Integrating Human and Ecological Networks

Humans have caused significant impacts to ecological networks because of their fishing in coastal food webs – they are “keystone” species. Intensive fishing by humans often causes a trophic cascade (indirect effect), disproportionately affecting other species not the target of the fishery. To examine the potential for such indirect effects in both ecosystems and social systems, we prepared social and ecological networks of fishing activities in Core Sound, NC (USA). We analyzed the food web networks in adjacent bays where the use of trawling and other commercial fishing gears has been intensive or restricted for 30 years, creating a natural comparative study of ecosystems with differing levels of fisheries extractions. We integrated the species-node ecological networks in the intensively fished areas with a fisherman (actor) by gear-species (event) behavioral affiliation network, which allowed us to examine how changes in human behavior can impact food web structure and how changes in the food web structure can impact the human behavioral network, including the robustness of human behavioral networks. Fishermen were most strongly affiliated in the gill net fisheries for southern flounder and red drum (> 70 participants), hard clam raking (> 30 participants), pound netting and shrimp trawling (> 15 participants). We estimated the ecological impacts of each of these fisherman affiliation groups using an ecological network model based on the fishermen’s reported catches. Restriction of fishing with gill nets may increase trawling and clamming activities, increasing the ecosystem impacts associated with those gears. Conversely, reducing shrimp trawling may cause fisherman to shift to gill netting for declining species (like flounder and red drum). Because single-species management plans have indirect impacts both on ecosystems and the social systems, the integration of social and ecological network models are useful tools for fishery management.