Growth, condition, and maturity schedules of an estuarine fish species change in estuaries following increased hypoxia due to climate change

Abstract

Understanding challenges posed by climate change to estuaries and their faunas remains a high priority for managing these systems and their communities. Freshwater discharge into a range of estuary types in south‐western Australia between 1990 and 2015 is shown to be related to rainfall. This largely accounts for decreases in discharge in this microtidal region being more pronounced on the west coast than south coast, where rainfall decline was less. Results of an oxygen‐balance model imply that, as demonstrated by empirical data for the Swan River Estuary, declines in discharge into a range of estuary types would be accompanied by increases in the extent of hypoxia. In 2013–15, growth and body condition of the teleost Acanthopagrus butcheri varied markedly among three permanently open, one intermittently‐open, one seasonally‐closed and one normally‐closed estuary, with average time taken by females to reach the minimum legal length (MLL) of 250 mm ranging from 3.6 to 17.7 years. It is proposed that, in a given restricted period, these inter‐estuary variations in biological characteristics are related more to differences in factors, such as food resources and density, than to temperature and salinity. The biological characteristics of A. butcheri in the four estuaries, for which there are historical data, changed markedly between 1993–96 and 2013–15. Growth of both sexes, and also body condition in all but the normally‐closed estuary, declined, with females taking between 1.7 and 2.9 times longer to attain the MLL. Irrespective of period, body condition, and growth are positively related. Age at maturity typically increased between periods, but length at maturity declined only in the estuary in which growth was greatest. The plasticity of the biological characteristics of A. butcheri, allied with confinement to its natal estuary and ability to tolerate a wide range of environmental conditions, makes this sparid and comparable species excellent subjects for assessing estuarine “health.”

Otolith chemistry indicates recent worsened Baltic cod condition is linked to hypoxia exposure

“…As deoxygenation spreads due to climate warming and continued eutrophication [19], more organisms and ecological communities will be confronted with low oxygen as a metabolic constraint (e.g. [17,[20][21][22][23]. Eastern Baltic Sea cod present a dramatic case of a population being driven into decline by a combination of environmental pressures and overfishing [24].…”

An hypoxia‐tolerant flatfish: consequences of sustained stress on the slender sole Lyopsetta exilis (Pleuronectidae) in the context of a changing ocean

“…Energy conservation requires shunting metabolic resources away from food acquisition and processing, as well as from growth and reproduction under sustained hypoxia (Sokolova et al ., ). Our work documents the direct effect of hypoxia on growth in situ , whereas other studies implicate hypoxia effects as fish are crowded into oxygenated regions with subsequent density‐dependent growth outcomes (Cottingham et al ., ; Eby et al ., ). Keller et al .…”

The Fish Community Index: A Practical Management Tool for Monitoring and Reporting Estuarine Ecological Condition

“…Given ongoing support to continue the annual monitoring and reporting program, the FCI will enable longer term trends in the ecological health of the Swan Canning Estuary, including those expected as a result of continuing climate change, to be tracked and where necessary responded to. Declining rainfall and river flows across SWA since the 1970s have already contributed to increasingly marine conditions and declining O levels in parts of the Swan Canning and other estuaries across the region, which has been reflected by the fish communities and populations of key species in these systems (Valesini et al 2017; Cottingham et al ). Ongoing decreases in freshwater flows are predicted for SWA in coming decades, leading to the further marinization of many estuaries in this region, and hypoxia is expected to increase in the middle to upper reaches of these systems (Hallett et al ).…”