International Commission For The Conservation Of Atlantic Tunas Research Articles

Estimating tag-reporting rates for Atlantic tropical tuna fleets using coincidental tag return and tag seeding experiment data

One of the most important biases to consider in tagging capture-recapture data for stock assessment studies is the proportion of reported tags among the actual recaptures, i.e., the tag-reporting rate. In this study, we used the model developed by Kimura (1976) and adapted in a Bayesian framework by Carruthers et al. (2015) to estimate the reporting rates for thirteen Atlantic Ocean tuna fleets using coincidental tagging data and catch data disaggregated by species, school-type (Fish Aggregating Device and Free Swimming Schools), location and time. The method was applied on recaptures and tag seeding experiments conducted during the Atlantic Ocean Tropical Tuna Tagging Program (AOTTP) of the ICCAT (International Commission for the Conservation of Atlantic Tunas). Tag seeding consists of secretly planting tags on fish by observers onboard fishing vessels to estimate how many tags are found during later stages (landing, processing, etc.) and reported to scientific authorities. Our results showed that the tag-reporting rate was as large as 84.70% (80.58–88.39%) for the European Union purse seiner fleet (Spain and France) but decreased for several surface fleets from 72.79% (67.49–77.77%) for the Spanish baitboats (operating off Senegal or in Canary islands) to 22.83% (15.26–31.24%) for the Ghanaian mixed purse seiner-baitboat fishery. Overall, we conclude that given the very low reporting rate for several important fleets operating in the Atlantic Ocean, it is crucial to account for the reporting rate estimates to avoid highly biased results in future stock assessment using tagging data.

Updated growth models for bigeye tuna (Thunnus obesus) in the Atlantic Ocean

The International Commission for the Conservation of Atlantic Tunas (ICCAT) concluded the Atlantic Ocean tropical Tuna Tagging Programme (AOTTP) in 2021. This project had the objectives of enhancing food security, stimulating economic growth, and improving management through research on tropical tuna resources in the Atlantic Ocean, including bigeye tuna (Thunnus obesus). Here, we combine tagging data and otolith data from the AOTTP program, Panama City Lab and the Pelagic Fisheries Lab at the University of Maine with historical tagging data and otolith data from ICCAT and other sources to fit integrated growth models with the goal of providing the most complete growth curve (in terms of data inclusion and validation of age-at-length) for bigeye tuna in the Atlantic Ocean. Both Richards and von Bertalanffy growth models were fitted. A variety of models were fitted to subsets of the data to investigate the consistency of growth information. In all cases for the integrated model, the Richards and von Bertalanffy models were very similar with the von Bertalannfy model being preferred for parsimony. The preferred model, based on fit to old fish, was the von Bertalanffy curve based on length-age pair data from multiple sources. The addition of tagging data to create an integrated model showed patterns of lack of fit to both the tagging and otolith data suggesting conflict between the tagging and otolith data. The preferred model (length-age pair data only) gave the estimates: asymptotic length L∞ (fork length) equals 161.21 cm (95% bootstrap CI 154.39, 166.84), growth parameter K equals 0.392 yr−1 (95% bootstrap CI 0.355, 0.441), and the time-axis intercept t0 equals − 0.239 yr (95% bootstrap CI –0.306, −0.175). For the best fitting integrated model, the asymptotic length L∞(fork length, in cm) was estimated to be 185.78 (SD 6.298), the growth parameter K was 0.252 yr−1 (SD 0.014), and the time-axis intercept t0 was − 0.524 yr (SE 0.025). The value for asymptotic length L∞ from the integrated model was larger than the lengths of all the old fish in the sample whereas the value for the curve based on otoliths passes through the cloud of points for old fish.

ICCAT Inspections in Turkey and Turkey's National Legislation Compliance With the ICCAT Recommendations

It was determined that bluefin tuna fishing within the scope of the International Commission for the Conservation of Atlantic Tunas (ICCAT) inspections was carried out in accordance with the 19-04 ICCAT Recommendation in Turkey. In the swordfish fishery, it was observed that the 16-05 ICCAT Recommendation was not completely compatible with Turkey’s national legislation. In the 16-05 ICCAT Recommendation; the fishing gear was determined as the longline in swordfish fishery, the length of the pelagic longlines and the number of hooks were limited, the minimum weight limit was set on swordfish, and the transshipment operations at sea of swordfish was prohibited in the fishing season. However, these legal regulations were not available in Turkey’s national legislation. The following issues could be evaluated as the reasons why these regulations were not included in Turkey’s national legislation; the majority of the fishing vessels engaged in swordfish fishery in the seas of Turkey are less than 12 meters in total length, the fishing vessels of 12 meters in length or more can only use the first fishing gear, the length of pelagic swordfish longlines and the number of hooks used in Turkey are far below the regulations set forth in 16-05 ICCAT Recommendation, the caught swordfish are landed as a whole, and the majority of swordfish fishery vessels stay for a day or 2-3 days for fishing at sea. The ICCAT inspections in the swordfish fishery were carried out according to the 16-05 ICCAT Recommendation in Turkey. The necessary information and incentives should be provided for the fishing vessels of less than 12 m in length, which had obtained swordfish fishery permits, to use fuel without special consumption tax, in order to monitor them electronically via Vessel Tracking Module. In order to control the quota in swordfish fishery, it should be obligatory to use a paper logbook for fishing vessels less than 12 meters in length. In addition, an application can also be made to install a Vessel Monitoring System on fishing vessels less than 12 m that will catch swordfish.

Shortfin mako hot sets – Defining high bycatch conditions as a basis for bycatch mitigation

Shortfin mako sharks, Isurus oxyrinchus, were listed under Appendix II of CITES in 2019 in part due to the results of the last stock assessment for the North Atlantic population, which determined the population is overfished and experiencing overfishing. With population numbers expected to continue to decline, the managing body, the International Commission for the Conservation of Atlantic Tunas (ICCAT), has called for efforts to reduce shortfin mako bycatch. We evaluate the potential for reducing mako bycatch by identifying mako hot sets, those with particularly high shortfin mako bycatch. Environmental conditions were evaluated for their influence on catch per unit effort (CPUE) of shortfin mako sharks. Standardized CPUEs were calculated from the US pelagic longline observer program (2004–2012) using a generalized additive model (GAM) with a delta-lognormal approach applied to the environmental variables sea surface height, sea surface temperature, bathymetry, and chlorophyll-a concentration. Quantile regression (QR) was also performed to evaluate whether environmental variables can predict fishing conditions with high CPUE. The results of the GAM and QR methods were compared and assessed for their ability to predict and identify locations where shortfin mako CPUE is particularly high. The results suggest that using the binomial portion of the delta-lognormal model, the probability of positive bycatch, is the best basis to define an algorithm to avoid setting in conditions that might have high mako bycatch. Bycatch avoidance strategies built from probability of positive bycatch perform well enough at identifying hot sets to avoid half the shortfin mako bycatch with only a 20% reduction in effort.

Assessing illegal fishing and trade of Atlantic billfish and swordfish by DNA-based identification

Due to the morphological similarity between some billfish species, the International Commission for the Conservation of Atlantic Tunas (ICCAT) recommends the use of molecular tools to identify billfish at the species level to properly manage this imperiled group. In this study, species-specific swordfish and billfish identification was carried out by using PCR-RFLP and multiplex PCR of the mitochondrial COI gene. Samples were obtained during landings of the tuna fleet at the Public Fisheries Port of Santos (PFPS) and in the General Warehouse Company of Sao Paulo (CEAGESP), Brazil. A total of 87 samples from PFPS were identified: Kajikia albida, Tetrapturus georgii, T. pfluegeri, Makaira nigricans, and Istiophorus platypterus. At CEAGESP, 432 individuals were collected, and three species were detected: Xiphias gladius, I. platypterus and T. georgii. Some samples presented an unknown band pattern for PCR-RFLP, which were sequenced and identified as X. gladius. These findings demonstrate that billfishes protected by law are being caught by industrial fisheries, but they are not traded at the CEAGESP. We advocate continuous onboard and of landings fishing monitoring using molecular identification tools in accordance with ICCAT recommendations. We provided evidence that DNA-based methods are efficient in overcoming billfish misidentification in the Atlantic Ocean.

Sustain or phase out: Transformation of Taiwan’s management scheme on distant water tuna longline fisheries

Fishing nations worldwide have introduced various measures to manage their fisheries. However, many have failed including Taiwan. Taiwan operated one of the world’s largest and most productive distant water tuna longline fleets but overcapacity and an incommensurate fisheries management scheme (FMS) resulted in illegal, unreported, and unregulated (IUU) fishing activities by the fleet. As a result, Taiwan received serious punitive sanction by the International Commission for the Conservation of Atlantic Tunas (ICCAT) in 2005 for illegal “fish laundering” activities. Ten years later, it also received a “yellow card” warning from the European Union (EU) under the EU IUU Regulation. Taiwan struggled to transform its FMS to meet the requirements imposed under the two events through three FMS transformation projects. The ICCAT sanction was lifted in 2006, the EU yellow card was lifted in mid-2019, and the resulting FMS is considered close to completion and a useful example of global best practice. This study reviews the failure of Taiwan’s FMS for tuna longline fisheries and identifies the potential drivers: low policy priority, weak institutional arrangements, and insufficient enforcement resources. It documents the evolution of the FMS which was painful but could offer valuable lessons for fisheries managers and scholars worldwide. Key effects of the transformation projects and some recommendations for the future are also provided.

Pelagic ecoregions: Operationalizing an ecosystem approach to fisheries management in the Atlantic Ocean

Tuna Regional Fisheries Management Organizations have committed to adopting an ecosystem approach to fisheries management (EAFM). Yet their progress has been relatively slow and patchy, lacking a long-term vision and a formalized plan to prescribe how fisheries will be managed from an ecosystem perspective. We argue that one of the impediments in this process has been the lack of well-defined spatial management units that are ecologically meaningful, as well as practical for fisheries management, to guide ecosystem-based planning, research and indicator assessments, to ultimately produce better integrated management advice. In this study, we propose seven potential ecoregions within the convention area of the International Commission for the Conservation of Atlantic Tunas (ICCAT). The boundaries of the ecoregions rest on three pillars of information: the existing knowledge of biogeographic classifications of the pelagic environment, the spatial distribution of tuna and billfish species, and the spatial dynamics of the main fishing fleets targeting them. Each ecoregion is characterized by a set of ecologically meaningful biogeographic and oceanographic characteristics, tuna and billfish communities and fishing fleet patterns. The pelagic ecoregions proposed here aim to focus species- and fisheries-specific management of the tuna and billfish fisheries on specified regions. The proposed ecoregions represent an optimal, ecologically sound starting point, based on the best science available, to foster debate and consultative process in ICCAT for moving forward the implementation of the EAFM.

The role of Brazil in the International Commission for the Conservation of Atlantic Tunas (ICCAT)

Although Brazil has been an active voice in ICCAT in the past ten years, its leadership has been declining. This paper examines what might explain the variation of international influence Brazil has had in addressing the issues at ICCAT and argues that if Brazil wants to preserve its leadership, it must demonstrate commitment to its own waters while strengthening governmental institutions.

IS POWER LISTENING TO SCIENCE? THE CASE OF ICCAT AND THE EASTERN BLUEFIN TUNA (2004-2014)

Abstract During the international tuna fishery management crisis in 2009, an epistemic community emerged at the International Commission for the Conservation of Atlantic Tunas (ICCAT) that employed collective efforts to deal with shared problems and improved the effectiveness of agreements, in terms of the recovery of Eastern Blue Fin Tuna (EBFT) stocks. This event resulted in the question: when and why does power listen to science? Through a combination of elite interviews and process tracing, this investigation analyzed the roles and influences of science and epistemic communities in the ICCAT EBFT political decisions, from 2004 to 2014. We have concluded that the EBFT case illustrates a situation where effective agreements to handle a fishery crisis in an uncertain environment were enhanced, when a transnational network of non-governmental organizations (NGOs) and the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES), helped to pressure the decision-makers.

Testing robustness of CPUE standardization and inclusion of environmental variables with simulated longline catch datasets

Environmental variability changes the distribution, migratory patterns, and susceptibility to various fishing gears for highly migratory marine fish. These changes become especially problematic when they affect the indices of abundance (such as those based on catch-per-unit-effort: CPUE) used to assess the status of fish stocks. The use of simulated CPUE data sets with known values of underlying population trends has been recommended by ICCAT (International Commission for the Conservation of Atlantic Tunas) to test the robustness of CPUE standardization methods. A longline CPUE data simulator was developed to meet this objective and simulate fisheries data from a population with distinct habitat preferences. The simulation was used to test several statistical hypotheses regarding best practices for index standardization aimed at accurate estimation of population trends. Effort data from the US pelagic longline fleet was paired with a volume-weighted habitat suitability model for blue marlin (Makaira nigricans) to derive a simulated time series of blue marlin catch and effort from 1986 to 2015 with four different underlying population trends. The simulated CPUE data were provided to stock assessment scientists to determine if the underlying population abundance trend could accurately be detected with different methods of CPUE standardization that did or did not incorporate environmental data. While the analysts’ approach to the data and the modeling structure differed, the underlying population trends were captured, some more successfully than others. In general, the inclusion of environmental and habitat variables aided the standardization process. However, differences in approaches highlight the importance of how explanatory variables are categorized and the criteria for including those variables. A set of lessons learned from this study was developed as recommendations for best practices for CPUE standardization.

Billfishes in a changing world

Abstract The 6th International Billfish Symposium (IBS) was held in September 2016 at the headquarters of the International Game Fish Association in Dania Beach, Florida (USA). In addition to providing a venue for presenting new research on istiophorid and xiphiid billfishes, the IBS’s objective was to highlight known uncertainties about the biology and fisheries of these species, particularly at the level of regional fisheries management organizations, such as the International Commission for the Conservation of Atlantic Tunas (ICCAT). The 6th IBS was attended by 60 participants from seven countries, contributing a total of 34 oral and five poster presentations. One of the other goals of the IBS was to collectively develop a plan for future IBS events. The next IBS is tentatively scheduled for 2021. We summarize here the main outcomes of the 6th IBS and preface the articles presented at the symposium that are included in this article theme set.

A ‘machine learning’ technique for discriminating captive-reared from wild Atlantic bluefin tuna, Thunnus thynnus (Osteichthyes: Scombridae), based on differential fin spine bone resorption

The Atlantic bluefin tuna (ABFT) fishery is regulated by the International Commission for the Conservation of Atlantic Tunas (ICCAT), which establishes the allowable annual yield and the minimum capture size, and allocates capture quotas to the Contracting Parties. Despite fishery monitoring, a considerable amount of captures escapes ICCAT control. In the Mediterranean Sea, the purse seine fishery supports ABFT farming, a capture-based aquaculture activity that involves catching fish from the wild and rearing them in sea cages for a few months. The first spine of the cranial dorsal fin undergoes a continuous bone remodeling process consisting in old bone (primary bone) resorption and new bone (secondary bone) apposition. A marked increase of spine bone resorption was shown in captive-reared ABFT with respect to wild specimens. In this paper, the Random Forest (RF), a Computer Aided Detection system, was applied to distinguish captive-reared from wild ABFT based on fish age, fish fork length, total surface of spine cross section, and surface of remodeled bone tissue in the spine cross section (sum of reabsorbed bone tissue and secondary cancellous bone). The RF system was also compared to the Logistic Regression method (LR). The percentages of properly classified animals, either wild or captive-reared, with respect to the overall number of animals, i.e. accuracy, was 95.3±2.6% and 79.0±5.1% for RF and LR, respectively. The percentages of the properly classified captive-reared specimens, i.e. sensitivity, were 93.5±3.1% and 75.8±5.3% for RF and LR, respectively. The percentages of the properly classified wild specimens was 96.7±2.2% and 81.4±4.9%, for RF and LR, respectively. The proposed technique appears to be a reliable investigation tool anytime the suspicion arises that illegally caught ABFT are sold as aquaculture products.

Transboundary movements, unmonitored fishing mortality, and ineffective international fisheries management pose risks for pelagic sharks in the Northwest Atlantic

The shortfin mako (Isurus oxyrinchus), porbeagle (Lamna nasus), and blue shark (Prionace glauca) are three frequently caught shark species in the northwestern Atlantic Ocean. Satellite tagging studies show that all three species range widely across many national boundaries but spend up to 92% of their time on the high seas, where they are largely unregulated and unmonitored. All are caught in large numbers by swordfish and tuna fishing fleets from a large number of nations, usually unintentionally, and all are unproductive by fish standards, which makes them particularly sensitive to fishing pressure. Landing statistics that grossly underrepresent actual catches, unreported discards that often exceed landings, and high discard mortality rates are threats to the populations and roadblocks to useful population monitoring. The influence of these threats is greatly magnified by inattention and ineffective management from the responsible management agency, the International Commission for the Conservation of Atlantic Tunas (ICCAT), whose prime focus is the more valuable swordfish and tuna stocks. Although practical management options are available, none will be possible if organizations like ICCAT continue to treat sharks like pests.

Age, Growth and Spatial Distribution of the Life Stages of the Shortfin Mako, Isurus oxyrinchus (Rafinesque, 1810) Caught in the Western and Central Atlantic.

The shortfin mako (Isurus oxyrinchus) is a highly migratory pelagic shark that preferentially inhabits oceanic regions in practically all oceans. The wide distribution range of this species renders it susceptible to coastal and oceanic fishing operations. The International Union for Conservation of Nature (IUCN) and the International Commission for the Conservation of Atlantic Tunas (ICCAT) consider this species to be highly vulnerable, especially due to its biological parameters, which are different from those of other sharks that occupy the same niche (e.g., Prionace glauca). Consequently, considerable declines in abundance have been detected over various parts of its range, most of which are linked to oceanic longline fishing. The species has conflicting life history parameters in studies conducted in the last 30 years, especially with regard to age and growth. The main discrepancies regard the interpretation of the periodicity of the deposition of band pairs (BPs) on vertebrae and the possibility of ontogenetic variations in growth. Shortfin mako sharks (n = 1325) were sampled by onboard observers of the Brazilian chartered pelagic longline fleet based in northeast Brazil from 2005 to 2011. Lengths were 79 to 250 and 73 to 296 cm (fork length, FL) for males and females, respectively, with a statistically significant difference in size between sexes and differences in the proportion of individuals in each size class. The onboard observers collected a subsample of vertebrae (n = 467), only 234 of which were suitable for analyses. Reliability between readings was satisfactory. However, it was not possible to validate periodicity in the formation of age bands in the sample. Thus, the von Bertalanffy growth function was used to calculate growth rates for the species through the interpretation of BPs in different scenarios: one BP per year (s1), two BPs per year (s2) and two BPs per year until five years of life (s3). Growth parameters varied for both females (Linf = 309.7[s3] to 441.6[s1]; k = 0.04[s1] to 0.13[s3]; t0 = -7.08[s1] and -3.27[s3]) and males (Linf = 291.5[s3] to 340.2[s1]; k = 0.04[s1] to 0.13[s3]; t0 = -7.08[s1] and -3.27[s3]). To advance the understanding of the use of habitat, the first analysis of the spatial distribution of the life stages of the shortfin mako sharks caught by commercial longline fishing operations in the South Atlantic was performed. The findings indicate that the portion of the population exploited by the fleets is predominantly juvenile and future actions should take the following issues into account: improvements in the efficiency of data collection procedures, the reestablishment of the onboard observer program, emergency investments in studies that can contribute to a better understanding of habitat use and life history theory.

Verifier of the maximum sustainable yield estimates of the southern Atlantic albacore, Thunnus alalunga, stock

AbstractMaximum sustainable yield (MSY) has generally been accepted as one of the target biological reference points. Albacore, Thunnus alalunga Bonnaterre, is a temperate tuna species widely distributed in marine waters. The International Commission for the Conservation of Atlantic Tunas (ICCAT) and the International Seafood Sustainability Foundation (ISSF) had reported the southern Atlantic albacore stock status with different MSY reference points. In addition, the European Commission's Advisory Committee on Fisheries and Aquaculture (ACFA), on 15 September 2006, proposed to amend the Common Fisheries Policy according to the MSY principle, but there is little information on the verifier of the MSY estimates of this albacore stock. This study verifies the MSY estimates of this albacore (T. alalunga) stock to support the management (i.e. setting of MSY) for the southern Atlantic albacore (T. alalunga) stock. The MSY estimates of the albacore stock were evaluated and verified by different models (i.e. Bayesian surplus production model [BSPM], continuous time delay‐difference model [CD‐DM] and Fox surplus production model [SPM]). The MSY estimates from BSPM and CD‐DM were lower than those from conventional estimates; the relative biomass ratio (B2011/BMSY) and relative fishing mortality ratio (F2011/FMSY) from BSPM and CD‐DM were higher than those from ICCAT, which showed that measures should be taken for the sustainable utilisation of this fish stock.

Sex‐related variation in the vulnerability of wandering albatrosses to pelagic longline fleets

AbstractThe population of wandering albatrosses Diomedea exulans at South Georgia is decreasing because of bycatch in longline fisheries. Until at least the early 1990s, the survival rate of females was lower than males, consistent with the adult female‐biased bycatch reported for fisheries operating around the Brazil‐Falklands Confluence (BFC). Here we use extensive tracking data (1990–2012) from breeding birds at South Georgia to investigate overlap with longline fishing effort reported to the International Commission for the Conservation of Atlantic Tunas (ICCAT). Using data from multiple years, we conclude that breeding females are at higher risk than males from all the main pelagic longline fleets in the south‐west Atlantic. Our overlap index (based on fishing effort and bird distributions) correlated positively with numbers of ringed birds reported dead on longliners, indicating that the metric was a good proxy of bycatch risk. The consistent sex bias in overlap across years, and the likely resulting sex‐biased mortality, could account for lower adult female survival rate at the colony. The risk from fisheries changed seasonally; both sexes overlapped with pelagic longline effort during incubation (January–March), and particularly during post‐brood chick‐rearing (May–December), whereas overlap was negligible during brooding (April). The highest percentage of overlap was with the Taiwanese fleet, then vessels flagged to Brazil, Uruguay, Spain, Japan and Portugal. Females were consistently at greatest risk in the BFC region, whereas males showed lower and more variable levels of overlap with fisheries from 35 to 45°S. Our results have important implications for management of ICCAT longline fisheries and conservation of this highly threatened albatross population.

Combining fairness and stability concerns for global commons: The case of East Atlantic and Mediterranean tuna

The paper examines the issue of allocating fishing rights for the management of East Atlantic and Mediterranean tuna. Although it is well-known that fairness plays a crucial role for the acceptability of international environmental agreements, usually there is a trade-off between fairness and stability. Our results confirm such a trade-off between fairness and stability that prevails over international agreements and this paper examines a way to reconcile it. The proposed approach comprises three stages. First, various equitable sharing rules (originated from the “bankruptcy” literature) are used to allocate the fishing rights. Second, fairness and stability criteria are used to assess the eligibility of the examined allocation rules. The final choice is facilitated by using a social choice rule. The chosen rationing rule, namely the A-min, represents a specific weighted average of the two focal rationales in the sharing problems, namely the equal shares and the proportional ones. Setting aside the institutional inertia, the A-min rule dominates, in terms of stability and fairness, the existing rule used by the International Commission for the Conservation of Atlantic Tunas (ICCAT). Furthermore, it is a transparent and easy to justify allocation rule so, it may be proved to be a strong candidate for future policy changes concerning the allocation of fishing rights.

Estimating individual growth variability in albacore (Thunnus alalunga) from the North Atlantic stock: Aging for assessment purposes

Length-frequency data and derived catch at age matrices are used in north Atlantic albacore (Thunnus alalunga) stock assessment conducted within the International Commission for the Conservation of Atlantic Tunas (ICCAT). Growth is assumed to follow the von Bertalanffy model with the assumption that growth parameters are constant over time and the same for all fish. However, individual growth variability is an important factor not considered and affecting the input into the modelling of the population. This study describes a Bayesian hierarchical model applied to model the individual variability in the parameters asymptotic length (L∞) and growth rate (K) of the von Bertalanffy growth model for North Atlantic albacore. The method assumes that the L∞ and K values for each individual fish are drawn from a random distribution centered on the population mean values, with estimated variances. Multiple observations of spine diameter at age for individual fish were obtained by direct reading of spine sections collected in 2011 and 2012. A suite of back calculation methods were then applied to the measurements of annuli diameters in the aged individuals observed to back-calculate lengths at each age. The von Bertalanffy model was fitted to the measured and back-calculated lengths. Models with and without individual growth variability were compared using the deviance information criterion (DIC) to find the best model. Normal and log-normal error distribution models were used to analyse the data. Additionally, subsamples of the data were used to evaluate whether an unbalanced age-distribution in the data affects estimates of growth parameters. It was found that North Atlantic albacore asymptotic length (L∞) varies significantly between individual fish but not individual rate growth (K), for all back-calculation methods. Furthermore, negatively correlated relationships between von Bertalanffy growth parameters of asymptotic mean (L∞) and growth rate (K) were estimated for North Atlantic albacore with the array of models explored. The overall estimated values of K and population mean L∞ parameters were similar to values estimates in previous north Atlantic albacore growth studies.

Relationship between temporal–spatial distribution of fishing grounds of bigeye tuna (Thunnus obesus) and thermocline characteristics in the Atlantic Ocean

We evaluated the isoline distribution of thermocline characteristics (the upper and lower boundary temperatures and depths) in the bigeye tuna (Thunnus obesus) fishing grounds in the tropical Atlantic Ocean. We plotted the thermocline characteristics contour on a spatial overlay map using data collected on a monthly basis from Argo buoys and monthly CPUE (catch per unit effort) from bigeye tuna long-lines from the International Commission for the Conservation of Atlantic Tunas (ICCAT). In addition, frequency analysis and the empirical cumulative distribution function (ECDF) were used to calculate the optimum ranges of thermocline characteristics of the central fishing grounds. Our analysis suggested that there were significant seasonal variations in the upper boundary temperature and depth of thermocline in the central fishing grounds, which significantly influenced the temporal and spatial distribution of the bigeye tuna population. The overlay maps suggest that the central fishing ground of the bigeye tuna is located in the enclosed curve region between the higher value (70 m) and the lower value (40 m) of the upper boundary depth, from December to March of each year. After that, the fishing grounds spread to the north and south on both sides. CPUE is highest in areas where the upper boundary depths of the thermocline are between 40 and 60 m to the north of the equator. This extends to between 60 and 100 m to the south of the equator. The CPUE is highest in areas where the upper boundary temperature of the thermocline is between 24 and 26.9 °C in the low-latitude Atlantic Ocean, but decreases to 18 °C offshore of Namibia during July to October. The overlay maps showed that the lower boundary temperature and depth of thermocline have little seasonal variation. The lower boundary depth of the thermocline isoline depth showed that the higher depth area (>250 m) was shaped like the letter ‘W’. Similarly, the lower boundary temperature of thermocline isoline depth suggests that the temperature is higher besides the equator and lower around the equator area. The lower boundary water depth in the central fishing ground of the bigeye tuna ranged between 150 m and 250 m in the low-latitude Atlantic Ocean over the year, whereas the CPUE was low when the depth exceeded 250 m. In addition, the lower boundary water depth in the central fishing ground of the bigeye tuna decreased to between 140 and 160 m offshore of Namibia from April to October. The lower boundary temperature in the central fishing ground was about 12 °C in the low-latitude Atlantic Ocean and 14 °C offshore of Namibia. Conversely, if the temperature is >15 °C, the CPUE tends to be low. The numerical computation results suggest that the optimum ranges for the upper boundary thermocline temperature and depth were between 23 and 26.9 °C, and 30 and 70 m, respectively. The optimum ranges were 12–14.9 °C and 150–230 m for the lower boundary thermocline temperature and depth, respectively. We documented the distribution interval range of thermocline characteristics for the central fishing ground of the bigeye tuna in the Atlantic Ocean. Our results provide a reference for improving the efficiency of the bigeye tuna long-line fleet and aids tuna resource management in the Atlantic Ocean.

热带大西洋黄鳍金枪鱼垂直分布空间分析

PDF HTML阅读 XML下载 导出引用 引用提醒 热带大西洋黄鳍金枪鱼垂直分布空间分析 DOI: 10.5846/stxb201401060036 作者: 作者单位: 中国水产科学研究院渔业资源与遥感信息技术重点开放实验室 上海;农业部东海与远洋渔业资源开发利用重点实验室;同济大学法学院/知识产权学院;卫星海洋环境动力学国家重点实验室,同济大学法学院/知识产权学院,卫星海洋环境动力学国家重点实验室,中国水产科学研究院渔业资源与遥感信息技术重点开放实验室 上海,中国水产科学研究院渔业资源与遥感信息技术重点开放实验室 上海,中国水产科学研究院渔业资源与遥感信息技术重点开放实验室 上海 作者简介: 通讯作者: 中图分类号: S931.3 基金项目: 上海市自然科学基金(14ZR1449900);科技支撑计划项目(2013BAD13B01);上海市科技创新行动计划(12231203901) Spatial analysis of the horizontal and vertical distribution of yellowfin tuna Thunnus albacares in the tropical Atlantic Ocean Author: Affiliation: Key and Open Laboratory of Remote Sensing Information Technology in Fishing Resource,Chinese Academy of Fishery Sciences;China;Key Laboratory of East China Sea Oceanic Fishery Resources Exploitation and Utilization,Ministry of Agriculture,PRChina;China;School of Law School of Intellectural Property,Tongji University;China,School of Law School of Intellectural Property,Tongji University,,Key and Open Laboratory of Remote Sensing Information Technology in Fishing Resource,Chinese Academy of Fishery Sciences,Key and Open Laboratory of Remote Sensing Information Technology in Fishing Resource,Chinese Academy of Fishery Sciences,Key and Open Laboratory of Remote Sensing Information Technology in Fishing Resource,Chinese Academy of Fishery Sciences Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:为了解热带大西洋黄鳍金枪鱼(Thunnus albacares)延绳钓适宜渔获水温的等温线时空分布,分析黄鳍适宜的垂直和水平空间分布范围,采用Argo浮标剖面温度数据重构热带大西洋13 ℃和距海洋表层水温8℃(Δ8 ℃)的月平均等温线场,网格化计算了13 ℃和Δ8 ℃等温线深度值和温跃层下界深度差,并结合大西洋金枪鱼会委员(International Commission for the Conservation of Atlantic Tunas ICCAT)的黄鳍金枪鱼延绳钓渔业数据,绘制了13 ℃和Δ8 ℃等温线深度与月平均CPUE的空间叠加图,用于分析热带大西洋黄鳍金枪鱼中心渔场单位捕捞努力渔获量(Catch per unit effort CPUE)时空分布和次表层环境季节性变化关系。结果表明,13 ℃等温线,在高值CPUE出现的海域深度值大多小于250 m,主要在170-249 m,深度值超过250 m的海域CPUE普遍较小。5° S-9° N区域,Δ8 ℃等温线高值CPUE出现的海域深度值大多小于150 m,主要在50-139 m;7-10月份在南半球的非洲西海岸,在Δ8 ℃等温线深度值为150-350 m的海域也会出现中心渔场。全年在低纬度区域,高渔获率的垂直分布深度更加集中。13 ℃等温线影响热带大西洋黄鳍金枪鱼的空间分布,温跃层下界温度影响黄鳍金枪鱼的垂直分布。采用频次分析和经验累积分布函数计算其适宜次表层环境因子分布,13 ℃等温线180-240 m;Δ8 ℃等温线50-139 m;与下界深度差:13 ℃等温线-70-29 m;海表以下8 ℃等温线30-149 m。文章初步得出热带大西洋黄鳍金枪鱼适宜的水平、垂直深度分布区间。结果可以辅助渔情预报,为热带大西洋黄鳍金枪鱼实际生产作业和资源管理提供参考依据。 Abstract:In order to investigate the distribution of the yellowfin tuna (Thunnus albacares) in the fishing grounds in the tropical Atlantic Ocean, the isothermal distribution of subsurface temperatures in the yellowfin tuna fishing grounds was evaluated. The depths of 13℃ and 8℃ isotherm from the sea surface temperature (SST) (Delta 8℃), were plotted on spatial overlay maps using data collected on a monthly basis from Argo buoys and monthly CPUE data (catch per unit effort) from Thunnus albacares long-lines supplied by the International Commission for the Conservation of Atlantic Tunas (ICCAT). In addition, the differences in depth between the 13℃ and delta 8℃ isolines at the lower boundary of the thermocline were computed to determine the relationship between Thunnus albacares vertical distribution and thermocline depth. The overlay maps suggest that the delta 8℃ isothermal depth distribution showed obvious seasonal variation, roughly in the zonal striped distribution on the annual mode. The spatial distribution of the delta 8℃ isothermal depth is deep in winter and shallow in summer. The delta 8℃ isothermal depth is shallow, lying at 150 m in the low latitude area throughout the year. The topography of the 13℃ isothermal depth showed little seasonal variation. The 13℃ isothermal depth was greater than 250 m to the north of the slope, which started 15°N of West Africa and ended 10°N of South America, and to the south of the slope, which started from 10°S of South America and ended 30°S of West Africa. In the triangular area between these two slopes, the 13℃ isothermal depth distribution ranged from 150 m to 200 m. The CPUE is highest in areas where the 13℃ isothermal depth was shallower than 250 m (mode: 170-249 m). Conversely, if the depth is greater than 250 m, the CPUE tends to be low. Similarly, the highest CPUEs were observed in areas where the delta 8℃ isothermal depth was shallower than 150 m (mode: 50-139 m) in the latitude area between 5°S and 10°N throughout the year, whereas the delta 8℃ isothermal depth reached 150-350 m offshore of the west coast of Africa in the southern hemisphere from July to October. The vertical distribution of high hook rates was concentrated in the area between 5°S and 10°N. The horizontal distribution of Thunnus albacares in the tropical Atlantic Ocean was affected by the 13℃ isothermal depth, and the vertical distribution of Thunnus albacares was affected by the low boundary temperature and depth of the thermocline. Frequency analysis and the empirical cumulative distribution function were used to compute the optimum range of subsurface factors. The optimum ranges for 13℃ and delta 8℃ isothermal depths were 180-240 m and 50-139 m, respectively. The optimum depth difference ranges were 70-29 m for 13℃ isothermal depths and 30-149 m for delta 8℃ isothermal depths. The results were confirmed by using the Kolmogorov-Smirnov test. The distribution interval and vertical depth range for the central fishing ground of Thunnus albacares was documented, and the results provide a reference for improving the efficiency of long-line fleet and resource management. 参考文献 相似文献 引证文献