Figure 1.
The aerial survey track over Exmouth Gulf.
A typical course flown by the aircraft during surveys. This flight path was split into nine parallel transects spaced approximately 10 km apart.
Table 1.
A summary of the aerial surveys carried out during the 2004 and 2005 whale season (Aug – Nov) in Exmouth Gulf.
Figure 2.
The area occupied by an increasing number of pods nearest to the centre of aggregation.
The minimum polygon area (convex hull area) around whale pods was repeatedly calculated for each survey flight to include increasing number of pods closest to the centre of aggregation, starting at the nearest 10% until all pods were encompassed by the polygon. A scatter plot of these changes in area occupied reveals two patterns in area use; the first group of flights are indicated by open symbols (▵ flight 4, ⋄ flight 5, ○ flight 6, □ flight 8) and the second group by closed symbols (♦ flight 1, ▪ flight 2, ▴ flight 3, +flight 7, – flight 9, ♦ flight 10).
Figure 3.
A comparison of nearest neighbour distances with proximity to the centre of aggregation.
The nearest neighbour distance (mean of flights ± standard error) of groups of pods based on how close they are to the centre of aggregation, i.e. the 10% mark contains the closest 10% pods to the mean, the 20% mark contains the closest 10–20%, and so on up to the 90–100% group. The only group with a significantly different nearest neighbour distance was the 90–100%, which was much higher than the rest.
Figure 4.
The temporal changes in number of A) total whales, and B) calves, in Exmouth Gulf.
A) For each flight, the total number of whales resident in Exmouth Gulf was estimated using distance sampling. The error bars mark the 95% confidence interval, calculated using a bootstrap in Distance 6.0. There is clear temporal pulse of whales in the Gulf, with the peak occupancy towards the end of September. B) The total number of calves observed during each survey flight also displays a temporal pulse to occupancy, but the peak here is slightly later in the first week of October.
Figure 5.
The relationship between density and occupancy of whales in Exmouth Gulf.
The total area occupied was calculated as the convex hull area for each flight, and the density as number of whales per km2 in this area. The pattern emerging is that of a constant area used with increasing density, as highlighted by the grey shaded area. One survey (flight 5), marked as an open circle, is an outlier to this pattern.
Figure 6.
Boxplots comparing median nearest neighbour of A) the pod size and B) the pod type.
Neither pod size or type showed significant difference in median nearest neighbour distances (Kruskall-Wallis test: pod size p = 0.80, pod composition p = 0.58). For pod type, ‘wCP’ are pods with calves present and ‘nCP’ are pods with no calves observed.
Figure 7.
The proportion of the population with a pod within a fixed radius, and increasing radii.
Cumulative density plots of the proportion of population that have at least one pod within a specified radius, at increasing radii, for A) flight 1, B) flight 2, C) flight 3, D) flight 7, E) flight 9, and F) flight 10. Each plot was fit with an exponential curve using the least squares method, and the radius at which half the population have a pod within this radius was calculated from the curves. Theses radii are A) 2.09 km, B) 1.95 km, C) 2.50 km, D) 1.82 km, E) 1.61 km, and F) 1.62 km.
Table 2.
The carrying capacity estimates for method 1 (median nearest neighbour) and method 2 (50% of population with a pod within this radius).