1Estimating Fish Population Abundance1. Population differentiation2. Sample methodsa. Countsi. Total censusii. Partial count and extrapolate to entire area b. Indicesc. Mark-recapture3. Sample designSampling design and methods used are highly reliant on objectives and area.Management goal to accurately estimate population status and trends.¾ accurate ¾ repeatable¾ cost effectivePopulation differentiation: Defining the fish population unit.Life history strategy:Migratory Diadromous (anadromous, catadromous)Freshwater MarineResidentHabitat typeLakes (Ocean)River/stream reachesBoth¾Relatively easy to sample:migratory species – they come to you lake – closed population¾More difficultresident stream speciesIdaho Fishing Regulationshttp://fishandgame.idaho.gov/cms/fish/rules/clear.pdfPopulation differentiation Population units will be influenced by management actions.Sample Methods - Counts Total census – rarely made Migrants – counts at river towers or weirsSample Methods - Counts Total census – rarely made Migrants – counts at river towers or weirsSample Methods - Counts Total census – rarely made Migrants – counts at dams count stations .Some time gaps that are filled by extrapolation.2Sample Methods - Counts Total census – rarely made Migrants – counts at dams count stations .Some time gaps that are filled by extrapolation.Non-migrants – only for small streams, ponds, etc.Sample Methods - Counts Partial counts – more common, especially for resident fish.Sample Methods - Counts Partial counts – more common, especially for resident.Divide stream into sections (50 – 100m).Sample Methods - Counts Partial counts – more common, especially for resident.Divide stream into sections.Select sites to sample, count fish, measure area, calculate density.Extrapolate to whole area. Sample Methods - Counts Partial counts: ElectroshockingBlock nets up and downstream of site.Triple-pass removal.Should apply correction factorSample Methods - Counts Partial counts: Snorkel surveySnorkel crew move upstream through site counting fish.Need clear water.Only effective for fish in water column (trout).Requires good amount of training to be accurate and precise.3Sample Methods - Indices Redd surveysWalk streams or make aerial countsApply expansion factor for number of fish in spawner population.Requires a lot of information on study population. Sample Methods – Mark-recapture Migrant – collect migrants, mark them, release upstream, recapture.Calculate population estimate using CJS.Sample Methods – Mark-recapture Non Migrant – collect fish, mark, come back one or more times for recapture effort.ElectroshockingMinnow trapsNets, seine, cast, etc.AnglingEtc., Sampling (survey) DesignHow many sections of stream are sampled and where?Probabilistic sampling –Simple random samplingStratified random samplingSystematic samplingSimple Random Sampling (SRS). Simplest to design. Every potential sample location has equal chance to be selectedDivide stream into segments, arrange on list, Simple Random Sampling (SRS). Simplest to design. Every potential sample location has equal chance to be selectedDivide stream into segments, arrange on list, and select locations randomly.¾ Works best if habitat is relatively uniform throughout study area.¾ Access may be a problem.4Stratified Random Sampling Assumes heterogeneous habitats (strata). Every location within each strata has equal chance to be selected.Each strata sampled equally or proportional to abundance.¾Assumes you understand important strata and can identify them.Systematic Sampling. Pick random start point.Space sample locations evenly through study area.¾Sampling may overlap some natural pattern in stream habitat.¾Inaccessible spots may need to be dropped, which leaves gap in
View Full Document
Unlocking...