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SECTION 2
There are several hypotheses to explain
why marine mammals become entangled in fishing nets.
Here are some of them:
- Marine mammals that live in the open ocean do not
understand the concept of a large barrier such as a
gill net. They don't recognize nets as a danger, or
they make mistakes while trying to navigate around
nets.
- The animals become entangled while investigating
nets as strange, new objects.
- Marine mammals (especially seals and sea lions)
learn to associate nets with a "free lunch."
They are attracted to the fish caught in the nets
and become entangled themselves while eating the fish.
We also want to investigate when marine mammals use
echolocation (biological
sonar) and
when they use their sense of sight. It may be possible
that:
- Dolphins and porpoises do not see the nets with
their eyes because the water is murky (clouded) and
shallow where the nets are used, or they do not see
the nets at night.
- Dolphins and porpoises are able to "see"
gill nets with their echolocation. However, they panic
when they run into nets at times when they are not
using their echolocation.
- Marine mammals would see the nets if they were
designed to be easily detected by the
animals' biological sonar.
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We can also use a variety of research techniques with
captive animals that are difficult or impossible to
use in the wild. We can use both under- and above-water
video cameras to observe an animal's behavior. We can
use hydrophones (underwater microphones) mounted in
the pools to record the calls and echolocation of the
dolphins and porpoises. We can see whether the animals
become used to the pingers by controlling how often,
and for how long, we let different species hear the
sounds.
