The Drift Effect: How carcasses can distort conservation planning

Stranding-only models predict far too much habitat, and can lead to protecting the wrong areas. Discover why direct observations are critical for accuracy

In the absence of sightings, stranding records can be used to parameterize habitat models for marine mammal conservation. However, their reliability for identifying suitable habitat remains uncertain. We assessed how stranding data influence the habitat predictions for American manatee (Trichechus manatus) in the Potiguar Basin, Brazil. Using MaxEnt, we compared models built using: (1) sightings and telemetry data, (2) stranding records alone, and (3) all three data sources combined. We found that the first model based solely on sightings and telemetry produced the most accurate and ecologically meaningful predictions. In contrast, the stranding- only model overestimated suitable habitat by more than threefold, while the combined model overpredicted it by more than twofold. These differences between model predictions are best explained by carcass drift and detection biases and indicate that stranding locations do not reliably reflect areas of actual habitat use. This quantitative assessment provides new insights into the significant biases stranding data can introduce into habitat suitability models. Our findings also highlight the need to prioritize direct observations, and to apply drift modeling and validation against direct observations when using stranding data, to ensure accurate and actionable conservation planning.

Publication

2026
Stranding data can significantly bias marine mammal habitat suitability models. Meirelles, A.C.O., I.C. Normande, M.D.O. Alves, K.F. Choi, V.L. Carvalho, J.C.G. Borges and A.W. Trites. 2026. Ecological Modelling Vol 512 pp. 111394 abstract In the absence of sightings, stranding records can be used to parameterize habitat models for marine mammal conservation. However, their reliability for identifying suitable habitat remains uncertain. We assessed how stranding data influence the habitat predictions for American manatee (Trichechus manatus) in the Potiguar Basin, Brazil. Using MaxEnt, we compared models built using: (1) sightings and telemetry data, (2) stranding records alone, and (3) all three data sources combined. We found that the first model based solely on sightings and telemetry produced the most accurate and ecologically meaningful predictions. In contrast, the stranding- only model overestimated suitable habitat by more than threefold, while the combined model overpredicted it by more than twofold. These differences between model predictions are best explained by carcass drift and detection biases and indicate that stranding locations do not reliably reflect areas of actual habitat use. This quantitative assessment provides new insights into the significant biases stranding data can introduce into habitat suitability models. Our findings also highlight the need to prioritize direct observations, and to apply drift modeling and validation against direct observations when using stranding data, to ensure accurate and actionable conservation planning.

Carol Meirelles is a Research Associate at the Marine Mammal Research Unit at the University of British Columbia