Living until proven dead: addressing mortality in acoustic telemetry research

Neglecting to account for the mortality of study animals in ecological research has the potential to lead to biased interpretation of behaviour. Considering the widespread use of acoustic telemetry to track the presence and movements of aquatic animals, if mortality is not appropriately addressed, conservation or management decisions affecting important resources may be distorted. Although mortality can be difficult to identify, it is unclear how frequent mortality is considered or incorporated in acoustic telemetry research, particularly studies relating to the behaviour of tagged animals. The main objective of this review was to characterize if and how mortality was incorporated in recent acoustic telemetry articles published during 2015–2019. For the 640 articles reviewed, criteria used to address mortality were summarized across study and animal types, providing a comprehensive view of ‘mortality consideration’. Also, we discuss the common approaches that have been used in previous studies to incorporate mortality, as well as emerging tools, major concerns, and advice to help guide its inclusion in future work. We found that 50% of ecology/behaviour articles tracking the movements of elasmobranchs, bony fishes, and other aquatic animals did not communicate that mortality was either contemplated, investigated, or integrated into the study. For the studies that did incorporate mortality, 75% identified mortality events equating to an average of ~ 11% of animals tagged in each study. The criteria used to assess mortality varied among study types with horizontal movement, movements between adjacent receiver stations, and direct observation of fate as the most common for ecology/behaviour, mortality/survival, and tagging effects articles, respectively. We conclude that reporting of and methods to assess mortality should be more widespread in acoustic telemetry research, especially since movement ecology is increasingly being used to inform management decisions.