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In the site survey of a four-sided traverse, internal angles are essential to ensure geometric accuracy. The survey revealed that the sum of the measured internal angles was 359 degrees and 48 minutes, which is 12 minutes less than the expected 360 degrees. This discrepancy signals an error likely arising from measurement inaccuracies during the fieldwork.To rectify this error, the adjustment process involved distributing the 12-minute shortfall equally across the four internal angles. By...
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Tapes are essential in surveying for accurate, durable, and short-distance measurements. Made from lightweight, nylon-coated steel, they offer flexibility and strength for rugged outdoor use. The nylon coating protects against rust and wear, extending the tape's life. Standard lengths, around 30 meters, are marked in meters and millimeters for precision.Surveyors select tapes based on site conditions and accuracy needs. Lightweight, nylon-coated tapes are commonly used for ease of handling and...
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Development of New Methods for Quantifying Fish Density Using Underwater Stereo-video Tools
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Estimating effective survey duration in camera trap distance sampling surveys.

Hjalmar S Kühl1,2,3, Stephen T Buckland4, Maik Henrich5,6

  • 1Senckenberg Museum for Natural History Görlitz Senckenberg - Member of the Leibniz Association Görlitz Germany.

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Camera trap distance sampling (CTDS) was extended to account for delays in still image capture, crucial for accurate animal abundance estimation. Ignoring these delays can lead to significant underestimations of population density.

Keywords:
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Area of Science:

  • Wildlife ecology
  • Population estimation
  • Camera trap methodology

Background:

  • Camera trap distance sampling (CTDS) is a method for estimating animal abundance in unmarked populations.
  • CTDS was originally formulated for video, measuring distances at 'snapshot moments'.
  • Still image camera traps have delays (recovery and retrigger) that affect temporal survey effort calculations.

Purpose of the Study:

  • To extend the CTDS model for still image camera traps using passive infrared motion sensors.
  • To incorporate camera recovery time and retrigger delays into abundance estimation.
  • To prevent downwardly biased abundance estimates caused by inaccurate temporal survey effort.

Main Methods:

  • Extended the CTDS model to accommodate single images or short photo series from passive infrared motion sensors.
  • Proposed estimating 'mean time intervals between triggers' using Gamma and Exponential functions from consecutive picture intervals.
  • Applied the approach to survey data for red deer, roe deer, and wild boar.

Main Results:

  • Empirically estimated and model-derived mean time intervals between triggers were similar.
  • Estimated mean time intervals between retrigger delays ranged from 8.28 to 15.05 seconds, depending on truncation times and species.
  • Failure to account for these intervals could lead to density underestimation by up to 96% due to overestimated temporal survey effort.

Conclusions:

  • The proposed CTDS extension is applicable to any taxa surveyed with camera traps using still images.
  • This method addresses the common preference for still images over video due to lower energy and memory consumption.
  • The approach is expected to have broad applications in camera trap studies, including methods beyond CTDS.