- 1Sea Mammal Research Unit, Scottish Oceans Institute, University of St Andrews, St Andrews, Fife, KY16 8LB UK.
- 2Sea Mammal Research Unit, Scottish Oceans Institute, University of St Andrews, St Andrews, Fife, KY16 8LB UK ; Scottish Association for Marine Science, University of the Highlands and Islands, Scottish Marine Institute, Oban, Argyll PA37 1QA UK.
- 3Centre for Research into Ecological and Environmental Modelling, The Observatory, University of St Andrews, Fife, Scotland KY16 9LZ UK.
Abstract
ABSTRACT:
Previous
studies have found that predators utilise habitat corridors to ambush
prey moving through them. In the marine environment, coastal channels
effectively act as habitat corridors for prey movements, and sightings
of predators in such areas suggest that they may target these for
foraging. Unlike terrestrial systems where the underlying habitat
structure is generally static, corridors in marine systems are in
episodic flux due to water movements created by tidal processes.
Although these hydrographic features can be highly complex, there is
generally a predictable underlying cyclic tidal pattern to their
structure. For marine predators that must find prey that is often patchy
and widely distributed, the underlying temporal predictability in
potential foraging opportunities in marine corridors may be important
drivers in their use. Here, we used data from land-based sightings and
19 harbour seals (Phoca vitulina) tagged with high-resolution GPS
telemetry to investigate the spatial and temporal distribution patterns
of seals in a narrow tidal channel. These seals showed a striking
pattern in their distribution; all seals spent a high proportion of
their time around the narrowest point of the channel. There was also a
distinctive tidal pattern in the use of the channel; sightings of seals
in the water peaked during the flood tide and were at a minimum during
the ebb tide. This pattern is likely to be related to prey availability
and/or foraging efficiency driven by the underlying tidal pattern in the
water movements through the channel.
SIGNIFICANCE STATEMENT:
To
maximise foraging efficiency, predators often make use of narrow
constrictions in habitat to intercept prey using these corridors for
movement. In the marine environment, narrow channels may act as
corridors, and sightings of predators suggest that they may target these
for foraging. Despite this, there is little information on how
individual predators use such areas. Here, we investigate how individual
harbour seals use a narrow coastal channel subject to strong tidal
currents; results showed that seals spent the majority of their time at
the narrowest point of the channel foraging during peak tidal currents.
This highlights the importance of narrow channels for marine predators
and suggests that this usually wide-ranging predator may restrict its
geographic range to forage in the channel as a result of increased prey
availability and/or foraging efficiency driven by water movements
through the narrow corridor.
KEYWORDS:
Diving; Foraging; Marine mammal; Oceanographic; Pinniped; Predator
