Previous Studies
This
study is expanding upon the work of Dr. Tom Clarke who conducted the first major study of
hammerhead shark pup ecology in Kaneohe Bay (published in Pacific Science 1971). Clarke
used gill nets to estimate catch per unit effort (CPUE) of neonate sharks within the bay.
He also fished for shark pups with long lines, tagged them with plastic dart tags and
released them. From this he was able to estimate that 5,000-10,000 shark pups are born
into Kaneohe Bay each year and that the pups remain in the bay only 3-4 months after being
born. He also noticed that many of his recaptured pups actually weighed less than at the
time of first capture.
Later tagging work by the Holland lab (unpublished 1996) estimated only 1,106-4,446 pups
in Kaneohe Bay. This estimate was obtained by hand-line fishing for shark pups, tagging
with t-bar (clothing) tags, and releasing them. The Holland lab noticed a significant
variation in the population size between years. This new data also raised questions about
the energetic requirements of pups verses the availability of prey items in the bay.
This Study
Because of the large difference in population size estimates and because both studies used
mark-recapture information from the southern portion of the bay, there remain many
questions about the population of hammerhead pups in Kaneohe Bay. The aim of this current
study then, is to sample throughout the north, mid, and southern portions of the bay over
at least two pupping seasons (2 years). We hope to address questions such as how many pups
are in the bay and what is the variation like between years. By tagging sharks with
individual numbers we will also be looking at their distribution and large-scale movement
patterns within the bay. In addition, we will be looking at field growth rates and at
time-at-liberty (to estimate residency time). Furthermore, we are collecting fin clip
samples of the pups for genetic analysis.
In The Field
We
are hand-line fishing for hammerhead pups throughout Kaneohe Bay. Once caught, pups are
de-hooked, measured, tagged in the dorsal fin with 1/2 inch peterson disks, fin clipped
for genetic analysis, weighed, sexed, and released. The entire process takes less than 2
minutes and requires one shark handler and one data recorder. As of 29 Aug 2001, we have
tagged over 2,000 hammerhead pups and had over 100 recaptures.
This
program incorporates the help of a large number of volunteers. Research assistants
participate in standardized weekly shark tagging and volunteers from around the community
come to Kaneohe for our large monthly fishing effort. Tag returns from fishermen in
Kaneohe Bay are also a significant component of this project. IF YOU HAVE CAUGHT A TAGGED HAMMBERHEAD SHARK, PLEASE CALL
808-247-6633 TO REPORT IT (this number is for tag recaptures only). Information about this program was recently
published in Hawaii
Fishing News. For more information, email Kanesa Duncan: kanesa@hawaii.edu.
Extra thanks for the success of this project are due to the Pauley Summer Program 2000
students and organizers (Dr. Brad Wetherbee and Dr. Chris Lowe), Holland lab members (Dr.
Kim Holland, Tim Fitzgerald, Steve Kajiura, Aaron Bush, and Carl Meyer), undergraduate
researchers (Uilani Lingo, Andi Sluker, Jim Franks, Erik Rutka, Mike Doig, and Keith
Kanako), and our highschool volunteers (Jeremy Grad, John Chock, and Leilani Itano).
In Captivity
We
are holding 25 hammerhead shark pups in our natural outdoor ponds in order to test the
effect of different tag types on the hammerhead pups. We are monitoring attrition rates,
growth rates, tag retention, biofowling, and general health of the tagged individuals. Tag
types being tested include peterson disks, rototags (and mini-rototags), and PIT tags. We
also hope that holding these sharks in captivity for a prolonged period will allow us to
obtain estimates of yearly growth rate and estimates of yearly anuli formation in the
vertebrae. This will help us to test the hypotheses that the larger juvenile sharks caught
in Kaneohe Bay are second or third year sharks and that hammerheads in Hawaii form only
one anulus per year.
This research is supported by a NSF
predoctoral fellowship, Shark Trust, and an incredible number of community volunteers.
Also visit the hammerhead tagging
Image Gallery
