Pearl perch: biological monitoring update

  • A recreational fisher lands a pearl perch.
    The length and sex of this pearl perch will be recorded and its otoliths removed for ageing.

In Queensland, pearl perch (Glaucosoma scapulare) are generally caught offshore in waters deeper than 40 m from Mackay (approximately 21° S) to the Queensland–New South Wales border. Peak fishing season is spring through to autumn. Pearl perch have a minimum legal size of 35 cm and an in-possession limit for recreational fishers of five fish.

Since 2006, a variety of strategies have been used to collect biological information (length, sex and age) for pearl perch caught in Queensland waters. The information is used to help assess the status and sustainability of the stock.

Fish length

Length information collected indicates that both recreational and commercial fishers retain a similar size range of fish, but larger fish (e.g. in 2012, fish ≥ 55 cm) comprised a greater percentage of the commercial catch compared with the recreational catch (see length frequency graph).

  • Length structure graph (total length v frequrency) of the 2012 commercial (grey) and recreational (blue) fishery for pearl perch.
    The length frequency of pearl perch retained by the commercial and recreational sectors in 2012 (excludes fish caught on charter boats).
  • Age structure of the 2010 (top) 2011(middle) 2012 (bottom) commercial (grey) and recreational (blue) catch.
    The age frequency of pearl perch retained by the commercial and recreational sectors for the years 2010 – 2012 (excludes fish caught on charter boats).

Fish Age

Biological samples collected during the monitoring program include otoliths (ear bones). Otoliths contain growth rings which are visible once sectioned and viewed under a microscope. These growth rings are then counted to help estimate the fish's age.

Between 2010 and 2012 most of the pearl perch kept by fishers were between three and seven years old. Very few fish aged 10 years or older were observed in the catch (see age frequency graph). 

The length and age information collected during the sampling program indicate variable growth rates. For example, in 2012, the longest pearl perch measured was 71 cm and was aged at 16 years old but the oldest fish, which was aged at 20 years old, only measured 65 cm in length. The variability in growth rates means a significant number of three, four and five year old pearl perch are less than 35 cm, and are therefore protected by the minimum legal size limit.

A recent study showed that pearl perch can be reproductively mature at two to three years of age. Which means that they can spawn for several years before they reach the minimum legal size. This variability is an important consideration when assessing the sustainability of the fishery.

  • Age-at-length graph for Pearl perch. Shaded sections show the 5th to the 95th percentile from each length category.  Points mark the median age. Sample size is 2090 fish.
    Age-at-length graph for pearl perch.

How old is your fish?

The age information collected during the monitoring program has been used to illustrate the age-at-length relationship for pearl perch. After measuring the total length of your fish, you can estimate its age using the age-at-length graph. For example a 49-50 cm pearl perch is most likely six years of age but could easily be as young as four or as old as nine.

Support and assistance

Thank you to everyone who has generously assisted with the monitoring of pearl perch by donating frames or allowing us to measure their fish.

Last updated 11 March 2015