[MARMAM] New articles on harbor seal open water grouping behavior and kleptoparasitism by bald eagles during marine mammal foraging events

Cindy Elliser cindy.elliser at pacmam.org
Fri Jul 8 00:18:28 PDT 2022

Dear colleagues,

On behalf of my co-authors I am happy to announce our two recent
publications in Behaviour:

*Open water grouping behaviour in harbour seals (Phoca vitulina richardii)
of the Salish Sea*
Cindy R. Elliser, David Anderson, Trevor Derie, Katrina MacIver, and Laurie

Article link:

Abstract:  Harbour seals (Phoca vitulina) commonly form larger
congregations at haul out locations during times of rest and pupping
season, but are generally thought to be solitary at sea. Occasionally
larger clusters of individuals may be observed swimming near haul out
sites, forced bottlenecking channels or mouths of rivers with concentrated
prey and restricted space. Recently, isolated occurrences of mass
gatherings of harbour seals have been observed in the Salish Sea that were
distanced from haul out sites (over 1 km away) or forced bottlenecking
regions. In April-June (but primarily May) 2019–2021 juvenile and adult
harbour seals in Burrows Pass (Anacortes, WA, USA) were observed in large
groups (N=31) ranging in size from 6–50 individuals (x‾=16.8) within 1-2
body lengths of each other and periodically diving down seemingly hunting
and chasing prey. These groupings primarily occurred during flood and slack
high tides. Based on the surface level activity observed, habitat type, the
frequency of individuals using the area for foraging year round and the
tidal preferences during the occurrences, it is likely these are foraging
events. Similar large groups have been documented (N=10) in the South Puget
Sound and Central Puget Sound, first observed in 2016 and officially
documented in February of 2017. These groupings (from 20–30 to 150+)
occurred year round and at varied tidal states. While some sightings were
obviously foraging behaviour, others appeared to be resting, traveling or
socializing. Open water behaviour of harbour seals is not well documented,
and a literature review found no other published accounts of large in-water
groupings. Investigation of ecological relationships (like prey spawning,
prey abundance, or other environmental correlates) and observation of
underwater harbour seal behaviour will aid in determining the reason for
this seemingly novel behaviour.


*Kleptoparasitic interactions by bald eagles (Haliaeetus leucocephalus)
during marine mammal foraging events*
Cindy R. Elliser, Ciera Edison, Katrina MacIver, and Lauren B. Rust

Article link:

Abstract: Stealing of food items from another animal, or kleptoparasitism,
has been well studied in bird species. Bald eagles are known
kleptoparasites of other birds and occasionally other species, however
kleptoparasitic interactions with mammals are relatively uncommon. We
describe instances of bald eagles taking, or attempting to take, fish and
mammal prey from three species of cetaceans (bottlenose dolphins (Tursiops
truncatus), harbour porpoises (Phocoena phocoena vomerina) and killer
whales (Orcinus orca)) and one species of pinniped (harbour seal (Phoca
vitulina richardii)) on the east and west coast of the United States of
America. We discuss possible drivers of this emerging behaviour, including
bald eagle population increases, reductions in other prey abundance, and
changes in prey choice (for harbour porpoises). Further research is needed
to determine if this behaviour is opportunistic in nature, or a more common
foraging strategy.


Cindy Elliser, PhD

Research Director

Pacific Mammal Research


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