To determine habitat preferences of SBT involves a number of steps.
- Choose the area of the ocean and timeframe to use for determining habitat preference. In this example we use the GAB (30-40°S, 120-140°E) for months Dec-Mar (corresponding to the summer fishing season) in years 1998-2009 (all years for which we have archival tag data, as used in step 4).
- Choose the environmental variables to include in the analysis. For now we use only sea surface temperature (SST).
- Extract the environmental data for the whole area of the ocean within the chosen area and time period.
- Extract the environmental data for only those locations where SBT were found within the chosen area and time period. Here we use tracks from SBT with archival tags to determine locations where fish were found within the GAB during Dec-Mar of 1998-2009. Below is one example of an SBT track used in our analysis. Note that the tracks are estimated based on light and temperature data and contain much uncertainty — for more information, see Archival tag tracks.
Track produced by T. Patterson, CSIRO, using methods similar to Pedersen et al. (2011); see also Basson et al. (2012)
- Compare the environmental data from the fish locations with the environmental data from the whole area to see which conditions the fish tend to 'prefer'. In the figure below, preferred SST values are where the blue bars (fish) are higher than the green bars (ocean) because these are temperatures where fish were found in greater proportion than they occurred in the ocean.