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Lecture 3 review: life history trajectories

The eggie. First juvenile nursery area: small, strong density-dependence in mortality. Juvenile migration. Larval drift, density-independent mortality. Spread into larger juvenile nursery area(s), mortality much lower. Spawning migration.

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Lecture 3 review: life history trajectories

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  1. The eggie First juvenile nursery area: small, strong density-dependence in mortality Juvenile migration Larval drift, density-independent mortality Spread into larger juvenile nursery area(s), mortality much lower Spawning migration Adult foraging areas, most often with complex seasonal migration patterns Lecture 3 review: life history trajectories ALWAYS ASK: -HOW OLD IS IT? -WHERE DID IT COME FROM? -WHERE IS IT GOING? Fractal, complex diurnal movement

  2. Lecture 4 topics (Foraging Arena Theory I: stock-recruitment) • Most stock-recruitment data sets show the pattern predicted by Beverton and Holt when they assumed cohorts die off at rates dN/dt=-MN, with varying over time as M=mo+m1N, i.e. linearly density-dependent M. • Foraging arena theory predicts this pattern of density dependence to arise from risk-sensitive foraging behavior where fish try to balance need to grow with risks of foraging to achieve that growth.

  3. Testable predictions of foraging arena theory (thesis topics?) • Spatially and temporally restricted activity is a universal observation, no test needed • Spatial restriction is caused by predation risk (there are other possible causes) • Increased density causes • Reduced prey density and food intake/foraging time • Increased activity (foraging time) • Increased predation mortality rate • There is an upper limit on prey mortality rate as predator density increases

  4. SURVIVING RECRUITS EGGS What is a “stock-recruit relationship” as used in developing harvest management policies? • It is NOT a deterministic prediction of the exact recruitment to be seen at each adult stock size or egg deposition. • Rather, it is a collection of probability distributions whose means vary in a relatively simple way with stock size:

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