Biol. 317 - Lecture notes –
Chapter 17 (Oil pollution)
Ch. 17 – Additions of
Materials to the Oceans
Additional review questions:
What are the sources of pollution
entering oceans?
shipwrecks,
dumping, airborne
What are PAHs and why do they tend
to become concentrated in marine sediments?
How does “oil” differ
depending on the variety?
What is the behavior of spilled
oil?
What are treatments for dealing
with oil spills?
Why is there a question about
whether or not to spray dispersants on oil spills?
Lecture notes – Chapter 18
(Harvesting the sea)
Fishing adds a predator
Affects
target species
–
largest individuals are taken first
–
average size of individuals decreases
Examples:
Canadian
West Coast ling cod
Peruvean
anchovies
South
African pilchards
–
not necessarily damaging until size decreases to
size
of reproductive maturity
Affects
predators of target species
Example:
Pinnipeds
feeding on pollock in Alaska
Affects
prey of target species
Example:
Krill
near Antarctica
Fishing can impact non-target
species
Examples:
Pacific
squid drift nets and incidental catch
1989
season:
500
turtles
4,000
northern fur seals
14,000
albatrosses
24,000
dolphins
186,000
dark shearwaters
228,000
skipjack tunas
1,163,000
blue sharks
1,377,000
albacores
31,748,000
pomfrets
Pacific
yellowfin tuna fishery in 1960s
200,000
to 500,000 dolphins
Ghost
fishing (abandoned gear or nets)
Overfishing – fishing harder
than needed
It
is probable that we could catch more fish with less effort in most fisheries
Maximum
sustained yield (MSY)
maximum
tonnage of organisms that could be taken from a harvested
population
each year without eventually destroying the population
measured
in metric tons (tonnes)
Catch
per unit effort (CPUE)
tonnage
of the catch divided by the amount of effort invested in
obtaining
it
–
CPUE goes up quickly in unexploited population
–
increases until MSY level is reached
–
then CPUE goes down
–
best if intermediate-size individuals are selectively taken
–
this leaves the fewer, larger, individuals for reproduction
Examples:
plaice
prior to WWII
Global
fisheries –
Are
we close to the MSY for all the oceans?
–
United Nations estimates by Food and Agriculture Organization (FAO)
–
these do not include “artisanal” catch (taken by individuals for
their own
food
or for trading)
–
artisanal catch is estimated to add another 28%
John
Ryther (WHOI) has estimated the productivity of all oceans (Fig. 18-9)
–
his estimate of 242 million tonnes is approx. 3X 1987 harvest levels
–
estimates for MSY for all oceans varies from 60 to 100 million tonnes
–
United Nations assessment from 1987 reports that only 25 of the
280
stocks of fishes worldwide are presently “underexploited”
or
“moderately exploited”
Krill
is the most significant stock that is presently underutilized
–
these are near Antarctica (as unaccessible as they can get, making
their
havest costly)
–
they taste/appear like cooked maggots
–
market for “fish meal” is uncertain
–
present high levels are likely a reflection of removal of baleen whales
–
exploiting these stocks would likely affect the many mammals and
birds
that depend on them
Aquaculture
In
terrestrial environments, we vastly increase the amount of food
that
is produced by farming
Some
types of aquaculture have tremendous potential for producing
protein
–
even though we get only 2% of our calories from
the
sea, we get 12% of our protein
Examples:
Shellfish
Nori
–
both take advantage of tides to bring food/nutrients to
farmed
organisms
–
both produce much more protein per unit area than
comparable
farms on land
Salmon
rearing to fry stage is similar in that it takes advantage of the ocean’s
nutrients/food
Other
types of aquaculture require 4 to 8 times more protein than they provide
Example:
Salmon
farming
Aquaculture
can also have many damaging effects
disease
compete
with native populations
introduction
of invasive species