Capture histories and body size data for a population of mangrove diamond-backed terrapins (Malaclemys terrapin rhizophorarum) Everglades National Park, Florida, USA, 2001-2019

We used an 18-year dataset (2001 to 2019) incorporating year, sex, hurricane occurrence and sampling effort to estimate survival using Cormack–Jolly–Seber (CJS) models in Program Mark. Annual survivorship estimates were high from 2001-2003 for both sexes (91-96%) and variable from 2006-2014 (77-92%). Beginning in 2015 survival estimates exhibited a steeper decline (females: 65%, males 75%), and dropped to below 36% by 2018. Because the driver of this apparent population decline is unknown, we created a population projection matrix and used model-estimated annual survival to simulate annual terrapin population size. We then generated competing scenarios of low survival at various age classes to attempt to reproduce a simulated decline mirroring what we observed from our capture data. A scenario of low adult survival (75-85%) from 2012 to 2018, possibly in conjunction with no reproduction after 2010, provides estimates of abundance that appear to match simulated annual population size and may indicate that adult emigration/human removal or a drastic drop in recruitment could be responsible for the apparent decline in survival.