The Cumulative Effects of Fishing, Plankton Productivity, and Marine Mammal Consumption in a Marine Ecosystem

Abstract

The marine ecosystem off British Columbia (BC), Canada, has experienced various changes in the last two decades, including reduced lipid-rich zooplankton biomass, increased marine mammals, and deteriorated commercial fisheries, particularly those targeting pelagic species such as Pacific Herring (Clupea pallasii). Understanding how stressors interactively and cumulatively affect commercially important fish species is key to moving toward ecosystem-based fisheries management. Because it is challenging to assess the cumulative effects of multiple stressors by using empirical data alone, a dynamic, individual-based spatially explicit ecosystem modeling platform such as Object-oriented Simulator of Marine Ecosystems (OSMOSE) represents a valuable tool to simulate ecological processes and comprehensively evaluate how stressors cumulatively impact modeled species. In this study, we employed OSMOSE to investigate the cumulative effects of fishing, plankton biomass change, and marine mammal consumption on the dynamics of some fish species and the BC marine ecosystem as a whole. We specifically simulated ecosystem dynamics during the last 20 years under two sets of scenarios: (1) unfavorable conditions from the perspective of commercial fish species (i.e., doubling fishing mortality rates, halving plankton biomass, and doubling marine mammal biomass, acting individually or collectively); and (2) favorable conditions with the three factors having opposite changes (i.e., halving fishing mortality rates, doubling plankton biomass, and halving marine mammal biomass, acting individually or collectively). Our results indicate that, under unfavorable conditions, the degree to which species biomass was reduced varied among species, and that negative synergistic and negative dampened effects were dominant under historical and doubled fishing mortality rates, respectively. Under favorable conditions, species biomasses did not increase as much as expected due to the existence of complex predator-prey interactions among fish species, and positive synergistic and positive dampened effects were prevailing under historical and halved fishing mortality rates, respectively. The

Evaluating Impacts of Trophic Interactions on the Effectiveness of Single-Species Fisheries Management

“…The changes of other species fisheries were more likely to influence age-0 S. schlegelii (Figure 4B). The food condition influences the growth of fish population especially for low-trophic-level species (Fu et al, 2020). There was a positive relationship between O. oratoria biomass and starvation mortality.…”

“…Trophic interactions play an important role in influencing the fish population (Fu et al, 2020;Xing et al, 2020a). The impacts of fishing other species on the low-trophic-level mantis shrimp O. oratoria were complex.…”

“…Moullec et al (2019) report the sea warming will result in a decline in the proportion of large fishes. Climate change can influence fishes by changing the primary productivity (Fu et al, 2020). The changes in fishing and environmental factors will likely influence the population processes such as fish growth and recruitment (Szuwalski and Hollowed, 2016;Martino et al, 2019).…”

Diving deeper: Mesopelagic fish biomass estimates comparison using two different models

“…Our results show that the non-linearity affects how mesopelagic fish respond to variability in their food, which is produced by environmental changes. As a multispecies model, OSMOSE is also useful for exploring fishing strategies in an ecosystem-based fisheries management context (Briton et al, 2019;Fu et al, 2019;Guo et al, 2019;Fu et al, 2020). There is growing evidence of the importance of mesopelagic fish in deep water food chains (Mann, 1984;Davison et al, 2015a;Saunders et al, 2019).…”

A data‐driven approach to multiple‐stressor impact assessment for a marine protected area

“…Land‐based activities introduce nutrients and pollutants into coastal waters that influence estuarine and marine coastal ecosystems (Brown et al., 2017; Lefébure et al., 2013). Marine‐based activities, including fishing, have direct impacts on fish biomass and indirect effects on ecosystems through changes in food webs (Fu et al., 2020; Jennings & Polunin, 1997) and have seen considerable growth in the last 2 decades (Halpern et al., 2019). Climate change threats, although regionally unmanageable, have direct and indirect impacts on species and ecosystems (Trisos et al., 2020).…”