Entrainment and retention of the coastal larval fish assemblage by a short‐lived, submesoscale, frontal eddy of the East Australian Current

Abstract

We examined the fate of larval fish assemblages after the East Australian Current (EAC) had separated from the coast and larval fish were advected eastward along the Tasman Front. There was no difference in the assemblages at four stations as the EAC meandered from the continental shelf to 220 km eastward. At a fifth station, we sampled a submesoscale, frontal eddy that had formed at the EAC separation zone 11 d earlier and had entrained shelf water. Zooplankton biomass was greater within the eddy compared to the adjacent shelf. The larval fish assemblage in the eddy was significantly different from all other stations. There was an order of magnitude greater abundance of three species characteristic of the shelf: sardine (Sardinops sagax; Clupeidae), blue mackerel (Scomber australasicus; Scombridae), and yellowtail scad (Trachurus novaezelandiae; Carangidae), which were also significantly larger than larvae from a station on the adjacent shelf. In particular, S. sagax in the eddy were , 5 mm longer and , 10 d older, although growth rates were similar. Larval retention in the eddy was inferred from the co-occurrence of small and large larvae of all three species compared to the adjacent shelf. The EAC is only 20-30 km from the inner-shelf water, where frontal eddies may facilitate three stages of successful recruitment: entrainment, enrichment, and retention. Frontal eddies off southeastern Australia entrain preconditioned shelf water, move slower than the mean flow of the EAC, decreasing transport rates, and may sustain planktonic communities through eddy uplift. These eddies are frequent and short-lived (2 to 4 weeks), and we suspect they are of fisheries importance as their duration is sufficient for fish larvae to complete their early life history and, presumably, recruit back to the coast.

Late winter larval fish assemblage in the southern East China Sea, with emphasis on spatial relations between mesopelagic and commercial pelagic fish larvae

“…Similar processes of offshore larval transport of coastal fishes by currents, and associated meanders, and other mesoscale features are reported in other current systems such as the Gulf Stream, Leeuwin Current, and East Australian Current (Hare et al, 2002;Holliday et al, 2012;Mullaney and Suthers, 2013). This is supported by our results that the larvae belonging to Group I occurred (1) in the area south of the Kuroshio front between 124 and 125°E due to the southward meandering of the Kuroshio and (2) along the Kuroshio frontal area east of 125°E, showing northeastward larval entrainment by the Kuroshio (Fig.…”

A tale of two eddies: The biophysical characteristics of two contrasting cyclonic eddies in the East Australian Current System

“…Although frontal eddies are short lived (1–4 weeks), this time frame is consistent with the larval period of many coastal fish species [e.g., Syahailatua et al ., ; Matis et al ., ]. An EAC frontal eddy was opportunistically sampled for biological productivity and larval fish composition and abundance in October 2006 revealing a distinctive community of fish larvae and zooplankton [ Mullaney and Suthers , ]. Subsequently Matis et al .…”

Zooplankton trophic niches respond to different water types of the western Tasman Sea: A stable isotope analysis

“…Off southeast Australia, the western Tasman Sea has different water types including cyclonic cold core eddies (CCE), anti-cyclonic warm core (WCE) eddies (Nilsson and Cresswell, 1981) and nutrient-rich inner shelf (IS) waters (Henschke et al, 2011). CCEs may entrain IS water (Mullaney and Suthers, 2013), resulting in a 16% increase in chlorophyll a compared to surrounding waters (Everett et al, 2012). As well as enhanced primary production, coastal CCEs have been shown to promote zooplankton production (Kimura et al, 2000), and aid in the recruitment and survival of larval fish (Kasai et al, 2002).…”