Module 4. The Georges Bank Fisheries

Transcription

1 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 depth zone dissolved gases bottom material nutrient enrichment motion, size salinity producers consumers decomposers potential organisms resulting community 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 1

2 Ocean & Coastal Ecosystems Interaction between land and sea influence productivity Labrador Current Gulf Stream Georges Bank 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) Georges Bank bottom topography, currents, and nutrients influence productivity population dynamics are modified by environmental factors & human exploitation Biology 105 Module 4 2

3 Georges Bank Resources Labrador Current upwelling Cape Cod 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. 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 3

4 Phytoplankton Primary producers Diatoms, coccolithophores, and dinoflagellates Oceanic Productivity Resources delivered by ocean currents, upwelling, & rivers High productivity Low productivity nutrient-rich currents supply resources to the ecosystem phytoplankton productivity establishes base of food web Biology 105 Module 4 4

5 Oceanic Food Web The flows of energy & nutrients are complex Georges Bank food web includes a variety of top predators, including humans Trophic Pyramid for Coastal Systems Biomass pyramids differ from energy pyramids humans big fish (cod & haddock) small fish (capelin) zooplankton phytoplankton decomposers biomass flows from primary producers to rest of ecosystem biomass pyramid differs from total energy pyramid Biology 105 Module 4 5

6 Population Dynamics The balance between potentials and resistances potentials exceed resistances Population size carrying capacity resistances exceed potentials Time 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 6

7 cod Groundfish Habitat Habitat and fish stock productivity haddock distribution spawning 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 7

8 Technological Change Increased losses from groundfish populations Gill net Otter trawl Distant Water Fleets Technology grew to enhance catches from dwindling stocks 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 8

9 Ground Fish Populations on Georges Bank 160 haddock cod steampowered trawlers Birdseye deep freeze sonar & factory ships Soviet bloc fleet 200 mile limit imposed moratorium catch (thousands of tonnes) dories & handlines Date 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 A patch of seafloor off Swan's Island, Maine, before (left) and after the area was swept by a scallop dragger. preserve habitat to ensure future population growth extract resources at a rate ensuring replenishment Biology 105 Module 4 9

10 Hypoxia - Dead Zones Nutrient additions change ecosystem equilibria 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 10