Analysis of otolith ⁸⁷Sr/⁸⁶Sr to elucidate salinity histories of Nurseryfish Kurtus gulliveri (Perciformes:Kurtidae) in a tropical lowland river in northern Australia

Abstract

The Nurseryfish Kurtus gulliveri is found in estuarine and freshwater reaches of tropical rivers in northern Australia and southern New Guinea. Nurseryfish have been recorded in salinities ranging from freshwater to seawater (salinity <0.5-36‰), but almost nothing is known of their movements. We conducted coreto-edge transect analyses of 87 Sr/ 86 Sr in the otoliths of 16 male and 14 female Nurseryfish collected from a tropical river in northern Australia to examine their movements across a freshwater-estuarine salinity gradient. Comparisons between water and otolith 87 Sr/ 86 Sr showed that most fish had 87 Sr/ 86 Sr values indicative of periods of saline (salinity > 4‰) residence during their early life history, usually followed by a distinct transition into brackish (0.5-4‰) or fresh water (<0.5‰) later in life. No differences were discernible between the salinity histories of male and female Nurseryfish. Analysis of the relationship between the otolith core-to-edge distance and fish mass indicated that most growth occurred in brackish water. We conclude that Nurseryfish are euryhaline rather than diadromous and that analysis of water and otolith 87 Sr/ 86 Sr is an effective method for assessing the movements of tropical riverine fishes and the potential importance of fish migration in driving foodweb subsidies.

Sr Isotope Ratios (87Sr/86Sr) in Water and Fish Otoliths as Estuarine Salinity Tracers: Case Studies from Three NW African Rivers

“…9, data presented in Table S1), out of which the Marrakai Creek in northern Australia exhibits the most radiogenic (0.77785) Sr isotopic signatures with coincidingly lowest concentrations (ca. 0.002 mg/L Sr; Crook et al 2015). Our findings confirm estimates of Sr concentrations modelled for large-scale drainage areas compiled by Peucker-Ehrenbrink and Fiske (2019), suggesting Western African catchments to have the lowest annual average Sr contents globally with regional minimum values of ~ 0.015 mg/L and generally limited continental runoff.…”

Do upstream migrating, juvenile amphidromous shrimps, provide a marine subsidy to river ecosystems?

“…The analysis of shrimp exoskeleton 87 Sr/ 86 Sr ratio may be an effective alternative. While this technique has been widely applied to fish otoliths (Crook et al., ; McCulloch, Cappo, Aumend, & Müller, ), to our knowledge it has not previously been applied to the analysis of decapod exoskeletons. These findings confirm the suitability of exoskeleton material for 87 Sr/ 86 Sr analysis and represent a promising new approach for tracing the migrations of decapod crustaceans across marine/freshwater interfaces.…”

“…In addition to using sulphur stable isotopes to detect a marine signature we analysed the strontium isotope ratio ( 87 Sr/ 86 Sr), a technique commonly used for detecting marine signatures in fish otoliths (Crook, Wedd, & Berra, ). Decapod exoskeletons are also constructed from a calcium carbonate matrix (Soejoko & Tjia, ) and analysis of 87 Sr/ 86 Sr in exoskeletons of shrimps could also be useful for detecting marine signatures.…”

“…The analysis was undertaken using a multi‐collector laser ablation inductively coupled plasma mass spectrometer (LA‐ICPMS) operated by the University of Melbourne using methods comprehensively detailed in Crook et al. (). Each sample was analysed over a 40 s ablation period using laser spot size of 93 nm, a repetition rate of 5 Hz and a laser energy of approximately 90 mJ.…”

Tropical freshwater sciences: an overview of ongoing tropical research

“…In this issue, Novak et al (2015) discuss the life history of a shrimp species from a large tropical river in Australia that follows this pattern. In addition, Crook et al (2015) discuss how the study of otolith microchemistry can aid in understanding the life histories of fish species that inhabit coastal rivers.…”