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Fishery Status Reports 2006



Fishery Status Reports 2006

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Dept. of Primary Industry, Fisheries and Mines.


Fishery reports; Reports; PublicationNT; Fishery report ; no. 87




Made available via the Publications (Legal Deposit) Act 2004 (NT).






Fishery resources -- Northern Territory -- Periodicals; Fisheries -- Northern Territory -- Periodicals; Shark fisheries -- Northern Territory -- Periodicals; Mackerel fisheries -- Northern Territory -- Periodicals; Crab fisheries -- Northern Territory -- Periodicals; Giant perch fisheries -- Northern Territory -- Periodicals; Lutjanidae fisheries -- Northern Territory -- Periodicals

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Dept. of Primary Industry, Fisheries and Mines

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Fishery report ; no. 87



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F I S H E R Y S T A T U S R E P O R T S 2 0 0 6 19 pattern of cyclic abundance with high numbers of recruits every second year. An estimated 892 barramundi were in the 450 m site in 2006 (95 per cent confidence interval between 596 and 1190). This was higher than the 20-year average of 793 fish. Most fish (88.5 per cent) were less than one year old and between 30 and 45 cm long, demonstrating that barramundi are reproducing successfully in the Mary River system. Research effort between 1996 and 2001 focussed on the assessment of the possible impacts of saline intrusion control activity on barramundi in the Mary River wetlands region (de Lestang and Griffin, 2000; de Lestang et al., 2001). It was identified that the placement of saline intrusion control walls along the wetlands significantly reduced the composition and relative numbers of fish, including barramundi, in areas impacted by control works. Such a reduction has the potential to impact on the growth rate and ultimate survival of juvenile barramundi. The placement of spillways within the walls was found to negate the negative effects of the control walls, facilitating access for both juvenile barramundi and other species. Between 2002 and 2004, research effort concentrated on quantifying the survival and physiological effects of angler catch-and-release on barramundi in a freshwater habitat. This showed that around 90 per cent of barramundi survived after being caught and released in fresh water and that the action of hooking and landing barramundi elicited a physiological (plasma cortisol) and a metabolic (plasma lactate) stress response. Survival also varied significantly throughout the year. Those fish sampled in warmer months suffered more stress and lower survival (80 per cent) compared with fish caught in cooler months (100 per cent survival) (de Lestang et al., 2004). The effects of different landing nets on fish health were also investigated. Fish friendly knotless nets cause significantly less damage to fish skin and fins than more traditional knotted mesh nets. Knotless nets are recommended to minimise injuries and increase the chance of post-release survival. Incorporation into Management Monitoring of barramundi stocks in the Mary River during 1986 and 1987 provided vital information to support major changes to the management of commercial and recreational sectors. Research in the Mary River wetlands identified the beneficial effects of spillways within saline intrusion control walls. The findings of this research have been incorporated into the future planning of saline intrusion control works. Data from creel surveys and population monitoring in the Mary River has made significant contributions to the adjustment of fishing controls in the region, including the size limit and banning the use of live bait and treble hooks at the Shady Camp Barrage. The long-term monitoring of the barramundi population at Corroboree Billabong has led to a greatly improved understanding of reasons behind fluctuations in the population. It provides informed responses to concerns about reported and perceived declines in fishing success. The results from the post-release survival study strongly support the use of catch-and-release as both a management tool and conservation practice for barramundi in a freshwater environment. The effect of season on both the stress response and post-release survival of barramundi is significant and will be used as a guide for future management strategies.