Large Lake Exploitation Data

by Joe Thorley

A photograph of a Rainbow Trout recovering post-tagging
Figure 1. A Rainbow Trout recovers post-tagging by Alistair Fraser ©.

Background

Large lake exploitation studies typically involve the capture and tagging of fish whose subsequest movements are detected using acoustic receivers. The detections, in conjunction with angler reports of externally tagged fish, are used to estimate the proportion of individuals that are captured by anglers versus die of natural causes.

While lots of information can be recorded, there is a limited amount of data that must be recorded to allow exploitation to be estimated.

The following tables list what we consider to be the key information.

Captures

Table 1. Capture data.

Column Description
DateTimeReleased The date and time at which the individual was released (yyyy-mm-dd HH:MM:SS)
LongitudeReleased The longitude at which the individual was released (dd.ddddd)
LatitudeReleased The latitude at which the individual was released (dd.ddddd)
CaptureMethod The capture method (typically rod or net or trap)
FishSpecies The fish species
FishLength The fish fork length (mm)
AcousticTagNumber The unique acoustic tag number (leave blank if not applicable)
ExternalTagNumber1 The unique first external tag number (leave blank if not applicable)
ExternalTagNumber2 The unique second external tag number (leave blank if not applicable)

All fish should be released within 100 m of the point of capture. Fish in poor condition should not be tagged.

Receivers

Table 2. Receiver data.

Column Description
ReceiverNumber The unique acoustic receiver number
DateTimeDeployed The date and time at which the receiver was deployed (yyyy-mm-dd HH:MM:SS)
LongitudeDeployed The longitude at which the receiver was deployed (dd.ddddd)
LatitudeDeployed The latitude at which the receiver was deployed (dd.ddddd)
DateTimeRetrieved The date and time at which the receiver was retrieved (yyyy-mm-dd HH:MM:SS)
LongitudeRetrieved The longitude at which the receiver was retrieved (dd.ddddd)
LatitudeRetrieved The latitude at which the receiver was retrieved (dd.ddddd)

Only receivers which are successfully retrieved and downloaded should be recorded. The raw data file from each receiver retrieval should be saved to file and provided as is.

Recaptures

Table 3. Recapture data.

Column Description
DateRecapture The date of recapture (yyyy-mm-dd)
ExternalTagNumber1 The first external tag number (leave blank if missing or not applicable)
ExternalTagNumber2 The second external tag number (leave blank if missing or not applicable)

Anglers must return all non-missing external tags to receive the reward.

Acoustic Tags

Table 4. Acoustic tag data.

Column Description
AcousticTagNumber The unique acoustic tag number
AcousticTagModel The manufacturers tag model code
AcousticTagLife The acoustic tag life (days)

Recovered acoustic tags should not be reused in the same study.

External Tags

Table 5. External tag data.

Column Description
ExternalTagNumber The unique external tag number
ExternalTagValue The reward value of the tag ($0 if a standard tag)
ExternalTagColor The color of the tag

External tags must include the text REWARD with the reward value and a phone number for reporting purposes.

Summary

For accuracy, all latitudes and longitudes should be recorded as decimal degrees to five decimal places. To minimize conversions, all latitudes and longitudes should be recorded in WGS84 (the internal format of most GPS units). For consistency, all dates and times should be recorded in local daylight-savings time.

For details of a more comprehensive but consistent data collection program see the Ocean Tracking Network.