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It is accepted that mangroves are important nursery areas for prawns and fish, including some of major commercial importance, but little is known about how these mobilc animals use the mangrove forests. \Me recorded the dlstnbution of juvenile banana prd\-\,ns Penaeus nierguiensis and of f~s h in an intertidal mangrove forest adjacent to a small creek In northern Australia in November 1992 and In h4arch 1993. Four discrete areas of the forest were enclosed w~t h a 100 m long, 2 mm mesh stake net 2 at the creek mangrove 11-inge and 2 at further distances into the mangroves. The mean distance of each sanlpling s~t e inland from the creek mangrove frlnge ranged from 13 to 59 m and the area of the sites ranged from 480 to 640 m< Two mangrove communities, one dominated by the structurally complex Rhlzophora stylosd, the other b? the more open Ceriops tagal were sampled. A large size range of juvenile prawns and small flsh moved at least 43 m Into the mangroves at high tide, and the density of prawns near the creek mangrove fringe was inversely related to the maximum tide height. The highest density of juvenile P. merguiensis recorded in the mangroves in November was 18.3 prawns 100 m-' and in hlarch was 334.5 prawns 100 m-'. Mean fish density over all samples was 83.0 fish 100 ni--' and mean fish biomass was 3.9 g m 2 ; 55 species of f~s h were caught during the sampling. P. merguiensis showed no apparent preference for either of the 2 mangrove communities sampled; however, more fish (101 fish 100 m-2) and more fish species (26) were caught a t the creek mangrove fringe site than a t the other more inland sites; the lowest numbers of fish (27 fish m-2) and species (13) were caught at the inland site (Ceriops). On average, fish caught a t the fringe site were also longer and heavier than fish caught at the other sites. By moving well into the mangrove forest, prawns and small fish are probably less vulnerable to predat~on by larger fish.

Punt, A. E., Deng, R. A., Dichmont, C. M., Kompas, T., Venables, W. N., Zhou, S., Pascoe, S., Hutton, T., Kenyon, R., van der Velde, T., and Kienzle, M. 2010. Integrating size-structured assessment and bioeconomic management advice in Australia's northern prawn fishery. – ICES Journal of Marine Science, 67: 1785–1801. Three species in Australia's northern prawn fishery (Penaeus semisulcatus, P. esculentus, and Metapenaeus endeavouri) are assessed using a size-structured population model that operates on a weekly time-step. The parameters of this multispecies population model are estimated using data on catches, catch rates, length frequency data from surveys and the fishery, and tag release–recapture data. The model allows for the technical interaction among the three species. The results from the multispecies stock assessment are used to calculate the time-series of catches and levels of fishing effort that maximize net present value. The bioeconomic model takes into account costs which are proportional to catches and those which are proportional to fishing effort, as well as fixed costs. The sensitivity of the results is examined by changing the assumptions regarding the values for the economic parameters of the bioeconomic model as well as those on which the assessment are based. The results suggest that fishing effort needs to be reduced in the short term to achieve economic goals, although most stocks are estimated currently to be above the stock size corresponding to maximum sustainable yield. Short-term catches and effort levels are sensitive to model assumptions, and in particular, to trends in prices and costs.

Flood events typically enhance primary productivity in estuaries via the increased nutrient inputs from land runoff. This study examined the drivers of phytoplankton biomass accumulation and productivity in a tropical estuary with a distinct wet-dry seasonality, i.e. months of little or no rainfall, and a highly episodic extended wet season. The study found that over two wet seasons, there was little evidence of freshwater inputs increasing nutrient concentrations, and chlorophyll a concentrations and phytoplankton productivity rates decreased in the water column, probably due to low water residence times. The magnitude and duration of freshwater flows in the wet season appeared to affect the scale of reduction of phytoplankton productivity and biomass accumulation. In contrast to many studies, there was also no evidence of post-flooding stimulation of chlorophyll a concentration with net export of nutrients in both the wet and dry seasons. Nitrogen (N) and light appeared to be key limiting factors for phytoplankton growth with estuarine DIN rapidly turned over by phytoplankton, no evidence of N fixation by phytoplankton, and a response to N, but not phosphorus (P), in algal bioassays. Tidal resuspension of sediments was an important physical process that limited light availability for primary productivity. The lack of higher nutrient concentrations as a result of freshwater inputs, and lack of post-flood algal growth stimulation contrasts with the findings of studies in eutrophied systems. in turn, fuel primary production in the months during and post-flooding once flow and turbidity have decreased, and salinity has increased (Mallin et al., 1993; Gillanders and Kingsford, 2002; Murrell et al., 2007). Wet and dry tropical/subtropical river systems account for 68% of Australian estuaries, meaning that they are an important contributor to the productivity of estuarine and coastal systems (Bucher and Saenger, 1994). Indeed studies have shown a correlation between catches of estuarine fish and crustaceans, and measures of freshwater flow which suggests that freshwater inputs may be providing nutrients and carbon to fuel productivity in estuaries (Gillanders and Kingsford, 2002; Robins et al., 2005). Conversely, estuarine productivity appears to be negatively affected if the upstream river is regulated, reducing the magnitude of high flow events (Kenyon et al., 2004; Burford et al., 2011). Eyre (2000) has proposed that estuaries of the wet and dry tropics/subtropics have four regime states throughout a typical year. During floods, freshwater flushes nutrients and sediments out to sea. This is followed by a recovery phase where turbidity begins to decrease, however low light availability prevents phytoplankton growth. In the medium flow phase, increasing light and nutrient availability stimulates phytoplankton biomass. Finally, in the dry season, phytoplankton become nutrient limited again, with a resulting decrease in biomass. This study therefore examined the role of freshwater nutrient inputs in stimulating phytopl...

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