Age validation, growth and population characteristics of greenback flounder (Rhombosolea tapirina) in a large temperate estuary

Abstract

The greenback flounder (Rhombosolea tapirina) is an important fishery species in southern Australia and New Zealand, whose demographic processes are poorly understood. This study developed an ageing protocol based on otolith interpretation and provided estimates of age-based data for an exploited population in the estuary of Australia's largest river system. The otoliths fulfilled three criteria that established their usefulness for ageing. Estimates of size and age were used to generate von Bertalanffy growth curves for male and female fish sampled from two areas within the estuary. There were no differences in growth between the sexes, despite the strong bias in number towards female fish. Spatial differences in growth were marginal. Populations involved only a few young age classes. Such truncation may relate to the fishery, to movement of older fish out of the system, or to recent poor environmental conditions limiting spawning and early life survivorship.

Seasonal Dynamics of Faunal Diversity and Population Ecology in an Estuarine Seagrass Bed

“…All flounder captured in this study were small young-of-the-year (all < 100 mm, which is less than 2-year-old flounder (Webb 1972)), suggesting that Duvauchelle Bay serves as an important nursery ground, especially given the abundance of food (e.g., shrimp) and habitat complexity. However, whether this pattern can be directly attributed to the seagrass is uncertain, because juvenile flounder did not show a strong preference for patchy or dense seagrass and are often also found on mudflats (Webb 1972;Earl et al 2014;Thomsen et al 2020). Additionally, our sampling method targets small fishes across small spatial scales, so the occupancy of the seagrass by adults is unknown.…”

“…As with the shrimp data, we modelled counts predicted by seagrass cover, season, and size class (≤ 10 mm, 10-20 mm, 20-50 mm, > 50 mm). All four size classes are considered juveniles as we did not catch any fish > 15 cm (Earl et al 2014). To assess the fit of the model, we visualised the residuals compared to each variable in the model to ensure residuals were centred around 0 and calculated the dispersion statistic as the Σ(residuals 2 )∕(N − p − 1) , where N is the number of individuals and p is the number of parameters (including interaction coefficients).…”

“…Estuaries with seagrass beds are known to harbour high biodiversity, in part because seagrass provides refugia to a large number of organisms (Orth and van Montfrans 1987;Orth et al 2006;Grech et al 2012), especially juvenile fish that rely on seagrass as a nursery habitat (Hemminga and Duarte 2000;Heck et al 2003;Gillanders 2006;Shibuno et al 2008;Bertelli and Unsworth 2014). Some species that use seagrass as a nursery include species important for fisheries industries, such as shrimp and prawns (Watson et al 1993;Haywood et al 1995;Schaffmeister et al 2006;Taylor et al 2017), flounder (Earl et al 2014;Hyndes et al 2018), and Australasian snapper (Schwarz et al 2006). By providing shelter for prey species, seagrass has the ability to alter predator-prey relationships while simultaneously supporting species in other trophic levels such as sea turtles, Communicated by Ronald Baker dugongs, tiger sharks, and marine birds (Aragones and Marsh 1999;Beck et al 2001;Heithaus et al 2002;Turner and Schwarz 2006;Bertelli and Unsworth 2014).…”

Age, growth, mortality, and yield‐per‐recruit of red spotted grouper Epinephelus akaara in the central Seto Inland Sea, Japan

“…In this species, age was determined by the otolith surface‐reading (Kayano, 2012) and section (Iino et al, 2021; Tawaratsumida et al, 2019) methods, and a comparison of these reports indicates that the maximum age of the surface‐reading method was lower than that of the section method. The surface‐reading method has been reported to underestimate the age of older fish in several coastal fishes, such as fat greenling, Hexagrammos otakii (Sekigawa et al, 2002); rockfish, Sebastes vulpes (Sekigawa et al, 2003); tonguefish, Cynoglossus abbreviates (Yamamoto et al, 2008); and greenback flounder, Phombosolea tapirina (Earl et al, 2014). In addition, the number of opaque zones in cultured fish determined by the section method was consistent with age, suggesting that this method is accurate (Iino et al, 2021).…”