Announcements

1. Announcements • No lecture on Wednesday, November 24th • Problem set is due that day • Midterm Exam will be handed out on Wednesday in lecture • Kevin will have office hours in Girvetz 2307 today

2. Summary from Friday • Biodiversity • ecosystem services • control of ecosystem services • redundancy • keystone species • island biogeography • patterns of biodiversity on islands • why islands can have high biodiversity • biodiversity “hotspots”

3. Two-minute quiz Based on what you know about patterns of biodiversity on islands, which of the channel islands would you expect to have the lowest biodiversity? What factors do you need to consider?

4. Factors to consider: • distance from mainland & other islands • age of the island • size of the island • land use history on the island • history of invasions • climate differences between islands • current • physical structure (elevation, etc.)

5. Fisheries A “fishery” can be defined as: human harvest of wild marine resources for food and industry It’s not just fish: also crustaceans, mollusks, marine mammals, turtles, etc.

6. People keep catching more

7. Why do we care about fisheries? • Humans must be fed • cheap source of protein • 16% of global human animal consumption • Catch continues to rise • hypothesis 1: fish are abundant, we can continue to harvest more and more • hypothesis 2: we are approaching a maximum harvest and catch will stabilize • hypothesis 3: we are already over-fishing and collapse is eminent

8. Where does fishing occur? • Major fishing areas are closely associated with net primary production in the ocean • estuarine areas • continental shelf • upwelling zones • Many fishing zones are in international waters

9. Where does fishing occur?

10. Small-scale operations traditional methods small boats hand-pulled nets small area, near shore  less developed countries Large-scale operations fully mechanized large vessels lots of technology larger area, offshore  more developed countries How do people fish?

11. higher trophic level fish are preferred larger more tasty eating lower on the food chain more environmentally sound not by choice- but because large fish are gone What do people fish? boom and crash of anchovy fishery

13. Fish occupy a variety of different niches Some are opportunists, some are competitors Competitors take longer to recover when over-fished Currently, even opportunist species are having difficulty recovering Cod has a huge reproductive capacity Despite complete closure of Georges Bank fishery, it has had difficulty coming back What do people fish?

15. Is fishing efficient? • ecological efficiency: energy captured vs. energy used by the fisher • large-scale fishery has higher bycatch

16. Drift net fishing • Notoriously high bycatch • “Wall of death”

17. Announcements • Midterm will be handed out at end of class • No class on Wednesday, Nov. 24th • Ask questions about the problem set now!

18. Summary from Monday • Fisheries aren’t just fish • Why do we care about fisheries? • reduction in catch over time • Where do people fish? • What do people fish? • How do people fish? • the efficiency of fishing • preventing and reducing bycatch

19. Two minute quiz True or False: • Purse seine nets are also known as “walls of death” due to the overwhelming bycatch of dolphins caught in them while fishing for tuna. • The cod population on Georges Bank is having a difficult time recovering because they reproduce slowly. • Aquaculture makes up about 50% of the total fish harvest of the world.

20. Reducing Bycatch • charismatic species get attention • dolphins swim above schools of tuna • 400,000 killed each year in 1970’s and 1980’s • legislation passed for “dolphin-safe” measures • drop one side of net to allow dolphins to swim out • turtles swim near shrimp • trawl nets have large turtle bycatch • turtle excluder devices (TED) • turtles naturally swim towards surface

21. Dolphins can be released from purse seine nets by dropping one edge of the net Longline fishing has a low risk of dolphin bycatch

22. Reducing Bycatch • charismatic species get attention • dolphins swim above schools of tuna • 400,000 killed each year in 1970’s and 1980’s • legislation passed for “dolphin-safe” measures • drop one side of net to allow dolphins to swim out • turtles swim near shrimp • trawl nets have large turtle bycatch • turtle excluder devices (TED) • turtles naturally swim towards surface

23. Is fishing efficient? • agricultural efficiency: energy produced vs. energy spent on production • large-scale fishery spends much more energy

24. ratio of 1 energy inputs = energy outputs

25. Is fishing efficient? • economic efficiency: benefits derived vs. costs incurred • in a large-scale fishing operation, people make more money • why? smaller operations just cover costs

26. Is fishing efficient? • economic efficiency: benefits derived vs. costs incurred • in a large-scale fishing operation, people make more money • why? smaller operations just cover costs  economics override ecological or agricultural measures of efficiency

27. Tragedy of the Commons • no one owns the sea, but everybody uses it • first-come, first-served • catch as much as you can as fast as possible • who will police sustainable use? • environmentalists? • countries that depend on fishing? • subsidies • provide jobs • encourage over-fishing

28. Why are fisheries difficult to manage? • Interface of biology and economics • Biology is often oversimplified • models can be difficult to build, because it is hard to know how many fish are out there • what is the maximum # of fish that can be removed without causing the population to decline?

29. Building a simple model • Assume logistic growth • Density-dependent factors govern growth • Sustainability is possible if: • rate of catch < rate of growth

30. Maximum Sustainable Yield (MSY): • The maximum harvest that is possible without reducing future harvest. • Rate of catch is ≤ rate of growth

31. Harvesting at MSY is dangerous • Harvesting right at maximum sustainable yield should NOT be the goal because: • assumes the following are known exactly • Population size • Population growth rate • Relationship between size & growth • Harvest level

32. Now add economics: • Assumptions: • Prices for fish are constant • additional cost of catching an extra fish is constant • amount of fish caught per unit effort is proportional to population size • Thus, rate of harvest = rate of benefit or income

33. Consider Effort: • Harvest = benefit = income = gross profit • Assumption: • harvest at rate of growth • Effort (expressed as a percentage) • Assumptions: • cost increases linearly with effort • effort is low when population is high • effort is high when population is low • Fishers need to fish at a rate where benefit is at least equal to cost

34. Announcements • No class on Wednesday, Nov. 24th • Ask questions about the problem set now!

35. Summary from Wednesday • Reducing bycatch • turtle excluder devices • Fishing efficiency • agricultural efficiency • economic efficiency • Why fisheries are difficult to manage • Tragedy of the commons • Building a simple model

36. Fisheries Models

37. harvesting in the red zone (greater than maximum sustainable yield) is not sustainable

38. harvest (benefit or income) benefit matches cost at this point cost Rate of harvest (benefit or income) Cost minimum population where fishing is economically viable K 0 Population Size 0% Effort 100%

39. Expensive fishery only profitable when population sizes are large, likely to be sustainable cost benefit matches cost at this point Rate of harvest (benefit or income) Cost minimum population where fishing is economically viable K 0 Population Size 0% Effort 100%

40. Cheap fishery profitable at small population size, likely to be unsustainable benefit matches cost at this point Rate of harvest (benefit or income) Cost cost minimum population where fishing is economically viable K 0 Population Size 0% Effort 100%

41. When a fish becomes rare, the price increases population is further reduced by fishing pressure benefit matches cost at this point Rate of harvest (benefit or income) Cost cost minimum population where fishing is economically viable K 0 Population Size 0% Effort 100%

42. Government subsidies maintain jobs, provide protein, but lead to over- fishing Unsubsidized cost Rate of harvest (benefit or income) Subsidized or Unsubsidized cost Subsidized cost minimum population where fishing is economically viable K 0 Population Size 0% Effort 100%

43. What causes over-fishing? • Overly-simplistic models • little attention to how age and size structure affect population growth • little attention to density-independent factors that influence recruitment • currents • climate • Bad management • large government subsidies • emphasis on short-term benefit rather than sustainability

44. Can an over-fished fishery recover? • Sometimes… • if enough breeding pairs still exist • if the habitat has not been degraded by fishing • if another species has not taken over the habitat, shifting food web dynamics

45. Solutions to over-fishing • Reduce bycatch • Cut back on fishing in general • loss of jobs • loss of food • loss of culture • Aquaculture

46. Aquaculture • farming fish and shellfish for commercial use • in 1977, 14% (by $) of fish sold were farmed • in ponds, lakes, estuaries or coastal regions • create a fenced off area for fish • fertilization to increase primary productivity • problems • high density of fish  disease • pollution in water  pollution in fish • pathogens in shellfish • fish kills in eutrophic waters

47. Biological Magnification • toxins accumulate in organisms • often stored in fatty tissue • magnification as you move up the food chain

48. Salmon farm - Pacific Northwest Fish cages - France Fish cages – Burma/Myanmar

49. Aquaculture • artificial ponds  more controlled • benefits: • flowing water flushes waste material away • controlled diet and disease monitoring • harvest when growth slows  maximize profit • artificial spawning • problems • high cost  certain fish favored • farmed fish escape into the wild (Tilapia in Everglades) • destruction of natural habitat to make ponds

50. Case Study: Salmon Farming • People like salmon • Wild populations are threatened • Farming used as a solution for providing people with the fish they want to eat