Towards Sustainable Fisheries ESM 201 April 15, 2004 Population cohorts Dynamics of a stock cohort Age or stage structured models: Survivorship Age or stage structured models: Fecundity Stage-structured sea turtle model Leslie Matrix Leslie Matrix for Loggerheads Crowder et al. Ecol. Appl Sensitivity analysis Sensitivity is change in growth rate for a given change in matrix element Elasticity is proportional change in growth rate for a given change in matrix element puts fecundity and survival on commensurate scales Sea turtle elasticities Projected turtle population increases using TEDs Issues in Managing F (fishing mortality) Defining harvestable stock How many fish? Which fish? When? Where? Managing F Limit Effort Boats Time Equipment Access Quotas Precautionary use of MSY? Pew Oceans Commission Report Marine Reserves Habitat conservation Elimination of F for larger and more fecund individuals of target species Restoration of foodwebs Spillover of target species to neighboring areas Mahimahi (Corphaena hippurus) Tambaqui Pacific hake, Puget Sound Halpern, B. Ecological Applications 2003. Spillover effect as f(species dispersal and reserve size) Networks of marine reserves? Aquaculture Does it present an alternative to non- sustainable wild fisheries? Ecological effects? Wild fish inputs Habitat modification Genetic pollution of wild stocks ~ 220 species currently farmed worldwide many different extensive to intensive systems ~ 30 million metric tons/yr 90% of production in Asia Naylor et al Table 2 details 10 most widely farmed fish require an average of 1.9 kg wild fish/kg farmed fish Carnivorous fish require kg wild fish/kg of farmed fish Figure 1 Flow chart of capture and farmed fisheries products from aquatic primary production. Numbers refer to 1997 data and are in units of megatons (million metric tonnes) of fish. From Naylor et al Nature 405:1017. A few summary points Many reasons for decline and over-exploitation of marine fisheries Most ocean fish that we consume are carnivores at the end of relatively long food chains Fisheries are managed for surplus yield based on premise of natural population regulation Difficult to establish maximum sustainable yield Aquaculture is rapidly increasing, with many negative consequences as currently practiced (but improving)