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T he sleeping
sharks of Juno Ledge, an expedition into a
natural marine mystery
Introduction: The lemon shark is one of 39 shark species
protected by the US Government through the Department of
Commerce. Although it is one of the best studied sharks
virtually nothing is known about the adult phase of its
life. Thus any opportunity to investigate mature lemon
sharks will produce new information to complete our
understanding of the life history of an endangered shark
species
On January 2001 sport divers located a large, mixed
aggregation of lemon sharks in 25 m of water approximately 8
km east of Jupiter Inlet, Florida. A year later a similar
aggregation was reported in the same area. The finding of a
potentially accessible group of mature lemon sharks thus
opened a unique opportunity to study the adult stages of
this protected species.
Techniques developed in our laboratory for the field study
of the lemon shark combined with new methods adapted for
specifically investigating the aggregation can be now be
applied to this aggregation of adults gather evidence
supporting, refuting or modifying the experimental
hypotheses we will develop.
Objective and Significance: The first, most obvious question
is why are sharks aggregating? This overarching research
question can be placed in a framework of known information
about the lemon shark to generate hypotheses about the
function of this unique social structure. The first step
will be to describe the biological characteristics of the
group: When do the sharks arrive; how do the sizes, numbers
and sex ratios change over time; what are the movements of
the shark etc.?
The second step, the causal phase will involve concerted
sampling and experimental work to (1) monitor activity and
(2) build a genetic profile of the sharks. With these data,
collected over a period of at least three years we will be
able to test hypotheses about the cause and function of the
aggregation. If our theories based on past lemon shark
research are correct we will be able to answer the
questions: (1) Why are the shark there; and (2) what are
they doing? The importance of this work is that, for the
first time, we will gain insight into the adult phase of the
life history of the lemon shark, as well as confirming the
general breeding pattern revealed by the a decade of genetic
research at Bimini, Bahamas.
Experimental Question and Hypothesis: Over the past decade
we (Feldheim, Gruber, and Ashley) have been unraveling the
breeding biology of the lemon shark. As is true for most
large, active sharks courtship and mating have never been
observed and thus to understand breeding activity, we have
had to use indirect molecular methods. The genetics
investigations demonstrated many unknown facts about the
mating system of lemon sharks which we now know is
characterized by polyandry (multiple fathers sire each
litter), no male skewed success (no dominant or alpha males)
biennial reproduction (births every two years), female
philopatry (females home back to the same birthing and
mating round each year) and nomadic males (males only
infrequently return to the same mating group). Applying this
information to the Jupiter aggregation we have developed a
theory of how and why these lemon sharks are grouping and
what they are doing.
Theory of Male Recruitment: We hypothesize that the Jupiter
aggregation is not unique but repeated through the range of
the lemon shark. Philopatric, homing females gather near
their nursery grounds several months prior to mating and to
recruit the nomadic males. If this is true, the aggregation
must first be composed primarily of females. Over periods of
2-3 months (late November to mid February) as mature females
emit sexual pheromones into the strong current randomly
passing males are attracted and the group grows into a mixed
aggregation. Around late February the sharks leave deeper
waters and migrate inshore to begin the birthing and mating
process. We hypothesize that the same females return to the
site year after year while most males are recruited on a
chance basis and would not be expected to show up annually.
Where and when mating and parturition occur may remain
unknown.
This hypothesis subsumes many obvious observational and
experimental questions: Why do sharks aggregate; is Jupiter
unique; is the aggregation an annual event; do the same
sharks reappear; what is the sequence of group formation;
what behavioral, physiological and/or genetic patterns are
involved etc.?
Preliminary meeting on the Yacht Animal House 12.20.04:
Research Cruise Planning
Walt Stearns, Pierce Hoover and Samuel Gruber meet with the
crew and Captain, Tony Little of the Yacht Animal House
December 20, 2004. They discussed the research operations
planned for late January.
The visitors received a tour of the vessel and were shown
her extensive diving and endurance capabilities. The vessel
presently docked in Fort Lauderdale will move to the
Rybovich-Spencer Marina 4200 Flagler Drive West Palm Beach
on January 15, 2005. The run from marina to the lemon shark
aggregation site is about 45 minutes.
Timing: The campaign could start on January 22, 2005 and run
for two or possibly three weeks. The plan is to keep the
vessel on site for as long as possible, using the 22' Tiara
tender as the dive boat. The vessel would return to port in
inclement weather.
The campaign will be divided into two phases:
1. Reconnaissance phase where the dive crew will search for
the lemon shark aggregation using various visual-census
techniques including closed circuit rebreathers and mobile
scooter devices
2. The observation phase where the dive crew will use closed
and semi closed rebreathers to observe, photo-document and
census the aggregation. Attempts will be made to catch one
or more of the group and to take DNA samples by biopsy
spear. If an ROV can be obtained we will try to make remote
observations and counts.
Crew composition and numbers: The vessel can entertain at
most 8-10 guests at a time but is legally set up for 16
persons which includes a Capt. and crew of 5.
Final planning meeting for the expedition "The Sleeping
Sharks of Juno Ledge" January 23, 2005.
The meeting was held in the salon of the M/V Animal House.
Pierce Hoover, Expedition Coordinator chaired the meeting of
members of the Search and Dive Support team and the Research
Team. A summary report was distributed giving a short
history of the discovery of the sleeping lemon sharks and
abstract of the research hypotheses, objectives and methods.
The expedition title will be "The Sleeping Sharks of Juno
Ledge." Pierce noted that the expedition would be divided
into two phases: Search and Research.
In addition to the M/V Animal House’s, crew, 23’ tender,
dive accessories and accommodations, Pierce mentioned some
of the other resources potentially available to the
expedition:
Open and closed circuit underwater TV
Side Scan sonar
Underwater personal vehicles
Compact ROV with sonar, manipulator and garage courtesy of
Steve van Meter
Dive equipment courtesy of Dennis Bulin
Telemetry tracking gear and transmitters courtesy of Bimini
Biological Field Station
Mitzi Graff, IT coordinator set up a personal email alias
for messages to be sent to a central depository--expeditionarchives@yahoo.com.
She will also establish a website on the Yahoo server.
Walt Sterns, Dive/Search team organizer handed out a list of
11 potential sites to be searched. He showed some aerial
photographs and discussed the plans for finding the
aggregation.
Samuel Gruber Research Organizer discussed the objectives
and methods to be attempted:
1. Catching several adult lemon sharks using hook and line
fishing. These sharks will be marked with NMFS dart tags,
PIT electronic tags and 75 KHz ultrasonic transmitters
externally applied. The sharks will be measured, sexed and
DNA samples taken then released.
2. Tracking of the telemetered shark throughout the
expedition to understand their local movements and to be
able to rapidly find the group if it moves.
3. Characterization of the group in terms of numbers of
individuals, gender, reproductive state, mature vs. immature
and observations anything unusual
4. Measuring environmental variables--water temperature,
salinity, current, sea state etc
ROV operator/developer Steve van Meter gave a demonstration
of the ROV's capabilities through a PowerPoint presentation
with video. Much of the meeting was videographed for the
archives by Larry Kingston.
Tony Little, master of the M/V Animal House suggested that
the teams would be able to use the vessel through March 1,
2005. The key factor in getting the expedition underway will
be the weather which will steadily improve through the
weekend. Walt Sterns will decide on the expedition start
date.
The meeting ended at 15:00h with a group photograph taken on
the fantail of the M/V Animal House. Since this will be an
Explorers Club flag expedition, the photograph was taken
with Explorers Club flag # 83. Dr. Stan Spielman, president
of the Southern Florida Chapter of Explorers club hopes to
be an expedition member along with members Pierce Hoover and
Tim Taylor
Randy Jordan, Owner, Jupiter Dive Shop: Mr. Jordan been and
enthusiastic and active supporter of our research efforts.
He has participated unselfishly and generously in all
aspects from organizing his divers in an attempt to observe
and characterize the aggregation to hand feeding the lemon
sharks baited hooks. Therefore I would like to gratefully
acknowledge Randy's help and critical insights with respect
to the lemon sharks. He unselfishly shared his vast
knowledge of the local reef conditions, freely gave us the
use of his vessel Republic IV and even helped us catch the
lemon sharks.
Gruber narrative: Field Party: Walt Sterns, Grant Johnson,
Todd Gedemke, Mark Corcoran, Samuel Gruber; ship’s crew,
Captain Tony Little, Craig, Ali, Andre
Feb 7, 2005. After many months of planning and preparations
I collected Grant Johnson at Ft Lauderdale Executive Airport
and we drove to the Spencer-Rybovitch Marina in West Palm
Beach where we boarded the M/V Animal House. We set up our
state rooms, stowed gear and had dinner. After dinner we
modified the telemetry-transmitters by attaching metal
darts. I turned in early without planning the next day’s
activities.
Feb 8. Arose 07:30 grabbed breakfast and drove to a bait
shop to purchase lures and other fishing gear. We quickly
planned the day’s operations, met Susan Cocking, Miami
Herald outdoor reporter and got underway to the Sasha wreck
off Palm Beach to fish for and spear barracuda as shark
bait. My plan was to fish for lemon sharks as we do in the
Keys but since this was a deep water situation the Keys
method did not really work. We eventually had to modify the
fishing techniques to fit the situation. We speared three
barracudas, returned to the M/V Animal House for other gear
and lunch then ran to Jupiter and the MG111 wreck—45 minutes
north of Palm Beach inlet. At the 111 wreck we dove to see
if there were any lemon sharks on the site—there were! Being
inexperienced, poorly prepared and working under
deteriorating weather we got no sharks and had a long,
miserable ride back the Palm Beach, empty handed. After
dinner we had a long planning meeting decide how to improve
our chances. We made a plan and modified our fishing
techniques to reflect the deep water situation.
Feb 9. After buying more chum and gear at the bait shop at
07:30 we got underway quickly to the Sasha wreck and speared
three good sized barracudas. As the weather was better we
were able to run quickly up to the MG111 wreck and again
sent divers down to asses the currents and confirm the
presence of lemon sharks which were still there. Based on
current speed and direction we anchored 250 m south of the
wreck and began chumming with ground fish and menhaden oil.
We also put out the barracuda carcasses to add to the scent
trail. We quickly caught a 12 kg jack cravelle and put it
out on the carcass line as well. After seeing two relatively
small great hammerhead sharks around the boat, a 4m great
hammerhead shark swam directly in and tried to grab the
bait. But it was frightened by the ropes and left quickly.
After about 40 minutes of fishing we hooked a 251 cm female
lemon shark and brought her to the skiff, tying her along
side. We did a full workup including measuring lengths,
taking a genetic sample, placing a NOAA tag, photographing
some parasitic lesions and finally darting in transmitter
number 366. We tracked this female for about 20 minutes
before heading back to the M/V Animal House. The trip home
was again rough due to engine trouble from bad gasoline
(water in the fuel) and rising wind. Back on the ship we had
dinner and planned our next effort. We thought we understood
the fishing situation and had developed a viable method. We
were delighted to have actually caught a mature lemon shark
which, unless we were extremely lucky, confirmed what many
fishers had told us, namely that lemon sharks at the Jupiter
wrecks will take bait.
Feb 10. After breakfast we quickly ran out to the Sasha
wreck intent on spearing more barracuda. But we were
unprepared for the low visibility and complete absence of
barracudas in the area. We guessed that the visibility might
be better to the north and quickly ran up the MG 111 wreck.
Although the water was murky, our divers put on SCUBA gear
and were able to spear some bait. After fishing for a while
we contacted Randy Jordan of the Jupiter Dive Center who was
on a site called the Jupiter Ball, 9 km south of the 111
wreck. Randy saw lemon sharks there and suggested that we
come to his boat the Republic IV and he would hand feed
individual sharks a baited hook. We were skeptical but raced
to meet him. Indeed he was able to feed the bait to a shark
but it was the wrong species—it was a reef shark! We
eventually got it along side, worked it up, removing several
hooks from earlier encounters and released it unharmed. At
noon I had to leave the expedition but was told that Randy
fed bait to a reef shark later that afternoon. Even thought
it was the wrong species Randy stated that he has hand-fed
lemon sharks dozens of times. This suggests that will be
entirely possible to feed a particular lemon shark a baited
hook.
Summary of Events on “Sleeping Sharks of Juno Beach”
expedition
By Todd Gedamke--edited
Feb 12, 2005. Drove to Key West to meet Tim Taylor and pick
up re-breathers and dive equipment for use off Jupiter.
Feb 13, 2005. Did basic instructional overview on
re-breathers and enriched oxygen diving in Key West.
Feb 14. Drive from Key West to MV Animal House in Palm Beach
to drop off diving equipment including 3 Drager semi-closed
re-breathers and 2 Inspiration closed circuit systems. Walt
Stearns and Capt Tony Little asked me to stay onboard as
their dive partner. Many dives were planned as the weather
was forecast to be fine for several days
Feb 15. We made two dives at the Cap’n Kurel reef with Walt
Stearns as dive partner. Captain Tony and Mate Shamus were
surface support. I dove with open-circuit Nitrox and Walt
dove on Drager semi-closed system. The weather was fine and
currents fairly strong (about 2 km/h.) with approx 15-20 m
visibility. Bottom time for both dives was 35-40 minutes at
approx 28m depth. Lemon sharks were present but nervously
swimming at approx 1.5m ft off the bottom in a large circle
from the sand bottom 20 m to the ridge of live rock to the
west that makes up Cap’n Kurel reef. I observed 20-30
different individuals but kept some distance so as not to
disturb Walt’s camera work by disturbing the lemons with my
bubbles. A few individuals (<4 at a time) were lying on sand
bottom in the center of the rocky ridge. Toward the end of
both dives I drifted about 2 km north in the current into
slightly deeper water of 30m where the reef gave way to flat
sandy bottom covered with brown algal mats. Bottom type
suggested and area of reduced currents compared to the
center of the Kurel. Second dive was late afternoon and the
lemons appeared more active than earlier in the day which
agrees with many similar observations by Walt Stearns.
Feb16. I made two dives on open-circuit nitrox at the Cap’n
Kurel with Capt. Tony as dive partner. Walt Stearns and
Pierce Hoover dove on Drager semi-closed systems. Andrea
acted as surface support. Visibility and current were both
reduced slightly but dive conditions were similar to the
previous day. Lemon sharks were present in about the same
concentration, centered on the Kurel. Behavior of lemons was
similar to the previous day and didn’t really allow us to
approach closer that about 8m. As we approached visual range
sharks were clearly aware and unnerved by our presence. With
both Pierce and Walt were shooting stills and video, Tony
and I just covered a lot of ground around the Kurel. Same
basic conclusions—shark aggregation was focused at Cap’n
Kurel; only moving, solitary individuals were found outside
of the core of the aggregation. As we moved off the reef
into the deeper sandy areas north of the Kurel the sharks
disappeared. Tim Taylor arrived that evening and began
training Tony and me on the use of semi-closed re-breathers.
He went through a power point show of the mechanics and
basics of diving on a re-breathing system. We disassembled,
inspected and tested the Drager units and prepared for
diving the following day.
Feb 17. The day began with a training dive just outside of
the Palm Beach inlet jetties in 6m of water. Tim again
instructed Tony and me on the use of the equipment, got us
in the water and ran through basic exercises on the gear
(dumping and clearing breathing loop, gas shut off test,
switch to bail out, general comfort level with gear, etc.).
With that experience we headed up to Cap’n Kurel and did two
dives: Tony and I on Drager systems and Walt and Tim on
fully closed Inspiration systems. We carried an extra 40 ft3
pony bottle for safety. It was immediately obvious that I
had entered a new world of diving. There were lemon sharks
swimming around everywhere. We dropped into the northern
edge of the Kurel and I saw what Walt had been describing
for the past two days. I felt as if I were visiting rather
than intruding as the lemon sharks zone of comfort was
reduced to less than 3m. Walt began taking photographs and
Tim, Tony and I just dumped our BCs rested quietly on the
bottom at the center and watched as the lemon sharks
habituated to our presence and again came to rest on the
bottom next to us. I observed two different individuals with
NOAA dart-type tags placed 20cm forward of the first dorsal
and 8 cm down on the left side of the body. I saw them
swimming together like a tagged outcast couple. I would
estimate that at any point during that dive I could account
for 50-60 individuals suggesting that there were close to
100 individuals aggregating on the Kurel. It was difficult
to keep track of individuals so a coded visual tag should be
considered for future studies. We were able to approach
close enough that a spear gun with a modified tip could be
used to deploy such tags. A number of pregnant females and
large males were present with approx 10-15 smaller (~1.5-2m)
individuals mixed in. It seemed that the sex ratio slightly
favored females. We surfaced from the second dive at around
16:30h and the lemon sharks again appeared a little more
active than earlier in the day. Bottom times were close to
an hour for each dive at 28 meters. Water temperature was 24
C at the bottom. Water temperatures were 23-25 C for all
dives this week. Current speed seemed to be an important
factor for the aggregation.
Feb18. Weather is beginning to turn with a strong breeze
developing out of the N\NW. The same teams and gear headed
out to the Sasha wreck, just south of the Palm Beach inlet.
We observed 10-15 lemons in between the wrecks. The
structure of the wrecks appeared to be creating an area of
increased current where the lemon sharks were sitting on the
bottom. This group appeared to be a little more skittish and
I was unable to get closer than 5m to an individual. However
the gunwales on the wreck acted like a blind and perfect
observation points. Individuals at this location appeared
more solitary in addition to their larger comfort personal
space. By the time we surfaced a 3 foot chop had developed
and we decided to call it a day. We all packed up for the
weekend and left the M/V Animal House for the last time.
Gruber narrative leg 2: Field Party: Walt Sterns, Katie
Grudecki, Bryan Franks, Samuel Gruber; ship’s crew, Captain
Tony Little, Shane, Ali, Andre.
Feb 20. I returned yesterday from Bimini with Katie Grudecki
and Bryan Franks and drove to West Palm Beach to meet the
ship arriving 20:30h. We stowed gear, had dinner and turned
in.
Feb 21. In the morning Tim Taylor gave us a short
illustrated course on the operation and functions of the
Drager semi-closed circuit system. After lunch we did
checked out dives at the Palm Beach Divers pool and 5 m-deep
water tank. Using the Drager units was easy and comfortable.
Later in the afternoon we tried to fish for lemon sharks but
were not able to get any barracuda for bait. We returned to
the vessel and prepared for the next day’s diving.
Feb. 22. Arose to a perfect day with calm seas and clear
waters. I bought some bait and asked the crew to spear some
barracuda for later fishing efforts. The rest of us drove by
car to the Jupiter Dive Center to board the M/V Republic IV
and dive with Randy Jordan using Dragers on the Kurel. The
dive team consisted of Walt Stearns, Tim Taylor, Katie,
Bryan and me. Katie and Bryan dove together after my dive.
Walt stayed on the bottom and Tim stayed with the new
divers. There were about 15 active, skittish lemon sharks on
the sand to the west of the reef ridge. They were probably
responding to noise created by bubbles from the open circuit
sport divers. While Tim and Walt took photographs we sat
quietly on the bottom observing the sharks. We noted several
large gravid females and some mature males. As time
progressed the sharks came closer to us. At noon we
transferred the M/V Animal House’s skiff and commenced
fishing operations at the MG111 wreck. We quickly caught and
worked up a 195 cm male lemon shark which was fitted with
the second transmitter, PIT and Dart tags. We took a DNA
sample, released it and it swam away well apparently
unharmed. We tracked him for a few minutes. Later we caught
a 2.5 m great hammerhead which was quickly released with the
dehooker. We then rendezvoused again with the Republic IV so
that Randy could try to feed a baited hook to the lemon
sharks we saw earlier at the Kurel. We hooked up two lemon
sharks by hand feeding but were unable to bring them to the
skiff due to gear failure. But the technique was proven.
Feb 23. Again Walt Tim and I went to the dive shop while
Katie and Bryan went on the Skiff with Tony to spear
barracudas—getting two. At the Kurel Randy took us along the
reef ridge pointing out some of the rich and amazing marine
life. I must admit that reefs off Jupiter were the richest
in Florida I have seen in more than 30 years. There were no
lemon sharks at all so we met up with the skiff and followed
Randy to a new spot called Mike’s reef or Area 51 where they
saw 17 lemon sharks. Randy was going to return for more
tanks to hand feed the sharks but once we started fishing,
every 10 minutes we hooked up a lemon shark. At times we had
two on simultaneously! Eventually we worked up three lemon
sharks, one barely mature, placing the third transmitter
(348) and releasing all in good condition. One shark was
badly hooked so we had to bring him into the skiff and
surgically remove the hook but it swam well once back in the
water. We returned to the M/V Animal House and prepared the
gear for leaving the next day. I took the crew and team out
to dinner at a Japanese restaurant where we had a good tike
all around.
Feb 24. Next morning we loaded all the gear, bade our
farewells to the immensely helpful crew and wonderful
accommodations on the M/V Animal House and left for
Lauderdale Executive Airport. End
The primary objective of the expedition was achieved. Over a
period of just a few days we were able to catch and work
with five individual lemon sharks, placing a variety of tags
and transmitters on the individuals. This is the key to
carrying out the experiments and observations described
above. The chart below gives a summary of the catch data:
Date Time Location Species gender PCL FL TL Comments
Feb 8 16:58 MG 111 N. brevirostris F 191 216 251 Parasitic
infection on caudal and anal Fin;
Mature; Not Gravid; Transmitter 366 attached
Feb 10 13:10 Capt. Kurel C. perezi F - - 194 Healthy.
Removed 7 hooks, handfed bait
Feb 10 16:00 Capt. Kurel C. perezi F - - 166 Healthy Handfed
bait
Feb 22 13:30 MG 111 N. brevirostris M 157 168 195 Immature;
Transmitter 333 attached
Feb 23 14:16 Area 51 N. brevirostris M 154 167 197 Immature
healthy
Feb 23 15:20 Area 51 N. brevirostris M 180 201 230 Just
Mature; Transmitter 348 attached
Feb 23 15:59 Area 51 N. brevirostris M 134 150 169 Hard
de-hooking; brought in boat; swam well
Plans for next year’s campaign are just emerging. In the
likely event that the M/V Animal House is not available next
year, plan is to rent a house in Jupiter and obtain the use
of a 28-30' skiff to dive and fish from. We plan to recruit
a number of volunteers to spend up to 6 weeks on site
tagging, catching lemon sharks, obtaining genetic samples
and biological data, setting up an array of acoustic VR-2
monitors to automatically track the movements of tagged
sharks, and doing manual tracking. We are seeking funding
from the National Geographic Society if successful we will
place satellite transmitters on six sharks during the 2006
research period. We will also plan on behavior observations
with closed circuit rebreathers combined with and manual
tracking and personal underwater vehicles to locate the
aggregation. The goal will be to catch at least 20 adult
lemon sharks and instrument all of them with electronic tags
and surgically implanted transmitters.
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