For example, after Cyclone Justin in 1997 there were significant shifts in sediment on some of the inshore grounds, such as Yorkeys Knob near Cairns and broodstock were widely dispersed. The lunar cycle is inextricably linked to tidal cycles. Broodstock collectors indicate that catchability can be predicted from lunar cycles. In addition to the perceived influence of lunar cycles on catchability there is also a correlated pulse of spawning activity during the week leading up to the full moon. It has been reported that this is followed by a synchronous molt within the broodstock population 2 to 5 days following a full moon.
Temperature has a profound influence on catchability.
Once sea temperatures drop below 24 C in autumn most spawning activity ceases. Although non-gravid broodstock may be caught on inshore grounds during winter, catch rates usually decline as broodstock become less active. A collector from Innisfail considers that broodstock enter a dormant period which lasts one week either of early July to late August. Although fraught with difficulties and potentially dangerous, broodstock can be caught on the shallow inshore grounds at this time if nets can be bogged into the soft mud. This marks the beginning of the spring spawning season when gravid females can usually be obtained in reasonable numbers from inshore spawning grounds.