Laboratory Study of Foraging by Atlantic Mackere , Sc~mber P. Pepin,' J. A. Koslow, and S. Pearre jr. Department of Oceanography, Balhousie University, Halifax, NOS. B3M 4)! Pepin, P., ). A. Koslcpw, and S. Pearre Jr. 1988. Foraging of Atlantic mackerel, Sesmber sesmbrus, on natural zosplanktsn assemblages. Can. j. Fish. Aquat. Sci. 45: 879-887. This study reports on the behavioural response of captive Atlantic mackerel, Scsmber scombrus, to changes in composition and abundance sf natural zooplankton assemblages. Filter-feeding activity and swimming s p e d increase with increasing prey concentration. Swimming speed also increases with increasing prey size. Prey preference shows a size selective pattern that is slightly influenced by the size of the largest available prey! but not by variations in total prey abundance or density of individual size categories. Feeding rates under average natural conditions of prey abundance (0.1 g wet weightsm-3) indicate that mackerel would be unable to satiate during a foraging period restricted to daylight hours. Although prey aggregation or night feeding may enable mackerel to attain their maximum ration in the wild, a review 0% the literature suggests that plagic fish seldom satiate. The dynamic response of mackerel to changes in prey abundance can have impartant consequences to the impact that mackerel and other planktivorous fish may have on the dynamics sf rnultispecies zooplankton and ichthyoglanktsn communities. L'etude pcprte sur la reponse comportementale de maquereaux bleus (Sesmber sesmbaus) en cagtivite 2 des modifications de la composition et de l'abndance d'assernblages naaurels de zosplancton. L'activite de filtrage et la vitesse de nage augmentent avec la concentration des prsies. La vitesse de nage augrnente aussi avec la taille des proies. bes prkfkrences en matiere de prsies suivent un regime de selection en fonction de la taille qui est Jeg&rement influence par la taille des proies les plus grosses, mais non par les variations de l'abondance totale des proies ni par [a densit6 des catggcpries de taille. Les taux de consommation dans des conditions naturelles rnoyennes d'abondance des proies @,I g de poids hurnide . m-3)indiquent que le maquereau ne psurrait pas atteindre la sati$t& si sa periode d'alimentation etait Bimitee A la phase eclairee. Bien que la concentration des proies ou l'alimentation nocturne puissent permettre aux maquereaux d'atteindre leur ration maximale dans le milieu naturel, Ifexamen de [a documentation rnsntre que les ploissons pelagiques atteignent rarernent la satikt6. La r6ponse dynamique des maquereakex aux changernents dans l'abondance des proies put avoir des cons&- quences importantes en ce qui concerne les effets qkee peuvent avoir les maquereaux et les autres poissons planctivores sur la dynamique des communautes plurisp6cifiques de zosplanctsn et d'ichtyoglancton. Received September 3, 7984 Accepted February 9, 1988 (J8926) everal species of pelagic schooling fish 4e.g. sardine, anchovy, herring, and mackerel) feed pri-iim~ly on zoo- plankton (Scott 1920; Savage 1937; Lasker 1 970) md are considered important consumers of secondary grsductisn (Steele 2974; Andersen and Ursin 1977;Jones 1984). Although species such as herring, anchovy, md mackerel are heavily exploited and are important members of pelagic ecosystems, relatively little is known a b u t their foraging khaviour. Pelagic fish are traditionally treated as blwk components in production models (Skele 1974; Bones 1984). They are assumed to take a certain proportion of secondary production, regadless of changes in prey abundance or composition. On the sther hmd, studies of the foraging of freshwder planktivorous fish focus primarily on patterns of prey selection and feeding behaviour, their relationship to optimal foraging strategies, and the eon- sequences to prey populations. Lhsent add~ss: Department of Fisheries and Oceans, Northwest Atlantic Fisheries Centre, Science Branch, Pe8. Box 5667, St. John's, Nfld. A1C 5x1. Pelagic fish can maximize their net energy intake by altering their absolute seach rate (i.e. s w i m i n g speed) as prey abun- dance and/or composition varies (Ware 1978). Maine plank- tivorous fish may also dter their pattern of prey selection as prey size composition changes (Koslow 198 1). W en faced with different prey assemblages, many pldtivsrous fish can switch their mode of feeding on zooplankton, foraging either by pa- ticulate or filter-feeding, in order to maximize their net energy intake (Crowder 1985). The foraging of marine p l ~ t i v s r o u s fish has been studied in the laboratory by manipulating simple prey assemblages con- sisting of luge and small prey items ge.$. studies by 09Connell 1972; 07Connell and Zweifel 197%). However, natural situa- tions are seldom so simple. Z o o p l d t s n prey assemblages cover a continuum of sizes md the abundance of prey of dif- ferent sizes is highly variable. We therefore used natural zso- plankton assemblages in two laboratory experiments to study the (1) feeding behaviour and (2) prey selwtion of Atlantic mackerel, Scomber scombrus. Results of these experiments wiU Can. J. Fish. Aquat. Sci. Downloaded from www.nrcresearchpress.com by Renmin University of China on 06/07/13 For personal use only.