SUSTAINABLE YIELD SUSTAINABLE YIELD Sustainable yield is the
SUSTAINABLE YIELD
SUSTAINABLE YIELD • Sustainable yield is the rate of increase in natural capital that can be exploited without depleting the original resource base of its potential replenishment • Examples of natural capital (lumber, fish, water) • SY= ((total biomass/energy) at time t + 1)/ - ((total biomass/energy) at time t) • SY = (annual growth and recruitment) – (annual death and emigration) • In other words, the max # of individuals that can be harvested now that will allow population to return to its carrying capacity as quickly as possible
• Sustainable yield is a real-life issue • Industries want to harvest natural capital and sell for a profit • Industries are more interested in Maximum Sustainable Yield • Largest amount of raw material that can be exploited without depleting the stock • If you want maximum yield, harvest them all, right? • Not very good idea long term!! • Sustainable yield can vary over time • Think how a forest fire might effect the yield of the forest • Or a drought or reduced snow pack on water tables • For sustainable yield to be accurate, the data has to be accurate • How do you count all the fish in an area? • Might be easier to measure water levels in an aquifer
HOW DO YOU MEASURE • What tools are available • Technology has been somewhat of a game change • ICT systems like GIS (Geographic Information Systems) have allowed more accurate data to be collected • Again it’s dependent on the resources (forest vs. fish? ) • So industries want to know what they can take and allow population to return to carrying capacity • The problem is the carrying capacity is dependent on many factors • Reproductive capability • Longevity • Indigenous resources of t he ecosystem or habitat
MAX SUSTAINABLE YIELD & CARRYING CAPACITY • Remember when a population is growing the fastest? • At half of its carrying capacity • But calculating k is not easy • It can change day to day, month to month, year to year • Do all individuals contribute to birth and death rates equally? • What if you harvest too many breading individuals, or not enough dying individuals, or too many young ones • Here in lies one of the many problems about sustainable yield, but we have become more aware of the problem in the past few decades • Read pg. 108 in Cambridge and think about the EU Common Fisheries Policy and the connections to the Tragedy of the Commons
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