Sirenews
(ISSN 1017-3439) appears twice a year
in
April and October and is edited by Daryl P. Domning,
Department
of Anatomy, Howard University, Washington, D.C. 20059 USA
(fax:
202-265-7055). It is supported by the U.S. Marine Mammal Commission.
NUMBER
22 OCTOBER 1994
IN THIS ISSUE: -
RELEASING REHABILITATED MANATEES
IN FLORIDA AND PUERTO RICO (pp. 4, 10)
-
DUGONG STATUS IN MADAGASCAR (p.
6)
-
MANATEES AT NUREMBERG ZOO ACHIEVE
SPECTACULAR BREEDING SUCCESS (p.
5)
IS
THE CATCH OF DUGONGS IN TORRES STRAIT SUSTAINABLE?
The results of the aerial survey I conducted in
1992 indicate that at least 24,225
+_ s.e. 3,276 dugongs
live in Torres Strait, the tract
of sea between northern Australia and
Papua New Guinea (PNG). Torres
Strait is thus the most important dugong habitat in Australia
and probably the world.
Torres Strait
is a relatively pristine environment and the major impact on dugongs
is traditional hunting. Thanks to a comprehensive study by Aubrey
Harris and his
co-workers from CSIRO, we now have better information on this dugong
fishery than ever before.
Dugong hunting,
a traditional test of manhood, is still solely
a male activity.
The skilled hunter enjoys considerable prestige in the community and
hunting is considered to be an important expression of Islander culture, which
is undergoing a resurgence coincident with
the increasing recognition of the rights of Indigenous Australians.
Dugongs are still a prized traditional
food source for Torres Strait Islanders and for the Kiwai people of the Western
Province of PNG. The meat of dugongs still ranks highest among traditional
foods in Torres Strait, and
no celebration is
considered complete without dugong on the menu. This is reflected
in the seasonality of catch,
which is highest in the period of festivity leading up to Christmas and the New Year. This is also the season when
the weather is most suitable for hunting.
In the early 1980's, Brydget Barker-Hudson
questioned the sustainability of the
Kiwai dugong catch. Harris' data indicate that the catch from the
Australian islands is much higher than the catch recorded by
Barker-Hudson in PNG.
Harris conducted a comprehensive quantitative study
of traditional hunting and fishing
conducted by the residents of 14
communities in the Protected Zone, the area covered by the
Torres Strait Treaty, an international
agreement between PNG and Australia. He did
not collect data from communities outside this area,
i.e., along the Papuan coast or
from Australian islands south of
the Zone.
Harris estimated that the wet weight of dugongs
landed in the Protected Zone in
1991-93 was higher than the
weight of any other component of the seafood catch, including
finfish or turtle. On an average day, four boats land 645 +_
s.e. 102 kg of dugong in the Zone. This equates
to an estimated annual harvest of
1226 +_ 204 dugongs or 5% of my minimum
mean estimate of the dugong population of the whole region.
Given that the catch statistics do not include
any data from outside the Protected Zone, these
figures are worryingly close to the
estimated maximum sustainable yield if my mean estimate of the dugong
population is close to an absolute estimate.
It
is impossible to evaluate the situation more accurately without information on:
-
absolute estimates of dugong numbers,
-
catch statistics for PNG, and
-
current life history statistics for dugongs in Torres Strait,
but the situation certainly warrants close
scrutiny.
Fortunately, the Torres Strait Islanders are demanding
increasing responsibility for the
management of their marine resources. They are involved in
the ongoing monitoring of the
dugong catch and hunting effort and the aerial surveys. - Helene Marsh
WANTED: INFORMATION ON SIRENIAN LEGISLATION
Professor Patricia
Birnie has been
commissioned by UNEP
to undertake a comprehensive review and analysis of the
existing legal system for the protection of all aquatic mammals. She
is having difficulty finding examples of
legislation specifically concerning sirenians, and
would appreciate receipt of copies of such legislation from
all sirenian-range countries. Materials
should be sent
directly to her, as
follows: Prof. P.
W. Birnie, 78 Windmill Street, Brill, Aylesbury, Bucks
HP18 9TG, England; tel. & fax: 44-844-237-880.
SPANISH-LANGUAGE
MANATEE LEAFLETS AVAILABLE
The Florida Power & Light Company has
produced a Spanish version of its 1992
leaflet entitled "Guidelines for Protecting
Manatees." This leaflet is designed for
use in Florida and
includes facts about manatee
biology as well as guidelines for swimming and
boating in manatee areas.
Limited quantities of the new
"Guia para Proteger al Manati"
are available from Dr. J. Ross
WIlcox, Chief Ecologist, Environmental Affairs, Florida Power & Light Co.
P.O. Box 088801, North Palm Beach, Florida 33408-8801.
LOCAL
NEWS
AUSTRALIA
Satellite Tracking
of Dugongs in Northern
Australia. - I've
been satellite-tracking dugongs
in a remote area of the Gulf of
Carpentaria since May. Aerial surveys
in 1984-5 indicated that this area had one of the highest
dugong concentrations known. However, in the following two years
the area was pounded by two cyclones and
most of the seagrass areas were
lost. We do not know what impact this
had on the dugong population,
but preliminary data suggest
that there are far fewer dugongs in the area today. An October aerial survey should clarify this.
The area is of considerable
interest as it is
the site of a large lead and
zinc mine development. A port
for the export of
this ore is being constructed smack in the middle of
important dugong habitat.
The dugongs are hunted
by the traditional owners of the area,
the Yanyuwa people, who are
understandably very concerned
about the impacts of
ore spillages and
boat traffic on
the dugong population. They are
also concerned about the
level of dugong mortality in nets used by professional barramundi fishers.
It is hard to determine how many dugongs die as a
result of hunting and gillnets, so
the scale of the problem remains
unclear.
The tracking is being used to identify the
dugongs' important habitat
areas and determine their
movement patterns. Previous
attempts met with limited success, primarily because of
difficulties keeping the
PTT transmitters on the
animals. This is not
simply a matter of having a strong tether
that does not constrict or irritate the dugong.
It must also have
a weak link,
allowing the PTT to be shed if caught amongst mangrove roots or coral outcrops. The transmitter must also
detach from the dugong before
the batteries expire,
so it can be retrieved and re-used.
Our
earlier attempts used
modifications of the
weak link and corrodible
link used on manatees.
Perversely, our dugongs seem
to live in a much more corrosive
and shark-infested environment
than their northern cousins.
The corrodible links
lasted 6 weeks instead of 6 months, and large sharks had a propensity to test the weak
links. After trying various
variations on the
manatee theme, it became
apparent that a new
approach was required. In
collaboration with Andrew Hunter, an engineer at James Cook University, we developed an all-new
tether incorporating a stack of
camera batteries, a computer
chip, and an explosive fuse.
The chip acts as a clock and is
wired to
explode the fuse at a set time (3.5 or 7 months in our case).
The fuse shatters the end-cap
of the canister, and
the silicon-sheathed nylon webbing that ties around the dugong's
peduncle is released. By being able
to anticipate when the PTT will be shed, it is possible
to be in the area, thus
maximizing the chances of
recovering it. The
weak link was
also redesigned, and the method
of adjusting the fit
of the webbing was greatly simplified.
I also simplified the tagging
operation, which now involves just one
boat and three people, although an
aircraft is very useful
to help locate and pursue the
dugongs.
Two
dugongs were tracked for
113 and 114 days,
and at this
writing (early October) another three tags are still on after 136 days (4.5 months). If all goes
well, these animals will be
tracked until about
21 November. Of the first two, one
PTT was shed as a
result of an unusual and, as
yet, inexplicable break in the
3-m flexible nylon rod that connects the peduncle tether
and the buoyant PTT housing. The second PTT was due to release from its dugong after
about 90 days, but
failed to do
so. Fortunately we were
able to recapture
this animal and remove
the transmitter. It turned out
that at least one of the batteries in the
tether was faulty. Due
to the phase-out
of mercury batteries (owing
to their contribution to mercury
pollution), it looks like we
got one that had been on the
shelf too long. The other tethers may also have bad batteries. We have now modified the tether to use lithium
batteries.
The five dugongs have so far provided
three important pieces of
information. First, dugongs are not just dugongs, they are individuals. Second, the dugongs in this
area are highly social,
and third, they
move over much larger areas than
previously thought.
Starting with
the last point,
the dugongs thought nothing of
popping 50 km along
the coast to spend a day or two
with some other dugongs, and then hopping the 50 km back to their current core area. The five dugongs
were all caught from one
herd of about 200
near the Bing Bong Creek
area. Three spent time at a site
50 km to the west (Rosie
Creek area). Two of these also
spent time 100 km
west of the
capture site (Limmen Bight
River). One spent some time 50 km east of the capture area. One that had spent
over two months in the Limmen
Bight River-Rosie Creek areas
then traveled, apparently without significant stops, 400 km east
of the capture area, where she has
spent the past two months. Hence, her range
has spanned more than 500 km of coastline.
While
that dugong has
been very mobile, another has been remarkably sedentary.
With the exception of one or two
brief sojourns about 10 km
to the east, she
has spent the past 4.5 months
within a couple of km of the site of her
capture. The other three dugongs
have tended to
divide their time unevenly between two or three sites
separated by about 50 km. It would be
premature to generalize too
much about the
movement patterns of the Bing
Bong dugongs; they are surprisingly
individualistic.
They are also highly social. As I have
said, each has
used 1-3 preferred
areas. Excluding the area 400 km to the east (about which
I know very little), the five
dugongs collectively use just
five preferred areas. Aerial surveys have confirmed that herds of 50-200
dugongs occurred at each of
these preferred sites. So although they move about a
lot, and move about independently
of one another, they
have all been moving among the
same five dugong herds.
Significantly, very few were seen on
the shoreline aerial surveys that were not in these herds.
I
also attached time-depth
recorders (TDRs) to the
tethers of the
five tagged dugongs. I have data from one of these, and a very preliminary scan indicates that
the data are very interesting.
Watch this space!
- Tony Preen
CUBA
Manatee Workshop. -
Representatives from governmental
organizations, the Ministries of
Agriculture, Fisheries, Science and Technology, the University of Havana,
the Center for
Marine Studies and
the Academy of Sciences
attended a two-day national workshop on the
conservation of the West Indian manatee which was held on 19-20 May 1994 in Havana.
Various sectors
of the government expressed their willingness to join efforts in the management of manatees, and act
cooperatively to accomplish the tasks they
agreed should be tackled first. Some of
the topics covered were
the biology and status of the
manatee in Cuba; the manatee in Laguna
del Tesoro and the
experiment conducted on manatee capture, transport and handling.
The National Plan for
the Conservation of the
Manatee in Cuba was also presented.
Some
of the conclusions included the
need for a)
the preparation of
a general proposal to try to
obtain financial support for the activities
in the next
few months; b) production of the proceedings of the
meeting; c) starting of a
manatee national network; and
d) convening of a second workshop
in November 1995.
For
more information contact: Dra. Delice
Salabarria, Ministerio de
Ciencias y Tecnologia, (COMARNA), Avenida 17, No. 5008
e 50 y 52 Playa, Codigo Postal
11300, La Habana, Cuba;
telephone (537) 330102; telefax (537)
330101. - (reprinted
from CEPNEWS (UNEP) 8(3),
Sept. 1994.)
FLORIDA
New Staging
Area for "Soft" Releases of
Manatees. - The
Captive Manatee
Interagency/Oceanaria Group
(CMIG) was created
several years ago to
advise the Florida Manatee Recovery
Team on issues related to
captive manatees. The CMIG
first discussed the concept
of a
pre-release enclosure over
2 years ago,
as a means of
conditioning long-term captives, especially manatees born in
captivity, before releasing them
into the wild.
The cost of maintaining manatees in captivity is high,
and the five major
facilities currently holding manatees must
release some of their
long-term residents to
make room for
sick or injured manatees in need
of veterinary care.
The
soft-release enclosure program has
been a cooperative effort, headed by
the U.S. Fish & Wildlife
Service's Field Office in Jacksonville.
Other cooperators include the National Biological Survey's Sirenia Project, Merritt Island
National Wildlife Refuge, Kennedy Space Center, Florida Department of Environmental Protection, Sea
World, and Save the Manatee Club.
The
work conducted in the enclosure
this past summer could be regarded as a
pilot project to assess: (1) the suitability and safety of the
enclosure design; (2)
if and when manatees in the enclosure would begin feeding on available vegetation; (3) the
impact of manatee grazing on the
vegetation within the enclosure; and
(4) manatee behavior in the enclosure and interactions with those
outside. The Sirenia Project
also conducted PTT transmitter accuracy tests using the
impounded manatees.
Construction of
the enclosure was completed in August. It lies within the Merritt
Island National Wildlife Refuge
and the Kennedy Space Center, and comprises three adjacent pens with a total area of 4.5
acres.
The
first manatee placed in it was a
rehabilitated male who had been in captivity for 6 months. He immediately began
interacting with wild manatees outside the enclosure, and within 5 days was grazing on seagrasses growing inside it. He then received a
companion, an orphaned 3-year-old male,
who was next to the first animal within minutes of his introduction into
the pen. They remained together
constantly at first, but the periods of time
when they were
apart increased in frequency, duration, and distance over
time.
Both
animals were recaptured at the end
of August to be reweighed
and blood-sampled. Neither
had lost or
gained an appreciable amount
of weight. They
were then put back
into separate pens,
and the second manatee
was placed with
another young orphaned male. The first manatee was released
to the wild with a radio tag
on 1 September. He has since stayed in the upper Banana
River, but has not come back
to the enclosure site.
The
other two stayed close together, feeding on
algae and seagrass,
and often interacted with
manatees outside the
fence that were apparently
attracted to the site by the
captives. Both were recaptured
and returned to
Sea World on
15 September. Although they appeared to adapt quickly
to their new saltwater surroundings,
they must be given
ample time to
find warm water sources
before cold weather
arrives. They will probably
be among the first
manatees placed in the enclosure
next spring, and will make good
"mentors" for captive-born manatees that
have never been exposed
to natural conditions.
Comparison of before-and-after aerial photographs and
vegetation maps of
the enclosure should allow a reasonable
estimate of biomass removal.
While grazing impacts were evident, the overall impact on
seagrasses has not been as large as
expected. This may be
explained by the presence of
large amounts of algae (primarily
Gracilaria spp. and
Chaetomorpha), which
the manatees readily consumed;
their tendency to spread out
their grazing activity; and the
possibility that they were
eating less than
normal amounts. We also may
have overestimated their
consumption rate.
This
first trial of
the soft-release program was
encouraging. The enclosure design appears
safe and "manatee-proof," though keeping the structure free of encrusting
organisms and drift
vegetation may become a
problem. Learning by
example from experienced manatees within the
pen, and possibly from wild
ones outside, may expedite
feeding and other behaviors. Grazing
impacts should allow
at least a
crude estimate of carrying
capacity. Grazed areas within
the enclosure should recover
by next summer. Monitoring
of released manatees will still be necessary, to determine if
long-term captives can
find their way to
warm water sources and other
resources used by wild manatees. - Lynn Lefebvre
GERMANY
Manatee Breeding
Successes in Nuremberg. - Recently, my husband and I
visited the zoological
park in Nuremberg, Germany to meet with the veterinarian,
Dr. Anton Gauckler, and observe the West Indian manatees at
their facility. Our
visit was sparked by a concerned visitor's letter to the Save
the Manatee Club regarding
the manatees in the zoo.
The
zoo is located
on 63 hectares within the city limits and is home to approximately 2000 animals from around the
world. The manatees are housed
in the "Tropical House" in an approximately
80 m2 (750 ft2)
by 1.8 m (6 ft) deep
cement/Plexiglas pool. The Tropical
House opened in
1977 and contains other
tropical animals such as the
hippopotamus, tapirs, etc.
In
1979 the zoo acquired a male and female
(both about 2
years of age)
wild-caught manatee pair from
Guyana. On 27 July
1981 the pair gave birth to
their first calf. This
was celebrated as a big event
as this was only the second baby
manatee born in captivity in all of Europe.
Unfortunately the calf was not
accepted by its mother, but was successfully hand-raised. Following
this, 12 calves were born (including two sets
of twins), of which 10 were
successfully raised by the mother. The
other two calves died as a result of
heart degeneration and a condition known as hydrocephalus (an
accumulation of cerebrospinal fluid in
the brain).
The
pool is presently the home of 6
manatees, ranging from
large adults to a
young nursing calf. The others are located
in other zoos or sea life
parks internationally, including
Japan and Singapore. The Nuremberg zoo has found that their animals
thrive extremely well on
an English ray
grass, Lolium perenne, which
they grow themselves on a large farm
nearby. They also supplement
the grass with
corn, wheat, Antibe lettuce, cabbage, and minerals.
The animals are in a freshwater
recirculating pool with a
UV light
as a water disinfectant unit. They do not chlorinate the pools
as numerous facilities in the
U.S. do; thus the
pools have a
patchy slight green algal
growth which is similar to
the natural environment. In
addition, the water is seined in a
decreasing-size metal mesh before going
into the
sand filtration system. As
anyone who has worked with manatees knows,
the voluminous amount of
feces the animals produce is a constant challenge to
filtration systems, and I found
their system to be very efficient.
The
pool appears to be a bit crowded
with the
number of animals it holds.
They have plans to enlarge it into the adjacent tank in the
near future, which should allow
the animals much greater mobility.
They
plan to participate
in genetic studies with Freiburg
University, and when I asked Dr. Gauckler
if he would be interested in participating
in such a
study with the Caribbean Stranding Network and investigators in the United States, he
agreed.
Dr.
Gauckler has traveled to Guyana
and is quite familiar with the animals' natural habitat. He
studied in Munich and Vienna, and has been a zoo veterinarian for
23 years. I would like to thank him for
taking the time to show us the entire
facility and the dolphinarium. This was a spontaneous visit and he spent
several hours discussing at length
the manatee facility and future
expansion plans, as well as numerous veterinary medical
and nutritional aspects of manatees in captivity. - Dr.
Debra P. Moore (Caribbean
Stranding Network, Puerto Rico)
[EDITOR'S NOTE:
Eleven completed pregnancies in
15 years, starting at the age of 2 or 3, is an unprecedented record for a
nursing manatee mother, as is
a pair of twin births in captivity. This report
is doubly surprising as, to my
knowledge, no reports of the births at Nuremberg
subsequent to the first
one have found their way into
even the popular, let
alone the scientific, literature. Artificial insemination was,
however, reportedly used. Further
documentation of this breeding program would be welcome.
I
also note with a certain smug
satisfaction the zoo's dependence on pasture grass as a
source of manatee
fodder. Since our success with raising manatees on this
kind of food years
ago at INPA in Manaus, I have often and unsuccessfully urged U.S.
oceanaria to adopt
this inexpensive expedient. Manatees, in my
view, are designed to run best on ordinary grass (Gramineae) of
various sorts; certainly they keep well on it, and it
has always seemed to me to be a better
and cheaper option than the usual lettuce. Hydroponically-grown grasses
have the apparent advantage of being available
year-round, but somehow the
Nuremberg zoo seems to be
getting a year-round supply of
farm-grown grass even at
the temperate latitudes
of Germany! Again, more details would certainly be welcome.
Finally, can any correspondents fill
us in on the
previously unreported manatee facility in Singapore?]
MADAGASCAR
Status and Exploitation of
Madagascar's Coastal Marine Resources. - In an effort to assess
and monitor the coastal zones of western
Indian Ocean states, the Centre for Dolphin Studies - Port Elizabeth
Museum (CDS-PEM), South Africa, began in
1991 a cooperative, long-term
program of coastal zone
research and monitoring of the
southwestern Indian Ocean region. Primarily, this work
is aimed at determining,
through the status of
marine mammals and
reptiles in particular, the
'health' of the coastal
zone systems of western
Indian Ocean
states. Circumstantial evidence suggests a decline in numbers
of these species in almost all
areas, possibly due to
coastal zone degradation, including the
increased use of
gillnets by artisanal fishermen.
The CDS-PEM has so far undertaken or planned limited
preliminary studies in Mozambique, Kenya and Madagascar.
The
uniqueness and diversity
of Madagascar's terrestrial biota
are well
recognized, and an immense amount of
effort and money is spent educating Madagascans in its value and the
need for its conservation. In
contrast, little thought is given
to the
fauna and flora of the coastal marine
environment, which is equally
diverse and deserving
of conservation.
CDS-PEM conducted
a preliminary investigation of
these resources in
August through November of 1993.
Time, financial and language constraints precluded a survey of the entire 4500 km of Madagascar's
coast. Nevertheless, observational, anecdotal
and incidental data were gathered from
individuals and organizations
in as many areas
as possible.
Primary survey effort
was restricted to two areas:
- The
west coast, especially the southwest,
where most turtle hatcheries occur and there are
also extensive seagrass beds,
a known food of
both dugongs and
turtles. Also, though the
Toliara region has
a relatively high human population and the coastal
zone is, therefore, quite
heavily exploited, the west
coast generally has
a lower human density and probably less
exploitation.
- An area on the northeast coast, the Masoala
Peninsula, provided comparative data for a relatively unpopulated area on the
east coast.
The
two areas differ greatly in
oceanographic and climatic
features. The Toliara region is
semi-desert, with a
coral barrier reef. Mangroves
occur throughout, but are concentrated near river mouths. The
Masoala Peninsula is covered
in coastal lowland rain forest. Coral and mangroves are found on
both sides of
the peninsula, the
latter principally bordering river mouths.
Information gathered by an interview survey indicates that dugongs occur only on the west and northeast coasts of Madagascar, though their distribution appears
to be highly fragmented and not
continuous.
On
the west coast, fishermen report seeing a group of about 5 to 10
dugongs in an area approximately 100 km south of Toliara. However, in the
Toliara region itself,
dugongs have not
been seen since
the mid-1960s and young fishermen do not know the Malagasy word for dugong.
Fishermen report
that six dugongs were
caught in October 1992 in
Morombe, approximately 200 km
north of Toliara, though there
are apparently no
dugongs between the two
areas. Though the
coast north of Morombe, as far
as Mahajunga, is isolated and relatively uninhabited,
fishermen report the existence
of extensive seagrass beds and
there are confirmed
reports of dugong captures in
Soalala. One dugong was captured in the
Mahajunga region in 1991. For the coast between Mahajunga
and Diego Suarez there is little
information, as this area is also sparsely
populated and seldom
frequented, even by tourists (the exception is the popular resort at
Nosy Be). Nevertheless, the northwest
coast is characterized
by large sheltered bays,
apparently with extensive seagrass meadows.
There
are no recent reports
of dugongs on
the east coast
between Fort Dauphin and Tamatave.
Divers and tourists report sightings of two dugongs at Isle Saint Marie,
north of Tamatave, prior to
spring 1992, but there
are no recent
confirmed sightings. No information is available for the area
between Tamatave and
Maroantsetra, but the area is
relatively densely populated, suggesting that dugong occurrence is unlikely.
Between Maroantsetra and Antalaha, fishermen rate
dugongs as abundant,
but report that their numbers
are declining, and attribute their
apparent decline to
fishing pressure (F. Odendaal, pers. comm.). There has
been only one
reported recent (since 1992) dugong capture from the
villages visited on the Masoala Peninsula. However, prior to 1992, there were many reports of dugong captures. In
Ambohitralana, up to
two dugongs per week were caught until
1990, but only one subsequently (December 1993). Most
recent sightings for the
area are
from the Bay of Antongil and Cap Est.
Dugongs are also reported north of Antalaha,
up to Diego Suarez, with a confirmed sighting
in the Bay of Diego Suarez.
Large seagrass beds were found in both the southwest and northeast regions. Seagrass generally occurs at depths of about 1-10 m. In the Toliara region, four species were identified, Thalassia hemprichii, Thalassodendron, Syringodium isoetifolium and Cymodocea sp., although other species are known to have occurred. Seagrass beds generally occur between the coral reef flat and the shore and none were observed outside the reef areas in the Toliara region. On