Pretty patterns but a simple strategy: predator-prey interactions between juvenile herring and Atlantic puffins observed with multibeam sonar

Abstract

Predator-prey interactions between Atlantic puffins (Fratercula arctica) and newly metamorphosed herring (Clupea harengus) were studied in the Lofoten-Røst area in northern Norway using a high-resolution multibeam sonar system. Attacks from diving puffins and predatory fish induced massive predator-response patterns at the school level, including bend, vacuole, hourglass, pseudopodium, herd, and split. All patterns have previously been observed, using the same sonar, in schools of adult herring attacked by groups of killer whales. Tight ball, the prevailing response pattern in adult fish under predation, was not observed, but a new pattern, intraschool density propagation, was found and interpreted as an analogue to tight-ball formations moving rapidly within the school. The observed patterns persisted much longer than in schools of adult herring attacked by killer whales, reflecting the different hunting strategies. Traditionally, the repertoire of predator responses observed in schooling fish has been interpreted as a range of cooperative tactics to trick predators, but this has recently been challenged by authors who suggested that fish that behave the same way produce different patterns at group level simply by maintaining a minimum approach distance to predators and hiding behind conspecifics (the "selfish herd"), and that the particular combination of group size and number and behaviour of predators, rather than different individual tactics, determines the outcome at group level. Our findings support the latter hypothesis.Résumé : Nous avons étudié les interactions prédateurs-proies entre des Macareux moines (Fratercula arctica) et des Harengs (Clupea harengus) fraîchement métamorphosés dans la région de Lofoten-Røst, dans le nord de la Norvège au moyen d'un sonar de haute résolution à faisceaux multiples. Les attaques des oiseaux en plongée et des poissons prédateurs déclenchent des patterns de réaction massive au sein des bancs de harengs : repliement, vacuole, sablier, pseudopode, troupeau et séparation, types de comportement déjà observés, au moyen du même sonar, dans des bancs de harengs adultes attaqués par des épaulards. La formation d'une boule compacte, la réaction la plus fréquente des poissons adultes face à des prédateurs, n'a pas été observée, mais il s'est produit un nouveau pattern dans les bancs de harengs, la pulsion de densité, interprétée comme analogue à la formation d'une boule compacte, mais se déplaçant rapidement dans le banc. Ces patterns ont duré beaucoup plus longtemps que ceux observés dans les bancs de harengs adultes attaqués par des épaulards, ce qui reflète la diversité des stratégies de chasse. Traditionnellement, le répertoire des réactions aux prédateurs observé au sein des bancs de poissons est considéré comme une série de tactiques de coopération pour tromper les prédateurs, mais cette théorie a été remise en question par les auteurs qui croient que ces poissons qui se comportent de la même façon produisent des patterns différents quand ils sont en groupe en s'approchant...

Active acoustic examination of the diving behavior of murres foraging on patchy prey

“…While diving birds have been shown to be de tectable using sonar , Axelsen et al 2001, Brierley & Fernandes 2001, and Axelsen et al (2001) used acoustics to qualitatively examine the relationship be tween seabird predators and their prey, this is the first published account using quantitative fisheries acous tics techniques to examine sea bird−prey interactions. Se veral advantages of using fisheries acous tics techniques are apparent: (1) the approach is non-invasive; (2) in addition to bird horizontal position, it allows the depth of birds to be measured up to about 200 m; (3) it is not limited by visual conditions like fog and darkness; (4) it excludes nondiving birds that are not actively foraging; (5) ple sizes, allowing population le vel res ponses to be ob served (N = 5140 in the present study); and (6) it allows simultaneous sampling of birds and the quantification of the type, depth, distribution, and density of potential prey, permitting the horizontal and vertical overlap between predator and prey to be examined at the same resolution and scale.…”

Climate change and condition of herring (Clupea harengus) explain long-term trends in extent of skipped reproduction

“…First, favourable conditions early in life can result in high survival but reduced growth and condition due to reduced per capita food intake, as a density-dependent effect (Barros and Toresen 1998). Second, strong year-classes, characterised by reduced growth and condition indices (Toresen 1990;Holst 1996) may suffer less predation and exploitation mortality due to the dilution effect (Axelsen et al 2001). Alternatively, if skipped 375 reproduction is not restricted to the second spawning season but also occurs in older spawners, then the inverse relationship between condition and survival might even be the result of skipped reproduction per se.…”

Dynamic 3-dimensional structure of thin zooplankton layers is impacted by foraging fish

“…Axelsen et al 2001, Benoit-Bird & Au 2003. Analysis of underway data showed that more fish were correlated with more of the same-sized holes, while bigger fish were correlated with bigger individual holes.…”

“…Prey in benthic systems have been found to aggregate into discrete patches as a mechanism to avoid predators (see, for example, Hildrew & Townsend 1982), changing not only the prey animals' density but also their distribution. While numerous studies in pelagic systems have investigated the effects of prey distribution on predator behavior, and studies in benthic habitats have revealed the significant impacts predators can have on prey distribution (see a review in Cooper et al 1990), relatively few field studies outside the schooling fish literature have investigated the effects of predator behaviors on prey distribution in pelagic systems (Orr 1981, Axelsen et al 2001, De Robertis et al 2003, Benoit-Bird & Au 2009). These interactions can have effects on individual animals, their competitors and predators, as well as the measurements obtained of them and their environment.…”