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: 1-202-265-7055). It is
supported by the U.S. Marine Mammal Commission
and Sea World, Inc.
NUMBER 25
APRIL 1996
IN THIS ISSUE: - MASSIVE MANATEE
DIEOFF IN FLORIDA (p. 6)
-
ON CULTIVATION GRAZING BY DUGONGS (p. 8)
-
WHEN SEACOWS WALKED ON FOUR LEGS (p. 10)
EDITORIAL: BAD NEWS OR GOOD?
Several significant
developments for Florida
manatees have occurred since
our last issue. One is the
publication of the workshop volume on manatee population biology edited by Tom
O'Shea, Bruce Ackerman, and Franklin Percival (see
Recent Literature, below).
The upshot of the two decades of painstaking work
summarized in this impressive
compilation is that Florida
manatees actually seem to have increased in numbers since protective
efforts were begun. At
the end of
the volume, O'Shea and Ackerman
conclude that "the
increases in numbers of manatees
counted in aggregation areas in winter reflected an increase in the Florida
population from the
1970's through the 1980's .... We are uncertain whether
such a trend continued in the
1990's." Furthermore, "Reproduction parameters revealed by
studies presented in these proceedings ... indicated the potential for
more rapid growth than previously recognized": as high as 7% per year at
Crystal River. "This higher potential for
population growth makes the probability of true population growth in
other areas during the 1970's and 1980's more plausible than previously
thought...."
These conclusions
were promptly underlined by the results of
two statewide aerial surveys conducted by the Florida Department of Environmental Protection
after cold fronts in January and
February 1996: total counts of
2,274 and 2,639 manatees, respectively. These numbers are
dramatically higher than the previous high count of 1,856, made in 1992;
and as minimum estimates
of actual manatee abundance, they show that the true population
size is
closer to 3,000 than to the figure of
2,000 routinely quoted in recent years.
Although survey coordinator
Bruce Ackerman noted in a press release that weather conditions nearly perfect
for
counting manatees accounted
in part for this result, the evidence
for a growing manatee
population seems to be mounting.
What are
we to make of this? Is the manatee population on the road to
recovery and removal from the
endangered species list? Have all the protective regulations had their desired effect, so that no further constraints on boaters or developers are
needed? If manatee numbers have grown along with human numbers in Florida,
does that not show that human
population growth is harmless
to wildlife, maybe
even beneficial? Was the
whole uproar over
the supposed plight of the manatee in fact just an environmentalist hoax
to begin with? Or (to put a more charitable face on it) is this a demonstration
of the self-correcting nature of science in the light of new data?
Before jumping to any of these conclusions, we
should read more of what O'Shea and
Ackerman had to say: "Possible increases in manatee population size since
the mid-1970's may be attributable to
intensified conservation. However, the threats to manatee
survival and habitat loss
have accelerated and
are expected to increase. A turning
point may soon
be reached, if it
has not already. This contention
is supported by the
possibility that upward trends in counts at power plants
in winter may have diminished in the late
1980's and early 1990's ...; by the
lack of a notable increase of
counts and a higher number of
deaths in southwestern Florida
...; by the high number of recovered carcasses in 1994 [plus a still higher
number in 1995 and a disastrous start to 1996 - see other news in this issue];
and by increased numbers of boats and the more complex technology of
high-speed boating.... Because of the lack
of accuracy and precision in estimates of population size, the size of
the Florida manatee population could decrease even while counts may seem to
increase or be stable.... Given that negative effects on manatee
populations will continue to
increase with burgeoning
human populations in Florida and that decreases in adult mortality can
result in growth and long-term
persistence of Florida
manatee populations ..., no prudent alternatives exist
to maintaining proactive,
vigorous management aimed at mortality reduction."
In short, the catch is
that even if the manatee population has grown under the protection it has
received, we are
rapidly approaching the
limits of the
protective measures now envisioned. The legally-mandated
Manatee Protection Plans are already in place in at least four of the 13
Florida counties considered critical for manatee protection, and further
tightening of regulation beyond
what is in these plans is likely to be strenuously opposed. Meanwhile,
the numbers of humans,
boats, and new
developments continue to grow without
limit. An aggressive manatee-protection campaign has bought the population valuable
time, but the onslaught of demography will soon throw the manatee and its allies
back on the defensive, facing
ever-grimmer odds. The population recruitment suggested by the latest synoptic
surveys may still prove to have been no more than reinforcements thrown into a
losing battle.
The shape
of this battle is already
evident to those who read the published
evidence more closely. O'Shea
and Ackerman cite "data ... that suggest substantial population
growth from internal recruitment
at the Crystal River and at
Blue Spring and
slower growth or stability on the Atlantic
Coast...." These
preliminary results show,
in other words,
that manatees have increased in precisely those areas where
they are most strictly protected,
but may have been unable to do
so where boating activity and boat-caused mortality are heaviest. What we see here, in fact, is an inadvertent experiment
to determine what level
of human harassment manatee populations can tolerate. The
results neatly demonstrate both their
ability to flourish, given reasonable protection, and (more
realistically) their likely inability to survive much longer, as the worst that
Florida is presently throwing at them worsens still further.
This was
not, however, the message that
was reaching the public in the wake of
the 1996 synoptic surveys. As manatee researchers anticipated
when the State of Florida
began these surveys several years ago, they are two-edged weapons. While
it is always useful to have minimum counts to plug into population models, the
danger is that these minimum counts
will be taken as
actual estimates of
population size, and
growth in these
numbers will be misinterpreted as actual growth in
population. They are in fact being misinterpreted this way in the Florida
press, by boating advocates and others, and some have
even begun to call for downlisting of the Florida manatee to a
less endangered status.
The issue of downlisting should, in principle,
be easy to dismiss. The revised Florida Manatee Recovery Plan (1996
version, due to be published in a few
weeks) states that "downlisting should be considered when
... the population
is growing or
stable, when mortality factors
are controlled at
acceptable levels or are decreasing,
and when critical habitats are secure and threats to
them are controlled or decreasing." Of these three criteria, it is
obvious that the latter two are not likely to be met in the
foreseeable future: human-caused mortality continues
to rise, and the threats of human population
growth and development pressures are
anything but "controlled or
decreasing." In practice,
however, only the
first criterion readily registers in the public consciousness, where
higher manatee counts necessarily mean a recovering population.
Sometimes, however,
one problem is solved by another; and
the misleading press coverage of the January and February
surveys was fortuitously swept from the headlines by the disastrous manatee
dieoff in March. For the moment, this antidote
of well-founded alarm seems to have taken effect, but spells
of complacency are bound to recur. When they do - and whenever any of us
has occasion to communicate with the public or the mass media on
these issues - we need to emphasize as strongly as possible the
following points:
1. The statewide synoptic surveys provide
only minimum counts, not estimates of
the total population; they
are extremely sensitive
to weather conditions
and cannot be compared statistically with each other
or with estimates
derived from other techniques.
2. While it
is possible that the total manatee population in Florida has
increased, it is more certain (and more significant) that increases have
occurred in precisely those areas where manatees are best
protected, while in areas of lesser protection there has been little or no increase (and none that is likely to be
sustained).
3. We can take no comfort in
any numerical increases that have been achieved, because the protective measures
that made them
possible are approaching
the limits of political acceptability, while the
threats to manatees
only increase and
can be expected to
wipe out the recent gains. For
this reason, no talk of
downlisting the Florida manatee
is even remotely justified.
4. The manatee
population is still small in
absolute terms, and always
vulnerable to unexpected
catastrophes like the March 1996 dieoff - especially when, as in this case,
the victims are predominately adults in their prime, which are
the animals most essential to survival of the population. When some 2% of that
population can be wiped out in one such event - over and
above all other sources of mortality - there
is ample cause for concern about the species' future.
Not all these points are easy to make in sound bites, but
this is the message we
urgently need to get out. - DPD
DEATH REPORTED
Jesse R. White, D.V.M.
Dr. Jesse White,
well-known marine mammal veterinarian, died on 23 January 1996 at his home in Dunnellon, Florida, at the
age of 61 years. A native of Oklahoma, he received his D.V.M. degree
from Texas A&M University at College Station in 1962. He served as
Staff Veterinarian at the
Miami Seaquarium, 1967-86, and Marine Mammal Veterinarian for the Florida Department of Natural Resources,
Homosassa, Florida, 1986-87. In 1984, he
founded the Florida Manatee Research and Education Foundation, an
organization for which he always served as
Director and President. He was an Adjunct Professor at the College of
Veterinary Medicine, University
of Florida, 1983-87, and Clinical Professor in the Department of Small Animal Medicine at the
same institution from 1987 until
his death. He
received several lifetime
achievement and conservation awards from professional associations, and was the
first veterinarian to serve
on the U.S. Marine Mammal
Commission's Committee of
Scientific Advisors. His publications focused on manatees and marine
mammal care and maintenance. He was particularly interested
in captive breeding of manatees, and it was during his tenure at the
Miami Seaquarium that
the first successful
and regular breeding
of captive Florida manatees began. (John
R. Twiss, Jr. and DPD)
SHOULD THE SIRENIA SPECIALIST
GROUP ESTABLISH A HOME PAGE
ON THE WORLD WIDE WEB?
A couple
of weeks ago,
I attended a
meeting of the
IUCN Species Survival Commission (SSC)
Steering Committee which was held in Australia. I was invited to
attend the meeting as
an observer along with other Specialist Group Chairs from
the region. The Australians enjoyed being the only delegates not suffering from jet lag, a
reverse of the usual situation.
The issue
of communication among and within Specialist Groups was discussed.
The SSC is planning
to set up a home page on the World Wide Web which will concentrate
on being a link among the home
pages established and maintained by various
Specialist Groups. This
initiative raises questions for the Sirenia Specialist Group:
_ How many members would have access to a Sirenia SSG home page on the
World Wide Web if one were established?
_ Is there anyone who is
prepared to establish and maintain such a page?
The page would have many advantages. Here are a few:
_ It would be a source of
up-to-date information on manatees and dugongs.
_ It would be an additional
method of distributing this newsletter.
_ It could enable Group
members to access the gray literature and
publications lists of other members, etc.
_ It could be an effective
method of distributing the Dugong and Manatee Action Plans when they are
finalized.
I do not see a Sirenia Specialist Group home page duplicating the role of
MARMAM.
Your reactions, please;
and is there a volunteer who is willing to establish and maintain the
page? - Helene Marsh
NIRS BREAKS THROUGH SIRENIAN
FOLIAGE
The conventional methods used for
analyzing nutrient contents
of seagrasses are laborious and expensive. This is essentially why most studies dealing
with sirenian and/or seagrass nutritional ecology have
limited numbers of replications. This may now be a thing of the past.
Near-infrared reflectance
spectroscopy (NIRS) has been in
use for the
analysis of agricultural and
food products since the late 1960's. This technique
makes use of a small segment of the electromagnetic
spectrum (just above the visible region, 700 nm to the edge of the
infrared region, 2500
nm), called near-infrared (NIR). The NIR
spectrum contains information on
the major building blocks of the biological world (CH, OH, and NH groups).
I applied this technique in my research
entitled "The ecology of seagrasses as food for dugongs and green
turtles" at James Cook University. It allowed
me to predict multiple
constituents of seagrass
relevant to a dugong's (and green turtle's) perspective, for a
large number of samples
(ca. 1,200, which
would have been
expensive and laborious
using conventional
methods). This technique
allowed me to
select the "best" (most typical)
calibration set (15-20% of the total),
based on the population's spectral variability, for which precise conventional nutritional/chemical analyses
were performed. These
calibration data were then used for the development of predictive
equations for each constituent using a
cross-validation technique. The
predicted values have a good agreement with the laboratory values. The
r² values for the different constituents were: 0.99 for nitrogen,
0.96 for organic matter, 0.94 for neutral detergent fiber, 0.91 for acid detergent fiber, 0.90
for lignin, 0.91 for water-soluble
carbohydrates, and 0.92 for in vitro
dry matter digestibility.
NIRS analysis
offers several advantages. It is rapid,
nondestructive, and
environmentally safe. One
of its most important features is that it can analyze samples
for multiple constituents. Even though this technique has existed for
more than 20 years, it
has never been employed in nutritional
ecology of wildlife. This technique will certainly simplify the task of
trying to understand why sirenians prefer certain species of
foliage. - Lem V. Aragones
COURSES ON ZOO ANIMAL BEHAVIOR
AND WELFARE
Edinburgh Zoo,
in conjunction with the University of Edinburgh, is again offering
a two-week summer school
course from 15 to 26 July
1996 on Zoo Animal Behaviour
and Welfare. It is designed for
all those involved in management and husbandry of captive animal populations, and
will update participants on the latest
scientific theory and
its practical
implementation. Registration deadline
is 31 May 1996.
A new two-module short
course on Assessment and Implementation of Animal Welfare Programmes
will also be
offered on 1-3 November and
6-8 December 1996.
(The first weekend module will
cover scientific assessment of animal welfare; the second, animal welfare in
practice.) Covering aspects of the new Royal College of Veterinary Surgeons'
Certificate in Animal Welfare, Ethics
and Law, this course will introduce the current scientific methods that are used to assess and understand
animal welfare and demonstrate how these can be practically implemented.
For information
on either course, contact Hamish Macandrew, UnivEd Technologies
Ltd., FREEPOST, 16 Buccleuch Place,
Edinburgh EH8 0LL, UK; tel.: 0131-650-3475;
fax: 0131-650-3474.
LOCAL NEWS
AUSTRALIA
Dugongs Take Years
to Recover From Seagrass
Loss. - Preen and
Marsh (1995) report dugong
deaths associated with the loss
of some 1000 km²
of seagrass in Hervey
Bay, Queensland, Australia,
following a flood and two cyclones in 1992. Aerial surveys have been used to track the resultant changes in dugong numbers in the region.
The surveys suggest
that the decline
had ceased by 1993:
Date Population Estimate
1988 2206 ± s.e. 420
1992 1109 ± s.e. 383
1993 579-629 ± s.e. 126
1994 807 ± s.e. 151
However, calf counts
associated with the surveys suggest that the population
may take even longer to recover than originally
predicted.
Date % Calves
1988 22
1993 2.2
1994 1.5
These figures parallel changes in the pregnancy rate and proportion of reproductively active males in Torres
Strait dugongs coincident with
an extensive seagrass dieback in
that region in
the mid-1970's (Marsh 1995). Data from Australia
suggest that large-scale diebacks
of tropical seagrasses, often associated with extreme
weather events such as
floods or cyclones,
are relatively common (Poiner
and Peterken, 1995).
In addition to any direct mortality of
dugongs associated with such
diebacks, their impacts on the life
history of dugongs in the affected
area is likely to be serious and
long-lasting. The only data I know of concerning temporal changes in the pregnancy rates of
manatees are from Marmontel (1995), who provides
evidence that suggests an increase in Florida from 1976 to 1991.
Does anyone
else have any
data suggesting temporal changes
in the life history parameters of sirenians?
References
Marmontel, M.
1995. Age and reproduction in Florida
manatees. In: T.J.
O'Shea, B.B. Ackerman, and
H.F. Percival (eds.). Population biology of the Florida manatee. Information &
Technology Report (U.S. Dept. Interior, Natl. Biological Service) 1:
98-119.
Marsh, H. 1995. The life history, pattern of breeding, and population dynamics of the dugong. In: T.J.
O'Shea, B.B. Ackerman, and H.F.
Percival (eds.). Population
biology of the
Florida manatee. Information
& Technology Report
(U.S. Dept. Interior, Natl.
Biological Service) 1: 75-84.
Poiner, I.R., and C. Peterken. 1995. Seagrasses. In:
L.P. Zann and
P. Kailola (eds.). The
state of the marine environment report
for Australia. Technical Annexe: 1. The marine
environment. Canberra,
Australia, Dept. of Environment,
Sport and Territories.
Preen, A., and H. Marsh. 1995. Response of dugongs to
large-scale loss of
seagrass from Hervey Bay, Queensland, Australia. Wildlife Research 22: 507-519.
- Helene Marsh
CARIBBEAN REGION
Manatee Plans and Materials Being Developed. - The regional
management plan for the West Indian Manatee in
the Wider Caribbean was approved
at the Third Meeting of the Interim
Scientific and Technical Advisory Committee
to the Protocol Concerning Specially Protected Areas and
Wildlife (SPAW) in the Wider Caribbean Region (Kingston, Jamaica,
11-13 October 1995). The
plan will be
published in English, French, and Spanish.
The Caribbean
Environment Programme is also
supporting the preparation of manatee
recovery plans in Belize, Colombia,
Honduras, Mexico, Suriname,
Trinidad and Tobago, and Venezuela, and
the development of educational activities on manatee conservation in
Belize, Jamaica, Mexico,
and Suriname. It
is also producing
a number of educational materials for children
in English, Spanish, and French on
manatee conservation as part of a region-wide public awareness and
education campaign. A
number of these products (poster, coloring book,
and bumper stickers) are
available, as is a directory
of manatee experts and
institutions from the Wider
Caribbean including Brazil.
Address: Regional Coordination Unit for the Caribbean Environment Programme, 14-20 Port Royal Street, Kingston, Jamaica;
tel.: 1-809-922-9267/9268/9269; fax:
1-809-922-9292. - (Source: The
Pilot [UNEP], No. 13.)
FLORIDA
Major Manatee Dieoff in
Southwest Florida. - Beginning 5 March 1996, fresh manatee carcasses began turning up in southwest Florida between Englewood
and Marco Island. The animals were large adults, and the only gross
abnormality was a diffuse
bilateral pneumonia. By 10 March,
as many as four carcasses were
being reported per day.
By the 13th there were reports of
11 deaths in one day, and
the Florida Department of Environmental Protection's (DEP) Marine
Mammal Pathobiology Laboratory in St. Petersburg, which was handling
the necropsies, moved its
operation to a
field station on Sanibel Island
to process the carcasses
more efficiently. As of 4
April, the total number of
carcasses reported in the area since 5 March
amounted to 110, with
the total continuing to
mount as this
went to press. Even if a few of
these turn out to have died from causes
other than that of the majority,
this will still easily rank as by
far the largest single mass mortality of West Indian manatees in recorded history.
All of the carcasses
so far necropsied were in good
flesh; none had any indication of cold stress and all had pulmonary
lesions characterized as
diffuse, bilateral discoloration of purple and bright red
on the
serosal surface of the lungs. On a cut surface, the lungs
were congested and bled. In
the more severe cases, the
primary airways were filled with a
serosanguinous exudate that
was adherent and occluded the secondary airways. In the
less severe cases, the
airways were open, but
the pulmonary parenchyma
appeared the same in all cases
and there was a conspicuous absence
of inflammation. All other organs appeared grossly
normal. Death was rapid
and the result of pulmonary
failure.
The vast
majority of animals
were large (275 cm or more); the smallest were 191
cm and there were no
perinatal-sized animals
involved. At least
seven animals were pregnant. Tunicates were not observed in
any of the GI tracts.
Microbiological results indicated a diversity of bacteria that, in the absence of an inflammatory
response and of consistency between cases, were
considered secondary to the event.
Following the
guidelines of the Marine Mammal Protection Act, the
Florida DEP has requested technical advice from the Working Group for Unusual Marine Mammal
Mortality Events. In addition to State biologists,
Federal scientists from the U.S.
Fish and Wildlife Service,
National Biological
Service, National Marine Fisheries Service, and Armed Forces Institute of
Pathology are cooperating in the response to the dieoff, as well
as scientists from
the University of Florida, University of Miami, Miami
Seaquarium, Sea World, and Erasmus University in The Netherlands.
In 1995, Florida reported a total of 201 manatee deaths. This year, 200 have died in Florida's waterways in little more
than three months.
The same
area of southwest Florida was
the scene of another mass mortality
in 1982 in which some 37 manatees died. These deaths were
traced to ingestion of tunicates that contained red-tide organisms. That outbreak included cases of manatees behaving abnormally,
and some animals recovered; but in this case there have been no reports of sick
or strangely-acting manatees,
only deaths. Although
the 1996 incident
has coincided with a
red tide that has killed sea
birds and other marine animals, preliminary screening of manatee blood for red-tide
toxins has been negative. Neither have
any of the other analyses so
far produced any
conclusive evidence of a cause.
On 1 April,
researchers captured six manatees in the area of the
dieoff and extracted
blood from them
in an attempt to obtain a
control group of live
animals with which to
compare analytical findings from the
carcasses. For instance, if the
live animals have been exposed to the disease, they might
show unusual blood
cell counts or perhaps antibodies. Alternatively,
whatever is causing the disease
may be present in
the control group's blood but
for some reason absent from the blood of
the animals that have
died. Passive Integrated
Transponder (PIT) tags were also placed in the
captured animals, so if any of them turn up dead in the near future, they could provide insight
into the incubation period if an
infectious disease is to
blame, or possibly
give other clues about the cause of death. At this
time a viral infection is
considered a likely
culprit, but unusual bacteria
and natural or
man-made toxins have not
been ruled out.
(Source: Florida DEP)
Award and New Job for Pat Rose. - Patrick M. Rose, who has
headed the Florida Department of Environmental Protection's (DEP)
manatee program for the
past twelve years, was
recently the recipient of a 1995 special edition National Conservation Achievement
Award sponsored by the
National Wildlife Federation (NWF).
This award
recognizes contributions
made by dedicated public servants
in the cause of conservation.
Recipients are selected by the Awards Committee of the NWF Board of Directors.
Pat has
long been known
for his aggressive championing of boat speed zones and
other protective regulations on behalf
of the Florida manatee, and has borne the brunt of many hard-fought
intra-agency political battles,
as well as much bitter public criticism incurred in the course of
regulatory controversies. To
him belongs much of the credit for
the great success DEP has had to date
in enacting manatee protection.
Pat instituted
the Florida Audubon Society's manatee program, then
became the U.S. Fish and Wildlife
Service's first Manatee Coordinator,
before starting DEP's manatee
program. He is
also a noted manatee
photographer, and his still and motion pictures have
appeared in many publications and films.
In recent
weeks he has left DEP
to become the new
Director of Government Relations for
the Save the
Manatee Club, which has
opened a new satellite office
in Tallahassee in order
to become more
involved in advocacy
for stronger manatee protection. Pat's dedication and government experience will be major assets
to this effort, and his
many friends and
colleagues are happy that his talents will not be lost to
the cause of manatee
conservation. (Sources: DEP, Save the Manatee Club Newsletter)
Save the Manatee
Club Goes Online. -
Visit the Save the Manatee Club's new
web site! Facts about manatees, information about the Adopt-A-Manatee program (including an online adoption
application), and materials for
educators are all featured. Address: http://objectlinks.com/manatee.
GERMANY
More on Manatee Breeding in Nuremberg. - A letter to the
U.S. Marine Mammal Commission from
Dr. Peter Mühling,
Director, Tiergarten Nürnberg, supplements the information reported in Sirenews No. 22. He reports that
between 1981 and 1995, 14 manatees in two generations were born at his zoo,
including two births
of twins. The founding stock came from Guyana.
The manatee pool is 1.6 m
deep with a surface area of some 50 m² (not
including an island). The
manatees often rest in
the shallow areas, while ducks
in the
enclosure rest in turn on the manatees' exposed backs.
No behavioral
problems have been observed, even with up to ten manatees
in the pool at once.
As of June 1995, only
four animals were still
held, the others
having been transferred to the
Arnheim Zoo, Tierpark Berlin, Singapore Zoo, and Seapalace in Japan. Plans are
now underway to enlarge the manatee
pool and make more room for
continued breeding.
INDONESIA
Cultivation Grazing by Dugongs in the Moluccas. - From
1990 to 1995
we studied the interactions between seagrasses and
dugongs in the Moluccas, East Indonesia. This project was a collaboration
between the Pattimura University at Ambon, LIPI Jakarta/Ambon and The Centre for Environmental Science of Leyden University, The
Netherlands. We found
convincing evidence that dugongs practice "cultivation
grazing."
Preen (1993) postulated that seasonal nutritional stress in subtropical areas, and
a response to this stress by "cultivation grazing,"
would be major factors in the observed
difference in dugong herd size between tropical and subtropical areas.
An impact of environmental
stress on herd size has also been
observed for terrestrial herbivores.
Increased densities of African elephants caused
by restriction in available habitat led to an
increase in group
size (Laws, 1975). According
to Preen (1993, 1995), "cultivation"
grazing occurs when herds
of dugongs forage
intensively in an area,
effecting a high
level of seagrass removal over a large area.
"'Cultivation' grazing allows dugongs to improve the quality of their diet
by one or more of the following: (1) maintaining the
meadow at a younger, actively growing
stage, so the
seagrasses contain less fiber; (2) converting the meadow to a lower seral stage composed of preferred and nutritionally superior
seagrasses; and (3) concentrating the
regrowth vegetation into areas
that can be
efficiently cropped. The nutritional benefits of these modifications
to the seagrass meadows would maximize the fitness of individual dugongs." McNaughton (1979) postulated that the
fitness benefits gained by
individual animals through
increased foraging efficiency
could lead to the development of
herding behavior in
ungulates. According to Preen
(1993, 1995), due to their mode of
feeding, these benefits could only be
achieved if the dugongs fed in large
herds.
Preen (1993, 1995) also
stated that in tropical areas,
the benefits of
cultivation grazing may not be necessary, or relevant, in which case there may be no pressure to feed in large herds.
The conclusions of Preen (1993, 1995) are contradicted by the
findings of our study, since we observed concentrated feeding
plots inside both
intertidal and subtidal seagrass meadows in the
Lease Islands, caused by
cultivation grazing practice
by small herds of dugongs (2-6 animals). These small herds could
sufficiently disturb the seagrass bed, through a dense
grazing pattern, to
maintain monospecific meadows (Halodule uninervis and Halophila
ovalis) of low standing crop.
The principal
effect of cultivation grazing in an intertidal
multispecies meadow in our study area (Nang) was the creation of monospecific Halodule uninervis pioneer meadows surrounded by multispecies associations. This
pattern of grazing,
similar to patterns described
for Moreton Bay by Preen (1993, 1995),
leads to the spatial containment of
less favored species, like (in
our study) Thalassia hemprichii and Cymodocea rotundata.
The principal
effect of cultivation grazing in a subtidal monospecific Halodule
meadow in our study (Haruku) was a higher in vitro digestibility inside the
grazing plots, compared with the
undisturbed meadow. This phenomenon has not been described by Preen (1993, 1995) for Moreton Bay. Cultivation grazing in monospecific meadows results
in patches with lower standing
crop, but with a higher in vitro
digestibility, indicating a feeding strategy along a productivity
gradient as described by Van der Koppel et al. (1995).
During our study we have identified at least
five permanent feeding
plots with concentrated, regular patterns of recropping by dugongs. We concluded that
dugongs in these plots
grazed in facultative feeding assemblages
with loose social
interaction rather than in fixed
herds with strong social bonds. Cultivation grazing benefits all
individual dugongs through an
increased rate of digestibility and
energy intake, but lowers the amount
per bite and overall
biomass in the grazing plots.
With a computer model
we calculated the maximum
sustained population size for Haruku
Strait as 11 dugongs. With a
maximum sustained number of 90 dugongs and the estimated minimum population of 22-37 dugongs for the study area,
the quantity of the available seagrass
in combination with mortality from accidental capture
by man may be major factors
determining population size, but
seagrass quality seems to determine
herd size and dispersion.
A "cultivation" effect similar to
that observed for small groups
of dugongs in the present study
has been observed for
small herds of manatees in
Florida (Lefebvre and Powell, 1990). Florida manatees, with muzzles less
specialized for bottom feeding, do not produce feeding trails in the
manner of dugongs. Instead,
when they feed
on seagrasses, they crop
circular patches (mean 27 m²).
Interestingly, there is some evidence
that they return to the same patches in subsequent years.
Our study confirms that the
practice of recropping permanent
grazing plots through cultivation grazing is moreover part of
a permanent evolutionary pattern of adaptations of the dugong
as a species in response to
its low-quality forage, rather than a
temporary response to seasonal
nutritional stress as postulated by Preen (1993, 1995).
References
Laws, R.M. 1975.
Elephants and
their habitats. Oxford, Clarendon
Press: 1-376.
McNaughton, S.J. 1979.
Grazing as an optimization process:
grass-ungulate relationship in
the Serengeti. Amer. Nat. 113(5): 691-703.
Preen, A. 1993.
Interactions between
dugongs and seagrasses in a
subtropical environment.
Ph.D. thesis, Dept.
of Zoology, James Cook Univ.,
Australia: 1-265.
Preen, A. 1995. Impacts of dugong
foraging on seagrass habitats:
observational and
experimental evidence for
cultivation grazing. Marine
Ecology Progress Series 124:
201-213.
Van der Koppel, J., J. Huisman, R. Van
der Wal, and M. Olff. 1995. Patterns of herbivory along a gradient of primary
productivity: an empirical
and theoretical investigation. Ecology (in press).
- Hans De Iongh (Centre
for Environmental Science, Leiden
University, The Netherlands)
[EDITOR'S NOTE: I
strongly suspect that production
of feeding trails is a function
of seagrass and substrate type
and density, not of degree
of muzzle specialization. If seagrasses are sparse, delicate,
and easy to uproot,
a sirenian can
maintain headway while removing most of the biomass, thereby
producing a trail
during a single dive.
If the foliage is thicker and/or the
rhizomes are harder to dig out,
only a small patch
can be cleared during a
single feeding bout (dive), and there is no
reason for patches cleared on
successive dives to be linearly aligned, so a large circular
feeding scar results. If
manatees were observed feeding on (e.g.) sparse Halophila beds, they might be found to
make trails too!]
PREEN RESPONDS: It
is very pleasing that
cultivation grazing has
been documented from a tropical area, and that the process seems identical to that in subtropical Moreton Bay,
where I did my
study. The only substantive differences appear to be the size
of the dugong herds and the size
of the cultivation patches.
In Moreton Bay
the median herd size
was 140, and
cultivated areas were up to 75
ha within 11,054 ha of seagrass. In Hans De
Iongh's study, the herds
were 2-6 dugongs and the study
area (Nang Bay) was 6 ha.
Hans has misunderstood the
nature of cultivation grazing in Moreton Bay. It is not "a temporary response to
seasonal nutritional stress." Rather,
I speculated that
seasonal stress may necessitate
cultivation grazing (and omnivory; Preen, 1995, Jour. Mamm. 76:163-171) by
dugongs when they live at the extremities of their range.
However, this is not to suggest that cultivation grazing
(or omnivory) are seasonal in
Moreton Bay, as they are not,
or to imply that cultivation grazing could
not occur in
more tropical areas. Indeed, in the Gulf of Carpentaria, in northern
Australia (15.5° S), I have subsequently found that large herds
of dugongs persistently feed
in the same locations for extended periods, and that
they appear to return
to these areas, perhaps on an
annual cycle.
Interestingly, in
this area that
is overwhelmingly dominated by an
abundance of dense Syringodium isoetifolium, the dugongs feed more
in the manner described for manatees. Rather than
forming feeding trails, they
tend to form small oval feeding patches (ca. 30 x 50 cm) from
which they remove only the leaves. These patches grow and coalesce, and eventually very
large areas are substantially denuded. It is
only after most of
the shoots have been
removed that they start
removing substantial amounts of rhizomes. The extent to which this
grazing favors species like
Halophila ovalis and Halodule uninervis depends on the extent to which
the rhizomes of Syringodium are removed. Mere cropping of the leaves results in a
rapid and vigorous
shooting by the Syringodium. - Tony Preen
JAMAICA
The World's
Most Primitive Seacow. - With support
from the National Geographic Society, I have been working in Jamaica
for the last three
years, collecting fossils of Prorastomus,
the oldest and most primitive sirenian known. A site in
the hills south of Montego Bay,
originally discovered by Roger Portell of the Florida Museum
of Natural History, is
yielding abundant postcranial bones of this Early to
Middle Eocene animal, which was previously known almost entirely from a single skull found at
another Jamaican site in the 1850's. Assisting Portell and myself in the field are Steve Donovan of the
University of the West Indies,
Kingston, Jamaica, and Kevin
Schindler of the Lowell
Observatory, Flagstaff, Arizona.
The new material may represent
a new species distinct from the type
species P. sirenoides.
In addition to numerous ribs (which are typically sirenian
in their bulk and density) and vertebrae, we have found a
scapula, two humeri, an ulna, several pelvic bones, three femora, a tibia, a metapodial, a
phalanx, and several skull elements and
teeth. Much of the material
collected remains to
be prepared, and probably includes still other parts of the skeleton.
The appendicular bones of
these pig-sized, 50-million-year-old seacows resemble those of land mammals
far more than
do bones of Protosiren, the next most
primitive seacow known. Since
even Protosiren retained well-developed hind limbs and
was obviously amphibious, it
seems that prorastomids were even more capable of terrestrial locomotion,
although their aquatic
adaptations (retracted nasal
opening, dense ribs) indicate that most of their time was spent in the water. They still
possessed two or more sacral
vertebrae that were
connected to the pelvis, but these
vertebrae were not fused to each other,
indicating a degree
of spinal flexibility
comparable to that of early whales
like Rodhocetus. Prorastomids also
seem to lack an enlarged tail like that of later
sirenians, so they may have used the hind limbs to swim, like the
primitive whale Ambulocetus.
Further fieldwork is
planned, and as collecting and preparation proceed, we
expect to rapidly learn more about the
anatomy and lifestyle of this true "missing link"
between land mammals and sirenians.
- DPD
MEXICO
Manatee Rescue in Chiapas.
- One of the most important areas for
manatees in Mexico is
the Usumacinta River
and its basin, with
streams and many lakes, in the states
of Chiapas and Tabasco. The
number of manatees in this area has not been estimated, but it appears
they are fairly common.
During the first months of 1995,
the southeastern states of
Mexico suffered an extensive drought; the water levels
of many streams and lakes
decreased to critical levels. On 29 May
we received news of a group of manatees isolated in an
almost dry lake named
San Juan (17°46'44" N,
91°55'45" W), located in the municipality of Catazajá in
Chiapas. Manatees have been sighted in this lake for more than 10 years.
In March and April, the people from villages nearby took grass to
the water to feed the manatees, because they
realized that the water level in the
lake was dropping fast, and the manatees had nothing to eat. By late May, authorities of Chiapas decided to
rescue the manatees.
The rescue work lasted from 31 May to 4 June. Seventeen manatees were captured and moved. From the second day of
capture we collected data on
morphology and sex, and also took five samples of blood and
eight of skin for genetic analysis.
The animals
were corralled with
a 100-m-long fishing net and then caught by hand by
slipping a rope around their
peduncles while the
net was contracted
slowly. They showed an
extraordinary ability to escape from the net by lifting the
lower edge with their
noses. During transport,
which lasted about 30
min, all animals
showed passive behavior until they were
successfully released.
The authorities
decided to free
the rescued manatees in the Catazajá Lake, which has a
maximum area of 16,000
ha in the rainy season, and
where the local fishermen estimate a
population of 50-80 manatees.
Of the
17 captured manatees,
five were adults and
the rest were
juveniles, including at least one calf. The sexed animals were seven
females and four males.
The Chiapas state
authorities are now planning to
initiate an educational and
research program in the region
with the aid of the Quintana Roo Research Center, where a research
program on the Antillean
manatee was started in 1987.
A video of this rescue is available (8 minutes
long, VHS). For information, fax: 983-20447 in Chetumal, Mexico. - Benjamín
Morales Vela and
David Olivera Gómez
(El Colegio de
la Frontera Sur [ECOSUR], Apdo. Postal 424, C.P.
77000, Chetumal, Q. Roo, Mexico)
NEW CALEDONIA
New Dugong Studies.
- Jean-Philippe Das has been conducting studies of dugongs in
New Caledonia, and in October 1995
he produced a wide-ranging 97-page
privately-printed report
entitled Etude des dugongs en Province-Nord: Compte-rendu. It covers
the distribution, ecology, and
status of dugongs in the province, giving data from aerial
and interview surveys, catch
data, and ethnobiological information. In 1994 he
produced another report, Etude des dugongs en Province-Sud. He
can be contacted at:
18 Rue Rameau, 91160
Longjumeau, France (tel./fax:
33-90-49-55-28) or at CEMMEN -
Conservation et Etude
des Mammifères Marins en
Nouvelle-Calédonie, BP 13098, 98800 Nouméa, New Caledonia
(tel./fax: 687-44-22-34).
PHILIPPINES
Symposium on Cetaceans and Dugongs. - A Symposium and Workshop on the Biology
and Conservation of
Small Cetaceans and Dugongs
of Southeast Asia was held in Dumaguete, Negros
Oriental, on 26-30 June 1995 and hosted by the Silliman University Marine Laboratory. The one-day Symposium was attended by over
120 participants from 10 countries.
The group agreed that its
work should include the dugong, since it faces many
of the same threats
as small cetaceans
and because in several nations dugongs and small cetaceans are studied by many of the same researchers.
The Workshop agreed to establish a small cetacean
interest group in
Southeast Asia, with a regional newsletter appearing at least
three times a year (to be published
by the Ocean Park
Conservation Foundation). The proceedings of the Workshop are being edited by Dr. W. F. Perrin and will be
published as a
UNEP East Asian
Technical Series Report. - (source: The
Pilot [UNEP], No. 13.)
WASHINGTON, D.C.
U.S. Postage
Stamp to Feature Manatee. - For the first
time, a manatee is to appear on a United States postage stamp. Part of a sheet of 15 multicolored stamps
featuring 15 different
endangered species, the 32-cent stamp
depicting a Florida
manatee is scheduled for
its first day
of issue on
2 October 1996 in San Diego, California.
The U.S. is late in
joining the club of nations
that have put
sirenians on their stamps: at least 31
other countries have already done so. The first were
apparently Niger and Cameroon in 1962. Still conspicuously absent from the list is Australia.
How about it down there?? It's a
cheap and easy way for a
government to help
raise consciousness about
sirenians among children and other collectors the world
over. - DPD
Publication of Sirenian Bibliography Still Approaching!
- After further delays caused
by the
past winter's government
furloughs and shutdowns (what else can go wrong?),
Domning's Bibliography and Index
of the Sirenia and Desmostylia is now expected
to appear this summer
as Number 80
in the series Smithsonian Contributions to Paleobiology. It
will consist of a single
sewn, paperbound volume (about
8" x 10" format) of over 610 pages. It is an exhaustive, annotated and indexed compilation of 500
years of scientific and popular literature on the biology, paleobiology, and ethnobiology of sirenians
and desmostylians. Since
the Smithsonian does not retail its series publications to the general public,
arrangements have been made
for the Save
the Manatee Club
to obtain a limited
supply of copies for sale to individuals. The retail price has been tentatively
set at around US$25.00 per copy.
If you wish to acquire a copy
for personal use, please contact
the Save the Manatee
Club, 500 N. Maitland
Ave., Maitland, Florida 32751, USA (phone: 1-800-432-5646), as soon as possible to reserve a copy and obtain up-to-date information on price
and handling costs. To repeat, copies
are not available for shipment at
this time, but
will be ready sometime in the next months. - DPD
ABSTRACTS
The following
abstracts are of papers and
posters presented at the Eleventh
Biennial Conference on the Biology of Marine Mammals, held at
Orlando, Florida, 14-18 December 1995.
RECENT LITERATURE
Anderson,
P.K., and R.M.R. Barclay. 1995.
Acoustic signals of solitary dugongs:
physical characteristics and behavioral correlates. Jour. Mamm. 76(4): 1226-1237.
Bizzarini,
F. 1994. Osservazioni sull'Halitherium schinzi Kaup, 1838
(Sirenia, Mammalia) conservato
presso il Museo Civico di Storia Naturale di Venezia. Boll. Mus. Civ. Stor. Nat.
Venezia 43: 163-171. [In Italian; Engl. summ.]
Brownell,
R.L., Jr., K. Ralls, and W.E.
Perrin. 1995. Marine mammal biodiversity: three diverse orders encompass 119 species. Oceanus 38(2): 30-33.
Cashman,
M.E., T.L. Ness,
W.B. Roess, W.G. Bradley, and
J.E. Reynolds III.
1996. Isolation and characterization of a cDNA encoding interleukin
2 from the Florida manatee, Trichechus manatus latirostris. Mar. Mamm. Sci. 12(1): 89-98.
De Iongh, H.H.,
B.J. Wenno, B. Bierhuizen, and B. Van Orden. 1995. Aerial survey of
the dugong (Dugong dugon Müller,
1776) in coastal waters of
the Lease Islands,
East Indonesia. Mar. Freshwater
Res. 46(4): 759-761.
Domning,
D.P., S.K. Donovan, H.L. Dixon, R.W. Portell, and K.
Schindler. 1995. The world's
most primitive seacow:
a new sirenian site in western
Jamaica. [Abstract] Geol. Soc. Amer. Abstrs. With Progs. 27(6):
A386.
Domning, D.P.,
and H. Furusawa. 1995. Summary of taxa and distribution of Sirenia in
the North Pacific Ocean. The
Island Arc 3(4): 506-512.
Duignan,
P.J., C. House,
M.T. Walsh, T.
Campbell, G.D. Bossart,
N. Duffy, P.J. Fernandes, B.K. Rima, S. Wright, and
J.R. Geraci. 1995. Morbillivirus
infection in manatees. Mar. Mamm. Sci. 11(4): 441-451.
Gingerich,
P.D., M. Arif, M.A. Bhatti, H.A.
Raza, and S.M. Raza. 1995. Protosiren and Babiacetus (Mammalia,
Sirenia and Cetacea)
from the Middle
Eocene Drazinda Formation, Sulaiman
Range, Punjab (Pakistan). Contr.
Mus. Pal. Univ.
Michigan 29(12): 331-357. [Protosiren
sattaensis, new species]
Hasegawa,
Y., T. Muramatsu, and Y. Miyazawa. 1995. A desmostylian tooth
from the Tomikusa Group, Nagano
Prefecture. Sci. Repts. Yokohama Natl.
Univ., Sec. II, Biol. & Geol.
No. 41/42: 1-11. [In Japanese; Engl. summ.]
Hasegawa,
Y., Y. Taketani, H. Taru, O. Sakamoto, and M. Manabe.
1995. On sexual dimorphism in Paleoparadoxia tabatai. The
Island Arc 3(4): 513-521.
Heizmann, E.P.J.
1992. Das Tertiär in Südwestdeutschland. Stuttgart
Beitr. Naturk., Ser. C: Allg. Aufsätze
33: 1-61. [Mentions Halitherium.]
Inuzuka, N.,
D.P. Domning, and C.E. Ray. Summary of taxa and morphological adaptations of the Desmostylia. The Island Arc 3(4): 522-537.
Kamiya, T. 1994. [Steller's sea cow.] Toba Super Aquarium No. 12: 14-15. [In
Japanese.]
Kataoka, T.
1987. "Sirenology" [general biology of the dugong]. Jour. Mie
Prefecture Zool. Soc. No. 9:
3-7. [In Japanese.]
Kataoka, T., T.
Mori, Y. Wakai, J.A.M. Palma, A.A.S.P. Yaptinchay, R.R. de Veyra,
and R.B. Trono. 1995. Dugongs Dugong
dugon (Müller, 1776) of the Philippines:
A report of the joint dugong research and conservation program. Pawikan
Conservation Project, Philippines, and Toba Aquarium, Japan: 1-168.
Kettembeil, S. 1995. Dugong vom Aussterben bedroht. Naturwiss. Rundschau 48(1): 29.
Kimura, M., H. Furusawa, T. Sagayama, Y. Igarashi, A.
Suzuki, and H. Fukusawa. 1995. Geologic age and paleoenvironment of fossil sirenian-bearing deposits (Kinkomanai
Formation) in the Shosambetsu region of
northern Hokkaido, Japan. Jour. Geol.
Soc. Japan 101(5): 345-352. [In Japanese; Engl. summ.]
Kobayashi, S.,
H. Horikawa, and S. Miyazaki. 1995. A new species of Sirenia (Mammalia:
Hydrodamalinae) from the
Shiotsubo Formation in
Takasato, Aizu, Fukushima Prefecture, Japan. Jour. Vert. Pal. 15(4): 815-829. [Dusisiren takasatensis, n.sp.; Late
Miocene]
Kraus, J.
1995. Florida manatee soft
release. Endangered Species Tech. Bull.
(U.S. Fish & Wildl. Serv.) 20(5): 8-9.
Lockett, J.
1996. Dugongs dine with the herd. BBC
Wildlife 14(1): 20-21.
[Popular account of cultivation
grazing, based on Preen, 1995.]
Marmontel, M.,
T.J. O'Shea, H.I. Kochman, and S.R. Humphrey. 1996. Age determination in manatees using
growth-layer-group counts in bone. Mar.
Mamm. Sci. 12(1): 54-88.
O'Shea, T.J.,
B.B. Ackerman, and H.F. Percival (eds.). 1995. Population
biology of the Florida manatee. Information
& Technology Report
(U.S. Dept. Interior,
Natl. Biological Service) 1: vi + 289. [Comprises 18 articles resulting
from the workshop on manatee population biology held at the University of
Florida in 1992.]
Papastavrou,
V. 1995. Gentle
giant's furry fate: why the Steller's sea cow died out.
BBC Wildlife 13(11): 26.
Pirika Sirenia
Research Group. 1992.
Report on excavation of sirenian
fossil from Pirika Imakane, southwestern Hokkaido. Imakane
(Japan), Imakane Township
Board of Education: [vi] + 133. [In Japanese; Engl. summ.
Concerns a Pleistocene skeleton of Hydrodamalis sp.]
Preen, A.R.
1995. Impacts of
dugong foraging on
seagrass habitats: observational and experimental evidence for cultivation grazing. Mar. Ecol. Prog. Ser. 124: 201-213.
Preen, A.R., and
H. Marsh. 1995. Response of dugongs to large-scale loss of seagrass
from Hervey Bay, Queensland, Australia. Wildl. Res. 22: 507-519.
Schindler, T., and K. Schindler. 1992. Ein Fund von
Säugerzähnen im Oberen
Meeressand (Rupelium,
Oligozän) von Bad Kreuznach (Mainzer Becken, SW-Deutschland) mit Anmerkungen zum Aufschluss und zum sonstigen Fossilinhalt. Mainzer Geowiss. Mitt. 21: 35-40. [Engl.
summ.; mentions Halitherium schinzii.]
Schiro, A.,
and D. Fertl. 1995. Mermaids
sighted in Galveston Bay. Soundings (Galveston Bay Foundation) 7(3): 4-5.
[Sightings of West Indian manatees in Texas.]
Schuhmann, H.-J.
1995. Der Manati, Trichechus senegalensis,
im Rio Geba, Guinea-Bissau. Natur und
Museum (Frankfurt a. M.) 125(12): 402-409.
Schwartz, F.J.
1995. Florida manatees, Trichechus
manatus (Sirenia: Trichechidae) in
North Carolina 1919-1994. Brimleyana
No. 22: 53-60.
Takamura, N., and
R. Sakai. 1994. [Stars of the Toba
Aquarium: dugong.] Toba Super Aquarium No. 12: 10-13. [In
Japanese.]
Wallace, R.L. 1994. The Florida manatee: organizational
learning and a model for improving
recovery programs. In: T.W. Clark, R.P. Reading, & A.
Clarke (eds.), Endangered
species recovery: finding the lessons, improving the process. Covelo
(Calif.), Island Press: 131-155.
CHANGES
OF ADDRESS
Benjamín
Morales Vela, ECOSUR,
Apdo. Postal 424,
Chetumal, Quintana Roo
77000, MEXICO (fax: 983-20447)
Leslee Parr,
Dept. of Biology, Portland State University, P.O.
Box 751, Portland, Oregon 97207,
USA
Patrick M. Rose, 2545 Blair Stone Pines Dr.,
Tallahassee, Florida 32301
Essam Samson, Forest Engineer, P. O. Box 11287, Yaounde,
CAMEROON
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