Biology of a marine estuarine-opportunist fish species in a microtidal estuary, including comparisons among decades and with coastal waters

Abstract

The biological characteristics of a marine and macrophyte-associated species (Pelates octolineatus) in a large microtidal, eutrophic estuary in 2008–10 were determined. Comparisons are made with those of individuals remaining in coastal waters and during two earlier periods in the estuary when plant biomass differed markedly. P. octolineatus start entering the Peel–Harvey Estuary in mid-summer, soon after metamorphosis, with many remaining there until autumn when they are ~15 months old. These individuals, and older fish that re-entered the estuary in summer, then return to the sea where they spawn from late spring to early summer. Most P. octolineatus in the estuary were less than or equal to the length at maturity and all were <4 years old, whereas individuals up to 10 years old were caught in coastal embayments, emphasising that the estuary acts mainly as a nursery for this terapontid. Growth in the estuary was seasonal and peaked earlier and was greater than in marine waters. Abundance of P. octolineatus in the estuary was greater in 2008–10 and 1980–81 than in 1996–97, when macrophytes were less abundant. The results demonstrate how a marine estuarine-opportunist can benefit from using both estuaries and coastal waters as a nursery area and capitalise on variations in environmental conditions.