Using incidental mark‐encounter data to improve survival estimation. Issue 1 (8th December 2019)

• Record Type: Journal Article
• Authors: Harju, Seth M.; Cambrin, Scott M.; Averill‐Murray, Roy C.; Nafus, Melia; Field, Kimberleigh J.; Allison, Linda J.
• Is Part Of: Ecology and evolution. Volume 10:Issue 1(2020)
• Page Start: 360
• Page End: 370
• Publication Date: 2019-12-08
• Subjects: combined datasets -- incidental data -- mark‐encounter -- Mojave desert tortoise -- radiotelemetry -- survival -- translocation; Ecology -- Periodicals; Evolution -- Periodicals; 577.05
• DOI: 10.1002/ece3.5900
• Languages: English
• ISSNs: 2045-7758

Abstract

Abstract: Obtaining robust survival estimates is critical, but sample size limitations often result in imprecise estimates or the failure to obtain estimates for population subgroups. Concurrently, data are often recorded on incidental reencounters of marked individuals, but these incidental data are often unused in survival analyses. We evaluated the utility of supplementing a traditional survival dataset with incidental data on marked individuals that were collected ad hoc. We used a continuous time‐to‐event exponential survival model to leverage the matching information contained in both datasets and assessed differences in survival among adult and juvenile and resident and translocated Mojave desert tortoises ( Gopherus agassizii ). Incorporation of the incidental mark‐encounter data improved precision of all annual survival point estimates, with a 3.4%–37.5% reduction in the spread of the 95% Bayesian credible intervals. We were able to estimate annual survival for three subgroup combinations that were previously inestimable. Point estimates between the radiotelemetry and combined datasets were within |0.029| percentage points of each other, suggesting minimal to no bias induced by the incidental data. Annual survival rates were high (>0.89) for resident adult and juvenile tortoises in both study sites and for translocated adults in the southern site. Annual survival rates for translocated juveniles at both sites and translocated adults in the northern site were between 0.73 and 0.76. At both sites, translocated adults and juveniles had significantly lower survival than resident adults. High mortality in the northern site was driven primarily by a single pulse in mortalities. Using exponential survival models to leverage matching information across traditional survival studies and incidental data on marked individuals may serve as a useful tool to improve the precision and estimability of survival rates. This can improve the efficacy of understanding basic population ecology and population monitoring for imperiled species. Abstract : Survival estimation using radio‐telemetry datasets is often hampered by small sample size. We found that combining incidental sighting data on marked individuals with radio‐telemetry data improved survival estimation by reducing the spread of 95% credible intervals in all cases with minimal and inconsistent effects on point estimates. In three of eight sub‐groups, survival estimates were only obtainable after inclusion of the incidental encounter data.