FISHERIES PT.2 Flashcards
what is Fishing down marine food webs
Target bigger top organisms, when they run out they move to the next trophic level down - Leads to trophic cascades
Bottom up control
abundance or biomass of a given trophic level is dependent on the abundance of the level below
Top down control
abundance or biomass of a given trophic level is controlled by the level above
whats Phase shift in ecosystems
a fundamental change in an ecosystem to a new community – might not be reversable
what is max sustainable yield (MSY)
largest catch that can be taken from a fish population over an indefinite period without causing long-term depletion
how much have elasmobranchs declined since 70s
50-80%
why do elasmobranchs have accelerated targeting
- Decline in other target species
- Increased buying power among asian nations
- Shark meat
- Shark fins – shark fin soup
- Squalamine – anticancer agent
- Cartilage
- Costa rica grind 235000 shark/month for pills
Shark fishing countries
India
Taiwan
Indonesia
US
Pakistan
Mexico
elasmobranch life history characteristics
Slow growing
Late maturing
Apex predators
Long gestation
Low fecundities
how did New england groundfish fishery exploit marine resources
16th cen – oil, fur, leather
Great auk extinct in 1844
6 largest takes of New England fisheries
Gadoids – cod, pollock, haddock
Flatfishes
Redfish
Goosefish
Spiny dogfish
Skates
how were cod stocks described in 1516
“they stayed the passage of ships” - they were so dense in the water that they slowed ships down
mismanagement of cod fisheries
- Spawning stock biomass decresed 60-fold
- Fishable biomass overstimated by 220% since 1970s
- 60-80s – catch exceeded
history of flatfish fisheries
- Peaked in 1968
- Halibut – up to 3m
- Crashed by 1839
- Late maturation
- Ended 1850s due to overexploitation
history of haddock fisheries
- Targeted in 1920s
- Crashed 1930s
- Nova scotia peaked 1965
characteristics of Small pelagic fisheries
Silvery
Streamlined
Oily
Schools
Migrate
Near surface
Upwelling areas
Feed low on food chain
Sensitive to Climate variability
the typical cycle of overfishing
- Boom - rapid growth in the fishery due to high pop
- Bust - overfishing reduces pop
- Crash - fish stocks collapse
- Redirect new species, new geo location
8 reasons management has failed
- Based on single species management
- Cumulative effects of fishing
- Incessant sociopolitical pressure to maintain catches at high levels
- Intrinsic uncertainty with predicting stock collapse
- Warning signs ignored
- Failure to account for certain life history changes e.g. sex changes
- Overcapitalization
- Big one – unaccounted mortality
what does the reported catch exclude
- Highgrading – selectively harvesting best quality / most vulnerable fish
- Bycatch
- Injured but not captured
- Habitat loss
- Ghost traps / nets
- IUU fishing – illegal, unregulated + unreported (30% of global catch)
what is the highest amount of biomass taken from worlds oceans
80 mmt in 1998
whats our total take from the worlds oceans
120-130 mmt - exceeded total capacity of oceans by 20-30%
