3  Allocation

There are three types of data from New Zealand’s commercial fisheries that quantify catches:

MHR/QMR data are the key information used in the balancing of commercial catch against the Total Allowable Commercial Catch (TACC) for a stock; however, they provide information at a relatively coarse resolution of client, stock, and month. QMRs provided a record of the total monthly catch of each QMS fishstock for each quota holder, by month from December 1986 to September 2001. MHRs replaced QMRs from October 2001 and record data on the harvest of both QMS and non-QMS species.

The finest-scale catch information is provided by estimated catches, which are reported per species per fishing event. However, estimated catch data are not necessarily comprehensive or accurate; this is because not all species caught are required to be reported for each event, and the quantities reported are estimated rather than weighed.

Landings and disposals provide data on the catches of all stocks, generally at the fishing trip resolution, with quantities verified (where practicable, for example, when landed at the end of a trip) by weighing. Under the Electronic Reporting regime introduced by the Fisheries (Reporting) Regulations 2017, these data provide a comprehensive record of catches per trip, with the fate of those catches indicated by a destination code. The set of available destinations has become more comprehensive as reporting regulations have evolved.

3.1 Allocation of catches to fishing events

The landings data that define the catches and removals for a stock are generally reported at the resolution of the fishing trip. The quantities recorded in the landings data may represent the first occasion on which the fish have been accurately weighed. Furthermore, trips can be lengthy (exceeding a month) and carry out fishing over a wide area. As a result, catches are most usefully allocated to individual fishing events.

Two allocation approaches have been developed: trip-based allocation and annual scaling. The kahawai database implements both approaches in order that the appropriate approach can be chosen for a particular analysis.

3.1.1 Trip-based allocation

The trip-based approach allocates the catches of a species during a trip to the fishing event records from the trip using the hierarchical method of Starr (2007). If a species is included in the estimated catch for at least one of the fishing event records on a trip, then catches are allocated in proportion to the estimated catch for each record (Estimated catch allocation). If no estimated catch of a species is recorded on a trip, but a single fishing method was used during the trip, then catches are allocated in proportion to the number of fishing events per record (Effort number allocation). If neither of the previous approaches applies for a species on a trip then catches are allocated equally across the fishing effort records (Equal allocation).

3.1.2 Annual scaling

In fisheries where there is significant use of intermediate destinations, the trip-based approach breaks down because catches may no longer be recorded in the same trip as the fishing effort that gave rise to those catches. In these cases, the annual ratio of summed catches to summed estimated catch for each vessel and species is calculated, and the estimated catch of the species for each fishing event within the year is scaled by this ratio.