Sand whiting monitoring
Sand whiting (Sillago ciliata) is one of the many species monitored by Fisheries Queensland. It is a key target species for both recreational and commercial fishing sectors, with estimated harvests in 2014 of 102 tonnes and an average of 238 tonnes between 2010 and 2018 respectively.
The routine collection of length and age data for sand whiting began in 2007, with a focus on commercial and recreational catches between Baffle Creek (north of Bundaberg) and the Queensland - New South Wales border.
Similar data were collected sporadically in Queensland from the 1970s to the early 1990s by several short-term research projects. These studies were primarily designed to determine some important biological features of sand whiting, such as the length and age at which fish mature. Biological research and monitoring of sand whiting has also been undertaken by other state agencies (i.e. New South Wales).
The information is used to help assess trends in the status of the sand whiting stock to ensure the sustainability of the fishery and to evaluate the effectiveness of fisheries management strategies. Sand whiting in Queensland is currently assessed as sustainably fished.
The monitoring program is reliant on the participation of recreational and commercial fishers, who allow scientific staff to measure fish and collect frames.
Fish length and age
Both sectors harvest a similar length range of sand whiting (23cm total length to over 40 cm total length). The most frequently harvested length class is 25-26 cm. A higher proportion of the recreational harvest is made up of fish larger than 28 cm total length than for the commercial harvest (figure 1), and this is likely to be related to the selectivity of the fishing gear used.
The age of many fish species can be determined by examining their otoliths (ear bones). Fish age, in years, can be estimated by identifying and counting the number of opaque bands, like growth rings in a tree. Due to their size and shape, sand whiting otoliths require sectioning to enable the identification and counting of opaque bands. Sectioning involves encasing the otolith in a block of resin and cutting a thin wafer (320 micron) through its centre.
Sand whiting caught by both the commercial and recreational fishery sectors are dominated by three and four year old fish (figure 2). The oldest fish aged by the program to date were 11 years of age and ranged in size from 33 cm to 44 cm total length.