Abstract:
Ecosystems based fisheries management (EBFM) requires an understanding of not only key ecosystem functioning, but also ecosystem indicators to measure and communicate ecosystem changes in meaningful ways. Ecosystem processes are highly complex and indicators sensitive to pressures within an ecosystem can be an efficient communicator of ecosystem health, making them an effective tool for environmental and fisheries management. The Chatham Rise extends 1400km east off central New Zealand where subtropical and sub- Antarctic waters converge, providing conditions for high productivity and biodiversity. As New Zealand’s most important fishing grounds, a NIWA scientific fisheries trawl survey has been conducted on the Chatham Rise on an almost annual basis since 1992. These surveys are designed to monitor the abundance of target species, and provide the weight and length composition of fish species. This forms an opportunity to examine patterns in fish communities and to develop ecosystem indicators. This study explores the Chatham Rise to develop a set of fish based indicators for EBFM. Candidate indicators were reviewed and investigated using univariate techniques. Multivariate techniques such as principal components analysis, clustering methods and Sequential T-test Analysis of Regime-Shifts techniques were applied to detect intrinsic and extrinsic shifts in ecological communities. Lastly Dynamic Factor Analysis was used to identify indicators which were complementary, creating an indicator set. The ecological indicator suite included metrics of proportion of target species, average vulnerability, Margalef’s species richness, Hill’s N1, average taxonomic diversity and Large Fish Indicator (LFI). This suite of indicators is ecologically representative and communicable, making it an effective tool for EBFM on the Chatham Rise. This indicator suite shows the Chatham Rise experienced a decrease in target species during 2000-2005 with a recent recovery, with a highly vulnerable ecosystem found in the Shallow North region. High variation in this region suggested an approaching tipping point while other all regions experienced only small shifts in community functioning during the time series. While this study has focused on the Chatham Rise, methods of indicators development may be applicable to other New Zealand surveys like the sub-Antarctic or inshore trawl surveys, thus facilitating New Zealand’s progress towards EBFM.