Estimation Methods for Fish Population Abundance
Explore the various assumptions and effects of violations on estimating fish population abundance using methods like the Petersen method. Understand how factors like marking, recapture, immigration, and mortality can impact the accuracy of abundance estimates in fisheries management.
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Presentation Transcript
Abundance Estimates Natural Mortality Recruitment Population Numbers Fishing Mortality Immigration Emigration
Assumptions Petersen Methods The population is closed. no losses due to emigration or mortality. no gains due to immigration or recruitment. All fish have the same chance of being caught. Tagging fish does not affect their catchability. Fish do not lose their tags. All tagged fish are observed/reported when recaptured. 2 Abundance
Assumptions Effect of Violations n=19 Scenario #1 m=3 M=16 Scenario #2 m=10 Which scenario would result in a larger estimate of N? Marking N=?? Recapture 3 Abundance
Assumptions Effect of Violations If M and n are constant then anything that makes m smaller will result in an increase estimate of N. Alternatively anything that reduces the ratio of marked to unmarked fish will result in an increased estimate of N. 4 Abundance
Assumptions Effect of Violations What happens to estimate of N if unmarked fish immigrate into the population? There are proportionately fewer marked fish so m will be lower; thus N1OVERestimated Marking Recapture 5 Abundance
Assumptions Effect of Violations What happens to estimate of N if marked fish die at a disproportionately higher rate? There are proportionately fewer marked fish so m will be lower; thus N1OVERestimated Marking Recapture 6 Abundance
