The blue swimmer crab (BSC, Portunus armatus) is an economically and culturally important species distributed throughout the coastal waters of the Indo-Pacific region. Reproduction of BSC is poorly understood in southeastern Australia, a region that is experiencing substantial tropicalisation from global warming. We examined gonadal development, egg-mass relationships, and the influence of temperature on gonadal development and egg production within five different estuaries spanning ,2.58 of latitude. A negative correlation between the gonadosomatic index (GSI, an index of gonadal development and reproductive investment) and hepatosomatic index (HSI, an index of energy storage) was observed in only the final stages of ovarian development. The weight of the egg mass increased logarithmically with body mass, accounting for up to 55% of total body mass, which was significantly larger than observed in other studies. Thermal performance curves showed a peak in individual reproductive output at a mean monthly temperature of ,248C, at which the individual egg mass weight reached a maximum and the HSI reached a minimum. Environmentally driven variation in BSC reproduction has implications for population productivity and inter-annual variation in recruitment.

1. Gillnets are used widely in fisheries throughout the world and known to cause the death of thousands of seabirds each year. Currently few practical or technical options are available to fishers for preventing seabird mortalities.2. The ability of little penguins (Eudyptula minor) to differentiate between different coloured netting materials was tested under controlled conditions to ascertain if changes in gillnet colour could facilitate a potential mitigation measure by improving visibility of nets.3. The study involved a repeated-measures design with penguins exposed to variously coloured mono-filament threads creating a gillnet mimic. The gillnet mimic was made up of gillnet material configured as a series of vertical lines 25 mm apart stretched tightly across a stainless steel frame that measured 1160 mm × 1540 mm and divided into two equal panel areas. The panels were placed in a large tank within an enclosure that housed 25 penguins. Penguins were able to readily access the tank and swim freely. The frame was always introduced into the tank with one panel containing a gillnet mimic, and the other panel left empty as a control.4. Gillnet filament colours tested were clear, green and orange. Orange coloured monofilament lines resulted in lower collision rates (5.5%), while clear and green monofilament lines resulted in higher rates of collision (35.9% and 30.8%, respectively). 5. These results suggest that orange-coloured lines were more apparent to the birds. Constructing nets of orange-coloured material may be effective in reducing bycatch in gillnets set in shallow waters and high light levels where seabirds are able to identify fine colour differences.6. Further testing under experimental conditions, accompanied with at-sea trials to verify effectiveness in varied light conditions is warranted, together with an assessment of the effect of gillnet colour on catch efficiency of target species.

Larval dispersal and connectivity have important implications for fisheries management, especially for species with life cycles influenced by ocean boundary currents.Giant Mud Crab (Scylla serrata) and Blue Swimmer Crab (Portunus armatus) are two estuarine portunid crabs (Family: Portunidae) that support significant commercial and recreational harvest in eastern Australia. Giant Mud Crab migrate to coastal waters to spawn, and while Blue Swimmer Crab spawn primarily within estuaries they occasionally migrate to coastal waters to spawn, followed by larval dispersal in the East Australian Current (EAC). Here, we coupled a high-resolution oceanographic model with a Lagrangian particle tracking framework to simulate larval dispersal and determine the extent of population connectivity in this region. Our simulations indicate broad-scale connectivity ($40-400 km), characterised by high inter-estuary connectivity. Overall, our results suggest a north-to-south source-sink structure for both species, with contributions of particles from the north ranging from 51% to 99%.Recruitment to a given estuary is dependent on the proximity of mesoscale oceanographic features of the EAC. Most notably, the EAC separation acts as a barrier to recruitment between spawning and settlement to the north/south of this region. This significantly limits interjurisdictional connectivity for these species, especially Blue Swimmer Crab, likely due to a shorter pelagic larval duration than Giant Mud Crab.Our results provide evidence to inform the assessment and management of these species.