title: Foraging, bioenergetic and predation constraints on diel vertical migration: field observations and modelling of reverse migration by young-of-the-year herring Clupea harengus.
abstract: Diel vertical migration (DVM) of young-of-the-year (YOY) herring Clupea harengus and one of their major predators, pikeperch Sander lucioperca, was examined using bottom-mounted hydroacoustics in Himmerfjärden, a brackish bay of the Baltic Sea, in summer. In contrast to previous studies on DVM of C. harengus aggregated across size and age classes, YOY C. harengus showed a reverse DVM trajectory, deeper at night and, on average, shallower during the day. This pattern was observed consistently on five acoustic sampling occasions in 3 years and was corroborated by two out of three trawl surveys. Large acoustic targets (target strength >-33 dB, probably piscivorous S. lucioperca >45 cm) showed a classic DVM trajectory, shallow at night and deeper during the day. Variability in YOY C. harengus vertical distribution peaked at dawn and dusk, and their vertical distribution at midday was distinctly bimodal. This reverse DVM pattern was consistent with bioenergetic model predictions for YOY C. harengus which have rapid gut evacuation rates and do not feed at night. Reverse DVM also resulted in low spatial overlap with predators.
authors.affiliation: University of Wisconsin Center for Limnology, 680 N. Park Street, Madison, WI 53706, U.S.A. ojensen@marine.rutgers.edu
authors.forename: O P
authors.initials: OP
authors.lastname: Jensen
authors.forename: S
authors.initials: S
authors.lastname: Hansson
authors.forename: T
authors.initials: T
authors.lastname: Didrikas
authors.forename: J D
authors.initials: JD
authors.lastname: Stockwell
authors.forename: T R
authors.initials: TR
authors.lastname: Hrabik
authors.forename: T
authors.initials: T
authors.lastname: Axenrot
authors.forename: J F
authors.initials: JF
authors.lastname: Kitchell
mesh_terms: D000162:Acoustics; D025041:Animal Migration; D000818:Animals; D001070:Appetitive Behavior; D004734:Energy Metabolism; D005399:Fishes / Q000502:physiology*; D010507:Periodicity; D011235:Predatory Behavior; D012623:Seawater / Q000032:analysis