Jed I. Macdonald

A Method for Improving the Estimation of Natal Chemical Signatures in Otoliths

Abstract Laser ablation-inductively coupled plasma mass spectrometry has been widely used in studies aimed at identifying the natal sites of fish through analysis of the otolith core region. It is critical, then, that measurements of chemistry at the core accurately represent the natal chemical environment, rather than reflecting potential physiological and ontogenetic influences on elemental incorporation during the embryonic and early larval phases. We analyzed sagittal otoliths from 840 age-0 and age-1 Australian smelt Retropinna semoni using a 193-nm Ar-F excimer laser system with a fast response two-volume sample cell to demonstrate a rapid depth-profiling method that enables more accurate estimations of the natal chemistry by sampling a target region of the otolith that excludes the primordium. The method involves (1) examination of validated daily growth increments to identify the target region; (2) measurement of the amount of otolith material removed by each laser pulse; and (3) use of elevated 5...

Evidence of diadromous movements in a coastal population of southern smelts (Retropinninae: Retropinna) from Victoria, Australia

Understanding the migratory behaviour of fishes is critical to the conservation and management of fish assemblages in coastal rivers. We analysed the otolith chemical signatures of smelt, Retropinna sp., from inland and coastal populations in mainland south-eastern Australia to determine whether individuals within coastal populations of the species were diadromous. Assessments of otolith chemical composition combined with water chemistry data were used to make inferences about the migration histories of individual fish. A proportion of the smelt collected from the freshwater reaches of a coastal river exhibited diadromous movements, with the majority of fish analysed showing evidence of estuarine or marine occupation as larvae/juveniles and a minority inhabiting freshwater throughout their life histories. A broad range in the daily ages of upstream migration into freshwater (15-106 days) and the timing of these migrations suggest that spawning and migration occur over several months during the summer/autumn period. The results of this study suggest that southern smelts are an ecologically variable taxonomic group and that conservation and management actions should take into account the range of migratory behaviours exhibited both within populations and across regions.

Catadromous migrations by female tupong (Pseudaphritis urvillii) in coastal streams in Victoria, Australia

Understanding migratory requirements is critical for the conservation of diadromous fishes. Tupong (Pseudaphritis urvillii) are diadromous fishes found in freshwater and estuarine regions of south-eastern Australia. Previous studies have hypothesised that mature female tupong undertake downstream spawning migrations from freshwater to the estuary or sea, with a compensatory return of juveniles, and possibly spent fish, back upstream. We applied acoustic telemetry to test this hypothesis. We tagged 55 female tupong in two river systems in Victoria, Australia, and tracked movements for 4- to 6-month periods over 2 years. Thirty-one fish undertook rapid downstream migrations and then appeared to move through the estuary and out to sea between May and August in each year. Migration was associated with relatively high river discharges, and movement from the estuary to the sea tended to occur most frequently during intermediate moon phases. Low rates of movement between September and April suggested that tupong inhabited restricted home ranges outside of the spawning season. The apparently disparate migratory patterns of female (catadromous) and male (non-diadromous) tupong are rare amongst fishes globally. Differential exertion of a range of selective pressures may have resulted in the evolution of sexual differences in migratory modes in this species.

Low interbasin connectivity in a facultatively diadromous fish: evidence from genetics and otolith chemistry.

Southern smelts (Retropinna spp.) in coastal rivers of Australia are facultatively diadromous, with populations potentially containing individuals with diadromous or wholly freshwater life histories. The presence of diadromous individuals is expected to reduce genetic structuring between river basins due to larval dispersal via the sea. We use otolith chemistry to distinguish between diadromous and nondiadromous life histories and population genetics to examine interbasin connectivity resulting from diadromy. Otolith strontium isotope (87Sr:86Sr) transects identified three main life history patterns: amphidromy, freshwater residency and estuarine/marine residency. Despite the potential for interbasin connectivity via larval mixing in the marine environment, we found unprecedented levels of genetic structure for an amphidromous species. Strong hierarchical structure along putative taxonomic boundaries was detected, along with highly structured populations within groups using microsatellites (FST = 0.046–0.181), and mtDNA (ΦST = 0.498–0.816). The presence of strong genetic subdivision, despite the fact that many individuals reside in saline water during their early life history, appears incongruous. However, analysis of multielemental signatures in the otolith cores of diadromous fish revealed strong discrimination between river basins, suggesting that diadromous fish spend their early lives within chemically distinct estuaries rather than the more homogenous marine environment, thus avoiding dispersal and maintaining genetic structure.

Do invasive eastern gambusia (Gambusia holbrooki) shape wetland fish assemblage structure in south-eastern Australia?

Defining the ecological impacts conferred by invasive fishes provides a framework for evaluating the feasibility of control efforts in invaded waterways, and for predicting the consequences of future incursions. Eastern gambusia (Gambusiaholbrooki)isaremarkablysuccessful invaderof freshwatersystems worldwide,withthecapacity to detrimentally impact native fishes both directly (e.g. competition, predation, agonistic interactions) and indirectly (e.g. triggering trophic cascades). Here, we modelled the influence of eastern gambusia and several environmental covariatesonfishspeciesdiversity,abundanceandconditionbasedonquantitativesurveydatacollectedfrom93wetlands in south-eastern Australia. We predicted that small-bodied, wetland specialist species sharing dietary- and habitat-niches with eastern gambusia would be most severely impacted, and that environmental stressors associated with wetland drying during late summer would magnify these impacts. Eastern gambusia influenced the occurrence, abundance and/or body condition of most common wetland species; however, the direction and level of impact appeared dependent on bothbiotic and environmental forces. From these results, we postulate that generalist life-history strategies that permit niche- segregation may release some native species from competitive/predatory pressures, allowing coexistence with eastern gambusia in resource-limited, environmentally harsh habitats, whilst specialist species that occupy narrower ecological niches may be less resistant. Additional keywords: alien species, Murray-Darling Basin, native fishes, niche overlap, occupancy models.

Migration history and stock structure of two putatively diadromous teleost fishes, as determined by genetic and otolith chemistry analyses

Abstract: Migratory life cycles and population structure of 2 putatively diadromous Australian fishes were examined using otolith chemistry (87Sr/86Sr) and genetics (microsatellites and mitochondrial deoxyribonucleic acid [mtDNA]). Australian whitebait (Lovettia sealii) is widely considered to be one of only a few anadromous fish species in the southern hemisphere. The congolli or tupong (Pseudaphritis urvillii) is reported to undertake an unusual form of sexually segregated catadromous migration, where females switch habitats between marine and freshwater, while males remain in marine or estuarine environments. Sr-isotope profiles of L. sealii showed this species does not move into fully freshwater habitats during its life cycle, suggesting it should be considered semianadromous or estuarine-dependent, rather than truly anadromous. This life-history strategy is unique among the Galaxiidae. Lovettia sealii is regionally divided into at least 3 well differentiated genetic stocks: northern and southern Tasmanian coasts and mainland Australia. Sr-isotope profiles of P. urvillii showed that females are catadromous, with the early life history spent in the marine environment and a single migratory transition from marine to freshwater occurring at an early point in the life history. Lack of bidirectional adult migration between freshwater and the sea suggests that female P. urvillii are semelparous, returning to the marine habitat to mate with resident males after an extended period of freshwater residence. Pseudaphritis exhibit weak genetic structure across their mainland range. An isolation-by-distance relationship describes the genetic structure of this species, a pattern it shares with several other nearshore-restricted catadromous fishes.

Asteriscus v. lapillus: comparing the chemistry of two otolith types and their ability to delineate riverine populations of common carp Cyprinus carpio

The chemical composition of common carp Cyprinus carpio asteriscus (vaterite) and lapillus (aragonite) otoliths from the same individual and reflecting the same growth period was measured to (1) determine whether there are differences in the uptake of trace metals (Mg:Ca, Mn:Ca, Sr:Ca and Ba:Ca ) and Sr isotope ratios ((87)Sr:(86)Sr) in co-precipitating lapilli and asterisci and (2) compare the ability of multi-element and isotopic signatures from lapilli, asterisci and both otolith types combined to discriminate C. carpio populations over a large spatial scale within a river basin. Depth profile analyses at the otolith edge using laser-ablation inductively coupled plasma mass spectrometry showed that asterisci were enriched in Mg and Mn and depleted in Sr and Ba relative to lapilli, whilst (87)Sr:(86)Sr values were nearly identical in both otolith types. Significant spatial differences among capture locations were found when all trace element and Sr isotope ratio data were aggregated into a multi-element and isotopic signature, regardless of which otolith type was used or if they were used in combination. Discriminatory power was enhanced, however, when data for both otolith types were combined, suggesting that analysis of multiple otolith types may be useful for studies attempting to delineate C. carpio populations at finer spatial or temporal scales.