Epidemiological models to control the spread of information in marine mammals

Abstract

Socially transmitted wildlife behaviours that create human-wildlife conflict are an emerging problem for conservation efforts, but also provide a unique opportunity to apply principles of infectious disease control to wildlife management. As an example, California sea lions (Zalophus californianus) have learned to exploit concentrations of migratory adult salmonids below the fish ladders at Bonneville Dam, impeding endangered salmonid recovery. Proliferation of this foraging behaviour in the sea lion population has resulted in a controversial culling programme of individual sea lions at the dam, but the impact of such culling remains unclear. To evaluate the effectiveness of current and alternative culling strategies, we used network-based diffusion analysis on a long-term dataset to demonstrate that social transmission is implicated in the increase in dam-foraging behaviour and then studied different culling strategies within an epidemiological model of the behavioural transmission data. We show that current levels of lethal control have substantially reduced the rate of social transmission, but failed to effectively reduce overall sea lion recruitment. Earlier implementation of culling could have substantially reduced the extent of behavioural transmission and, ultimately, resulted in fewer animals being culled. Epidemiological analyses offer a promising tool to understand and control socially transmissible behaviours.

Social associations between California sea lions influence the use of a novel foraging ground

“…We previously used network-based diffusion analysis and epidemiological models to demonstrate that the knowledge of the foraging resources at Bonneville was transmitted like a disease [11]. We extended this to show that, like a disease, an individual's network centrality influences the transmission process.…”

“…We quantified the social networks of individually identified sea lions at the EMB and found that an individual's centrality in their network influenced discovery of the Bonneville Dam and whether they subsequently returned the following season. We previously used network-based diffusion analysis and epidemiological models to demonstrate that the knowledge of the foraging resources at Bonneville was transmitted like a disease [ 11 ]. We extended this to show that, like a disease, an individual's network centrality influences the transmission process.…”

“…Little is known about male California sea lion social relationships, but males migrate from breeding grounds on the Channel Islands off California. We previously found that individual co-occurrence in the EMB provides a coarse estimate of social ties [ 11 ]. For the current analysis, we elected to use the repeated co-occurrence on a haulout within the EMB as a more precise measure of social ties because it measures social relationships over time, and across haul-out locations ( figure 2 ).…”

“…In a previous study, we showed that knowledge of a novel food source has been socially transmitted through the population via California sea lion ( Zalophus californianus ) social networks [11]. Specifically, we described the socially mediated increase of sea lions exploiting concentrated salmonids at the Bonneville Dam.…”

“…In the Pacific Northwest of the USA, dam construction in salmon spawning rivers create novel concentrations of salmonids that congregate below fish ladders while migrating upriver. In a previous study, we showed that knowledge of a novel food source has been socially transmitted through the population via California sea lion ( Zalophus californianus ) social networks [ 11 ]. Specifically, we described the socially mediated increase of sea lions exploiting concentrated salmonids at the Bonneville Dam.…”