Patterns of Movement and Habitat Use in Female Leopard Sharks in

Movements and Habitat Use of Female
Leopard Sharks in Elkhorn Slough, CA
Aaron Carlisle
Moss Landing Marine Laboratories
Leopard Sharks (Triakis semifasciata)
• The leopard shark is an abundant coastal shark that ranges
from Willipa Bay, WA to Mazatlan, Mexico
• Opportunistic predators that feed on a variety of benthic
prey
– feed intertidally on fat innkeeper worms (Urechis caupo)
• Susceptible to overfishing and loss of important habitats
(e.g. nursery areas) is also of concern
Nursery Areas
• Bays and estuaries often are nursery
areas
– Few predators
– Abundance of prey
– Favorable environmental conditions
• Nursery areas may be primary or
secondary
New England Aquarium
www.mbs.maine.edu
Elkhorn Slough, CA
• Used extensively by
leopard sharks
• Seasonally abundant
• Fat innkeeper worm
(Urechis caupo) is primary
prey
• Serves as a primary and
secondary nursery area
HABITAT ALTERATION
• Elkhorn Slough has changed
greatly due to erosion
• Mudflats are now the primary
habitat found in the slough
• This has affected the type and
amount of available habitat and
the diversity and availability of
prey
Objectives
1) To identify habitats and regions that are important to female
leopard sharks in Elkhorn Slough, especially nursery areas
2) To examine patterns of movement and habitat use within
Elkhorn Slough and how they vary with the tide
METHODS
Capture
• Sharks caught with tended gillnet sets in ESNERR and
main channel
Tagging
• Sharks anesthetized with MS-222
• Vemco V16 tags implanted
intraperitoneally
• Incision closed with sutures
• Sharks revived and released
Active Tracking
• 8 sharks (91-132 cm TL) tagged with continuous
transmitters
• Monitor small spatial and temporal patterns of movement
and habitat use
Acoustic
Monitoring
• 11 sharks (78-140 cm TL)
TL
with coded transmitters
• Monitor large spatial and
temporal patterns of
movement and regional
use
• Examine use of four
regions : ESNERR, upper,
mid, and lower
Receiver
Receiver Range
UPPER
Receivers & Regions in
Elkhorn Slough
6
MID
3
LOW
1
4
5
2
ESNERR
RECEIVER
6
5
4
6
3
2
1
TIME
3
4
5
1
2
RESULTS & DISCUSSION
General Results: Active Tracking
• 8 sharks actively tracked (7
adult, 1 juv)
– 91 to 132 cm TL
• Tracked for 432 h
– 19.9 to 71.4 h (54 h ± 7.5
SE
• Sharks in ESNERR used
smaller areas
• Sharks all left by early
December
• Sharks tracked in ESNERR
or main channel
General Results: Acoustic Monitoring
• 11 sharks acoustically monitored (8 adult, 3 juv)
– 79 – 140 cm TL
• Monitored for 4 – 280 d (117 d ± 101.9)
• 2 sharks returned from previous year
• All adult sharks left the slough by early December
• Tagged sharks largely remained in the slough
Seasonal Patterns of Regional Utilization
Pupping
Period
WINTER
LATE
FALL
EARLY-MID
SUMMER
SPRING
FALL
Seasonal Abundance
•
•
•
Leopard sharks remained in the slough once entered
Sharks exhibited inter-annual site fidelity to slough
Sharks are seasonally abundant in Elkhorn Slough
– Appeared to arrive in March, left by December
Environmental Influence on Regional
Distribution in Elkhorn Slough
• Temperature & salinity likely important in presence of
sharks in slough and regional distribution within Elkhorn
Slough
– Leopard sharks sensitive to low temperatures and salinities
(Hopkins & Cech Jr. 2003)
Temperature
Arrival
Salinity
Departure
Arrival
Departure
• Extensive use of ESNERR in spring - summer likely tied to
reproduction & foraging, possibly behavioral thermoregulation
• Use of ESNERR diminishes in late summer & fall, possibly
due to high temperatures and low levels of dissolved oxygen
Dissolved Oxygen in ESNERR
Temperature in Elkhorn Slough
Habitat Use in ESNERR
Intermediate
High
Low Tidal
TidalTidal
Levels
Levels
Levels
SELECTION
INDICES
FOR HIGH
LOW TIDAL
LEVELS
SELECTION
SELECTION
INDICES
INDICES
FOR INTERMEDIATE
FOR
TIDALTIDAL
LEVELS
LEVELS
(ESNERR SHARKS)
95%
50%
SUBSTRATE DEPTH (M)
>1
0.5 to 1
0 to 0.5
-0.5 to 0
-1 to -0.5
-2 to -1
-3 to -2
<-3
0
1
2
3
4
5
SELECTION INDEX
Selection Indices > 1 indicates selection
< 1 indicates avoidance
Sharks
restricted
tolower
channels
Sharksmoved
almost
exclusively
used
Sharks
out
of channels
and
ontointertidal
intertidalmudflats
mudflats
Habitat Use in Channel
Intermediate
High
Low Tidal
TidalTidal
Levels
Levels
Levels
SELECTION
SELECTION
SELECTION
INDICES
INDICES
INDICES
FOR INTERMEDIATE
FOR
FOR HIGH
LOW TIDAL
TIDALTIDAL
LEVELS
LEVELS
LEVELS
(MAIN CHANNEL SHARKS)
SUBSTRATE DEPTH (M)
>1
95%
50%
0.5 to 1
0 to 0.5
-0.5 to 0
-1 to -0.5
-2 to -1
-3 to -2
<-3
0
1
2
3
4
5
SELECTION INDEX
Selection Indices > 1 indicates selection
< 1 indicates avoidance
Sharks
used
deep to
subtidal
substrates,
generally
Sharks
Sharksused
continued
shallower
use
substrates,
deep
subtidal
werewere
substrates
generally
found
most
found
lower
parts
of the
main
channel
in in
areas
further
intensively
up
main
channel
Habitat Use in Elkhorn Slough
• In ESNERR sharks extensively utilized low intertidal
mudflats, main channel sharks primarily used subtidal
habitats
• Difference likely due to distribution of fat innkeeper
worms (primary prey) and mudflats in the two areas
• Feeding ecology of leopard sharks shifts depending on
the availability and distribution of prey (Webber and
Cech Jr. 1998)
www.jimschrempp.com
Elkhorn Slough as a Nursery Area
• Active Tracking: Sharks 54, 60 and 63 were pregnant
when they were tagged in ESNERR
95%
50%
60
63
• Acoustic Monitoring: Sharks 102 and 105
pregnant when tagged
102
105
• Shark 100 returned from 2003, likely pregnant
in 2004
Acoustic Monitoring: Juvenile
Sharks
• 3 juvenile sharks (103, 104 & 108) were monitored
during the study
Elkhorn Slough as a Nursery Area
• 3 acoustically monitored pregnant sharks (100, 102 &
105) spent pupping period in ESNERR
• 3 actively tracked pregnant sharks (54, 60 & 63) spent
pupping period in ESNERR
• 2 juveniles remained entirely within ESNERR
Dave Ebert
• Suggests that leopard sharks using ESNERR as
primary and possibly secondary nursery area
• Low intertidal mudflats likely nursery habitat in addition
to foraging habitat
Habitat Alteration and Nursery Function
• In 1970’s sharks used shallow tidal creeks as nursery
areas
• Tidal creeks have been heavily altered, but mudflats in
ESNERR have replaced them
• Leopard sharks have compensated for the
habitat alteration by using ESNERR
SUMMARY
• Leopard sharks are seasonally abundant in Elkhorn
Slough and largely residential
• Their occurrence within Elkhorn Slough and seasonal
distribution within the slough likely related to
environmental conditions and reproduction
• Foraging ecology of leopard sharks shifts depending
on the availability and distribution of prey
• ESNERR functions as a primary and secondary
nursery area
• Creation of ESNERR & its mudflats likely helped
compensate for habitat loss
ACKNOWLEDGEMENTS
• Funding provided by
– PADI Foundation
– Myers Oceanographic Trust
– Archimedes Scholarship
– PADI Project AWARE
– NOAA/NMFS to the National Shark Research
Consortium (NSRC) Pacific Shark Research Center
(PSRC)
– Packard Foundation
• This project was conducted under IACUC permit 813
My thesis committee: Greg Cailliet, Rick Starr, and Jim Harvey
Marin Plank, Maya Carlisle, Sarah Carlisle, Christopher Rinewalt, Megan Segal, Valerie
Hunt, Andrew Thurber, Rhea Sanders, Chanté Davis, Wade Smith, Joe Bizzarro, Tim
Schaadt, Elsie Tanadjaja, Briana Doolittle, Lisa Wertz, Eli Woolery, Rob Leaf, Laurie
McConnico, Aroon Melwani, Allan Willis, Hannah Nevins, Christy Schnitzler, Colleena
Perez, Ashley Greenley, Dawn Tanner, Joanna Grebel, Brooke Flammang, Jason Felton,
the Pelagic Shark Research Foundation and everybody who helped in the field during
this project
ESNERR (Kerstin Wasson & Becky Christianson) for allowing me to work in the reserve
The Benthic Lab and PSRC for employing me
Matt Levey for all of his GIS help
Joe Bizzarro, Larry Breaker & Michael Graham for help/brainstorming with analyses
Bill Watson for his help Elkhorn Slough tides
John Douglas, Scott Hanson, and everybody at small boats
Aldo, James, Bill & Ralph for help in the shop
Joan Parker and her library staff