An alternative method for estimating the level of illegal fishing using simulated scaling methods on detected effort
A new method for estimating illegal fishing effort is put forward. The results from this new method are similar to those of the Agnew and Kirkwood (2005) method, and this suggests that the current method is adequate under circumstances of low evasion and when good knowledge exists that zero observations reflect zero illegal fishing. The new method performs better in the case of zero detections and can potentially better handle the evasion of detection by illegal activity.
Both the new and the current method suffer from the fact that the observation method used directly affects the system. This is the prevention/detection problem, in which the greater the number of detections for a given level of illegal fishing, the more often the illegal fishers will curtail their fishing trips. This leads to a negative correlation between the amount of fishing and the estimated amount of fishing for a given number of illegal cruises.
As the number of illegal cruises increases, both the estimate and the average amount of illegal fishing increase. This gives some confidence that the method can produce results that have a degree of legitimacy. However, the range of actual fishing (in the simulation datasets) for a given estimated level of fishing is very large. This range of uncertainty increases as the evasion rate increases.
This research suggests that it would be possible to calculate a precautionary assessment of illegal fishing such that the actual number of illegal fishing days is less than, or equal to, the precautionary assessment with some given level of confidence (for example 80%)