Western And Central Pacific Ocean Research Articles

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.

The Environmental Niche of the Tuna Purse Seine Fleet in the Western and Central Pacific Ocean Based on Different Fisheries Data

Understanding the spatial pattern of human fishing activity is very important for fisheries resource monitoring and spatial management. The environmental preferences of tropical tuna purse seine fleet in the Western and Central Pacific Ocean (WCPO) were constructed and compared at different spatial scales based on the fishing effort (FE) data from the available automatic identification system (AIS) and commercial fishery data compiled from the Western and Central Pacific Fisheries Commission (WCPFC), using maximum entropy (MaxEnt) methods. The MaxEnt models were fitted with FE and commercial fishery data and remote sensing environmental data. Our results showed that the area under the curve (AUC) value each month based on the commercial fishery data (1°) and FE at 0.25° and 0.5° spatial scales was greater than 0.8. The AUC values each month based on the FE data at a 1° scale ranged from 0.775 to 0.829. The AUC values based on commercial fishing data at the 1° scale were comparable to the model results based on FE data at the 0.5° scale and inferior to the model results based on FE data at the 0.25° scales. Overall, the sea surface temperature (SST), temperature at 100 metres (T100), oxygen concentration at 100 metres (O100) and total primary production (PP) had the greatest influence on the distribution of the purse seine tuna fleet. The oxygen concentration at 200 metres (O200), distance to shore (DSH), dissolved oxygen (Dox), EKE, mixed layer depth (Mld), sea surface salinity (SSS), salinity at 100 metres (S100) and salinity at 200 metres (S200) had moderate influences, and other environmental variables had little influence. The suitable habitat areas varied in response to environmental conditions. The purse seine tuna fleet was mostly present at locations where the SST, T100, O100, O200 and PP were 28–30 °C, 27–29 °C, 150–200 mmol/m3 and 5–10 mg/m−3, respectively. The MaxEnt models enable the integration of AIS data and high-resolution environmental data from satellite remote sensing to describe the spatiotemporal distribution of the tuna purse seine fishery and the influence of environmental variables on the distribution, and can provide forecasts for fishing ground distributions based on future remote sensing environmental data.

Reproductive Biology of Yellowfin Tuna (Thunnus albacares) in Tropical Western and Central Pacific Ocean

A total of 756 yellowfin tuna (Thunnus albacares) caught by a Chinese drifting longliner in the tropical western and central Pacific Ocean (WCPO) from May 2018 to March 2019 were investigated to describe the reproductive biology of the species. Generalized linear model and polytomous logistic regression for the ordinal response model were employed to assess the effects of biometric and spatiotemporal factors (such as individual fork length (FL), fishing depth, dissolved oxygen, and month) on the reproductive traits of yellowfin tuna. The results showed that FLs ranged from 87 to 163 cm, averaging 115.8 cm (SD = ±14.2) for females and 121.8 cm (SD = ±16.8) for males. The proportion of males in the sampled fish was 0.61 (SD = ±0.29), and larger males (>130 cm) were proportionally predominant. Analyses based on the monthly variation of the gonadosomatic index and monthly proportion of sexual maturity stages of the gonads showed that the main spawning period of yellowfin tuna lasts from September to December. In addition, the 50% first maturity FLs of males and females were 111.96 cm (SD = ±1.04) and 119.64 cm (SD = ±1.30), respectively. This study provides new information on the reproductive development of T. albacares in the tropical WCPO region. These reproductive parameters reduce uncertainty in current stock assessment models, which will ultimately assist the fishery in becoming sustainable for future generations.

AMPLE: An R package for capacity building on fisheries harvest strategies.

Fisheries harvest strategies are formal frameworks that represent a best-practice approach for sustainable fisheries management. A key component of a harvest strategy is a 'pre-agreed rule', known as a harvest control rule (HCR), that sets fishing opportunities, e.g. catch limits, based on an estimate of fish stock status, e.g. estimated stock biomass. The harvest strategy development process is driven by stakeholders who are required to make a range of informed decisions, including on the selection of the preferred HCR. Capacity building may be required to facilitate the stakeholder engagement, particularly regarding the technical components of harvest strategies, including HCRs. The AMPLE package for R provides three interactive apps that support capacity building and stakeholder engagement on HCRs. These apps have been used during in-country national workshops around the western and central Pacific Ocean (WCPO) to support the development of harvest strategies for the Western and Central Pacific Fisheries Commission. These apps include several novel features: they take users from a gentle introduction to how HCRs work, to using methods for testing, comparing and selecting a preferred HCR from a suite of candidates. They include an introduction to the impact of uncertainty on the performance of an HCR, introduce performance indicators and discuss methods for selecting the preferred HCR based on management objectives. As such they provide a more detailed overview of HCRs than currently existing alternatives. These apps provide an effective platform for hands-on learning and have proven to be successful at supporting capacity building on HCRs in the WCPO. For example, using them for group activities and competitions stimulated productive discussions and increased understanding. As the model fishery in AMPLE is generic and not based on a real example, the apps will also be of interest to scientists, managers and stakeholders developing harvest strategies in other regions.

No Population Structure of Bigeye Tunas (Thunnus obesus) in the Western and Central Pacific Ocean Indicated by Single Nucleotide Polymorphisms

The current management of the bigeye tuna (Thunnus obesus) fishery in the Western and Central Pacific Ocean (WCPO) is based on a “single-stock” paradigm. We investigated the spatial and temporal distribution of the neutral and potentially adaptive genetic diversity in samples collected from waters near Micronesia, Marshall, Phoenix and Gilbert Islands and French Polynesia using genotyping by sequence and single nucleotide polymorphisms (SNP). Analysis of 144 individuals and 2,682 SNP did not provide any substantial evidence to challenge the current assumption of panmixia in the WCPO using putatively neutral loci. However, there was a signal of potentially adaptive divergence (FST range 0.11–0.24) of samples collected in 2013 in the exclusive economic zone of the Phoenix Islands, possibly because of exposure to differing selective constraints. The geographic origin of these tuna remains to be determined, as the samples originate from tagging cruises that sample large schools of tuna, and some of those tuna have subsequently showed substantial movement. We highly recommend further studies involving large sample sizes of larvae and young-of-the-year across the region and over multiple years to uncover the underlying processes that are potentially driving adaptive divergence and to infer any biological significance it may have on conservation and management of tropical bigeye tuna fishery stock.

Tuna is women's business too: Applying a gender lens to four cases in the Western and Central Pacific

AbstractThe USD6 billion Western and Central Pacific Ocean (WCPO) tuna fisheries produce over half the world's tuna and are important for coastal countries. Tuna fisheries policy, management and research currently focus on fisheries resources and industrial fishing on offshore vessels with all male crews, although women, as much as men, are employed in tuna processing and trading in domestic, informal and export value chains. We apply a gender lens to four WCPO case‐study tuna industries: Suva and Levuka in Fiji, Bitung in Indonesia, General Santos City in the Philippines and Western Province including Noro in Solomon Islands. The gender divisions of labour, livelihood opportunities and social impacts vary greatly across the value chain nodes, depending on the size, quantity and quality of fish handled, and the scale of operations. The gender lens also reveals the social impacts of fishing when husbands/fathers/sons are killed or injured, absent for long periods and engage in sex, drugs and alcohol behaviours in port. Despite the centrality of women in tuna industries, and the gendered social impacts, regional and national policies largely omit gender. The tuna discourse should be broadened from that of male‐dominated industrial fishing to whole of value chains including domestic and informal enterprises in which women are equally involved. Progress on gender equity needs collaboration by multiple stakeholders including industrial firms employing people in factories, offices and on fishing vessels, regional bodies and national governments responsible for policy, monitoring and regulation, and research agencies to build knowledge.

Fishing trip cost modeling using generalized linear model and machine learning methods - A case study with longline fisheries in the Pacific and an application in Regulatory Impact Analysis.

Fishing trip cost is an important element in evaluating economic performance of fisheries, assessing economic effects from fisheries management alternatives, and serving as input for ecosystem and bioeconomic modeling. However, many fisheries have limited trip-level data due to low observer coverage. This article introduces a generalized linear model (GLM) utilizing machine learning (ML) techniques to develop a modeling approach to estimate the functional forms and predict the fishing trip costs of unsampled trips. GLM with Lasso regularization and ML cross-validation of model are done simultaneously for predictor selection and evaluation of the predictive power of a model. This modeling approach is applied to estimate the trip-level fishing costs using the empirical sampled trip costs and the associated trip-level fishing operational data and vessel characteristics in the Hawaii and American Samoa longline fisheries. Using this approach to build models is particularly important when there is no strong theoretical guideline on predictor selection. Also, the modeling approach addresses the issue of skewed trip cost data and provides predictive power measurement, compared with the previous modeling efforts in trip cost estimation for the Hawaii longline fishery. As a result, fishing trip costs for all trips in the fishery can be estimated. Lastly, this study applies the estimated trip cost model to conduct an empirical analysis to evaluate the impacts on trip costs due to spatial regulations in the Hawaii longline fishery. The results show that closing the Western and Central Pacific Ocean (WCPO) could induce an average 14% increase in fishing trip costs, while the trip cost impacts of the Eastern Pacific Ocean (EPO) closures could be lower.

Virtual Regional Fisheries Management Meetings in the Western and Central Pacific Ocean Region: A Preliminary Appraisal of Performance and Fit

Regional fisheries meetings that support the management of Western and Central Pacific Ocean (WCPO) capture fisheries are usually held face-to-face and in-person. In 2020, the travel and gathering bans due to the global COVID-19 pandemic meant that these meetings were held “virtually,” primarily via videoconferencing. But can virtual meetings perform the same functions and deliver the same management outcomes as face-to-face meetings? This study is an initial investigation of the experiences, perceptions and attitudes of WCPO region government participants in a number of virtual regional fisheries meetings in 2020. Results indicate a strong preference for face-to-face regional meetings, with the perception that virtual meetings performed comparatively poorly at supporting a number of key meeting processes and outcomes. However, one-quarter to one-third of study participants consistently found no difference between format performance for many meeting processes and outcomes. Virtual formats were considered more appropriate for smaller and non-regional meetings, and allowed for greater staff attendance at meetings as well as cost and time savings for some, but not all, participants. Study participants believe that virtual regional meetings will be more common in the region in the future, despite nearly half indicating that virtual meeting are not a good fit for the region generally. Many of these experiences and perceptions are consistent with organizational behavior, communications media, and information systems literature. Some results appear unique to the region’s socially and culturally diverse Pacific island countries and territories, which are relative newcomers to the global information and communication technology “revolution.” A greater use of virtual regional fisheries meetings in the future requires meeting hosts and facilitators to carefully consider the potential impacts of virtual meetings on effective communication and inclusive participation in WCPO regional fisheries management and other governance outcomes.

Quantifying drifting Fish Aggregating Device use by the world's largest tuna fishery

Abstract Drifting Fish Aggregating Devices (dFADs) are a major fishing mode for tropical tuna purse seine fisheries worldwide. However, the extent of dFAD use remains poorly understood. We present novel approaches for estimating annual dFAD deployments and number of dFADs monitored by individual vessels, using empirical data and robust estimation procedures. We leveraged observer and logbook data, combined with new dFAD tracking data from the Western and Central Pacific Ocean (WCPO) purse seine fishery, the largest tuna fishery in the world, to evaluate trends in dFAD use across the entire WCPO between 2011 and 2019. Average estimates ranged between 20 000 and 40 000 deployments per year, depending on the methodology, with the total number of deployments appearing relatively stable over the last decade. The median number of active buoys monitored per vessel per day ranged from 45 to 75 depending on the year, well below the current management limit of 350. Our results contrast with other oceans, having fewer buoys monitored per vessel, a unique stable trend, but overall number of deployments two times higher than any other ocean. This study provides a basis for improved monitoring and management of dFAD use in the WCPO, with applicability for other regions.

Effects of Climate Change in Marine Ecosystems Based on the Spatiotemporal Age Structure of Top Predators: A Case Study of Bigeye Tuna in the Pacific Ocean

How top predators behave and are distributed depend on the conditions in their marine ecosystem through bottom−up forcing; this is because where and when these predators can feed and spawn are limited and change often. This study investigated how the catch rates of immature and mature cohorts of bigeye tuna (BET) varied across space and time; this was achieved by analyzing data on the Taiwanese longline fishery in the western and central Pacific Ocean (WCPO). We also conducted a case study on the time series patterns of BET cohorts to explore the processes that underlie the bottom-up control of the pelagic ecosystem that are influenced by decadal climate events. Wavelet analysis results revealed crucial synchronous shifts in the connection between the pelagic ecosystems at low trophic levels in relation to the immature BET cohort. Many variables exhibited decreasing trends after 2004–2005, and we followed the Pacific Decadal Oscillation (PDO) as a bottom-up control regulator. The results indicated that low recruitment into the mature cohort occurs 3 years after a decrease in the immature cohort’s food stocks, as indicated by a 3-year lag in our results. This finding demonstrated that, by exploring the connection between low-trophic-level species and top predators at various life stages, we can better understand how climate change affects the distribution and abundance of predator fish.

Predicting Skipjack Tuna Fishing Grounds in the Western and Central Pacific Ocean Based on High-Spatial-Temporal-Resolution Satellite Data

Skipjack tuna are the most abundant commercial species in Taiwan’s pelagic purse seine fisheries. However, the rapidly changing marine environment increases the challenge of locating target fish in the vast ocean. The aim of this study was to identify the potential fishing grounds of skipjack tuna in the Western and Central Pacific Ocean (WCPO). The fishing grounds of skipjack tuna were simulated using the habitat suitability index (HSI) on the basis of global fishing activities and remote sensing data from 2012 to 2015. The selected environmental factors included sea surface temperature and front, sea surface height, sea surface salinity, mixed layer depth, chlorophyll a concentration, and finite-size Lyapunov exponents. The final input factors were selected according to their percentage contribution to the total efforts. Overall, 68.3% of global datasets and 35.7% of Taiwanese logbooks’ fishing spots were recorded within 5 km of suitable habitat in the daily field. Moreover, 94.9% and 79.6% of global and Taiwan data, respectively, were identified within 50 km of suitable habitat. Our results showed that the model performed well in fitting daily forecast and actual fishing position data. Further, results from this study could benefit habitat monitoring and contribute to managing sustainable fisheries for skipjack tuna by providing wide spatial coverage information on habitat variation.

Managing Bigeye Tuna in the Western and Central Pacific Ocean

The Western and Central Pacific Fisheries Commission (WCPFC) is responsible for managing highly migratory species in the Western and Central Pacific Ocean (WCPO), and has been interested in managing bigeye tuna as stock assessments prior to 2017 indicated that the stock was experiencing overfishing. This paper provides some background on the primary fisheries catching bigeye tuna in the WCPO, describes the various policies within the conservation and management measures adopted by the WCPFC, discusses the effectiveness of such policies, and concludes with some suggestions for future policies for consideration.

Tuna trade‐offs: Balancing profit and social benefits in one of the world’s largest fisheries

AbstractThe western and central Pacific Ocean (WCPO) tuna fishery is one of the world's largest in terms of both catch volume and value, providing over half of global tuna catch with a landed value of US $5.84 billion in 2017. Fishing is conducted by both large‐ and small‐scale fleets, with fisheries subsidies disproportionately benefiting the former. The primary objective of this study was to determine the optimal distribution of effort between two large‐scale fisheries (LSF) and two small‐scale fisheries (SSF) in the WCPO under three scenarios: to maximize industry benefits, minimize subsidization or maximize food supply. The objective was approached using a bioeconomic game‐theoretic model. Results indicate opposite distributions of effort to maximize industry benefits (all fishing conducted by LSF) or to minimize subsidization (all fishing by SSF), with more balanced effort distributions to maximize food supply. Total value of capacity‐enhancing subsidies in optimal scenarios ranged from $1.4 billion when industry benefits were maximized to $0.2 billion when subsidization was minimized. Investigation of suboptimal scenarios reveals the flexibility of these results, with wide ranges in outputted state variables for a given goal. Difficulty was encountered in modelling the SSF sector due to data deficiencies, a well‐recognized issue in managing SSF. Investments towards “data equity” to help ensure that management decision‐making can properly account for the SSF sector would be useful. This study has implications for the objectives we set in fisheries management, and the potential trade‐offs, often value‐driven in nature, that we must make explicit in that management.

Biology and Environmental Preferences of Wahoo, Acanthocybium solandri (Cuvier, 1832), in the Western and Central Pacific Ocean (WCPO)

Wahoo Acanthocybium solandri is a common bycatch pelagic species in oceanic fisheries targeting tuna and tuna-like species. Biology and environmental preferences are important parameters in understanding life history of fish species including wahoo. Despite the socio-economic importance of wahoo in many coastal countries, little is known about their biological and fisheries information in the Western and Central Pacific Ocean (WCPO). These parameters were analyzed on the basis of samples collected via the Chinese tuna long-line Fishery Observer Programme in 2012. Results obtained from this study show that the fork length (FL) of wahoo ranged from 59 to 169 cm with an average of 111.3 cm, and two dominant size groups were identified at 100 to 130 cm for males and 90 to 130 cm for females. Body size did not significantly differ between female and male wahoo specimens. Wahoo specimens expressed a positive allometric growth (b = 3.183), and the sex ratio was 1.9:1 (female/male), which differed significantly between both sexes. Only female wahoo were observed in catches of FL > 150 cm. The estimated lengths at 50% maturity (FL50) of female and male wahoo were 84 cm and 83 cm, respectively. Gonadosomatic index (GSI) of wahoo was at its peak in November, and on the basis of the stomach content analysis, wahoo mainly preyed on fish (84.64%), cephalopods (14.26%), and crustaceans (1.1%), found on the basis of prey number. The optimal swimming depth and water temperature of wahoo in the WCPO were found to range between 70 and 110 m and 23.1 and 24 °C, respectively. The updated life history information presented in this work helps to address current data limitations and provides critical information for future assessments of wahoo stocks in the WCPO.

Environmental versus operational drivers of drifting FAD beaching in the Western and Central Pacific Ocean

In an effort to increase purse seine fishing efficiency for tropical tunas, over 30,000 drifting Fish Aggregating Devices (dFADs) are deployed every year by fishers in the Western and Central Pacific Ocean (WCPO). The use of dFADs also impacts ecosystems, in particular through marine pollution and dFAD beaching. This paper presents the first estimate of dFAD beaching events in the WCPO (>1300 in 2016–2017) and their distribution. Lagrangian simulations of virtual dFADs, released subject to contrasting deployment distributions, help us determine the relative importance of operational versus environmental drivers of dFADs drifting to beaching areas. The highest levels of beaching, occurring on Papua New Guinea and Solomon Islands, are likely a result of the prevailing westward oceanic circulation and subsequent local processes driving dFADs towards land. Similarly, high beaching rates in Tuvalu appear to be due to the general circulation of the WCPO. In contrast, beaching in Kiribati Gilbert Islands appear to be more strongly related to dFAD deployment strategy. These findings indicate that reducing beaching events via changes in deployment locations may be difficult. As such, management approaches combining dFAD deployment limits, the use of biodegradable dFADs, recoveries at-sea close to sensitive areas and/or beached dFAD removal should be considered.

RETRACTED: Close Kin Proximity in Yellowfin Tuna (Thunnus albacares) as a Driver of Population Genetic Structure in the Tropical Western and Central Pacific Ocean

Recent studies argue for the presence of genetic population structure in yellowfin tuna (Thunnus albacares) in all oceans. However, the persistence of family groups has never been considered a viable mechanism of structure, nor has it been measured. We analyzed genetic similarity among 280 yellowfin tunas from seven population samples collected in the Western and Central Pacific Ocean (WCPO) using single nucleotide polymorphisms, and found population structure that was significantly explained by the presence of 96 individuals involved in 332 half or full sib dyads. We found significantly higher mean and median relatedness between individuals from the same sample groups, compared to individuals from different groups; and high relatedness between individuals caught at the same fish-aggregating device (FAD) than between those caught in the wider exclusive economic zone (EEZ). Alternatively, the EEZ of the Federated States of Micronesia may harbor exceptionally large numbers of close kin. We conclude that yellowfin directly school with related individuals through their first year, and at least demonstrate tightly overlapping regional fidelity as adults. These results may explain, to some extent, the patterns of population genetic structure recently observed in yellowfin tuna.

A Model of Mercury Distribution in Tuna from the Western and Central Pacific Ocean: Influence of Physiology, Ecology and Environmental Factors.

Information on ocean scale drivers of methylmercury levels and variability in tuna is scarce, yet crucial in the context of anthropogenic mercury (Hg) inputs and potential threats to human health. Here we assess Hg concentrations in three commercial tuna species (bigeye, yellowfin, and albacore, n = 1000) from the Western and Central Pacific Ocean (WCPO). Models were developed to map regional Hg variance and understand the main drivers. Mercury concentrations are enriched in southern latitudes (10°S-20°S) relative to the equator (0°-10°S) for each species, with bigeye exhibiting the strongest spatial gradients. Fish size is the primary factor explaining Hg variance but physical oceanography also contributes, with higher Hg concentrations in regions exhibiting deeper thermoclines. Tuna trophic position and oceanic primary productivity were of weaker importance. Predictive models perform well in the Central Equatorial Pacific and Hawaii, but underestimate Hg concentrations in the Eastern Pacific. A literature review from the global ocean indicates that size tends to govern tuna Hg concentrations, however regional information on vertical habitats, methylmercury production, and/or Hg inputs are needed to understand Hg distribution at a broader scale. Finally, this study establishes a geographical context of Hg levels to weigh the risks and benefits of tuna consumption in the WCPO.

Management of Tuna Fisheries for Sustainable Development in the Pacific Islands

Cooperation by Pacific Island countries in the management of tuna fisheries is an important means of achieving sustainable development of these shared resources, in line with Sustainable Development Goal 14. The Western and Central Pacific Ocean (WCPO) tuna fishery is the largest tuna fishery in the world and two examples of arrangements based on regional cooperation are provided: • The purse seine Vessel Day Scheme (VDS) is a fisheries management system that is being implemented through the cooperation of the Parties to the Nauru Agreement (PNA), which regulates harvesting of tuna in line with SDG 14.4. The scheme also establishes rights in the shared fishery for small island developing states, increasing economic returns in support of SDG 14.7. • Regional cooperation in fisheries Monitoring Control and Surveillance is a unique collaboration between the members of the Forum Fisheries Agency (FFA) to address illegal, unreported and unregistered (IUU) fishing in support of SDG 14.4. A range of regionally agreed systems and tools is applied.

The use of electronic monitoring within tuna longline fisheries: implications for international data collection, analysis and reporting

Electronic monitoring (EM) consisting of on-board video imagery and on-shore analysis, offers an alternative or supplement to at-sea observer programs in commercial fisheries. In the western and central Pacific Ocean (WCPO), where observer coverage in most tuna longline fisheries has historically been < 5%, the advent of EM has been perceived as a tool for meeting international data collection and exchange obligations. However, the capability of EM to collect and support interpretation of records into data for all fields currently collected by at-sea observers is still under assessment. We use the Western and Central Pacific Fisheries Commission (WCPFC) as a case-study to evaluate the longline WCPFC regional observer programme minimum standard data fields, their current scientific application, the proportion of member countries exchanging data and the capability of EM technology to collect these fields. We identify that 78% of the longline fields can be collected with current EM technology, with 84% of these used in scientific analyses. For the 16% of fields not routinely used in scientific analyses, the introduction of EM may facilitate a sufficient increase in data availability to support their future use. Alternative tools would be required to collect fields that EM could not record to ensure data continuity and scientific rigour are not compromised. In examining the capability of EM in the context of WCPFC member state requirements under international law, we advocate for a holistic and integrated approach to the use of EM in future research and monitoring programs in both the WCPO and global longline fisheries.

Growth variability of juvenile skipjack tuna (Katsuwonus pelamis) in the western and central Pacific Ocean

We examined growth rates of juvenile skipjack tuna using otolith daily increment analysis to clarify geographic differences in early-life stage growth in the western and central Pacific Ocean (WCPO). We used a liner regression model to analyze the relationship between standard length (SL) and age (in days). The slope of growth model was significant difference between regions. There were rapid increases in the otolith mean daily increment width of juveniles at 7 days after hatching (DAH) and 10 DAH in the Western Pacific Warm Pool (WARM) and North Pacific Tropical Gyre area (NPTG), respectively. These periods correspond to the timing at which larvae complete their digestive-system development and start the piscivory. We found significant difference in logarithmic back-calculated SL between WARM and NPTG at 3 DAH (p < 0.01). Mean growth rates until 10 DAH, when the larvae metamorphose into juveniles, were positively correlated with sea surface temperature (r = 0.52). These results indicate that geographic difference in the growth of juvenile skipjack tuna caught in the WCPO in boreal winter cause in the larval stage, and that these differences are related to sea surface temperature.