The importance of sample size in marine megafauna tagging studies

Abstract

Telemetry is a key, widely used tool to understand marine megafauna distribution, habitat use, behavior, and physiology; however, a critical question remains: “How many animals should be tracked to acquire meaningful data sets?” This question has wide‐ranging implications including considerations of statistical power, animal ethics, logistics, and cost. While power analyses can inform sample sizes needed for statistical significance, they require some initial data inputs that are often unavailable. To inform the planning of telemetry and biologging studies of marine megafauna where few or no data are available or where resources are limited, we reviewed the types of information that have been obtained in previously published studies using different sample sizes. We considered sample sizes from one to >100 individuals and synthesized empirical findings, detailing the information that can be gathered with increasing sample sizes. We complement this review with simulations, using real data, to show the impact of sample size when trying to address various research questions in movement ecology of marine megafauna. We also highlight the value of collaborative, synthetic studies to enhance sample sizes and broaden the range, scale, and scope of questions that can be answered.

Regional Movements of Reef Manta Rays (Mobula alfredi) in Seychelles Waters

“…For this reason, future studies aiming to deploy additional satellite tags on M. alfredi in Seychelles to further examine home range size and the potential for large-scale (>200 km) movements in this population should continue to focus efforts on mature males and females, and endeavor to tag individuals at other Island Groups. This will facilitate a comparison of movement patterns between the sexes (Sequeira et al, 2019) and across a wider region of Seychelles.…”

Overhauling Ocean Spatial Planning to Improve Marine Megafauna Conservation

“…Despite its growing volume, the inaccessibility of global tracking data (of animals and other ocean users) hinders developments that would make the provisions in these conventions more effective. A key point is that important questions about how much information is available or lacking are not yet answered, however, we now have a good idea of how much data are needed to address specific questions (Sequeira et al, 2019). Many questions will, however, require 1000s of tracks, particularly those associated with broad scale biodiversity assessments.…”

Sex-differences in fine-scale home-range use in an upper-trophic level marine predator

“…In this study, the majority of individuals wore tracking instruments for the period immediately following the moult and up to the start of the breeding season, providing the maximum recording period (6-7 months). Recent studies have highlighted the need for large sample sizes (10 to 100) when estimating utilization distributions due to the high variability in movement behaviour among individuals of a given species [66][67][68]. In this study, instruments were deployed on 15 to 20 individuals each year for a seven-year period to provide an adequate sample size to account for individual variation, tag loss and instrument error.…”