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Movement Patterns of Horseshoe Crabs in Pleasant Bay, MA
Mary‐Jane James‐Pirri, PhDGraduate School of Oceanography
University of Rhode IslandUniversity of Rhode Island
Atlantic Horseshoe CrabLimulus polyphemusLimulus polyphemus
• Adults spawn on protected beaches in May‐June.
• In Delaware Bay, eggs are an important food resource for migrating shorebirds.
• Limulus amoebocyte lysate (LAL) is produced from blood. LAL is the standard test used to screen all medical equipment that comes in contact with blood or spinal fluid.
• Commercial fisheries (1850’s to 1950’s) for fertilizer & i l f d P k h t i D l B h d 4 illianimal feed. Peak harvests in Delaware Bay reached 4 million
crabs annually .
• Commercial bait fishery for American eel and whelk(1980’s to present).
Life CycleOlder juveniles and After adults reach sexual
Y j il
young adults migrate to deeper water
maturity (9‐10 years), they return to beaches to spawn in late spring to early summer
Young juveniles reside on
intertidal flatsMales intercept females at spawning beaches as they come ashore to
spawn
Larvae hatch in
Females dig a nest in sand and deposit 4,000 eggs. Males the
fertilize eggs Females may spawn
Eggs develop in a
Larvae hatch in 2 to 4 weeks
fertilize eggs. Females may spawn multiple times laying up to 80,000 eggs (Delaware Bay estimates)
nest on a beach
2008‐2009 surveys
Student Conservation Association
Pleasant Bay, MA
Committee for the Conservation of the Horseshoe crabToll Gate HS
Study Objectives2008‐20092008 2009
Funded by the National Park Service
• Resurvey spawning horseshoe crabs in Pleasant BayResurvey spawning horseshoe crabs in Pleasant Bay and compare spawning indices to 2000‐2002 data;
• Tag horseshoe crabs to determine larger scaleTag horseshoe crabs to determine larger scale (regional) movement patterns and provide data to the USFWS Cooperative Tagging Program ;
• Use sonar (acoustic) telemetry to understand small scale movement patterns in Pleasant Bay.p y
Spawning Survey Protocol modified from Delaware Bay surveysy y
• New and full moons in May & June;• 3 Night & 3 day high tides during each moon period;• 3 Night & 3 day high tides during each moon period;• All surveys on same days and tides;• Count male & female crabs in 5 x 5m quadrats along
a stretch of beach;• 40‐60 quadrats per survey.
Photos courtesy of A. Leschen
Pleasant Bay Spawning Indices
( 2 )(number of spawning females per 25m2 quadrat)
1.5+SE Marsh 2/3 (day surveys only)NPS closure
0.5
1
wning
Index
• NPS closed its boundaries to all harvesting in 2001;0Sp
aw
g ;• Spawning in Pleasant Bay is higher during the day;• Much lower spawning than DE Bay (25 females 25m2);• Best long‐term record is Marsh 2/3;• Generall lo er spa ning indices in recent ears
1.5
±SE
Hog Island
1
1.5
ex +SE Barley Point
night day
• Generally, lower spawning indices in recent years.
0.5
1
wning
Index Night Day
0.5
1
pawning
Inde
0Spaw 0
2008 2009
Sp
Spawning Sex Ratios(the ratio of females to males during spawning)
35
Site 2000 to2002
2008 2009 Historic (1950’s)
1
4
56
7
8
2002 (1950 s)Monomoy NWR 1 to 1.9 1: 2.2 1: 1.3 --Pleasant Bay 1 to 5.8 1: 9.5 1: 7.5 1 to 2.5
82Nauset Estuary 1 to 1.6 1: 1.3 1:1.3 --
Cape Cod Bay 1 to 2.9 1: 1.7 1 to 2.4
•Pleasant Bay has highly male skewed sex ratios;• Other Cape Cod sites have sex ratios of 1 female to 2‐3 males;• Delaware Bay spawning sex ratios are 1 female to 3‐4 males;• Unharvested populations (ME, FL) are 1 female to 2 males.
Pleasant Bay f h h b h f lPercent of spawning horseshoe crabs that are female
Percent of spawning crabs that are female at other Cape Cod beaches
50%
female at other Cape Cod beaches (2008 data, 31% to 48%)
30%
40%
emale
20%
Percen
t Fe
0%
10%
0%
Historic (1950's) 2000‐2002 2008‐2009
2008‐2009 TaggingUSFWS Cooperative Tagging Programgg g g
In Pleasant Bay
USFWS “button” tag
• 2027 crabs tagged in Pleasant Bay by URI/NPS in 2008‐2009.• 13% overall recapture rate; 10% live recapture rate (268 tags re‐sighted).• 85% of recaptures found within 2.5km of original tagging location.• All recaptures except 1 were observed in Pleasant Bay• All recaptures, except 1, were observed in Pleasant Bay.• No crabs tagged in other areas (Monomoy, Cape Cod Bay) have been reported as recaptured in Pleasant Bay.
70l
Pewter “reward” pin
40
50
60
ecap
ture
s Pleasant Bay Recaptures – 2008‐2009
10
20
30
40
Perc
ent o
f re
0
10
Same site Less 2.5km greater 2.5km
P
Sonar (acoustic) Telemetry in Pleasant Bayin Pleasant Bay
Sonar tracking tag on crab
T itt it i i l• Transmitter emits a unique sonar signal;• Crabs be tracked using an acoustic hydrophone and
continuously tracked with submersible ultrasonic receivers (SUR);( );
• Transmitters can be detected up to 500m (about 1/3 of a mile) – detection in shallow water is ~50‐100m;
• SURs scan for signals at 1‐2 min intervals and store the data.Listening for signals in Pleasant g g
Bay
SUR receiver
Sonar tag, archival depth tag, & button tag on crab
If you find a crab with this type of tag please contact me or MA Audubon!
Passive SonarTelemetry in Pleasant BayTelemetry in Pleasant Bay•6 SURs in Pleasant Bay in 2009 from
early May until Oct‐Dec.• 55 female crabs with transmitters in 2008
to 2009.• 85% of crabs with transmitters were
d ddetected• 40% of crabs fitted with transmitters in
2008 were detected one year later in 2009in 2009.
• Crabs were detected as late as November & December in the Bay
Location of SURs (sonar receivers) in 2009
Passive Sonar Telemetry Number of transmitter detections over time
S t b D b
SURs scan for transmitters every 1‐2minutes, 24hr a day36,000+ detections, 648 “crab‐days”
M J J l A t September ‐DecemberFall‐winter
Number of
May‐JuneSpawning period
July‐AugustPost spawning period
6 21 to 500
detections
501 to 1000 2429
1114
1121001 to 2000
2001 to 400011 6
11
8
6
14001 to 8000
1
11
Number of 8
13
6
Location of SURs (sonar receivers) in 2009
1X Number of
crabs8
Horseshoe Crab Movement In Pleasant Bay
Crab # 108Released
Last detection Crab # 118 MayCrab # 108 Last detection Crab # 118Released 5/19/08
2009
Released 5/28/08
June 2009
July2009
5/28/08 July 2008
Location of SURs (sonar receivers) in 2009 Location of SURs (sonar receivers) in 2009
Horseshoe Crab Movement In Pleasant Bay
Crab # 110Released
Last detection Crab # 156Crab # 110
Released
Last detection Crab # 156Released 5/21/09
Released 5/22/08
July2009
June 2009
Oct‐Dec 2009Last
July
detection 12/8/09
July2009
Location of SURs (sonar receivers) in 2009 Location of SURs (sonar receivers) in 2009
Horseshoe Crab Movement In Pleasant BayReleased
Last detection Crab # 127Crab # 128 Last detection Crab # 127Crab # 128
Released 5/11/09Released Aug
2009
Released 5/11/09
June 2009
Oct‐Dec 2009Last
June 2009Oct
2009Last
detection10/5/09
Sept2009July‐Sept
detection 12/4/09
/ /
2009
Location of SURs (sonar receivers) in 2009 Location of SURs (sonar receivers) in 2009
Horseshoe Crab Movement In Pleasant BayReleased
Last detectionCrab # 161 Released Crab # 162Last detectionCrab # 161 Released 5/21/09
June
Crab # 162
Released June 2009
June 2009 Aug
2009
5/21/09
Oct 2009Last
detection 10/5/09
Oct‐Nov 2009Last
detection
Sept
/ / detection 11/1/09
2009
Location of SURs (sonar receivers) in 2009 Location of SURs (sonar receivers) in 2009
SummaryHorseshoe crabs in Pleasant Bay
• Spawning indices (number of females per quadrat) are higher during the day than at night;
S i i di b i l l i (• Spawning indices appear to be equivalent or lower in recent years (but… comprehensive data analyses still need to be conducted);
• Spawning sex ratios are extremely male biased (an indicator of harvest• Spawning sex ratios are extremely male biased (an indicator of harvest pressure). This is a continuation of a trend observed in 2000 to 2002;
• Tagging data indicate crabs in Pleasant Bay tend to remain at or near theTagging data indicate crabs in Pleasant Bay tend to remain at or near the same beaches during the spawning season;
• Telemetry data show that crabs remain in the bay through the late summer y y gto winter months, possibly overwintering in the deeper portions of the Bay;
• Tagging and telemetry observations indicate that horseshoe crabs in Pleasant Bay could be a localized population (stock).
Thanks!• National Park Service, Cape Cod National Seashore
• NPS Bio Technicians – Nate Gavin, Matt Holt, Chris Keon, Molly Williams• Student Conservation Association Interns
h ll b h h h ll ll l• Michelle Fabie, Christopher Guy, Tessa Mosher, Kelly Racette, Kelly Bowman, Nicole Kirkton, Stacey Ng, & Meg Swecker
• The many volunteers and others who helped… but especially•Erica Parra her family & friendsErica Parra, her family, & friends•Alison Leschen, Brad Chase, & Scott Kaplan (MA Division of Marine Fisheries)•Krista Lee & Kelly Medeiros (National Park Service)• Stuart Smith & Dawson Farber (Harbor Masters, Chatham & Orleans)
f k k ( d )• Jennifer Mattei & Mark Beekey (Sacred Heart University)
Horseshoe crab egg densities
500
gs per Nauset Estuary 500
per Hog Island
250
e nu
mbe
r of e
ggcore 250
numbe
r of e
ggs
core
No eggs
0
2001 2002 2008 2009
Averag No eggs observed
0
2001 2002 2008 2009
Average
ggobserved<1 egg
500
f eggs p
er Marsh 2/3 500
r of e
ggs p
er
e
Barley Point
Pochet Inlet
0
250
erage nu
mbe
r ocore
0
250Average nu
mbe
rcore
0
2001 2002 2008 2009
Av
0
2008 2009
A
But… Some horseshoe crabs do move out of the Bay• 11 of 15 crabs detected from mid‐June to Sept 1, 2008• 4 crabs stayed in upper bay, 4 moved to lower bay4 crabs stayed in upper bay, 4 moved to lower bay
• 3 crabs moved from upper bay to lower bay, & then returned to upper bay
Crab #78:Stayed in upper bay
June & July, 2008
Sept 1, 2008P d i t
Stayed in upper bay in June, 2008
Passed into lower bay on June 30, 2008
late July –early Aug,
2008 Recaptured by trawler on
July 21, 2008
Cape Cod Spawning Indices2(number of spawning females per 25m2 quadrat)
1.5+SE Marsh 2/3 (day surveys only)
0.5
1
wning
Index +
0Spaw
1 5
2
SE
Nauset EstuaryNight
Day1 5
2
SE
Monomoy NWRNight
Day
0 5
1
1.5
awning
Index ±S Day
0 5
1
1.5
pawnig Index ±S
0
0.5
2001 2002 2008 2009
Spa
0
0.5
2000 2001 2002 2008 2009
Sp
Telemetry( )• Passive sonar (acoustic) telemetry in Pleasant Bay was very
successful in detecting crabs, even after one year;
• There appears to be a pattern of crabs frequenting the northern sections of the bay during the spawning season;
• In mid‐summer the crabs move throughout the middle portions of the Bay;
• Crabs have been detected during the winter months in the deeper sections of the Bay;p y
• SURs will be placed in the Bay again during the 2010 spawning season in hopes of detecting the crabs againseason in hopes of detecting the crabs again.