Blue-green algal blooms and the commercial fishery of a large Australian estuary

Abstract

Massive increases in macroalgae ( Cladophora and Chaetomorpha spp.) in the large Peel-Harvey Estuary during the 1970s, resulting from increased nutrient run-off from surrounding agricultural land, were accompanied by a marked increase in catch per unit effort (CPUE) and therefore apparently fish abundance. Despite the additional presence since the late 1970s of seasonal and extremely dense blooms of a potentially detrimental blue-green alga ( Nodularia spumigena) in the Harvey Estuary, the CPUE for the whole system has also risen over recent years. However, the dense blooms of Nodularia in the Harvey Estuary greatly reduce water clarity, and also apparently fish abundance. When this occurs, Harvey Estuary fishermen shift their activities to the Peel Inlet where water clarity is far greater and they can switch from gill to haul netting, which relies on the visual detection of schools of fish.