Disentangling fishery and population changes during ocean warming and a marine heatwave in a biogeographical transition zone

Dr David Fairclough1, Mr Brett Crisafulli1, Dr Gary Jackson1

1Department Of Primary Industries And Regional Development Western Australia, Perth, Australia

Realised predictions of the effects of ocean warming include changes to the distribution, abundance and biology of fishes. In the tropical-temperate region off the west coast of Australia, an ocean warming hot-spot, there are few long-term regional-scale data available for identifying change. Trends in fisheries catch and biological data may be influenced by environmental drivers, but also by fishery behaviour and natural variability. Examples include (1) increasing numbers of tropical species in commercial catches between 1999 and 2017, which may reflect ‘tropicalisation’ or improvements in catch recording. (2) Following a marine heatwave in 2011, catches of the temperate Chrysophrys auratus in northern parts of its range decreased, while catches of the tropical Lethrinus miniatus increased at its southern limits. (3) Recent catch trends for C. auratus were consistent with changes in catch rate, historical periods of high and low catch and its episodic recruitment. However, at its northern limits, declining catch and catch rate after the heatwave may be linked to temporary effects on spawning/recruitment. (4) Increasing mean lengths of younger age classes of C. auratus and Glaucosoma hebraicum may also be influenced by increasing temperature. These complementary fishery-dependent data indicate recent and/or cumulative changes in species composition, biology and/or productivity, not explained by fishery behaviour alone, and potentially offer insight into future scenarios. There is a critical need to monitor such biological change, develop fishery independent measures of abundance/recruitment and understand relationships with environmental characteristics. This would improve assessment and predictability of population trends under expected environmental change.


David Fairclough has 20 years experience in the biological studies of fishes, including reproductive biology, growth, ageing, movement, resource partitioning, stock connectivity and stock status monitoring. David currently oversees the monitoring program for one of the key demersal fisheries on the west coast of Australia, covering approximately 1000 km of coastline and is interested in exploring the effects of environmental change on these fish resources to support ongoing sustainable management.

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