Fisheries

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• Lecture 20
• Fisheries

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• Nature of fisheries is there a crisis?
• What is meant by sustainable yield?
• Do we understand and work with normal population
  changes in fish stocks?
• Ecological consequences of modern fishing
  techniques and preferences for catch
• The marine food web and fishing
• Fish farms? Some good and some not so good

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• Fisheries Not all areas equally productive
• Inshore fisheries 90 of yield
• Shallow nutrient rich seas
• Upwelling areas
• Predator species most concentrated
• Deep-Sea fisheries
• beyond continental shelf
• Diffuse, widely dispersed populations

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http//www.wri.org/biodiv/topic_content.cfm?cid41
91
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• Overfished
• New England groundfish and flounder
• Southeast Spiny Lobster
• Atlantic Bluefin Tuna and Swordfish
• Main Hawaiian Island Bottomfish and Pelagic
  Armorhead
• Large Coastal Sharks
• Gulf of Mexico King Mackerel and Pink Shrimp
• Atlantic/Gulf of Mexico/Caribbean Reef Fish
  Complex
• Pacific Ocean Perch
• North Pacific Albacore
• Oysters, Hard Clams, and Abalones in many
  location

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Source FAO
Peak catch year of some fish species
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• Trends in Fishing
• Increasing Sophistication and Investment
• Larger boats and larger nets
• Capacity to fish in deeper waters
• Sonar
• GPS to precisely locate desirable fishing grounds

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FAO http//www.fao.org/figis/servlet/static?domro
otxmltech/profile/sea_profile.xml
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• Sustainable Yield? Prediction Model
• Assume fish populations
• Follow logistic growth
• Governed by density-dependent factors
• Conclusion Sustainable if catch is less than
  recruitment
• Maximum Sustainable Yield
• Requires understanding of density dependent
  factors, K (carrying capacity) and size of
  population with respect to K

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• Whose fish are they? Long term profits
  optimized at sustainable yield
• Competition
• Common property
• Who regulates
• FAO Food and Agriculture Organization of UN
• International treaty
• Subsidies arise from political pressure

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• What impacts fish populations
• Density independent factors
• Cyclic changes (unknown causes)
• Fishing pressure adds to risk of collapse of
  population during lows
• Recruitment limitation major factor in fish
  populations
• Opportunist species and competitor species have
  different life histories- may stand pressures
  differently
• Fishing pressure may select for smaller
  reproductive sizes

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Cyclic population variation Density Independent
Factors Sustainable Yield difficult to set
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• Peruvian Anchovy Story
• Opportunistic species
• Before 1950 domestic use only
• 1953 Fish meal plants developed
• Export becomes major business
• 1970 scientists in the Peruvian government
  issued a warning of potential collapse
• Warnings ignored, economic reasons
• 1972 collapse due to overfishing El Nino

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Annual catch of the PeruvianAnchovy Fishery from
1960-1990
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• A Paradox "Fishing Down" reduces yields
• Simplifies Food Web
• Removal of competitor/predator species
• Habitat destruction
• From Science 279860, 6 Feb 1998
• 1950 to 1994, shift high-trophic species (e.g.
  cod and haddock) to low-trophic-level fish and
  invertebrates such as anchovy and krill.
• competitors (such as inedible jellyfish) fill the
  void.
• "If things go unchecked, we might end up with a
  marine junkyard dominated by plankton."

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• Habitat Modification by Over fishing
• Physical damage to habitat due to dragging of
  heavy equipment (bottom trawls)
• Removal of species Chesapeake Bay Oyster catch
• Decreased ? less filtration of water column
• Less filtration input of nutrients ? higher
  plankton levels in water column

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over fishing ? modification of ecosystem ?
habitat modification less able to support
desirable prey species
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Impacts of Bottom Trawling Non-trawled
Trawled
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• Impacts on Non-Target Species
• Competition Stellar Sea Lions
• Birds, mammals, turtles
• Non-target fish by catch
• Young fish
• Dolphins, other cetaceans

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• Fish Farms
• Issues
• Crowding
• Disease
• Waste products
• Culture of carnivore spp. relies on ocean
  resources
• Positive Aspects
• Inland facilities can contain waste
• May be virtually self contained, eliminates many
  issues assoc. with fishing