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Responses of ecological indicators to fishing pressure under environmental change: Exploring non-linearity and thresholds

Fu, Caihong
Xu, Yi
Grüss, Arnaud
Bundy, Alida
Shannon, Lynne
Heymans, Johanna J.
Halouani, Ghassen
Akoğlu, Ekin
Lynam, Christopher P.
Coll, Marta
Fulton, Elizabeth A.
Velez, Laure
Shin, Yunne-Jai
© International Council for the Exploration of the Sea 2019. All rights reserved.Marine ecosystems are influenced by multiple stressors in both linear and non-linear ways. Using generalized additive models (GAMs) fitted to outputs from a multi-ecosystem, multi-model simulation experiment, we investigated 14 major ecological indicators across ten marine ecosystems about their responses to fishing pressure under: (i) three different fishing strategies (focusing on low-, high-, or all-trophic-level taxa); and (ii) four different scenarios of directional or random primary productivity change, a proxy for environmental change. From this work, we draw four major conclusions: (i) responses of indicators to fishing mortality in shapes, directions, and thresholds depend on the fishing strategies considered; (ii) most of the indicators demonstrate decreasing trends with increasing fishing mortality, with a few exceptions depending on the type of fishing strategy; (iii) most of the indicators respond to fishing mortality in a linear way, particularly for community and biomass-based indicators; and (iv) occurrence of threshold for non-linear-mixed type (i.e. non-linear with inflection points) is not prevalent within the fishing mortality rates explored. The conclusions drawn from the present study provide a knowledge base in indicators’ dynamics under different fishing and primary productivity levels, thereby facilitating the application of ecosystem-based fisheries management worldwide.