and the OCEAN ENVIRONMENT
Low O2, high temp., dredging, wastes
Removal of marsh lands and wet lands
Benefits of the sea
Uses of ocean to man
history the ocean has played a vital role in the development and growth of
civilization, and humans have considered the ocean to be an unlimited source of
food and a bottomless garbage dump. With a population of 6.5 billion most
fisheries are fully exploited and ocean dumping is causing measurable
contamination of the food supply.
negative influences of man...
1. The use of
pesticides and other agricultural chemicals to help crop yield on land has
harmed food production in the ocean.
2. A process
called BIO-MAGNIFICATION, concentrates toxins such as DDT, PCB'S and mercury in
tissues of consumer organisms...many of which are used for human consumption.
to ocean dumping must be sought to prevent further contamination of the food
and ethical issues of commercial whaling works these animals toward extinction.
Destruction of marshlands by draining and dredging and attempts to control
beach erosion in spite of a world wide rise in sea level.
Convention discourages dumping at sea
The London Convention is a nickname for a United Nations administered agreement
on preventing pollution produced by dumping wastes and other harmful substances
at sea. This treaty classifies materials according to potential harm to marine
life and humans. It bans dumping some substances and regulates dumping others §.
U.S. dumps only dredged materials, although other countries still dump sewage
sludge and non-toxic industrial waste §.
The U.S. and other parties to the London Convention are observing a moratorium
on dumping low-level radioactive waste
For the past
100 years, contaminants like oil, PCB, DDT, heavy metals, radioactive wastes,
sewage sludge and garbage is introduced into the sea .
OIL due to
tanker accidents, oil rig blowouts, daily oil washed off roadways into sewers
and into water, ships pumping waste oil from bilges/ballast, seepage from
garbage dumps and
seepage from the ocean bottom. (the largest discovered off Trinidad at 100m
/100m thick and contains 1 megaton of oil)
Oil harms the
2. birds die
of starvation because they can't fly and no insulation
3. ingest oil
from feathers while trying to clean
4. damage the
liver and vital organs
oil released into the sea usually floats although some sinks .
intertidal zones...tides bring a new blanket of oil to cover oysters, clams,
mussels etc interfering with feeding and breathing. The devastation usually
occurs initially but recovery usually occurs with time. More serious than the
oil itself has been the various chemicals used such as detergents used to break
it up or disperse the oil into
The Tory Canyon disaster in 1967 the chemicals were shown to cause more mortality
to marine organisms than the oil itself.
When it comes
to mixing oil and water, oceans suffer from far more than an occasional
devastating spill. Disasters make headlines, but hundreds of millions of
gallons of oil quietly end up in the seas every year, mostly from
non-accidental sources §
below shows how many millions of gallons of oil each source puts into
the oceans worldwide each year
Down the Drain: 363 Million Gallons
oil can end up in waterways. An average oil change uses five quarts; one change
can contaminate a million gallons of fresh water. Much oil in runoff from land
and municipal and industrial wastes ends up in the oceans. 363 million gallons §
Every year oily road runoff from a city of 5 million could contain as much oil
as one large tanker spill §.
Routine Maintenance: 137 Million Gallons
bilge cleaning and other ship operations release millions of gallons of oil
into navigable waters, in thousands of discharges of just a few gallons each.
137 million gallons §
Up in Smoke: 92 Million Gallons
pollution, mainly from cars and industry, places hundreds of tons of hydrocarbons
into the oceans each year. Particles settle, and rain washes hydrocarbons from
the air into the oceans §.
Seeps: 62 Million Gallons
oil "pollution" is natural. Seepage from the ocean bottom and eroding
sedimentary rocks releases oil.
37 Million Gallons
Only about 5
percent of oil pollution in oceans is due to major tanker accidents, but one
big spill can disrupt sea and shore life for miles §.
37 million gallons §
from a tanker that ran aground
Kill Van Kull Channel, between Staten Island and New Jersey, 1991
Drilling: 15 Million Gallons
production can cause ocean oil pollution, from spills and operational discharges.
and larva drift in oil slicks, they can't swim and there is less
tar...some components evaporate or dissolve but lots sink to the bottom to be
trapped in sediments.
ingest floating tar and sperm whales feed off bottom sediments (complete with
of human sewage and garbage into the coastal waters is practiced throughout the
world. The sewage may or may not have had some treatment before discharge. It
adds a large volume of small particles to the water and also large amounts of
volumes and with adequate diffusing pipes, it is difficult to detect long-term
effect on the communities of the open coast. In large volumes and in semi
enclosed embayments, the effect can be devastating.
California..LA area discharges 330 million of sewage per day at the Whites
Point outfall off the Palos Verdes Penn.
around the outfall and others in the area revealed that sewage has caused
significant degradation in benthic invertebrate communities in areas near the
outfall, kelp beds disappeared near the outfall, more urchins, diseased fish
more prevalent and about 4.6% of the Southern Cal. mainland shelf has been
changed or degraded as a result of sewage discharge from 4 major outfalls.
Bay on Oahu's east side was subjected to a 10-fold increase in population and
the bay was subjected to massive domestic sewage discharges, siltation from
runoff during storms and resulted in the total destruction of the once
beautiful coral reefs of this shallow bay. Once the discharges were eliminated
from the bay, a remarkable recovery of corals and water clarity was reported!
to sewage, large amounts of garbage are dumped into the ocean every year.
there is New York. The city dumps dredge spoils, sewage, chemicals, garbage,
construction materials, which are dumped in such large numbers its visible from
satellites. Sewage alone the 127 municipal discharges contribute 2.6 x 109
or 2,600,000,000 billion gallons per day.
has dropped O2 levels near zero over extensive bottom areas off New Jersey, led
to massive fish and shellfish mortalities, and even though most are dumped many
miles offshore, some returns to contaminate bathing beaches (needles).
oil or sewage, which are at least visible, are various toxic chemicals produced
by the industrialized nations which find their way into the oceans
ecosystems.These chemicals are often transferred through the food chains in the
sea and exert their effects in animals and places removed in time and space
from its source.
marine organisms also enhance the toxic effects of many chemicals because of
their ability to accumulate the substances in their bodies far above that found
in the surrounding water. Another factor that tends to increase the effects of
chemicals on living systems is biomagnification in which the chemical increases
in concentration in the bodies of organisms with succeeding tropic level
....this can lead
to very high concentrations
in the top predator. ..sometimes man!
the late 1930's, the Chisso Corp. of Japan established a factory on the shores
of Minimata Bay to produce vinyl chloride and formaldehyde. By-products from
the plant contained mercury and were discharged into the bay. Through
biomagnification, the marine fishes and shellfish accumulated high
concentrations of the toxic compound methyl-mercury chloride.
and shell fish were in turn consumed by the inhabitants of the area. About 15
years after the dumping of the mercury into the bay began, a strange
permanently disabling neurological disorder began to appear among the
inhabitants, especially the children. It was called Minimata Disease. The cause
was diagnosed as mercury poisoning in 1959 but it took until the early 60's to
discover the source from the factories.
and until the
1970's before Japan to stop dumping mercury into the sea.
Pelicans etc Radioactive wastes
how DDT becomes concentrated as it passes through a food chain
shows how DDT becomes concentrated in the tissues of organisms representing
four successive trophic levels in a food chain.
concentration effect occurs because DDT is metabolized and excreted much more
slowly than the nutrients that are passed from one trophic level to the next.
So DDT accumulates in the bodies (especially in fat). Thus most of the DDT
ingested as part of gross production is still present in the net production
that remains at that trophic level.
This is why
the hazard of DDT to nontarget animals is particularly acute for those species
living at the top of food chains.
spraying a marsh to
control mosquitoes will cause trace amounts of DDT to accumulate in the cells
of microscopic aquatic organisms, the plankton, in the marsh.
In feeding on the
plankton, filter-feeders, like clams and some fish, harvest DDT as well as
food. (Concentrations of DDT 10 times greater than those in the plankton have
been measured in clams.)
of concentration goes right on up the food chain from one trophic level to the
next. Gulls, which feed on clams, may accumulate DDT to 40 or more times the
concentration in their prey.
This represents a
400-fold increase in concentration along the length of this short food chain.
abundant evidence that some carnivores at the ends of longer food chains (e.g.
ospreys, pelicans, falcons, and eagles) suffered serious declines in fecundity
and hence in population size because of this phenomenon in the years before use
of DDT was banned (1972) in the United States.
dredged deeper and wider so boats won't run into each other or run aground and
until the day comes when
(1) no more
boats are built, (2) they don't increase in length, beam and draft or (3)
moving water stop dumping silt into channels, they will continue to be dredged.
damage by tearing up marine habitat by releasing silt which smothers shellfish
and cuts down sunlight penetration into the water, changes water current
holes in an otherwise shallow and even bottom and the holes can collect
detritus and form low oxygen conditions and the worse is the dredged material
is usually dumped on the protective marshlands. Deeper channels can also allow
denser salt water to travel further up the estuary increasing the salinities
and bringing predators to an otherwise low salinity environment which can then
feed of the oysters etc.
nations, with limited inland sources of building materials, turn to coastal
coral to process for lime, Solomon Islands, 1988 Mining coral removes habitat
of local marine species, and weakens coastal storm defenses. Rebuilding coral
takes time because colonies of tiny coral animals grow slowly. Mined or dredged
areas take a very long time to recover
for landfill, Belize Sand and gravel are in demand as fill, and as an
ingredient of concrete. Mining near shores may lead directly to beach erosion.
Removing sand from river beds may also cause beach loss, because floods would
have eventually brought that sand to beaches
the sea can add to world food production. (growing aquatic is aquaculture).
Japanese/Chinese raised fish and Japan raised fish and the Japanese grew
seaweed on ropes but the main problem with mariculture is
1. lack of
suitable domestic organisms
2. gaps in
knowledge of nutritional requirements and life cycles (larva stages)
3. need to
duplicate the natural environment
4. lack of
knowledge in relation to diseases of marine organisms.
trying to find all these, a way around it is to work out some, which can be
done by interrupting the natural stages and leave the rest to nature.
There are 2
broad types of mariculture.
2. Grow more
effectively in the natural environment
settings are used in growing lobsters, shrimp, fish.
Ranching--rear young from artificially fertilized eggs and release 3 year old
fish to ocean.
mortality occurs during 1st year of life)
Other Metals Deep ocean basins are strewn with
metallic nodules §.
Composed mostly of manganese, they also contain nickel, copper, and cobalt.
Pipelines running to ships or platforms could "vacuum" up these
nodules, but no country or consortium is yet mining them, in part because of
high costs compared to land-based mining §.
manganese "marbles" lie strewn on the abyssal mud of the ocean's
deepest basins. Most are larger than golf balls §.
Each appears to have grown, pearl-like, around some nucleus-- perhaps a shark's
science, maximum sustainable yield or MSY is the largest long-term average
yield/catch that can be taken from a stock of fish without depressing the
species' ability to reproduce.
A typical MSY
is about 80% of the total population biomass of the mature fish capable of
reproduction. The maximum sustainable yield is usually higher than the optimum
values for fishing effort and catch per unit effort is not as straight forward
as one would like. Catch is made up of:
that retained for its
value and eventually marketed
that discarded at sea or
dockside (typically 30-40%).
portions of commercial
species having little value (heads and guts)
species with no commercial value
restricted take individuals
Catch is often lumped by fishers or
processors into broad market categories including several species.
Effort includes both gear and
Effort may be simple: feet of gill
netting or number of hooks on a long line per day or hour
but it may also be complex, needing to
varying mesh size
otter board size
horsepower of boat
use of electric "ticklers" to
cause bottom fish to swim up into a trawl
whether the boat uses a sonar fish
locator and how up-to-date it is
how experienced the captain is
Even time can be complicated. Fisheries
which involve pelagic schooling fish have both a search component and a fishing
component. Employment of spotter planes will shorten the search time but not
the fishing time.
Obviously commercial records by themselves
are inadequate, the fisheries manager must conduct additional surveys,
sampling, and perhaps even covert observation to accurately determine both
catch and effort.
from the commercial catch should always be supplemented from fishery-independent
data. Complicated statistical analysis is essential.
years we have been managing commercial fisheries based largely on CPUE data.
New reports of failed fisheries surface almost daily. Obviously fisheries
management has been less than a sterling success. There are three main
categories of reasons.
Fisherpersons continually upgrade their gear, adding the latest gimmicks if
they think they will help them turn a profit. Nets have become stronger and
lighter; boat motors more powerful; refrigeration better so the fleets can
remain out longer; fish-locators and navigational aids and record keeping
vastly more accurate and afordable. We have been basing catch per unit effort
on an effort component which has become subtly but vastly more efficient.
Every management decision has a political component. Whenever a fishing
restriction creates a real or imagined hardship for people, they protest,
sometimes violently. Considering the tenuous data available, the efficacy of
almost any management recommendation can be questioned. Politicians and
bureaucrats tend to err on the side of people rather than fish (fish rarely
High seas fisheries are
governed by international treaties. Often the effect on the fish population is
secondary to some other bargining point.
CPUE and Sustainable Yield are based on
the assumption that an unexploited population will behave in a predictable
fashion. An unexploited population is a fallacy. The process of evolution
produced something to exploit any available resource.
Much of our historic success at
harvesting huge quantities from the sea resulted from the co-harvest of the
other species that naturally exploited the species we were harvesting. We
virtually eliminated most marine mammals and the largest species of fish very
early on. That, of course, left their food supply for us to exploit and as we
reduced them, we began to harvest their food supply. The history of our
exploitation of the sea has been one of migration down the food chain.
Predator species can't recover, even if
we would let them, because we are taking all their food. Imagine trying to
balance a MSY for anchovetta and tuna at the same time.
Ecosystem destruction has resulted from
many technological innovations including fish harvest techniques.
Dams and diversions have disrupted life
cycles of anadromous species,
Dredging and filling to create
residential, commercial, and agricultural properties has eliminated or damaged
nursery grounds for many coastal species.
Bottom trawls crisscrossing the most
productive parts of the ocean floor have destroyed the substratum on which fish
and their foods depended.
Untold quantities of myriad industrial,
agricultural, and medical chemicals have entered the ocean and potentially
concentrated in biological systems where their effects include reproductive
MARK RECAPTURE RELEASE
studies of marked individuals basic tool in wildlife ecology providing
life history and reproductive biology: growth, maturation, mating patterns,
of gain (immigration + births) and loss (emigration plus deaths)
external - scars, coloration patterns
internal: DNA fingerprints
but not scientist induced: scars (propeller wounds manatees)
tags, bands, brands, color marks etc
tags: Discovery tags, PIT tags
Attach with minimal trauma
Not impede movement
Not alter susceptibility to predation,
disease, or other mortality agents
Be difficult to dislodge (False -)
Last for lifetime of animal (or study)
Unambiguously identify individuals (false
m2 / n2 = n1
N = n1
n2 / m2
n1 = number caught and marked at T1
n2 = number caught at T2
m2 = number of marked individuals caught at T2
N = population size at T1 if population experiences
losses but no gains
N = population size at T2 if population experiences
gains but no losses
SE = variance0.5
to track trends need precise estimates of population size
... depends on population size and level of
e.g. MRR methods usually prohibitive for large populations CV<5%
population >500 and probability of capture >0.5
Assumptions of Lincoln Petersen Estimate
No loss of
marks between T1 and T2
Tagging process does not
distributed at random through population
Capture and tagging
process does not affect probability that an animal dies or migrates
All individuals are
All individuals equally
likely to die or emigrate and emigration is just as permanent as tag loss
there is either no recruitment or no loss or neither recruitment or loss (and
one needs to know which of these circumstances is operative) (Lincoln
Family of MRR models
Petersen - 2
samples : 1 marking, 1 recapture
Triple Catch- 3 samples (2 marking and one recapture)
Jolly-Seber: 3 or
more sampling occasions multiple marks and recaptures
recapture models allow estimates of loss rates, gain rates between each size
Computer programs e.g. Capture - allow
testing of and adjustment with respect
to assumptions - closed or open populations, capture heterogeneity etc.
Assumptions re use of natural marks
Natural marks do not
change with time
Natural markings are
No errors in
identification - more likely with natural than dedicated artificial marks
Marked animals have same
probability of capture as unmarked *****
equal probability of
sighting - distribution and behavior
equal probability of
photographing natural marks
Equal probability of
survival - age specific rates but cannot age wild individuals
re use of natural marks for estimating population size
studied must be geographically closed
must be representative of the population
sizes must be sufficiently large
re use of natural marks for estimating survival
survivorship most influential life history parameter in demography of most
marine wildlife species
studies often best method of measurement
must be sufficiently long - for long-lived species such as whales - 10 years.
of recapture must be high >0.2
Probability of individual identification
should be homogeneous
study 1: southern right whales off South Africa
study 1: southern right whales off South Africa
aerial surveys photographs of females with calves
calve 2-4 years - probabilities of recapture unequal between years
built model for closed populations built to handle unequal capture
estimate 286 adult females (95% CI 265-301)
study 2: Antarctic minke whales
study 2: Antarctic minke whales
can be identified
effort required to obtain photographs
model assumptions satisfied
size of 100,000
of 0.25 - (95% CI 75,000 - 125,000)
ship days yr 1, 296 yr 2
cruise likely to be more efficient
Case study 3: Florida manatees at 3 winter aggregations sites
Case study 3: Florida manatees at 3 winter aggregations sites
size ? But 677 marked individuals
populations: No - not assumed
method: Photo ID propeller scars
capture probability - unlikely
of study: 13 yrs (2 locations) 6 yrs (1)
Precise population estimate - not
attempted because of heterogeneous capture probability across whole population
-some animals unmarked or unavailable
Case study 3: Florida manatees at 3 winter aggregations sites
Adult and juvenile
survival -assumed homogeneous capture probability of marked population
Capture probability high
>0.5 (2 sites >0.7)
Assumption of equal survival between sampling intervals-
individuals sampled early in period < survival to next
interval than those sampled late
grouped into 2 age groups: juveniles and
confined sampling period
each year 1 November - 31 March
multiple sampling within
Assumption- identifying one individual in
sample does not affect probability of sampling others - okay as no defined
excellent precise estimates of survival
e.g., adult Crystal River 0.962 s.e. 0.009 95% CI 0.943-0.981
study 4: Dugongs in Moreton Bay
study 4: Dugongs in Moreton Bay
population ? but unlikely - dugongs move
method - rodeo capture and PTT tag/DNA fingerprint
of capture mortality ~ 1%
capture probability - unlikely
population estimate - capture probability 0.3-0.5
- capture probability 0.5 and 10 year study
studies are more than mucking about in boats with marine mammals!!!!!
mathematical evaluation before you start to consider likely effort required to
achieve meaningful results
to test assumptions of MRR model
access to long-term funding
to address ethical issues if actual capture involved
Caughley, G. and
Sinclair, A.R.E.1994. Wildlife Ecology and Management. Balckwell Scientific
Hammond, P. (1986)
Estimating the size of naturally marked whale populations using
capture-recapture techniques.Reports of International Whaling Commission
Special Issue 8: 253-282.
Hammond, P., Mizroch,
S.A. and Donovan, G. eds (1990) Individual recognition of cetaceans: Use of
photo-identification and other techniques to estimate populations
parameters. Reports of International
Whaling Commission Special Issue 12.
OShea T J., and Langtimm
C.A. 1995.Estimation of survival of adult Florida manatees in the Crystal
River, at Blue Spring and on the Atlantic Coast. Pages 194-222 in T.J. OShea,
B.B. Ackerman and H.F. Percival (eds). Population Biology of the Florida Manatee. US Department of the
Interior. National Biological Service, Information and Technology Report 1.
Remnants of the Subungulate Radiation
Character states: Proboscidea Hyracoidea Sirenia
Carpal & tarsal bones x
Short, hoof-like nails
5/4 or 4/3 4 /3 4/
No clavicle x x
Pectoral mammaries x
Abdominal testes x x x
tooth replacement x x x
Unique among all orders?
and diet ________ & _________
remnant of a once diverse group (20 genera) of the Miocene
Distribution: Dugongidae & Trichechidae
Four extant & one recently extinct species
Unique among all orders?
and diet ________ & _________
mere remnant of a once diverse group (20 genera) of the Miocene
& Trichechidae compared
(with forked tails): one species
Dugong of Indonesia (Stellars sea cow: extinct)
Distribution of 3 species: W.
and West Indian or
West Indian Manatee
of four species in a declining, endangered (?) order
of endangered species
characteristics and distribution
requirements & Feeding behavior
Reproduction: 5-15% of
population in 1st year calves
Major causes of mortality
Conservation: Recovery Plan & recent issues
status: n ~ 1900, ~ 8% annual mortality
of Endangered Species :
Adapted to stable, undisturbed
Low natality and low natural mortality
Specialized, narrow habitat or
Historically restricted in distribution,
on periphery of range or low in density
Natural History of Manatees
meters long, 350-450 kg, no hind limbs
range reduced to Florida & Puerto Rico
Habitat: Shallow, warm fresh to marine waters with
abundant aquatic vegetation
4-6 hrs/day, consuming 25-35 kg/day
breed at 4-6 yrs, every 3-4 years thereafter
- single calf, 390 day gestation, nurse ~1 year
this characteristic of an endangered species?
. HISTORICAL EXTINCTION EVENTS
Some survivors from the Pleistocene have been driven to
extinction during historical times by over-exploitation:
This was heavy, slow-swimming marine mammal related to the
manatee and dugong (Sirenians), but much larger (25-30 feet long). It was
discovered in 1741 in the ocean around the Pribilof Islands in Bering Sea (far
north Pacific Ocean).
. It was used as food by visiting sea-otter
hunters, and was extinct by 1768, 27 years after its discovery.
A smaller (12 feet long) relative of the sea cow that is
endangered by human activities is the Manatee (West Indian or Florida
Manatee), a slow-swimming, friendly marine mammal that feeds on sea grass and
lives in the coastal waterways of Florida and in other coastal
. areas around the Caribbean. There are
about 2,000 animals in the population, but at least 200 die each year, mainly
from collisions with speedboats. Florida's response to this problem has been to
post "go-slow" signs on the waterways, and to rely mainly on
voluntary compliance. They have also established some very small sanctuaries. These efforts are not working very well.
The death rate has not declined; in fact collisions with boats
. killed a record number of 95 manatees in
2002. Save the Manatee Club is now filing
lawsuits to try to get the government agencies to better enforce the laws
. Despite the manatee's precarious
situation, a consortium of Florida business interests is lobbying to get the
mammal removed from the federal Endangered Species list.
The other surviving relative of the sea cow, the dugong,
is also in serious trouble.
Dugongs are found in a huge area from the Red Sea to the Pacific Coast of
Australia and the Solomon Islands. They are so dispersed that accurate population counts have not
been possible. The population at the southern end of the
Great Barrier Reef was estimated at ~50,000 in the 1960's, but the number has
fallen to about 4,000
. since then, due to habitat loss,
entanglement in fishing nets and nets used to protect swimming areas from
sharks . The Great Barrier Reef Marine Park
Authority has established a chain of dugong sanctuaries to try to
protect the remaining animals.
sea cows as they are sometimes called, are marine animals which can grow to
about three metres in length and weigh as much as 400 kilograms. They are the
only marine mammals in Australia that live mainly on plants. The name sea cow
refers to the fact that they graze on the seagrasses, which form meadows in
sheltered coastal waters. As dugongs feed, whole plants are uprooted and a
telltale-feeding trail is left.
more closely related to elephants than to marine mammals such as whales and
dolphins, but their closest living aquatic relatives are the manatees. Manatees
are aquatic mammals that live in freshwater rivers and coastal waters of West
Africa, the Caribbean, South America and the southern United States (Florida).
Another close relative was Stellers sea
previously found in the northern Pacific. It was hunted to extinction in the
1700s by sealers for its meat. It grew almost three times as long as the dugong
and fed on large algae (kelp).
inhabit shallow, tropical waters throughout the Indo-Pacific region. Most of
the worlds population of dugongs is now found in northern Australian waters
between Shark Bay in
Australia and Moreton Bay in Queensland.
Life in the
using their whale-like fluked tail and they use their front flippers for
balance and turning. Their movements are often slow and graceful. Early
explorers and sailors believed that they were mermaids because of their
streamlined bodies and the large teats at the base of their flippers.
. They have a
rounded head with small eyes and a large snout. The nostrils are at the top of
the snout and, like mammals, dugongs must surface to breathe. However, unlike
other aquatic mammals such as some whales, dolphins and porpoises, dugongs
cannot hold their breath under water for very long. It is generally for only a
few minutes, especially if they are swimming fast.
poor eyesight but acute hearing. They find and grasp seagrass with the aid of
coarse, sensitive bristles, which cover the upper lip of their large and fleshy
snout. Small tusks can be seen in adult males and some old females. During the
mating season, male dugongs use their tusks to fight each other.
Life history Dugong
list history is made of finely balanced population parameters.
. The slow
breeding rate and long life span mean that dugongs are particularly susceptible
to factors that threaten their survival. Throughout their worldwide range they
are threatened by human impacts, particularly on their habitat.
numbers have declined dramatically in the past 40 years in the southern part of
the Great Barrier Reef World Heritage Area south of Cooktown. Surveys indicate
that numbers now appear to be fluctuating around a level that is far less than
in the early 1960s, and probably before. Whether the southern Great Barrier
Reef population is continuing to decline
. , or is
stable, or increasing, and at what rate, will not be known for many years but
the species undoubtedly faces the threat of disappearing from the southern
Great Barrier Reef. The Great Barrier Reef Ministerial Council, comprising the
Commonwealth and Queensland Ministers for the Environment and for Tourism, is
concerned about the decline and has instigated a number of actions to
. reverse the
trend. Government departments, community groups and industry organisations are
working to minimise the number of dugong deaths from human-related causes
consider that the decline in dugong numbers is due to unsustainable mortality
from human-related causes such as habitat loss or degradation, commercial mesh
nets (fish nets), shark nets set for bather protection, indigenous hunting,
boat strikes, defence activities and illegal take.
1999 surveys showed that
numbers in the southern Area were back at 1986-87 levels (3993 ± 644),
Russian traders had exhausted the terrestrial fur-bearing animals they turned
their attention to the sea otters that were discovered in 1741 in the
north Pacific, on the Russian and Alaskan coasts. At that time, there
were between 150,000 and 300,000 otters living along the north American coast
from Alaska to Baja California.
. From 1750
to 1790 most of the animals were killed by hunters, then they were too scarce
to be worth hunting (they had reached "commercial extinction") and
the trade collapsed. By 1911, when the otters received some protection through
the International Fur Seal Treaty, there were only 1-2,000 animals left
throughout their range. The population recovered well and the Alaskan (Aleutian
. reached a
peak in the mid-1970s of about 50,000-100,000 animals. But from 1992 to 2000 it
declined by 95% and now as few as 6,000 otters may remain in the entire
Aleutian chain. This is just one part of a catastrophic ecosystem
collapse that is occurring in the area.
population of about 2,400 sea otters survives along the California coast
between Point Conception and Monterey Bay.
. They are
coming into increasing conflict with inshore fisheries for sea urchins.
seals. The loss of furs from other sources was a major incentive leading
to massive hunts for various types of seal. The animals were usually clubbed to
death when they came ashore to breed. The pattern was familiar - the discovery
of large populations of target species, the development of intensive hunting leading
to extermination or depletion,
. the move to
a new area. The first phase (1780-1820) was directed at the southern fur seal
in many areas of the southern hemisphere and was carried out by sealers from
Europe, Russia, Canada and the U.S. Each of the following areas was the site of
a fur seal hunt until the population was either commercially extinct (depleted
to the level where it was not profitable to hunt) or really extinct:
. Off the
west coast of Namibia in Africa, 40- 50,000 cape fur seal are taken each
year. This is about 10% of the world's sealing activity, and much of the
profit comes from the sale of penises for the aphrodisiac trade in Asia.
Most of the seals are being killed by clubbing to death, which is claimed to be
a humane method.
. In the North
Pacific, the northern fur seal was hunted on the Pribilof Islands in the
Bering Sea, first by the Russians using Inuit labor after they had wiped out
the sea otters. The slaughter went from 127,000 in 1791 down to 7,000 a year in
the 1820's after 2.5 million had been killed. The population recovered after
the Russian hunters moved to other areas, but after Alaska was sold to the U.S.
in 1867 the hunting level
. went back
up to 250,000 per year. This reduced the population again so that in the 1890's
the number killed was down to 17,000 a year. It is now illegal to hunt fur
seals, except for an exemption allowing Indians, Aleuts, and Eskimos to
continue to hunt at a subsistence level (about 2000 a year).
A massive seal hunt also developed in the North Atlantic
. , taking
advantage of the huge harp seal population that breeds on the pack ice in
winter around Labrador and Newfoundland. The sealers, from Newfoundland,
focused on the newborn seals with pure white fur, although adults were also
taken for their oil as well as fur. The Newfoundland sealing industry began in
the early 19th century and peaked at about 600,000 animals per year in the
1850's. This ultimately
. led to
reduction in the size of the herd to about one fifth of its original size, and
the industry went into decline in the early 20th century. A 1998 study shows
that the current level of hunting (350,000 animals killed in one season) is not
sustainable, and 12 members of Congress have written to Secretary of State
Madeleine Albright declaring their opposition to this hunt. Again in 1999
Canada is being criticized for
275,000 of these animals to be killed in spite of public opinion against
it. The adult harp seals are also hunted on a subsistence level further
north by Inuit hunters, who use the meat for food but also sell the skins in
order to pay for the snowmobiles, rifles, gasoline and ammunition that are used
in their hunting activities.
of harp seals, at Jan Mayen Island in the Arctic ocean, was
. wiped out
by a rapid boom and bust between 1840 and 1860.
Seals were hunted in the Pacific in the 1800s by whalers who wanted to
supplement their catch. They were hunted for their oil rather than their fur or
skin. Hundreds of thousands of these animals were killed in the southern ocean
and along the coast of California. The southern population (a distinct
. saved when
the Kerguelen and Macquarie Islands were turned into nature reserves, but in
1884 it appeared that the northern subspecies had been lost. However, a small
colony of about 50-100 had survived on Guadalupe Island off the coast of Baja
California. The species was given protection by the Mexican and U.S.
governments in the 1920s and the stock is now doing quite well. Today, there
160,000 northern elephant seals! A large breeding population (~2000) now
congregates on the beach at Ano Nuevo, fifty-five miles south of San Francisco,
every winter. Seals and sea lions may have had many more breeding colonies on
the mainland before they were eliminated by prehistoric hunting.
killed for three centuries for their oil, skin, and ivory
. from their
tusks. They were once abundant in the North Pacific, North Atlantic and the
Arctic Oceans, but like the other seals, walruses were hunted almost to
extinction. They are now protected in this country and the walrus population
appears stable at about 200,000 individuals.