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Ecosystem-based fisheries management: an introduction Villy Christensen and Daniel Pauly Fisheries Centre University of British Columbia Vancouver, Canada.

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Presentation on theme: "Ecosystem-based fisheries management: an introduction Villy Christensen and Daniel Pauly Fisheries Centre University of British Columbia Vancouver, Canada."— Presentation transcript:

1 Ecosystem-based fisheries management: an introduction Villy Christensen and Daniel Pauly Fisheries Centre University of British Columbia Vancouver, Canada Villy Christensen and Daniel Pauly Fisheries Centre University of British Columbia Vancouver, Canada December 16, 2002 United Nations University Fisheries Training Programme, Institute of Marine Research, Reykjavik, Iceland

2 Under the UN Convention on the Law of the Sea, nations have accepted: A mutual obligation to consider the impact of their policies on marine ecosystems; to take all appropriate actions to preserve the marine environment; and to manage ecosystem resources based on the interdependence of the system components... “in accordance with their capabilities.” A mutual obligation to consider the impact of their policies on marine ecosystems; to take all appropriate actions to preserve the marine environment; and to manage ecosystem resources based on the interdependence of the system components... “in accordance with their capabilities.”

3 We are not the only ones to eat fish

4 V. Christensen, Rev. Fish Biol. Fisheries 1996, 6: Fishery catch Fish eaten by fish Upwelling Trop. shelves Other shelves Coastal Freshwater Global catches and fish predation (million t; 1991) We are not the only ones to eat fish

5 We cannot and should not replace the top predators Many examples exist of ecosystem disasters due to fishing down of predators; To maintain or improve catches we must maintain functioning ecosystems; We already assert major influence over the marine environment: Many examples exist of ecosystem disasters due to fishing down of predators; To maintain or improve catches we must maintain functioning ecosystems; We already assert major influence over the marine environment:

6 Ecosystem effects of fishing Removal of large sharks in South Africa  more small sharks  less of their prey fish; Removal of grazers (such as these surgeonfishes) led to Jamaican reefs being overgrown by algae and more susceptible to hurricane damage. Removal of large sharks in South Africa  more small sharks  less of their prey fish; Removal of grazers (such as these surgeonfishes) led to Jamaican reefs being overgrown by algae and more susceptible to hurricane damage.

7 Ecosystem effects of fishing Overfishing triggerfish, pufferfish, hump-head wrasse, and triton (which all feed on juvenile crown-of-thorns) led to crown-of-thorns outbreaks on coral reefs

8 Ecosystem effects of fishing Overfishing removed pufferfishes, the predators of sea urchins:

9 Ecosystem effects of fishing Overfishing removes the predators of sea urchins: pufferfishes

10 Sea urchin population explosions caused severe damage to reefs

11 Trophic level: the concept Trophic level Phytoplankton Top predators Prey fish Zooplankton * *.*. *.*.  10% *

12 Initially fisheries target the upper-trophic level species, the top predators; As these decline in abundance focus is gradually shifted toward the prey of the top predators; Ultimately only the lower-trophic level species (small fish and invertebrates) are left to be caught. Initially fisheries target the upper-trophic level species, the top predators; As these decline in abundance focus is gradually shifted toward the prey of the top predators; Ultimately only the lower-trophic level species (small fish and invertebrates) are left to be caught. Processes involved in ‘fishing down’

13 Fishing down the food web: succession of target organisms Time Top predators Prey species Catch

14 Fishing down the food web: succession of target organisms Time Top predators Prey species Catch Sustainability?

15 Artisanal Semi-industrial Industrial Time Fishing effort Fishing down the food web: succession of fleets

16 Science March 1998, 279 Marine Freshwater Global fishing down the food web

17 Fishing down the food web 1960s: fishing started; 1980s: severely overfished Gulf of Thailand

18 Gulf of Thailand fisheries Science, October 1998 Fishing down the food web

19 Gulf of Thailand fisheries Science, October 1998

20 Norway pout in the North Sea

21 Feeding triangles: North Sea Other fish Krill Norway pout Copepods

22 Other fish Other fish Krill Norway pout Copepods Feeding triangles: North Sea

23 Other fish Other fish Krill Norway pout Copepods Feeding triangles: North Sea

24 Requirements for adoption of ecosystem-based approaches: A framework for integrating the wealth of information available at the species level; B asic understanding of ecosystem structure and function; C oncepts and software integrating first two items in a transparent, practice-oriented context. A framework for integrating the wealth of information available at the species level; B asic understanding of ecosystem structure and function; C oncepts and software integrating first two items in a transparent, practice-oriented context.

25 Do we have tools for ecosystem-based management? Yes, using Ecopath with Ecosim we can incorporate ecological, economic and social considerations into a rigorous framework Based thereon we can use Ecosim and Ecospace to explore policy options for ecosystem based management Yes, using Ecopath with Ecosim we can incorporate ecological, economic and social considerations into a rigorous framework Based thereon we can use Ecosim and Ecospace to explore policy options for ecosystem based management

26 Policy exploration Policy may be defined as an approach towards reaching a broadly defined goal; In fisheries policies are often implemented via TACs that are recalculated annually, and through regulation that affects fleet and deployment; The task of fisheries scientists is to advise both on policy formulation and on its implementation; So far much fisheries research is on implementation only; Ecosystem-based policy exploration is in its infancy. Policy may be defined as an approach towards reaching a broadly defined goal; In fisheries policies are often implemented via TACs that are recalculated annually, and through regulation that affects fleet and deployment; The task of fisheries scientists is to advise both on policy formulation and on its implementation; So far much fisheries research is on implementation only; Ecosystem-based policy exploration is in its infancy.

27 Some policy objectives 1Maximize fisheries rent; 2Maximize social benefits; 3Mandated rebuilding of species; 4Maximize ecosystem ‘health.’ Ecopath with Ecosim offers a method for evaluating the fleet configuration and effort levels that optimizes each of these objectives individually or jointly.

28 Maximizing profit 1Profits are calculated as: the value of the landings (landings * price, by species) less the cost of fishing (fixed + variable costs); 2Often optimization is achieved by: phasing out most fleets except the most profitable ones; and wiping out ecosystems groups competing with or preying on the more valuable target species.

29 Maximizing social benefits 1 Social benefits are expressed through the employment supported by each fleet; 2The benefits are calculated as job / catch value, and is fleet specific; 3Therefore social benefits are largely proportional to fishing effort; 4Optimizing efforts often leads to more extreme scenarios than optimizing profit.

30 Mandated rebuilding 1External pressure (or legal decisions) may force policy makers to concentrate on preserving or rebuilding the population of a given species in a given area; 2In Ecosim this corresponds to setting a threshold biomass (relative to the biomass in Ecopath) and optimizing towards the fleet effort structure that will ensure this objective; 3Implications will be case-specific: consider Monk seal/shark interaction in Hawaii, or Steller sea lion/Alaska pollock in the Eastern Bering Sea.

31 Maximizing ecosystem ‘health’ 1The ecosystem ‘health’ definition is inspired by Odum’s description of ecosystem ‘maturity’, wherein mature ecosystems are dominated by large, long-lived organisms; The group-specific biomass/production ratio provides the default weighting factor for the maximization of overall biomass; The ‘health’ optimization often implies: phasing out of all fisheries except those targeting species with low weighting factors.

32 Balancing economic, social and ecological objectives 1The starting values of the objective functions have each been standardized relative to their base values (from Ecopath), making them roughly comparable; 2Two of the measures tend to pull towards increasing fishing, and two pull towards reducing fishing. Care should be taken to consider this balance when giving relative weightings to the objectives; 3Optimizations should be performed with a range of weighting factors for each objective function.

33 Optimization: GoThailand

34 Conclusions: A transition to ecosystem-based management of fisheries is unavoidable, if we are not to lose more of our fisheries resources Such transition if actually happening in some countries, if only in the form of ecosystem consideration informing single-species management; In the longer term, detailed simulation of trophic interactions within exploited ecosystems, along with explicit consideration of environmental effects, may allow for forms of fishing that are compatible with the continued existence of the underlying ecosystem, something we presently do not have. Thanks for your attention.


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