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Juvenile mangrove jack in Weipa (May 2004)

Fisheries Long Term Monitoring Program

DB Rose, CP Lunow, JM Stapley and SL Kistle
Publication details:
Department of Primary Industries and Fisheries, Brisbane, Australia
March 2005
Bibliographic details:
10 pages

Report summary

Cover of Fisheries Long Term Monitoring Program - Preliminary Assessement of Juvenile Mangrove Jack around Weipa, May 2004

Because of concerns raised by the Gulf Fisheries Management Advisory Committee, Fisheries Long Term Monitoring Program (LTMP) staff were asked by the fishery manager to investigate the presence, abundance and size class distribution of juvenile mangrove jack around Weipa.

The mangrove jack survey in fresh and upper estuarine waters near Weipa was conducted in the first week of May 2004. The survey was timed to coincide with the LTMP Weipa mud crab survey to utilise available field staff and minimise costs. Of the 88 mangrove jack observed, 64 were captured and released. Ninety per cent were tagged before being released. The smallest fish was 57 mm TL and the largest sampled was 460 mm TL. The most commonly caught size class within the sample was 300 mm to 350 mm. Only four fish within the 0+ age group (under 100 mm TL), were captured.

Although limited, there was evidence for recruitment of mangrove jack from the 2003-04 spawning event. Low water clarity in two of the three sampling locations may have affected the ability of the survey to detect the 'young of the year' fish (less than a year old). Timing of any future surveys later in the year may address this problem. However, previous work indicates fish in this first age class are typically in the lower reaches of the estuaries where the electrofishing survey technique is not appropriate. Developing a technique to target these 'young of the year' fish in the lower estuarine areas is extremely difficult, as the technique would need to be non-destructive and standardised to allow for annual comparisons of trends within a time series data set.

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Last updated 11 March 2015