Does unreported catch lead to overfishing?

ArticleinFish and Fisheries · September 2016with 270 Reads
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Abstract
Catches are commonly misreported in many fisheries worldwide, resulting in inaccurate data that hinder our ability to assess population status and manage fisheries sustainably. Under-reported catch is generally perceived to lead to overfishing, and hence, catch reconstructions are increasingly used to account for sectors that may be unreliably reported, including illegal harvest, recreational and subsistence fisheries, and discards. However, improved monitoring and/or catch reconstructions only aid in the first step of a fisheries management plan: collecting data to make inferences on stock status. Misreported catch impacts estimates of population parameters, which in turn influences management decisions, but the pattern and degree of these impacts are not necessarily intuitive. We conducted a simulation study to test the effect of different patterns of catch misreporting on estimated fishery status and recommended catches. If, for example, 50% of all fishery catches are consistently unreported, estimates of population size and sustainable yield will be 50% lower, but estimates of current exploitation rate and fishery status will be unbiased. As a result, constant under-or over-reporting of catches results in recommended catches that are sustainable. However, when there are trends in catch reporting over time, the estimates of important parameters are inaccurate, generally leading to underutilization when reporting rates improve, and overfishing when reporting rates degrade. Thus, while quantifying total catch is necessary for understanding the impact of fisheries on businesses, communities and ecosystems, detecting trends in reporting rates is more important for estimating fishery status and setting sustainable catches into the future.

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    We conservatively estimate the distant-water fleet catch of the People's Republic of China for 2000–2011, using a newly assembled database of reported occurrence of Chinese fishing vessels in various parts of the world and information on the annual catch by vessel type. Given the unreliability of official statistics, uncertainty of results was estimated through a regionally stratified Monte Carlo approach, which documents the presence and number of Chinese vessels in Exclusive Economic Zones and then multiplies these by the expected annual catch per vessel. We find that China, which over-reports its domestic catch, substantially under-reports the catch of its distant-water fleets. This catch, estimated at 4.6 million t year−1 (95% central distribution, 3.4–6.1 million t year−1) from 2000 to 2011 (compared with an average of 368 000 t·year−1 reported by China to FAO), corresponds to an ex-vessel landed value of 8.93 billion € year−1 (95% central distribution, 6.3–12.3 billion). Chinese distant-water fleets extract the largest catch in African waters (3.1 million t year−1, 95% central distribution, 2.0–4.4 million t), followed by Asia (1.0 million t year−1, 0.56–1.5 million t), Oceania (198 000 t year−1, 144 000–262 000 t), Central and South America (182 000 t year−1, 94 000–299 000 t) and Antarctica (48 000 t year−1, 8 000–129 000 t). The uncertainty of these estimates is relatively high, but several sources of inaccuracy could not be fully resolved given the constraints inherent in the underlying data and method, which also prevented us from distinguishing between legal and illegal catch.
  • Article
    Full-text available
    Recent reports suggest that many well-assessed fisheries in developed countries are moving toward sustainability. We examined whether the same conclusion holds for fisheries lacking formal assessment, which comprise >80% of global catch. We developed a method using species’ life-history, catch, and fishery development data to estimate the status of thousands of unassessed fisheries worldwide. We found that small unassessed fisheries are in substantially worse condition than assessed fisheries, but that large unassessed fisheries may be performing nearly as well as their assessed counterparts. Both small and large stocks, however, continue to decline; 64% of unassessed stocks could provide increased sustainable harvest if rebuilt. Our results suggest that global fishery recovery would simultaneously create increases in abundance (56%) and fishery yields (8 to 40%).
  • Article
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    Under-reporting of fishery catches can severely affect the precision of stock assessment estimates, which require accurate information on catch and catch rate. Under-reporting of catches of South Coast rock lobster Palinurus gilchristi over the past decade was estimated from verified daily catch rates and the number of days spent at sea by the commercial fleet. The malpractice increased sharply between the 1997/98 and 2000/01 fishing seasons. The index of abundance for the resource (standardized catch per unit effort) increased by 2% for 1998/99, 12% for 1999/00 and 14% for 2000/01, after eliminating under-reported information from the input data. An age-structured production model, with the adjusted abundance index as an input, and including known and estimated over-catches between 1991/92 and 2000/01, increased the maximum sustainable yield estimate from 360 to 390 tons tail mass. The Total Allowable Catch (TAC) management regulation that was historically used in the fishery failed to address over-harvesting as a result of poor compliance. A combined TAC and Total Allowable Effort management strategy was introduced in 2000/01 to restrict fishing effort (days at sea) on the basis of quota size and vessel efficiency. Changes in management strategy, which include cancellation of the license of a fishing company responsible for systematic under-reporting and over-harvesting, decrease in fishing effort, reduction in over-capacity of vessels and other infrastructure and stabilization of trap catch rates have improved the outlook for the fishery.
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    Many criteria for statistical parameter estimation, such as maximum likelihood, are formulated as a nonlinear optimization problem. Automatic Differentiation Model Builder (ADMB) is a programming framework based on automatic differentiation, aimed at highly nonlinear models with a large number of parameters. The benefits of using AD are computational efficiency and high numerical accuracy, both crucial in many practical problems. We describe the basic components and the underlying philosophy of ADMB, with an emphasis on functionality found in no other statistical software. One example of such a feature is the generic implementation of Laplace approximation of high-dimensional integrals for use in latent variable models. We also review the literature in which ADMB has been used, and discuss future development of ADMB as an open source project. Overall, the main advantages of ADMB are flexibility, speed, precision, stability and built-in methods to quantify uncertainty.
  • Article
    Informative data in fisheries stock assessment are those that lead to accurate estimates of abundance and reference points. In practice, the accuracy of estimated abundance is unknown and it is often unclear which features of the data make them informative or uninformative. Neither is it obvious which model assumptions will improve estimation performance, given a particular data set. In this simulation study, 10 hypotheses are addressed using multiple scenarios, estimation models, and reference points. The simulated data scenarios all share the same biological and fleet characteristics, but vary in terms of the fishing history. The estimation models are based on a common statistical catch-at-age framework, but estimate different parameters and have different parts of the data available to them. Among the findings is that a ‘one-way trip’ scenario, where harvest rate gradually increases while abundance decreases, proved no less informative than a contrasted catch history. Models that excluded either abundance index or catch at age performed surprisingly well, compared to models that included both data types. Natural mortality rate, M, was estimated with some reliability when age-composition data were available from before major catches were removed. Stock-recruitment steepness, h, was estimated with some reliability when abundance-index or age-composition data were available from years of very low abundance. Understanding what makes fisheries data informative or uninformative enables scientists to identify fisheries for which stock assessment models are likely to be biased or imprecise. Managers can also benefit from guidelines on how to distribute funding and manpower among different data collection programmes to gather the most information.
  • Article
    Patterson, K. R. 1998. Assessing fish stocks when catches are misreported: model, simulation tests, and application to cod, haddock, and whiting in the ICES area. – ICES Journal of Marine Science, 55: 878–891. Reporting of catches from several of the most commercially-important gadoid stocks in the North Sea and the west of Scotland areas (ICES Divisions IV and VIa) is believed to have become incomplete in recent years. This study uses a modification of a stock-assessment model due to Haist et al. (1993) (Canadian Special Publications in Fisheries and Aquatic Science, 120, 269–282) to explore the precision, accuracy and bias of estimates of parameters of management interest when catch information is incomplete but survey estimate of stock size and biological sampling of the age-structure of catches are known. It is concluded that the model can be used to estimate stock size, and hence the future catch for a known fishing mortality, with quite good accuracy even when catches are under-reported. However, estimates of actual catches and of fishing mortality were very imprecise and very inaccurate. Parameter estimates from the model had less bias, similar precision, and greater accuracy than a conventional ''tuned-VPA'' calculation. The model was used to assess population parameters in stocks of cod (Gadus morhua) in the North Sea and off the west of Scotland, and of whiting (Merlangius merlangus) off the west of Scotland. Results from this analysis confirm the present belief that catches of west Scotland cod have been substantially misreported since 1991 but that reported North Sea catches are approxi-mately correct. It is proposed that the model may be a useful addition to present methods used to assess these stocks, and the conclusion is proposed on the basis of the simulation experiments that in cases where misreporting is important, catch forecasts for a target fishing mortality will be more accurate than forecasts made for status quo fishing mortality.
  • Article
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    We present a new model to estimate capture probabilities, survival, abundance, and recruitment using traditional Jolly-Seber capture-recapture methods within a standard fisheries virtual population analysis framework. This approach compares the numbers of marked and unmarked fish at age captured in each year of sampling with predictions based on estimated vulnerabilities and abundance in a likelihood function. Recruitment to the earliest age at which fish can be tagged is estimated by using a virtual population analysis method to back-calculate the expected numbers of unmarked fish at risk of capture. By using information from both marked and unmarked animals in a standard fisheries age structure framework, this approach is well suited to the sparse data situations common in long-term capture-recapture programs with variable sampling effort.
  • Article
    Abstract To evaluate the impacts of ¢shing on marine ecosystems, the total extraction of ¢sh must be known. Putting a ¢gure on total extraction entails the di⁄cult task of estimat- ing, in addition to reported landings, discards, illegal and unmandated catches. Unre- ported catches cast various types of shadow, which may be tracked and estimated quantitatively. Some shadows of unreported catches are reviewed, for example, an innovative, well-funded NGO publicizes illegal catch in the Southern Ocean. For various reasons, o⁄cial ¢gures often have the implicit but unacceptable assumption that such categories are null. We present an estimation procedure,based on adjustment,factors taken from observer reports, correspondents and published information that track changes in a regulatory regime, and hence re£ect incentives and disincentives to misre- port. Monte Carlo simulations address uncertainty,using multiple sources of informa- tion to provide upper and lower estimates. Once in place, this method provides preliminary,estimates that may,be re¢ned without,disruption. The method,is demon- strated for ¢sheries in Iceland and,Morocco. We use,a ‘by-species’ approach,for Icelandic cod and haddock, while the Moroccan catch is divided into demersal and pelagic categories. Results suggest that Icelandic cod catches may,have been under- estimated by between 1 and 14% at di¡erent times, and haddock by between 1 and 28%. Underestimation,of Moroccan,catches appears to have been as much,as by 50%. These case studies show that it is possible to obtain estimates of misreporting, even when,direct data are lacking. Our method,encourages,transparency,because,sources of information are presented so that uncertain values are easily identi¢ed, o¡ering a Correspondence: T.J. Pitcher, Fisheries Centre, 2204 Main Mall, University of British Columbia, Vancouver, British Columbia, Canada
  • Article
    Meta-analyses of stock assessments can provide novel insight into marine population dynamics and the status of fished species, but the world’s main stock assessment database (the Myers Stock-Recruitment Database) is now outdated. To facilitate new analyses, we developed a new database, the RAM Legacy Stock Assessment Database, for commercially exploited marine fishes and invertebrates. Time series of total biomass, spawner biomass, recruits, fishing mortality and catch/landings form the core of the database. Assessments were assembled from 21 national and international management agencies for a total of 331 stocks (295 fish stocks representing 46 families and 36 invertebrate stocks representing 12 families), including nine of the world’s 10 largest fisheries. Stock assessments were available from 27 large marine ecosystems, the Caspian Sea and four High Seas regions, and include the Atlantic, Pacific, Indian, Arctic and Antarctic Oceans. Most assessments came from the USA, Europe, Canada, New Zealand and Australia. Assessed marine stocks represent a small proportion of harvested fish taxa (16%), and an even smaller proportion of marine fish biodiversity (1%), but provide high-quality data for intensively studied stocks. The database provides new insight into the status of exploited populations: 58% of stocks with reference points (n = 214) were estimated to be below the biomass resulting in maximum sustainable yield (BMSY) and 30% had exploitation levels above the exploitation rate resulting in maximum sustainable yield (UMSY). We anticipate that the database will facilitate new research in population dynamics and fishery management, and we encourage further data contributions from stock assessment scientists.
  • Article
    The bottom-fish stocks of the Main Hawaiian Islands (MHI) are intensively fished, both commercially and recreationally. Recent assessments of the Bottomfish Management Unit Species (BMUS) complex suggested overfishing, and expressed concerns about missing non-commercial data. We used reported commercial time-series data and estimation ratios to indirectly estimate non-commercial catches for non-pelagic species (i.e., excluding tuna and billfishes) for 1950–2005. Using adjustment ratios, we also accounted for commercial under-reporting, which suggested that total commercial non-pelagic catches were 28–128% higher than reported commercial catches for any given year. Estimated non-commercial catches for 1950–2005 were 2.1 times higher than reported commercial catches. Reported catches underestimated likely total catches (reported and un-reported commercial plus non-commercial) of non-pelagic species and BMUS components for 1950–2005 by a factor of 3.9 and 2.9, respectively. We incorporated the reconstructed BMUS non-commercial catches into stock assessments of the officially reported commercial BMUS catches via a Schaefer production model. Total catch increased by 2.5–3.5 times with the addition of non-commercial BMUS catch estimates, which in turn increased model estimates of MSY and carrying capacity (k) by approximately four times compared to analyses with reported commercial data alone. As the CPUE data lacked information to resolve the confounding between large, unproductive and small, productive stocks, an informative prior was used for fishing mortality rate to attain MSY (FMSY). To address uncertainty in key management parameters, independent estimates of exploitation rate, or fisheries independent estimates of abundance, and informative trends in recreational effort or catches are required.
  • Article
    This paper presents an overview of the key characteristics of small-scale coastal marine fisheries in Latin America and the Caribbean as well as an examination of some of the weaknesses, gaps, and challenges faced in fisheries assessment and management within the region. The information here is based largely on discussions involving a range of scientists, managers and fishers at the first CoastFish conference (“Coastal fisheries in Latin America and the Caribbean”) held in Merida, Mexico in 2004 and literature review. Small-scale fisheries in this region, as elsewhere, share similar characteristics including multi-gear and multispecies, low capital and labour intensive, remote landing sites, large number of migrant and seasonal workers, and weak market and bargaining power among fishers. Common issues facing these fisheries are resource overexploitation, complex and dynamic fleet interactions, competition and conflicts between fleets (small-scale, industrial and recreational), and post-harvest problems, such as lack of infrastructure. Research in the region focuses mainly on biological–ecological aspects, with limited attention paid to socio-economic issues. Collection of catch data is common in most countries, at least for the main target species, but its reliability has been questioned in many cases, especially when a multi-species fishery is in place. Management tools frequently used are ‘input control’, e.g., size limit, gear restriction, closed season, closed area, and fishing permits. Finally, legal frameworks typically exist to regulate fisheries in most countries, but lack of success in management could be attributed to a lack of surveillance, weak institutions, unclear legal management instruments, and limited involvement of fishers in the management process. Based on the above, we discuss ways to address gaps and challenges in the assessment and management of small-scale fisheries in Latin America and the Caribbean.
  • Article
    There are differences in perception of the status of fisheries around the world that may partly stem from how data on trends in catches over time have been used. On the basis of catch trends, it has been suggested that about 70% of all stocks are overexploited due to unsustainable harvesting and 30% of all stocks have collapsed to <10% of unfished levels. Catch trends also suggest that over time an increasing number of stocks will be overexploited and collapsed. We evaluated how use of catch data affects assessment of fisheries stock status. We analyzed simulated random catch data with no trend. We examined well-studied stocks classified as collapsed on the basis of catch data to determine whether these stocks actually were collapsed. We also used stock assessments to compare stock status derived from catch data with status derived from biomass data. Status of stocks derived from catch trends was almost identical to what one would expect if catches were randomly generated with no trend. Most classifications of collapse assigned on the basis of catch data were due to taxonomic reclassification, regulatory changes in fisheries, and market changes. In our comparison of biomass data with catch trends, catch trends overestimated the percentage of overexploited and collapsed stocks. Although our biomass data were primarily from industrial fisheries in developed countries, the status of these stocks estimated from catch data was similar to the status of stocks in the rest of the world estimated from catch data. We conclude that at present 28-33% of all stocks are overexploited and 7-13% of all stocks are collapsed. Additionally, the proportion of fished stocks that are overexploited or collapsed has been fairly stable in recent years.
  • Article
    Unselective fishing catches non-target organisms as 'bycatch'--an issue of critical ocean conservation and resource management concern. However, the situation is confused because perceptions of target and non-target catch vary widely, impeding efforts to estimate bycatch globally. To remedy this, the term needs to be redefined as a consistent definition that establishes what should be considered bycatch. A new definition is put forward as: 'bycatch is catch that is either unused or unmanaged'. Applying this definition to global marine fisheries data conservatively indicates that bycatch represents 40.4 percent of global marine catches, exposing systemic gaps in fisheries policy and management.
  • Article
    Landings statistics can be lower than true catches because many fish are discarded or landed illegally. Since many discards do not survive, treating landings as true catches can lead to biased stock assessments. This paper proposes treating catch as censored by bounding it below by the landings, L, and above by cL (for scalar c > 1). We demonstrate the approach with a simulation study, using a Schaefer surplus production model. Parameters were estimated in a Bayesian framework with BUGS software using two sets of priors. Both the traditional true-catch method and a survey-and-effort method (which was landings free) performed worse on average than the censored approach, as measured by the Bayes risk associated with estimates of maximum sustainable yield (MSY) and of an index of depletion (X). Recursive partitioning (regression trees) was used to associate simulation parameters to best-performing methods, showing that higher commercial fish catchability favoured the censored method at estimating X. In conclusion, censored methods provide a means of dealing with discarding and misreporting that can outperform some traditional alternatives.
  • Article
    Full-text available
    Illegal and unreported fishing contributes to overexploitation of fish stocks and is a hindrance to the recovery of fish populations and ecosystems. This study is the first to undertake a world-wide analysis of illegal and unreported fishing. Reviewing the situation in 54 countries and on the high seas, we estimate that lower and upper estimates of the total value of current illegal and unreported fishing losses worldwide are between $10 bn and $23.5 bn annually, representing between 11 and 26 million tonnes. Our data are of sufficient resolution to detect regional differences in the level and trend of illegal fishing over the last 20 years, and we can report a significant correlation between governance and the level of illegal fishing. Developing countries are most at risk from illegal fishing, with total estimated catches in West Africa being 40% higher than reported catches. Such levels of exploitation severely hamper the sustainable management of marine ecosystems. Although there have been some successes in reducing the level of illegal fishing in some areas, these developments are relatively recent and follow growing international focus on the problem. This paper provides the baseline against which successful action to curb illegal fishing can be judged.
  • Article
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    Over 75% of the world marine fisheries catch (over 80 million tonnes per year) is sold on international markets, in contrast to other food commodities (such as rice). At present, only one institution, the Food and Agriculture Organization of the United Nations (FAO) maintains global fisheries statistics. As an intergovernmental organization, however, FAO must generally rely on the statistics provided by member countries, even if it is doubtful that these correspond to reality. Here we show that misreporting by countries with large fisheries, combined with the large and widely fluctuating catch of species such as the Peruvian anchoveta, can cause globally spurious trends. Such trends influence unwise investment decisions by firms in the fishing sector and by banks, and prevent the effective management of international fisheries.
  • Article
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    We evaluated the commercial and recreational fishery landings over the past 22 years, first at the national level, then for populations of concern (those that are overfished or experiencing overfishing), and finally by region. Recreational landings in 2002 account for 4% of total marine fish landed in the United States. With large industrial fisheries excluded (e.g., menhaden and pollock), the recreational component rises to 10%. Among populations of concern, recreational landings in 2002 account for 23% of the total nationwide, rising to 38% in the South Atlantic and 64% in the Gulf of Mexico. Moreover, it affects many of the most-valued overfished species—including red drum, bocaccio, and red snapper—all of which are taken primarily in the recreational fishery.
  • Article
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    Fisheries around the world are managed with a broad range of institutional structures. Some of these have been quite disastrous, whereas others have proven both biologically and economically successful. Unsuccessful systems have generally involved either open access, attempts at top-down control with poor ability to monitor and implement regulations, or reliance on consensus. Successful systems range from local cooperatives to strong governmental control, to various forms of property rights, but usually involve institutional systems that provide incentives to individual operators that lead to behaviour consistent with conservation.
  • Article
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    Human-dominated marine ecosystems are experiencing accelerating loss of populations and species, with largely unknown consequences. We analyzed local experiments, long-term regional time series, and global fisheries data to test how biodiversity loss affects marine ecosystem services across temporal and spatial scales. Overall, rates of resource collapse increased and recovery potential, stability, and water quality decreased exponentially with declining diversity. Restoration of biodiversity, in contrast, increased productivity fourfold and decreased variability by 21%, on average. We conclude that marine biodiversity loss is increasingly impairing the ocean's capacity to provide food, maintain water quality, and recover from perturbations. Yet available data suggest that at this point, these trends are still reversible.