Mixed species aggregations feeding upon herring and sandlance schools in a nearshore archipelago depend on flooding tidal currents

Abstract

Tidal rips and jets are common features associated with archipelagos and complex coastlines. In habitats where rips and jets develop, energy flow to piscivorous predators is hypothesized to be strongly associated with tidal phase due to interactions between currents, plankton, and schooling planktivorous fishes (the 'tidal coupling hypothesis'). This study tests 1 component of the tidal coupling hypothesis, that the feeding activity of piscivorous predators and the availability of planktivorous fishes are both strongly associated with the same tidal phase. During 1994 to 1997, I made visual counts of actively feeding, mixed-species seabird flocks and hydroacoustic measurements of the relative abundance and distribution of schooling fishes. Median feeding activity, median backscatter m -1 transect, and median prey encounter probabilities were greatest during the tidal periods Slow flood 1 and Fast flood. Positive feeding anomalies and positive prey-encounter anomalies were significantly associated with tidal flood phases, but positive backscatter anomalies were not. The results support the tidal-coupling hypothesis, but suggest that changes in the distribution or behavior of schooling fish are as important as, if not more important than, changes in relative fish abundance when determining prey availability and predator foraging-success. The data show that tidal currents can play an important role in structuring nearshore predator-prey interactions.

Fine-scale biophysical interactions drive prey availability at a migratory stopover site for Phalaropus spp. in the Bay of Fundy, Canada

“…Several studies have found associations between foraging seabirds and tidally-driven oce anographic features, and some have demonstrated that temporal components of these features were important factors influencing seabird abundance and distribution (Braune & Gaskin 1982, Zamon 2003. However, the mechanism by which these features create regions of increased prey for foraging seabirds was not investigated specifically.…”

Riding the tide: use of a moving tidal-stream habitat by harbour porpoises

“…Plankton have traditionally been assumed to become entrained within tidal structures, attracting fish and their predators such as harbour porpoises at particular tidal phases (the 'tidal coupling hypothesis'; Uda & Ishino 1958, Wolanski & Hamner 1988, Zamon 2002, 2003. However, cycles of prey behaviour and availability in these environments may be more important in attracting predators than absolute prey abundance (Zamon 2002).…”

Consequences of ecological connectivity: the coastal ecosystem mosaic

“…Consequently, these areas are foci for intense predation events at a multiplicity of scales (Acha et al 2004, Bakun 2006 involving animals as diverse as zooplankton (Genin 2004), larval fish (Bakun 2006), predatory fish (Zamon 2003), sea birds (Davoren et al 2003, Weimerskirch et al 2004), planktivorous sharks (Sims et al 2003), and cetaceans (Atkins et al 2004). These are areas that many members of the CEM occupy during feeding or life-history migrations, and are often integral links in connectivity between units of the CEM.…”