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Development of New Methods for Quantifying Fish Density Using Underwater Stereo-video Tools
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Double-observer line transect methods: levels of independence.

Stephen T Buckland1, Jeffrey L Laake, David L Borchers

  • 1Centre for Research into Ecological and Environmental Modelling, University of St Andrews, The Observatory, Buchanan Gardens, St Andrews, Fife KY16 9LZ, Scotland. steve@mcs.st-and.ac.uk

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Double-observer line transect methods improve marine mammal abundance estimates by integrating mark-recapture data with distance information. This approach accounts for detection heterogeneity, offering more reliable analyses for aerial and shipboard surveys.

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Area of Science:

  • Ecology
  • Wildlife Biology
  • Statistical Ecology

Background:

  • Double-observer line transect methods are increasingly used for marine mammal abundance estimation.
  • These methods combine distance sampling with two-sample mark-recapture data.
  • Estimating abundance with these methods faces challenges due to heterogeneity in detection probability.

Purpose of the Study:

  • To develop a framework for more reliable analysis of double-observer line transect data.
  • To address estimation problems arising from heterogeneity in mark-recapture data.
  • To utilize distance from the transect line as a covariate to diagnose unmodeled heterogeneity.

Main Methods:

  • Modeling the covariance in detection probabilities with distance from the transect line.
  • Formulating the estimation problem using different levels of independence between observers.
  • Testing the proposed methods through simulation and analysis of known-abundance datasets.

Main Results:

  • The framework allows for a spectrum of models, from full independence (Petersen estimator) to limited independence.
  • Accounting for distance-dependent detection improves the diagnosis of unmodeled heterogeneity.
  • The methods provide more reliable abundance estimates compared to conventional approaches.

Conclusions:

  • The developed framework offers a robust approach for analyzing double-observer line transect data.
  • This method enhances the accuracy of marine mammal abundance estimates from surveys.
  • The approach is applicable to real-world datasets, such as minke whale sightings.