Fisheries recruitment is generally variable and seldom related to spawning stock size, except in the case of salmonid fishes. Environmental variability has a large effect on recruitment that can be stronger than the effect of stock size. It is difficult to understand whether fishing pressure is affecting stock sizes unless we have some understanding of how the environment affects the populations of exploited species. While the environment is known to significantly affect recruitment, the relationship is complex and multivariate. To gain insight into the relationship, we need to assemble a range of environmental variables for appropriate statistical analyses. These data are often scattered, and have varying spatial and temporal resolutions and quality. An important step along the way to elucidating relationships between environment and recruitment is to compile the datasets into a form that can be spatially matched, appropriately averaged and statistically scaled to extract the environmental signal from the background noise that could otherwise obscure a relationship with recruitment.

If environmental indices are related to fisheries recruitment of specific species (e.g. marine scale fish, rock lobsters and prawns) then management can use the indices (1) to understand the physical processes that account for variability in recruitment and fishery productivity, (2) possibly predict recruitment a year or two in advance, and (3) to speculate about the effects of global warming on our fisheries.

Pearce et al. (FRDC 94/032) compiled time series of environmental variables in Western Australia, and found that variations in the strength and path of the Leeuwin Current affected mainly the larval stages of commercial species. The magnitude and sign (positive or negative) of the effect differed by species. We will build on this study, incorporating some of their recommendations, to gain insight into the processes affecting recruitment.