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This overview examines Maximum Sustainable Yield (MSY) principles essential for effective population regulation, especially in commercial fishing. It elaborates on the logistic equation governing population dynamics, emphasizing the need for intermediate population sizes for optimal harvests. The U.S. Fishery Conservation and Management Act of 1976 defines MSY, highlighting the balance between ecological sustainability and economic benefits. Key concepts include fixed quota harvesting, individual fishing quotas (IFQs), and population viability analysis (PVA) for endangered species like the Florida panther and Sumatran rhino.
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Artificial Population Regulation • For regulation of populations • For commercial harvest • Maximum Sustained Yield (MSY) • Based on the logistic equation: • dN/dt = rN((K-N)/K) • Generally found at 1/2 the carrying capacity (K) • Formula for MSY • H = (Kr)/4
Frequency of Harvest The most frequent harvests can be taken at intermediate population sizes.
Maximum sustainable yield (MSY) Anchovy MSY Krebs: Fig. 17.3
Optimum yield Below MSY because of other interests • Defined in the U.S. Fishery Conservation and Management Act of 1976 • “the quantity . . . (1) that will provide the greatest overall benefit to the nation, with reference to food production and recreation and • (2) that is prescribed as such on the basis of maximum sustained yield as modified by any relevant economic, social, or ecological factors.
Reproduction curves & replacement 45o line is density independent replacement level r populations K type populations
Whale harvests Note the lack of whaling during WWII
Predictions • Garrod & Jones (1974) • Cod fishery • Ignored by fisheries managers
Multiple equilibria in harvesting Declining harvest efficiency with increased density Eo would harvest to extinction U= unstable equilibrium
IFQ’s • Individual fishing quota • Allowable catch divided into %’s awarded to or purchased by fisherman and companies • Avoids “fishing derby” • Can be sold or traded • High cost excludes many fishermen • Can be overcome if community quotas are allowed
Dynamic pool example • Plaice (Krebs, Fig. 17.5) • Best harvest rate would have been about 1/2 of actual level
Interface with economics ? - + + + - + - + - + + + + + - + + + + - - +
Cycle Catch + - + Effort Price Includes political pressure to increase effort
Biological Conservation • Population viability analysis (PVA) • How vulnerable to extinction? Includes minimum viable population (MVP) • Three general methods • Long term studies - biogeographical patterns • Subjective expert assessment • General mathematical model • Simulation models seem to hold the most promise • Problems with the analysis: • Changing conditions • Stochastic forces
Causes of rarity • Habitable areas are: • Short-lived • Small • Isolated • Resources sparse • Predators • Genetic variation lacking
Management decisions Sumatran Rhino
