Understanding drivers of effort and catch is important for sustainable management of recreational fisheries. For the Pipi (Latona deltoides) fishery in South Australia as a case study, publicly available datasets on fisher demography, market forces and internet connectivity improved understanding of fisher motivations and capabilities, identified different historical periods in the fishery and addressed temporal gaps in effort and catch estimates from on-site surveys. Most variables were correlated with recreational effort and catch estimates from on-site surveys and principal component analysis identified 2013-2014, 2015-2018 and 2019-2022 as distinct periods in the Pipi fishery. Results corroborated studies and anecdotal information that suggested declining availability and higher prices of local, commercially caught Pipi, and reduced imports of bivalves from Asia that previously supplied the South Australian bait market. Reduced availability and higher prices of Pipi likely motivated recreational fishers to gather their own bait to increase catch over the years. Similarly, increased internet and smartphone access and increased numbers of utility vehicles aided recreational catch efficiency of Pipi. Effective management of recreationally harvested resources requires understanding of external processes that drive fisher motivations and capabilities, particularly for stocks that are shared among fisheries. The need for improved data on fisher behaviour for management of recreational fisheries can be addressed by leveraging external information from available datasets. We recommend that the temporal gap between surveys should be less than 5 years, supplemented by analysing behavioural information collected from fishers during interviews.

Exploited abalone (genus Haliotis) populations are prone to serial depletion and stock collapse. Spatial management units (MUs) aim to separate monitoring and management of meta-populations with varying productivity. In the South Australian Southern Zone blacklip abalone (Haliotis rubra rubra, Leach) fishery, spatial terms at scales of kilometres (reporting areas, RAs) and tens of kilometres (MUs) explained a greater proportion of variability in daily catches than effort in linear mixed models. Temporal patterns in spatial structures of catches among RAs were consistent with those among MUs based on similar productivity. Results of this study support the hypothesis that changes in the spatial distribution of catches differs among management regimes based on minimum legal lengths (MLLs) and annual total allowable commercial catches (TACCs). Stable distribution of catches during 1992-2012 occurred contemporaneously with zonal TACCs combined with catch caps (sub-TACCs) and MLLs applied to areas of low productivity providing a reference for future management. The number of MUs fished annually by each licence increased during this period. Results of this study suggest that successful spatial management of abalone fisheries requires MUs at scales based on biological productivity combined with MLLs and mandatory, conservative catch caps applied to each MU.

This study aimed to determine if population dynamics and demography of the sandy beach bivalve, Donax deltoides, varied under different levels of biomass. To achieve this, population parameters for D. deltoides in south-eastern Australia were compared across a range of spatial and temporal scales during periods of low-moderate and high relative biomass. Estimates of relative harvestable biomass were lower in 2008–12 (2.3 ± 0.03 kg m2), compared to 2013–17 (3.7 ± 0.11 kg m2; P < 0.001), and also differed among years (P < 0.001), and 3 month periods within years (P < 0.001), although there was no difference between repeated days. Relative biomass also varied across six, 10 km sections of the 60 km study area with the central third of the study area relatively stable among years and the north-western and south-eastern thirds more variable. Mean and maximum length of D. deltoides varied across temporal and spatial scales similar to those of relative biomass. Growth performance in 2008–12 (φ’ = 3.32) was higher than that in 2013–17, (φ’ = 2.99) although the difference was not statistically detectable (P > 0.05). Instantaneous mortality (Z) also differed between 2008–12 and 2013–17 (P < 0.05). High relative biomass in 2013–17, following successive years of successful recruitment, occurred contemporaneously with decreased growth performance and likely suppression of subsequent recruitment, suggesting possible density dependence and growth over-compensation. Reduced growth rates under higher relative biomass imply that attainment of sexual maturity may be delayed, or alternatively maturity may occur at a smaller size, both of which have implications for individual lifetime egg production. Improved understanding of population dynamics, demography and exploitation patterns across a range of temporal and spatial scales has important implications for implementation of spatially explicit management.

Mulloway (Argyrosomus japonicus) are an iconic recreational, indigenous, and commercial fishery species with declining numbers across some parts of their range, with relatively little known about their movements. During the Austral summers and autumns from 2011 to 2014, we deployed 19 pop-up satellite archival tags (PSATs) on mature mulloway at an aggregation site within the Great Australian Bight Marine Park (GABMP), to examine their movement patterns. Twelve tags provided data from deployments ranging from 8 to 110 days including five tags that gathered data over autumn and seven over summer. Five of the seven mulloway tagged during summer likely remained in the vicinity of the tagging location and hence within or in close proximity to marine-protected areas (MPAs) over summer; however, relatively large horizontal movements were observed over autumn for most fish, including a maximum net displacement of ~ 550 km. The median pop-up distance from deployment was 51 and 212 km for summer-and autumn-tagged fish, respectively. Depths encountered by the tagged mulloway ranged from the surface to 56.5 m deep. Our study provides new information on the dispersal of a poorly understood fish species which could aid their conservation.

The sensitivity of species to environmental change is dependent on their ecological requirements (i.e. specialist v. generalist), and hence likely to be species-specific. Identifying species level variation in environmental sensitivity informs assessments of community vulnerability and assists in developing adaptive management strategies. We investigated species-specific sensitivity in fish to understand the vulnerability of differing life histories and ecological requirements to rapid environmental alteration (i.e. drought). Biochronologies of fish growth, based on increment widths in otoliths, were analysed using a mixed modelling approach. We assessed multi-decadal responses in fish growth to environmental variation in the terminal system of Australia's largest river, for three long-lived fish species with differing life histories and ecological requirements: a freshwater specialist and two estuarine generalists. Biochronologies were between 20 and 38 years long, spanned a decade of severe drought and showed considerable inter-annual variation in growth. Precipitation influenced the growth of the obligate freshwater specialist, Macquaria ambigua ambigua. Temperature and salinity influenced the growth of the two estuarine generalists: Argyrosomus japonicus (estuarine opportunist) and Acanthopagrus butcheri (estuarine dependent), respectively. These results suggest that generalisations about how species respond to environmental change may mask species-specific responses to dependent on the constraints of their ecological requirements (i.e. specialist v. generalist). These findings also highlight the importance of considering the diversity of life history strategies that inhabit an ecosystem when developing conservation and management strategies. (C) 2016 Elsevier Ltd. All rights reserved.

Population structure in marine teleosts is often investigated to aid conservation and fisheries management (e.g. to assess population structure to inform restocking programs). We assessed genetic population structure of the important estuary-associated marine fish, mulloway (Argyrosomus japonicus), within Australian waters and between Australia and South Africa. Genetic variation was investigated at 13 polymorphic microsatellite markers. FST values and Bayesian estimates in STRUCTURE suggested population differentiation of mulloway within Australia and confirm strong differentiation between South Africa and Australia. The 12 Australian sample sets fell into one of four spatially separated genetic clusters. Initially, a significant signal of isolation-by-distance (IBD) was evident among Australian populations. However, further investigation by decomposed-pairwise-regression (DPR) suggested five sample sets were influenced more by genetic-drift, rather than gene-flow and drift equilibrium, as expected in strong IBD cases. Cryptic oceanographic and topographical influences may isolate mulloway populations from south-western Australia. The results demonstrate that DPR is suitable to assess population structure of coastal marine species where barriers to gene flow may be less obvious than in freshwater systems. Information on the relative strengths of gene flow and genetic drift facilitates a more comprehensive understanding of the evolutionary forces that lead to population structure, which in turn informs fisheries and assists conservation management. Large-bodied predatory scale-fish may be under increasing pressure on a global scale, owing to a variety of anthropogenic reasons. In southern Australia, the iconic sciaenid A. japonicus (mulloway, jewfish or kob) is no exception. Despite the species supporting important fisheries, much of its ecology is poorly understood. It is possible that a greater understanding of their genetic population structure can help ensure a sustainable future for the only southern Australian sciaenid.

Anthropogenic modification of catchments and river flow can significantly alter estuarine habitats, hydrology and nutrient delivery with implications for fisheries productivity. The Coorong estuary at the terminus of Australia's River Murray supports an economically important fishery as well as being recognised internationally as a critical site for migratory birds. Salinity near the Murray Mouth varies between fresh and marine depending upon river flow, but the Coorong becomes increasingly saline along its 120 km length. Freshwater flow to the Coorong is naturally variable but has significantly reduced by extraction for irrigated agriculture and domestic use upstream. Extreme drought from 2000 to 2010 and over-allocation of water resources resulted in the cessation of freshwater flow to the Coorong, significantly increasing salinity. During this period the diversity and abundance of organisms in the Coorong declined which reduced food web complexity. During lower flows the system generally becomes less productive as evidenced by: lower nutrient concentrations and loads, lower chlorophyll and primary productivity, a decrease in the abundance of fish-prey items (zooplankton, macroinvertebrates and small fish), a decrease in fish abundance, although this is not well reflected in fishery catch data because of the concentration of fishing in available habitat. The maintenance of flow is the only management strategy that stimulates recruitment, delivers nutrient resources to the estuary and ensures maintenance of habitable area by maintaining appropriate salinity.

Estimates of biomass or relative biomass are required for monitoring the recovery of depleted bivalve resources and for the management of newly exploited resources. Uncertainty around fishery catch per unit effort (CPUE) as a proxy for biomass highlights the need for fishery-independent assessments. Following a prolonged period of decline in Australia's largest fishery for surf clam Donax deltoides, robust estimates of biomass were required to monitor recovery and to set appropriate total allowable commercial catches. Estimates of relative biomass were derived from fishery-independent surveys (FIS) conducted cooperatively by researchers and fishers. The FIS assessed both the spatial (m to km) and temporal (months to years) dynamics of the fishery and enabled comparisons with CPUE. Concurrent size-frequency distributions provided information on the mechanisms underlying variability in resource status across the fishery. Increasing relative biomass and complexity of size structures indicated recovery of the resource from 2009, although spatial contraction of the resource also occurred. Relative biomass from FIS provides a robust fishery performance indicator that is appropriate to the scale of the fishery and has advantages over fishery-dependent CPUE of finer temporal and spatial resolution and consistent sampling efficiency. Performance indicators based on FIS provide improved understanding of the changes in resource status. Active engagement of fishers contributes to enhanced economic and environmental outcomes.

The life-history of the sciaenid Argyrosomus japonicus in South Australia was investigated to inform a review of fisheries management. Validated, otolith-based growth coefficients for females (Linf=1430.52, K=0.137, t0=−0.303, n=209) and males (Linf=1356.23, K=0.159, t0=0.000, n=185) suggested high asymptotic size and low growth rates, relative to other populations. A growth performance index (ω) was lower for A. japonicus in South Australia than for other populations. Sizes at 50 and 95% maturity (SAM50,95) were 850 and 1028mm TL, respectively for females and 778 and 923mm TL, respectively for males. Age structures from 2011 appeared truncated compared to those from 2001 and 2002 with no individuals greater than 10 years old. The dominant year class observed in age structures from 2001 and 2002 was not present in 2011. This may reflect the combined effects of historically severe drought from 2002 to 2010 and fishing. This population is vulnerable to fishing as juveniles in estuarine habitat and as adults in spawning aggregations in marine habitat. Loss of protected estuarine habitat for juveniles from flow regulation and drought may make this population particularly vulnerable to overfishing. Whilst maintenance of appropriately timed freshwater inflows to estuarine habitat is important for this population their availability is uncertain. Populations of A. japonicus in South Australia would benefit from management measures that: (i) aim to preserve capacity for egg production; (ii) allow recruits to enter the adult population; and that (iii) rebuild and maintain long-tailed age structures. Amendments to the legal minimum size and the protection of juveniles in estuaries and the adult spawning/feeding aggregations are recommended.

We analysed a 25-year time series of fishery catch and effort data, and age/size information for four large-bodied, native fish species to investigate the hypotheses that under conditions of reduced freshwater inflows and high fishing pressure: (1) the structure of fish assemblages in the lower Murray River system have changed, (2) species diversity of fishes has declined and (3) population age structures of large-bodied, late-maturing, native fish ( Macquaria ambigua , Argyrosomus japonicus , Rhombosolea tapirina and Acanthopagrus butcheri ) have been reduced. Annual catches and effort in the lower Murray River system were stable for 25 years, but proportional contribution to the total catch from each of freshwater, estuarine and adjacent marine habitats, and the species within them varied. Fish assemblages generally differed between subsequent 5-year periods, with the exception of 1989–1993 when floods occurred in 4 out of 5 years, and the following 5-year period (1994–1998). Species richness declined steeply over 25 years in freshwater and estuarine habitat and species diversity (Hill’s H 2 ) also declined after 2001 in estuarine habitat. Species with rapid growth and early maturation (opportunistic strategists), increasingly dominated catches, whilst species with slow growth and late maturation (periodic strategists) declined. Truncated population age structures suggested longevity overfishing of three periodic strategist species: golden perch ( M. ambigua ), black bream ( A. butcheri ), mulloway ( A. japonicus ) and a fourth species with an intermediate strategy, greenback flounder ( R. tapirina ). This has implications for management because loss of older/larger individuals suggests reduced capacity to withstand or recover from deteriorated environmental conditions associated with a historically extreme drought in the lower Murray River system. Management of these species should seek to preserve the remnant population age structures and then to rebuild age structures by allowing recruits to become established in the adult population. We recommend that assessment of multi-species fisheries in changeable environments, such as occur in estuaries and other end-river environments, requires a suite of indicators that address changes in fish assemblages and populations.

Otolith based methods have the potential to discriminate between stocks, an important requirement for sustainable management of fish. The abilities of two otolith based methods to investigate stock structure of the sciaenid Argyrosomus japonicus in South Australia were compared: (i) elemental signatures (Sr:Ca, Ba:Ca, and Mg:Ca) from the otolith edge, and (ii) shape characteristics (otolith morphometrics and overall shape) of whole otoliths. Comparison of elemental signatures indicated that Ba:Ca levels were low in the western coast, intermediate in the central coast and high in the eastern coast. Constrained Canonical Analysis of Principal Coordinates (CAP) allocated elemental concentrations of individual otoliths to regions with 100, 100, and 87% success for western, central and eastern coasts respectively. Otolith shape (elliptical Fourier descriptors and morphological indices) supported results from the elemental study with allocation success of 85, 57, and 85% for western, central and eastern coasts respectively. Shape analysis was then used to investigate the origin of individuals caught in marine waters but suspected of being from an aquaculture facility. The two stock discrimination methods were complementary because trace-element analysis of the otolith edge provided very high classification success and gave a snapshot of differences between groups from different geographic areas, while shape analysis indicated that these discrete groups of fish experienced different environmental conditions over a long period of time. Results from this study highlight the importance of multiple methods in stock discrimination and suggest sub-structuring of the stock of A. japonicus in South Australia, (C) 2011 Elsevier B.V. All rights reserved.

We analysed a 25 year time-series of fishery catch and effort data, and age/size information for four large-bodied, native fish species to investigate the hypotheses, that under conditions of reduced freshwater inflows and high fishing pressure; (i) the structure of fish assemblages in the lower River Murray system have changed, (ii) species diversity of fishes has declined, and (iii) population age structures of large-bodied, late-maturing, native fish have been reduced. Annual catch and effort in the lower Murray River system were stable for 25 years but proportional contribution from each of freshwater, estuarine and adjacent marine habitats, and the species within them, varied. Fish assemblages generally differed between` subsequent 5-year periods, with the exception of 1989-93 when floods occurred in 4 out of 5 years, and the following 5-year period (1994-98). Species richness declined steeply over 25 years in freshwater and estuarine habitat and species diversity (Hill’s H2) also declined after 2001 in estuarine habitat. Species with rapid growth and early maturation (opportunistic strategists), increasingly dominated catches while species with slow growth and late maturation (periodic strategists) declined. Truncated population age structures suggested longevity overfishing of three periodic strategist species; golden perch (Macquaria ambigua), black bream (Acanthopagrus butcheri), mulloway (Argyrosomus japonicus), and a fourth species with an intermediate strategy, greenback flounder (Rhombosolea tapirina). This has implications for management because loss of older/larger individuals suggests reduced capacity to withstand, or recover from deteriorating environmental conditions as the lower Murray River system experiences historically extreme drought. Management of these species should seek to preserve the remnant population age structures, then to rebuild age structures by allowing recruits to become established in the adult population. We recommend that assessment of multi-species fisheries, in changeable environments, such as occur in estuaries and other end-river environments requires a suite of indicators that address changes in fish assemblages and populations.

The foraging behaviour. territory size and diet of the scalyfin, Parma victoriae, were studied at three sites in South Australia. Two sites were in Ecklonia habitat on an exposed coast, one of them, Site 1, in a marine reserve at West I., and the other, Site 2, in an intensely fished area at The Bluff, Victor Harbor. The third, Site 3, was sheltered, in a fucoid community in Groper Bay, Flinders I., in the eastern Great Australian Bight. The algal food supply was highest at the reserve site (1) and lowest at the sheltered site (3). The scalyfin spent a greater proportion of time foraging, and a lower proportion of time sheltering, at the reserve site (1), than at the Bluff site (2). At Site 3, territories were about seven times larger than at the other two sites, and fish spent a higher proportion of time in defence and aggressive interactions than at the other sites. The diet at all sites was predominantly browsed rhodophytes, but at Site 3 the rhodophytes eaten were almost entirely epiphytic on fucoid algae and in low abundance. At the exposed sites (1, 2), where food algae were patchy, scalyfin removed Ecklonia sporophytes experimentally placed in their territories, but not at Site 3, dominated by fucoids. At the exposed sites they employed a saltatory foraging mode, whereas at Site 3 they adopted a cruise search foraging behaviour over their larger territories. Both modes seem optimal in their respective habitats.