Jan-Olaf Meynecke

Life-history, movement, and habitat use of Scylla serrata (Decapoda, Portunidae): current knowledge and future challenges

The mud crab Scylla serrata is a highly exploited species, associated to mangrove ecosystems in the Indo-West-Pacific. It has a complex life cycle with a dispersing larvae phase, and benthic juveniles and adults. The former are stenohaline depending on high-salinity conditions to survive, whereas the latter are physiologically well adapted to changing temperatures and salinities, conditions that typically occur in mangrove habitats. Movement and habitat use of large juveniles and adults are well studied, and these life stages are known to utilize and move between various habitats within the mangrove ecosystem: intertidal flats as well as subtidal channels and flats. Females undertake long movements from brackish inshore waters to waters with oceanic conditions for spawning. Sensory abilities—of early stages and adult stages—have hardly been studied, and little is known about larval and early benthic stages in the wild. Summarizing, the literature revealed substantial gaps in the understanding of the spatiotemporal dynamics of the different life stages and of the clues that trigger recruitment, movement, and other behavior. This is the first comprehensive review on the life history, movement patterns, habitat use, and systemic role of S. serrata with emphasis on the respective life stages and geographic differences. We emphasize the need for further research into these processes as a basis for the sustainable management and conservation of this species.

Giant mud crab (Scylla serrata) catches and climate drivers in Australia – a large scale comparison

Patterns in the Southern Oscillation Index (SOI) affect the life history of many aquatic organisms in the southern hemisphere. We examined the effect of this phenomenon and other factors (i.e. rainfall, river flow and sea surface temperature, SST) on the commercial harvest of the giant mud crab (Scylla serrata) in Australia, given the large inter-annual variations in the catch of this species over the last 15 years, particularly in the north. Regression models were applied to concurrent environmental and catch data for giant mud crab caught from 29 catchments that provided a combined harvest of >20 000 tonnes. Non-metric multidimensional scaling (nMDS) was also used to explore potential regional differences in catch trends. A combination of SOI, SST and rainfall/river flow explained 30–70% of the variability in commercial catches, with mean summer temperature being most influential at higher latitudes. The nMDS revealed distinct groupings of river systems that coincided with biogeographic regions. This work highlights the importance of climatic events on the harvest of giant mud crabs and reinforces the need to adopt a bioregional approach when assessing the performance of fisheries targeting this species.

Filming and snorkelling as visual techniques to survey fauna in difficult to access tropical rainforest streams

Dense tropical rainforest, waterfalls and shallow riffle-run-pool sequences pose challenges for researcher access to remote reaches of streams for surveying aquatic fauna, particularly when using capture-based collecting techniques (e.g. trapping, backpack and boat electrofishing). We compared the detection of aquatic species (vertebrates and invertebrates >1 cm in body length) within pool habitats of a rainforest stream obtained by two visual techniques during both the wet and dry season: active visual survey by snorkelling and baited remote underwater video stations (BRUVSs). Snorkelling detected more species than a single BRUVS at each site, both within and among seasons. Snorkelling was most effective for recording the presence and abundance of diurnally active small-bodied species (adult size <150 mm total length), although both techniques were comparable in detecting large-bodied taxa (turtles, fish and eels). On the current evidence, snorkelling provides the most sensitive and rapid visual technique for detecting rainforest stream fauna. However, in stream sections dangerous to human observers (e.g. inhabited by crocodiles, entanglement, extreme flows), we recommend a stratified deployment of multiple BRUVSs across a range of stream microhabitats within each site.

Effect of climate parameters on mud crab (Scylla serrata) production in Australia

The speculation that climate change may impact on fish production suggests a need to understand how these effects influence fisheries catch on a broad scale. Mud crabs (Scylla serrata) are a highly valued commercial species and the demand as well as their catch rates have increased continuously over the past decade throughout Australia. Scylla serrata has lifecycles related to rainfall and temperature patterns but a quantification of the link is yet to be undertaken. The difficulty involved in explaining the effect of climate driven parameters arising from limited knowledge the species biology may be overcome by relating climate parameters with long-term catch data for specific regions. Transformed catch per unit effort (CPUE), freshwater flow, air temperature and sea surface temperature and catch time series for specific combinations of time intervals and estuaries have been explored using correlation analysis. Correlation of catches of mud crab catch (Scylla serrata) with rainfall suggests that rainfall and temperature thresholds exists and if exceeded can cause loss of production. This fishery may therefore be sensitive to effects of climate change. The most significant relationships between mud crab catch, rainfall and temperature were detected for South-East Australia with a trend to weaker relationships towards the north. However, catches lagged by 2 years in the tropical north showed a distinct relationship with freshwater flow events which was also supported by meta-analysis. This approach allowed a first evaluation of the consequences of environmental factors on mud crab fisheries, thus highlighting the need to develop further studies and forecast models to provide information for managing this fishery in the face of climate change.

Whale watch or no watch: the Australian whale watching tourism industry and climate change

Abstract Whale watching is a billion dollar industry worldwide. One of the most popular species for whale watching is the humpback whale (Megaptera novaeangliae). The migratory corridors, feeding, resting and calving sites which are used for whale watching may be influenced by changing ocean currents and water temperatures. Here, we used an innovative approach addressing the emerging issue of climate change on the whale watch industry. This involved participatory modelling using key stakeholders for the whale watching industry to develop a systems conceptualisation model for evaluating the potential effects of climate change based on a case study from the east coast of Australia. This participatory approach allowed us to identify the causal linkages (including feedback pathways) between different “Elements” of the system within which the whale watching industry operates. It also allowed us to integrate multiple drivers covering socio-economic and environmental aspects including climate change (e.g. temperature), policy (e.g. number of boats), ecology (e.g. number of whales) and socio-economics (e.g. number of tourists) to evaluate the changes in the overall system. We then developed a Bayesian belief network model from the systems conceptualisation on which stakeholders identified a priority issue (Profitability). Stakeholders provided the structure and the quantification of this model, and a sensitivity analysis was carried out to help identify important intervention points for the industry. Overall, our research illustrates how such a modelling process can assist local tourism operators and authorities in making rational management decisions within a holistic or systems-based framework and its approach is applicable to other regions.

Effect of environmental conditions on cetacean entanglements: a case study from the Gold Coast, Australia

Entanglement of marine mammals in fishing gear is recognised worldwide and is a continuous management concern. Gill-net entanglement data from the Queensland Shark Control Program (QSCP) on the Gold Coast, Australia, from 1990 to 2012 were analysed in the present study. Environmental drivers that may affect entanglements of humpback whales (Megaptera novaeangliae) and common dolphins (Delphinus delphis) were selected. M. novaeangliae entanglements coincided with their annual migration, with the greatest occurrences in September. D. delphis were mostly entangled from March to November, with the greatest occurrences in June. For both species, entanglements primarily occurred when the wave height was between 0.5 and 1.25m, the wave power was between 0 and 5kWm–1 and the wind speed was between 12 and 19kmh–1. M. novaeangliae entanglements were significantly more likely to occur in low rainfall (<6mmh–1), and D. delphis entanglements were more likely to occur during spring tides. There was a correlation between entanglements and the position of the East Australian Current’s (EAC) maximum velocity, with 73% of M. novaeangliae entanglements and 79% of D. delphis entanglements occurring when the EAC’s maximum velocity was west (shoreward) of its average position at 154°E. The present study provides the first set of possible management intervention targets associated with environmental conditions.