RU BL 410 - Life History of Aquatic Organisms

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Life History of Aquatic Organisms•Life History = “birth,” growth, reproduction, & death of an organism --- Trade Offs•Life history characteristics vary.Rate of growth (How long to sexual maturity?)Number of offspringFrequency of reproductionNumber, size, and sex ratio of offspringAge of deathSalmon Life HistoryLife History•Reproductive Value = the average number of offspring in a population that remain to be born to individuals of a certain age.agereproductivevalueimmediately beforefirst reproduction•Fecudity = # of ova produced by a female.•Fertility = # of offspring produced by a female.Fecundity ≠ Fertility Fertility ≤ Fecundity= expected if directly proportionalFish Fecundity with AgeAGEFECUNDITYsexual maturity= observedDifferenceinvested in growth etc.Iteroparity & Semelparity•Iteroparity = individuals may reproduce in >1 reproductive season during its life. (most organisms)•Semelparity = individuals may reproduce in 1 reproductive season during its life. “BIG BANG” reproduction; all energy to repro. (squid, octopus, some Pacific salmon)Parental Care• Broadcast Spawning = buoyant eggs externally fert.; no parental care; many small eggs.• Egg Scattering = non-buoyant, non-adhesive eggs externally fert.; no parental care; many small eggs. • Shelter Spawning = non-buoyant, adhesive eggs laid in existing shelter; parental care via guarding & egg care in many. • Nest Building = non-buoyant, eggs laid in created shelters; parental care in nest construction, many guard & clean eggs. • Brooding/Bearing = non-buoyant, adhesive eggs externally fert. & laid on a parent; care extensive. • Livebearing = eggs fertilized inside female and develop there; female parental care extensive.Parental Care (or lack thereof) Growth of IndividualsAGESIZEFishAGESIZECrustacean•Fishes are said to have indeterminate (never ending) growth. However, growth does plateau.Populations in Fisheries Context•Population = individuals of one species that simultaneously occupy a defined area•Deme = individuals of one species that form a distinct reproductive community•(Fisheries) Stock = individuals of one species that share common production characteristicsand support the same basic fisheries.•Year Class (Cohort) = All the individuals in a population born/hatched in a single “year”•Year Class Strength = the number of individuals in a year class•Older individuals (esp. fish) usually are larger.•Year class structure can often be seen in the size distribution of individuals in a population.Size of Individuals in a Pop.SIZE#Individuals in a Seasonally Reproducing PopulationSurvivorship & Mortality•Survivorship = percent / proportion of the initial year class that survives•Mortality = percent / proportion of the year class that dies over a given time period•Most commercial species exhibit high mortality when young, AND with great year to year mortality variation due to climate. This is associated withHIGH FECUNDITY.Why?Population/Stock Change•Population size = (births + immigration) -(deaths + emigration)•Stock size = (recruitment + immigration) -(harvest + predation + emigration)•Recruit = individual enters the catchable population.•Recruitment = number of recruits that enter a stock over a given time period.Year classes may all recruit around the same time if size variation is low.Population Growth•Logistic growth•rmax= rate of increase, N = pop. size•K = carrying capacity•dN/dt =rmaxN [(K-N)/K]A “bad year”can lower K& a “good year”can elevate K.NtK1/2 KPopulation GrowthNtK1/2 K•Logistic growth•rmax= rate of increase, N = pop. size•K = carrying capacity•dN/dt =rmaxN [(K-N)/K]higher fecunditylower fecundity Population GrowthdN/dtN1/2 KK•Logistic growth•rmax= rate of increase, N = pop. size•K = carrying capacity•dN/dt =rmaxN [(K-N)/K]Would higheror lower fecundityaffect this?Predation•Interspecific Predation = Consumption of an individual of one species by another•Cannibalism (Intraspecific Predation) = consumption of an individual by a member of the same species (includes egg cannibalism)Density Dependent - increases with density•Predation direct effects = death or injury•Predation indirect effects = predation avoidance  reduced movement, reduced feeding, &/or reduced breeding reduced individual condition &/or pop. sizeDensity & Predation Risk•Density Independent Predation = predation risk per individual is independent of prey density•Direct Density Dependent Predation = predation risk increases with prey density•Inverse Density Dependent Predation(Depensatory) = predation risk decreases with prey density (swamping)Competition•Intraspecific Competition usually more significant than interspecific competition.•Effects density dependent and usually indirect (less to go around).•When two species are using the same resource…1. they are competing… or2. the resource is not limiting (e.g., seasonally abundant).Lepomis CompetitionLepomis cyanellusLepomis gibbosusLepomis macrochirussmall fish, surface insects, & macrophytic inverts.snails & benthic inverts.zooplanktonPopulation Management•Which populations can stand the greatest harvest?Ones with a high reproductive rate. (usually have low early survivorship)Have many offspring.Reproduce frequently.Mature quickly.•Which individuals are harvested?What is the reproductive value of harvested individuals? Population ManagementFisheries Recruitment Models•Used to predict stock size to manage stocks.How much, where, and when can we harvest?•Beverton-Holt Model - Recruitment increases with stock size but comes to an asymptote at some level. (More adults = more recruits but pre-recruits resource limited.)•Ricker Model - Recruitment peaks at some intermediate level of stock abundance and declines at higher abundance. (More adults = more cannibalism/competition & pre-recruits resource limited.)Recruitment ModelsStock BiomassRecruit-mentBiomassStock BiomassRecruit-mentBiomassBeverton-HoltRickerBeverton-Holt & Ricker Models•Which model applies to which stock? Pre-recruit competition and cannibalsim?•Used in the 1970s but abandoned in 1980s.•Theory supported but most data didn’t really support. Year to year variance very high.•What other things do you think might affect recruitment? (i.e. What caused the variance?)Stock Growth•k = intrinsic rate of stock increase (≈ rmax) •B = stock biomass (≈


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RU BL 410 - Life History of Aquatic Organisms

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