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Humans and Dolphins
The World of Dolphin
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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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