Management areas are used in marine spatial planning to conserve biodiversity of marine ecosystems and to protect fish from fishing pressure. To evaluate the effectiveness of these protected areas, observational techniques are used to determine densities, sizes, biomass, habitat types and distribution of fish species in and around management areas. Two types of observational techniques are used in spatial monitoring: (1) fishery-independent techniques, which include underwater visual census (UVC), underwater video, remote sensing, acoustics, and experimental catch and effort data; and (2) fishery-dependent techniques, which include catch, effort and catch per unit effort data from commercial and recreational fisheries. This review summarises the applications, advantages, disadvantages and biases of each of these observational categories and highlights emerging technologies. The main finding from this review was that a combination of observational techniques, rather than a single method, was the most effective approach to marine spatial monitoring. For example, a combination of hydroacoustics for habitat mapping and UVC or video for fish surveys was one of the most cost-effective and efficient means of obtaining fish-habitat linkages and fish assemblage data. There are also emerging technologies that could increase the precision and efficiency of monitoring surveys. There is a need for continued development of non-intrusive technology for marine monitoring studies.

Abstract. Estuaries are especially vulnerable to the impacts of climate change because changes in climatic and hydrologic variables that influence freshwater and marine systems will also affect estuaries. We review potential impacts of climate change on Australian estuaries and their fish. Geographic differences are likely because southern Australian climates are predicted to become warmer and drier, whereas northern regions may see increased precipitation. Environmental factors, including salinity gradients, suspended sediment, dissolved oxygen and nutrient concentrations, will be influenced by changing freshwater input and other climate variables. Potential impacts will vary depending on the geomorphology of the estuary and the level of build-up of sand bars across estuarine entrances. Changes to estuarine fish assemblages will depend on associated changes to salinity and estuarine-mouth morphology. Marine migrants may be severely affected by closure of estuarine mouths, depending on whether species 'must' use estuarine habitat and the level of migratory v. resident individuals. Depending on how fish in coastal waters locate estuaries, there may be reduced cues associated with estuarine mouths, particularly in southern Australia, potentially influencing abundance. In summary, climate change is expected to have major consequences for Australian estuaries and associated fish, although the nature of impacts will show significant regional variation.

No abstract

Spatial variation in the chemistry (Mg, Mn, Sr and Ba) of recently deposited otolith material (last 20-30 days of life) was compared between two demersal fish species; snapper Pagrus auratus (Sparidae) and sand flathead Platycephalus bassensis (Platycephalidae), that were collected simultaneously at 12 sites across three bays in Victoria, south-eastern Australia. Otolith chemistry was also compared with ambient water chemistry and among three sampling positions adjacent to the proximal otolith margin. For both species, variation in otolith chemistry among bays was significant for Ba, Mn and Sr; however, differences among bays were only similar between species for Ba and Mn. Only Ba showed significant variation at the site level. Across the 12 sites, mean otolith Ba levels were significantly positively correlated between species. Further, although incorporation rates differed, mean ambient Ba levels for both species were positively correlated with ambient Ba levels. Spatial variation in multielement otolith chemistry was also broadly similar between species and with multi-element water chemistry. Partition coefficients clearly indicated species-specific incorporation of elements into otoliths. Mg and Mn were consistently higher in snapper than sand flathead otoliths (mean AE S.D., Mg snapper 22Á1 AE 3Á8 and sand flathead 9Á9 AE 1Á5 mg g À1 , Mn snapper 4Á4 AE 2Á6 and sand flathead 0Á5 AE 0Á3 mg g À1 ), Sr was generally higher in sand flathead otoliths (sand flathead 1570 AE 235 and snapper 1346 AE 104 mg g À1 ) and Ba was generally higher in snapper otoliths (snapper 12Á1 AE 12Á8 and sand flathead 1Á8 AE 1Á4 mg g À1 ). For both species, Mg and Mn were higher in the faster accreting regions of the otolith margin, Sr was lower in the slower accreting region and Ba showed negligible variation among the three sampling regions. This pattern was consistent with the higher Mg and Mn, and generally lower Sr observed in the faster accreting snapper otoliths. It is hypothesized that the differences between species in the incorporation of these elements may be at least partly related to differences in metabolic and otolith accretion rate. Although rates of elemental incorporation into otoliths appear species specific, for elements such as Ba where incorporation appears consistently related to ambient concentrations, spatial variation in otolith chemistry should show similarity among co-occurring species.

Post-settlement King George whiting Sillaginodes punctata were sampled every 3 to 4 d from mid-September to the end of October 1993, at 3 seagrass sites within Port Phillip Bay, Australia. The site closest to the entrance (St Leonards) showed short-lived pulses of recruits in low numbers. The site of intermediate distance into the bay (Grassy Point) showed a similar pattern; however, in this case there was a marked accumulation of recruits over time. In contrast, recruitment was low at the site furthest into the bay (Grand Scenlc), and the pattern was unlike the other sites. We simulated the transport of S punctata larvae into Port Phillip Bay over t h~s penod using 2-and 3-dimensional hydrodynamic and dlspersal models. A hlgh proportion (two-thirds) of the variation in recruitment at St Leonards and Grassy Point could be explained by 2 factors. the predicted arrival of larvae based on passlve transport by currents, and disturbance of individual seagrass sites by wave action. Patterns of recruitment at Grand Scenic, however, a site that was at the 11m1t of larval dlspersal into the bay, were unrelated to model predictions or environmental variables. The daily pattern of arrival of larvae to Port Phllllp Bay was estimated from recruits using a transition in otolith microstructure. The daily pattern of arrlval estimated for individuals collected from St Leonards was slgnlficantly correlated with westerly wind stress and residual sea level, and negatively correlated with barometnc pressure. It appears that strong westerly winds and low barometric pressure associated with the passage of weather systems lead to positive sea level anomalies in Port Phillip Bay, and the passive transport of larvae into the bay. Interannual variability in weather patterns would be expected to lead to interannual variability in larval supply to Port Phillip Bay.