Hello marine biology students.
In this video we're going to talk about fisheries
and management.
[Intro Music]
So clearly, fisheries have been overfishing
in the past.
To learn more about this and also how they
might be managed, we need to understand some
concepts about optimal yield and population
growth.
Marine species are renewable resources, but
in order for a fishery to last indefinitely
it must be fished in a sustainable way.
The sustainable yield 
is the amount that can be caught from a population
and yet still maintain a constant population
size.
Now, at first guess you might assume that
any sort of collecting from a population would
result in that population size going down,
but that's not exactly the case.
If you have a very large population, the population
growth will actually be reduced due to competition
within that population for resources, for
space and for other materials.
If that large population has individuals taken
from it, it will actually allow for rapid
growth to replace those lost individuals.
Keeping the harvesting of a population in
that range, where it can replace those individuals
which were collected, is the ideal area.
This is the sustainable yield, and a fishery
that stays in a sustainable yield will last
indefinitely.
The maximum sustainable yield, in business
terms, is the ideal, because that is the highest
catch that can be maintained year after year
without affecting the stock.
Maximum sustainable yield would result in
the highest profits on the business side of
things and yet allow that population to not
start being depleted or going below its replacement
size.
If catches fall, despite increased fishing
effort, then overfishing has occurred.
This means that even if you increase your
fishing effort but you do not catch more fish,
you are overfishing this particular population.
Now, market forces, the laws of economics,
often cause this to happen, because if fishermen
are making money, then other fishermen will
be attracted to the fishery and causes overfishing
to occur.
The long-term survival of a fishery should
be the goal both of the fishers and of the
market and of the managers and it often is,
but when some individuals start collecting
more fish, they get more profits and yet the
cost is distributed to everyone else.
And so, in strict terms of capitalism, there
is often little reason to restrain from collecting
as much as you can for yourself before stock
is depleted, and unfortunately that results
in this overfishing that has been seen again
and again.
It is estimated that about 70% of marine fishes
are already overfished.
This is especially true for large species
like tuna, swordfish, and sharks.
In many of these species, the fish that are
harvested today are about half the size of
those that were harvested 20 years ago.
As one example, big eye tuna were two times
as heavy and eight times more abundant in
the 1950s than they are today.
In the swordfish fishery, catches fell 70
percent between the 1960's and the late 1990’s
and this wasn't due to lack of effort.
Remember, this effort was probably increasing
three to four times what it had been.
A campaign 
to reduce consumption of these fish has been
successful and we've seen that some swordfish
populations
are recovering as we've reduced some of this
pressure on them.
Other dangers to fisheries include not just
the depleting stocks of fish, but also habitat
destruction, especially if this habitat destruction
happens at critical breeding grounds like
seagrass beds, estuaries, and mangroves that
are being rapidly destroyed.
This is especially detrimental since 75% of
commercially important species use estuarine
areas 
as nursery areas.
Another very damaging fishing practice is
that known as bottom trawling and that's because
these trawls damage the ocean floor, which
is detrimental
to demersal and benthic species.
A fishery is regarded as collapsed 
if numbers fall to 10% of their historic highs.
It is estimated that one third of fisheries
have already collapsed.
A recent study has indicated that all major
fisheries will collapse by 2050 if protective
measures are not taken to better manage and
protect these resources.
Now, this isn't all bad news, because some
of these protective measures are working,
yet it's not easy.
Management can be difficult for many reasons.
This is because, one, the maximum sustainable
yield is a difficult number to calculate.
How much can you take from a population and
still allow that population to recover in
size?
Well, how much food is available this year?
Are there any reasons this year is different
than previous years?
What has the catch been and what was the mortality
been?
These are all pieces of information that you
need to get an accurate answer here and a
lot of times those numbers are simply unavailable
or prohibitively difficult to obtain.
Sometimes your understanding of a species
and its method of competing with other species
takes into account its current population
size, but if the harvested species’ population
size falls, the harvested species may not
be able to compete with other species as effectively
and that may mean that population may not
rebound as quickly or replace the numbers
that were expected.
It also turns out that real fisheries are
more complex than the models that are used
to predict them.
Another difficulty is that the high seas are
common property and rules of regulation of
one country that fishermen might follow may
not necessarily prevent fishermen from other
countries from collecting from that common
area and thereby depleting the stocks.
Another difficulty is that fisheries often
underreport how much they've collected and
so if the managers are trying to figure out
the population size and its ability to rebuild,
their estimations are only as good as the
data that they use.
So what are ways to limit a fishery?
Well, one, you can declare a certain catch
that can be collected from an area and you
can close that fishery once that catch is
met.
Another is by controlling the length of the
fishing season that is allowed.
Another is by determining which areas are
open for fishing.
Again, it's not that fishing of any sort needs
to be banned, it just needs to be managed.
Other ways to limit a fishery is by limiting
the number of boats that are permitted to
fish, the type or the size of the fishing
gear that's used, the allowable size of the
fish that are caught, the number of catches
that are allowed per boat, are also limiting
the fishing methods.
Here in this image we can see the effect of
using nets with three different mesh sizes.
In the first size, all fish are caught, of
all species.
In the second one, fish of the smaller species,
the sardines, they are allowed to go free,
whereas the larger fish are kept behind.
If the mesh on that net was even wider, it
might allow only for the harvesting of the
largest of individuals from that population,
and so that would allow the younger individuals
to continue to grow and reproduce.
Now, it all depends on the population you're
working on, because sometimes it's the larger
individuals that are hundreds even thousands
of times more reproductively successful than
the middle sized individuals and so maybe
it's the middle sized individuals that should
be collected.
In 1996 the U.S. sustainable Fisheries Act
was passed and this sustainable Fisheries
Act required federal fisheries managers to
develop plans to avoid overfishing, to restore
depleted stock, to reduce bycatch (which are
organisms that are caught that are other than
the targeted species and often have little
to no commercial value and end up getting
dumped back into the ocean usually dead and
dying).
This act required all fisheries to be managed
in a way that they would be sustainable that
U.S. fishermen must abide by the rules as
well as foreign fishermen with valid permits
who are fishing within the U.S.
The Pews Ocean Commission also calls for management
of ecosystems in addition to just fishery
stocks.
Another way to manage fisheries is by developing
new fisheries.
These new fisheries may be developed 
by increasing the use of discarded bycatch.
While some of these species may not be appealing
to customers, some species like pollock may
actually be used in making different types
of products such as surimi or imitation crab.
Other untapped potential fisheries include
some species of squids, which are found in
high abundance, flying fish, which are not
regularly fished at this point and also lantern
fish 
of the mesopelagic.
In fact, these lantern fish might be one of
the largest untapped fisheries at this point
and if they are harvested in a sustainable
way, their populations would be able to replace
themselves and many of the current industrial
practices that use clupeoid fishes might be
just as effective using lantern fish.
Aquaculture is another method of trying to
help protect native populations.
Aquaculture 
is the application of farming techniques to
the growth and harvesting of aquatic organisms.
The term mariculture 
apply specifically to the culturing of marine
organisms.
Now, the number of marine organisms harvested
through mariculture has risen threefold since
1990.
As an example, farmed shrimp now account for
25% of all annual consumption of shrimp.
Now, this is great in some ways, but shrimp
farming has its own impact on the environment
and so needs to be done in a properly managed
way.
Other farm species include milk fish, mullets,
Atlantic salmon, seaweeds, abalone, and scallops.
Here we see a chart showing some of the commonly
raised both freshwater and marine organisms
through aquaculture and mariculture.
The fish include things like salmon, cod and
flatfish, milk fish, mullets and even efforts
going into raising tuna.
There are also many molluscs that are raised,
such as abalone, clams, and mussels and oysters
and scallops.
Shrimp are the most commonly raised crustaceans
and there's also mariculture of seaweeds.
Here we can see a floating pen holding milk
fish and you can see the fishermen and their
catch.
There are some problems with aquaculture and
mariculture.
The first is that of disease and parasites
because these organisms are often raised to
such high densities in such small areas that
disease and parasites can easily spread.
Another difficulty of mariculture is maintaining
water quality.
There can be eutrophication 
due to uneaten or excess food and also the
waste of the organisms that are being grown.
Also, unfortunately, mangroves and other estuarine
communities are often being destroyed to create
ponds for farming shrimp and fishes.
Additional problems with aquaculture could
happen if farmed species escape, because they
may breed with wild stocks and dilute the
genome of those wild populations.
Pollution from farm ponds can also leak into
nearby waters.
Some of the difficulties in aquaculture is
that sometimes there are different food requirements
that are needed by these organisms as they
are raised through their different life stages
and also there are simply difficulties 
when it comes to farming open water species.
Now, some of the other reasons why marine
organisms are harvested include commerce and
recreation.
Mangroves can be chopped down for timber and
charcoal, pearls, shells, coral and sea turtle
shells are used for jewelry and fashion, with
tortoise shell being commonly used in glasses
and other decorative items.
There are some species that are harvested
for chemical compounds that can be used as
marine natural products.
Amateur anglers are another way that marine
resources are used.
They can be caught by recreational fishermen
and this ends up being about 30 percent of
the amount caught by commercial fishermen.
The number of individuals of some species
caught each year may be solely from recreational
anglers.
Another way that marine resources are used
is through the aquarium trade.
They are harvested from natural environments
and sold worldwide in aquarium and pet shops.
Since aquarium organisms must be alive in
order to be marketable, often hundreds of
individuals are collected and died before
reaching market for the few that actually
make it there.
There are nonliving resources collected from
the ocean as well, things like oil and gas,
sand and gravel, salt, desalinization for
freshwater, tidal and wave energy, and polymetallic
nodules, which might be collected in the form
of undersea mining.
In this image we see an example of a power
generator that uses tidal energy and in some
ways this might be a great source of green
renewable electricity, but in other ways this
needs to be held back by a structure much
like a dam and that totally changes the dynamics
of the coastal region around these power plants
in order for them to be effective.
Now, it's not that nothing good can come of
it, but the costs and the benefits need to
be weighed for these types of projects.
And that takes us to the end of our discussion
of resources that we get from the ocean.
Now, before our next video I want you to think
“How good a job do you think humans are
doing in taking care of the oceans?”
We'll talk about that next week.
See you then.
