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.
Click on any map to open a full-size image in another window.
- 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.
(Tracks produced by T. Patterson, CSIRO)