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A history of whaling 10th Century – records of whaling 1400-1700 Atlantic Arctic fishery – targeting the right whale 1600-1900 the Pacific fishery – more right whales 1800-1970s Sperm whale fishery Quantity of oil in a sperm whale made it an attractive target Innovation: Possible to make margarine of almost 100 percent whale oil. Sperm Whale (Physeter macrocephalus) 1712 – Americans hunt sperm whale 1860 – Norwegians introduce steampowered boats and explosive harpoons Factory ships and newer technologies more species, more oceans, more countries Blue whale Minke whale Sei whale Fin whale 1946 17 nations signed a license where the International Whaling Commission (IWC) set a maximum catch in the Antarctic. 1949-1960 – IWC sets annual “fixed” quotas for all whaling 1972 - the United Nations called for a cessation of whaling and the United States Congress passed an Endangered Species Act 1987 - whale sanctuaries were declared in the 1970s and ’80s, and a general moratorium on commercial whaling, adopted by the IWC in 1982, took effect in 1987 Odocoileus virginianus Clupea harengus Populations III: Harvest Models Oncorhynchus tshawytscha Pinus sylvestris Review r – intrinsic or per capita growth rate dN/dt = r*N – exponential growth Nt=N0*ert (We’re keeping it discrete) 1600 N 1200 800 400 Bye bye fuzzy duckling!! 0 0 20 Time 40 Rabbits in Australia – invasive species can grow exponentially at first Review N Logistic growth – S-shaped or sigmoid curve K – carrying capacity Modify with “unused” component of K (K-N)/K = (1-N/K) – used interchangeably dN/dt = r*N*(1-N/K) 120 100 80 60 40 20 0 Logistic growth r=0.25 K=100 0 20 40 Time 60 Review Ceratotherium simum 200 Exponential N 150 K=100 100 Logistic 50 0 0 20 40 Time 60 Review Environmental resistance Exponential K=100 Logistic How do we use this information to create harvesting quotas? Two types of mortality: Additive – added mortality causes a reduction in survival any hunting is added mortality if we want to control a population of invasives Compensatory – added mortality does not affect survival, up to a threshold harvesting/ hunting is mortality “that would have happened anyway” e.g. starvation, predation, disease We assume that a “compensatory” decrease in non-harvest mortality occurs – perhaps due to extra food availability N 110 100 90 80 70 60 50 40 30 20 10 0 K Inflection point K/2 Logistic growth r=0.25 K=100 0 10 20 30 Time 40 50 60 MSY = Maximum Sustainable Yield K/2 7 MSY 6 Recuitment K 5 4 3 2 1 0 0 Logistic growth r=0.25 K=100 10 20 30 40 50 60 70 80 90 100 Population size N ? 7 K/2 ? K MSY h Recuitment 6 5 4 3 2 1 0 0 Logistic growth r=0.25 K=100 10 20 30 40 50 60 70 80 90 100 Population size N OSY – Optimal Sustainable Yield Problems with setting quotas Estimating numbers is not easy hard to obtain reliable MSY You can’t just stop people that easily noncompliance is a huge issue Recruitment K varies with environment = MSY changes MSY? N K K K Factors that affect K • Density-independent factors – Weather (storms, cold, drought) – Density-independent diseases (DDT poisoning) • Density-dependent factors – Food – Space (territories, denning sites, nest cavities) – Density-dependent epizootics (rabies, SARS) Trophic effects on K – remove large fish, remove fish waste, removes fertilizer, removes smaller fish, up the food chain, less fish to catch H=q*E*N Fixed Effort harvest Yield = efficiency*Effort*Population Recuitment or Harvesting rate, h E2 7 6 5 E1 EMSY 4 3 E2 > E1 > EMSY 2 1 0 0 10 20 30 40 50 60 70 80 90 100 Population size N Hindsight always helps – the Allee effect Low population density is prone to sudden extinction Fewer mating opportunities; simply too few to be fit enough Logistic Allee model dN/dt N Peruvian anchoveta (Engraulis ringens) • • • • • 1960-1972 – world’s largest fishery MSY estimated at 10 million tonnes/year Expanded fishing fleet plus El Niño events meant collapse 20,000 people relied on it, so politically harmful to close Repeated collapses – 1973, 1986 – still not recovered. Peruvian Anchoveta Global capture estimate (tonnes) source: FAO 14000000 12000000 10000000 8000000 6000000 4000000 2000000 0 1950 1953 1956 1959 1962 1965 1968 1971 1974 1977 1980 1983 1986 1989 1992 1995 1998 2001 Making a better model Fish, deer, trees are not all one size or age – We prefer adult or mature organisms – Life-history events – reproduction, growth occur at different times – Next Lecture: life-tables and age-structure