title: Drivers of Daily Routines in an Ectothermic Marine Predator: Hunt Warm, Rest Warmer?
abstract: Animal daily routines represent a compromise between maximizing foraging success and optimizing physiological performance, while minimizing the risk of predation. For ectothermic predators, ambient temperature may also influence daily routines through its effects on physiological performance. Temperatures can fluctuate significantly over the diel cycle and ectotherms may synchronize behaviour to match thermal regimes in order to optimize fitness. We used bio-logging to quantify activity and body temperature of blacktip reef sharks (Carcharhinus melanopterus) at a tropical atoll. Behavioural observations were used to concurrently measure bite rates in herbivorous reef fishes, as an index of activity for potential diurnal prey. Sharks showed early evening peaks in activity, particularly during ebbing high tides, while body temperatures peaked several hours prior to the period of maximal activity. Herbivores also displayed peaks in activity several hours earlier than the peaks in shark activity. Sharks appeared to be least active while their body temperatures were highest and most active while temperatures were cooling, although we hypothesize that due to thermal inertia they were still warmer than their smaller prey during this period. Sharks may be most active during early evening periods as they have a sensory advantage under low light conditions and/or a thermal advantage over cooler prey. Sharks swam into shallow water during daytime low tide periods potentially to warm up and increase rates of digestion before the nocturnal activity period, which may be a strategy to maximize ingestion rates. "Hunt warm, rest warmer" may help explain the early evening activity seen in other ectothermic predators.
authors.affiliation: School of Biology, Scottish Oceans Institute, University of St Andrews, St Andrews, Scotland, United Kingdom.
authors.forename: Yannis P
authors.initials: YP
authors.lastname: Papastamatiou
authors.affiliation: National Institute of Polar Research, Tachikawa, Tokyo, Japan; SOKENDAI (The Graduate University for Advanced Studies), Tachikawa, Tokyo, Japan.
authors.forename: Yuuki Y
authors.initials: YY
authors.lastname: Watanabe
authors.affiliation: Bren School of Environmental Science and Management, University of California Santa Barbara, Santa Barbara, California, United States of America.
authors.forename: Darcy
authors.initials: D
authors.lastname: Bradley
authors.affiliation: Bren School of Environmental Science and Management, University of California Santa Barbara, Santa Barbara, California, United States of America.
authors.forename: Laura E
authors.initials: LE
authors.lastname: Dee
authors.affiliation: Department of Fisheries Science, Virginia Institute of Marine Science, Gloucester Point, Virginia, United States of America.
authors.forename: Kevin
authors.initials: K
authors.lastname: Weng
authors.affiliation: Department of Biological Sciences, California State University Long Beach, Long Beach, California, United States of America.
authors.forename: Christopher G
authors.initials: CG
authors.lastname: Lowe
authors.affiliation: Marine Science Institute, University of California Santa Barbara, Santa Barbara, California, United States of America.
authors.forename: Jennifer E
authors.initials: JE
authors.lastname: Caselle
mesh_terms: D000818:Animals; D002940:Circadian Rhythm; D004063:Digestion; D017753:Ecosystem; D005260:Female; D011235:Predatory Behavior; D012146:Rest; D012754:Sharks / Q000502:physiology*; D013696:Temperature