Catch per unit effort is basically the average weight of eels caught in a standard fyke net per set. When this data is collated for an area over a number of years, it informs us of changes in abundance for each species of eel.
Whilst simple in principle, the devil is in the detail. Great care needs to be exercised and each data set must be standardised or placed on a level playing field.
Since introduction of the QMS in 2004 we have seen a significant upward trend for shortfins in 11 of the 12 sub areas and a mixed but generally flat trend for longfins.
In 2008 MPI introduced a prohibition on landing all longfins above 4kgs for the purpose of protecting large females for breeding. MPI also heavily reduced the commercial longfin catch (TACC) to increase abundance of longfins. Both of those regulatory changes have artificially skewed the cpue index downward.
In some waterways, we are seeing the fruits of those actions in larger longfin eels at an abundance that is pleasing at the same time as creating extra grading work to return them.
It should be remembered that only 22% of available North Island habitat is commercially fished! The cpue indices only refer to fished areas