应用贝叶斯方法对有效信息较少的渔业资源进行资源评估-以印度洋长鳍金枪鱼的资源评估为例

众所周知,对有效信息较少的渔业资源进行资源评估面临很大的挑战,而贝叶斯方法在数据数量较少、质量较差的情况下能利用其它种群高质量的数据或已知的先验信息提高资源评估结果的可靠性。由于印度洋长鳍金枪鱼的数据质量较差而数据量有限,长鳍金枪鱼的资源评估结果存在很大的不确定性,为此,本文以印度洋长鳍金枪鱼的资源评估为例,以调查贝叶斯方法在有效信息较少的资源评估中的优势。本文根据不同的先验假设与捕捞数据系列,共构建了8个贝叶斯动态产量模型,以评估长鳍金枪鱼资源。结果表明:(1)分析参数的后验分布能提高捕捞数据系列选择与参数假设的合理性; (2) 利用种群统计学方法为内禀增长率(r)构建有信息先验,能提高资源评估结果的可靠性。与传统方法相比,当基于贝叶斯框架时,能将已知的知识表示为先验信息并能分析参数的后验分布,从而在数据较少或数据质量较差的情况下,能利用各种信息提高参数估计的合理性与资源评估的可靠性。因此,对数据量较少或数据质量较差情况下的渔业资源评估而言,贝叶斯方法非常有效,如本文所示的印度洋长鳍金枪鱼的资源评估。     

Biology, fishery, conservation and management of Indian Ocean tuna fisheries

The focus of the study is to explore the recent trend of the world tuna fishery with special reference to the Indian Ocean tuna fisheries and its conservation and sustainable management. In the Indian Ocean, tuna catches have increased rapidly from about 179959 t in 1980 to about 832246 t in 1995. They have continued to increase up to 2005; the catch that year was 1201465 t, forming about 26% of the world catch. Since 2006 onwards there has been a decline in the volume of catches and in 2008 the catch was only 913625 t. The Principal species caught in the Indian Ocean are skipjack and yellowfin. Western Indian Ocean contributed 78.2% and eastern Indian Ocean 21.8% of the total tuna production from the Indian Ocean. The Indian Ocean stock is currently overfished and IOTC has made some recommendations for management regulations aimed at sustaining the tuna stock. Fishing operations can cause ecological impacts of different types: by catches, damage of the habitat, mortalities caused by lost or discarded gear, pollution, generation of marine debris, etc. Periodic reassessment of the tuna potential is also required with adequate inputs from exploratory surveys as well as commercial landings and this may prevent any unsustainable trends in the development of the tuna fishing industry in the Indian Ocean.     

利用后向预报方法分析印度洋黄鳍金枪鱼资源评估模型

当前,对渔业资源评估模型的诊断与选择,主要依赖于模型对观察数据的拟合度,很少评价模型的预测能力、并将其作为评价渔业资源评估与管理质量的依据。为此,本文利用后向预报方法评价了印度洋黄鳍金枪鱼(Thunnus albacores)资源评估模型的预测能力,并在此基础上分析了印度洋黄鳍金枪鱼的资源评估与管理质量。研究表明,在利用贝叶斯剩余产量模型对印度洋黄鳍金枪鱼进行资源评估时,存在如下问题:(1)拟合较好的模型其预测能力较差;(2)利用不同时段数据拟合模型时,采用DIC(Deviance Information Criterion)选择的最佳模型缺少稳定性;(3)不同模型估计的TAC (Total Allowable Catch)存在较大差异。据此可以判断,利用贝叶斯剩余产量模型对印度洋黄鳍金枪鱼进行资源评估与管理效果较差。本研究结果表明:(1)利用后向预报方法可评价模型的预测能力、DIC选择模型的稳定性,从而能在一定程度上判断模型模拟的种群演化动态是否正确、资源评估结果是否存在问题;(2)利用后向预报方法可揭示评估结果的不确定性及其可能引起的渔业管理风险,从而有利于避免渔业管理风险、实现渔业管理目标。     

印度洋金枪鱼渔业现状

报道了印度洋海域金枪鱼渔业近十年的生产概况，结果显示，印度洋金枪鱼渔业从业国家和地区已达40个，从业国家(地区)中以欧共体、印度尼西亚、印度、伊朗、斯里兰卡、中国台湾、马尔代夫等所占份额较高，以2000年计占当年印度洋金枪鱼渔业总产量的68．17％。产量140万吨，以金枪鱼类所占份额最高．主要金枪鱼渔获种类依次为鲣、黄鳍金枪鱼和大眼金枪鱼，主要渔业方式为金枪鱼围网、刺网及延绳钓。中国在印度洋海域金枪鱼渔业中年占份额较小，捕捞产量从1995年的444吨逐渐上升到2000年的6408吨。     

基于深度卷积嵌入式聚类（DCEC）的海洋环境特征提取对渔情预报模型的改进研究

In order to improve the forecasting ability of the fishery forecast model for the longline bigeye tuna (Thunnus obesus), we proposed a marine environment feature extraction method based on deep convolutional embedded clustering (DCEC), combined with generalized additive model (GAM) for forecasting the longline bigeye tuna fishing grounds in the Southwest Indian Ocean. We used the MODIS-Aqua and MODIS-Terra sea surface temperature (SST) three-level inversion image data (in days) from January to December in 2018 at 0.041 6°×0.041 6° to construct a DCEC model, determined the optimal number of clusters based on the Davies-Bouldi index (DBI), and extracted the category feature value (F_M) of each month’s sea surface temperature (SST); we used monthly 1°×1° bigeye tuna longline fishery data from January to December in 2018 generated from the Indian Ocean Tuna Commission (IOTC), and calculated the catch per unit effort (CPUE); we matched the monthly category feature value F_M and the monthly average value of Chl a concentration with the CPUE data to construct an improved GAM; we matched the monthly average SST, the monthly average Chl a concentration and CPUE data to build a basic GAM; we used the joint hypothesis test (F test) to verify the influence of model explanatory variables; we used akaike information criterion (AIC), mean square error (MSE), and draw the frequency distribution diagrams and box diagrams of measured and predicted values, etc., to analysis the improvement effect of the improved GAM compared to the basic GAM. The results showed that: (1) the category feature value (F_M) extracted based on the DCEC model could better reflect the temporal and spatial dynamic characteristics of SST in the Southwest Indian Ocean, and was related with the climatic conditions, monsoon conditions, and hydrological characteristics in the Southwest Indian Ocean; (2) the factor interpretation of F_M was higher than that of the monthly average SST in GAM, which means F_M had more significant impact on the CPUE of bigeye tuna. The high catch rate was concentrated in the areas where the F_M category was 2, 10, 24 with intersections between the warm and cold currents; (3) the AIC of the improved GAM was reduced by 9.17% than that of the basic GAM and MSE of the improved GAM was reduced by 26.7% than that of the basic GAM; the frequency distribution of the CPUE logarithmic value predicted by the improved GAM was closer to the normal distribution, and the high frequency distribution interval was closer to that of the measured value; the scatter plot showed that the CPUE predicted by the improved GAM had a significant correlation with the measured CPUE, with r equaled to 0.60. This study proves the effectiveness of the DCEC model in extracting marine environmental features, and can provide a reference for the further study on the bigeye tuna fishery forecast.     

自然死亡和亲体补充关系对黄鳍金枪鱼资源评估的影响

黄鳍金枪鱼(Thunnus albacares)是全球经济和生态价值最重要的鱼类之一,其资源养护和管理受到各方的高度关注。本文依据年龄结构产量模型研究了印度洋黄鳍金枪鱼的资源状态,着重探讨了其生活史特征的不确定性对资源评估结果的影响。研究结果显示,1960-1985年间印度洋黄鳍金枪鱼资源量保持相对稳定,之后开始逐渐下降,相应的捕捞死亡系数也在2010年之后迅速增加,目前其种群可能存在过度捕捞(F₂₀₂₀/F_MSY>1,SSB₂₀₂₀/SSB_MSY<1)。印度洋黄鳍金枪鱼的资源评估结果对自然死亡系数(M)和亲体-补充量关系陡度参数(h)的改变较为敏感。当h增大时,SSB_MSY和初始SSB(即SSB₀)的变化较大,分别减少了约25.53万t和34.04万t;F₂₀₂₀/F_MSY减小了1.15。当M增大时,F₂₀₂₀/F_MSY、SSB_MSY...     

Data-moderate assessments of Cape monkfish Lophius vomerinus and west coast sole Austroglossus microlepis in Namibian waters

There is global interest in providing scientific advice on optimal harvesting of all commercially exploited fish stocks. Nevertheless, many commercially important stocks lack analytical assessments. Therefore, we evaluate a data-moderate stock assessment method: the stochastic surplus production model in continuous time (SPiCT). The method was applied to two Namibian stocks: (i) the data-rich Cape monkfish Lophius vomerinus, where results are compared to a new data-rich assessment using a state–space assessment model (SAM); and (ii) the data-moderate west coast sole Austroglossus microlepis, which is an important bycatch species in the Cape monkfish fishery, but currently unassessed. The information available to the data-moderate assessment is total commercial catch, commercial catch per unit effort (CPUE), and survey CPUE. SPiCT and SAM gave largely consistent estimates of relative fishing mortality (F/F_MSY) and relative exploitable biomass (B/B_MSY) for the Cape monkfish stock, although with some discrepancies. Differences in the biomass estimates between the two assessments suggest that further investigation is required to understand the cause, and that some caution is necessary when considering the biomass of the stock. SPiCT shows that the west coast sole may be overexploited, although the confidence bounds were too wide for a firm conclusion. Similarity in the estimates of F/F_MSY for Cape monkfish in recent years, using SPiCT relative to SAM, likewise indicates the suitability of SPiCT for managing west coast sole.     

大西洋大眼金枪鱼渔业概况

大西洋大眼金枪鱼（Ｔｈｕｎｎｕｓ ｏｂｅｓｕｓ）是高经济价值鱼种,其分布几乎覆盖整个大西洋水域。研究大西洋大眼金枪鱼的渔业对于我国远洋渔业意义重大。所以在此对其渔业及资源状况进行研究。根据三种主要渔业（延绳钓、围网和竿钓）的渔获量,可看出大眼金枪鱼渔业的发展概况。为了分析资源状况,文中使用了Ｗａｌｔｉｒｓ ａｎｄ Ｈｉｌｂｏｒｎ（１９７６）产量模型。其结果是９９．６千公吨的最大持续产量和１１４．７     

应用Catch-MSY模型评估印度洋蓝枪鱼资源

Catch-MSY模型可仅依靠渔获量数据进行渔业资源评估,在数据缺乏状况下能暂时替代标准资源评估模型。本研究以印度洋蓝枪鱼(Makaira nigricans)为例,根据有、无信息的内禀增长率r和环境容纳量K的先验分布,设立15组情景进行模型灵敏度分析、资源评估和预测。结果表明,参数r和K呈强烈的负相关,而最大可持续产量(Maximum Sustainable Yield,MSY)与参数r呈正相关;数据时间序列长度对评估结果影响有限,而模型对起止年渔获量较为敏感。资源状况评估表明,印度洋蓝枪鱼资源生物量状况良好,即B₂₀₁₅/B_MSY大于1;而开发状况除其中两种情景外,均为过度捕捞,即F₂₀₁₅/F_MSY大于1。资源预测表明,为使未来10年内B/B_MSY>1的概率超过50%,需将渔获量缩减至当前渔获量的90%(13.86 kt);考虑到该模型在数据缺乏状况下会更加保守,若将当前渔获量的100%～110%(15.40～16.94 kt)设为管理目标,则未来5年内B/B_MSY >1的概率超过50%。     

大西洋金枪鱼渔业现状分析

本文采用大西洋国际金抢鱼保护委员会ICCAT的报告和统计常设委员会（SCRS）数据库，统计分析了1978-2002年大西洋金抢鱼的渔获种类及渔具渔法。结果表明：按种类分黄鳍金枪鱼（占28％）、鲣鱼（22％）、长鳍金枪鱼（15％）、大眼金枪鱼（11％）、其他种类（8％）；按渔具分围网（42％）、延绳钓（29％）、饵钓（22％）、其它渔具（7％）。同时分析了不同海域的渔获种类、渔获量波动情况和原因。     

Ecological risk assessment of the Marshall Islands longline tuna fishery

To support implementing an ecosystem approach to fisheries management, ecological risk assessment (ERA) methods have recently been developed for the continuum of data-deficient to data-rich fisheries. A semi-quantitative ERA was conducted for the Marshall Islands longline bigeye tuna (Thunnus obesus) fishery. The study used information from analyses of observer data, surveys of captains and crew and inventories of gear and equipment. Relative risks were evaluated through a consideration of phylogenetic uniqueness, risk of population extirpation, risk of species extinction and importance in ecosystem regulation. The fishery presents a highest relative risk to leatherback (Dermochelys coriacea), hawksbill (Eretmochelys imbricata), green (Chelonia mydas) and olive Ridley (Lepidochelys olivacea) sea turtle Regional Management Units that overlap with the fishery, in that order. The next highest relative risk is to affected stocks of oceanic whitetip (Carcharhinus longimanus), blue (Prionace glauca), and silky (Carcharhinus falciformis) sharks, in that sequence. Seabird bycatch is likely not problematic. There was inadequate information to assess risks to cetacean populations. Risks to stocks of market and non-market species of marine fishes with r-selected life history characteristics were not assessed. This is because estimates of critical threshold levels of local and absolute abundance and current biomass are not known for many of these stocks. Several best practice gear technology methods to mitigate problematic catch of vulnerable species groups are currently employed: monofilament leaders, whole fish for bait, single-hooking fish bait, no lightsticks, and no fishing at shallow submerged features. Setting terminal tackle below 100 m and carrying and using best practice handling and release equipment were methods identified to reduce fishing mortality and injury of vulnerable species. More information is needed to determine if weaker hooks should be prescribed to mitigate cetacean bycatch. The large benefit to sea turtles of replacing remaining J-shaped hooks with circle hooks might outweigh a possible small increase in elasmobranch catch rates. The consumption of 2024 l of fuel per tonne of landed catch, which is within the range of available estimated rates from similar fisheries, could be reduced, reducing greenhouse gas emissions, through more frequent maintenance and upgrading vessel equipment and materials. Observer data quality may be adequate to support a quantitative Level 3 ERA to determine the significance of the effect of various factors on standardized catch rates and to estimate population-level effects from fishing mortality.     

中部太平洋大眼金枪鱼种群遗传结构的初步研究

大眼金枪鱼是世界最重要的渔业资源之一,经济价值较高,捕捞压力的加大使中部太平洋大眼金枪鱼过度捕捞程度愈发严重。开展种群遗传结构研究将为大眼金枪鱼资源的可持续利用与开发提供科学依据。本文以取自中西太平洋和中东太平洋共182尾大眼金枪鱼个体为研究对象,分析研究其线粒体DNA控制区第一个高变区（the first hypervariable region,HVR-1）457bp的序列,共发现115个变异位点,定义了178种单倍型。序列多样性分析结果显示8个采样点核苷酸多样性在0.03074-0.04362间,单倍型多样性在各个采样点都较高,变动范围在0.996-1.000之间;分子方差分析显示99.97%的遗传变异性来自于种群内;群体间的高基因交流值Nm和低分化指数Fst揭示中东太平洋与中西太平洋群体间基因交流频繁,不存在显著的遗传分化。     

Distributing the bigeye conservation burden in the western and central pacific fisheries

The Western and Central Pacific Ocean is home to the world's most productive tuna fisheries, with the majority of tuna catches occurring inside the exclusive economic zones (EEZs) of the region's developing coastal States. It is important that these fisheries are managed effectively throughout their range, both within and between EEZs and on the high seas. Unrestrained exploitation in a particular EEZ or on the high seas has the potential to significantly impact on catches elsewhere with potentially devastating consequences for developing coastal States, some of which have few alternate resources. The Western and Central Pacific Fisheries Commission (WCPFC) was established in 2004 to manage the region's highly migratory tuna fisheries. However, the WCPFC has since repeatedly failed to adopt conservation and management measures that are sufficient to meet the WCPFC's conservation and sustainable use objectives. This paper analyses catch data from the WCPFC and suggests that the weak position of bigeye (in a strategic political context), the unwillingness of members to compromise their interests and the lack of a transparent framework for distributing the burden of conservation are key factors in the WCPFC's failure to adopt sufficiently strong conservation and management measures.     

Indonesia tuna fisheries development and future strategy

Tuna has made a significant contribution to Indonesian and world fisheries. Indonesian tuna fisheries were introduced from Japan, Taiwan and Korea. Longline fishing was introduced in 1962, and purse seine gear was first used in 1974. Many foreign vessels have reflagged to the Indonesian flag. The Indonesian government developed its own tuna fisheries and closed the chartering program in 2006. Through these efforts, Indonesia became the number one tuna production country in 2004 and has further targeted an increase in marine capture fisheries catch of 0.5%/year from 2010 to 2014. Tuna resources remain under pressure globally. The tuna regional fisheries management organizations attempt to manage tuna fisheries by strengthening conservation of stocks. To enhance international cooperation, Indonesia ratified the 1982 Convention on the Law of the Sea in 1985 and the Agreement for the Implementation of the Provisions of the United Nations Convention on the Law of the Sea of 10 December 1982 relating to Conservation and Management of Straddling Fish Stocks and Highly Migratory Fish Stocks in 2005 and became a member of Indian Ocean Tuna Commission and Commission for the Conservation of Southern Bluefin Tuna and a cooperating non-member of Western and Central Pacific Fisheries Commission in the 2000s. Consequently, Indonesia adopted domestic regulations to comply with management measures. For future sustainable development, Indonesia needs to build its capacity, improve its compliance with the tuna RFMOs’ conservation and management measures, strengthen data collection, develop its products to increase their quality and diversification, and enhance its international cooperation.     

帕劳群岛附近海域延绳钓渔场大眼金枪鱼(Thunnus obesus)的环境偏好

2005年8—12月,利用金枪鱼延绳钓渔船对帕劳群岛附近海域进行调查,研究大眼金枪鱼的环境偏好。所获数据包括:①温度、盐度、溶解氧垂直分布,测定的钓钩深度;②作业参数;③渔场气象数据;④渔获统计数据。分析方法和步骤为:①应用逐步回归的方法,建立钓钩预测深度计算模型;②根据温度、盐度、溶解氧垂直分布曲线、预测深度、取样数据,利用统计和聚类分析的方法分析大眼金枪鱼的环境偏好。结果表明:①在帕劳群岛附近海域,大眼金枪鱼偏好的水层为180.0—219.9m、水温范围为11.0—12.9℃、盐度范围为34.50—34.99、溶解氧范围为3.00—3.99mg/L;②一般情况下,水温及其体温的变化决定成熟大眼金枪鱼的活动水层,其偏好的水温为10.0—14.0℃;③大眼金枪鱼的适盐性较广;④溶解氧高于门限值(0.8mg/L)时,大眼金枪鱼的分布由其它环境因子决定。     

Stock assessment for Atlantic yellowfin tuna based on extended surplus production model considering life history

The modern fishery stock assessment could be conducted by various models, such as Stock Synthesis model with high data requirement and complicated model structure, and the basic surplus production model, which fails to incorporate individual growth, maturity, and fishery selectivity, etc. In this study, the Just Another Bayesian Biomass Assessment (JABBA) Select which is relatively balanced between complex and simple models, was used to conduct stock assessment for yellowfin tuna (Thunnus albacares) in the Atlantic Ocean. Its population dynamics was evaluated, considering the influence of selectivity patterns and different catch per unit effort (CPUE) indices on the stock assessment results. The model with three joint longline standardized CPUE indices and logistic selectivity pattern performed well, without significant retrospective pattern. The results indicated that the stock is not overfished and not subject to overfishing in 2018. Sensitivity analyses indicated that stock assessment results are robust to natural mortality but sensitive to steepness of the stock-recruitment relationship and fishing selectivity. High steepness was revealed to be more appropriate for this stock, while the fishing selectivity has greater influence to the assessment results than life history parameters. Overall, JABBA-Select is suitable for the stock assessment of Atlantic yellowfin tuna with different selectivity patterns, and the assumptions of natural mortality and selectivity pattern should be improved to reduce uncertainties.     

A spatial ecosystem and populations dynamics model (SEAPODYM) – Modeling of tuna and tuna-like populations

An enhanced version of the spatial ecosystem and population dynamics model SEAPODYM is presented to describe spatial dynamics of tuna and tuna-like species in the Pacific Ocean at monthly resolution over 1° grid-boxes. The simulations are driven by a bio-physical environment predicted from a coupled ocean physical–biogeochemical model. This new version of SEAPODYM includes expanded definitions of habitat indices, movements, and natural mortality based on empirical evidences. A thermal habitat of tuna species is derived from an individual heat budget model. The feeding habitat is computed according to the accessibility of tuna predator cohorts to different vertically migrating and non-migrating micronekton (mid-trophic) functional groups. The spawning habitat is based on temperature and the coincidence of spawning fish with presence or absence of predators and food for larvae. The successful larval recruitment is linked to spawning stock biomass. Larvae drift with currents, while immature and adult tuna can move of their own volition, in addition to being advected by currents. A food requirement index is computed to adjust locally the natural mortality of cohorts based on food demand and accessibility to available forage components. Together these mechanisms induce bottom-up and top-down effects, and intra- (i.e. between cohorts) and inter-species interactions. The model is now fully operational for running multi-species, multi-fisheries simulations, and the structure of the model allows a validation from multiple data sources. An application with two tuna species showing different biological characteristics, skipjack (Katsuwonus pelamis) and bigeye (Thunnus obesus), is presented to illustrate the capacity of the model to capture many important features of spatial dynamics of these two different tuna species in the Pacific Ocean. The actual validation is presented in a companion paper describing the approach to have a rigorous mathematical parameter optimization [Senina, I., Sibert, J., Lehodey, P., 2008. Parameter estimation for basin-scale ecosystem-linked population models of large pelagic predators: application to skipjack tuna. Progress in Oceanography]. Once this evaluation and parameterization is complete, it may be possible to use the model for management of tuna stocks in the context of climate and ecosystem variability, and to investigate potential changes due to anthropogenic activities including global warming and fisheries pressures and management scenarios.     

Tuna longline catch rates in the Indian Ocean: Did industrial fishing result in a 90% rapid decline in the abundance of large predatory species?

Myers and Worm claim that their analyses of catch rates following the commencement of industrial longline fishing for tuna and billfishes show that these longline fisheries rapidly depleted the abundance of these large oceanic predators by 90% (Myers RA, Worm B. Rapid worldwide depletion of predatory fish communities. Nature 2003;423:280–3). Their analyses were published in a high profile science journal along with an accompanying press release, which then attracted substantial international media focus and public attention. This media focus in turn has been used as a base for advocating major marine policy changes for pelagic tuna fisheries (e.g. a minimum of a 50% reduction in catches and establishment of extensive marine reserves). However, among numerous scientific experts involved in tuna and pelagic fishery research substantial concerns exist that Myers and Worm's analyses provide a misleading picture of the status of large predatory pelagic fishes. These concerns are reviewed using data from the Indian Ocean for illustrative purposes and indicate that the initial longline catches were not responsible for a rapid depletion of the main tuna and billfish stocks nor were they threatening the overall sustainability of these stocks. However, the status of a number of theses stocks is of concern as a result of large increases in catches in more recent years. The debate sparked by Myers and Worm's paper should not distract from the critical problem of developing and implementing effective international management policies. In addition to implications for fishery management, the publication, peer-review, scientific response and publicity process associated with the publication of Myers and Worm's paper are discussed. Concerns are raised that if these become standard practices for articles in high profile science journals that this would undermine the trust placed in such journal to provide an accurate and well-balanced representation of the most important new scientific findings and in their role to inform policy decisions based on these findings.     

Assessment of IUU fishing for Southern Bluefin Tuna

Illegal, unreported and unregulated (IUU) fishing is recognized as one of the largest threats to the sustainability of the world's fisheries. This paper focuses on IUU fishing in the context of unreported catches by members or co-operating non-members of regional fisheries management organizations (RFMOs) and their implications for scientific assessments of stock status and management advice. A review of Japanese market statistics was undertaken in 2006 by an independent panel in relation to catches of southern bluefin tuna (SBT). Based on this review, the Commission for the Conservation of Southern Bluefin Tuna (CCSBT) concluded that very substantial and continuous unreported catches of SBT had been taken by longline vessels since at least the early 1990s. While uncertainty exists about the fleets contributing to these IUU catches, the assumption used within the CCSBT Scientific Committee is that a significant proportion of these were taken by Japanese longliners. Implications of these unreported catches for the stock assessments by RFMOs are discussed in light of the central role that Japanese vessel reported data have in the assessment of the world's tuna and billfish stocks. Results indicate that it is plausible that the unreported catches of SBT stem from the misreporting of catches as other tuna species and/or the location of fishing effort. The magnitude and extended period of the unreported SBT catches highlight the wide-spread risks of relying on fishery dependent logbook data in the absence of verification. An urgent need exists for minimum standards of verification of catch, effort and landing statistics for use in scientific assessments. The fisheries science community needs to be more pro-active in the development of such standards and the implementation of independent monitoring and verification. In addition, there is a need to reform the operation of the scientific bodies of RFMOs in terms of transparency, the treatment of uncertainty and the burden of proof if they are to be effective in providing objective scientific advice consistent with the intent of international agreements.     

An indicator-based adaptive management framework and its development for data-limited fisheries in Belize

Decisions regarding the selection and implementation of management strategies that constrain fishing pressure can be among the most difficult choices that fisheries managers and stakeholders must make. These types of decisions often need to be confronted in a data-limited context, where few if any management measures are currently in place or fisheries are managed independent of adequate scientific advice. This situation can sometimes create a high risk of overfishing and potential loss of economic and social benefits. To address this situation, simple model-free indicator-based frameworks have the potential to be effective decision-making platforms for fisheries where quantitative estimates of biomass and fishing mortality based reference points are lacking. In this paper, a multi-indicator framework is developed that enables decision-makers to proceed with management decisions in data-limited situations. Model-free indicators are calculated using trends in observed data, rather than stock assessment derived estimates of biomass and fishing mortality. The framework developed is adaptive so that adjustments to catch or effort are recursive and can respond to changing environments, socioeconomic conditions, and fishing practices. Using stakeholder-defined objectives as a foundation, indicators and reference points of fishery performance are chosen that can be evaluated easily by undertaking analyses of available data. Indicators from multiple data streams are used so that uncertainty in one indicator can be hedged through careful interpretation and corroboration of information from alternative indicators. During the adaptive management cycle, managers and stakeholders evaluate each indicator against the associated reference points to determine performance measures, interpret the results using scientific and local knowledge, and adjust fishery management tactics accordingly using pre-defined harvest control rules. The framework facilitates the interpretation of situations in which performance measures suggest divergent stock abundance or productivity levels. A case study is presented on this framework's development for conch and lobster fisheries of Belize.