Dear colleagues,
We are pleased to announce the publication of a set of papers that
make up a special section on North Atlantic killer whales in the
current issue of the JMBA. The papers are largely based around
presentations at a workshop held at the 2012 European Cetacean Society
meeting in Galway. This meeting marked the 25th anniversary of a
previous workshop on North Atlantic killer whales and aimed to
summarise the progress made during the past 25-years. We would like to
thank all the authors for their valuable contributions. Please contact
the corresponding authors directly with any reprint requests or
enquiries.
Andy Foote, Sanna Kuningas and Filipa Samarra
Foreword: North Atlantic killer whale research; past, present and future
Andrew D. Foote, Sanna Kuningas and Filipa I.P. Samarra
Using opportunistic photo-identifications to detect a population
decline of killer whales (Orcinus orca) in British and Irish waters
Suzanne Beck, Andrew D. Foote, Sandra Kotter, Olivia Harries, Laura
Mandleberg, Peter T. Stevick , Padraig Whooley and John W. Durban
Email: biodiversityofficer(a)hwdt.org
An assemblage of killer whales that has been sighted in waters off the
west coast of the British Isles and Ireland has previously been shown
to be isolated from other North Atlantic killer whale communities
based on association patterns. By applying a Bayesian formulation of
the Jolly–Seber mark-recapture model to the photo-identification data
compiled from opportunistic photographic encounters with this
population of killer whales, we show that such sparse and
opportunistically-collected data can still be valuable in estimating
population dynamics of small, wide-ranging groups. Good quality
photo-identification data was collected from 32 encounters over 19
years. Despite a cumulative total of 77 identifications from these
encounters, just ten individuals were identified and the remaining 67
identifications were re-sights of these ten animals. There was no
detected recruitment through births during the study and, as a result,
the population appears to be in a slight decline. The demography of
the population was highly skewed towards older individuals and had an
unusually high ratio of adult males, and we suggest that demographic
stochasticity due to a small population size may be further impacting
the population growth rate. We recommend that this population be
managed as a separate conservation unit from neighbouring killer whale
populations.
Killer whale (Orcinus orca) occurrence and predation in the Bahamas
Charlotte Dunn and Diane Claridge
Email: cdunn(a)bahamaswhales.org
Killer whales (Orcinus orca) have a cosmopolitan distribution, yet
little is known about populations that inhabit tropical waters. We
compiled 34 sightings of killer whales in the Bahamas, recorded from
1913 to 2011. Group sizes were generally small (mean 1⁄4 4.2, range
1⁄4 1–12, SD 1⁄4 2.6). Thirteen sightings were documented with
photographs and/or video of sufficient quality to allow individual
photo-identification analysis. Of the 45 whales photographed, 14
unique individual killer whales were identified, eight of which were
re-sighted between two and nine times. An adult female (Oo6) and a
now-adult male (Oo4), were first seen together in 1995, and have been
re-sighted together eight times over a 16-yr period. To date, killer
whales in the Bahamas have only been observed preying on marine
mammals, including Atlantic spotted dolphin (Stenella frontalis),
Fraser’s dolphin (Lagenodelphis hosei), pygmy sperm whale (Kogia
breviceps) and dwarf sperm whale (Kogia sima), all of which are
previously unrecorded prey species for Orcinus orca.
Identifying key habitat and seasonal patterns of a critically
endangered population of killer whales
Ruth Esteban, Philippe Verborgh, Pauline Gauffier, Joan Gimenez,
Isabel Afan, Ana Canadas, Pedro Garcia, Jose Luis Murcia, Sara
Magalhaes, Ezequiel Andreu and Renaud de Stephanis
Email: ruthesteban(a)gmail.com
Killer whales have been described in the Gulf of Cadiz, southern
Spain, in spring and in the Strait of Gibraltar in summer. A total of
11,276 cetaceans sightings coming from different sources (dedicated
research surveys, whale watching companies and opportunistic
observations) were used to create two presence – ‘pseudo-absence’
predictive generalized additive models (GAM), where presence data were
defined as sightings of killer whales and ‘pseudo-absence’ data as
sightings of other cetacean species. One model was created using
spring data when killer whales’ main prey, Atlantic bluefin tuna,
enter the Mediterranean Sea, and the other model used summer data when
Atlantic bluefin tuna return to the Atlantic Ocean. Both model
predictions show that killer whales are highly associated with a
probable distribution of bluefin tuna during their migration
throughout the study area, constraining their distribution to the Gulf
of Cadiz in spring and the Strait of Gibraltar in spring and summer.
Knowledge of the distribution of killer whales in the study area is
essential to establish conservation measures for this population.
Distribution and abundance of killer whales (Orcinus orca) in Nunavut,
Canada—an Inuit knowledge survey
Jeff W. Higdon, Kristin H. Westdal and Steven H. Ferguson
Email: steve.ferguson(a)dfo-mpo.gc.ca
Traditional ecological knowledge is being increasingly used in
wildlife management in northern regions, and Inuit harvesters in
Nunavut, Canada, have extensive knowledge about local wildlife
species. We collected Inuit knowledge on killer whales (Orcinus orca)
through 105 semi-directed interviews in 11 Nunavut communities from
2007 to 2010. Interviewees provided extensive information on killer
whale movements, seasonal presence, distribution and abundance in the
eastern Canadian Arctic. Observations from different communities were
often complementary, and there was consistency in interview comments
both within and among regions. Nearly all participants had seen killer
whales at least once, and the whales were present every summer
(July–September) in all regions, although movements depended on ice
conditions. Relative abundance of killer whales varied by region, and
they were reported more often in North Baffin communities than in
other regions. Killer whales migrated through Hudson Strait and
Lancaster Sound following their marine mammal prey. Estimates of local
population sizes were variable, with suggested numbers that varied
from tens to the low hundreds. Most interviewees in the Foxe Basin,
Hudson Bay and north Baffin regions thought that killer whale presence
was increasing. In contrast, half the South Baffin interviewees noted
declines in past abundance due to the 1977 harvest of 14 whales that
became trapped in a saltwater lake. Interviews provided information at
a long temporal and wide spatial record. Inuit are reliable observers
and continued killer whale research will be most effective if it
integrates modern science approaches with the traditional skills,
knowledge and experience of Inuit harvesters.
Population size, survival and reproductive rates of northern Norwegian
killer whales (Orcinus orca) in 1986–2003
Sanna Kuningas, Tiu Simila and Philip S. Hammond
Email: sanna.kuningas(a)gmail.com
A long-term photo-identification study of killer whales (Orcinus orca)
in northern Norway was initiated in 1986, when their prey the
Norwegian spring-spawning herring (Clupea harengus) started to winter
in a complex fjord system. The aim of this work was to estimate
population size and apparent survival rates in this killer whale
population using photo-identification and mark–recapture techniques
with data collected during October–December 1986–2003. Total
population size was estimated to be highest in 2003: 731 individuals
(SE 1⁄4 139, 95% CI 1⁄4 505–1059) using a model taking heterogeneity
of capture probabilities into account. Apparent survival of adult
males and adult females was estimated using the Cormack – Jolly –
Seber model as 0.971 (SE 1⁄4 0.008) and 0.977 (SE 1⁄4 0.009),
respectively. Calving intervals ranged from 3 to 14 years (mean 1⁄4
5.06, SE 1⁄4 0.722). These are the first estimates of northern
Norwegian killer whale population parameters, allowing their dynamics
to be investigated and comparisons to be made with killer whale
populations globally.
Historic and current distribution patterns, and minimum abundance of
killer whales (Orcinus orca) in the north-west Atlantic
Jack W. Lawson and Tara S. Stevens
Email: jack.lawson(a)dfo-mpo.gc.ca
This study represents the first comprehensive examination of the
distribution and abundance of killer whales (Orcinus orca) in the
north-west Atlantic. Based on a collation of sightings data and a
multi-year photographic catalogue of killer whales, 836 sighting
events have been recorded between 1758 and 2012, with most occurring
in the last ten years. Killer whales were most commonly observed
during June–September in Newfoundland/Labrador, Canada. Most sightings
were made close to shore, although many occurred beyond coastal shelf
areas and in water depths in excess of 3000 m. Relatively fewer
sightings were recorded on the Scotian Shelf, in the Gulf of St
Lawrence or the north-eastern USA, despite appreciable aerial and
vessel-based cetacean survey effort. In the north-west Atlantic,
killer whales have been sighted both alone and in groups, with group
sizes ranging from 2 to 30 whales (rarely more than 15, although an
aggregation of 100 was reported 43 years ago). Groups usually
comprised 2–6 individuals. Based on photographic records, there are at
least 67 identified killer whales in the northwest Atlantic; this is
an underestimate, since a large portion of our image collection was
not of sufficient quality to be considered in the analysis, and many
of the whales do not have easily discernible markings. The discovery
curve of newly-identified whales has not plateaued, suggesting that
there are more whales to identify. These data allow us to better
understand the ecology of these killer whales, and provide a baseline
against which population changes and distribution patterns can be
assessed.
Spatial segregation and similar trophic-level diet among eastern
Canadian Arctic/ north-west Atlantic killer whales inferred from bulk
and compound specific isotopic analysis
Cory J.D. Matthews and Steven H. Ferguson
Email: cory_matthews(a)umanitoba.ca
Killer whales in the Eastern Canadian Arctic (ECA) prey on narwhal,
beluga, bowhead whales and seals, while further south in the
north-west Atlantic (NWA), killer whales off the coast of Newfoundland
and Labrador prey on both marine mammals and fish. Bulk and amino acid
(AA) specific isotopic composition of dentinal collagen in teeth of 13
ECA/NWA killer whales were analysed to assess the degree, if any, of
dietary specialization of killer whales across the region. Dentine was
sampled from within annual growth layer groups (GLGs) to construct
chronological profiles of stable nitrogen (d15N) and carbon (d13C)
isotopic compositions for individual whales spanning 3–25 years.
Interannual isotopic variation across GLGs was less than that among
individuals, and median bulk d15N values differed by up to 5‰ among
individuals. Significant correlation between bulk d15N values and
baseline (source AA) d15N values indicates much of the observed
isotopic variation among individuals reflects foraging within
isotopically distinct food webs, rather than diet differences. This
interpretation is supported by consistent differences in bulk d13C
values between the two individuals with lowest source AA d15N values
and the remaining whales. After accounting for baseline isotopic
variation, comparable d15N values among individuals indicates similar
trophic-level diet, although uncertainties in relative trophic 15N
enrichment of individual AAs currently limits trophic position
estimates for top consumers. Further research is required to clarify
seasonal movement patterns and possible diet shifts of ECA/NWA killer
whales to better define their role in marine ecosystems across the
region.
A quantitative and qualitative comparison of pigmentation features
among North Atlantic killer whale (Orcinus orca) populations
Pirjo Mäkeläinen, Ruth Esteban, Andrew D. Foote, Sanna Kuningas,
Julius Nielsen, Filipa I.P. Samarra, Tiu Similä, Nienke C.F. Vangeel
and Gísli A. Víkingsson
E-mail: pirjo.makelainen(a)saunalahti.fi
Whilst previous studies of North Atlantic killer whales have
qualitatively compared pigmentation patterns, here we present the
first quantitative comparison of saddle and eye patch patterns of
killer whales from Norwegian, Icelandic, British, Spanish and
Greenlandic waters. We found only a small amount of variation in
saddle patch shapes, which may reflect a recent phylogenetic
divergence from the most recent common ancestor. Eye patch shapes were
more variable than saddle patches in small details. Most individuals
had patches with parallel orientation, with the exception of a small
group of killer whales from Hebrides, which as previously reported had
angular eye patches that sloped downward at the anterior end. This
differentiation in pigmentation patterns of the Hebridean killer
whales from neighbouring populations may reflect one or more of
several evolutionary processes, including a deeper phylogenetic
divergence, low gene flow with other populations and drift.
Differential rates of killer whale attacks on humpback whales in the
North Atlantic as determined by scarification
Jessica A. McCordic, Sean K. Todd and Peter T. Stevick
Email: jamccord(a)syr.edu
As in other populations of killer whales, Orcinus orca, prey
selectivity in the North Atlantic population may indicate
behaviourally or ecologically distinct types of killer whales. Some
killer whale ecotypes are known to prey on large whales, but the
ecological impact of such predation events is unknown. Since killer
whale attacks on humpback whales, Megaptera novaeangliae, are rarely
witnessed, resultant scars may be used to determine the frequency of
non-fatal predatory interactions. Using images from the North Atlantic
Humpback Whale Catalogue (NAHWC), we examined humpback whale flukes
for the presence of rake marks from killer whales (N 1⁄4 5040).
Scarring frequencies range from 2.7 to 17.4% and differ significantly
among five regions of the North Atlantic (Gulf of Maine, Canada, West
Greenland, Iceland and Norway). The scarring rate in the Canada region
is significantly higher than all other regions, and Norway has a
significantly lower scarring rate than all other regions, despite more
frequently reported killer whale sightings in that region. Within the
western North Atlantic, Canada has a scarring rate nearly twice that
of either the Gulf of Maine or West Greenland. These data may reflect
differential prey choice among killer whale ecotypes and/or the
distribution of specific ecotypes across the North Atlantic basin.
Prey switching by killer whales in the north-east Atlantic:
observational evidence and experimental insights
Dag Vongraven and Anna Bisther
Email: vongraven(a)npolar.no
Studies in the Pacific have identified distinct killer whale ecotypes
that are either specialized mammal- or fish-eaters. The different
types have developed hunting strategies that would suggest
specialization could be more advantageous than generalism. However, it
has been suggested, based on long-term dietary markers of tooth wear
and stable isotope values, that lineages in the North Atlantic are
generalist, but with individual variation in the proportion of prey
types consumed. Here, we present the results of ten years of
observational and photo-identification data of a population of killer
whales that follows the Norwegian spring-spawning stock of Atlantic
herring. Although the whales were predominantly observed while feeding
upon herring, one pod of herring-eating whales was also observed
interacting with seals. This supports the hypothesis based on the
long-term markers, of a degree of specialization, with a small number
of groups persistently feeding upon mammals, but switching between
herring and seals. We further investigated this prey switching by
conducting playbacks of herring-eating killer whale sounds to harbour
seals at haul-out sites on the herring spawning grounds. We recorded
changes in behaviour consistent with an anti-predator response,
suggesting the seals perceived the herring-eating killer whales as a
potential predatory threat and had not habituated to their calls. This
could be due to the risk of herring-eating killer whales switching to
mammalian prey, or the difficulty of discriminating between killer
whale pods due to the large population size and number of killer whale
call dialects in this population, or a combination of both.
