Archival tag tracks

Tracks estimated from archival tags deployed on juvenile southern bluefin tuna were used in determining their habitat preferences in the Great Australian Bight (see Estimating habitat preferences). A number of methods exist for estimating location from archival tag data; the method used in this study was developed at CSIRO using methods similar to Pedersen et al. (2011); see also Basson et al. (2012). It can be summarized as follows:

  • Discrete space and time state-space model with data inputs:
    • Approximate longitude estimates (calculated from light record on tag);
    • Sea surface temperature from tag (compared to remote sensing SST data).
  • Error distributions on data inputs:
    • Error in longitude estimates derived from tags at known locations and assumed to follow a Normal + t-distribution mixture.
    • Error in SST modelled using a Normal distribution accounting for bias in sensors.
  • Process model is a simple random walk/diffusion model.
  • Model output is the posterior probability of the fish being in each of the possible discrete space grid locations at each half-day time step.
  • Estimated track is the weighted average of the posterior probabilities across space at each time step.

 

Example tracks

  • Release date, recapture date, and length of fish at release are given in the title.
  • A black circle marks the release location; a black triangle marks the recapture location.
Click on any map to open a full-size image in another window.

 

Archival tag track
Archival tag track
Archival tag track
Archival tag track
Archival tag track
Archival tag track

(Tracks produced by T. Patterson, CSIRO)