Estimating population size is an essential part of many management and conservation decisions. The goal of our study is to compare the effectiveness and cost/sampling effort trade-offs of three techniques: traditional mark-recapture, DNA-based capture-recapture, and wildlife camera traps. Each method has its advantages and disadvantages in regards to invasiveness, cost, type of data obtained, and labor/time required. The model organism for this test, the raccoon, is common on the island of Ruler’s Bar Hassock (RBH), in Jamaica Bay, New York. Each technique was conducted over four sessions from 2015-2016. During each session 20-25 of each trap type were placed at different locations across RBH. Traditional mark-recapture involved Tomahawk traps baited with cat food. Captured raccoons were sedated with Telazol and microchipped for future identification. DNA-based capture-recapture involved collection of hair samples from baited “cubbies”, 5-gallon buckets anchored on their sides with barbed wire strands suspended inside in an inverted ‘V’. DNA was successfully extracted from samples and amplified using standard PCR techniques and raccoon-specific primers. The results of microsatellite fragment analysis will provide a genetic fingerprint allowing individual identification and population size estimation using MARK. Unbaited wildlife camera traps were attached to vertical objects and facing open ground.
Results/Conclusions
Mark-recapture data was analyzed using programs MARK and DENSITY for calculating population estimates. Using traditional mark-recapture data, the population size during this period was estimated as 11.2 raccoons and density was 0.47 individuals/ha. Preliminary results from camera traps show raccoons were active from 1730 – 0700 h and were responsible for 5.3% of camera trigger events. Review of the literature shows raccoon movement rates vary from 161-380 m/h, with a mean of 197.88 m/h. These results will be used to estimate population size following a random gas model proposed by Rowcliffe et al. (2008), which scales trapping rate linearly with animal density, based on biological variables (average animal group size and speed) and camera parameters. The benefit of this model is that it does not require individuals to have uniquely recognizable markings. On a local scale, the results from this study can inform management decisions made by the National Park Service. In RBH raccoon predation results in high levels of predation of unprotected diamondback terrapin nests. On a broader scale, this study will help researchers interested in estimating population size by providing a basic framework for selecting a technique that balances cost, labor, and time with short and long term goals.