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Summary course Fisheries Ecology
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Summary Fisheries Ecology
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Week 1 + 2L1: Fished species
1450 categories of fishes in world’s catches, 20 categories make up >50%, and 80 categories >80% of the catches.
Main global landings: bony fish/Vertebrata, Mollusca, Crustacea
Main invertebrates: Northern prawn, Argentine shortfin squid, Japanese flying squid, Antartic krill, Akiami paste shrimp
(thus: shrimp/prawn, squid and krill. Next: crabs/lobsters, oysters/mussels, snails)
Minor invertebrate phyla: Sponges, corals, sea urchins, jellyfish, sea cucumbers, sea squirts, horseshoe crab, palolo worm
Dominant fish species: Peruvian anchovy, Alaska pollock, Atlantic herring, Chub mackerel, Chilean jack mackerel, skipjack
tuna→ palagic species dominate
Northwest Pacific: Alaska pollock/Japanese anchovy
Northeast Atlantic: Atlantic herring
Western Central Pacific: Skipjack & yellowfin tuna
Southeast Pacific: Anchoveta
Variability in landings: El Nino – La Nina
Biological aspects and life history:
Maximize fitness by optimal combination of growth,
maturity, fecundity, egg size. Depending on
physical/ancestral constraints and costs-benefits of environment
Sex – sex changes
Size advantage model: sex change should occur when individual fitness increase with size (or age) at a faster rate
through one sex function than through the other
→ Bigger females have higher fecundity
→ Bigger males are more successful in aggressive encounters
→ Direction of sex change predicted by polygamy potential
Growth
,Latitudinal ranges are larger when midpoint of range is closer to equator → reason for differences in ranges is the smaller
temperature changes around the equator
Lecture 2: World fisheries history, production and yield
Fisheries history: evidence: archaeological data, books and paintings, archival data (landings, sale values)
Shifting baseline syndrome: loss of perception of change that occurs when each generation redefines what is ‘natural’.
Historic fisheries
Small scale fisheries: Artisanal along coastline
Large scale fisheries: Whaling, Cod fisheries Newfoundland / Grand Banks, Herring fisheries Baltic & North Sea
“industrial’ fishing gears: Harpoon (whales), Drift nets (herring, Hook and line (cod), Bottom trawls for flatfish
Historic important fisheries North Sea: Migration of whales along Dutch shore, Herring fisheries, Plaice trawlers, Longliners
Up to 1800s: sailing vessels (beam trawl, long line) (industrial revolution, establishment ICES)
Since mid-1800: steam trawlers (otter trawl)
Since 1900: motor trawlers (otter trawl, seine)
Since 1960: heavy beam trawls
Scaling up (vessel size, engine power, nets), Auxiliary equipment (radar, navigation, fish finders, freezers)
Polar migration theory 19th century: home of herring is under polar
ice, excess migrates southwards → explaining year to year fluctuation
in herring landings and seasonal appearance along European coast
→ consequences: international coordinated research project, studies
at large spatial scale, focus on relation fish and oceanography
1940, Hjort: population dynamic theory: fluctuations due to good and
poor year (classes), focus on populations and age determination
Big paradigm changes:
From the inexhaustibility of fish (1882) to finite stocks (1914)
From Polar Migration theory (1746) to Population thinking (1914)
From population dynamics to community dynamics (2000+)
Scale and fish yield:
Recruitment to the population: addition of juvenile fish to the population
Recruitment to the fishery: length at which a cohort of fish enters the fishery
Phytoplankton production: ocean 88,5% area, 81,1% Net Primary Production
(NPP), Coast 7,2% area, 8,5% NPP
Non-phytoplankton production: 4,3% are, 10,4% NPP
Kelp forests, macroalgae 1,8% area, 4,8% NPP
Mangroves 0,3% area, 2,1% NPP
Coral algae 0,16% area, 1,1% NPP
Sea grasses, marsh plants 0,3% area, 1,8% NPP
Microphytobenthos, tidal flats 1,8% area, 0,3% NPP
, Equatorial upwelling – divergence of currents N and S of equator (west trade winds, coriolis forces)
Coastal upwelling – wind induced upwelling
Marine pelagic food chain:
Export: Positively correlated with productivity, up to 50% of fixed C in coastal areas, equilibrium autotroph/heterotroph
(limited leakage from system →microbial loop), Variable systems (no equilibrium, lot of leakage)
Going up the food chain:
Gross Growth Efficiency (% prey C converted to predator C)
Transfer efficiency (TE): GGE * predation efficiency (PE, %)
TE higher at higher trophic levels, generally set at 10%
Lecture 3: Data of stock dynamics
Gillnets tend to overestimate larger fish
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