Straight Line Foraging in Yellow-Eyed Penguins: New Insights into Cascading Fisheries Effects and Orientation Capabilities of Marine Predators

<div><p>Free-ranging marine predators rarely search for prey along straight lines because dynamic ocean processes usually require complex search strategies. If linear movement patterns occur they are usually associated with travelling events or migratory behaviour. However, recent fine scale tracking of flying seabirds has revealed straight-line movements while birds followed fishing vessels. Unlike flying seabirds, penguins are not known to target and follow fishing vessels. Yet yellow-eyed penguins from New Zealand often exhibit directed movement patterns while searching for prey at the seafloor, a behaviour that seems to contradict common movement ecology theories. While deploying GPS dive loggers on yellow-eyed penguins from the Otago Peninsula we found that the birds frequently followed straight lines for several kilometres with little horizontal deviation. In several cases individuals swam up and down the same line, while some of the lines were followed by more than one individual. Using a remote operated vehicle (ROV) we found a highly visible furrow on the seafloor most likely caused by an otter board of a demersal fish trawl, which ran in a straight line exactly matching the trajectory of a recent line identified from penguin tracks. We noted high abundances of benthic scavengers associated with fisheries-related bottom disturbance. While our data demonstrate the acute way-finding capabilities of benthic foraging yellow-eyed penguins, they also highlight how hidden cascading effects of coastal fisheries may alter behaviour and potentially even population dynamics of marine predators, an often overlooked fact in the examination of fisheries’ impacts. </p></div

Foraging patterns of Yellow-eyed penguins.

<p>Mid-shelf foraging tracks of yellow-eyed penguins recorded in 2004 (A), 2005 (B) and 2012 (C) that feature straight-line patterns. Foraging track segments in light grey represent outgoing and incoming stages of foraging trips; dark grey segments highlight the foraging stage. Dashed line segments indicate where linearity of the track is a result of interpolation. Track portions that met line criteria (see Methods) are highlighted in different colours; line identifiers shown in capital letters of the same colour. Small arrows in (D) indicate sites of ROV deployments in February 2013. Trips with lines from all three seasons are combined in (D).</p

Comparison of basic foraging parameters in relation to breeding season and occurrence of linear patterns.

<p>Box-and-whiskers plots illustrate differences in foraging parameters between trips with and without linear patterns (A), and between the three breeding seasons (B & C). Bold horizontal lines indicate median and circles represent outliers. Note that graphs A and B are based on all recorded foraging trips, while for C only trips that met straight line criteria were used. Sample sizes are provided below x-axis labels.</p

Foraging parameters of yellow-eyed penguins fitted with GPS dive loggers.

<p>Foraging parameters of yellow-eyed penguins fitted with GPS dive loggers. </p

Screen capture of ROV footage recorded on line “C”.

<p>Main: Highly visible furrow running in a straight line along the seafloor at water depth of ca. 67 m. Note the echinoderms that have settled inside the furrow. Inset: Detail of blue cod in pursuit of ROV; scaling lasers represent 5 cm. See also (<a href="http://vimeo.com/64689982" target="_blank">http://vimeo.com/64689982</a>).</p