Paul J. Rago - National Marine Fisheries Service; Northeast Fisheries Science Center; Woods Hole, MA
Why is Fisheries Management so Difficult?
• common property resource - no ownership
• shifting baselines - history is lost
• allocation - fisheries, states, ports
• inelastic demand - pay any price
• increases in fishing power - electronics; speed, capacity
• multiple jurisdictions - federal, state, local
• law suits - 100+ pending
• multiple species - no-selective harvest, varying productivity
Technical Challenges:
• Can we engineer our way out of the problem?
• Are closed areas effective?
• Is there a downside to closing areas without additional controls? - Jensen Inequality
• How do we deal with environmental change?
• How do we deal with tradeoffs among non-commensurate (not-measurable, non-monetary) quantities?
• Closed areas don't correct conditions that lead to need of closed areas - excess effort. -> merely displace fishing fleets
Large Scale Experiments
• Foreign fleets
• EEZ (exclusive economic zone) and increase in domestic fleet
• Closed areas
• Effort reductions -> inefficient use of capital resources (non-ownership)
Graham-Schaefer Model: Discrete Time Surplus Production (1-species)
• At equilibrium, biomass B*=K(1-qE/r)
• Graham's Theory of Sustainable Fishing (1935)
o If removals can be replaced by stock production each year, the fishery is sustainable.
o If stock size is maintained at half its carrying capacity, the population growth rate is fastest, and sustainable yield is sustainable.
• Managing at the Margins
o Balancing a population at Bmsy can be precarious
• Changes in stock size can occur due to many factors - many of which cannot be controlled
• Targeting for a population size greater than Bmsy creates a "reserve" that reduces yield slightly and protects against ...
o Balancing a population at Fmsy can be precarious also
Status determination is based on a comparison of current estimates of fishing mortality and spawning stock biomass with their respective biological reference points. The comparison is based on the ratio of the current value to the reference value...
Managing at the margin makes changes in stock status very likely given the expected variation in assessments.
Managing away from the margin makes changes in stock status less likely and increases the ...
Current year stock status - status determination [diagram]?
Results of 2005 groundfish assessment review meeting: comparisons with reference points -> groundfish stock status 2004
Changes in average weight at age:
• causal mechanisms = environmental change, density dependence, earlier maturation/genetic selection, etc.
• implications if patterns persist = lower yields, slower rebuilding, possible changes in rebuilding targets
majority of fish caught near margins of closed area
JENSEN'S INEQUALITY - function of the mean is >= mean of function
• fishermen focus on highest concentrations of fish that can be found, subject to cost constraints and regulations
• gradients - space (closure areas), target age classes, school effects
• mixture of populations
scallop example: reopening of closed area II in 1999 (closed since 12/1994)
• scallop fishery subjected to individual trip limits (10 k lb), overall yellowtail flounder bycatch cap (yellowtail heavily affected by scallop dredge)
• effect: fleet dispersed, caught less scallop to avoid yellowtail cap
• areas with higher density: more catch weight per contact hour, less discard
optimal solutions = border between feasible & infeasible solutions
• each represents a different spatial distribution of fleet
• either reduce bycatch or yield loss