Estimation of non-target fish catches in the tuna longline fishery

Project: Estimation of non-target fish catches in the tuna longline fishery
Project Code: TUN2004/01
Start Date: 1 October 2004
Completion Date: 15 May 2006
Vessel Use: None

Overall Objectives:

1. To estimate the level of non-target fish catch and the level of discards of target and nontarget fish species in the tuna longline fishery.

Specific Objectives:

1. To estimate the catch rates of non-target fish in the longline fisheries for tuna using data from the Observer Programme and commercial fishing returns for the 2002/03, 2003/04 and 2004/05 fishing years.
2. To estimate the quantities of non-target fish caught in the longline fisheries for tuna using data from the Observer Programme and commercial fishing returns for the 2002/03, 2003/04 and 2004/05 fishing years.
3. To estimate the discards of non-target fish in the longline fisheries for tuna using data from the Observer Programme and commercial fishing returns for the 2002/03, 2003/04 and 2004/05 fishing years.
4. To describe trends in the non-target fish catches in the tuna longline fisheries using data from this project and the results of previous similar projects.
5. To compare and contrast the data provided on the revised TLCELR form implemented in 2003 with the Observer data.

Note:

Previous analyses have shown that this project requires observer coverage of the domestic tuna longline fishery to be at about 5-10% of effort in all months and areas, and observer coverage of the charter tuna longline fishery to be at about 80% of effort in all months and areas for robust estimates. This level of coverage was achieved in the 2002/03 year for the charter tuna longline fishery and is expected to be achieved in the 2003/04 and 2004/05 fishing years for both fisheries. The number of days achieved in 2002/03 in the domestic tuna longline fishery is thought to be adequate for at least an exploratory analysis of the non-target catches in that fishery.

The duration of this project will be 19 months, from 1 October 2004 to 15 May 2006. This is to allow the successful tenderer time to analyse the results from the entire 2002/03, 2003/04 and 2004/05 fishing years and report their findings to the Pelagic Fisheries Stock Assessment Working Group during February-March 2006.

Rationale:

General

What are the non-target catches and the discards in the tuna longline fishery? Estimates of non-target catches and discards of target and non-target catches can be made by means of ratio estimation from observer coverage of the tuna longline fishery. The precision of these estimates will rely on the nature and extent of previous observer coverage.

The Ministry of Fisheries has the responsibility to determine the effects of fishing on associated or dependent species and on the aquatic environment. Associated or dependent species include non-target fish species taken incidentally during normal fishing operations.

This responsibility requires regular estimates of the catch and catch rates of non-target fish and estimates of the quantity of target and non-target fish discarded.

New Zealand also has an obligation to provide estimates of the numbers of non-target fish species taken in the tuna longline fishery as part of its contribution to the Ecologically Related Species Working Group under the Convention for the Conservation of Southern Bluefin Tuna, and the Billfish and Bycatch Working Group of the Standing Committee on Tuna and Billfish. The tuna commission about to be established in the Western and Central Pacific Ocean has also in its preparatory conference process highlighted the need for these estimates.

Successful stock assessment and fisheries management requires good data on the true catch and mortality of fish species. Estimates of the total catch are needed, and not just that which is landed or reported. Such data also contributes to an improved understanding of fish communities, and the possible effect of fishing on the long-term sustainability of ecosystems.

Quantitative estimates of the catch rates of non-target fish species can be used to assess the potential effect of fishing on associated or dependent fish species. Estimates of the discards of non-target fish species can be used to assess the level of fishing induced mortality. Results can be incorporated into any stock assessments of non-target species to improve estimates for the total level of removals from the stock.

This project continues a time series of estimates from the tuna longline fishery.

The estimates have been used for a variety of purposes including consideration of the effects of increases and decreases of TACs on associated and dependent species and the detection of specific issues requiring further research.

The tuna longline fishery is one of the largest fisheries in New Zealand on the basis of vessel numbers and the associated non-target fish catches are varied and an important component of the fishery. It is two years since the last estimates of non-target catches in the tuna longline fishery, significant changes in the fishery have occurred in that time, and accordingly, the previous estimates are now uncertain. The proposed method has been previously proven feasible for this fishery and available data are likely to have improved since the last estimates were made. The information is of particular use to Fisheries Managers in addressing concerns about the effects of this fishery on the aquatic environment. Accordingly, this research is considered a high priority.

Objectives 1, 2 & 3

In the tuna longline fishery, a substantive portion of the catch is non-target fish (including in particular oceanic sharks and billfish). However, until 2003 fisher supplied data only allows accurate estimation of the catch of target species. Fishing effort has increased dramatically in this fishery over the last six years, so levels of non-target catch are also likely to be rising and changing as fishing practices develop.

This desktop analysis will estimate the catch-rates, quantity caught, and discard amounts for these non-target fish, particularly oceanic shark species and billfish species, caught in the longline fisheries for tuna. The estimation techniques used must consider the samples size involved and any correlation between sampling units. Stratification should follow the north/south and east/west splits described in ENV2002/01. The data for this project come from the Ministry of Fisheries observer programme and commercial fishing returns.

Previous projects (ENV1997/02, ENV2000/03 and ENV2002/01) have reviewed non-target catches in the tuna longline fishery up to the 2001/2002 fishing year.

Subsequent research into the estimation of non-target catch and discards has improved the techniques used, and improvements in observer coverage and catch & effort reporting are likely to have improved the data available for this estimation. For the tuna longline fishery, the inter-annual variation in areas fished and catch patterns in the fishery also suggest that substantive changes in non-target catches occur.

This project will consider the data from the 2002/03, 2003/04 and 2004/05 fishing years. In the previous study, to be completed in 2003/04, the low levels of observer coverage of the domestic fleet have hampered the estimation of the numbers of non-target species caught in 2000/01 and 2001/02. Observer coverage has now increased (and is being targeted towards 10%), making it possible to better estimate catches and discards. Accordingly, this project is a high priority as it will be at least four years since the last estimates were available for some species in this fishery. Estimates from this project will be of particular importance as inputs to the National Plan of Action – Sharks initiative.

Objective 4

This project will add to a time series of non-target catch estimates for the tuna longline fishery. Since the last review of this data, the tuna longline fishery will have undergone further significant changes. The spatial and seasonal dynamics of the fishery will have changed, and more recently the effects of the decision to introduce tuna species into the QMS will have induced changes in fishing patterns. These changes are likely to have resulted in changes to the non-target catch in the fishery.

Objective 5

A new tuna longline catch effort landing return (TLCELR) form was introduced to the fishery in 2003. The form has been designed with input from fishers and should significantly improve the quality and quantum of data collected from the tuna longline fishery. The form allows the reporting of all catch, and the fate of all catch on a set-by-set basis.

These data should be compared with the Observer data to check for consistency between the two d ta sets. The review will provide information for any future review of the TLCELR and also help in providing further education to fishers to improve data collection.

Strategic Relevance

This project forms a part of the programme to provide the information on sustainable yields and stock status required for the sustainable utilisation of New Zealand’s fisheries resources, in

particular to assess the effects of fishing on non-target fish catch by obtaining accurate estimates of the size and distribution of commercial catch and estimates of fishery-induced mortality. The project is a part of the pelagic fisheries medium term research plan and is consistent with the Ministry of Fisheries Strategic Research Directions document.

Cost Recovery Information:

The percentage allocation for this project will be attributed to the following Fishstocks according to rule 9.2 of the Fisheries (Cost Recovery) Rules 2001:

• All ALB, BIG, STN, SWO, TOR, YFN, Fishstocks

The project is estimated to cost between $50,000 - $100,000.