Fishing efficiency of competitive largemouth bass tournament anglers has increased since early 21st century

Tournament fishing has risen in popularity over the last half a century. As such, social and financial incentives combined with technological advancements are expected to drive changes in angler's capacity to exploit tournament‐eligible fish stocks, as has been observed in commercial fisheries. The aim of this study was to quantify temporal trends in angler efficiency and their ability to exploit a given fish stock relative to effort in largemouth bass fishing tournaments. A collective analysis across seven Illinois reservoirs comparing change through time in angler catch rates and relative population abundances indicated that angler efficiency has generally improved through time. For the decade from 2005 to 2015, a greater than threefold increase in the efficiency of anglers to exploit a static population of largemouth bass was estimated. Anglers have become more efficient at exploiting populations, which is likely to influence management decisions in the future, particularly in harvest‐orientated fisheries and those reliant upon fishery‐dependent surveys.     

Can catch share fisheries better track management targets?

Fisheries management based on catch shares – divisions of annual fleet‐wide quotas among individuals or groups – has been strongly supported for their economic benefits, but biological consequences have not been rigorously quantified. We used a global meta‐analysis of 345 stocks to assess whether fisheries under catch shares were more likely to track management targets set for sustainable harvest than fisheries managed only by fleet‐wide quota caps or effort controls. We examined three ratios: catch‐to‐quota, current exploitation rate to target exploitation rate and current biomass to target biomass. For each, we calculated the mean response, variation around the target and the frequency of undesirable outcomes with respect to these targets. Regional effects were stronger than any other explanatory variable we examined. After accounting for region, we found the effects of catch shares primarily on catch‐to‐quota ratios: these ratios were less variable over time than in other fisheries. Over‐exploitation occurred in only 9% of stocks under catch shares compared to 13% of stocks under fleet‐wide quota caps. Additionally, over‐exploitation occurred in 41% of stocks under effort controls, suggesting a substantial benefit of quota caps alone. In contrast, there was no evidence for a response in the biomass of exploited populations because of either fleet‐wide quota caps or individual catch shares. Thus, for many fisheries, management controls improve under catch shares in terms of reduced variation in catch around quota targets, but ecological benefits in terms of increased biomass may not be realized by catch shares alone.     

The role of environmental conditions and exploitation in determining dynamics of redfish (Sebastes species) in the Northwest Atlantic

The six stocks of redfish (Sebastes spp.) in the Northwest Atlantic have been fished for the past 60 years, during which time they have also experienced considerable variability in environmental conditions. Despite their close proximity and with life‐history features characteristic of many deep‐sea fishes (long‐lived, slow‐growing, late‐maturing, relatively low fecundity), each redfish stock has displayed quite different dynamics. Some have been able to support apparently sustainable fisheries, whereas others have been forced to close. The causes of such differences are unclear. We used dynamic factor analysis to determine the relative impacts of exploitation (days fishing for redfish, days fishing for shrimp, days fished by all fisheries, catch in the redfish fishery, total redfish catch) and environment (North Atlantic Oscillation, surface temperature, salinity, shallow, middle, and deep bottom temperatures) on trends of abundance in each stock over the years 1960–2004. The results showed that a mix of exploitation and environmental variability, with various and different lag times, accounted for observed trends. The Gulf of St. Lawrence stock was affected most by exploitation. Flemish Cap and northern Newfoundland‐Labrador stocks were mostly affected by environmental factors with longer time lags than more southerly stocks. We conclude that management of redfish must take into account individual responses to exploitation and environment over the time periods during which such factors operate, often decades or more, as opposed to the usual practice of reviewing only dynamics of the past few years. Deep‐sea populations cannot be managed on the same scales as shelf fisheries.     

Feasibility of a single-species quota system for management of the Malaysian multispecies purse-seine fishery

Malaysian fisheries employ multiple measures to improve management; however, not all are well-suited to the multispecies fisheries. As part of a pilot project, an individual quota system was introduced for the purse-seine fishery off the East Coast of Peninsular Malaysia (ECPM), but no assessment of this particular measure nor the feasibly of its implementation has been confirmed. Therefore, this study analysed spatial and temporal patterns of purse-seine fishing, by collecting catch composition data per landing and its fishing ground within three period fishery surveys between August 2017 and September 2018 at six different landing sites. Similarity and cluster analysis examined species composition and diversity to determine the feasibility of implementing a single-species quota system in this multispecies fishery. Some overlapped of indices results and minor difference in catch composition were found due to changes in spatial and temporal fishing activities. However, no specific spatial or temporal patterns were discernible as structuring the fishing grounds used by purse-seiners. The absence of patterns, using the available data, might be attributable to huge species aggregations and widely distributed and homogenously mixed fish stocks. Thus, it is likely impractical to manage species individually in such a multispecies fishery.     

A simple method for estimating MSY from catch and resilience

The Law of the Sea requires that fish stocks are maintained at levels that can produce the maximum sustainable yield (MSY). However, for most fish stocks, no estimates of MSY are currently available. Here, we present a new method for estimating MSY from catch data, resilience of the respective species, and simple assumptions about relative stock sizes at the first and final year of the catch data time series. We compare our results with 146 MSY estimates derived from full stock assessments and find excellent agreement. We present principles for fisheries management of data‐poor stocks, based only on information about catches and MSY.     

Does unreported catch lead to overfishing?

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.     

The dynamics of collapse in world fisheries

The fear of a rapid depletion of world fish stocks because of over‐exploitation is increasing. Analysis of 1519 main series of the FAO world fisheries catch database over the last 50 years reveals that 366 fisheries’ collapses occurred, that is nearly one fishery of four. The robustness of this result is tested by performing several complementary analyses using different conservative options. The number of collapses has been stable through time since 1950s indicating no improvement in the overall fisheries management. Three typical patterns emerge from the analysis of catch series during the period preceding the collapses: smooth collapse (33%), i.e. a long regular decline, erratic collapse (45%), i.e. a fall after several ups and downs, and a plateau‐shaped collapse (21%), i.e. a sudden fall after a relatively long and stable persistence of high level of catches. Using a simple mathematical model, we relate the plateau‐shaped collapses (which are, by nature, the most difficult to predict) to surreptitiously increasing exploitation and a depensatory mechanism at low population levels. Thus, a stable level of catch over several years is shown to conceal the risk of a sudden collapse. This jeopardizes the common assumption that considers the stability of catch as a goal for fisheries sustainability.     

鱼类自然死亡系数评估研究进展

自然死亡系数是渔业资源评估中不可或缺的重要参数,其准确度直接决定了资源评估结果的可靠性,进而影响渔业管理策略的制定。本文从生活史参数、标志回捕和年龄结构3个方面列举了国内外自然死亡系数的常用评估方法,讨论了相关方法的优缺点及影响因素,并以犬齿牙鲆(Paralichthys dentatus)和中国近海鱼类为例对比分析不同模型的计算结果。在此基础上,着重介绍了Pauly经验公式在中国近海主要经济鱼类自然死亡系数评估中的应用进展及存在问题。根据渔业资源调查和研究数据现状,认为现阶段使用Pauly经验公式评估中国近海经济鱼类自然死亡系数具有积极作用。     

Inland fish stock assessment: Applying data‐poor methods from marine systems

Inland fisheries can be diverse, local and highly seasonal. This complexity creates challenges for monitoring, and consequently, many inland fish stocks have few data and cannot be assessed using methods typically applied to industrial marine fisheries. In such situations, there may be a role for methods recently developed for assessment of data‐poor fish stocks. Herein, three established data‐poor assessment tools from marine systems are demonstrated to highlight their value to inland fisheries management. A case study application uses archived length, catch and catch‐per‐unit‐effort data to characterise the ecological status of an important recreational brown trout stock in an Irish lake. This case study is of specific use to management of freshwater sport fisheries, but the broader purpose of the paper was to provide a crossover between marine and inland fisheries science, and to highlight accessible data‐poor assessment approaches that may be applicable in diverse inland systems.     

Broadbill swordfish: status of established fisheries and lessons for developing fisheries

Guidelines for the assessment and management of developing swordfish fisheries are derived through an examination of five swordfish fisheries. As they develop, swordfish fisheries may be inclined to local depletion around underwater features, such as seamounts and banks. Few nations have applied the precautionary approach in managing their developing swordfish fisheries. Without controls, swordfish fisheries expand geographically and fishing effort increases, often overshooting optimum levels. However, it is difficult to distinguish clear evidence of fishery collapse; modern longliners harvest widely distributed tuna and swordfish and they are able to relocate to distant areas or switch between target species in response to fluctuations in species abundance and price. Furthermore, the wide distribution of swordfish combined with year‐round spawning and high growth rates amongst juveniles probably contribute to the apparent resilience of swordfish stocks to intensive harvesting. Over half the world’s swordfish catch is taken as an incidental catch of longliners fishing for tuna. In several areas, such as the North Atlantic, catch quotas have sometimes caused tuna longline fishers to discard swordfish. Minimum size limits have also resulted in discarding of swordfish in tuna fisheries and in dedicated swordfish fisheries. In addition to weakening the effectiveness of those management measures, bycatch and discarding add to the complexities of managing swordfish fisheries and to uncertainties in assessing the stocks. Longliners that target swordfish often fish at high latitudes where interactions with marine wildlife, such as seabird, are generally more frequent than at low latitudes. Concern over incidental catches of marine wildlife and other species is becoming a driving force in the management of several swordfish fisheries. Fishery management organisations will need to implement management measures to protect non‐target species and gather reliable data and information on the situation by placing observers on boats fishing for swordfish.     

Relationships among long'term fisheries abundances, hydrographic variables, and gross pollution indicators in northeastern U.S. estuaries

Categorical time series regression was applied to 55 fish stocks in the Potomac, Hudson, Narragansett, Delaware, and Connecticut estuaries for the period 1929–1975. Interannual variability in catch per unit effort (CPUE) was related to CPUE, hydrographic variables, and pollution variables, lagged back in time to represent the conditions contributing to the multiple ages comprising each fishery. Hydrographic variables included water temperature and flow in the estuary– and, for offshore spawning stocks, wind direction and magnitude–during the months of spawning and early life stage development. Pollution variables included measures of dissolved oxygen conditions in the estuaries, volume of material dredged, and sewage loading (or human population). Lagged CPUE, hydrographic variables, and pollution variables all played important roles in explaining historical variability in CPUE. Lagged CPUE was significant in 45 of 55 stocks generally accounting for 5–35% of the variability. Lagged hydrographic variables were significant in 53 of 55 stocks, explaining an additional 5–40% of the variability unaccounted for by lagged CPUE. Lagged pollution variables were significant in 35 of 55 stocks, generally accounting for an additional 5–30% of the variability not explained by lagged CPUE and hydrographic variables. Results did not exhibit expected patterns of consistency in the importance of lagged CPUE for a species across estuaries or consistency in the importance of pollution variables across estuaries. Results did exhibit the expected north-to-south longitudinal pattern in the importance of timing of the hydrographic variables, the months of importance being one or two months later in more northerly estuaries. Higher-order interaction effects were important in almost all stocks that were well-modeled by categorical time series regression. Of the 30 stocks with final regression models having R² > 0.55, 26 stocks involved significant interaction effects, five had only significant interaction effects (no significant main effects), and 20 stocks had significant interactions involving variables not significant as main effects. The difficulties involved in analyzing long-term trends in fish populations and partitioning variability between natural and anthropogenic sources are discussed.     

An exploration of the shapes and stability of population–selection curves

Fishing operations on any given stock rarely generate fishing mortality that is uniform across all ages and sizes. Population‐selectivity refers to a scaled version of the age‐ or size‐specific fishing mortality experienced by a fish population. Although it is common to apply a sigmoid logistic curve for the selectivity produced by many kinds of fishing gear, the general characteristics of population–selection curves have not been well examined. In this study, generalized additive models were fit to sets of selection coefficients taken from 15 recent stock assessments conducted using the virtual population analysis approach. The selection coefficients predicted by the models provided smoothed representations of the shapes and temporal dynamics of selectivity. Four broad types of selectivity were found: increasing, asymptotic, domed, and having a saddle. Four specific cases, each dominated by one type of selection curve, were examined in detail. For all 15 stocks, the population–selection curves were not stable through time but underwent changes in shape, which in some cases were quite radical. Temporal variation in population‐selectivity has important implications for the conduct of fisheries modelling activities such as evaluating management strategies and forecasting catch and stock size.     

Keep it simple: three indicators to deal with overfishing

Three simple fisheries indicators are presented: (i) percentage of mature fish in catch, with 100% as target; (ii) percent of specimens with optimum length in catch, with 100% as target; and (iii) percentage of ‘mega‐spawners‘ in catch, with 0% as target, and 30–40% as representative of reasonable stock structure if no upper size limit exists. Application of these indicators to stocks of Gadus morhua, Sardinella aurita and Epinephelus aeneus demonstrate their usefulness. It is argued that such simple indicators have the potential to allow more stakeholders such as fishers, fish dealers, supermarket managers, consumers and politicians to participate in fisheries management and eventually hold and reverse the global pattern of convenience overfishing, which is defined here as deliberate overfishing sanctioned by official bodies who find it more convenient to risk eventual collapse of fish stocks than to risk social and political conflicts.     

A stochastic surplus production model in continuous time

Surplus production modelling has a long history as a method for managing data‐limited fish stocks. Recent advancements have cast surplus production models as state‐space models that separate random variability of stock dynamics from error in observed indices of biomass. We present a stochastic surplus production model in continuous time (SPiCT), which in addition to stock dynamics also models the dynamics of the fisheries. This enables error in the catch process to be reflected in the uncertainty of estimated model parameters and management quantities. Benefits of the continuous‐time state‐space model formulation include the ability to provide estimates of exploitable biomass and fishing mortality at any point in time from data sampled at arbitrary and possibly irregular intervals. We show in a simulation that the ability to analyse subannual data can increase the effective sample size and improve estimation of reference points relative to discrete‐time analysis of aggregated annual data. Finally, subannual data from five North Sea stocks are analysed with particular focus on using residual analysis to diagnose model insufficiencies and identify necessary model extensions such as robust estimation and incorporation of seasonality. We argue that including all known sources of uncertainty, propagation of that uncertainty to reference points and checking of model assumptions using residuals are critical prerequisites to rigorous fish stock management based on surplus production models.     

Reconstructing historical trends of small pelagic fish in the Java Sea using standardized commercial trip based catch per unit of effort

Pelagic fish stocks in the Java Sea have been exploited intensively since the beginning of the 1970s. However, due to the effect of increased fishing power of the fleets and the changing nature of spatial and temporal distribution of the fishing effort, assessment of stock trends based on commercial data of catch and effort requires the standardization of both effort and catch data. Here we present the first attempt to reconstruct a standardized time series of commercial catch per unit of effort (CPUE) for the main pelagic species exploited by the purse seine fleet in the Java Sea. The results showed that all the stocks analysed have largely declined since the beginning of the 1990s. For bigeye scad, Indian mackerel and sardine, current estimates are only between 3 and 19% of the maximum observed value while round scads and spotted sardine biomass estimates lie between 18 and 34%. However, our assumptions about the effect of lamp power and level of creeping and the fact that the influence of fish density on catchability and the effect of targeting were not taken into account thus observed decline is a rather conservative estimate of the real decline of the stocks. If effective management actions are not put in place as a matter of urgency in the Java Sea for small pelagic fisheries, one runs the risk of adding those species to the long list of overexploited stocks of the world oceans.     

A socio-economic perspective on gear-based management in an artisanal fishery in south-west Madagascar

Abstract  Artisanal fisheries are important socially, nutritionally and economically. Poverty is common in communities dependent on such fisheries, making sustainable management difficult. Poverty based on material style of life (MSL) was assessed, livelihoods surveyed and the relationship between these factors and fishery data collected using a fish landing study were examined. Species richness, diversity, size and mean trophic level of catches were determined for six fishing gears in an artisanal fishery in south-west Madagascar. There was little livelihood diversification and respondents were highly dependent on the fishery. No relationship was found between poverty and gear use. This suggests that poverty does not have a major impact on the nature of the fishery; however, this study was dominated by poor households, so it remains possible that communities with more variation in wealth might show differences in fishing methods according to this parameter. The fishery was heavily exploited with a predominance of small fish in the catches. Beach seines caught some of the smallest fish, overlapped in selectivity with gill nets and also had the highest catch per fishers. Thus, a reduction in the number of beach seines could help reduce the catch of small fish and the overlap in selectivity among gears.     

Shooting fish in a barrel? Assessing fisher‐driven changes in catchability within tropical tuna purse seine fleets

With constant innovation to find more efficient ways to find, catch and process fish, catchability in wild fisheries can increase. Catchability is a combination of resource abundance, fishing effort and fishing efficiency: any increase in fleet efficiency can lead to undesirable effects not only on stocks, but also on the ability to assess them. When using effort controls as part of management, it is necessary to adjust for the increase in catchability due to the increases in efficiency over time to avoid stock depletion. Accounting for changes in catchability can be problematic for pelagic stocks, due to the changes in fishing behaviour and the continual change in fishing efficiency. This study investigates the success in finding patches of fish for fleets operating within the western and central Pacific purse seine fishery between 1993 and 2012. Three indices, widely used in ecological research, were used to study how spatial variation in fisher behaviour for sets on fish aggregating devices (FADs) and free‐school sets was related to catchability. For free‐school set types, the diversity index was negatively correlated with Katsuwonus pelamis catchability. When this index was low, catch rates were at their highest and there was a reduction in the area fished. In contrast, for FAD sets, catches increase when the patchiness index was low, implying a degree of random behaviour, potentially due to advances in FAD technology. An improved understanding of the spatial allocation of effort can improve catchability estimates widely used for fisheries stock assessments and in indices of global biodiversity.     

Harvest control rules used in US federal fisheries management and implications for climate resilience

Climate change is altering the productivity of marine fisheries and challenging the effectiveness of historical fisheries management. Harvest control rules, which describe the process for determining catch limits in fisheries, represent one pathway for promoting climate resilience. In the USA, flexibility in how regional management councils specify harvest control rules has spawned diverse approaches for reducing catch limits to precautionarily buffer against scientific and management uncertainty, some of which may be more or less resilient to climate change. Here, we synthesize the control rules used to manage all 507 US federally managed fish stocks and stock complexes. We classified these rules into seven typologies: (1) catch-based; (2) constant catch; (3) constant escapement; (4) constant F; (5) stepped F; (6) ramped F and (7) both stepped and ramped F. We also recorded whether the control rules included a biomass limit (‘cut-off’) value or were environmentally linked as well as the type and size of the buffers used to protect against scientific and/or management uncertainty. Finally, we review the advantages and disadvantages of each typology for managing fisheries under climate change and provide seven recommendations for updating harvest control rules to improve the resilience of US federally managed fisheries to climate change.     

Fish stock assessment of the northern New Caledonian lagoons:1 – Structure and stocks of coral reef fish communities

Lagoon fish in New Caledonia are mainly caught by artisanal fisheries and subsistence fishing. Reef fish are the major component of this catch. The present study aimed at estimating these reef fish standing stocks and at finding the main factors influencing the distribution of these fish. Sampling of 904 stations was stratified according to three zones (north, east and west) and three reef types (barrier, intermediate and fringing). Fish communities exhibited strong heterogeneity in their distribution, showing higher biomass (maximum of 447 g·m^–2) and total standing stock (43 000 tonnes) in the north zone than in the east and west zones. Similarly, observed patterns were dependent on reef types: higher biomass and total standing stock being observed on barrier reefs than on intermediate or fringing reefs. The total standing stocks, which were about 65 000 t, were mainly composed of herbivorous fish families such as the Acanthuridae and Scaridae. The differences in the patterns of distribution of species, individuals and standing stocks between reef types may be explained by variations in terrestrial influences and reef morphology, whereas differences among zones were most likely due to accessibility of fishing areas and fishing pressure. The latter is almost non-existent in the north zone, which can thus be considered to be almost unexploited commercially. This most likely explains the high proportion, 77 %, of long-lived species in the biomass of this zone. The results might have implications in management of reefs elsewhere in the South Pacific, for which similar data are only scarcely available.     

Natural mortality augments population fluctuations of forage fish

Forage fish are a vital part of marine ecosystems, partly by supporting some of the largest fisheries worldwide, but also due to their role in food webs as prey for larger fish and other predators. One of the unresolved questions about forage fish dynamics is the causes of their significant temporal fluctuations. These fluctuations are often attributed to changes in environmental conditions, but direct correlations have proven hard to find. Here, we show how time‐varying predation mortality additionally plays a substantial role in forage fish population fluctuations. By analysing 10 stocks that have estimates of natural mortality changes through time, we find that natural mortality on average increases as population biomass declines towards a trough, and to a lesser degree decreases, when their biomass is growing towards a peak. While depensatory mortality was dominant on average in biomass dynamics leading up to peaks or troughs, some of the stocks exhibited compensatory mortality emphasizing variation between stocks. Furthermore, we show that the magnitude of natural mortality and productivity is generally higher than fishing mortality. The results underscore the importance of top‐down control on the dynamics of forage fish. We conclude that a holistic ecosystem analysis is required for a better ecological understanding of forage fish dynamics.