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Fisheries
Population Dynamics
| Question | Answer |
|---|---|
| Big three drivers of fish pop. dynamics | growth, mortality, recruitment |
| Types of growth | Length, width, height, weight |
| Why is growth important? | Weight --> fecundity Age-Length- density Recruitment Harvest Predation |
| Indeterminate growth? | Length of a growing season changes between years |
| How to calculate age vs length in final exam question? | Use excel to make a curve and add y and r^2 to enter the age and see what length should be |
| What is a von Bertalanffy curve? | At given age what length should fish be? |
| Weight versus length calculation? | Enter in excel and use POWER trend-line to find what the weight should be given the length =(a*(length)^b)) in excel W= aL^b |
| Survivorship in excel | S= N1/N0 *100 |
| Why is there no equilibrium in nature? | Environmental conditions, habitat quality and quantity, natural and fishing mortality, predator/prey conditions |
| Recruitment | number of young fish entering the population or a life-history stage |
| Natural vs fishing mortality | Natural = M Fishing = U |
| Natural mortality | very high during early life stages (larval and juvenile) in adults disease predation parasitism |
| Fishing mortality | |
| What do population models do? | Helps managers make decisions, provides objectivity, identifies gaps in knowledge |
| Limitations of a model? | All models are wrong, some are useful |
| Two rate types of mortality | Instantaneous and annual |
| Annual versus instantaneous mortality | A= annual A= 1-S Z=instantaneous |
| Two types of instantaneous total mortality | Instantaneous Natural Mortality, M = Z-F Instantaneous Fishing Mortality |
| Instantaneous Fishing Mortality | F- focus of fisheries management (more likely to “control”) Harvest limits (number to harvest) Slot limits (size of harvested) Seasons (when to harvest) |
| How to calculate instantaneous mortality | S = e ^-z Z = -loge(S) |
| Calculating natural mortality and fishing mortality | A = cf + cm – (cf x cm) A = u + v – (u x v) |
| Assumptions for mark and recapture | No tag loss Anglers report tagged fish No changes in survival due to tag No births or deaths in the population Marked individuals have equal capture probability No emigration or immigration of population (closed population) |
| Difference between CPUE and pop estimate | CPUE is index of relative abundance NOT POP ESTIMATE |
| Telemetry advantages? | Additional info (movement and ecology) Does not rely on angler report More discrete time scales |
| Telemetry disadvantages? | Fish still alive may not move May not find a fish each time Cost and time of managers Natural emigration from system |
| Recruitment | Fish that survive to age 1 Fish that survive to a “life-stage” Fish that can be captured (commercial) |
| Recruitment changes influence | Abundance, age structure, number ind. breeding, density-dependent interactions |
| Density dependent (recruitment) | spawner abundance |
| Density independent (recruitment) | Stochastic events abiotic events |
| Abiotic conditions that may change recruitment | Flow, water levels, stochastic events, aquatic plant abundance, water temp |
| Methods of CPUE | Electrofishing, trawls, angling (hook and line) |
| Problem with saying _____x fish in one area than other when only did CPUE? | ____ times as many indicates density or count measured |
Created by:
llamaandlearning