Spatial Distribution Of Effort Research Articles

Fishery dynamics of blue whiting, Micromesistius poutassou, a highly discarded bycatch species in the NW Mediterranean Sea

This study characterized the fishery dynamics of blue whiting, a bycatch species of the bottom trawl Norway lobster fishery, in the NW Mediterranean. Landings and effort data over the last two decades were combined with current information on the spatial distribution of effort and catch, and with the size and age structure of blue whiting over the year. Recruitment to the demersal habitat occurred from 5 cm total length (TL) over the shelf break in spring (April-May), when discards showed the highest values (>95% of the catch). Adults were located over the upper slope, and large individuals (≥26 cm TL) were abundant during the reproductive period (January-March). A decline in landings has been observed in the last decade, probably related to the absence of intense deep convection processes in winter since 2013, which favour recruitment of the species. The effect of exploitation on the decrease in landings cannot be disregarded considering that the bulk of the catch is made up of immature (age 0) individuals, and the presence of old individuals is very low.

Bycatch Estimates From a Pacific Tuna Longline Fishery Provide a Baseline for Understanding the Long-Term Benefits of a Large, Blue Water Marine Sanctuary

Bycatch on pelagic tuna longlines has contributed to population declines in several far-ranging, oceanic species and presents a conservation challenge that area-based management tools are increasingly promoted to address. In January 2020 the Republic of Palau, concerned about the impacts of longline fishing in its waters, closed 80% of its exclusive economic zone to all extractive activities, reserving the remaining 20% for a domestic fishing zone (DFZ). One of a growing number of very large marine protected areas, the Palau National Marine Sanctuary (PNMS) spans ∼500,000 km2 and was established inter alia to allow for the recovery of fish stocks adversely impacted by tuna longline fleets. Given that the main tuna stocks targeted in the western Pacific are not overexploited, the benefits of protection potentially afforded by the sanctuary are likely greater for vulnerable bycatch species. Evaluations of the sanctuary’s performance require, in part, a baseline of historical catch rates and effort distribution in the distant-water fleet (DWF) and locally based fleet (LBF) operating in Palau prior to sanctuary implementation. We describe the fishing effort, catch rates, catch estimates and fishing mortality in Palau’s longline fishery based on logbook, observer and electronic monitoring data. We defined bycatch as any species, retained or discarded, other than targeted tunas. Between 2010 and 2020, 104.8 million hooks were deployed, catching over 2 million individuals from 117 taxa at an overall target:bycatch ratio of 1:1, with a retention rate of ∼62%. Pronounced differences in fishing strategies and spatial distribution of effort between fleets were associated with large variations in catch rates and composition. The LBF had a larger effect on populations of at-risk species relative to the DWF, with higher catch rates and magnitudes for several vulnerable species and higher observable fishing mortality rates (64% vs 50% in the DWF). The sanctuary reshaped Palau’s longline fishery, contracting the fishery’s area and capacity. The relocation of the DFZ eliminated the LBF and constrained the DWF to an area where the fleet’s total catch rates and those of a number of vulnerable species were historically lower relative to former fishing grounds now closed by the sanctuary. Our results highlight the importance of consistent bycatch monitoring and emphasize the need for regional area-based approaches for managing longline fisheries.

Unintended changes of artisanal fisheries métiers upon implementation of an MPA

Establishing marine protected areas (MPAs) is one of the most significant measures governments can take to halt the degradation of marine ecosystems and fisheries overexploitation. Although MPAs can be created with the support of current stakeholders, mainly fishers, implementation of spatial restrictions and of no-take zones in particular, force adjustments to the existing fisheries in the area. The Llevant de Mallorca-Cala Rajada MPA (Spain, Western Mediterranean) was created in 2007 under the patronage of the artisanal fishermen association of Cala Rajada. This study uses onboard observer data of the existing artisanal fisheries practices (métiers), their seasonality and spatial distribution of effort in the area before (2003–2007) and after (2008–2012) MPA designation, to illustrate how fishing restrictions and regulations have changed the structure and dynamics of local fishery métiers, with inshore fishing effort partially reallocated to offshore fishing grounds farther from port. Unforeseen effects of MPA restrictions concerned coastal artisanal métiers – impinging on the smaller boats and the oldest and most knowledgeable fishers – and the expansion of métiers that use newer boats and manned by younger, less experienced fishermen. Studies like this are needed to inform the design of future fisheries spatial management measures for Mediterranean artisanal fisheries that take into account foreseeable socio-economic outcomes and loss of knowledge.

Calculation of population-level fishing mortality for single- versus multi-area models: application to models with spatial structure

Spatial considerations in stock assessment models can be used to account for differences in fish population dynamics and fleet distributions, which, if otherwise unaccounted for, could result in model misspecification leading to bias in model results. Calculating an overall fishing mortality rate (F) across spatial components is not straightforward but is often required for harvest management. We examined effects of spatial assumptions on model results under different approaches for calculating F. We show that (i) F can differ by as much as 50% depending on the spatial structure of the model; (ii) for multi-area models, F changes with size of area for all but one approach; and (iii) results are sensitive to model assumptions about catchability between areas and the spatial distribution of effort and abundance. Findings suggest caution be taken when interpreting results between models with different spatial structures. When comparing single- with multi-area models, we recommend adding F across areas when catchability is the same between areas and either effort or abundance is proportional to area. Otherwise no single approach can be expected to be superior in all cases. We suggest simulation be used to evaluate the best approach to meet particular management objectives.

Effect of species‐counting protocols and the spatial distribution of effort on rarefaction curves in relation to decision making in environmental‐impact assessments

AbstractRarefaction Curves are frequently used in Environmental Impact Assessments to evaluate sampling sufficiency, but without clear guidelines of how to ensure that the assumptions of the methods are met. Infrastructure projects in the Brazilian Amazon and elsewhere often occupy extensive areas in remote locations with difficult access, and random sampling under such conditions is impractical. We tested the influence of sampling unit (sample or individual), and geographic distance between samples on rarefaction curve s, and evaluated the magnitude of errors resulting from the misuse of rarefaction curve in decision making, using frogs from four Amazonian sampling sites. Individual‐based rarefaction curve were steeper than those generated by sample‐based rarefaction curve. Geographic distance influenced the number of exclusive species in a predictable fashion only in one area, and not in the Environmental Impact Assessment site. Misuse of rarefaction curve generated large errors in the identification of vulnerable taxa. Because the rarefaction curve model is sensitive to the assumption of randomness and geographic distance can influence it unpredictably, we suggest that rarefaction curve should generally not be used to estimate sample completeness when making management decisions for environmental licensing purposes.

Effects of spatial heterogeneity in growth and fishing effort on yield-per-recruit models: an application to the US Atlantic sea scallop fishery

Abstract Conventional yield-per-recruit (Y/R) and spawning-stock biomass-per-recruit (SSB/R) models make no allowance for spatial heterogeneity in fishing mortality, natural mortality, or growth across the stock area, although variability in these processes can affect model results. For example, areas with higher growth and/or lower natural mortality rates should be fished at a lower rate to maximize Y/R; however, these areas may be especially attractive to fishers and are often fished harder. Here, Y/R and SSB/R models are developed that simultaneously account for spatial heterogeneity in growth and fishing effort. These models are applied to the US Atlantic sea scallop (Placopecten magellanicus) fishery. The spatial variability in growth uses depth-integrated models from the literature and variability in effort is based on, alternatively, uniform, observed, and relative-optimal spatial harvesting distributions. The observed effort patterns are derived from vessel monitoring system positions, and illustrate one application for these widely collected but underutilized spatial data. In this example, the distribution of observed fishing effort reduces Y/R compared with the relative-optimal, or the uniform effort distribution implicitly assumed by conventional Y/R analysis. SSB/R was in some cases considerably higher under the relative-optimal distribution of effort than when calculated using observed or uniform effort patterns. Such more realistic spatially integrated Y/R and SSB/R models can help to evaluate the impact of effort patterns on fishery yield and stock egg production. These models demonstrate that the spatial distribution of effort can be as important as the overall average fishing mortality when managing fisheries to optimize Y/R, SSB/R, and yield.

Evaluation of the effects on rockfish and kelp artisanal fisheries of the proposed Mejillones Peninsula marine protected area (northern Chile, SE Pacific coast)

•One shortcoming of marine protected areas (MPA) implementation is the potential for unintended consequences, such as fisheries effort displacement, that cause negative economic and social effects for fishermen and undermine social support for MPA implementation efforts.•The objective of this work is to analyse the effects of a proposed MPA system on fisheries in a biodiversity conservation priority site in northern Chile using a spatial dynamic modelling approach and incorporating ecological, social and economic criteria.•We developed an Ecospace model representing the ecological benthic subsystems dominated by kelp beds off the Mejillones Peninsula, Chile. We compared changes in fisheries indicators and the spatial distribution of effort among a no-MPA baseline scenario and four scenarios using proposed MPA core and buffer zones with high or low dispersal rates for the species in the model.•An overlay analysis was performed to identify which zones and users of the fishing grounds would be affected by the proposed MPA system and to what degree.•We found a high degree of overlap of the proposed MPA site with fishing grounds of high economic importance and with a fishing ground where women are allowed to work, this can cause significant displacement of women that have no alternative livelihood, with possible undesired social impacts on the fishing community.•Results from the kelp forest spatial food web model reveals that the biomass build-up of fished species is sensitive to dispersal rates, especially in scenarios with small reserves. A general pattern of fishing effort reallocation at the border of individual MPAs and open areas closer to the port was observed. Fisheries indicators show negative effects for both MPA scenarios, with undesirable changes in catch and profits for rockfish and kelp exploitation.•Our results suggest that implementation of the MPA proposal for the Mejillones Peninsula could generate negative consequences for the fishing community of Constitución cove. The inclusion of fisheries management objectives along with biodiversity conservation in the planning process of the Mejillones Peninsula MPA system may help to address putative negative effects on fisheries and may allow for the creation of support for future MPAs from the fishermen community.

Spatial Management of a Fishery Under Parameter Uncertainty

Spatial management of a fishery under parameter uncertainty is analyzed. The habitat is divided into two areas, and the effort level in the two areas may be different. The migration of biomass between the areas follows a diffusion process; two different specifications are considered. The model features logistic growth and Schaefer production functions. The intrinsic growth rate is treated as uncertain; the uncertainty is symmetric and spatially homogeneous. It is found that the optimal, spatial distribution of effort with respect to expected harvest is neither homogeneous or heterogeneous everywhere, but homogenous for a given subset of the parameter space and heterogeneous elsewhere.

Eco-labeling and dolphin avoidance: A dynamic model of tuna fishing in the Eastern Tropical Pacific

This paper examines the impact of dolphin-safe eco-labeling on the spatial distribution of fishing effort and fishermen's willingness to pay to avoid dolphins using a dynamic discrete choice model applied to the Eastern Tropical Pacific tuna fishery. This estimator couples the contemporaneous expected utility associated with fishing a specific site with the expected value of future optimal behavior for all future location choices on the cruise. We show that producers attempting to avoid dolphins faced a smaller set of viable sites as compared to producers actively targeting dolphins. Thus, the spatial distribution of effort within the fishery was significantly altered following the implementation of “dolphin-safe” tuna labeling in the early 1990s. We also show that vessels attempting to meet the label criteria were willing to pay substantial amounts to increase the spatial distribution of fishing grounds amenable to dolphin avoidance, but a mandatory eco-label would have been quite costly to all fishermen in the Eastern Tropical Pacific Ocean (ETP) compared to the voluntary label implemented in 1990.

Triple benefits from spatial resource management

Standard fishery management models suggest that regulations designed to produce maximum rent should reduce effort – and thus employment – from its open-access level. Using a simple diffusion model, we show that the opposite can be true when the spatial distribution of effort, as well as the total amount of effort, can be controlled. Under certain ecological and economic circumstances that we describe, optimal spatial management can produce “triple benefits” compared to open access: an increase in rent, an increase in standing stock, and an increase in employment.

Spatial distribution of effort by artisanal fishers: Exploring economic factors affecting the lobster fisheries of the Corn Islands, Nicaragua

Spatial distribution of fishing effort is increasingly recognised as an important consideration for fisheries management, as it can affect trends in catch rates, and be incorporated into planning of spatial management tools like marine protected areas (MPAs). One hundred and ninety-eight household questionnaires provided a coarse indication of effort distribution of artisanal lobster fishers around the Corn Islands, and 32 semi-structured interviews with skippers were used to map individual fishing sites and describe the operating costs and revenues of typical dive and trap-fishing operations. Artisanal fisheries had ranges of up to 50 km, and had moved significantly offshore within the previous 10 years. At the scale of a 5 × 5 min latitude/longitude grid, trap fishing effort was highly aggregated (dispersion coefficient = 3.5), while diving had a regular dispersion (d.c. = 0.1). Descriptions of catch composition at each site showed a clear spatial pattern in the distribution of two locally recognised types of lobster, potentially indicating local stock structures. Economic information was summarised into balance sheets for typical fishers and suggested that fuel accounted for about 52 and 37% of the operating costs of dive and trap fishing captains, respectively. Qualitative questions highlighted trap theft, adoption of geographical positioning system (GPS) technology and fuel costs as major factors affecting spatial behaviour. The costs and benefits of using more distant grounds were examined by testing for relationships between stated typical catch rates and distance of 90 trap-fishing grounds and between fuel expenditure and catches in 291 daily records of the activities of 3 divers. Maximum catch rates stated by trap fishers were significantly higher at more distant sites and daily catches by divers had a positive relationship with fuel expenditure, which suggested that increasing fuel expenditure to target more distant sites would lead to higher gross revenue as well as higher net revenues, after considering variable operating costs. Thus, there appears to be an economic incentive to extend the range of the fishery. However, fishers may not perceive these positive trends in catch rate with distance due to catch variability, and costs other than fuel, which complicate the trade-off between catch and distance.

Spatial evidence for information exchange and competition in the Gulf of St. Lawrence snow crab (Chionoecetes opilio) fishery

Throughout the 1990s, the Gulf of St. Lawrence snow crab (Chionoecetes opilio) harvest provided an example of effective co-management in a developing fishery. The Department of Fisheries and Oceans Canada (DFO) and the snow crab fleet (the fleet) shared information that coordinated management and exploitation throughout the season. A preseason survey by DFO provided resource distributions prior to the fishery's opening. In-season monitoring allowed managers to track spatial and temporal variation in crab availability. This level of detail allowed the application of the ideal free distribution as a management and conservation tool. However, proper justification for its application requires the demonstration of information exchange and competitive effects. The spatial distribution of effort suggests that both of these are present. Fishing effort was influenced by public information and potential information exchange within the fleet. Reduced aggregation at smaller spatial scales suggests competition in trap placement. Thus, increasing fleet size may have a disproportionately small impact on fishing mortality because of limitations in information exchange and the lack of personal information in the new vessels. However, the nonlinear relationship between crab abundance and catch rates suggests that managers should avoid policies that increase fishing effort during times of low crab abundance.

Benefits of Spatial Regulation in a Multispecies System

Spatial heterogeneity in multispecies systems affects both ecological interactions and the composition of harvest. A bioeconomic model is used to analyze the nonselective harvest of two stocks with generalized ecological interaction and different persistent distributions across two spatial strata. Harvester response to aggregate effort controls is shown to partially dissipate rents relative to the case where the spatial distribution of effort can be specified. Numerical solutions for time paths of spatial (first-best) and aggregate (secondbest) input constraints indicate factors affecting their relative efficiency. In the scenarios studied, benefits of spatial specificity range from 0 to 15% of total net present value (NPV), depending upon the spatial correlation of stocks, their relative growth rates and prices, and the cost gradient across space. The benefits of spatial regulation are also heightened by the presence of ecological interaction, especially predator-prey dynamics.

Evaluating stock and catchability trends: Annual average catch per unit effort is an inadequate indicator of stock and catchability trends in fisheries

Changes in the distribution of fishing effort over the season can influence trends in annual catch per unit effort (CPUE) because the vulnerability of the target species varies seasonally. We use annual and monthly time series analysis of CPUE data for a lobster fishery to show that time trends in CPUE are dependent upon the time interval selected. Changes in the spatial distribution of effort will almost certainly have similar consequences. Modellers and managers of fisheries need to quantify the effects of economic and regulatory changes on the temporal and spatial allocation of fishing effort.