scholarly journals Balanced harvesting is the bioeconomic equilibrium of a size-structured Beverton-Holt model

2016 ◽  
Vol 74 (1) ◽  
pp. 112-120 ◽  
Author(s):  
Michael J. Plank
Keyword(s):  
Single Species ◽  
Size Spectrum ◽  
Ecosystem Structure ◽  
Fishing Mortality ◽  
Biomass Transfer ◽  
Body Sizes ◽  
Relative Production ◽  
Ecosystem Structure And Functioning ◽  
Classical Size ◽  
Spectrum Model

Balanced harvesting (BH) was introduced as an alternative strategy to size-at-entry fishing with the aim of maintaining ecosystem structure and functioning. BH has been criticized on a number of grounds, including that it would require an infeasible level of micromanagement and enforcement. Recent results from a size-spectrum model show that the distribution of fishing mortality across body sizes that emerges from the behaviour of a large number of fishing agents corresponds to BH in a single species. Size-spectrum models differ from classical size-structured models used in fisheries as they are based on a bookkeeping of biomass transfer from prey to predator rather than a von Bertalanffy growth model. Here we investigate a classical Beverton-Holt model coupled with the Gordon-Schaefer harvesting model extended to allow for differential fishing pressure at different body sizes. This models an open-access fishery in which individual fishing agents act to maximize their own economic return. We show that the equilibrium of the harvesting model produces an aggregate fishing mortality that is closely matched to the production at different body sizes, in other words BH of a single species. These results have significant implications because they show that the robustness of BH does not depend on arguments about the relative production levels of small versus large fish.

Shifts in plankton size spectra modulate growth and coexistence of anchovy and sardine in upwelling systems

2016 ◽  
Vol 73 (4) ◽  
pp. 611-621 ◽  
Author(s):  
T. Mariella Canales ◽  
Richard Law ◽  
Julia L. Blanchard
Keyword(s):  
Size Structure ◽  
Prey Availability ◽  
Empirical Work ◽  
Size Composition ◽  
Size Spectrum ◽  
Small Particles ◽  
Size Spectra ◽  
Factors Influencing ◽  
Spectrum Model ◽  
Model Scenarios

Fluctuations in the abundance of anchovy (Engraulis spp.) and sardine (Sardinops sagax) are widespread in marine ecosystems, but the causes still remain uncertain. Differences between the planktonic prey availability, selectivity, and predation between anchovy and sardine have been suggested as factors influencing their dynamics. Using a dynamical multispecies size-spectrum model, we explore the consequences of changes in plankton size composition, together with intraguild predation and cannibalism, on the coexistence of these species. The shift towards smaller plankton has led to a reduction in the growth rate of both species. The effect was more deleterious on anchovy growth because it is unable to filter small particles. In model scenarios that included the effects of cannibalism and predation, anchovy typically collapsed under conditions favouring smaller sized plankton. The two species coexisted under conditions of larger sized plankton, although strong predation in conjunction with weak cannibalism led to the loss of sardine. The model provides new testable predictions for the consequences of plankton size structure on anchovy and sardine fluctuations. Further empirical work is needed to test these predictions in the context of climate change.

scholarly journals Bridging fisheries management and biodiversity conservation norms: potential and challenges of balancing harvest in ecosystem-based frameworks

2015 ◽  
Vol 73 (6) ◽  
pp. 1659-1667 ◽  
Author(s):  
S. M. Garcia ◽  
J. Rice ◽  
A. Charles
Keyword(s):  
Decision Making ◽  
Fisheries Management ◽  
Biological Diversity ◽  
Population Level ◽  
System Level ◽  
Convention On Biological Diversity ◽  
Management Decision ◽  
Size Spectrum ◽  
Ecosystem Structure ◽  
Management Decision Making

Abstract Balanced harvesting has been proposed as a way for fisheries management to achieve the requirements of both the Law of the Sea Convention (LOSC)—to maintain stocks at the level at which they could produce MSY—and the Convention on Biological Diversity (CBD)—to maintain ecosystem structure and functioning. This paper examines these requirements and briefly presents four system-level relationships (spectra), representing ecosystem structures that might guide management decision-making aiming to meet both requirements. These spectra would fit in the widely accepted frameworks of the Ecosystem Approach enshrined in the CBD and adopted by FAO for Fisheries. A size spectrum, relating biomass to body length, is used as an example to illustrate its potential to support management decision-making—much like present stock-based harvest control rules—in more ecosystem-compliant fishing strategies at a sector or ecosystem level, as a complement to those currently used at a stock/population level.

scholarly journals The MARAS dataset, vegetation and soil characteristics of dryland rangelands across Patagonia

2020 ◽  
Vol 7 (1) ◽  
Author(s):  
Gabriel Oliva ◽  
Eder dos Santos ◽  
Osiris Sofía ◽  
Fernando Umaña ◽  
Virginia Massara ◽  
...  
Keyword(s):  
Soil Analysis ◽  
Soil Surface ◽  
Surface Characteristics ◽  
Spatial Pattern Analysis ◽  
Ecosystem Structure ◽  
Species List ◽  
Plant Soil ◽  
Rangeland Monitoring ◽  
Ecosystem Structure And Functioning ◽  
Line Intercept

Abstract We present the MARAS (Environmental Monitoring of Arid and Semiarid Regions) dataset, which stores vegetation and soil data of 426 rangeland monitoring plots installed throughout Patagonia, a 624.500 km2 area of southern Argentina and Chile. Data for each monitoring plot includes basic climatic and landscape features, photographs, 500 point intercepts for vegetation cover, plant species list and biodiversity indexes, 50-m line-intercept transect for vegetation spatial pattern analysis, land function indexes drawn from 11 measures of soil surface characteristics and laboratory soil analysis (pH, conductivity, organic matter, N and texture). Monitoring plots were installed between 2007 and 2019, and are being reassessed at 5-year intervals (247 have been surveyed twice). The MARAS dataset provides a baseline from which to evaluate the impacts of climate change and changes in land use intensity in Patagonian ecosystems, which collectively constitute one of the world´s largest rangeland areas. This dataset will be of interest to scientists exploring key ecological questions such as biodiversity-ecosystem functioning relationships, plant-soil interactions and climatic controls on ecosystem structure and functioning.

A functional size-spectrum model of the global marine ecosystem that resolves zooplankton composition

2020 ◽  
Vol 435 ◽  
pp. 109265
Author(s):  
Ryan F. Heneghan ◽  
Jason D. Everett ◽  
Patrick Sykes ◽  
Sonia D. Batten ◽  
Martin Edwards ◽  
...  
Keyword(s):  
Marine Ecosystem ◽  
Size Spectrum ◽  
Spectrum Model ◽  
Functional Size

scholarly journals A feeding guild indicator to assess environmental change impacts on marine ecosystem structure and functioning

2020 ◽  
Vol 57 (9) ◽  
pp. 1769-1781 ◽  
Author(s):  
Murray S. A. Thompson ◽  
Hugo Pontalier ◽  
Michael A. Spence ◽  
John K. Pinnegar ◽  
Simon P. R. Greenstreet ◽  
...  
Keyword(s):  
Environmental Change ◽  
Marine Ecosystem ◽  
Ecosystem Structure ◽  
Feeding Guild ◽  
Ecosystem Structure And Functioning

scholarly journals Modeling the Dynamics of Multispecies Fisheries: A Case Study in the Coastal Water of North Yellow Sea, China

2020 ◽  
Vol 7 ◽  
Author(s):  
Jia Wo ◽  
Chongliang Zhang ◽  
Xindong Pan ◽  
Binduo Xu ◽  
Ying Xue ◽  
...  
Keyword(s):  
Model Validation ◽  
Fisheries Management ◽  
Yellow Sea ◽  
Sensitivity Analyses ◽  
Size Spectrum ◽  
Quality Of Data ◽  
Estimation Model ◽  
North Yellow Sea ◽  
Multispecies Fisheries ◽  
Spectrum Model

Ecosystem models have been developed for detecting community responses to fishing pressure and have been widely applied to predict the ecological effects of fisheries management. Key challenges of ecosystem modeling lie in the insufficient quantity and quality of data, which is unfortunately common in the marine ecosystems of many developing countries. In this study, we aim to model the dynamics of multispecies fisheries under data-limited circumstances, using a multispecies size-spectrum model (MSSM) implemented in the coastal ecosystem of North Yellow Sea, China. To make most of available data, we incorporated a range of data-limited methods for estimating the life-history parameters and conducted model validation according to empirical data. Additionally, sensitivity analyses were conducted to evaluate the impacts of input parameters on model predictions regarding the uncertainty of data and estimating methods. Our results showed that MSSM could provide reasonable predictions of community size spectra and appropriately reflect the community composition in the studied area, whereas the predictions of fisheries yields were biased for certain species. Errors in recruitment parameters were most influential on the prediction of species abundance, and errors in fishing efforts substantially affected community-level indicators. This study built a framework to integrate parameter estimation, model validation, and sensitivity analyses altogether, which could guide model development in similar mixed and data-limited fisheries and promote the use of size-spectrum model for ecosystem-based fisheries management.

Ecosystem-based management of seaweed harvesting

2019 ◽  
Vol 62 (5) ◽  
pp. 395-409 ◽  
Author(s):  
Heike K. Lotze ◽  
Inka Milewski ◽  
Julia Fast ◽  
Lauren Kay ◽  
Boris Worm
Keyword(s):  
Primary Production ◽  
Human Impacts ◽  
Single Species ◽  
Ecosystem Structure ◽  
Ecosystem Impacts ◽  
Red Macroalgae ◽  
Ecosystem Based Management ◽  
Potential Habitat ◽  
Relevant Today ◽  
Recovery Potential

Abstract Harvesting wild seaweeds has a long history and is still relevant today, even though aquaculture now supplies >96% of global seaweed production. Current wild harvests mostly target canopy-forming kelp, rockweed and red macroalgae that provide important ecosystem roles, including primary production, carbon storage, nutrient cycling, habitat provision, biodiversity and fisheries support. Harvest methods range from selective hand-cutting to bottom trawling. Resulting ecosystem impacts depend on extraction method and scale, ranging from changes in primary production to habitat disruption, fragmentation, food-web alterations and bycatch of non-target species. Current management often aims for sustainable harvesting in a single-species context, although some agencies acknowledge the wider ecosystem structure, functions and services seaweeds provide. We outline potential ecosystem-based management approaches that would help sustain productive and diverse seaweed-based ecosystems. These include maintaining high canopy biomass, recovery potential, habitat structure and connectivity, limiting bycatch and discards, while incorporating seasonal closures and harvest-exclusion zones into spatial management plans. Other sustainability considerations concern monitoring, enforcement and certification standards, a shift to aquaculture, and addressing cumulative human impacts, invasive species and climate change. Our review provides a concise overview on how to define and operationalize ecosystem-based management of seaweed harvesting that can inform ongoing management and conservation efforts.

scholarly journals Parameter uncertainty of a dynamic multispecies size spectrum model

2016 ◽  
Vol 73 (4) ◽  
pp. 589-597 ◽  
Author(s):  
Michael A. Spence ◽  
Paul G. Blackwell ◽  
Julia L. Blanchard
Keyword(s):  
Time Series ◽  
Time Series Data ◽  
Size Structure ◽  
Management Strategies ◽  
Optimization Methods ◽  
Series Data ◽  
Size Spectrum ◽  
Aquatic Communities ◽  
The North ◽  
Spectrum Model

Dynamic size spectrum models have been recognized as an effective way of describing how size-based interactions can give rise to the size structure of aquatic communities. They are intermediate-complexity ecological models that are solutions to partial differential equations driven by the size-dependent processes of predation, growth, mortality, and reproduction in a community of interacting species and sizes. To be useful for quantitative fisheries management these models need to be developed further in a formal statistical framework. Previous work has used time-averaged data to “calibrate” the model using optimization methods with the disadvantage of losing detailed time-series information. Using a published multispecies size spectrum model parameterized for the North Sea comprising 12 interacting fish species and a background resource, we fit the model to time-series data using a Bayesian framework for the first time. We capture the 1967–2010 period using annual estimates of fishing mortality rates as input to the model and time series of fisheries landings data to fit the model to output. We estimate 38 key parameters representing the carrying capacity of each species and background resource, as well as initial inputs of the dynamical system and errors on the model output. We then forecast the model forward to evaluate how uncertainty propagates through to population- and community-level indicators under alternative management strategies.

scholarly journals Using trophic flows and ecosystem structure to model the effects of fishing in the Jurien Bay Marine Park, temperate Western Australia

2011 ◽  
Vol 62 (5) ◽  
pp. 421 ◽  
Author(s):  
Hector M. Lozano-Montes ◽  
Neil R. Loneragan ◽  
Russell C. Babcock ◽  
Kelsie Jackson
Keyword(s):  
Western Australia ◽  
Negative Impact ◽  
Limiting Factor ◽  
Commercial Fishing ◽  
Ecosystem Structure ◽  
Fishing Mortality ◽  
Benthic Primary Production ◽  
Cascading Effects ◽  
Marine Park ◽  
The Impact

Understanding the impacts of fishing on the trophic structure of systems has become increasingly important because of the introduction of Ecosystem Based Fisheries Management and the legislative requirements of fisheries to demonstrate that they are not having a negative impact on other species. A biomass-based dynamic model of Jurien Bay Marine Park (∼30°S) was constructed using Ecopath to investigate the ecosystem impacts of fishing (mainly commercial rock lobster, Panulirus cygnus) in the park, as an example of the potential responses of temperate marine ecosystems in Western Australia to commercial fishing. A simulated 50% reduction in fishing mortality for commercial finfish predicted that after 20 years, the biomass of important fished species (i.e. Pagrus auratus and Choerodon rubescens) would increase by up to 30%. A simulated total fishing closure resulted in much larger (2.5–8 fold) increases in targeted populations, but did not result in any predicted cascading effects on grazing invertebrates and benthic primary producers. The simulations suggest that the structure of this ecosystem is characterised more by bottom-up than top-down processes; i.e. benthic primary production is a major limiting factor. The present study identified trophic linkages and ecosystem processes such as the role of both low and high trophic-level groups and the impact of fishing mortality in the marine park, an essential step towards distinguishing the impacts of fishing from those attributable to natural or other human-induced changes.

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