4.3 Flashcards
marine trophic levels
- primary producers: phytoplankton and seaweeds
- primary consumers: zooplankton
- secondary consumers: small predators (small or young fish and jellyfish)
- tertiary consumers: top predators –> e.g. large fish (cod, sharks, tuna), marina mammals (dolphins, seals), and birds (penguins, albatross)
what is primary productivity dependent on
- amount of sunlight, temp, and nutrient levels
what is thermal stratification and when does it happen
Thermal Stratification = when the surface layer of water warmed by sun becomes less dense than water beneath (prevents mixing)
- when particles (nutrients) float out of the top layer the thermal strat presents the movement of nutrients back into water column
Occurs when:
- sunlight heating top layer –> results in temp variation
-water movement below surface is reduced due to calm weather
- strong winds and coastal currents can cause mixing and break up thermocline –> redistributing nutrients into water column (upwelling)
define upwelling
vertical mixing
- upwelling contributes to primary productivity by mixing nutrients into the top layers of water
why coastal and shallow waters are more productive
- river input brings in more nutrients
- sunlight penetrates down to sea floor = high levels of light that drives photosynthesis
freshwater trophic levels
- primary producers: phytoplankton and macrophytes
- primary consumer: zooplankton
- secondary consumer: fish, birds, and frogs
- tertiary consumer: large fish (trout), large birds, and mammals (otters)
factors contributing to fish demand increase
- growth in pop
- promotion of health benefits of consuming fish
- growth of a pop that can afford fish
hunting seals case study
- traditionally carried out for 4000 years –> for clothing, food, materials for tools, and shelter
- considered an important part of Inuit culture and traditions
- threat to seal numbers - esp in Canada
- considered controversial because: threat to species becoming exinct, only pelts used so meat wasted, methods to kill seals seen as inhumane, melting of ice already reducing their habitat
REGULATION ATTEMPTS IN CANADA: - use of quotas –> limiting allowed hunting numbers
- adoption of open and closed seasons
- banning hunting of seals that aren’t mature yet
energy efficiency of food systems
- aquatic less efficient than terrestrial
- primary producers recieve less sunlight compared to terrestrial –> light absorbed and reflected by water
- humans eat organisms higher on food chain so more energy loss as you go up the chain
- BUT aquatic systems have less biomass lost as indigestible skeleton = more efficient energy transfer
calc for average percent increase per year capita
- find difference between the two numbers (18.9-9=9.9)
- divide the difference by the original number (9.9/9=1.1)
- divide the previous number by the number of years between increase (1.1/50=0.022)
- multiply the final number by 100 to find % (0.022x100=2.2%)
what’s done to meet fish demand
- growth in # and size of fishing fleets
- improvements in ship storage
- larger ships allowing for more time at sea = more harvest of fish
- development of solar, radar, and satellite to detect groups of fish
- ability to freeze and preserve fish on ship
different types of fishing nets
Trawler Nets –> used to catch demersal fish by dragging a funnel-shaped net along seabed
- net damages seabed and can kill organisms living on the floor
Purse-seine Net –> used to catch big groups of pelagic species
- nets surround the fish and close to trap
- these nets produce a lot of bycatch
Drift Nets –> hung vertically in water to catch pelagic groups of fish
- produces high amount of bycatch
fish yield and max sustainable yield
- fish stocks only renewable if rate of removal doesn’t exceed growth rate
- the MSY = the optimum harvest that can be obtained annually without affecting its ability to replenish
management of cod fisheries: Newfoundland vs Iceland
NEWFOUNDLAND
- had the largest cod stocks in the world –> fishing efforts increasing with modern tech
- despite warnings from scientists the gov didn’t do anything about the decrease in fish numbers
- by 1992 fish stock was significantly lower so they had to close down all fisheries –> many job and money losses
Iceland
- after seeing decline in cod fish stock the gov took action allowing people to continue fishing but at a sustainable rate:
- strict quotas
- catching a variety of other fish to relieve pressure off of cod stocks
- use of exclusive zones
- not allowing foreign fishers to fish
reasons for fish demand increase
- low in saturated fats, carbohydrates, and cholesterol
- high source of protein and nutrients
- seen as an ecocentric choice
- growth of a population that can afford fish
