Metapenaeus Macleayi Research Articles

Polychlorinated dibenzodioxins/furans and dioxin-like polychlorinated biphenyls in fish and crustaceans of a recreationally fished estuary, following targeted remediation

Polychlorinated dibenzo-p-dioxins and furans (PCDD/Fs) and dioxin-like polychlorinated biphenyls (dl-PCBs) are a suite of harmful chemicals (hereafter collectively referred to as ‘dioxins’), and their emission into aquatic habitats leads to persistent contamination of sediments, aquatic food-webs, and seafoods. Quantifying contaminant levels in seafood species is important for the ongoing management of exposure risk by fishers, particularly after any remediation actions. We present dioxin concentrations in four seafood species (Yellowfin Bream Acanthopagrus australis, Sea Mullet Mugil cephalus, Eastern School Prawn Metapenaeus macleayi, and Eastern King Prawn Penaeus plebejus) in a recreationally fished estuary, in relation to a contaminated site that has undergone a remediation process, partially removing contaminated sediments (Homebush Bay, Port Jackson, New South Wales, Australia). Dioxin concentrations in these species were measured before (2005/6) and after (2015/16) remediation at a range of locations in and around the remediated site. Dioxin concentrations and congener profiles differed substantially among taxa, and concentrations were frequently higher than Australian screening criteria. The two prawn species showed evidence of a decline in dioxin concentrations after remediation, but the fish species only showed a declining dioxin concentration with distance from the contaminated site (not between periods). There were some minor changes in the congener profile for some species following remediation. While there was evidence for greatly reduced dioxin concentrations in prawn species following remediation, the complex patterns for fish were likely affected by environmental changes, species-specific and temporal changes in lipid content, and animal movement patterns. Future monitoring may aid interpretation of the patterns and modelling of exposure risk associated with seafood consumption into the future.

Relative performance of two bycatch reduction devices for excluding juvenile mulloway, Argyrosomus japonicus and other fish from south-eastern Australian penaeid trawls

Mulloway, Argyrosomus japonicus is an economically valuable species across southern Australia, but the south-eastern population is considered depleted owing to excessive historical commercial and recreational fishing mortality. To address this concern, stock-recovery initiatives have been implemented in New South Wales, which include minimising unaccounted fishing mortality by regional penaeid trawlers targeting school prawns, Metapenaeus macleayi. This study presents four experiments to evaluate the relative effectiveness of two mandated bycatch reduction devices (BRDs) to reduce incidental catches of mulloway across volunteer estuarine penaeid trawlers. Both BRDs were ‘mechanical separators’ designed to partition catches based on size. The first design (termed the ‘blubber-chute’) is the most commonly used in the assessed fisheries and comprised a funnel of 96-mm mesh inside the extension that directed larger organisms through a posterior, top opening. The second design (‘Nordmøre-grid’), comprised a 400- × 872-mm aluminium grid with 20-mm bar spacings and inserted at 33° in the extension. Organisms larger than the bar spaces were directed upwards to an escape exit similar in size to that in the blubber-chute. The BRDs were assessed using covers on single-rigged trawlers and simultaneously without covers on double-rigged trawlers. Trawls with the BRDs had the same quantities of school prawns but those with the blubber-chute retained significantly more total incidental catches (by up to 5.2 ×) and mulloway > 20 cm TL (up to 9 ×) than those with the Nordmøre-grid. Relatively greater numbers of unwanted juveniles of another economically important species, tailor, Pomatous saltatrix, and others were also excluded by the Nordmøre-grid. The results support preferential use of the conventional Nordmøre-grid for eliminating the bycatch of mulloway >20 cm TL. Secondary BRDs that mitigate the capture of smaller fish warrant ongoing assessment.

Assessing T45 vs T0 and T90 meshes and covered codend effects in southeastern Australian penaeid trawls

Square-mesh codends (i.e. turned 45 degrees or ‘T45′) made from a minimum stretched mesh opening (SMO) of 27-mm mesh hung on the bar are mandated for estuarine-trawl fisheries targeting penaeids (mostly school prawns, Metapenaeus macleayi) in New South Wales, Australia. However, owing to variable mesh shrinkage over time, often slightly larger SMOs are supplied, and sometime too large to be oriented as T45 for the targeted school prawns (>13–15 cm carapace length; CL). During three experiments involving paired trawls with and without codend covers, we sought to investigate if, compared to a conventional 27-mm T45 codend, lateral openings in 30-mm SMO could be appropriately maintained by orientating diamond-shaped (‘T0′) meshes at narrow (experiment 1) or normal (experiment 2) circumferences, or turned 90 degrees (‘T90′; experiment 3). Analyses of size selection was done after first testing for species-specific cover effects, which required fish sizes to be assessed via a paired-hauls approach while sizes for school prawns were modelled using a covered-codend approach. Compared to the 27-mm T45 codend, only the T0 mesh hung at a normal circumference provided the same size selection for school prawns, with the two other alternative configurations producing wider selection. But, while incidental fish catches were low (14% of total catch), all new codends caught between ∼2 and 7 × more individuals of some small fish cross all sizes, including juveniles of an economically important species (tailor, Pomatomus saltarix). The data reiterate that among the codends tested, T45 mesh is the optimal configuration for regional penaeid trawls in terms of consistently maximining school prawn size selection and the escape of small fish, and so high-quality material in the required sizes needs to be sourced.

Impacts of seasonal temperatures, ocean warming and marine heatwaves on the nutritional quality of eastern school prawns (Metapenaeus macleayi)

Ocean warming and marine heatwaves significantly alter environmental conditions in marine and estuarine environments. Despite their potential global importance for nutrient security and human health, it is not well understood how thermal impacts could alter the nutritional quality of harvested marine resources. We tested whether short-term experimental exposure to seasonal temperatures, projected ocean-warming temperatures, and marine heatwaves affected the nutritional quality of the eastern school prawn (Metapenaeus macleayi). In addition, we tested whether nutritional quality was affected by the duration of exposure to warm temperatures. We show the nutritional quality of M. macleayi is likely to be resilient to short- (28 d), but not longer-term (56 d) exposure to warming temperatures. The proximate, fatty acid and metabolite compositions of M. macleayi were unchanged after 28 d exposure to simulated ocean warming and marine heatwaves. The ocean-warming scenario did, however, show potential for elevated sulphur, iron and silver levels after 28 d. Decreasing saturation of fatty acids in M. macleayi after 28 d exposure to cooler temperatures indicates homeoviscous adaptation to seasonal changes. We found that 11 % of measured response variables were significantly different between 28 and 56 d when exposed to the same treatment, indicating the duration of exposure time and time of sampling are critical when measuring this species' nutritional response. Further, we found that future acute warming events could reduce harvestable biomass, despite survivors retaining their nutritional quality. Developing a combined knowledge of the variability in seafood nutrient content with shifts in the availability of harvested seafood is crucial for understanding seafood-derived nutrient security in a changing climate.

Improving the performance of a generic fisheye as a secondary bycatch reduction device in a south-eastern Australian penaeid-trawl fishery

The utility of a generic device (termed a ‘fisheye’) and its simple modification for cumulatively reducing bycatch in penaeid trawls was assessed during two experiments in a south-eastern Australian fishery. In the first experiment, conventional trawls (with no fisheye) were compared to simultaneously towed, identical trawls installed with a typical fisheye (termed ‘mesh fisheye’) comprising an open triangular frame terminating in a semi-elliptical vertical opening (350 × 150 mm) in the top of the trawl extension at 1.1 m anterior to the codend drawstring. Trawls with the mesh fisheye maintained catches of penaeids (mostly school prawns, Metapenaeus macleayi) but retained significantly less total bycatch (by 39 %) and fewer unwanted southern herring, Herklotsichthys castelnaui (by 60 %) and tailor, Pomatomus saltatrix (by 52 %). During the second experiment, trawls with the mesh fisheye were simultaneously compared to those with a modified design comprising a solid panel of aluminium in the lower half of the triangular frame (termed the ‘solid fisheye’). The solid fisheye excluded significantly more bycatch (by 52 %) and small southern herring (by 47 %), and also the numbers of several other species, including mulloway (by 38–41 %) without affecting penaeid catches. The improved performance of the solid fisheye was attributed to its greater anterior displacement of water and posterior area of lower perceived flow for fish. The results and simplicity of the fisheye modification support not only its regional use, but also testing in other national and international fisheries.

Adaptive Spatial Management to Deal with Postflood Inshore Bycatch in a Penaeid Trawl Fishery

AbstractAdaptive spatial management provides a way to balance the conservation of bycatch species and the potential economic effects of bycatch‐induced closures on a fishery, but implementation can be both data and resource intensive. We present a survey exploring a novel approach to adaptively manage an intermittent bycatch issue in an inshore trawl fishery where Sciaenidae bycatch species (including juvenile Mulloway Argyrosomus japonicus, a species of conservation concern) co‐occur with large aggregations of a valuable target species (eastern school prawn Metapenaeus macleayi), following flood‐induced egression from estuarine habitats. Diurnal sampling surveys followed three flood events and targeted permanent inshore closure zones (designed to protect the normally nocturnally harvested eastern king prawn Melicertus plebejus) and adjacent inshore nonclosure areas. Sciaenidae abundance was mostly <10 fish/ha trawled, but larger catches generally corresponded with larger catches of eastern school prawn, and these relationships appeared to be steeper within nonclosure zones. There were only minor differences in the size structure of eastern school prawn between zones, and patterns were event and location specific. Negligible eastern king prawn were encountered. The results show that temporarily allowing fishers access to permanent trawl closures following floods may support the exploitation of aggregated target species with reduced interaction with bycatch species of concern. The approach presented here is relevant to the consideration of adaptive spatial management in other trawl fisheries.

Metapenaeus macleayi

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Diet‐tissue discrimination and turnover of δ13C and δ15N in muscle tissue of a penaeid prawn

RationaleStable isotopes are used to study trophic and movement ecology in aquatic systems, as they provide spatially distinct, time‐integrated signatures of diet. Stable isotope ecology has been used to quantify species‐habitat relationships in many important fisheries species (e.g., penaeid prawns), with approaches that typically assume constant values for diet‐tissue discrimination and diet‐tissue steady state, but these can be highly variable. Here we provide the first report of these processes in Metapenaeus macleayi (eastern school prawn).MethodsHere we explicitly measure and model carbon (δ13C) and nitrogen (δ15N) diet‐tissue discrimination and turnover in eastern school prawn muscle tissue as a function of experimental time following a change in diet to an isotopically distinct food source.ResultsDiet‐tissue discrimination factors were 5 and 0.6‰ for δ13C and δ15N, respectively. Prawn muscle tissue reached an approximate steady state after approximately 50 and 30 days for δ13C and δ15N. Half‐lives indicated faster turnover of δ15N (~8 days) than δ13C (~14 days).ConclusionsOur diet‐tissue discrimination factors deviate from ‘typical’ values with larger values for carbon than nitrogen isotopes, but are generally similar to those measured in other crustaceans. Similarly, our estimates of isotopic turnover align with those in other penaeid species. These findings confirm muscle tissue as a reliable indicator of long‐term diet and movement patterns in eastern school prawn.

Refining tickler chains for penaeid trawls

Tickler chains are simple additions to the ground gears of benthic trawls that can improve the catches of some target species, albeit with considerable variability. The purpose of this study was to decipher some of the technical variability associated with tickler chains used with generic, paired trawls targeting school prawns, Metapenaeus macleayi. In the first of two experiments, single tickler chains were either attached between the trawl otter boards or the wing ends and compared against each other and a control trawl (no tickler chain). Attaching the tickler chain to the otter boards significantly reduced wing-end spread and the trawled area without significantly affecting catches of school prawns. By comparison, attaching the tickler chain to the wing ends maintained spread and resulted in significantly more school prawns being caught (by 1.11 ×) than in the control trawl, and also fewer numbers of one teleost species, pink-breasted siphonfish, Siphamia roseigaster. In experiment two, a single tickler chain was compared against one with multiple chains and one with a double chain; all attached at the wing ends. Trawls with the multiple- and double-tickler chains had the same wing-end spread as those with the single tickler chain, while retaining up to 1.17 × more school prawns, and for the double-chain tickler, 45% fewer southern herring, Herklotsichthys castelnaui. The results are attributed to mechanical and visual stimuli affecting school prawns and some fish, respectively, and support maximising the surface area of tickler chains within the wing ends as a means for improving penaeid-trawl species selectivity without affecting swept area.

Effects of reduced pH on an estuarine penaeid shrimp (Metapenaeus macleayi).

Acid sulfate soils are a major problem in modified coastal floodplains and are thought to have substantial impacts on estuarine species. In New South Wales, Australia, acid sulfate soils occur in every estuary and are thought to impact important fisheries species, such as Eastern School Prawn (Metapenaeus macleayi). These fisheries have experienced declining productivity over the last ten years and increasing occurrence of catchment-derived stressors in estuaries contribute to this problem. We evaluated the effect of pH 4-7.5 on School Prawn survival at two salinities (27 and 14.5), pH 5, 6 and 7.5 on the predation escape response (PER) speed at two salinities (27 and 14.5), and pH 4 and 7.5 on respiration rates. While mortality appeared to be greater in the high salinity treatment, there was no significant relationship between proportional survival and pH for either salinity treatment. Respiration was significantly slower under acidic conditions and the average PER was almost twice as fast at pH 7.5 compared to pH 5 (p<0.05), indicating prawns may fall prey to predation more easily in acidic conditions. These findings confirm the hypothesised impacts of acidic water on penaeid prawns. Given that the conditions simulated in these experiments reflect those encountered in estuaries, acidic runoff may be contributing to bottlenecks for estuarine species and impacting fisheries productivity.

Survival, Growth, and Metabolic Changes in Eastern School Prawn (Metapenaeus macleayi) across a Spectrum of Salinities

Variation in salinity is one of the principal changes in estuarine physicochemistry that can impact the productivity of estuarine species. The effect of salinity on the mortality, growth, and metabolite profiles of juvenile Eastern School Prawn (Metapenaeus macleayi) was evaluated across a salinity gradient ranging from 0.2–36 over 60 days. Survival was >70% for salinity treatments other than the lowest salinity. Survival was 0% in the lowest salinity and all prawns had died within 3 days. Salinity did not appear to impact relative growth across the range of salinities examined. In contrast, relative somatic condition was greater at lower salinities and was negatively correlated with salinity, indicating lower salinities promote enhanced somatic condition in School Prawn. Total fatty acid concentration showed no relationship with salinity or somatic condition index. However, total fatty acid concentration did have a significant positive relationship with total amino acid concentration. Total amino acid concentration showed no linear relationship with salinity or somatic condition index. Quantitative profiling of individual fatty acids and amino acids showed some changes in response to salinity. Alpha-aminoadipic acid showed a significant positive relationship with salinity. These complex patterns suggest several shifts in cellular chemistry may occur throughout the salinity range investigated, potentially with metabolic consequences. These results highlight the complex responses of estuarine crustaceans to changes in salinity.

Lethal and sub-lethal effects of environmentally relevant levels of imidacloprid pesticide to Eastern School Prawn, Metapenaeus macleayi

Pesticides are frequently employed to enhance agricultural production. Neonicotinoid pesticides (including imidacloprid) are often used to control sucking insects but have been shown to impact aquatic crustaceans. Imidacloprid is highly water soluble and has been detected in estuaries where it has been applied in adjacent catchments. We examined the impact of environmentally relevant concentrations of imidacloprid on Eastern School Prawn (Metapenaeus macleayi), an important exploited crustacean in Australia. Prawns were held for 8 days in estuarine water containing 0–4 μg L−1 of imidacloprid to assess potential lethal and non-lethal impacts. There was a non-linear relationship between exposure concentration and tissue concentration, with tissue concentrations peaking at exposures of 1.4 μg L−1 (1.16 to 1.64 μg L−1, 90% C.I.). There was no evidence for direct mortality associated with imidacloprid exposure, but exposure did influence the organism metabolome which likely reflects alterations in metabolic homeostasis, such as changes in the fatty acid composition which indicate a shift in lipid homeostasis. There was a positive correlation between exposure concentration and moulting frequency. Shedding of the exoskeleton may represent a mechanism through which prawns can expel the contaminant from their bodies. These results indicate that prawns experience several different sub-lethal effects when exposed to these pesticides, which may have implications for the health of populations.

Improving penaeid-trawl efficiencies via ground gear with tickler chains

Penaeid trawls often have poor ecological efficiencies measured as unwanted bycatches (with high discard mortality) and <100% effectiveness for all penaeids interacting with the ground gear (with some escape mortality). This study investigated the utility of varying ground-chain size (8- vs 10-mm diameter (Ø) stainless-steel chain) and the present or absence of a tickler chain (4-mm Ø) for improving efficiencies an Australian fishery diurnally targeting school, Metapenaeus macleayi and eastern king prawns, Penaeus plebejus. There were no treatment effects on wing-end spread and therefore areas trawled. Irrespective of the tickler chain, increasing the ground-chain Ø reduced catches of total penaeids (by 14%) and jellyfish, Catostylus mosaicus (by 39%)—results speculatively attributed to variation in ground contact and/or a slightly higher footrope in trawls with the 10-mm Ø chain. By comparison, installing the tickler chain had no effect on eastern king prawns, but increased catches of school prawns (by 1.13×) and bycatches of blue swimmer crabs, Portunus armatus (1.52×; a species with a low discard mortality) and jellyfish (1.23×), while reducing bycatches of two species with high discard mortalities: southern herring, Herklotsichthys castelnaui (by 38%) and squid, Uroteuthis sp. (37%). The results were attributed to the tickler chain producing (1) mechanical stimuli that augmented the capture of benthic-orientated school prawns (but not eastern king prawns owing to diel variations in emergence from the substrata), blue swimmer crabs and jellyfish; and (2) visual stimuli that possibly enabled some southern herring and squid to detect the trawl and escape. The data show tickler chains can improve trawl efficiency for penaeids with at least some positive effects on bycatch that should be rationalised in terms of species-specific vulnerabilities to unaccounted fishing mortality.

Influence of top-panel orientation (lead-ahead) on targeted and incidental catches in a penaeid trawl

Various, low-cost modifications to the anterior sections of penaeid trawls have been shown to realise significant improvements in species selectivity. This study expands the existing options by quantifying the importance of top-panel orientation relative to the bottom panel (dictated by relative headline and footrope lengths; termed ‘lead-ahead' or ‘lead’) on targeted and incidental catches in an Australian penaeid-trawl fishery. Three trawls were compared in a double rig: (1) the conventional configuration with identical footrope and headline lengths (7.53 m) and a 200-mm diameter buoy attached to the latter (termed the ‘buoyed no-lead trawl’); (2) the same trawl, but with the buoy removed (‘no-lead trawl’); and (3) a trawl with the same headline length as above, but the footrope 1.14× longer, creating lead-ahead (‘lead trawl’). Between 11 and 26 deployments of each configuration were done over six fishing days. Compared to the buoyed no-lead trawl, both the no-lead and lead trawls had greater wing-end spreads and both caught less total bycatch (absolute and standardized weights ha–1 trawled reduced by up to 64 and 48 %, respectively) and fewer individual unwanted species, including jellyfish, Catostylus mosaicus (by up to 61 and 58 %) and southern herring, Herklotsichthys castelnaui (by up to 59 and 43 %). However, only the lead trawl maintained catches of the targeted school prawns, Metapenaeus macleayi. These target catches were reduced by 37 % in the no-lead trawl (without the buoy). The results imply a trawl without lead-ahead requires sufficient headline height to maximise catches of school prawns, but simply introducing lead-ahead and removing the buoy (lowering the headline) can maintain target catches while dramatically reducing bycatch. Similar subtle refinements may have application in other penaeid-trawl fisheries.

The influence of rainfall on recruitment success and commercial catch for the large sciaenid, Argyrosomus japonicus, in eastern Australia

Freshwater flows into estuaries influence fish populations through effects on recruitment, growth and mortality. We compared year class strength of a large sciaenid Argyrosomus japonicus with rainfall through a 16-year period in southeastern Australia, to understand the influence of freshwater input on this estuary-dependent and depleted population. Relative year class strength, estimated by back-calculating age composition data from commercial fishery landings, was positively related to rainfall within estuarine catchments (R2 = 52%). Commercial estuarine landings from a separate 29-year dataset were positively related to rainfall two and three years earlier (R2 = 21% and 44%, respectively). Year class strength of a key prey species, the penaeid prawn Metapenaeus macleayi, was also related to year class strength of A. japonicus (R2 = 39%), suggesting that rainfall influences recruitment of A. japonicus by affecting food availability. Several years of above average rainfall may be required to promote recruitment substantial enough to rebuild the population.

Stable isotopes reveal the importance of saltmarsh-derived nutrition for two exploited penaeid prawn species in a seagrass dominated system

Estuaries represent highly important nursery habitats for a range of species, with refuge and nutrition being two key benefits derived from estuaries. Quantifying these benefits provides us with a means for enhancing fisheries productivity. Metapenaeus macleayi (School Prawn) and Penaeus plebejus (Eastern King Prawn) are two commercially and recreationally important species in New South Wales that utilise estuarine nurseries throughout their life history. In this study, stable isotopes of carbon, nitrogen and sulfur were used to determine the proportional contribution of primary producers to prawn nutrition in Brisbane Water (NSW). Both the saltmarsh grass Sporobolus virginicus and seagrass Zostera muelleri were found to support a high trophic contribution to prawns (up to 53% and 40%, respectively). The contributions of other primary producers such as mangroves, fine benthic organic matter (FBOM) and C3 saltmarsh plants were generally found to be much lower (0.7–15%). Such findings are generally consistent with patterns observed in other south-east Australian estuaries, however such a dominant role of saltmarsh in the presence of seagrass is a novel finding. These results highlight linkages between habitats of conservation concern and highly valuable fisheries species, and the benefit of using sulfur as an additional marker in Bayesian mixing models examining estuarine food webs.

Lethal and sublethal effects of simultaneous exposure to hypoxia and aluminium on juvenile eastern school prawn

Estuarine waters are heavily influenced by catchment land use and run-off, and acid sulfate soils directly affect both dissolved oxygen (DO) and aluminium concentrations. This can affect harvested species (including benthic crustaceans) and can have concomitant effects on their productivity. In this study we evaluated the effects of hypoxia (DO concentrations &amp;lt;2mgL–1) on eastern school prawn (Metapenaeus macleayi) under enhanced and ambient aluminium concentrations (mean±s.d., 0.112±0.009 and 0.015±0.002mgL–1 respectively). There was a significant increase in survival with increasing DO and LC50 was ~0.9mgL–1, although survival decreased at higher DO concentrations in the presence of enhanced aluminium concentrations. Total fatty acid and amino acid concentrations were significantly greater in prawns subjected to hypoxia, regardless of aluminium exposure. Docosahexaenoic acid, stearic acid, palmitic acid and behenic acid (fatty acids) and leucine, isoleucine, phenylalanine and asparagine (amino acids) contributed to differences in fatty and amino acid profiles among treatments. Hypoxia and aluminium concentrations in nursery habitats of south-eastern Australian estuaries can exceed the conditions evaluated, and could thus affect survival of M. macleayi. More generally, these results have implications for other crustacean species in estuaries that drain coastal flood plains, and the fisheries that rely on them.

Adaptive bycatch reduction in penaeid trawls via rapid adjustments to headline height

AbstractPenaeid trawling is among the world's least selective fishing methods; a characteristic that has evoked spatial closures being implemented in some fisheries if certain bycatch limits are exceeded. For decades, considerable work has been done to develop modifications to penaeid trawls that reduce unwanted bycatches, with most focussed at the posterior section (i.e. codend). More recently, efforts have examined ways to prevent bycatch entry into trawls entirely—via modifications to anterior components. This study assessed the utility of proactively lowering the headlines of Australian penaeid trawls, using clips at the otter boards, to 68% and 54% of their conventional height, and demonstrated mean total bycatch reductions (by weight) of 69% and 79%, respectively, with no effects on the targeted Metapenaeus macleayi (Haswell). The results provide insights into the location and behaviour of various species in the water column preceding capture, and support a simple and easy method for regional fishers to use in situ to avoid excessive bycatch and associated fishing closures. More broadly, the data support ongoing efforts in other penaeid‐trawl fisheries to reduce bycatches via similar, rapid adjustments to anterior components, depending on species‐specific behaviours during capture.

Lethal and Sub-Lethal Effects of Aluminium on a Juvenile Penaeid Shrimp

Catchment degradation and exposure of acid sulphate soils can affect estuarine water quality, and this can have impacts on the health of estuarine species and adversely affect fishery productivity. In degraded catchments, aluminium (Al) is mobilised from clay minerals following oxidation of acid sulphate soils, and may be harmful to estuarine crustaceans. We tested the acute toxicity and sub-lethal effects of Al for School Prawn (Metapenaeus macleayi), through a series of experiments conducted under normal (pH 8) and acidic (pH 5) conditions. Experimental data were used to examine mortality. Also, histological examination of the gills and hepatopancreas was conducted to determine pathological consequences of exposure to these stressors. School Prawn did not experience mortality in response to acute exposure to Al under normal pH conditions, but mortality and tissue bioaccumulation of Al was greater under acidic conditions, suggesting an interactive effect of both stressors. Histology revealed sub-lethal effects of Al including structural abnormalities in the gills and hepatopancreas, and evidence of viral infection and immune response, particularly at lower pH and higher Al concentrations. These impacts may impede major vital functions such as respiration, osmotic regulation, metabolism and growth of juvenile School Prawn, which could contribute to productivity bottlenecks in degraded estuaries.

Catchment-derived stressors, recruitment, and fisheries productivity in an exploited penaeid shrimp

Many factors can affect growth, survival, reproduction, and fisheries productivity of estuarine species, including structural and physico-chemical habitats, and freshwater inflow to estuaries. Land-based activities can lead to poor catchment condition, and catchment-derived stressors can adversely impact estuarine systems. Using the Eastern School Prawn (Metapenaeus macleayi) in a south-eastern Australian estuary (Camden Haven Estuary) as a case study, we examine juvenile recruitment and fisheries productivity alongside a comprehensive suite of catchment-derived stressors, and interpret patterns in the context of existing studies of lethal and sub-lethal impacts of these stressors on penaeid prawns. Logged dissolved oxygen data indicated a moderate frequency of hypoxia throughout the system, with occasional periods of anoxia. Dissolved aluminium concentrations remained above the relevant marine water quality guideline for the majority of the study period, and concentrations tended to correlate with estuarine inflow. Hypoxia led to depressed prawn abundance, and both hypoxia and high estuary inflow led to decreased somatic condition in prawns. Long-term commercial catch negatively correlated with estuary inflow, which was the opposite of the expected pattern for the species. These patterns highlight the potential cumulative impacts of a complex array of catchment-derived stressors on an important exploited penaeid species. Similar patterns probably occur for prawn species across other floodplain estuaries across south-eastern Australia, and suggest a hitherto unquantified economic impact of degraded catchments through losses in fisheries productivity.