Seminar at AMOS, Melbourne, 7 February 2000

The marine environment and fisheries

David Griffin

CSIRO Marine Research, Hobart

Now that most fisheries around the world are either fully- or over-exploited, the emphasis is shifting from 'How can we catch more fish?' through 'How do we avoid wiping out the fish?' to 'how do we maximise the economic yield of the fishery and preserve the ecosystem on which it depends?'. To answer the latter two, we also need to answer the former, as I will try to explain. But to answer any of these and related questions, we need a much better understanding of how fish react to, or are dependent on, marine environmental conditions. Research in this area has always been severely hampered by insufficient data, both biological and physical. Recent advances in remote sensing, atmospheric and ocean modelling, data assimilation, and computing power are making it much more feasible now to estimate the physical variables with sufficient resolution and accuracy for sense to be made of fluctuations in the biological data.

To effectively manage a fish stock, managers need an estimate of stock size. For want of other data, fishery managers are often obliged to use commercial catch rates as an indicator of this. But some fisheries target spawning or feeding aggregations, the location and timing of which may be environmentally-cued. If fishers' success in locating fish aggregations is not random, then inaccurate estimates of the stock size can result. Hence, both fisher and manager need to know how catch rates are dependent on environmental conditions.

For some species, useful estimates of stock size come from estimates of environmentally-dependent mortality during the early life stages. Western Rock Lobster is an example of this and I will show how modelling of the winds and ocean currents off WA is shedding light on the question of why this fishery seems to vary in response to the Southern Oscillation Index.