Transcript What lies beneath the surface: Exploring our

What lies beneath the surface:
Exploring our fisheries in depth
The sea, once it casts its spell, holds
one in its net of wonder forever.
Jacques Yves Cousteau
Warm-up
Based on your research last night What do you think we should do about the
phenomenon of restaurants and fish markets
selling certain fish under pseudonyms?
Why do you think the recommendation for a
particular species might differ between
guides?
Pre-movie discussion
• Are you a ‘responsible’ fish eater?
• When did industrialized fishing begin?
• How do you think fish populations are doing
overall?
• Do you think there is a critical population size
for wild animals, below which they can’t
recover?
Where have all the fish gone?
• Economic and social
importance of one species
• Do you think this impacted
people outside of New
England? Why or why not?
• What would the rippling
effects of a fishery collapse
have on society/economy?
Recent history of fishing
• In groups of 4
• Examine the following scientific data related
to fishing
• Come to a consensus on what it means to be
‘overfished’
– Is this a label we can put on a single stock?
– Or is this a category for the whole ocean?
Data set 1 – Species Diversity
The maps you will study in this part of the
investigation are species density maps.
This means that the data you are looking at is the
total number of species per square kilometer (or
mile) of ocean, a measure of marine biodiversity
(variety of life in the oceans).
The data are for 1 decade for each of the following
decades: 1960’s, 1970’s, 1980’s, 1990’s
Species Diversity Index – 1960’s
Species Diversity Index – 1970’s
Species Diversity Index – 1980’s
Species Diversity Index – 1990’s
Data Set 1 - Stop and Discuss
1: How does the overall color of the map change
over time? What does this imply about the
overall diversity of fish in the sea?
2: Can you identify any "hotspots" (areas with
larger concentrations of species diversity than
the surrounding ocean)? Do they persist over
time?
Data Set 2 - Species Density Graphs
Experts have found that large numbers of predator fish like
tuna and billfish (large fish such as swordfish and marlins,
that are characterized by long sword-like bills) are
commonly found in biodiversity hotspots. This means that
the abundances (or species density) of tuna and billfish are
good indicators of overall marine biodiversity.
There is a striking contrast between the level of marine
biodiversity 50 years ago and that seen today.
Environmental changes are often responsible for
fluctuations in the sizes of fish communities from year-toyear. However, global declines in fish abundances over
longer timescales are believed to be primarily driven by
overfishing.
Interpreting Species Density Graphs
Data Set 2 - Stop and Discuss
1: Why is it important to have species diversity
in the oceans?
2: Why do you think large predatory fish are
important for maintaining the balance of
marine ecosystems? Why are they important
to the sustainability of the fishing industry?
Data Set 3 – Depletion of large
predatory fish
According to a 2003 paper published in Nature
industrialized fisheries typically reduced
community biomass by 80% within 15 years of
exploitation. The study’s authors concluded that
declines of large predators in coastal regions have
extended throughout the global ocean and could
have potentially serious consequences for
ecosystems. Their main point was this:
90 % of all large fish including tuna, marlin,
swordfish, sharks, cod and halibut are gone.
Data set 3 – Stop and Discuss
1: What role do large predators play in an
ecosystem?
2: What role do keystone species play in an
ecosystem?
3: What could happen to an ecosystem if large
predators and/or keystone species are
removed?
An animated map of changes in catch
per unit effort
• Link to Quicktime:
http://ram.biology.dal.ca/~myers/depletion/