfin Grouper (Mycteroperca olfax), a regionally endemic species showing signs of severe decline and targeted by the white-fin fishery, a multi-species coastal fishery of high market value. Within this context, the Galapagos National Park Directorate (GNPD) and local NGOs have designed a policy consistent in a product certification scheme aiming to shift fishing efforts from depleted coastal fisheries to healthier pelagic stocks, whilst supporting artisanal fisher’s livelihoods. Using a discrete choice experiment and accompanying survey data, the goal of this research is to analyze the preferences and tradeoffs made by individuals across attributes when purchasing certified fish in the Galapagos. In particular, we account for pro-environmental attitudes within a WTP space model specification and estimate the expected price premiums that tourists would be willing to pay for yellowfin tuna in the area in light of specific characteristics of its local value chain. We find that tourists visiting the Galapagos hold pro environmental attitudes as measured by the New-ecological paradigm and that there is a considerable increase in consumer’s utility from a certification scheme. Tourists care about the level of bycatch associated with their consumption, food safety, quality, and whether is locally sourced, and would be willing to pay for these attributes. This evidence, driven by location specific characteristics of consumers and tourists, supports the design of market-based mechanisms for sustainable yellow fin tuna fisheries in the Galapagos

Understanding fishery interactions and stock trajectory of yellowfin tuna exploited by Iranian fisheries in the Sea of Oman

Abstract The predominant policy for remedying the world fishing crisis aims at maximum sustainable yield (MSY) by adjusting gear selectivity and fishing effort to maintain sustainable stock levels. The yellowfin tuna (Thunnus albacares) fishery in the Sea of Oman has experienced intense increases in removals since 1980, with particularly high levels since the 1990s. Here, we apply a statistical catch-at-age model to time-series of catches and fishery-dependent length composition data to obtain a preliminary and general understanding of the population dynamics of this stock since the start of the fishery in 1950–2019. Despite limited data, population models consistently indicate a sharp decline in population status since the beginning of the time-series across a variety of assumptions on stock productivity and life history. The gillnet fishery takes almost exclusively immature individuals, with high fishing intensity and removal rates. Both reference models indicate the population is essentially at the same relative stock status in 2019 (10% of unfished), but with very different future projections and higher absolute stock size when recruitment is estimated. The yellowfin tuna population in 2019 is below estimated MSY reference points (based either on unfished size or spawning output at MSY) for current relative stock size, and over the fishing intensity at MSY, indicating current overfishing. Adjusting the interactions of that fishery with the population, while continuing to collected biological composition data representative of each fleet in the fishery, will help mitigate current stock decline and provide the ability to refine future population status determination and forecasts through more informed stock assessments.

A tale of two standards: A case study of the Fair Trade USA certified Maluku handline yellowfin tuna (Thunnus albacares) fishery

Fishery certification programs and ecolabels have emerged to promote fisheries and seafood sustainability. The Marine Stewardship Council (MSC) certification program is considered the largest, most recognized seafood certification program, yet has been criticized for its lack of accessibility to small-scale fisheries in developing countries and its purely ecological focus. New to the seafood industry, and in part filling the accessibility and social sustainability gap, is Fair Trade USA's (FTUSA) Capture Fisheries Program. Sixty percent of internationally-traded seafood products originate from developing regions of the world, so it is imperative to gain an understanding of how to best utilize seafood certifications in developing countries to promote ecological, economic, and social sustainability. This research focused on Maluku, Indonesia, which has a FT Certified™ handline yellowfin tuna fishery and is also working towards achieving wide-scale MSC certification across tuna fisheries, to understand the role of FTUSA in relation to MSC. The relevance and appropriateness of both the FTUSA and MSC standards in relation to the FAO Voluntary Guidelines for Securing Sustainable Small-Scale Fisheries was assessed, and focus groups and interviews with key informants were conducted. Results from this study suggest that FTUSA better aligns with the FAO Guidelines, delivers benefits more quickly to fishing communities, and seems to rely less on national level requirements. There is therefore merit in FTUSA standing alone as a credible certification for developing world small-scale fisheries, as opposed to being used as a kind of fisheries improvement project towards MSC, as some currently view it.

Mitogenomic differentiation in spinner (Stenella longirostris) and pantropical spotted dolphins (S. attenuata) from the eastern tropical Pacific Ocean

AbstractSpinner dolphins (Stenella longirostris) and pantropical spotted dolphins (S. attenuata) show high intraspecific morphological diversity and endemic subspecies in the eastern tropical Pacific Ocean (ETP). Previous studies of mitochondrial DNA have found low genetic differentiation among most of these groups, possibly due to demographic factors, ongoing gene flow, and/or recent divergence. These species were heavily depleted due to bycatch in the ETP yellowfin tuna fishery. Because understanding population structure is important for accurate management of the recovery of these species, we collected whole mitochondrial genome sequences from 104 spinner and 76 spotted dolphins to test structure hypotheses at multiple hierarchical taxonomic levels. Results show differences between subspecies of spinner and spotted dolphins, but no support for the division of existing offshore stocks of spotted dolphins. We compare these results to previous results of genome‐wide nuclear SNP data and suggest high haplotype diversity, female dispersal, and/or relative power of the two data sets explains the differences observed. Interestingly, increasing the amount of mitochondrial data (base pairs and genes) did not increase ability to delimit population units. This study supports a genetic basis for management units at the subspecies level, and provides critical information for mitigating historical and continued fisheries impacts.

Genomic analysis reveals multiple mismatches between biological and management units in yellowfin tuna (Thunnus albacares)

AbstractThe South African (SAF) yellowfin tuna (Thunnus albacares) fishery represents a potential example of misalignment between management units and biological processes. The SAF fishery spans an operational stock with a boundary at 20°E, either side of which fish are considered part of Atlantic or Indian Ocean regional stocks. However, the actual recruitment of fish from Atlantic and Indian Ocean spawning populations into SAF waters is unknown. To address this knowledge gap, genomic analysis (11 101 SNPs) was performed on samples from Atlantic and Indian Ocean spawning sites, including SAF sites spanning the current stock boundary. Outlier loci conferred high discriminatory power to assignment tests and revealed that all SAF fish were assigned to the Indian Ocean population and that no Atlantic Ocean fish appeared in the SAF samples. Additionally, several Indian Ocean migrants were detected at the Atlantic spawning site demonstrating asymmetric dispersal and the occurrence of a mixed-stock fishery in Atlantic waters. This study highlights both the spatial inaccuracy of current stock designations and a misunderstanding of interactions between the underlying biological units, which must be addressed in light of local and global declines of the species. Specifically, the entire SAF fishery must be managed as part of the Indian Ocean stock.

Evaluating effectiveness of biological reference points for bigeye tuna (Thunnus obesus) and yellowfin tuna (Thunnus albacares) fisheries in the Indian Ocean

Biological reference point (BRP) is one of the essential components in the management strategy evaluation that is used to determine the status of fishery stock and set management regulations. However, as BRPs can be derived from different models and many different BRPs are available, the effectiveness and consistency of different BRPs should be evaluated before being applied to fisheries management. In this study, we used a computation-intensive approach to identify optimal BRPs. We systematically evaluated 1500 combinations of alternative BRPs in managing the bigeye tuna (Thunnus obesus) and yellowfin tuna (Thunnus albacares) fisheries in the Indian Ocean. The effectiveness and consistency of these BRPs were evaluated using four performance measures related to fisheries landing performance and biomass conservation. Monte Carlo simulation was used to evaluate various uncertainties. The results suggest that the proposed computation-intensive approach can be effective in identifying optimal BRPs with respect to a set of defined performance measures. We found that the current maximum sustainable yield (MSY)-based BRP combinations are effective target BRPs to manage the bigeye and yellowfin tuna fisheries with the “linear” harvest control rule (HCR). However, using the “knife-edge” HCR, better BRPs could be found for both the bigeye and yellowfin tuna fisheries management with improved fisheries and conservation performance. The framework developed in this study can be used to identify suitable BRPs based on a set of defined performance measures for other fisheries.

Adaptive responses of tropical tuna purse-seiners under temporal regulations.

The failure to achieve fisheries management objectives has been broadly discussed in international meetings. Measuring the effects of fishery regulations is difficult due to the lack of detailed information. The yellowfin tuna fishery in the eastern Pacific Ocean offers an opportunity to evaluate the fishers' responses to temporal regulations. We used data from observers on-board Mexican purse-seine fleet, which is the main fleet fishing on dolphin-associated tuna schools. In 2002, the Inter-American Tropical Tuna Commission implemented a closed season to reduce fishing effort for this fishery. For the period 1992-2008, we analysed three fishery indicators using generalized estimating equations to evaluate the fishers' response to the closure. We found that purse-seiners decreased their time spent in port, increased their fishing sets, and maintained their proportion of successful fishing sets. Our results highlight the relevance of accounting for the fisher behaviour to understand fisheries dynamics when establishing management regulations.

Influence of Climatic Conditions on the Time Series Fluctuation of Yellowfin Tuna <i>Thunnus albacares</i> in the South Pacific Ocean

Yellowfin tuna (Thunnus albacares) is one of the most commercially important fish species for South Pacific island nations and territories and for effective conservation efforts it is important to understand the factors which affect its time series pattern. Our research was aimed at elucidating the climatic factors which affected the trajectory of the yellowfin tuna stock in the Eastern and Western South Pacific Ocean. We utilized various climatic factors for the years t - n with n = 0, 1, ..., 8 and investigated their statistical relationship with the catch per unit effort (CPUE) of yellowfin tuna stock from 1957-2008 for three South Pacific zones ranging from the East to the West Pacific Ocean within the coverage area of the Western and Central Pacific Convention Area. Results showed that the climatic conditions of: (i) the global mean land and ocean temperature index (LOTI), (ii) the Pacific warm pool index (PWI) and (iii) Southern Oscillation Index (SOI) had significant relationship with the CPUE of yellowfin tuna in all three zones. LOTI, PWI and SOI were used as independent variables and fitted through modeling to replicate the CPUE trajectory of the yellowfin tuna in Zone 1, Zone 2 and Zone 3. Model selection was based on significant parameter estimates (p < 0.05), Akaikes Information Criterion (AIC) and R2 values. Models selected for all three zones had LOTI, PWI and SOI as the independent variables. This study shows that LOTI, PWI and SOI are climatic conditions which have significant impact on the fluctuation pattern of the yellowfin tuna CPUE in the Eastern and Western South Pacific Ocean. From the findings of this study it can be recommended that when management decisions are made for yellowfin tuna fishery conservation and sustainability in the Eastern and Western South Pacific, it is imperative to take the effect of climatic factors into account.

Evaluating harvest control rules for bigeye tuna (Thunnus obesus) and yellowfin tuna (Thunnus albacares) fisheries in the Indian Ocean

Bigeye tuna (Thunnus obesus) and yellowfin tuna (Thunnus albacares) support two of the most important fisheries in the Indian Ocean. However, there is little research evaluating harvest control rules (HCRs) for their management. In this study we evaluated four HCRs, ‘knife-edged’, ‘linear’, ‘convex’, and ‘concave’, for these two species. These four HCRs defined management rules for how annual fishing mortality should be adjusted based on perceived stock status. Fishing mortality was adjusted linearly, convexly and concavely for the ‘linear’, ‘convex’, and ‘concave’ HCRs, respectively when the current spawning stock biomass (SSB) was between the limit and target SSB-based biological reference points (BRPs). Two age-structured operating models were developed to simulate fisheries managed under these HCRs for a 25-year management period. Implementation and process errors, and uncertainties in key fisheries parameters were considered as sources of uncertainty in this study. All four HCRs were found to be effective in driving both stocks to the status defined by maximum sustainable yield-based BRPs. The ‘knife-edged’ HCR, which has constant fishing mortality but switches fishing mortality to 0 when stock biomass is below the limit SSB-based BRP, led to relatively poor performance. Our results indicate that a simulation study is needed to evaluate the performance of BRPs and HCRs in managing bigeye tuna and yellowfin tuna fisheries in the Indian Ocean.

Towards better management of Coral Triangle tuna

Indonesia, the Philippines, and Papua New Guinea, all part of a regional sub-group known as the Coral Triangle, have sizeable skipjack, yellowfin and bigeye tuna fisheries. Recent figures suggest that as much as a third of tuna catch from the western and central Pacific Ocean can be attributed to the fleets of these countries. Historically, however, little attention has been paid to their fisheries and their regulations. Management of tuna fisheries in Indonesia and the Philippines faces many challenges, including bycatch of juveniles, lack of effective gear restrictions, subsidized fleets, and unreported catches. Papua New Guinea has countered the challenges of tuna management with several effective measures, including implementing the vessel day scheme, a type of effort quota system, and limiting the use of fish aggregating devices (FADs). This paper compares and contrasts tuna fisheries in the three countries, as well as their management regimes and current management challenges. By highlighting some of the successes that Papua New Guinea has had, we hope that Indonesia and the Philippines may be able to more effectively manage their fleets and their fish. And this in turn may lead to better regional management of a valuable transboundary resource.