Thirty years of fleet dynamics modelling using discrete‐choice models: What have we learned?

Anticipating fisher behaviour is necessary for successful fisheries management. Of the different concepts that have been developed to understand individual fisher behaviour, random utility models (RUMs) have attracted considerable attention in the past three decades, and more particularly so since the 2000s. This study aimed at summarizing and analysing the information gathered from RUMs used during the last three decades around the globe. A methodology has been developed to standardize information across different studies and compare RUM results. The studies selected focused on fishing effort allocation. Six types of fisher behaviour drivers were considered: the presence of other vessels in the same fishing area, tradition, expected revenue, species targeting, costs, and risk‐taking. Analyses were performed using three separate linear modelling approaches to assess the extent to which these different drivers impacted fisher behaviour in three fleet types: fleets fishing for demersal species using active gears, fleets fishing for demersal species using passive gears and fleets fishing for pelagic species. Fishers are attracted by higher expected revenue, tradition, species targeting and presence of others, but avoid choices involving large costs. Results also suggest that fishers fishing for demersal species using active gears are generally more influenced by past seasonal (long‐term) patterns than by the most recent (short‐term) information. Finally, the comparison of expected revenue with other fisher behaviour drivers highlights that demersal fishing vessels are risk‐averse and that tradition and species targeting influence fisher decisions more than expected revenue.     

Primary productivity demands of global fishing fleets

To be sustainable, the extractive process of fishing requires biomass renewal via primary production driven by solar energy. Primary production required (PPR) estimates how much primary production is needed to replace the biomass of fisheries landings removed from marine ecosystems. Here, we examine the historical fishing behaviour of global fishing fleets, which parts of the food web they rely on, which ecosystems they fish and how intensively. Highly mobile European and Asian fleets have moved to ever more distant productive waters since the 1970s, especially once they are faced with the costs of access agreements for exclusive economic zones (EEZs) declared by host countries. We examine fleet PPR demands in the context of large marine ecosystems (LMEs), which are frequently fished with PPR demands well above their average primary productivity (PP). In some cases, this was mitigated by subsequent emigration of fleets or by management intervention. Fleet movements, however, have stressed additional marine areas, including the EEZs of developing countries. This suggests the potential for spatial serial depletion, if fishing capacity is not reduced to more sustainable PP removal levels. Fundamentally, fishing is limited by solar‐powered PP limits. Fishing beyond solar production has occurred, but in the future, marine systems may not be as forgiving, especially if overfishing and climate change compromise their resilience.     

Reducing sea turtle by-catch in pelagic longline fisheries

Reducing by‐catch of sea turtles in pelagic longline fisheries, in concert with activities to reduce other anthropogenic sources of mortality, may contribute to the recovery of marine turtle populations. Here, we review research on strategies to reduce sea turtle by‐catch. Due to the state of management regimes in most longline fisheries, strategies to reduce turtle interactions must not only be effective but also must be commercially viable. Because most research has been initiated only recently, many results are not yet peer‐reviewed, published or readily accessible. Moreover, most experiments have small sample sizes and have been conducted over only a few seasons in a small number of fisheries; many study designs preclude drawing conclusions about the independent effect of single factors on turtle by‐catch and target catch rates; and few studies consider effects on other by‐catch species. In the US North Atlantic longline swordfish fishery, 4.9‐cm wide circle hooks with fish bait significantly reduced sea turtle by‐catch rates and the proportion of hard‐shell turtles that swallowed hooks vs. being hooked in the mouth compared to 4.0‐cm wide J hooks with squid bait without compromising commercial viability for some target species. But these large circle hooks might not be effective or economically viable in other longline fisheries. The effectiveness and commercial viability of a turtle avoidance strategy may be fishery‐specific, depending on the size and species of turtles and target fish and other differences between fleets. Testing of turtle avoidance methods in individual fleets may therefore be necessary. It is a priority to conduct trials in longline fleets that set gear shallow, those overlapping the most threatened turtle populations and fleets overlapping high densities of turtles such as those fishing near breeding colonies. In addition to trials using large 4.9‐cm wide circle hooks in place of smaller J and Japan tuna hooks, other fishing strategies are under assessment. These include: (i) using small circle hooks (≤ 4.6‐cm narrowest width) in place of smaller J and Japan tuna hooks; (ii) setting gear below turtle‐abundant depths; (iii) single hooking fish bait vs. multiple hook threading; (iv) reducing gear soak time and retrieval during daytime; and (v) avoiding by‐catch hotspots through fleet communication programmes and area and seasonal closures.     

Review of climate change impacts on marine fisheries in the UK and Ireland

相似文献   

The behavioural dynamics of fishers: management implications

In pursuing their livelihood, fishers develop strategies when faced with changes in regulations and other fishery conditions. Changes involve each individual in a decision‐making process governed by his/her own goals or constraints. Despite this reality, the complex dynamics of fishing has usually been ignored in designing management initiatives, which has contributed to management failures in many parts of the world. Fishers have generally been treated as fixed elements, with no consideration of individual attitudes based on their operating scales (geographical, ecological, social and economic) and personal goals. We review existing research on the social, economic and behavioural dynamics of fishing to provide insight into fisher behaviour and its implications for fisheries management. Emphasis is placed on fisher perception, and how fishers develop dynamic fishing tactics and strategies as an adaptive response to changes in resource abundance, environmental conditions and market or regulatory constraints. We conclude that knowledge of these dynamics is essential for effective management, and we discuss how such information can be collected, analysed and integrated into fisheries assessment and management. Particular emphasis is placed on small‐scale fisheries, but some examples from industrial fleets are provided to highlight similar issues in different types of fisheries.     

Modelling South Pacific jack mackerel spatial population dynamics and fisheries

Since the 1970s, South Pacific jack mackerel (Trachurus murphyi) is one of the world's most important commercial exploited fish stock. The peak in the catch was achieved in the 1990s, after which the catch for all fleets steadily decreased due to strong fishing mortality and potentially unfavourable environmental conditions. An application of the ecosystem and fish population model SEAPODYM was developed for this species in the South Pacific Ocean to determine the extent of environmental and fisheries drivers on the stock dynamics. We combined publicly available fishing data, acoustic biomass estimates and expert knowledge to optimise fish population dynamics parameters (habitats, movements, natural and fishing mortality). Despite a large proportion of missing catch over the simulation period, the model provides realistic distributions of biomass, a good fit‐to‐data and is in agreement with the literature. The feeding habitat is predicted to be delineated by water temperature between 15°C for the first cohorts and 8.5°C for the oldest and dissolved oxygen concentration above 1.8 ml/L. Optimal spawning temperature is estimated to 15.57°C (S.E.: 0.75°C). The core habitat is predicted off Central Chile which is also the main fishing ground. There are other areas of higher fish concentration east of New Zealand, in the eastern part of the southern convergence and off Peru and northern Chile. However, there is a clear continuity between these different large sub‐populations. Fishing is predicted to have by far the highest impact, a result that should be reinforced if all fishing mortality could be included.     

Fisheries management scenarios: trade‐offs between economic and biological objectives

An age‐structured, population biology submodel and an economic submodel with vessel‐specific dynamics were applied to a demersal fishery in the North Aegean (NE Mediterranean) that consists of three main stocks: European hake Merluccius merluccius (L.), red mullet Mullus barbatus L. and striped red mullet Mullus surmuletus L. The Mefisto model is a bioeconomic simulation model through which the biological and economic submodels (disaggregated at the vessel level) are linked by means of a fishing mortality vector. Alternative management scenarios were built and tested based on input controls, and the performance of these strategies was examined against those of current policies. Three alternative management strategies were as follows: (1) reducing the coastal fisheries' fleet units; (2) limiting the effort level (days at sea) of the trawl fleets; and (3) changing the selectivity patterns of the trawl by increasing mesh size. The results show that for all three species, any of the three management measures (input controls) would be beneficial to both the stock and the fleets (over the medium and long terms) compared with the projections over time for the status quo. Improving the selectivity of the fishing gear proved to be more beneficial than limiting nominal effort, which was in turn more beneficial than decreasing coastal fleet size.     

瑙鲁协议成员国VDS入渔模式及其对中西太平洋金枪鱼围网渔业的影响

瑙鲁协议成员国（PNA）自2007年起实施“按日计费入渔模式”（船天计划,VDS）,对中西太平洋金枪鱼围网渔业带来重大影响.本文阐述VDS渔业管理模式出台的背景、基本内容和管理体系,并结合中国船队生产中的实际情况,分析VDS管理体系实施后对各金枪鱼围网渔船队的影响,提出我国远洋渔业企业应采取措施,积极应对区域渔业管理的新趋势.     

Disentangling complexity of fishing fleets: using sequence analysis to classify distinguishable groups of vessels based on commercial landings

Capturing the diversity of fishing fleets and identifying distinct subgroups is essential for effectively directing research and management efforts. In this study, the German Baltic gillnet fleet was split into distinguishable groups of vessels by applying a stepwise approach. Monthly landing profiles were classified using clustering techniques and arranged as annual landing sequences, as the basis to form groups of vessels with distinct annual landing sequences using sequence analysis. Commercial landings from 1243 vessels across 11 years (2008–2018) resulted in 8031 annual landing sequences, which were clustered into eight groups, each with a characteristic, annually recurring, seasonal landing pattern (cod group, cod-herring group, herring-flounder group, herring group, freshwater fish group, pikeperch group, eel group and port group). The results highlight the heterogeneity of the fleet and a strong adaptation to regional and seasonal resource availability. Studying sequences of landings instead of isolated events in time provides insight into the interlinkage and succession of landings and can aid at classifying fishing fleets and better targeting groups of vessels of interest.     

Catch rate standardization for yellowfin tuna (Thunnus albacares) in Taiwan's distant-water longline fishery in the Western and Central Pacific Ocean,with consideration of target change

Catch per unit of effort (CPUE) needs to be standardized to remove the effects of factors such as fishing time and location, before it can be used as an index of abundance in fish stock assessments. One of the most substantial effects arises from a change of target species. This is particularly important for the Taiwanese distant-water longline fishery, which has a long history of fishery data from two fleets that target various tuna species across three oceans. We review the development of the Taiwanese distant-water longline fishery and compare five designs for standardizing the catch rate of yellowfin tuna (Thunnus albacares) in the western and central Pacific Ocean, using generalized linear models with lognormal and delta-lognormal error assumptions. Two approaches to address targeting effects were tested: separating fishing fleet data based on observer records, and including four target indicators calculated from catch data. Four statistical regions (relating to major fishing grounds) were treated as a single factor in the first three cases and were treated separately for the last two (one independent run for each region). The last case, which involved independent analyses for each fishing fleet for each region, and using the delta-lognormal approach, was considered to provide the most informative standardized CPUE trends for yellowfin tuna.     

Estimation of the overall fishing power: A study of the dynamics and fishing strategies of Brittany's industrial fleets

The present paper suggests a method for estimating the fishing power of vessels and for analysing fleet dynamics. The approach is based on quantification of stocks catchability (q), derived from fishing mortality coefficients (F) as calculated by virtual population analysis. Catchabilities for each harvested stock are thus estimated relatively to the fishing effort (f_n) of each vessel, according to the equation: q = (F/f_n). A linear model is then fitted to these catchabilities. The model allows the identification and quantification of trends in average mortality rates per fishing hour for each stock. Under some assumptions, trends are interpreted as variations in the overall fishing power of each fleet. The approach is applied to three industrial and semi-industrial fleets of Brittany (Lorient, Concarneau and Douarnenez) and to the main gadoid stocks they exploit off the west coast of Scotland (ICES area VIa), and in the Celtic Sea (ICES area VIIf,g,h) for Concameau. Results show large variations in fishing power. Particularly, a marked increase trend in the fishing power exerted on saithe (Pollachius virens) is highlighted for the three fleets, over the period 1983–1989. These variations can be explained by the redirection of fishing strategies, which may occur on a large scale. Thus, we show how the collapse of saithe stock at first led the three fleets to intensify the harvesting of saithe, and from 1989 on, to adopt different strategies. The possible causes of the observed dynamics are discussed, as well as their consequences for fisheries management. In particular, the relevance of direct control of fishing effort as a regulatory tool is questioned.     

Cumulative impacts of fisheries in the California Current

Ecosystem‐based fisheries management calls for the consideration of the indirect and cumulative effects of fishing, in addition to estimating direct fishing mortality. Here, we quantify such effects of fishing fleets, and their interactions, using a spatially explicit Atlantis simulation model of the food web and fisheries in the California Current. Simulations testing the effects of single fleets suggested that bottom trawl, fixed gear, and hake (Merluccius productus) trawl primarily have direct impacts on their target and bycatch species. Few indirect effects from these three fleets extended through predator–prey links to other parts of the food web. In contrast, effects of the purse seine fleet extended beyond the three groups it harvested, strongly altering the abundance of predators, planktonic prey, and benthos. In terms of nine ecosystem attributes, our experiments involving single fleets identified six fleets that caused the bulk of negative impacts. Specific fleets impacted different aspects of the ecosystem, for instance with groundfish gears causing reductions in piscivore abundance, and hake trawl and purse seine increasing krill through reducing abundance of planktivores. In terms of interactions among fleets' effects, the vast majority of effects were simply additive – the combined effect of two fleets was simply the sum of the individual fleets' effects. The analyses offer one way to sharpen the focus of ecosystem‐based fisheries management in the California Current, emphasizing impacts and interactions of particular stressors.     

Non-stationary effects of multiple drivers on the dynamics of Japanese sardine (Sardinops melanostictus,Clupeidae)

Non-stationary driver-response relationships are increasingly being recognized by scientists, underlining that a paradigm shift out of conventional stationary relationships is crucial. Japanese sardine (Sardinops melanostictus, Clupeidae) is a typical small pelagic fish in the northwestern Pacific with considerable fluctuations in productivity, bringing about great economic and ecological concerns. Numerous studies suggest that the population dynamics of Japanese sardine is an integrated process affected by multiple density-dependent, fishing and climatic drivers. However, little has hitherto been done to incorporate the non-stationary effects of multiple drivers, impeding progresses in understanding the population dynamics and in developing management strategies. In this study, we adopted variable coefficients generalized additive models to reveal the non-stationary effects of density dependence, fishing pressure and climatic conditions on the population dynamics of Japanese sardine. Results suggest that the dynamics of Japanese sardine from 1976 to 2018 could be divided into four periods: the 1980s when suitable climatic conditions from strong Siberian High pressure system sustained high abundance; the 1990s when negative density-dependent effects and degrading climatic conditions due to temperature increase led to population collapse; the 2000s when negative triple effects, particularly high fishing pressure, restricted the population increase; and the 2010s when favourable climatic conditions with re-strengthening Siberian High pressure system accompanied by low fishing pressure contributed to the population recovery. The study highlights that precise identifications of population status and climatic conditions are helpful to achieve good trade-offs between resource exploitation and protection and to facilitate ecosystem-based management for Japanese sardine fisheries.     

Analysing commercial catch and effort data from a Penaeid trawl fishery: A comparison of linear models, mixed models, and generalised estimating equations approaches

Statistical methods are often used to analyse commercial catch and effort data to provide standardised fishing effort and/or a relative index of fish abundance for input into stock assessment models. Achieving reliable results has proved difficult in Australia's Northern Prawn Fishery (NPF), due to a combination of such factors as the biological characteristics of the animals, some aspects of the fleet dynamics, and the changes in fishing technology. For this set of data, we compared four modelling approaches (linear models, mixed models, generalised estimating equations, and generalised linear models) with respect to the outcomes of the standardised fishing effort or the relative index of abundance. We also varied the number and form of vessel covariates in the models. Within a subset of data from this fishery, modelling correlation structures did not alter the conclusions from simpler statistical models. The random-effects models also yielded similar results. This is because the estimators are all consistent even if the correlation structure is mis-specified, and the data set is very large. However, the standard errors from different models differed, suggesting that different methods have different statistical efficiency. We suggest that there is value in modelling the variance function and the correlation structure, to make valid and efficient statistical inferences and gain insight into the data. We found that fishing power was separable from the indices of prawn abundance only when we offset the impact of vessel characteristics at assumed values from external sources. This may be due to the large degree of confounding within the data, and the extreme temporal changes in certain aspects of individual vessels, the fleet and the fleet dynamics.     

Realizing the potential of trait‐based approaches to advance fisheries science

Analysing how fish populations and their ecological communities respond to perturbations such as fishing and environmental variation is crucial to fisheries science. Researchers often predict fish population dynamics using species‐level life‐history parameters that are treated as fixed over time, while ignoring the impact of intraspecific variation on ecosystem dynamics. However, there is increasing recognition of the need to include processes operating at ecosystem levels (changes in drivers of productivity) while also accounting for variation over space, time and among individuals. To address similar challenges, community ecologists studying plants, insects and other taxa increasingly measure phenotypic characteristics of individual animals that affect fitness or ecological function (termed “functional traits”). Here, we review the history of trait‐based methods in fish and other taxa, and argue that fisheries science could see benefits by integrating trait‐based approaches within existing fisheries analyses. We argue that measuring and modelling functional traits can improve estimates of population and community dynamics, and rapidly detect responses to fishing and environmental drivers. We support this claim using three concrete examples: how trait‐based approaches could account for time‐varying parameters in population models; improve fisheries management and harvest control rules; and inform size‐based models of marine communities. We then present a step‐by‐step primer for how trait‐based methods could be adapted to complement existing models and analyses in fisheries science. Finally, we call for the creation and expansion of publicly available trait databases to facilitate adapting trait‐based methods in fisheries science, to complement existing public databases of life‐history parameters for marine organisms.     

Economic impacts of TAC regulation: A supply-driven SAM approach

The Galician fishing fleet is one of the most important of all the European fleets that fish in European Union waters and hake is its vital species. The aim of this article is to estimate some of the economic impacts that a reduction in the TAC of hake during the period 1999–2003 have on the entire Galician economy. We use a “supply-driven” Social Accounting Matrix (SDSAM) model for the Galician fishing sector that takes hake production as exogenously given. In this respect, the present work constitutes a first attempt at applying a SDSAM model to fisheries. It also presents both the traditional backward linkage effects as well as the lesser known forward linkage effects. The SDSAM model allows us not only to compute impacts on production but also to estimate the impact distribution on household incomes and production factors. Impacts on employment have also been calculated. These results may be useful to policy makers as they provide some perceptions into the consequences of one of the measures of the Common Fisheries Policy (CFP) and may help to design policy initiatives.     

HIV and AIDS among fisherfolk: a threat to ‘responsible fisheries'?

Fishing communities are often among the highest‐risk groups in countries with high overall rates of HIV/AIDS prevalence. Vulnerability to HIV/AIDS stems from complex, interacting causes that may include the mobility of many fisherfolk, the time fishermen spend away from home, their access to daily cash income in an overall context of poverty and vulnerability, their demographic profile, the ready availability of commercial sex in fishing ports and the subcultures of risk taking and hypermasculinity among some fishermen. The subordinate economic and social position of women in many fishing communities in low‐income countries makes them even more vulnerable. HIV/AIDS in fishing communities was first dealt with as a public health issue, and most projects were conducted by health sector agencies and NGOs, focusing on education and health care provision. More recently, as the social and economic impacts of the epidemic have become evident, wider social service provision and economic support have been added. In the last 3 years, many major fishery development programmes in Africa, South/South‐East Asia and the Asia‐Pacific region have incorporated HIV/AIDS awareness in their planning. The HIV/AIDS pandemic threatens the sustainability of fisheries by eclipsing the futures of many fisherfolk. The burden of illness puts additional stresses on households, preventing them from accumulating assets derived from fishing income. Premature death robs fishing communities of the knowledge gained by experience and reduces incentives for longer‐term and inter‐generational stewardship of resources. Recent projects championing local knowledge and resource‐user participation in management need to take these realities into account. If the fishing communities of developing countries that account for 95% of the world's fisherfolk and supply more than half the world's fish are adversely impacted by HIV/AIDS, then the global supply of fish, particularly to lower‐income consumers, may be jeopardized.     

Thirty years of change and the future of Alaskan fisheries: Shifts in fishing participation and diversification in response to environmental,regulatory and economic pressures

Heterogeneity in human responses and decision‐making can contribute to the resilience of social–ecological systems in the face of environmental, political and economic pressures. In fishery systems worldwide, the ability of harvesters to maintain a diverse portfolio of fishing strategies is important for building adaptive capacity. We used a case‐study approach to examine the complexity of factors that inhibit or promote diversification in fisheries of Alaska, one of the major fishing regions of the world. Through a combination of harvest records and literature review, we explored shifts in participation and portfolio diversity in Alaskan fisheries over three decades. The four case‐studies examined the responses of fishers, fleets and communities to multiple, intersecting pressures, including biological declines, market and price dynamics, fishery privatization and the 1989 Exxon Valdez oil spill. These cases illustrate how stressors acting at multiple scales can encourage or constrain opportunities for diversification, and that these opportunities may be spread inequitably across participants. Overall, we found evidence for reduced participation and increasing specialization in Alaskan commercial fisheries. While numerous factors explain these trends, policies like individual quota systems and the increasing cost of entry into fisheries are forcing consolidation at local to regional scales. A portfolio approach to managing fisheries that reduces barriers to diversification and includes broad representation of resource users and communities in management may help to maintain opportunity and choice for fishers.     

A strategic planning model for fisheries development

This paper presents a dynamic decision support model to aid coastal nations in the long-range planning of fishery development. The bioeconomic framework presented here provides a simple means for analysing complex interactions between fishery resource management, domestic fleet development, and the role of foreign fleets. The model includes explicit dynamics of the fish stock and the domestic fleet, and allows for harvest rate and investment rate controls. Several realistic behavioral components are also incorporated: (i) multi-objective optimization, balancing the direct benefits of rent generation with the indirect benefits of domestic fleet development; (ii) socio-political constraints, which lead the coastal state to accord its domestic fleet absolute priority in harvesting within coastal waters; (iii) limitations on access to capital, which restrict growth of the domestic fleet to that which can be financed through fishery revenues; (iv) interactions between the coastal state and the foreign fleets, in which the former is able to set a royalty rate, applied per unit of foreign harvest, while the foreign fleet responds to any specified royalty rate on a profit-maximizing basis. Analysis of the model indicates that optimal fishery development policies may depend particularly on the relative profitability of the domestic fleet, as well as the extent to which an explicit value is placed on the employment and secondary benefits of domestic fleet development.