Abstract
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.
Highlights
Growth of a deep-water, predatory fish is influenced by the productivity of a boundary current system
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
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
Summary
Growth of a deep-water, predatory fish is influenced by the productivity of a boundary current system. D emersal fishes that occupy relatively deep waters (around 200 m) at the edge of the continental shelf are likely to be vulnerable to the alterations in marine ecosystems predicted to occur under scenarios of climate change in the near future (50–100 years) In part, this vulnerability is due to strong associations with the seabed that may constrain their ability to move around barriers created by inappropriate habitats (see Part C in reference 1). Simultaneous changes to multiple aspects of marine systems mean that it is difficult to predict net impacts and to envisage how these might influence individual-level variables, such as growth rate, which will integrate this complex interplay of drivers In part, this is due to a lack of long-term (decadal) observational data sets sufficient to investigate the relationships between vital rates of fishes in natural environments and variation in climate
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