Longfin eel population modelling

Project: Longfin eel population modelling.
Project Code: EEL2004/04
Start Date: 1 October 2004
Completion Date: 30 September 2005
Vessel Use: None

Overall Objective:

1. To develop a population dynamics model for South Island long finned eels.

Specific Objectives:

1. To collate and summarise the available data on stock structure, recruitment, maturity, mortality, catch, size and age composition, and abundance of South Island longfin eels suitable for inclusion into an age-based population dynamics model.
2. To assess the feasibility of developing a population dynamics model for South Island longfin eels.

Note:

This project has a medium priority for 2004/05 and will proceed only if funding is available

Rationale:

Commercial catches of eels have been sampled in both the North and South Islands over three consecutive seasons from 1995–96 to 1997–98 and in 1999–2000. The results showed that the size, and sex composition of longfins has been dramatically altered compared to the shortfin. Longfin populations in some heavily fished areas are almost exclusively male, suggesting that females have been overfished relative to males. Analyses of catch effort data from throughout New Zealand for the period 1990–91 to 2000–01 indicate a general decline in CPUE for longfin eels. Current stock assessment of long finned eels currently relies on interpretation of CPUE indices, with supplementary information from catch and other sampling of South Island long finned eels.

No population model effective for stock assessment and management of eel fisheries has been developed for other eel stocks, particularly the northern hemisphere species, the European eel (Anguilla anguilla), the American eel (A. rostrata) and the Japanese eel (A. japonica), that are subject to extensive commercial exploitation. Stock assessment of eels presents particular difficulties because of the biology of the species. Eels in freshwater have a limited home range and each eel population in a river, stream or lake will have different population parameters in terms of growth, density, productivity and population structure. Any model developed might not have sufficient cost/effective predictive capability without the input of extensive data on growth.

This project will investigate the feasibility of developing a population dynamics model that might be developed into a more formal stock assessment of eels. This would allow a more quantitative assessment of eel stocks that would include explanations of current trends in CPUE, sex ratios, and recruitment indices. In addition, projected and longterm yield estimates could be investigated under a range of management scenarios, including, for example, net, legal size (lower or upper bounded), and sex based effort controls.

The project is aimed at collating existing data, and assessing the feasibility of developing a suitably structured population model. It would be expected that one outcome of this work would be an identification of those areas where the population model requires additional data collection, mathematical model development, or other research.

Strategic Relevance

This project is consistent with the Fisheries Resources goal and Strategic Objectives in 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 ANG stocks

The project is estimated to cost between $0 - $50,000.