Key Questions in Marine Megafauna Movement Ecology

Abstract

It is a golden age for animal movement studies and so an opportune time to assess priorities for future work. We assembled 40 experts to identify key questions in this field, focussing on marine megafauna, which include a broad range of birds, mammals, reptiles, and fish. Research on these taxa has both underpinned many of the recent technical developments and led to fundamental discoveries in the field. We show that the questions have broad applicability to other taxa, including terrestrial animals, flying insects, and swimming invertebrates, and, as such, this exercise provides a useful roadmap for targeted deployments and data syntheses that should advance the field of movement ecology.

Full text

Review
Key
Questions
in
Marine
Megafauna
Movement
Ecology
Graeme
C.
Hays,
1,
*
Luciana
C.
Ferreira,
2,3
Ana
M.M.
Sequeira,
2
Mark
G.
Meekan,
3
Carlos
M.
Duarte,
4
Helen
Bailey,
5
Fred
Bailleul,
6
W.
Don
Bowen,
7
M.
Julian
Caley,
8,9
Daniel
P.
Costa,
10
Victor
M.
Eguíluz,
11
Sabrina
Fossette,
12
Ari
S.
Friedlaender,
13
Nick
Gales,
14
Adrian
C.
Gleiss,
15
John
Gunn,
9
Rob
Harcourt,
16
Elliott
L.
Hazen,
17
Michael
R.
Heithaus,
18
Michelle
Heupel,
9,19
Kim
Holland,
20
Markus
Horning,
21
Ian
Jonsen,
16
Gerald
L.
Kooyman,
22
Christopher
G.
Lowe,
23
Peter
T.
Madsen,
24,25
Helene
Marsh,
26
Richard
A.
Phillips,
27
David
Righton,
28
Yan
Ropert-Coudert,
29
Katsufumi
Sato,
30
Scott
A.
Shaffer,
31
Colin
A.
Simpfendorfer,
19
David
W.
Sims,
32,33,34
Gregory
Skomal,
35
Akinori
Takahashi,
36
Philip
N.
Trathan,
27
Martin
Wikelski,
37,38
Jamie
N.
Womble,
39
and
Michele
Thums
3
It
is
a
golden
age
for
animal
movement
studies
and
so
an
opportune
time
to
assess
priorities
for
future
work.
We
assembled
40
experts
to
identify
key
questions
in
this
field,
focussing
on
marine
megafauna,
which
include
a
broad
range
of
birds,
mammals,
reptiles,
and
fish.
Research
on
these
taxa
has
both
underpinned
many
of
the
recent
technical
developments
and
led
to
fundamental
discoveries
in
the
field.
We
show
that
the
questions
have
broad
applicability
to
other
taxa,
including
terrestrial
animals,
flying
insects,
and
swimming
inverte-
brates,
and,
as
such,
this
exercise
provides
a
useful
roadmap
for
targeted
deployments
and
data
syntheses
that
should
advance
the
field
of
movement
ecology.
The
Breadth
of
Movement
Ecology
Studies
The
advent
of
a
range
of
small,
reliable
data-loggers
and
transmitters
that
can
record
horizontal
and
vertical
movements,
physiology,
and
reproductive
biology
has
led
to
many
new,
amazing
insights
into
the
ecology
of
taxa
ranging
from
insects
to
whales
[1,2]
(Figure
1).
For
example,
we
are
now
able
to
track
and
record
the
physiological
state
of
animals
as
they
travel
across
entire
ocean
basins
or
continents,
fly
over
the
highest
mountains,
or
dive
from
the
surface
to
the
ocean
depths
[3–6].
These
types
of
study
have
addressed
holistic
questions
encompassing
cross-taxa
comparisons
in
both
terrestrial
and
marine
systems
that
have
investigated
how
animals
optimize
their
locomotion
[7];
their
search
patterns
for
prey
[8];
and
the
factors
that
constrain
their
migration
distances
[9],
dive
performance
[10],
and
swimming
speed
[11]
(Figure
2).
Trends
Technical
advances
make
this
an
excit-
ing
time
for
animal
movement
studies,
with
a
range
of
small,
reliable
data-log-
gers
and
transmitters
that
can
record
horizontal
and
vertical
movements
as
well
as
aspects
of
physiology
and
reproductive
biology.
Forty
experts
identified
key
questions
in
the
field
of
movement
ecology.
Questions
have
broad
applicability
across
species,
habitats,
and
spatial
scales,
and
apply
to
animals
in
both
marine
and
terrestrial
habitats
as
well
as
both
vertebrates
and
invertebrates,
including
birds,
mammals,
reptiles,
fish,
insects,
and
plankton.
1
Deakin
University,
Geelong,
Australia,
School
of
Life
and
Environmental
Sciences,
Centre
for
Integrative
Ecology,
Warrnambool,
VIC
3280,
Australia
Trends
in
Ecology
&
Evolution,
June
2016,
Vol.
31,
No.
6
http://dx.doi.org/10.1016/j.tree.2016.02.015
463
©
2016
Elsevier
Ltd.
All
rights
reserved.

The
deployment
of
tracking
devices,
especially
for
extended
periods,
can
imp act
the
wellbe-
ing
of
equipped
animals
[12,13]
and
tags
and
deployment
efforts
can
also
be
costly.
For
these
reasons,
there
is
an
urgent
need
to
triage
the
most
important
fundamental
and
applied
questions
in
the
field
of
movement
ecology
(see
Glossary)
for
targeted
research,
particularly
in
the
case
of
marine
species,
for
which
technical
advances
in
tagging
have
been
profound.
To
this
end,
we
assembled
40
leading
experts
in
the
field
of
biologging
of
marine
megafauna
to
identify
key
questions.
We
illustrate
how
many
of
these
questions
apply
not
only
to
these
taxa,
but
also
to
terrestrial
vertebrates
and
other
animal
groups,
including
mobile
inverte-
brates
in
both
terrestrial
and
marine
environments.
Our
objective
was
to
focus
the
agenda
for
the
field
of
movement
ecology
in
an
informed
way
that
encompassed
both
fundamental
questions
of
high
interest
and
priority
qu estions
that
have
more
direct
impact
on
management
and
conservation.
2
IOMRC
and
The
UWA
Oceans
Institute,
School
of
Animal
Biology
and
Centre
for
Marine
Futures,
The
University
of
Western
Australia,
Crawley,
WA
6009,
Australia
3
Australian
Institute
of
Marine
Science,
c/o
The
UWA
Oceans
Institute,
University
of
Western
Australia,
35
Stirling
Highway,
Crawley,
WA
6009,
Australia
4
King
Abdullah
University
of
Science
and
Technology
(KAUST),
Red
Sea
Research
Center
(RSRC),
Thuwal,
23955-6900,
Saudi
Arabia
5
Chesapeake
Biological
Laboratory,
University
of
Maryland
Center
for
Environmental
Science,
Solomons,
MD
20688,
USA
6
South
Australian
Research
and
Development
Institute
(Aquatic
Sciences),
2
Hamra
Avenue,
West
Beach,
Adelaide,
SA
5024,
Australia
7
Population
Ecology
Division,
Bedford
Institute
of
Oceanography,
Dartmouth,
NS,
B2Y
4A2,
Canada
8
Australian
Research
Council
Centre
of
Excellence
for
Mathematical
and
Statistical
Frontiers,
Australia
9
Australian
Institute
of
Marine
Science,
PMB
No.
3,
Townsville,
QLD
4810,
Australia
10
Department
of
Ecology
and
Evolutionary
Biology,
University
of
California,
Santa
Cruz,
CA
95060,
USA
11
Instituto
de
Física
Interdisciplinar
y
Sistemas
Complejos
IFISC
(CSIC-UIB),
E-07122
Palma
de
Mallorca,
Spain
12
School
of
Animal
Biology,
University
of
Western
Australia,
35
Stirling
Highway,
Crawley,
WA
6009,
Australia
13
Department
of
Fisheries
and
Wildlife,
Marine
Mammal
Institute,
Oregon
State
University,
2030
Marine
Science
Drive,
Newport,
OR
97365,
USA
14
Australian
Antarctic
Division,
Department
of
the
Environment,
Australian
Government,
Kingston,
TAS
7050,
Australia
15
Centre
for
Fish
and
Fisheries
Research,
School
of
Veterinary
and
Life
Sciences,
Murdoch
University,
90
South
Street,
Murdoch,
WA
6150,
Australia
16
Department
of
Biological
Sciences,
Macquarie
University,
Sydney,
NSW
2109,
Australia
17
Environmental
Research
Division,
Southwest
Fisheries
Science
Center,
National
Oceanic
and
Atmospheric
Administration,
99
Pacific
St,
Suite
255A,
Monterey,
CA
93940,
USA
18
Department
of
Biological
Sciences,
Florida
International
University,
Miami,
FL
33174,
USA
19
Centre
for
Sustainable
Tropical
Fisheries
and
Aquaculture,
and
College
of
Marine
and
Environmental
Sciences,
James
Cook
University,
Townsville,
QLD
4811,
Australia
(A)
(B)
(D)
1000 km
100 km
10 km
(C)
Figure
1.
Commonalities
across
Species,
Habitats,
and
Spatial
Scales.
Similar
to
other
mobile
animals,
marine
megafauna
move
through
their
environment
to
obtain
resources,
such
as
prey,
breeding
grounds,
and
mates
(and,
in
the
case
of
divers,
they
surface
to
obtain
air)
and
so
movement
patterns
profoundly
impact
fitness.
Marine
megafauna
can
be
tracked,
in
high
resolution,
as
they
move
in
both
horizontal
and
vertical
dimensions.
As
a
corollary,
invertebrates,
including
crawling,
flying,
and
swimming
taxa,
as
well
as
a
range
of
terrestrial
species
can
likewise
be
tracked.
(A–C)
A
dragonfly
(Anax
junius),
a
koala
(Phascolarctos
cinereus),
and
a
northern
elephant
seal
(Mirounga
angustirostris)
each
equipped
with
a
tracking
tag.
The
small
size
of
tags,
to
reduce
impacts
on
behaviour,
means
that
they
are
difficult
to
see
in
(A)
and
(B).
(D)
Spatial
scale
of
movement.
Movement
patterns
can
be
examined
across
taxa
and
habitats
and
over
scales
from
a
few
cm
to
10
000s
of
km,
illustrated
schematically
here.
Across
this
breadth
of
studies,
many
common
questions
exist,
such
as
whether
general
‘rules’
might
underpin
complex
movements,
the
roles
of
learning,
navigation
cues
used,
the
role
of
predators
and
prey
distribution
in
shaping
movements,
and
how
climate
change
might
impact
movements.
This
track
could
equally
be
from
a
broad
range
of
taxa
that
walk,
fly,
or
swim,
and
any
of
the
scale
bars
might
apply.
In
this
case,
it
is
the
track
of
a
shearwater
(Puffinus
griseus)
flying
the
length
of
Pacific
[6].
Reproduced,
with
permission,
from
Martin
Wikelski
(A),
Desley
Whisson
(B),
and
Dan
Costa
(C).
464
Trends
in
Ecology
&
Evolution,
June
2016,
Vol.
31,
No.
6

20
Hawaii
Institute
of
Marine
Biology,
University
of
Hawaii
at
Manoa,
PO
Box
1346,
Kaneohe,
HI
98744,
USA
21
Science
Department,
Alaska
SeaLife
Center,
Seward,
AK
99664,
USA
22
Scripps
Institute
of
Oceanography,
University
of
California
San
Diego,
San
Diego,
CA
92093,
USA
23
Department
of
Biological
Sciences,
California
State
University,
Long
Beach,
Long
Beach,
CA
90840,
USA
24
Zoophysiology,
Department
of
Bioscience,
Aarhus
University,
Aarhus,
DK
8000,
Denmark
25
Murdoch
University
Cetacean
Research
Unit,
School
of
Veterinary
and
Life
Sciences,
Murdoch
University,
Perth,
WA
6150,
Australia
26
College
of
Marine
and
Environmental
Science,
James
Cook
University,
Townsville,
QLD
4810,
Australia
27
British
Antarctic
Survey,
Natural
Environment
Research
Council,
Cambridge,
CB3
0ET,
UK
28
Fisheries
and
Ecosystems
Division,
Cefas
Laboratory,
Pakefield
Road,
Lowestoft,
NR34
7RU,
UK
29
Centre
d’Etudes
Biologiques
de
Chizé,
Station
d’Écologie
de
Chizé-
Université
de
La
Rochelle,
CNRS
UMR
7372,
79360
Villiers-en-Bois,
France
30
Atmosphere
and
Ocean
Research
Institute,
The
University
of
Tokyo
5-1-
5
Kashiwanoha,
Kashiwa
City,
Chiba
Prefecture,
277-8564,
Japan
31
Department
of
Biological
Sciences,
San
Jose
State
University,
San
Jose,
CA
95192-0100,
USA
32
Marine
Biological
Association
of
the
United
Kingdom,
The
Laboratory,
Citadel
Hill,
Plymouth,
PL1
2PB,
UK
33
Ocean
and
Earth
Science,
National
Oceanography
Centre
Southampton,
University
of
Southampton,
Waterfront
Campus,
European
Way,
Southampton,
SO14
3ZH,
UK
34
Centre
for
Biological
Sciences,
Building
85,
University
of
Southampton,
Highfield
Campus,
Southampton,
SO17
1BJ,
UK
35
Massachusetts
Shark
Research
Project,
Division
of
Marine
Fisheries,
1213
Purchase
St,
New
Bedford,
MA
02740,
USA
36
National
Institute
of
Polar
Research,
Tachikawa,
Tokyo
190-8518,
Japan
37
Department
of
Migration
and
ImmunoEcology,
Max-Planck
Institute
for
Ornithology,
Am
Obstberg
1,
78315
Radolfzell,
Germany
38
Konstanz
University,
Department
of
Biology,
78457
Konstanz,
Germany
39
National
Park
Service,
Glacier
Bay
Field
Station,
3100
National
Park
Road,
Juneau,
AK
99801,
USA
*Correspondence:
g.hays@deakin.edu.au
(G.C.
Hays).
Materials
and
Methods
We
followed
a
similar
protocol
used
previously
[14]
of
identifying
leading
experts
in
the
field
and
soliciting
their
views
on
key
questions
in
a
selected
area.
The
process
began
with
a
meeting
organized
in
Perth
(November
17–21,
2014),
to
which
experts
in
the
area
of
biologging
of
marine
megafauna
were
invited
from
across
Australia
and
international
institutions.
These
experts
were
selected
based
on
their
publications
and
extent
of
work
in
this
area.
The
15
experts
who
attended
this
meeting
were
then
each
asked
to
select
other
individuals
from
around
the
world
who
should
be
invited
to
participate
in
this
process.
We
targeted
researchers
working
in
the
area
of
the
movement
of
marine
megafauna
and
also
the
broader
conservation
community,
including
government
and
nongovernment
conservation
agencies
(e.g.,
IUCN
and
NOAA).
The
extended
list
of
experts
were
then
each
asked
to
supply
up
to
ten
key
questions
to
advance
the
field
of
the
movement
ecology
of
marine
megafauna,
including
taxa
such
as
cetaceans,
elasmobranchs,
pinnipeds,
large
teleosts
(tunas,
billfish,
etc.),
sirenians,
seabirds,
and
marine
reptiles
(e.g.,
turtles).
Responses
were
compiled
and
similar
questions
were
grouped,
along
with
the
associated
votes,
into
a
single
qu estion.
The
full
list
was
then
distributed
and
participants
were
asked
to
vote
on
their
top
ten
qu estions
and
confirm
that
they
were
satisfied
with
the
rearticulation
of
questions.
The
votes
were
tallied
and
a
final
list
of
key
questions
was
circulated
and
agreed
upon.
This
final
list
of
questions
is
described
below
in
the
text,
boxes,
and
figures.
10.1
–6 –4
Adult cheloniidae
Key:
Adult dermochelyiidae
Flyers
Swimmers
Walkers
Juvenile cheloniidae
–2 0
2
4
0.1
5
4
3
2
1
1
3
(A)
(B)
10 100
1000
10000
Yes No
(RM endothermy)
Bony fish
Shark
Key:
Marine mammal
Sea turtle
Seabird
Body mass (kg)
Body mass (log
10
kg)
Migraon distance (log
10
km) Swim speed (m s
–1
)
100000
Figure
2.
The
Value
of
Comparisons
across
Taxa.
Tracking
data
from
a
range
of
taxa
can
be
used
to
address
overarching
questions
of
movement
and
ecology.
(A)
Comparison
of
different
swimmers
reveals
the
roles
of
body
size
and
endothermy
versus
ectothermy
in
influencing
cruising
swim
speed
[11].
(B)
Comparison
across
walkers,
flyers,
and
swimmers
shows
the
roles
of
body
size
and
gait
in
driving
maximum
migration
distances
[82].
Trends
in
Ecology
&
Evolution,
June
2016,
Vol.
31,
No.
6
465

Results
How
Can
Movement
Data
Be
Used
to
Support
Conservation
and
Management?
A
justification
for
many
tracking
studies
is
that
knowledge
of
the
movements
of
animals
might
help
inform
conservation
management
[15,16]
and,
indeed,
there
are
good
examples
of
how
data
can
be
used
in
this
way.
For
example,
in
the
Antarctic,
the
first
marine
protected
area
(MPA)
located
entirely
in
the
high
seas
was
partly
justified
by
the
movements
of
Adélie
penguins
(Pygoscelis
adeliae)
during
their
energy-intensive
premoult
period
[17],
while
in
the
Pacific
Ocean,
turtle
telemetry
data
have
been
used
to
create
habitat
models
based
on
ocean
conditions,
reducing
bycatch
through
dynamic
ocean
management
[18].
Similarly,
movement
data
have
shown
how
migratory
birds
are
often
not
protected
along
large
portions
of
their
migration
routes
[19].
However,
incorporation
of
movement
data
into
conservation
strategies
remains
underutilized.
Tracking
data
can
potentially
help
designate
the
location,
size,
and
timing
of
conservation
zones
and
test
their
efficacy.
Movement
data
can
also
aid
stock
assessments,
identification
of
stock
boundaries
for
species
of
conservation
concern,
ecosystem-based
management,
and
management
of
highly
migratory
species.
Are
there
Simple
Rules
Underlying
Seemingly
Complex
Movement
Patterns
and,
hence,
Common
Drivers
for
Movement
across
Species?
Common
patterns
of
search
behaviour
by
marine
predators
have
been
demonstrated
across
sharks,
bony
fish,
turtles,
and
seabirds,
which
move
in
spatial
patterns
that
can
be
approximated
by
a
theoretically
optimal
search
pattern
known
as
a
truncated
Lévy
walk
[8,20].
The
observed
patterns
of
movement
are
theoretically
optimal
for
locating
the
patchy
and
sparse
distributions
of
prey
that
occur
in
the
ocean
[8].
Although
a
truncated
Lévy
walk
and
other
simple
null
models
are
convenient
for
testing
commonalities
in
movement
among
taxonomically
well-separated
species
(Figure
1),
there
is
a
need
for
future
research
aimed
at
understanding
the
physiological
and
behavioural
mechanisms
underpinning
common
movement
patterns
[11],
their
evolutionary
origin
[21],
and
the
costs
and
benefits
of
different
patterns
(Box
1).
As
a
corollary,
addressing
this
question
of
commonalities
will
also
shed
light
on
the
levels
and
drivers
of
variation
in
vertical
and
horizontal
movements
(Figure
2).
Glossary
Biologging:
the
use
of
miniaturised
animal-attached
tags
for
logging
or
transmission
of
data
about
the
movements,
behaviour,
physiology,
or
environment
of
an
animal.
The
term
often
refers
to
marine
species.
Biotelemetry:
the
remote
transmission
of
data
from
electronic
tags
attached
to
animals
that
provide
for
example,
information
on
movement,
behaviour,
physiology,
and
the
environment.
We
use
the
term
here
synonymously
with
biologging,
which
also
encompasses
data
stored
on
tags
attached
to
animals
that
must
be
recovered
for
download.
Marine
megafauna:
large
animals
living
in
the
sea,
including
mammals,
reptiles,
large
fish,
and
seabirds.
Movement
ecology:
As
a
part
of
ecology,
animal
movement
is
a
research
field
which
is
dedicated
to
understanding
patterns,
drivers,
physiology
and
consequences
of
animal
movement
such
as
seasonal
migration,
dispersal
and
foraging.
Box
1.
What
Are
the
Costs
and
Benefits
of
Different
Movement
Patterns?
A
central
pillar
of
ecology
is
assessing
the
costs
and
benefits
of
various
behaviours.
This
applies
equally
to
movement
studies,
where
a
challenge
is
to
measure
costs
and
benefits
over
various
scales:
from
the
energy
expenditure
and
prey
capture
probability
of
an
individual
prey
pursuit
event,
up
to
the
cost
and
benefit
of
large-scale
migration.
Quantifying
the
metabolic
costs
of
movement
patterns
remains
a
challenge
and
is
central
to
assessing
the
cost
and
benefits
of
various
movement
patterns.
For
example,
doubly
labelled
water
can
be
used
for
approximating
metabolic
rate,
but
generally
only
provides
an
integrated
value
over
hours
or
days
and
is
not
feasible
for
fish
due
to
high
water
turnover
rates.
Laboratory
measurements
of
metabolic
rate
can
be
extrapolated
to
free-living
animals,
or
predicted
for
large
taxa
based
on
allometric
scaling
relations,
but
only
with
caution.
Energy
expenditure
derived
from
accelerometer
data
shows
great
promise
for
estimating
the
metabolic
rate
of
free-living
animals
by
providing
a
robust
measure
of
activity
(e.g.,
[83]
but
see
[84]),
allowing
various
models
of
optimal
movement
to
be
tested
[7].
Sensors
available
to
record
energy
intake
include
those
measuring
the
physiological
state
of
the
digestive
tract
(e.g.,
stomach
or
oesophageal
temperature),
those
measuring
the
mechanical
movement
of
the
head
and/or
jaws,
animal-
attached
cameras
allowing
direct
observations
of
prey
capture,
and
audio
recorders
to
record
the
sound
or
echoes
of
prey
capture
[85].
However,
the
quantification
of
benefits
of
different
movement
strategies
remains
a
challenge.
Most
studies
so
far
have
focussed
on
temporally
isolated
events,
such
as
the
structure
of
a
single
dive
or
foraging
trip.
The
benefits
associated
with
larger
scale
and/or
long-term
movements
(e.g.,
transit
versus
area
restricted
search)
remain
elusive,
due
to
the
generally
limited
recording
duration
of
data-loggers
(but
see
[86]
for
instance).
Despite
the
growing
toolkit
of
biologging
instruments,
linking
the
benefits
of
observed
movement
strategies
to
ecological
and
evolutionary
relevant
scales
(e.g.,
reproductive
success,
survival,
or
lifetime
reproductive
output)
remains
a
grand
challenge,
although
there
are
model
systems
that
allow
fitness
benefits
to
be
directly
measured.
For
example,
in
some
cases,
tracked
animals
return
to
provision
offspring
or
to
nest
(e.g.,
seabirds
or
turtles)
so
that
the
implications
of
their
previous
movements
can
be
assessed
in
terms
of
their
weight
change,
reproductive
investment,
and
survival
across
many
years.
Additionally,
it
might
sometimes
be
possible
to
assess
changes
in
their
body
condition
by
remotely
relayed
data,
as
in
the
case,
for
example,
of
buoyancy
changes
in
elephant
seals
that
are
related
to
body-fat
levels
[87].
466
Trends
in
Ecology
&
Evolution,
June
2016,
Vol.
31,
No.
6

How
Do
Learning
and
Memory
versus
Innate
Behaviours
Influence
Movement
Patterns,
including
Ontogenetic
Changes?
Relatively
little
is
known
about
the
effects
of
learning
and
memory
on
the
movement
patterns
of
marine
megafauna.
Scale-free
patterns
of
movement
suggest
that
some
marine
megafauna
search
for
prey
probabilistically
without
prior
knowledge
of
prey
distribution
[8],
but
it
is
likely
that
they
rely
on
learning
and
memory
to
some
extent
to
move
and
forage
efficiently
[22,23].
The
effects
of
learning
and
memory
are
often
inferred
from
foraging
site
fidelity,
but
quantifying
those
effects
remains
challenging
[16,24].
Identification
of
innate
behaviours
is
equally
problematic
because
of
the
difficulty
of
finding
‘naïve’
individuals
[25,26].
Tracking
studies
of
juveniles
are
relatively
infrequent
compared
with
those
of
adults
(often
called
‘lost-years’)
especially
in
sea
turtles,
seabirds,
and
some
marine
mammals,
because
tag
recovery
is
more
difficult
and
the
size
of
tags
is
often
less
suitable
for
juveniles
[27].
To
what
Degree
Do
Social
Interactions
Influence
Movements?
Many
species
occur
in
social
groups
during
both
short-term
(hours–weeks),
mesoscale
(km–
100s
km)
movements
(e.g.,
foraging
or
refuging),
and
during
long-distance
(1000s
km)
migra-
tions.
In
several
species
of
marine
mammals,
there
appears
to
be
coordination
during
feeding
events,
and
marine
birds
are
attracted
to
other
feeding
individuals
[28,29].
For
many,
successful
orientation
along
migration
routes
might
potentially
require
naive
animals
to
follow
experienced
individuals
or
reflect
the
transfer
of
navigational
information
among
individuals.
In
all
these
scenarios,
how
individuals
within
these
aggregations
influence
the
behaviour
of
the
larger
group
is
poorly
understood
because
generally
only
a
few
focal
individuals
are
tracked.
However,
breakthroughs
in
both
hardware
and
analysis
tools
show
promise
for
elucidating
social
inter-
actions
(e.g.,
[30,31]).
How
Does
the
Distribution
of
Prey
Impact
Movement?
Only
in
relatively
few
cases
has
the
prey
field
around
a
forager
been
measured
di rec tly,
yet
this
is
probably
a
fundamental
driver
of
movement
patterns
[32,33].
Animals
encountering
prey
are
likely
to
react
by
slowing
down
and
increasing
their
turning
rate,
behaviours
thought
to
increase
their
encounter
rate
with
prey.
Well-documented
examples
show
how
the
diel
diving
patterns
of
animals
are
linked
to
the
diel
vertical
migration
patterns
of
their
prey
and,
consequently,
there
is
debate
about
whether
movement
patterns
are
simply
an
emerging
property
from
a
forager
interacting
with
the
prey
field.
This
debate
is
further
fuelled
by
the
finding
that
movement
patterns
for
the
same
individual
can
vary
across
different
habitats
that
likely
have
different
prey
distributions
[20].
Moreover,
diving
behaviour,
in
particular,
is
unlikely
to
be
driven
by
environmental
drivers,
but
by
ecosystem
features,
such
as
depth
layers
(e.g.,
the
deep
scattering
layer)
offering
an
abundance
of
prey
[34].
Future
studies
will
need
to
assess,
with
more
rigour,
the
fine-scale
distribution
of
prey
while
animals
are
being
tracked.
What
Sensory
Information
Do
Animals
Use
to
Sense
Prey,
Breeding
Partners,
and
Environmental
Conditions?
Recent
technological
advances
have
allowed
for
increasingly
detailed
insights
into
marine
animal
sensing
in
the
wild.
Movement
data
can
shed
light
on
the
sensory
information
used
to
navigate
during
migration
(Box
2).
Light
levels
from
down-welling
light
and
bioluminescent
prey
have
recently
been
recorded
with
on-board
tags
[35]
that,
along
with
camera
tags,
offer
insights
into
how
visual
cues
guide
behaviour.
Intriguing
advances
have
been
made
with
sound
recording
tags
that
have
uncovered
how
echo
information
guides
prey-capture
movement
in
cetaceans
[36].
While
the
function
of
individual
sensory
systems
can
now
be
studied
in
detail,
a
challenge
to
overcome
is
that
animals
might
rely
on
complex
multimodal
sensing
to
inform
behavioural
changes
to
find
and
intercept
prey,
choose
breeding
partners,
and
navigate
(Box
2).
Trends
in
Ecology
&
Evolution,
June
2016,
Vol.
31,
No.
6
467

Can
Movement
Data
Provide
Information
on
the
Ecosystem
Role
of
Marine
Megafauna?
Marine
megafauna
can
have
important
roles
in
ecosystems
through
both
top-down
processes
(as
predators
and
herbivores)
[37]
and
bottom-up
processes,
including
the
redistribution
of
nutrients
[38].
Key
to
understanding
these
ecological
roles
are
analyses
of
spatiotemporal
patterns
of
abundance
and
behaviours
(e.g.,
foraging
and
resting),
which
are
driven
by
move-
ment
decisions.
For
example,
dolphins
foraging
offshore
can
move
nutrients
into
nearshore
waters
where
they
rest
[39],
whales
migrating
from
high
latitudes
could
translocate
nutrients
to
oligotrophic
tropical
systems
[38],
and
juvenile
bull
sharks
(Carcharhinus
leucas)
can
move
nutrients
upstream
in
estuaries
through
commuting
behaviour
[40].
Yet,
there
has
been
little
use
of
movement
data
in
this
context.
How
Much
Does
the
Physical
Environment
Influence
Movement?
Permanent
(e.g.,
bathymetry)
and
ephemeral
abiotic
factors
(e.g.,
temperature,
salinity,
and
dissolved
oxygen)
are
thought
to
strongly
influence
movements
[41].
These
factors
can
interact
directly
with
the
physiology
of
megafauna,
especially
ectotherms,
or
indirectly
via
the
physiology
of
their
prey
[42]
across
temporal
scales
ranging
from
hours
to
decades.
The
physical
structure
of
the
water
column
also
acts
to
accumulate
both
megafauna
and
prey
through
oceanographic
features
ranging
from
thermoclines
(10–100
m),
eddies
and
upwelling
zones
(10–100
km),
to
boundary
currents
(1000
km)
[6].
Disentangling
the
direct
effects
of
the
physical
environment
on
the
movement
and
behaviour
of
megafauna
from
indirect
effects
on
their
prey
remains
a
significant
challenge
[43].
How
Will
Climate
Change
Impact
Animal
Movements?
Climate
change,
including
extreme
events,
such
as
storms,
El
Niño
phenomena,
and
warm
water
anomalies,
are
likely
to
increase
in
frequency
and
might
impact
the
movements
and
phenology
of
large
marine
megafauna
by
changing
the
broad-scale
distribution
and
composition
of
prey
as
well
as
other
resources
(e.g.,
suitable
water
temperature,
resting,
and
breeding
substrate)
[44–47].
Migration
patterns
of
marine
megafauna
will
likely
change
to
be
more
poleward
with
warming
[48],
although
the
complex
effects
of
biotic
interactions
and
habitat
availability,
for
example,
can
lead
to
counter-intuitive
redistribution
patterns
in
some
taxa
[49].
Some
animals,
including
pinnipeds
and
penguins,
might
be
particularly
sensitive
to
large-scale
environmental
changes
when
they
are
tied
to
land-
or
ice-based
breeding
colonies
and,
hence,
have
limited
ability
to
shift
their
foraging
locations
[50].
Similarly,
the
rapid
loss
of
Arctic
sea
ice
might
affect
the
movement
patterns
of
Arctic
megafauna,
restricting
those
of
animals,
such
as
the
polar
bear
and
the
walrus
using
sea
ice
as
a
platform,
and
enhancing
ones
whose
access
to
the
Arctic
had
been
precluded
by
sea
ice.
The
complexities
of
the
drivers
of
animal
movements
make
predictions
of
climate
change
impacts
difficult
[51].
Box
2.
How
Do
Animals
Navigate
and
Orientate
in
the
Open
Sea?
Tracking
animals
can
both
shed
light
on
their
navigational
performance
and
hint
at
the
underlying
cues
used,
and
so
help
tackle
longstanding
questions
of
broad
interest
that
have
perplexed
scientists
for
>100
years
[88].
One
approach
to
identify
the
cues
used
in
movements
is
through
laboratory
trials
where
the
available
information
(e.g.,
geomagnetic
cues,
light,
or
wave
movements)
is
manipulated
[89].
This
approach
has
been
used,
for
example,
with
monarch
butterflies,
passerine
birds,
and
hatchling
sea
turtles.
However,
tracking
animals
can
reveal
information
about
their
navigational
ability.
At-sea
experiments
have
been
performed,
such
as
temporarily
attaching
magnets
or
making
animals
anosmic
and
then
tracking
individuals
[90],
although
typically
inferences
of
navigational
cues
are
made
from
animals
behaving
naturally.
Across
both
marine
birds
and
sea
turtles,
the
directed
approach
to
islands
from
downwind
suggests
the
use
of
wind-
borne
odours
in
island
and/or
prey
finding
[91].
Many
taxa,
from
a
range
of
habitats,
including
bees,
birds,
seals,
and
turtles,
likely
have
good
cognitive
maps
of
their
home
area,
but
can
still
navigate
to
distant
remote
areas
using
cues
such
as
geomagnetic
maps.
For
example,
direct
tracking
has
shown
that
sea
turtles
can
travel
many
1000s
of
km
between
breeding
and
foraging
grounds,
have
fidelity
to
both,
but
do
not
pin-point
these
targets
following
direct
routes,
and
can
sometimes
struggle
to
find
remote
targets,
such
as
small
islands
[92].
These
tracks
point
to
a
fairly
crude
map
sense
in
the
open
ocean,
a
conclusion
supporting
laboratory
evidence
of
broad-scale
geomagnetic
markers
[89].
As
with
terrestrial
birds
and
insects,
it
remains
a
challenge
to
acquire
detailed
information
about
environmental
flows
(winds
and
currents)
so
that
the
roles
of
active
movement
and
passive
advection
can
be
teased
apart
[69].
468
Trends
in
Ecology
&
Evolution,
June
2016,
Vol.
31,
No.
6

How
Can
Risks,
Consequences
and
Benefits
of
Biologging
at
the
Level
of
Individuals
and
Populations
Be
Evaluated?
Attaching
or
implanting
devices
to
streamlined
animals
comes
with
great
responsibility.
While
guidelines
and
reviews
are
regularly
produced
[52,53],
the
ethical
dimensions
of
the
risks
associated
with
capturing
and
instrumenting
an
animal
need
to
be
constantly
reinforced
within
the
scientific
community
and
must
be
quantified
[12].
There
are
technical
challenges
to
quantifying
such
risks,
because
often
the
absence
of
‘true’
controls
hampers
our
ability
to
determine
what
component(s)
of
the
biology
of
the
animal
is
most
affected.
However,
our
ability
to
do
this
is
paramount
to
the
conduct
of
future
experiments.
Consequently,
scientists
have
a
responsibility
to
behave
ethically
and
to
remind
the
public
that
they
constantly
balance
the
impact
of
scientific
investigations
with
the
necessity
to
collect
data
of
utmost
importance
to
the
understanding
of
the
biology
of
a
given
species
and
its
subsequent
conservation.
Reducing
the
impacts
of
devices
will
remain
an
ongoing
priority
as
will
carefully
defining
the
required
sample
size
(Box
3).
How
Do
We
Integrate
Physiological
Context
into
Tagging
Studies
to
Gain
a
More
Synoptic
Picture
of
Movement
and
Behaviour?
Although
there
have
been
distinct
challenges
in
studying
the
physiology
of
free-living
animals,
new
nonlethal
physiological
sampling
techniques
(muscle
biopsy,
blood,
and
exhalant),
biolog-
ging,
and
telemetry
sensors
have
allowed
a
better
understanding
of
behavioural
responses
to
broad-ranging
physical
conditions,
such
as
water
temperature
and
dissolved
oxygen
concen-
trations
[10,54].
Unfortunately,
many
of
these
physiological
measures
only
provide
a
brief
snapshot
of
the
physiological
state
of
the
animal
before
or
subsequent
to
the
tracking
of
their
movements.
In
many
cases,
there
remains
a
distinct
lack
of
information
on
physiological
constraints
of
species
movements
and
how
animals
will
physiologically
and
behaviourally
respond
to
changing
environmental
conditions.
What
Are
the
Major
Drivers
of
Long-Distance
Movements?
Long-distance
(1000s
km)
directed
movements
have
now
been
documented
in
a
broad
range
of
marine
megafauna.
Resources
that
vary
in
quality
in
space
and
time
are
often
thought
to
be
the
fundamental
drivers
of
these
movements
[55].
For
example,
suitable
conditions
for
breeding
and
foraging
might
be
found
in
different
areas
and
so
necessitate
reproductive
migrations,
or
sometimes
animals
might
move
seasonally
to
track
favourable
foraging
conditions
[6,42].
Maximum
migration
distances
generally
scale
with
body
size,
also
vary
with
taxa
and
mode
of
locomotion
(Figure
2),
and
are
thought
to
reflect
fuel
stores
and
cost
of
transport.
However,
Box
3.
Observational
Design
and
Inference:
How
Many
Tags
Are
Enough?
There
is
no
simple
answer
to
this
question,
but
rather
the
type
of
information
obtained
changes
as
sample
size
increases.
For
example,
tracking
one
individual
can
reveal
the
extent
of
movement
in
hitherto
unknown
detail,
tracking
a
handful
of
individuals
can
start
to
reveal
individual
variability,
while
tracking
30+
individuals
can
reveal
how
populations
behave
[93].
Tracking
individuals
from
a
population
across
many
years
can
start
to
reveal
climate
change
impacts.
The
issue
of
sample
size
is
fundamental
to
good
experimental
design
and
population-level
inference
in
movement
studies.
Approaches
using
satellite
telemetry
can
be
particularly
vulnerable
to
small
sample
sizes
because
the
high
cost
of
tags
restricts
the
number
that
can
be
deployed
(reviewed
in
[94]).
For
studies
that
aim
to
assess
spatial
and
temporal
distributions,
simulated
GPS
data
suggest
that
>20
tagged
individuals
are
a
minimum
sample
size
[80,95],
with
greater
numbers
required
where
movement
patterns
must
be
categorised
by
sex,
age,
geography,
and
time
period.
Furthermore,
in
species
such
as
marine
predators,
there
are
often
individual
specialisations
in
movement
patterns
[6,96,97].
Such
within-species
variation
combined
with
the
ongoing
decline
in
science
funding
means
that
few
studies
have
the
resources
to
collect
the
sample
sizes
needed
to
characterise
movement
patterns
of
whole
populations.
Two
approaches
might
overcome
these
problems.
First,
collaborative
studies
that
combine
efforts
to
increase
sample
sizes
to
create
synoptic
views
of
individual
and
multispecies
movement
patterns
[42,73,98].
Second,
the
development
of
global,
freely
available
databases
to
facilitate
data
sharing
in
animal
movement
ecology
[1,2,99].
These
approaches
will
be
key
to
achieving
the
sample
sizes
required
for
population-level
inference
and
ultimately
to
move
towards
an
understanding
of
the
emergent
properties
of
multiple
species
and
ecosystems.
Trends
in
Ecology
&
Evolution,
June
2016,
Vol.
31,
No.
6
469

the
specifics
of
how
animals
select
their
destinations
for
these
directed
movements
and
what
drives
their
timing,
plasticity,
and
variability
across
individuals
are
more
enigmatic,
as
are
the
roles
of
learning
versus
innate
behaviours.
In
some
cases,
migrations
are
initiated
when
conditions
aid
travel,
such
as
tail
winds
for
some
birds
and
insects,
and
currents
for
some
fish
[56].
Comparisons
between
terrestrial
bird
and
marine
predator
migrations
can
inform
our
understanding
of
processes
directing
targeted
movements.
How
Does
Predation
Risk
Influence
Movement
Strategies?
The
risk
of
predation
can
have
profound
impacts.
For
example,
risk
from
sharks
is
associated
with
foraging
habitat
shifts
by
dolphins,
sea
turtles,
sirenians,
and
seabirds
[57]
(Figure
3).
These
studies
echo
those
in
terrestrial
systems
and
with
invertebrates,
where
the
role
of
predators
in
shaping
animal
movements
is
well
defined
[58,59].
Much
work
remains
to
be
done.
Failure
to
explicitly
consider
predation
risk
in
movement
studies
could
lead
to
erroneous
conclusions,
for
example,
mistaking
refuging
areas
for
dense
prey
patches.
Furthermore,
how
do
we
measure
the
lack
of
behaviour
when
an
animal
does
not
do
something
because
of
the
predation
risk
associated
with
that
behaviour?
Future
studies
of
the
role
of
how
predation
risk
shapes
Body condion
Time
(A)
(D)
(B)
(C)
High risk
Low risk
Low risk
High risk
Figure
3.
Predators
Shape
Movements
across
Habitats.
Across
terrestrial,
freshwater,
and
marine
habitats,
recording
animal
movements
shows
that
the
risk
of
predation
can
have
a
profound
impact
on
animal
movements,
with
individuals
balancing
predation
risk
with
foraging
success
from
fine-scale
habitat
selection
to
migratory
patterns.
How
individuals
solve
the
food–risk
trade-off
can
vary
with
attributes
of
individuals.
(A)
Caribou
(Rangifer
tarandus)
movements
during
calving
are
orientated
to
areas
with
abundant
forage
and
lower
risk
of
predation
from
black
bears
(Ursus
americanus)
[100].
(B)
Green
turtles
(Chelonia
mydas)
balance
foraging
gain
with
risk
of
predation
from
tiger
sharks
in
shallow
sea
grass
pastures
by
selecting
habitats
relative
to
their
body
condition
[57].
(C)
Calanoid
copepods
have
a
lipid
sac
used
for
energy
storage.
Many
species
of
marine
copepod
show
daily
vertical
movements
ascending
to
shallow
depth
to
feed
at
night
when
their
risk
of
predation
is
lower
[59].
(D)
Predation
risk,
pattern
of
movement,
and
body
condition.
Across
systems,
the
use
of
high
risk
areas
can
be
driven
by
body
condition:
with
animals
in
poor
condition
more
likely
to
run
the
risk
of
predation
and
use
areas
with
great
food
availability.
Understanding
such
behaviour
is
critical
in
light
of
changes
to
both
food
availability
and
predation
risk
in
oceans
and
other
ecosystems.
High-resolution
tracking
in
relation
to
habitat
quality
might
reveal
these
trade-offs.
These
movements
have
profound
implications
for
the
vertical
and
horizontal
movements
of
many
marine
megafauna.
Reproduced,
with
permission,
from
Russell
Hopcroft,
R.D.
and
B.S.
Kirkby.
470
Trends
in
Ecology
&
Evolution,
June
2016,
Vol.
31,
No.
6

movement
are
important
in
light
of
declines
in
truly
apex
predatory
species
and
the
potential
for
predation
risk
to
induce
marine
trophic
cascades
[60].
Furthermore,
similar
to
predators,
pathogens
can
also
shape
movement
patterns
in
insects
and
birds
[61],
and
might
have
this
same
impact
in
some
marine
taxa.
What
Areas
Can
Be
Considered
Hotspots
for
Multiple
Species
on
a
Global
Scale?
Collation
of
individual
telemetry
data
sets
into
large,
multispecies
databases
that
are
linked
to
other
sources
of
relevant
data,
such
as
survey
data,
is
central
to
revealing
general
patterns
in
movement
behaviour
and
to
highlight
hotspots
for
multiple
species.
The
potential
of
such
effort
in
amassing
tracking
data
sets
has
been
highlighted
[42].
Therefore,
the
current
challenge
is
to
develop
this
approach
across
a
wider
range
of
species
and
ecosystems,
because
this
could
reveal
collective,
emergent
patterns
of
movement
behaviour
and
allow
identification
of
multi-
species
hotspots
at
a
worldwide
scale.
To
achieve
this,
a
large
partnership
akin
to
the
size
of
that
of
BirdLife
International
(the
largest
partnership
of
bird
conservation
organisations
in
the
world),
is
needed.
In
turn,
the
identification
of
such
hotspots
will
help
inform
current
approaches
increas-
ingly
used
to
assist
systematic
marine
spatial
planning,
such
as
the
Convention
on
Biological
Diversity's
Ecological
or
Biologically
Significant
Areas,
the
International
Maritime
Organisation's
Particularly
Sensitive
Sea
Areas,
IUCN's
Key
Biodiversity
Areas,
and
Biologically
Important
Areas
(adopted
by
the
USA
and
Australia).
How
Do
Anthropogenic
Activities
(e.g.,
Shipping,
Fishing,
and
Water
Management)
Affect
Movements?
Many
human
activities
pose
serious
threats
to
the
ecology
of
marine
megafauna.
For
example,
fishing
and
shipping
can
kill
or
injure
animals,
while
industrial
development
(oil
and
gas
extraction,
or
offshore
wind
farms),
pollution
(plastic,
chemical
wastes,
runoff,
and
noise),
and
space
use
(vessel
activity
and
aquaculture
production)
can
affect
megafauna
through
the
disruption
of
natural
behaviours
and
alteration
of
habitat
[62].
The
extent
to
which
interactions
with
anthropogenic
threats
ultimately
determine
the
behaviour,
survival,
and
fitness
of
mega-
fauna
is
largely
unknown.
However,
the
description
of
movement
patterns
can
provide
data
essential
for
the
identification
and
mitigation
of
potential
impacts.
For
example,
tracking
data
have
revealed
that
blue
whales
(Balaenoptera
musculus)
have
limited
ability
to
avoid
collisions
with
ships
[63]
and
that
small
shifts
in
traffic
routes
could
reduce
the
risk
of
ship
strike
[64].
The
description
of
movement
patterns
in
situations
and
at
times
when
marine
megafauna
are
exposed
to
potential
threats
from
anthropogenic
activities
must
be
a
key
goal
for
research
that
seeks
to
optimise
strategies
for
the
management,
conservation,
and
resilience
of
this
fauna
[48,65].
Concluding
Remarks
Many
of
the
questions
we
identify
here
apply
equally
to
other
taxa,
including
terrestrial
verte-
brates,
insects,
and
marine
invertebrates.
For
example,
the
use
of
movement
data
to
inform
conservation
also
applies
to
many
terrestrial
vertebrates
[66,67];
understanding
how
animals
orientate
and
navigate
is
relevant
to
movements
of
jellyfish,
flying
insects,
and
birds
[68,69];
examination
of
how
social
interactions
impact
movement
is
applicable
to
studies
of
pigeons
[70];
and
assessing
how
the
physical
environment
shapes
movement
is
relevant
to
studies
of
a
range
of
terrestrial
herbivores
[71].
As
such,
our
questions
likely
provide
a
solid
roadmap
for
the
general
field
of
animal
biotelemetry
(see
Outstanding
Questions).
Progress
will
sometimes
need
further
development
of
cross-discipline
collaborations.
For
example,
the
past
few
years
have
shown
the
immense
value
of
collaborations
among
ecologists,
mathematicians,
physicists,
oceanographers,
engineers,
and
information
technologists
to
iden-
tify
general
patterns
in
animal
movement
[8,42,72,73].
Additionally,
increasing
engagement
with
policy
makers
will
help
translate
tracking
data
into
real-world
conservation
benefits.
Step
Outstanding
Questions
Understanding
general
‘rules’
under-
pinning
complex
movements,
the
roles
of
learning,
navigation
cues
used,
the
role
of
predators
and
prey
distribution
in
shaping
movements,
levels
and
driv-
ers
of
variation
in
vertical
and
horizontal
movements,
and
how
climate
change
might
impact
movements.
Collaborations
among
ecologists,
mathematicians,
physicists,
oceanog-
raphers,
engineers,
and
information
technologists
will
help
tackle
key
ques-
tions
and
increasing
engagement
with
policy
makers
will
help
translate
track-
ing
data
into
real-world
conservation
benefits.
Increasing
miniaturisation
of
tags
will
allow
early
life-stages
to
be
tracked
and
development
of
new
techniques
may
be
needed
for
some
groups
that
remain
hard
to
track.
Across
studies,
the
tracking
of
individuals
needs
to
be
pur-
sued
with
consideration
of
the
ethical
concerns
of
the
impact
of
deployments.
Collation
of
individual
telemetry
data
sets
into
large,
multispecies
databases
linked
to
other
sources
of
relevant
data
(e.g.,
environmental)
will
help
reveal
general
patterns
in
movement
and
highlight
hotspots.
Trends
in
Ecology
&
Evolution,
June
2016,
Vol.
31,
No.
6
471

changes
in
the
duration
that
individuals
are
tracked
for
might
be
needed
to
address
ontogenetic
changes
in
movements,
the
roles
of
learnt
versus
innate
behaviours,
and
the
consequences
of
movement
to
the
fitness
of
individuals.
However,
the
tracking
of
individuals
for
longer
periods
needs
to
be
pursued
with
consideration
of
the
ethical
concerns
of
the
impact
of
very
long
deployments
in
some
species.
In
this
regard,
some
species
might
be
more
appropriate
models
for
tackling
particular
questions
than
others.
Long-term
studies,
albeit
not
necessarily
tracking
the
same
individuals
over
time,
will
also
be
needed
to
assess
climate
change
impacts
and
impacts
of
extreme
events.
While
technological
developments
have
facilitated
many
of
the
major
discoveries
of
marine
animal
movement
and
the
Argos
satellite
tracking
system
remains
integral
to
remote
data
relay
[2,74],
some
key
questions
also
point
to
the
need
for
further
developments.
For
example,
tracking
early
life-stages
might
require
increasing
miniaturisation
of
tags
and
new
techniques
might
need
to
be
developed
for
some
groups
that
remain
hard
to
track
for
long
periods
because
they
are
not
readily
accessible
or
live
in
habitats
where
direct
radio
reception
is
not
possible
(e.g.,
the
deep
sea
or
underground).
The
end-point
of
tracking
data
can
reveal
important
information
about
the
fate
of
that
tracked
animal.
For
example,
biologging
data
in
animals
as
diverse
as
raptors
and
eels
can
provide
evidence
that
individuals
have
died
[75,76]
and,
therefore,
tags
might
be
able
to
assess
mortality
rates
through
space
and
time
[77,78],
as
is
commonly
done
for
terrestrial
species
using
tags
equipped
with
mortality
switches
[79].
Variability
in
movement
patterns
across
a
range
of
scales
of
time
and
space
is
a
pervading
theme
across
tracking
studies,
yet
the
sources
of
this
variation
often
remain
obscure.
For
example,
within
the
same
population,
some
individuals
can
show
reproductive
migrations
spanning
1000s
of
km,
while
others
remain
in
the
vicinity
of
their
breeding
grounds
all
the
time
[80].
An
overarching
understanding
of
this
individual
variability
remains
elusive
and
will
need
consider-
ation
of
a
range
of
other
issues,
such
as
the
role
of
predators
in
constraining
the
movement
of
prey
species.
It
is
important
to
highlight
that
a
broad
range
of
taxa,
including
swimming
marine
species
and
flying
animals,
such
as
birds
and
insects,
are
subjected
to
flows
of
the
environment,
be
they
swimmers
subjected
to
currents
or
flyers
subjected
to
winds.
The
impact
of
flows
can
be
important,
with
the
movement
of
tracked
individuals
reflecting
the
summation
of
the
movement
of
that
individual
plus
the
wind
or
current
vector.
Disentangling
the
active
movement
of
an
animal
from
movement
due
to
environmental
flows
remains
a
challenge
[69].
In
theory,
tracked
animals
might
be
used
to
assess
local
flows
[81]:
for
example,
if
the
ground
track
of
an
animal
is
recorded,
while
at
the
same
time
its
orientation
and
movement
speed
is
logged
so
that
its
movement
vector
can
be
calculated,
then
the
difference
between
the
ground
track
and
the
movement
vector
equals
the
advection
due
to
the
environmental
flow,
be
it
current
or
wind.
While
the
questions
posed
above
reflect
a
consensus
on
priorities
among
experts
in
the
field,
we
acknowledge
that
consensus
is
but
one
pathway
to
scientific
breakthroughs.
Other
exciting
prospects
for
marine
animal
tracking
include
an
improved
understanding
of
the
marine
ecosys-
tem
by
complementing
the
random
or
stratified
designs
that
characterise
oceanographic
surveys
with
the
more
targeted
guidance
provided
by
the
perception
by
the
animal
of
the
environment,
developed
over
millions
of
years
of
evolution.
As
animal-based
platforms
are
increasingly
loaded
with
environmental
sensors,
animal
tracking
might
help
solve
fundamental
questions
in
oceanography,
particularly
in
challenging
and
undersampled
environments,
such
as
the
polar
oceans
and
the
deep
sea.
We
conducted
this
horizon-scanning
exercise
to
help
drive
the
field
of
marine
animal
movement
ecology
forward
through
the
identification
of
key
questions.
Although
we
do
not
claim
that
the
list
of
questions
is
exhaustive,
we
believe
that
it
captures
many
of
the
key
issues
and
challenges
facing
this
field
of
research
and
can
provide
a
roadmap
for
the
future.
472
Trends
in
Ecology
&
Evolution,
June
2016,
Vol.
31,
No.
6

Author
Contributions
G.C.H.
conceived
the
study
at
a
workshop
organized
by
M.T.,
A.M.M.S.,
M.M.,
V.M.E.,
and
C.M.D.
G.C.H.
assembled
the
questions
with
help
from
L.C.F.,
M.T.,
A.M.M.S.,
and
M.M.
All
authors
submitted
questions
and
voted
on
the
assembled
questions.
G.C.H.
wrote
the
manuscript
with
W.D.B.,
Y.R.C.,
E.L.H.,
M.M.,
A.M.M.S.,
D.W.S.,
A.T.,
L.C.F.,
M.T.,
P.N.T.,
and
P.T.M.
All
authors
commented
on
drafts.
Workshop
funding
was
granted
to
M.T.,
A.M.M.S.,
and
C.M.D.
by
the
UWA
Oceans
Institute,
the
Australian
Institute
of
Marine
Science,
and
the
Office
of
Sponsored
Research
at
King
Abdullah
University
of
Science
and
Technology
(KAUST).
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