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CensusIO CensusIO Guide

The estimators

CensusIO carries a library of standard estimators, grouped by the question they answer. Each runs automatically when its data is present, and reports a 95% confidence interval where one is defined.

The estimators, grouped Estimators grouped by what they answer: Abundance (Mark-recapture, Removal / depletion, Catch per unit effort); Size and condition (Length frequency, Size structure or PSD, Relative weight or Wr); and Other surveys (Disease prevalence, Distance sampling, Biomass, Harvest). Abundance Mark-recapture Removal / depletion Catch per unit effort Size and condition Length frequency Size structure (PSD) Relative weight (Wr) Other surveys Disease prevalence Distance sampling Biomass Harvest
Estimators grouped by what they answer.

Abundance

Section titled “Abundance”

These speak to how many animals are present, from a survey’s catch. Mark-recapture and removal give one estimate per event; catch per unit effort is a relative index pooled across events.

  • Mark-recapture: from animals marked and released, then a later catch in which some are recaptured. Returns an abundance estimate with a 95% confidence interval (the Chapman-modified Petersen estimator, which is less biased when few are recaptured).
  • Removal / depletion: from successive removal passes (such as electrofishing) on a closed reach. As the catch falls from pass to pass, the rate of decline gives the starting number. Two passes use a closed-form estimate with an interval; three or more use a maximum-likelihood (Zippin) fit.
  • Catch per unit effort: a relative-abundance index from catch divided by effort (net-nights, hours, trap-nights). Reports both the effort-weighted ratio of means and the mean of per-event ratios (with an interval), which answer slightly different questions.

Size and condition (per individual)

Section titled “Size and condition (per individual)”

These describe the measured animals, across all individuals.

  • Length frequency: a histogram of lengths in fixed-width size classes, so you can see the size distribution at a glance.
  • Size structure (PSD): the percent of stock-length fish that also reach quality length, indexed to standard length categories. See Fisheries metrics.
  • Relative weight (Wr): a body-condition index comparing each fish’s weight to the standard weight for its length and species. Around 100 is average. See Fisheries metrics.

Other surveys

Section titled “Other surveys”
  • Disease prevalence (per individual): the share of tested animals that are positive, with a 95% Wilson confidence interval that behaves well for small samples and extremes, and an optional per-species breakdown.
  • Distance sampling (per detection): density from the distances of detections to a transect line or point, accounting for animals missed farther out.
  • Biomass (per plot): standing stock per unit area from sampled plots, scaled to the whole study area, with an interval from the spread across plots.
  • Harvest (per party): from creel or bag-check parties, the total harvest, the mean per party, the success rate (with a Wilson interval), and catch per hour.