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Many cases of humans
interacting with dolphins, both positively and negatively,
exist. Humans have slaughtered millions of dolphins in the
name of wealth, while other humans have tried to save them.
Dolphins have been kept in captivity, causing a great deal of
controversy over the ethical implications of such activities
as research and performance. This section discusses three
major issues regarding the relationship between humans and
dolphins: threats, conservation, and dolphins in captivity.
Threats to Dolphins
- Types of
Threats
- Directed
Takes
- Incidental
Takes
- Habitat
Degradation
- Pollution
- Disturbance
- Specific
Cases
- Eastern
Tropical Pacific Tuna Purse-Seine Fishery
- The
Root of the Problem
- Dolphin
Behavior in the Nets
- History
of the Fishery
- Attempts
to Reduce Kills
- New
Concerns
- Black
Sea Fishery
- Chilean
Crab Bait Fishery
As with a lot of other types of
animals, the advancement of human civilization has started to
threaten the survival of many types of small cetaceans. Two
threats that profoundly affect small cetacean populations are
direct taking, where the target of the hunt is the dolphin
being caught, and incidental taking, where dolphins are caught
or killed as a side effect of the method being used to catch
other species. In addition, many species are affected by
habitat degradation, pollution, and disturbance. River
dolphins are especially vulnerable to these threats; the most
endangered species of small cetacean is the Yangtze river
dolphin or Baiji.
Types of Threats:
Directed Takes
In recent years, there has been a
general increase in the directed taking of small cetaceans in
lesser developed countries. These new and expanding fisheries
require careful, but tactful monitoring. Many fisheries are
for cetaceans in general rather than for specific types, so
managing them on the basis of individual species is difficult.
In Japanese waters, there is extensive directed take, mainly
for human consumption. Some fisheries are for certain species
of small cetacean, while others are generic. In South America,
some of the resident species are hunted for crab bait, and
many of those species are already vulnerable to incidental
take. Sri Lanka has many generic small cetacean fisheries
which might threaten some local populations.
Incidental Takes
Incidental takes most often occur
when specimens get caught in large nets set to catch fish.
Unable to escape or reach the surface, they drown and perish.
Certain types of fishing gear, such as set nets, are
particularly dangerous to small cetaceans. This problem may
represent a greater threat to cetaceans than directed takes.
For several populations, including the Baiji of the Yangtze
River, the hump-backed and bottlenose dolphins off eastern
South Africa, and the striped dolphins of the Mediterranean
Sea, the mortality rate due to incidental taking is greater
than the maximum amount that the population can sustain
without significant decline. The effects of this type of
threat on the dusky dolphins of the eastern South Pacific and
the northern right whale dolphins of the central North Pacific
is also a source of concern.
A major concern is large-scale
monofilament pelagic driftnetting. It causes overexploitation
of the fish population, and marine mammals and seabirds often
get entangled in them. Also, discarded nets, sometimes called
"ghost nets," remain active for several years,
during which they continue to entrap cetaceans. In a
resolution made on 22 December 1989, the United Nations
General Assembly agreed to end pelagic driftnetting by the end
of June, 1992 unless and until procedures to reduce the
problems of this type of fishery could be implemented. Some
countries took steps to forbid any use of pelagic driftnets
within 360 kilometers of their coasts.
Habitat Degradation
The encroachment of human
civilization on natural habitats also represents a serious
threat to the survival of some stocks. Coastal development may
destroy fish nursuries, eliminating the food supply of the
local cetaceans. Coastal mangrove swamps, found in tropical
regions, are a very important habitat for some species of
cetecean, especially the hump-backed dolphins of South Asia
and West Africa. These areas are both fish nursuries and
shelters for adult fish. Continued urban development and
industrialization threatens these regions. The damming of
rivers on such systems as the Ganges and the Amazon has a
nasty effect on riverine populations. In addition to the
ecological effect resulting from the change in the flow of
water, riverine populations may be permanently separated.
Individual stocks may not be viable in the long term and
seasonal migrations may be disrupted.
Pollution
Pollutants enter the food chain
near its bottom and build up in top predators, such as
cetaceans. In addition, cetaceans may injest the wastes and
debris from discarded fishing gear. Mineral exploration and
exploitation are also a concern, but unless cetaceans are
caught in survey explosions or oil spills, the danger is
probably minimal. The effects of such toxins on cetaceans are
not entirely clear. The death of cetaceans due to pollution is
difficult to recognize, especially when it occurs in large
numbers. In other mammals polychlorinated biphenyls (PCBs)
adversely affect reproduction, and the same may hold true for
cetaceans.
Disturbance
Ironically, an important method
of improving public awareness about cetaceans and promoting
conservation measures may also be a serious threat to these
creatures. In addition to normal ship traffic causing death
due to collisions and propeller injuries, the increase in
visitors that come for whale watching expeditions may disturb
these animals. Studies show that if the visitors are careful
and treat the resident cetaceans with propriety, the animals
will have no difficulty acclimating. Commercial whale watching
outfits are careful to ensure that visitors are tactful, but
private individuals may not understand all of the necessary
provisions.
Specific Cases
Eastern Tropical Pacific Tuna
Purse-Seine Fishery
Every year between 1959 and 1972,
the tuna fisherman of the eastern tropical Pacific killed
hundreds of thousands of dolphins, mostly spinners and spotted
dolphins. In a report by the National Marine Fisheries
Service's Southwest Fisheries Center made in 1979, the
estimated total number of dolphins killed between 1959 and
1972 was 3,796,658. That figure is probably an underestimate,
since it does not include individuals that were injured in the
nets and died later. The level of incidental take is
sufficient to pose a serious threat to the survival of some
stocks.
The Root of the Problem
The basis of the problem is that
the two main species involved associate in large numbers with
yellowfin tuna. The nature of the association between the
dolphins and the tuna is still a mystery, although there are
some theories that try to explain it. It is possible that the
relationship is symbiotic, as the tuna are most active during
the day and the dolphins are most active during the night, so
one group can rest while the other group feeds. A similar
relationship is seen between spinners and spotters.
Regardless of the reason, the
fact that the three species school together allows the tuna
fishermen to find schools of tuna very easily. In 1959, they
discovered this relationship and began to exploit it.
Fishermen look for a commotion on the horizon, indicating
feeding seabirds, leaping dolphins, or both, and could
indicate the presence of tuna Since spinners and spotters
aggregate in the thousands, schools are not difficult to see
even at a distance. When the tuna boat is in range, speedboats
known as pongas are lowered and herd the school together. When
the animals are compactly herded, the seiner lowers the net
and surrounds the herd, trying to trap both dolphins and tuna.
At first, the purse seine is about 1.6 km long and open,
forming a wall. It is also open at the bottom, but herded
individuals do not go under it to escape, probably because the
water at a depth of 200 meters is too cold. The pongas
continue to roar around the perimeter, making another barrier.
When the dolphin school is completely surrounded, it is
pursed, that is, it is closed at the bottom using a cable that
passes through a series of rings. Every creature in the school
is trapped. The net is then drawn onto the boat through a
power block, the one invention that made this kind of fishing
possible. Captured individuals are stacked methodically on the
deck as the enclosure shrinks.
Dolphin Behavior in the Nets
Further compounding the problem
is the fact that spinners and spotters tend to be timid,
easily frightened, and fearful of objects. They depend on the
presence of other dolphins and do not react well to new
situations. As a result, they tend to react to the purse
seines by panicing rather than by attempting to escape as they
easily could given their acrobatic abilities. The passive
behavior of these animals is described as a form of
"capture myopathy" and often leads to death.
Although normally a factor that aids their survival, in the
case of purse seines, their timid nature is deadly.
When not herded or chased,
spinners and spotters swim slowly and spread over a long
distance, often with between 20 and 30 body lengths between
different individuals. When they are chased, they crowd
together, leaving only 2 to 3 body lengths between them. They
also move more quickly, making low leaps from the water, as it
is the most efficient method of swimming. As the school is
surrounded by the nets, various behavior patterns emerge. In a
practice called milling, a large percentage of the school
stays in one area, swimming and diving. Early in the set,
there is some leaping, but that quickly subsides. In addition,
some individuals start rafting, where a group hangs vertically
in the water, head up. Individuals align themselves in layers,
discrete bands oriented horizontally. Groups of four to five
individuals make up each layer, and there may be up to four
layers stacked vertically. After surfacing to breath, always
return to their original position. Often some dolphins just
passively sink slowly to the bottom of the nets, probably as a
reaction to the stress from the boats, the noise, and the
wake. This type of behavior is understandable considering that
spinners and spotters are used to the open ocean where they
have no barriers or confinement. Although spinners usually
separate from the spotters in a net, they do exhibit similar
behavior. However, spinners tend to move around more in the
nets, and are located more in the periphery.
History of the Fishery
Before the fishermen discovered
the dolphin-tuna aggregations, they used a method of giving
the tuna bait until they were in a feeding frenzy, at which
point they would bite anything, including unbaited hooks. By
1960, however, the new purse seine method had largely replaced
the old method. In 1966, 62% of the tuna caught in the Pacific
were in association with dolphins.
In the early years of the purse
seine fishery, everything in the net was hauled aboard. The
valuable tuna was kept, while the dolphins and other fish were
tossed overboard. The tuna fishermen did not publicize this
slaughter, although the information did eventually leak. The
problem was noticed by William F. Perrin, who was working on a
Ph.D. dissertation on Stenella at UCLA. Scientists quickly
began a study of the dolphins from this fishery. Much
information was collected, and the species involved went from
little known to some of the most intensively studied.
Based on an extrapolation form
the early irregular data supplied by fishermen, some estimates
were made on the annual kill rate. In 1959, before the entire
fleet had switched to using purse-seine, up to 100,000
dolphins were killed. By 1960, when the entire fleet had
switched, an estimated 500,000 individuals were killed. Before
the examination started, no records were kept on the
proportions of species involved. Later studies showed that the
species most involved was the spotter, then the spinner, and
then the common dolphin. Several additional species were
involved in small quantities.
Attempts to Reduce Kills
As a by-product of the
tuna-dolphin problem, the Dedicated Vessel Program was
started. Under this program, a tuna boat performs its regular
duties with a team of biologists on board. These scientists
monitor the dolphin kills and the behavior of the dolphins in
the nets. As a result of these observations, much more care is
taken by the tuna fishermen. On one tuna boat in 1977, only 11
dolphins died in a total of 20 sets. On the Queen Mary in
1978, out of 17 sets, only three dolphins perished. In
addition, it was seen that some dolphins were already familiar
with the nets. They stopped swimming and knew how to escape
the net using the methods developed by the tuna fishermen to
lower the casualty rate.
Very soon after the purse-seine
fishery developed, various techniques were put into use to
protect the dolphins. These methods were used not necessarily
to help the dolphins, but to reduce the labor of removing the
dead dolphins from the deck, as well as to avoid depleting the
entire dolphin population, lest there be no more dolphins to
use. These strategies mostly revolved around releasing the
dolphins from the nets before they were killed. In one method,
known as "backing down," when one half of the net
had been hauled in, the vessel was put in reverse, and the net
was drawn into a finger-shaped configuration. At the far end
of the finger, the water pressure against the webbing cased
the net to sink. The dolphins literally have the net pulled
out from under them. Although this technique worked to some
degree, thousands still died every year. In addition, tuna
sometimes escaped during this maneuver, and some captains were
more interested in preserving the tuna then in preventing the
slaughter of the dolphins. Fine meshed panels like the Medina
panel and the super-apron were also developed to prevent
entanglement and facilitate the escape of the dolphins.
By the 1970s, the United States government was under a
great deal of pressure from humane and conservation groups and
began monitoring the situation. When the American public
noticed the problem, their outcry helped to cause the passage
of the Marine Mammal Protection Act of 1972. The tuna industry
was given a two year grace period to reduce dolphin kills.
They did not abide by this, and only after a long drawn-out
legal battle was any action taken. The techniques developed to
release the trapped dolphins were probably not strictly
enforced throughout the international tuna fleet. In addition,
some of the reduction in the reported kill may have been
because ships previously under United States registration
changed their flag to avoid strict US regulations.
Despite the problems in enforcing the legislation, the kill
rate was reduced significantly during the 1970s. Whereas in
1973, a total of 114,087 dolphins were killed, by 1978, only
21,805 were killed. The most important factor was the pressure
on the fishermen and the techniques to release trapped
dolphins. In October of 1980, a quota of 20,500 dolphins was
set for all species by the United States government. The
previous year's kills had not been that high, and it appeared
that the problem had vanished.
New Concerns
New concerns have cropped up, though. The Porpoise Stocks
Workship in La Jolla analyzed the earlier data and found that
the estimates on population were seriously flawed. The actual
number of spotters in the eastern tropical Pacific was much
lower than previously assumed. Earlier estimates were based on
the estimates of school size given by the observers and crew
members on tuna boats, while estimates in 1979 were based on
aerial observations. The 1979 report gave an estimated
offshore population of 34-55% of the 1959 level. This is below
the optimal sustainable pouplation, where the population level
leads to maximum net productivity. The same data analyzed in
1973 gave a population of 92-95% of the 1959 level, which is
in the OSP range. The population in 1959 was probably more
like three million than the four million originally assumed,
and as more than four million dolphins were killed between
1959 and 1978. Although some did reproduce, the population was
probably at a critical stage.
The government could declare the spotters depleted, if the
population has declined much over several years, and if the
decline continues it will be eligable for the Endagered
Species Conservation Act of 1969, or if the population is
below the optimum carrying capacity for the species or stock
within the environment. If it does so, no taking will be
allowed at all. Tuna fishermen complain that they will be shut
down entirely if this happens. They state that they have
cooperated with environmentalists and reduced kills
significantly. They threaten to change the flags of their
ships to countries without provisions if the government
declares the species depleted. Doing this would place the tuna
fishermen outside of the jurisdiction of the laws of the
United States and would free them to kill as many dolphins as
they wish. As a result, conservationists are sometimes on the
side of the tuna fishermen.
Black Sea Fishery
Between 1870 and 1983, in the Black Sea, there existed a
fishery for three species of cetacean: the bottlenose dolphin,
the harbor porpoise, and the common dolphin. The method of
catch was similar to that of the eastern tropical Pacific tuna
purse seine fishery, but the dolphins are the prime target
instead of the tuna. When herding the dolphins, fishermen
clang together cobblestones, causing the dolphins to panic and
run into the nets. When the fishery started operation,
harpoons were used, but that method was later replaced by
purse seining. The main products of the fishery were food and
oil.
Four countries were involved in this fishery: Turkey,
Romania, Bulgaria, and the USSR. An estimated total of 200,000
dolphins were taken each year, a shocking 20% of the
population. The effects of depletion became evident after the
Second World War, when the USSR could not reach the same rates
of catch as in the 1930s. Between 1931 and 1941, the USSR took
110,000-130,000 dolphins per year, but in later years, it only
averaged 75,000 per year. The Turkish fishery's destruction of
the breeding stock and the young during breeding season was
blamed for this. In 1966, the fishery operations in all
countries except Turkey stopped, due to a collapse of the
population. The Turkish fishery is not well documented, since
many individuals were killed from small boats using rifles and
shot guns, leading to a high loss rate.
The Turkish fishery was banned in 1983, however there is
much concern that it might reopen when a reassessment of the
stock is made. The fishing industry is putting forth much
pressure to end the ban. Although the European Community bans
the import of cetacean products of commerical uses, Japan is
an open market for the products of this fishery, and it is
already a destination of many of the products of current
Turkish fisheries. The Berne Convention includes an exemption
clause, allowing species listed under Appendix II to be taken
to prevent serious damage to fisheries, as long as the
survival of the species is not threatened. The fishery might
reopen under the provisions of this clause.
Chilean Crab Bait Fishery
The waters of the Strait of Magellan are an important
source of crab meat, and the fishery there is expanding.
Unfortunately, the fishermen who need bait to catch these
crabs have turned to the local dolphin population. Under
Chilean law, the slaughter of dolphins for crab bait is
illegal, but because the region is so remote, the laws are
difficult to enforce. As of the early 1990s, only four of the
26 companies operating in the Magellans provided crab bait to
the fishermen, and in most cases, the amount supplied wasn't
nearly adequate. The Commerson's and black dolphins are known
to be involved in this operation, as well as seals, sealions,
penguins, guancos, and other wildlife. There are very few
estimates of the level of take, but the dolphins killed may
number in the thousands. It is feared that the dolphins are
being killed too rapidly to be replenished naturally. |
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