Understanding fish recruitment processes at Ningaloo Reef

Annual underwater surveys of lethrinid juveniles (<5 cm TL) were collected over thirteen consecutive years across the northern and southern sectors of Ningaloo.

This study focussed on two species of tropical Emperor (Family Lethrinidae) that are common within the Ningaloo lagoon – the Spangled Emperor (Lethrinus nebulosus) and the Yellowtail Emperor (Lethrinus atkinsoni). Abundance of L. nebulosus and L. atkinsoni were estimated at 11 macroalgae sites within the Ningaloo lagoon and 11 sites within nearby coral reef. Sites were spread along 150 km of the Ningaloo coast, with 12 sites north of Point Cloates (northern sites, six coral and six macroalgae) and 10 sites south of Point Maud (southern sites, five coral and five macroalgae). Lethrinid surveys were conducted in the late Austral summer (February–March), immediately after the peak recruitment of fish at Ningaloo.

At each site the number and size (to the nearest cm) of all sub-adult (5–28 cm TL) and adult L. nebulosus (>28 cm TL) and L. atkinsoni (>25 cm TL) within nine 30 × 5m transects (1–6 m deep) were manually recorded by divers before a return run along the same transect recorded all juveniles lethrinids (<5 cm TL) to genus level in a 1m band.

Surveys for juveniles were repeated annually from 2010 to 2023, while larger bodied lethrinids were included in the annual surveys from 2013 to 2023