A new method for estimating illegal fishing effort is put forward. The results from this new method are similar to the Agnew and Kirkwood method and this suggests that the current method is adequate under circumstances of low evasion and for when good knowledge exists that zero observations reflects 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 type of observations method used, which 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 vessels.

As the number of illegal vessels increase, both the estimate and the average amount of illegal fishing increases. This gives us some confidence that the method can produce results that have a degree of legitimacy. However, the range of actual fishing (in the simulation data sets) 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 estimate with some given level of confidence (for example 80%).

Numéro du document:

WG-FSA-04/63

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