Module 4.
The Georges Bank Fisheries
Ocean Ecosystems
Resources
Energy Flow
Ocean Ecosystem Problems
Where is Georges Bank?
What Makes a Good Fishery?
Population Dynamics - the basics
Sustainable Yield
Threats to Ocean Ecosystems
“ Be content, there are fish enough…”
Dr. Thomas Fuller, 1732
Abiotic Factors in Aquatic Ecosystems
producers
consumers
decomposers
light,
temperature
dissolved
gases
depth
zone
potential organisms
nutrient
enrichment
bottom
material
salinity
producers
consumers
decomposers
motion,
size
resulting community
concepts:
• abiotic factors influence community structure
• these factors change in SPACE and TIME and are not necessarily
consistent from year to year
Biology 105 Module 4
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Ocean & Coastal Ecosystems
Interaction between land and sea influence productivity
Labrador Current
Georges Bank
Gulf Stream
concepts:
• productivity depends on nutrients, temperature, and oxygen
• large-scale ocean circulation delivers nutrients to specific regions
• river discharge influences salinity & nutrients
Depth Profile of George’s Bank
Nova Scotia
Cape Cod
Depth (m)
50
100
200
1000
Georges Bank
concepts:
• bottom topography, currents, and nutrients influence productivity
• population dynamics are modified by environmental factors
& human exploitation
Biology 105 Module 4
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Georges Bank Resources
Labrador
Current
Cape
Cod
upwelling
nutrients
Georges
Bank
Gulf
Stream
Labrador Current brings cold, nutrient rich water from the north. When
this current passes between Cape Cod and Georges Bank, it upwells
over the Bank, bringing nutrient rich water to the surface.
concepts:
• nutrient-rich currents supply resources to the ecosystem
• shallow sandy and rocky bottoms provide habitat
• resources + habitat = productivity
The Gulf of Maine Gyre
Complex currents deliver resources to Georges
From P.W. Conkling, “From Cape Cod to the Bay of Fundy”
Biology 105 Module 4
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Phytoplankton
Primary producers
Diatoms, coccolithophores, and dinoflagellates
Oceanic Productivity
Resources delivered by ocean currents, upwelling, & rivers
High productivity
Low productivity
concepts:
• nutrient-rich currents supply resources to the ecosystem
• phytoplankton productivity establishes base of food web
Biology 105 Module 4
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Oceanic Food Web
The flows of energy & nutrients are complex
Georges Bank food web
includes a variety of top
predators, including humans
http://www.britannica.com/bcom/eb/article/9/0,5716,127599+14+117267,00.html
Trophic Pyramid for Coastal Systems
Biomass pyramids differ from energy pyramids
humans
big fish (cod & haddock)
small fish (capelin)
zooplankton
phytoplankton
decomposers
concepts:
• biomass flows from primary producers to rest of ecosystem
• biomass pyramid differs from total energy pyramid
Biology 105 Module 4
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Population Dynamics
The balance between potentials and resistances
40000
Population
size
potentials exceed resistances
30000
carrying
capacity
20000
resistances exceed potentials
10000
0
0
5
10
15
20
25
Time
concepts:
• potentials: favorable abiotic conditions and biotic characteristics
• resistances: unfavorable abiotic conditions and limiting biotic
characteristics
Groundfish
Cod & haddock are primary bottom species on Georges Bank
Cod
Haddock
Biology 105 Module 4
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Groundfish Habitat
Habitat and fish stock productivity
cod
haddock
distribution
spawning
concepts:
• organisms require favorable habitat to prosper
• different life stages may require different habitat
• the entire range of habitat must be preserved to foster productivity
From P.W. Conkling, “From Cape Cod to the Bay of Fundy”
Early Fishing Techniques
Limited impact on existing populations
Fishermen in dories used the “New England line trawl”,
handlines with multiple hooks
Biology 105 Module 4
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Technological Change
Increased losses from groundfish populations
Gill net - 1878
Otter trawl - 1905
Distant Water Fleets
Technology grew to enhance catches from dwindling stocks
concepts:
• factory trawlers decimated stocks in distant waters
• in the U.S., this threat led to the Magnuson Act, which extended
jurisdiction to 200 miles
Biology 105 Module 4
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Ground Fish Populations on Georges Bank
haddock
cod
160
steam- Birdseye
powered deep
trawlers freeze
sonar
Soviet
&
bloc
factory ships fleet
200 mile limit imposed
1940
1970
moratorium
140
120
catch
(thousands
of tonnes)
100
dories
&
handlines
80
60
40
20
0
1900
1910
1920
1930
1950
1960
1980
1990
2000
Date
concepts:
• intensive fishing pressure exceeded maximum sustainable yield
• scientific and political decisions did not protect stocks
Resource Extraction Damages Habitat
Approach to resource extraction need to be sustainable
http://www.sciencemag.org/cgi/content/full/282/5397/2168b
A patch of seafloor off Swan's Island, Maine, before (left) and after the area was swept by a
scallop dragger.
concepts:
• preserve habitat to ensure future population growth
• extract resources at a rate ensuring replenishment
Biology 105 Module 4
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Hypoxia - Dead Zones
Nutrient additions change ecosystem equilibria
concepts:
• the ocean is the ultimate sink - activities on land degrade oceans
• excess nutrients stimulate algae growth, death, & decomposition
Other Activities Impacting Ocean
Ecosystems
Coastline development, aquaculture, and
resource extraction all have potentials to
damage coastal ecosystems
Biology 105 Module 4
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