A survey strategy and environmental monitoring network for an estuary supporting finfish cage culture

Abstract

The Huon estuary, in southeastern Tasmania, is an important location for finfish, and to a lesser extent shellfish, farming. The Huon catchment is a lightly populated rural and forested region in a cold temperate climate which supports agriculture (horticulture and livestock), forestry, and tourism. The estuary (40 km in length) is microtidal, with a stratified to partially mixed water column. Effective design of sampling procedures for either monitoring or interdisciplinary studies is essential for resolution of the key time and space scales, and the operational programme must be relevant for events and processes in both the water column and the sediments. We chose to track seasonal changes in physical, chemical, and biological parameters by doing quarterly samplings of the water column at a grid of stations (63 in all) that encompassed the entire estuary from a freshwater end-member to a designated marine boundary. More rapid events were captured by monitoring (both autonomous instrument systems and manual sampling), at hourly to weekly intervals, at a small representative subset of the estuarine stations. Underway measurements from the research vessel were used to map transient surface and near-surface features. Sediments are long-term integrators of processes in the water column and therefore an intensive spatial survey of the sediment characteristics has been made to characterize the long-term influence of human activities. Knowledge gained from field observations of the baseline study has been used to outline an autonomous monitoring network that will derive the environmental information critical for the prudent management of the waterway for both its natural and commercial values.