The Smithsonian MarineGEO project aims to understand near-shore biodiversity and ecosystem function in a changing world, using research as a tool for conservation and management policy. Of its varied approaches to this mission, MarineGEO monitors near-shore predation as an indicator of ecosystem health through its subproject Bitemap. The largest near-shore predation study of its kind, Bitemap relies on a simple, standardized assay of relative predation rates: the squidpop. Although squipops had been tested in cross-site comparisons, they had yet to be compared with near-shore tethering, the method that has been used to study this dynamic for decades. Because of this gap in our knowledge, squidpop data was difficult to contextualize historically, and had yet to be validated against established practice. To accurately compare the two, I set paired deployments of squidpops and live tethers across five sites on the Rhode River, a tributary to the Chesapeake Bay. Using the Smithsonian Environmental Research Center’s established tethering protocol, fish, shrimp, and crabs were deployed at the sites that had been monitored for predation every summer. Loggers were also deployed with these baits, which measured temperature, salinity, and light over the deployment period. Checks were made at 15 minutes, 30 minutes, one hour, and 24 hours after deployment.
To analyze the difference between predation of squidpops (“gone”, “not gone”) and live tethers, I used R to run T-tests comparing squidpop results to those of each of the live tethers (shrimp, fish, crabs). I next ran an ANOVA test to compare all bait types against each other, and Linear Regression to see if temperature, salinity, dissolved oxygen, and/or site significantly impacted predation rates. Confirming my hypotheses, squidpop predation rates proved statistically different (using a p-value of 0.05) from crab and shrimp data (p=0.047 and p<0.001, respectively); however, they were not significantly different from fish data (p=0.182). Interestingly, increased temperature correlated with decreased predation rates, the opposite trend from what is normally expected. However, this seems to have been due more to the confounding effects of site. The comparable predation rates of squidpops and fish tethers will allow for comparison of past, present, and future results of these and similar studies, contextualizing squidpop data in decades’ worth of near-shore predation data. Because squidpops represent an easy-to-use, universal bait, their continued in MarineGEO’s Bitemap project will allow for global comparison of near-shore ecosystem function, using predation as a proxy.