Human-caused conditions that can result in a marine mammal stranding
include trauma and harassment or disturbance. On average, 5-8%
of California sea lions treated here have sustained human interaction
injuries from net, fishing line or packing strap entanglement;
boat propellers; or gunshot. On average, 25% of harbor seal
pups admitted by The Center need to be rescued as a result of
human disturbance.
Entanglement
Marine mammals can become entangled in fishing nets, fishing
line, and various types of plastic debris. Most fishing nets
are made of plastic rope or nylon monofilament line. Monofilament
line is virtually invisible in the water. Gillnets capture
fish of a certain size when their gills become caught in the
mesh. To minimize accidental catch of marine mammals, gillnets
are only legal in specific offshore areas. Driftnets, which
are large gillnets several miles long, are illegal in U.S.
waters. Ghost nets are abandoned or lost pieces of nets that
float unattended, catching whatever they encounter.
A marine mammal can swim through openings (usually 4"-8"
in diameter) in these nets and plastic debris, and cannot
back out. As the animal continues to grow while the plastic
remains entangled around it, the net does not expand with
the animal. If the animal is entangled around the neck, it
can interfere with swallowing, obstruct major blood vessels
or interfere with the airway. If the net is large enough,
the weight of the net will interfere with the animal's ability
to forage.
Sea lions have also been admitted with packing straps around
their necks. These cause the same damage as a gillnet. If
the animal is caught and the netting or packing strap removed,
it has a good chance of surviving. Animals are treated with
antibiotics to help with secondary infections. The wounds
are kept clean to maximize healing.
Boat Propeller Wounds
Boat propeller wounds vary in severity. They can be anything
from minor lacerations to major amputations. One sea lion
that was admitted to The Center had one quarter of his upper
muzzle cut off by a boat propeller, but was rehabilitated
and released. These wounds are treated in the same manner
as shark bites and entanglements.
Firearm Wounds
Firearm wounds also vary in severity. Some marine mammals
have been admitted with one shotgun or rifle wound, others
have had thirty or more shotgun pellets embedded all over
their bodies. Generally, injuries are sustained to the head.
Eyes are often affected in shotgun injuries. Prognosis in
these cases varies greatly. Damage can be minor or so severe
that the animal must be euthanized. The bullets or pellets
can cause brain damage, nerve damage, paralysis, shattered
or broken bones, damage to internal organs, blindness, seizures
and pneumonia. Sometimes surgery can be performed to remove
bullets or bone fragments that are causing an infection and
to repair fractures.
Harassment
Harbor seal pups
are the most frequently documented victims of harassment or
disturbance at The Center. After giving birth, harbor seal
mothers will leave their tiny pups on beaches and rocks as
they forage offshore. Well-meaning coastal residents and visitors
who attempt to help these pups by taking them home, returning
them to the water, covering them with blankets or approaching
them too closely are actually doing more harm than good. Other
forms of harassment include allowing domestic pets to approach
pups too closely. In an average year, 25% of harbor seal pups
rescued by The Center suffer from maternal separation as a
result of some form of human interaction, including illegal
pickup, disturbance or harassment. A seal pup's best chance
for survival is to remain with its mother because the seal
mother's milk contains important antibodies no substitute
formula can provide.
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Human
Interaction: Trauma and Harassment