Evaluating ecosystem impacts of gear regulations in a data-limited fishery-comparing approaches to estimate predator-prey interactions in Ecopath with Ecosim

13 pages, 7 figures, 1 table, supplementary data https://doi.org/10.1093/icesjms/fsac077.-- Data availability statement: The questionnaire data are available at https://github.com/Jrehren/ICES-2021-Rehren-Evaluating-impacts-of-fishing-gear-regulations. The other data underlying this article will be shared on reasonable request to the corresponding author

Ecosystem models, such as Ecopath with Ecosim (EwE), are useful tools for developing ecosystem-based management strategies. Model development, however, requires data for the estimation of input parameters including time series for calibration. Most small-scale fisheries lack such information, making it difficult to reliably use ecosystem models for management strategy exploration. This is the case for the Chwaka Bay fishery (Zanzibar), where an increase in dragnets has led to concerns for unsustainable development. While EwE could help to explore the impacts of gear regulations in the bay, this is hampered by the lack of time series to estimate the predator–prey interactions (vulnerabilities) in the model. Here, we explore available approaches for estimating the vulnerabilities to simulate the effects of a dragnet prohibition with and without reallocation of fishing effort. Simulations suggest that banning dragnets would be beneficial for the fishing community judged by the increase in biomass of functional groups and fishers’ profits, but not if dragnet fishers were to continue fishing in the bay by reallocating to other gears, indicated by the reduced fish biomass and fishers’ profits. The overall trend (decreasing or increasing) in the changes of functional groups, ecosystem indicators, and profits were relatively consistent across vulnerability settings, illustrating that an unfitted EwE model can be used for qualitative management strategy exploration

This project was funded by the German Research Foundation (DFG) within a research fellowship programme (RE 4358/1–1). The data used in the analysis were collected in 2014 within a PhD programme (SUTAS) funded by the Leibniz Gemeinschaft. The questionnaires on fishers' perception of historical fisheries catches were conducted within the National Geographical Society Early Career Grant, #EC-67901C-20. MC acknowledges funding support by the European Union's Horizon 2020 research and innovation programme under grant agreement No 869300 (FutureMares). VC acknowledges support from the Natural Sciences and Engineering Research Council of Canada (NSERC), Discovery Grant RGPIN-2019–04901. This work acknowledges the “Severo Ochoa Centre of Excellence” accreditation (CEX2019-000928-S) to the Institute of Marine Science (ICM-CSIC)

Peer reviewed