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1. Sustainable Seas - Marine Fisheries
- Building a Fishery -  Fisheries and Culture
 

2. Upwelling and Nutrients
Wind blowing along the coast moves water toward or away from the coast
This water is "replaced" by water that moves vertically
In the northern hemisphere, winds from the north
- drive offshore  currents
- bring nutrient-rich water up from below ("upwelling")
- promote high productivity (lots of plant growth)
See Figures 9-10 and 14-10

3. Downwelling and Nutrients
In the northern hemisphere, winds from the south
- drive onshore  currents
- force nutrient-rich water even deeper ("downwelling")
- low plant productivity

4. Where are the Fish?
75% of the world's fish catch is caught in estuaries, nearshore regions and on the continental shelves
Source: National Academy of Sciences

5. Fishing Facts
36 million people worldwide earned their living by fishing in 1981
16 percent of animal protein consumed by people worldwide comes from fish.1
75% the world fish catch is used for human consumption 1
10 major species represent 35% of world catch2
Sources:  1= Food and Agriculture Organization of the United Nations, 2=National Academy of Sciences

6. Current Issues in the Marine
Fishing Industry
Viability of the Industry
- return on investment
- safety
- access to stocks
Resource Management
- sustainable yields
- bycatch
- impacts on habitat and ecology

7. Fishing Methods (a sampling)
Purse seine - floating net encircles school of fish
Trawling -weighted net dragged at mid-depth or along bottom
Longline - line with 1000's of baited hooks

8. Gear Selectivity
Trawls
- bycatch
- disturbance of bottom ecosystems
Purse seines
- can catch mammals, juvenile fish
Longlines and gillnets
- can catch seabirds
- abandoned equipment continues "fishing"
 

9. KEY CONCEPT  Maximum Sustainable Yield (MSY)
MSY: The maximum amount that can be caught without impairing future stocks
Managing at MSY must consider:
- need for breeding stock
- availability of food for animals higher in the food web

See Figures 14-16 to 14-17

10. Possible Consequences of Exceeding MSY
1. More effort required to catch a smaller amount of fish
2. Degradation of marine environment due to more invasive fishing techniques
3. Short-term collapse of the commercial fishery
4. Disruption of ecosystem if the fished species is replaced with  other species
5. Long-term collapse of the commercial fishery

11. Trends in World Fish Catch
World marine fish catch peaked in 1997 at 86 million tons
Source: Food and Agriculture Organization, United Nations

12. World Population and Per Capita Fish Catch

13. World Fisheries - Stages of Development
"In most regions, at least 70% of the stocks are already fully or over fished"
-United Nations Food and
   Agriculture Organization, Year 2000 Report
"Global marine fish catch is at or near its sustainable limit"
- National Research Council 1999 report

14. Peruvian Anchovies:  "Short-Term" Collapse of a Commercial Fishery
The rapid development of the fishery was followed by a collapse in the fish's population and slow
   recovery of the commercial fishery
 

15. Ecosystem Reorganization:  Lessons Learned from Georges Bank
After collapse of the Georges Bank (NW Atlantic) cod, haddock and flounder fishery in 1900-1930
   the fishery never recovered
Before stocks could rebuild, the ecological niche of these valuable commercial species was filled by
   "trash" fish - skates and dogfish

16. The Importance of Good Management -  Orange Roughy (aka Slimehead)
Clever marketing and good eating created a strong demand in the 1980's
1998  exports from New Zealand = $80 million
Management challenges:
- slow-growing, long-lived
- 20-30 years from birth to breeding  age
- small size (30-40cm)
- unknown juvenile ecology
Graphics: courtesy of New Zealand Ministry of Fisheries.

17. Mariculture and the Future
Mariculture = Farming of marine organisms (in estuaries, bays, nearshore environments or specially
   designed structures)
By 2030 aquaculture will dominate fish supplies, less than half of consumption will be from "captured" fish
-United Nations Food and Agriculture Organization, 2000 Report

18  Next Lecture:  Charismatic Megafauna

Focus question:  How have marine mammals adapted to the ocean?