Figure 4
From: Zero-tolerance biosecurity protects high-conservation-value island nature reserve
The patterns of quarantine hours, freight tonnage and corresponding border and post-border detections of Non Indigenous Species over the surveillance period. The most compelling correlations are between freight tonnes per month and border detections in the same month (Pearson’s r = 0.65, p < 1E-9), and between freight tonnes per month and quarantine hours in the subsequent month (r = 0.59, p < 1E-5). Correlations that were statistically significant but of smaller magnitude were found between quarantine hours per month and post-border detections in the same month (r = 0.26, p = 0.024) or in the subsequent month (r = 0.27, p = 0.021). Overall, there was an increase of 17.6 quarantine hours (s.e. = 2.5 hours) for every 100 tonne increase in freight in the same month. Post-border detections increased by 0.27 organisms (s.e. = 0.12) for every additional 5,000 quarantine hours in the same month, and by 0.29 organisms (s.e. = 0.12) for every additional 5,000 quarantine hours in the previous month. Monthly rainfall over the period was not strongly or significantly correlated with quarantine hours, border or post-border detections in the same month or subsequent months, with the largest correlation of 0.165 (n.s.) found between rain per month and post-border detections in the subsequent month.
