Abstract
One goal of ecosystem-based management is studying an ecosystem and its people, the socio-ecological system, in a qualitative and quantitative modeling approach that can provide management agencies with possible outcomes of their actions using scenario forecasting. Ecosystem-based fisheries management strives to use the socio-ecological system approach, including direct and indirect impacts on multiple species including the behavioral responses of fishers after a regulatory change (a gillnet ban). Here, we link fisher behavioral networks with a mass-balanced food-web ECOPATH network model of an estuarine ecosystem and its commercial fisheries for an analysis of fishing impacts after a gillnet ban on multiple species using ECOSIM. We modeled fisher behavioral networks using reported catches of species from individual fishers along with the gear fished to create nodes in a gear/species affiliation network. Individual fishers with common gear/species use are indicative of common fishing behavior. When such fishers have high network centrality and are engaged in multiple gear/species fisheries, they can transition to other gear/species fisheries along “switching pathways” when facing a regulatory change. We used an index of joint gear participation to identify likely gear switching pathways, and we predicted changes in fishing effort after a gill net ban. We simulated the gill net ban in ECOSIM under two scenarios of fishing effort: Scenario 1, gill net fishing effort of 0%; Scenario 2, gill net fishing effort of 0% with increased effort in the alternative gear fisheries using the predicted switching pathways for the affiliation network. Scenario 1 predicted an increase in flounder (Paralichthys spp.) biomass over a decade. Under Scenario 2, fishers targeting flounders were predicted to switch from gill nets to pound nets. Scenario 2 predicted a 7% decline in flounder biomass over ten years, rather than an increase in flounders. The gillnet ban with increased effort due to switching is predicted to have the opposite effect on the conservation goal, which was to increase flounder stocks. Fishery management that incorporates a socio-ecological approach modeling both fisher behaviors and multi-species ecosystem responses can reveal single-species responses that are in the opposite direction of the anticipated management goals.
Highlights
The influence of people on ecosystem function and the dynamics of ecosystem changes on human populations is the primary focus of most socio-ecological systems research
The effective trophic levels for each compartment were computed and it is apparent that the fisheries vary in their total harvest and effective trophic level, in ascending order of total catch: pound nets (0.0035 g/m2/yr, ETL = 3.51), gillnets (0.0042 g/m2/yr; ETL = 2.76), crab pots (0.0043 g/m2/yr; ETL = 2.98), skimmer trawling, haul seining (0.0154; ETL = 2.73), and shrimp trawling (0.0349 g/m2/yr; ETL = 2.83)
Because gill nets are among the most commonly used gear types in this ecosystem, and we have demonstrated here that they are the most central type of gear used in the behavioral network of fishers, switching to other gears will occur along the linked paths in our affiliation network model – we refer to these as gear-switching pathways
Summary
The influence of people on ecosystem function and the dynamics of ecosystem changes on human populations is the primary focus of most socio-ecological systems research. The goal of an environmental sustainability program is to change human behaviors in a way that ecosystem function and ecological services are restored or preserved within a complex socioecological system, taking into account various subsystems and levels of governance (Ostrom, 2009). An individual resource user does not often have a major impact on an ecosystem; it is the combined behavior of many people working together to build structures, alter topography, plant crops, harvest animals, and form organizations (tribes, associations, governments, corporations, etc.) that result in these resource and ecosystem changes. Individuals working together in a related profession like fishing, when their impacts are examined cumulatively, influence ecosystem function and trophic structure dramatically (Auster et al, 1996; Torres et al, 2013; Deehr et al, 2014; Chagaris et al, 2015). Sustainability and protection of ecological services will be achieved only through the understanding of both an ecosystem’s processes that produce ecological services and the social network of humans that influence and are influenced by the ecosystem processes
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