Diel vertical movements of short‐finned pilot whales in the Gulf of Mexico from time‐at‐temperature data

Resumen

We analysed 180 time‐at‐temperature (TAT) histograms from satellite‐linked LIMPET‐SPOT5 tags deployed in April 2018 on seven short‐finned pilot whales (Globicephala macrorhynchus) in the southwestern Gulf of Mexico to investigate diel patterns in vertical movements as a proxy of their diving behaviour. TAT data were transformed into time‐at‐depth (TAD) data using satellite‐Gravest Empirical Mode (satGEM) projections. TAD data were classified into four behavioural states: State 1 (surface movements < 20 m), State 2 (non‐foraging dives 20–45 m), State 3 (shallow foraging dives > 45–300 m), and State 4 (deep foraging dives > 300 m). A Bayesian ANOVA test was used to analyse the time budget between early morning, daytime and nighttime. Overall, pilot whales spent ~50% of their time in the surface strata (< 45 m) engaged in activities other than foraging, 38.3% performing shallow‐foraging dives, and only 11.2% in deep dives. The Bayesian ANOVA was inconclusive for States 1–2 but showed differences for shallow and deep foraging dives (States 3–4) across time periods. Post hoc comparisons showed that pilot whales spent less time in shallow‐foraging dives (State 3) during daylight hours compared to both early morning and night. Still, they spent more time in deep‐foraging dives (State 4) during the daytime and early morning than at night, a pattern consistent with the diel vertical migration of their main prey (squid). Despite the small number of tagged animals, our results are the first description of the vertical habitat use of deep‐diving cetaceans in the Gulf of Mexico, an essential component for understanding the ecological role of these large predators.