Anthony G. Miskiewicz’s research while affiliated with UNSW Sydney and other places

Distribution patterns of larval flatfish assemblages at 3 oceanographic monitoring stations off southeastern Australia (North Stradbroke Island [NSI], about 27°30′S; Port Hacking [PH], about 34°6′S; and Maria Island [MAI], about 42°30′S) are described from monthly ichthyoplankton samples collected between 2014 and 2021. A total of 4873 flatfish larvae were collected from 6 families: Bothidae (Arnoglossus spp., intermediate flounder [Asterorhombus intermedius], Crossorhombus spp., Engyprosopon spp., Grammatobothus spp., and crested flounder [Lophonectes gallus]), Cynoglossidae, Paralichthyidae (Pseudorhombus spp.), Pleuronectidae, Samaridae, and Soleidae. Abundances of different taxa varied seasonally, and the assemblage composition varied between season and years, but with no overall change in abundances over the study period. Markedly different larval flatfish assemblages were caught at the 3 stations, corresponding to the latitudinal variation in water mass characteristics (temperature, salinity, and chlorophyll). The number of larval flatfish taxa decreased with increasing latitude and were highest at the sub-tropical NSI and lowest at the temperate MAI. Most bothid larvae were caught at NSI and PH except crested flounder, which was only caught at PH and MAI. Cynoglossid, Pseudorhombus spp., samarid, and soleid larvae were only caught at NSI and PH, while pleuronectid larvae were only caught at MAI. These distinct larval assemblages provide a useful benchmark to monitor the progress of the strengthening East Australian Current in a known hotspot of climate change.

Estimating demographic changes in a population requires the measurement of some minimal combination of several vital rates, including the flux of individuals into a population, the population growth rate, individual growth rates and mortality rates. For larval fishes, the ratio of instantaneous mortality to growth (i.e., their ‘recruitment potential’) has been used to make inferences of cohort trajectory where measures of population growth rates are not attainable. Attaining estimates of mortality and growth is an arduous task, and use of the recruitment potential metric has been limited. Here, we relate size spectra of the broader plankton community to the recruitment potential of simultaneously sampled larval Pacific sardines (Sardinops sagax), from three voyages off eastern Australia. As the size structure of a population is determined by the ratio of mortality to growth, and there is remarkable consistency in size spectra across ecosystems, we test the hypothesis that the recruitment potential of larval fish is reflected in community‐level measures of plankton size spectra. Contrary to expectations, results from this study demonstrate a negative relationship between the slope of the plankton size spectra and the recruitment potential of larval Pacific sardine. However, we also demonstrate several other stronger relationships between recruitment potential and physical oceanographic parameters. Together, results suggest plankton size spectra are unlikely to reflect recruitment potential directly. Incorporating some size‐based aspects of the plankton community into a broader modelling framework with a range of oceanographic parameters could further our ability to determine how larval success varies across a seascape.

Surveys of larval fishes require accurate identifications of larvae, which are essential to understand early life history of fish, fish ecology and fisheries. However, the identification of larval fishes requires microscopic examination that is substantially more difficult than that of juvenile and adult fishes, as many larval stages remain undescribed. Furthermore, the traditional, formalin fixation of larval fishes were previously thought to prevent genetic sequencing compared to ethanol preserved larvae. In this study, we used an integrative taxonomic approach based on morphology, imaging and DNA barcoding of the mitochondrial (mtDNA) cytochrome c oxidase subunit (COI) gene. We used this approach in both cultured yellowtail kingfish, Seriola lalandi and wild sourced fish larvae that had been fixed in 5% formalin. Based on controlled and in-field formalin treatments, DNA barcoding and genetic species identification was 100% successful in cultured yellowtail kingfish fixed in formalin for up to 6 months, while barcoding of wild caught fish larvae enabled species identification of 93% of up to 8-weeks formalin fixed specimens. Furthermore, we demonstrated the viability of using either whole larval individuals or a single eyeball (<1 mm diameter, thus retaining the specimen intact) from formalin fixed larval fish for genetic species identification. While COI genetic identifications from the in-field experiments were patchier than the controlled experiments, our study highlights the possibility of recovering suitable DNA from larvae that have been fixed in formalin for up to six months. This was achieved by applying DNA extraction methods that use de-cross-linking steps and species identification based on both full-length reference and mini-barcodes. Our study provides the larval fish research community with a practical framework for undertaking both morphological and genetic identifications of larval fish assemblages, particularly when geographic relevant reference sequence databases (based on vouchered adult fishes) are available for interrogation. It also simplifies field-based collection of samples allowing their preservation in formalin without compromising the genetic identification of species.

Coastal winds transport water masses and larval fish onshore or offshore which may influence estuarine recruitment, yet our understanding of the mechanism underlying this relationship is limited. Here, we combine datasets from a historical database of larval fish off southeast Australia with a high‐resolution atmospheric reanalysis model to show that normalised abundance of coastally spawned larvae increased with weak to moderate upwelling favourable winds 14 days prior to sampling. The increase in abundance may reflect increased nutrient and plankton availability for larval fish. Normalised larval abundance decreased following strong upwelling favourable winds but increased after onshore (downwelling favourable) winds, due to wind‐driven transport. By combining a commercial estuarine fisheries catch‐rate dataset (4 species, 8 estuaries, 10 years) and the high‐resolution atmospheric reanalysis model, we show that negative effects of upwelling favourable winds during the spawning period can be detected in lagged estuarine commercial fisheries catch rates (lagged by 2–8 years depending on species' growth rates), potentially representing the same mechanism proposed for larval fish. Upwelling favourable winds in the southeast Australian region have increased since 1850 while onshore winds have decreased, which may have reduced larval recruitment to estuaries. Coastal winds are likely an important factor for estuarine recruitment in the southeast Australian region and future research on the estuarine recruitment of fish should incorporate coastal winds.

Across the world’s oceans, western boundary currents are strengthening and warming faster than the global average. This is expected to have large impacts on the distribution of pelagic fishes, as their dispersal and physiological range limits shift. Monitoring the distribution of larval fish assemblages, sampled with plankton nets, allows for population and community-level responses to climate-driven changes to be observed without reliance on fisheries data. Here, we characterise patterns in the distribution of larval fish over 15° of latitude with highly variable conditions driven by a western boundary current, the East Australian Current, using a newly available larval fish database supplemented with recently collected samples. Using generalized additive mixed models, we show strong non-linear relationships between larval fish taxonomic richness and abundance with latitude. During autumn, winter and spring, both larval fish abundance and richness are greater in equatorward latitudes (28°S) than in more poleward ones (43°S), with this pattern reversed during the summer. The region where the East Australian Current separates from the coast delineates a zone of marked change in larval fish richness and abundance. Analyses of larval fish assemblages using Gaussian copula graphics models revealed a strong association between assemblage composition and temperature. The direction of temperature effects on individual taxa varied greatly, highlighting the complex nature of possible climate-driven shifts. Our study highlights the utility of compiling multi-voyage databases and their role in monitoring the global oceans.

Cyclonic eddies are diverse in their size, age, upwelling and behaviour, which has significant implications for fisheries production and connectivity when they interact with the continental shelf. To ascertain coastal entrainment by eddies, we compared the larval fish community of 2 contrasting cyclonic eddies in 3 depth strata (0-5, 5-50, 50-100 m), and with the adjacent shelf community. The frontal cyclonic eddy was smaller and younger than the mesoscale cyclonic eddy. A larval fish entrainment index, based on the ratio of coastal to oceanic taxa, revealed the relative abundance of coastal larvae entrained into the upper mixed layer of the frontal eddy, consistent with published numerical modelling studies of similar eddies. The frontal eddy had a high abundance of commercially important coastal taxa entrained from the inner shelf. However, the adjacent inner shelf water and putative location for frontal eddy formation had recently been displaced by the East Australian Current, resulting in the larval fish community being dominated by oceanic taxa. The spatial and temporal dynamics of coastal entrainment into the larger, older cyclonic eddy and the adjacent shelf region were revealed by mixtures of coastal and oceanic taxa in each of the depth strata. The larger cyclonic eddy had a higher biomass of zooplankton, indicating the cumulative effects of eddy age and production. Eddies which interact with the shelf enable cross-shelf mixing and may contribute to coastal fisheries.

Historical data are often used as benchmarks or reference points for assessing regional changes in ecosystem structure and function. For that purpose, we provide historical (1991–1992)data concerning the spatial and temporal consistency of vertical structuring of a diverse assemblage of larval fishes in inner continental shelf waters adjacent to Sydney, Australia. Daytime vertically stratified sampling at seven depths (0–65 m)across four stations and five sampling seasons yielded 35,772 individuals of 94 identifiable taxa from 81 families. Assemblages displayed consistent vertical stratification between surface (0 and 5 m)and subsurface (15 m and deeper)waters, with further spatio-temporal sub-structuring of subsurface assemblages between upper (15–30 m)and lower (45 m and deeper)water column. Differences in assemblage structure between surface and subsurface waters were primarily driven by several species that predominantly occurred in one depth zone and not the other. In contrast, differentiation between subsurface assemblages was dynamic and driven by taxa common across upper and lower subsurface depths but occurring in differing densities in certain depth strata that was spatially and temporally variable and not related to thermal stratification of the water column. Despite significant small-scale spatio-temporal variability, larval taxonomic diversity and total abundance was most often greatest in the upper and mid water column (15–30 m), potentially a response to light levels and prey concentrations. Nevertheless, the data show that all depths in the water column provide important habitat for larval fishes that need to be considered in ecosystem functioning and climate change projections.