Lecture 4: Fisheries Flashcards
What is meant by flow type?
▪Total size of flow unaffected by use ▪Examples: Wind and solar energy
What is meant by stock type?
▪ Abiotic: Inanimate systems with exogenous supply (water, soils, …)
▪ Biotic : Populations of living organisms with endogenous
reproduction (fish, forests, …)
▪ Extraction reduces stock size, but stock can regenerate
▪ Danger of overexploitation (depletion)
To what extent has the fish biomass decreased?
about 10% of pre–industrial levels, in all seas
What is the impact of climate change?
• 3-25%: projected decrease in fish biomass by the end of the
century in low and high climate warming scenarios, respectively
• 3-10%: projected decrease in ocean net primary production due
to climate change alone by the end of the century
Explain the Gordon Schaefer model
Gordon (Gordon_Schaefer) model of optimal fish catch
Combination of biological processes and economic-decision making Central question
How does the property right system affect resource use / fishing activity?
Exact representation of reality?
• Not really:
- Model assumes non-migratory species
- Model assumes there is no minimum viable population - Model ignores population’s age structure
- No uncertainty in model (no random events), etc.
• But: reasonably accurate for analytical purposes in many instances!
Harvesting affects the size of the fish stock and growth rate
• Can we derive a sustainable harvesting level?
What are the dynamics of fish stock?
Stock size of the fishery changes over time due to:
- Net natural growth which depends on the stock size
- Harvesting by humans Interactive resources
There are tradeoffs involved in harvesting:
- The costs of the harvesting versus the benefits
- Catching fish now implies less growth (fish offspring) in the future
How would you define sustainable harvesting?
Sustainable harvesting: quantity harvested such that stock size does not decrease
What determines harvest quantity?
- Depends on the effort devoted to harvesting (defined as E, combination of “boat days”, size of ships, technology, number of fishing companies)
- The size of the fish stock
- Harvest is assumed to be proportional to the fish stock, holding effort
constant - A yield function can be derived, showing possible fish harvest in relation to fish stock, given a specific level of effort (E)
How is the economic optimal level of fishing effort (and harvest) determined? And how is it incorporated?
by maximizing the difference between:
▪ The total revenue of fishing
▪ The total costs of fishing
This is incorporated in the model by assuming:
▪ A constant price P for fish (plausible for open economies), implying harvest and total revenue are linear (Revenue = H × P)
▪ Constant marginal costs of fishing effort
What are the main points of the level?
▪ Open access to a common pool resource leads to market entry until short-run profit is zero, and does NOT lead to social optimum
▪ Identical sustainable harvest level exists with less effort, larger fish population and profit > 0
▪ Private ownership and/or group coordination can result in an optimum fishing effort for society!
How can we manage fisheries?
Non-exhaustive list of possible policy interventions
▪ Partition the seas (i.e. create ownership) – see model (exclusive economic zones)
▪ Remove subsidies / tax exemptions
▪ Limit fleet sizes or technology
▪ Establish quotas
▪ Improve enforcement/compliance
What is an exclusive economic zone?
An exclusive economic zone (EEZ) is a (200 miles) sea zone prescribed by
the United Nations Convention on the Law of the Sea (1982) over which
a state has special rights regarding the exploration and use of marine resources
