1. Marine Pollution

2. Low O2, high temp., dredging, wastes

3. Removal of marsh lands and wet lands

4. Benefits of the sea

5. Uses of ocean to man


Throughout 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.



 Some 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.


3. Alternates to ocean dumping must be sought to prevent further contamination of the food supply.

4. Economic and ethical issues of commercial whaling works these animals toward extinction.

5. Destruction of marshlands by draining and dredging and attempts to control beach erosion in spite of a world wide rise in sea level.


The London 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


Currently the 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


natural seepage from the ocean bottom. (the largest discovered off Trinidad at 100m /100m thick and contains 1 megaton of oil)

Oil harms the environment by

1. covering or poisoning

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


 Crude oil released into the sea usually floats although some sinks .

Oil in 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 water.. 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 §

The graph below shows how many millions of gallons of oil each source puts into the oceans worldwide each year



Down the Drain: 363 Million Gallons

Used engine 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 §

Road runoff adds up
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

Every year, 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

Air 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 §.


Natural Seeps: 62 Million Gallons

Some ocean oil "pollution" is natural. Seepage from the ocean bottom and eroding sedimentary rocks releases oil.

Big Spills: 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 §



Crude oil from a tanker that ran aground
Kill Van Kull Channel, between Staten Island and New Jersey, 1991

Offshore Drilling: 15 Million Gallons

Offshore oil production can cause ocean oil pollution, from spills and operational discharges.



Pelagic...eggs and larva drift in oil slicks, they can't swim and there is less photosynthesis.


Pelagic tar...some components evaporate or dissolve but lots sink to the bottom to be trapped in sediments.

Right whales ingest floating tar and sperm whales feed off bottom sediments (complete with tar!)


 Sewage and Garbage

The discharge 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 nutrients.


In small 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.

Two examples...

Southern California..LA area discharges 330 million of sewage per day at the Whites Point outfall off the Palos Verdes Penn.


Studies 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.


Hawaii-Kaneohe 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!


In addition to sewage, large amounts of garbage are dumped into the ocean every year.

And then 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.



The dumping 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).




Worse than 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.


Certain 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.


The fishes 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.

DDT and Pelicans etc Radioactive wastes 


Biomagnification: how DDT becomes concentrated as it passes through a food chain

The figure shows how DDT becomes concentrated in the tissues of organisms representing four successive trophic levels in a food chain.



The 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.

For example,

•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.)

•The process 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.

There is 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.






























Channel Dredging

Channels are 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.

Dredging can damage by tearing up marine habitat by releasing silt which smothers shellfish and cuts down sunlight penetration into the water, changes water current patterns,,


creates deep 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.


Sand, Gravel, and Coral

Island nations, with limited inland sources of building materials, turn to coastal sand and



Collecting 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



Mining sand 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






 Mariculture...farming the sea can add to world food production. (growing aquatic is aquaculture).

History...The 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.


Instead of 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.

1. Duplicate environment artificially

2. Grow more effectively in the natural environment



1. Artificial settings are used in growing lobsters, shrimp, fish.

2. Ranching--rear young from artificially fertilized eggs and release 3 year old fish to ocean.

(most mortality occurs during 1st year of life)




Manganese and 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 §.


Mysterious 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 tooth.





Maximum sustainable yield

In fisheries 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 sustainable yield.









•Practical Considerations:

•Obtaining realistic 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

•          undersized individuals

•          restricted take individuals

•            Catch is often lumped by fishers or processors into broad market categories including several species.

•            Effort includes both gear and time.

•            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 account for:

•            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.


•Data from the commercial catch should always be supplemented from fishery-independent data. Complicated statistical analysis is essential.

•Fatal Flaws:

•For 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.


•            Technical
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 complain).


High seas fisheries are governed by international treaties. Often the effect on the fish population is secondary to some other bargining point.

•            Biological

•            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 dysfunction.








•     Longitudinal studies of marked individuals basic tool in wildlife ecology providing information on:

–  Basic life history and reproductive biology: growth, maturation, mating patterns, social organization

–  Population size

–  Rates of gain (immigration + births) and loss (emigration plus deaths)


Types of marks

•     Natural external - scars, coloration patterns

–   photo-id

•     Natural internal: DNA fingerprints

•     Anthropogenic but not scientist induced: scars (propeller wounds manatees)

•     Exterior tags, bands, brands, color marks etc

•     Internal tags: Discovery tags, PIT tags




Mechanics of tagging

•     Tags should:

–    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) (false -)

–    Unambiguously identify individuals (false +)




Basic model:

         m2 / n2 = n1 /N

        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












•     Variance of N=

                 {(n1+1) (n2+1) (n1-m2) (n2-m2)}/

              {(m2+1)2 (m2+2)}

SE = variance0.5

to track trends need precise estimates of population size 

CV=se/mean ……... depends on population size and level of precision

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 affect ‘catchability’

•     Marked individuals distributed at random through population

•     Capture and tagging process does not affect probability that an animal dies or migrates

•     All individuals are equally catchable

•     All individuals equally likely to die or emigrate and emigration is just as permanent as tag loss

•     That 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 Petersen only)

Family of MRR models

•     Examples:

–    Petersen - 2 samples : 1 marking, 1 recapture

–    Bailey’s Triple Catch- 3 samples (2 marking and one recapture)

–    Jolly-Seber: 3 or more sampling occasions multiple marks and recaptures

•     Multiple recapture models allow estimates of loss rates, gain rates between each size estimate

•     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 unique

•     No errors in identification - more likely with natural than dedicated artificial marks -computer matching

•     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



Concerns re use of natural marks for estimating population size

•     Populations studied must be geographically closed

•     Samples must be representative of the population

•     Sample sizes must be sufficiently large


Concerns re use of natural marks for estimating survival

•     Adult survivorship most influential life history parameter in demography of most marine wildlife species

•     MRR studies often best method of measurement

•     Study must be sufficiently long - for long-lived species such as whales - 10 years.

•     Probability of recapture must be high >0.2

•     Probability of individual identification should be homogeneous

Case study 1: southern right whales off South Africa

Case study 1: southern right whales off South Africa

•     1979-1987 aerial surveys photographs of females with calves

•     Females calve 2-4 years - probabilities of recapture unequal between years

•     Population increasing

•     Purpose built model for closed populations built to handle unequal capture probabilities

•     Best estimate 286 adult females (95% CI 265-301)


Case study 2: Antarctic minke whales

Case study 2: Antarctic minke whales

•     Individuals can be identified

•     Extensive effort required to obtain photographs

•     Assume model assumptions satisfied

•     Assuming:

–    population size of 100,000

–    accuracy of 0.25  - (95% CI 75,000 - 125,000)

•     415 ship days yr 1, 296 yr 2

•     Sighting 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

•     Population size ? But 677 marked individuals

•     Closed populations: No - not assumed

•     Marking method: Photo ID propeller scars

•     Homogeneous capture probability - unlikely

•     Duration 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 only

•     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 adults

–   confined sampling period each year 1 November - 31 March

–   multiple sampling within sampling period

•     Assumption- identifying one individual in sample does not affect probability of sampling others - okay as no defined social groups

•     excellent precise estimates of survival e.g., adult Crystal River 0.962 s.e. 0.009 95% CI 0.943-0.981





Case study 4: Dugongs in Moreton Bay

Case study 4: Dugongs in Moreton Bay

•     Population size ~1000

•     Closed population ? but unlikely - dugongs move

•     Marking method - rodeo capture and PTT tag/DNA fingerprint

•     Risk of capture mortality ~ 1%

•     Homogeneous capture probability - unlikely

•     Precise population estimate - capture probability 0.3-0.5

•     Survivorship - capture probability 0.5 and 10 year study


Take-Home Message

•     Photo-ID studies are more than mucking about in boats with marine mammals!!!!!

•     Need mathematical evaluation before you start to consider likely effort required to achieve meaningful results

•     Need to test assumptions of MRR model

•     Need access to long-term funding

•     Need to address ethical issues if actual capture involved



•       Caughley, G. and Sinclair, A.R.E.1994. Wildlife Ecology and Management. Balckwell Scientific Publications.

•       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.

•       O’Shea 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. O’Shea, 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                x                  x

Short, hoof-like nails   5/4 or 4/3         4 /3       4/

No clavicle                x                x                  x

Pectoral mammaries   x                x                       x

Abdominal testes     x                   x                  x

 “Horizontal molariform

  tooth replacement     x                    x             x


SIRENIA:  Unique among all orders?

•     Habitat and diet  ________ &  _________

•     A mere remnant of a once diverse group (20 genera) of the Miocene

•     Distribution:   Dugongidae & Trichechidae

•      Four extant & one recently extinct species





SIRENIA:  Unique among all orders?

•     Habitat and diet  ________ &  _________

•     A mere remnant of a once diverse group (20 genera) of the Miocene

•     Dugongidae & Trichechidae compared

•     Dugongidae (with forked tails): one species                 Dugong of Indonesia (Stellar’s sea cow: extinct)

•     Trichechidae: Distribution of 3 species:            W. African, Amazonian,

    and West Indian or Florida Manatee

West Indian Manatee

•     One of four species in a declining,                     endangered (?) order

•     Characteristics of endangered species

•     Physical characteristics and distribution

•     Habitat requirements & Feeding behavior

•     Reproduction:  5-15% of population in 1st year calves

•      Major causes of mortality

•     Conservation:  Recovery Plan & recent issues

•     Current status:  n ~ 1900,  ~ 8% annual mortality


 Characteristics of Endangered Species :

•     Adapted to stable, undisturbed communities

•     Low natality and low natural mortality

•     Specialized, narrow habitat or environmental requirements

•     Historically restricted in distribution, on periphery of range or low in density

Natural History of Manatees

•     2-3 meters long, 350-450 kg, no hind limbs

•     Former range reduced to Florida & Puerto Rico

•     Habitat:  Shallow, warm fresh to marine waters with abundant aquatic vegetation

•     Feed 4-6 hrs/day, consuming 25-35 kg/day

•     Reproduction: Polygynous,

    - 1st breed at 4-6 yrs, every 3-4 years thereafter

    -  single calf, 390 day gestation,  nurse ~1 year

•     Is this characteristic of an endangered species?






Some survivors from the Pleistocene have been driven to extinction during historical times by over-exploitation:

Sea Cow

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.

Surviving relatives

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 protecting manatees.

. 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. 








Dugongs, or 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.



. Relatives

Dugongs are 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 Steller’s sea


. cow, 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).


Dugongs inhabit shallow, tropical waters throughout the Indo-Pacific region. Most of the world’s population of dugongs is now found in northern Australian waters between Shark Bay in


. Western Australia and Moreton Bay in Queensland.

Life in the sea

Dugongs swim 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.


Dugongs have 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.



. Declining numbers

Dugong 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 1960’s, 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




. Experts 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),


. Sea Otters

When the 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 Island) population


. 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.

Another 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.




Fur 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).

Harp seal.  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


. allowing 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.

Another herd of harp seals, at Jan Mayen Island in the Arctic ocean, was


. wiped out by a rapid boom and bust between 1840 and 1860.

Elephant 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 subspecies) was


. 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 are


. approximately 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.

Walruses were 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.