The effects of climate change on predatory fishes in deep shelf areas are difficult to predict because complex processes may govern food availability and temperature at depth. We characterised the net impact of recent environmental changes on hapuku (Polyprion oxygeneios), an apex predator found in continental slope habitats (>200 m depth) by using dendrochronology techniques to develop a multi-decadal record of growth from otoliths. Fish were sampled off temperate south-western Australia, a region strongly influenced by the Leeuwin Current, a poleward-flowing, eastern boundary current. The common variance among individual growth records was relatively low (3.4%), but the otolith chronology was positively correlated (r = 0.61, p < 0.02) with sea level at Fremantle, a proxy for the strength of the Leeuwin Current. The Leeuwin Current influences the primary productivity of shelf ecosystems, with a strong current favouring growth in hapuku. Leeuwin Current strength is predicted to decline under climate change models and this study provides evidence that associated productivity changes may flow through to higher trophic levels even in deep water habitats.

The demonstration by this study that the life cycle characteristics of the reef fish Nemadactylus valenciennesi differed markedly from those of other cheilodactylids led us to compare these differences and hypothesise on their evolutionary implications. The distribution, length and age compositions, growth and the length and age at maturity of N. valenciennesi in south-western Australian waters have been determined. The maximum age (21 years) of N. valenciennesi (maximum total length = 984 mm) is far less than those of the much smaller Cheilodactylus fuscus, Nemadactylus macropterus (both ~40 years) and Cheilodactylus spectabilis (97 years). Yet N. valenciennesi, N. macropterus and C. spectabilis mature at a similar young age (3–7 years). While, on the basis of data for other species, all three species mature at lengths consistent with their asymptotic lengths, the last two species mature at a far earlier age than would be predicted from their long life spans. The early attainment of maturity by N. macropterus and C. spectabilis may reflect a response to high juvenile mortality or constrained adult growth, whereas their long life spans could reflect a response to variable recruitment in the past or compensation for limited annual reproductive output due to very constrained adult growth.