Environmental Engineering Reference
In-Depth Information
polar to equatorial regions). Floating debris is well known to be the major cause of
injuries and deaths of numerous marine animals and birds, because they misinterpret
them for prey and eat them or sometimes become entangled in it. It has been reported
that in 1997, about 6.4 million tonnes of garbage reached the marine environment
every year. The United Nations Environment Program (UNEP) has reported that there
are currently over 13,000 pieces of plastic debris loating on every square kilometer
of ocean [8], whereas, in 2006 it was 18,000 pieces/km
2
per square kilometer [9].
There are many different sources of human made marine debris that are both from
the land and sea which include: littering, losses of plastics, landills, storm drains
and manufacturing plants, from land sources and ishing gear, recreational boats,
offshore drilling platforms, rigs and garbage from ships. So far 267 different species
are reported to have suffered from entanglement or ingestion of this marine debris
(including turtles, seabirds, sea lions, seals, mammals and ish). Derraik [10] reported
that marine debris present on the seabed can inhibit the exchange of gases between
the pore waters of the sediments and their overlaying water, that ultimately affects
the oxygen supply in the sediments. These oxygen deiciencies in turn interfere with
the organisms that are present on the seabed and inally affect the ecosystem and as
well as the organisms living on the seabed will also be at risk from ingestion of or
from entanglement with this marine debris [10].
1.3 Entanglement
Marine mammals, seabirds, seals, sea lions and sea turtles are found injured or killed
when they get entangled in marine debris. The major plastic debris includes ishing
nets, ropes, six-pack rings, packing strapping and monoilaments. They cause the
death of the organism by suffocation, drowning, starvation and from physical injuries.
About 7.9% of the sea animal population is reported to be entangled in marine debris.
In some cases this entanglement is a threat to endangered species. In the Southern
Ocean, it is estimated that about 58% of sea lion and seal species are known to have
been affected by entanglement which includes the Australian sea lion, hawaiian
monk seal, New Zealand fur seals and so on. Many different species of whales,
porpoises, dolphins, turtle and 51 species of seabirds are known to have been affected.
Ghost ishing (capture of a large quantity of marine organisms) from the discarded or
lost ishing nets and pots that trap/catch ish is a serious problem, even though they
are not in use. This results in a economic loss for the isheries [11]. Approximately
130,000 small cetaceans namely dolphins, porpoises and whales are caught in
discarded nets every year even though the exact amount may be much higher.
Entanglement of a sea animal impairs its ability to swim, which prevents it from
inding food or escaping from predators. Entangled seals must increase their metabolic
rate to compensate for increased drag force required during swimming.