MARS2014 Lecture Notes - Lecture 5: Aeration, Low Technology, Environmental Impact Assessment
Unit 4: Marine living resources
o Capture fisheries
▪ What is the current state of the capture fisheries?
• Under current management trends in Asia, there will be no fish stocks left by
2050
• International overfishing affects livelihoods
• “E Asia’s fisheries are near collapse from overfishing
• Shelf areas (where there is 90% of marine PP) we have fished very heavily
▪ Why are capture fisheries hard to manage?
• Process: Collecting data -> assessing status of stocks -> setting catch target -
> making regulations
• It’s aout trying to enable harvest without depleting stocks
▪ What is Maximum Sustainable Yield (MSY)?
• Trying to maintain catch at a level lower than or equal to recruitment rate
• Based off single-species stock assessment
• MSY is calculated for each species
▪ How do we develop single-species stock assessment models?
• The catch
o Recorded fish landings
o By-catch in other fisheries
o Age at catch
o Illegal fishing
o Recreational fishing
• Natural mortality
o Age of death in normal setting
o Predation (pressure, stock of predators)
o Environmental factors (run-off, climate changes etc.)
▪ What factors affect recruitment?
• Maturation age
• Habitat (is spawning or juvenile habitat degraded?)
• Temperature
• Prey abundance (is prey availability being reduced in another fishery?)
• Population size
▪ What MSY quota systems have been developed?
• TAC (total allowable catch)
• Defines a maximum total quota for 1 fishery to cover the entire fleet
• Disadvantage: skippers compete to catch fish at start of season, high
risk of overshooting quota
• ITQ (independent transferable quota)
• Allocates quotas to each fishing vessel for the season, unfished
credits may be sold on
• Advantages: Distributes fishing effort over whole season and rarely
results in overfishing
• Can be sold to compensate retiring fishers and aids in fleet
reduction
▪ Have these MSY quotas worked?
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• There have been no appreciable decline in fishery collapses over the last five
decades since introduction
▪ Why do quota systems fail?
• Total allowable catches are not predictable unless with very complex models
• Single species assessment models are often based on incorrect assumptions
• Depensation
o Scientists predicted that reduced stocks would reduce
competition for mates, habitats and feeding (Compensation)
o Instead reduced stock reduced spawning success
(Depensation)
• Recovery of stocks based on single-speies fisher losure do’t aout for
by-catch in other fisheries
• Fisherman in single-speies fisheries hae to thro ak a fish the do’t
have a quota to land (usually dead)
• Fishing down the food web
• Recovery of stoks ased o sigle speies stok assesset does’t
account for changes such as prey being depleted etc.
• Selectively depletes fish
o Species – we prefer to eat mostly predators
o Age and size – often the older, bigger ones we catch are the
ones that are most fecund (gear is designed to let smaller
prey escape, but larger females are often more fecund than
smaller ones)
• Shifting baselines
• To set targets, we need to know where we are going
• Most stock assessments are based on data from the start of
industrial fishing, but artisanal and pre-industrial fishing had a large
impact
• What stock levels do we aim our recovery plans at?
• How do we obtain data on earlier stock sizes and recovery?
▪ What factors influence stock recovery?
• Climate change
• Spawning and recruitment rates are significantly affected by warm
water temperature
• Distribution (fish thermometer) – where fish are moving into cooler
waters, away from the equator, could lead to a loss of true cold
water species
• Artisanal fishing
• Vital in developing countries
• Low technology
• Not considered to have a large impact but does through sheer
numbers, particularly in coastal reef habitats
• Most boats are now motorised and can go further
• Fish landings are not recorded
• Recreational fishing
• Largest partiipatio sport
• Makes up 4% of total marine fish landed
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