Modelling the advection of vertically migrating shrimp larvae

The role of larval advection in determining the complex, large-scale patterns of immigration of penaeid postlarvae in the Gulf of Carpentaria is investigated by modelling the interaction between diurnal vertical migration of larvae with wind-forced and tidal currents. Eight vertical migration schemes are modelled in which both the timing of the migration and the position of the larvae in the water column are varied. These schemes are then coupled with both two-dimensional and three-dimensional models of the currents of the Gulf, to examine horizontal advection of larvae. When the larvae migrate vertically with a diurnal period, their horizontal advection is enhanced. The largest horizontal advection distances occur when the larvae move diurnally from the water column into the bottom boundary layer. Advection distances of up to 165 km are possible during the two to three week planktonic larval period. This distance corresponds to, and may determine, the offshore extent of the adult distribution. The onshore advection pattern of larvae varies in both space and time (on a seasonal scale) and is consistent with the observed spatial and temporal recruitment patterns seen by sampling postlarval immigation into nursery areas. During the period of highest reproductive activity (March) in the southeastern corner of the Gulf, the area of the largest fishery, the advection of larvae is offshore and little recruitment of postlarvae to the nursery grounds is accomplished. Six months later, during the next period of reproductive activity (October), when the number of spawning female shrimp is much lower, the phase of the tidal currents, relative to the day-night cycle, has progressed 180° and the larvae are moved onshore allowing postlarvae access to their estuarine nursery grounds several months prior to the main fishing season (March)

Qualitative mathematical models to support ecosystem-based management of Australia's Northern Prawn Fishery

A major decline in the catch of the banana prawn [shrimp], Penaeus (Fenneropenaeus) merguiensis, occurred over a six-year period in the Weipa region of the northeastern Gulf of Carpentaria, Australia. Three main hypotheses have been developed to explain this decline: (1) prawn recruitment collapsed due to overfishing; (2) recruitment collapsed due to a change in the prawn's environment; and (3) adult banana prawns were still present, but fishers could no longer effectively find or catch them. Qualitative mathematical models were used to link population biology, environmental factors, and fishery dynamics to evaluate the alternative hypotheses. This modeling approach provides the means to rapidly integrate knowledge across disciplines and consider alternative hypotheses about how the structure and function of an ecosystem affects its dynamics. Alternative models were constructed to address the different hypotheses and also to encompass a diversity of opinion about the underlying dynamics of the system. Key findings from these analyses are that: instability in the system can arise when discarded fishery bycatch supports relatively high predation pressure; system stability can be enhanced by management of fishing effort or stock catchability; catch per unit effort is not necessarily a reliable indicator of stock abundance; a change in early-season rainfall should affect all stages in the banana prawn's life cycle; and a reduced catch in the Weipa region can create and reinforce a shift in fishing effort away from Weipa. Results from the models informed an approach to test the hypotheses (i.e., an experimental fishing program), and promoted understanding of the system among researchers, management agencies, and industry. The analytical tools developed in this work to address stages of a prawn life cycle and fishery dynamics are generally applicable to any exploited natural resource

An epibenthic sampler used to study the ontogeny of vertical migration of pandalus dordani (Decapoda caridea)

Pandalis jordani Rathbun, like many other species of pandalid shrimps, undergo regular diel changes in their vertical distribution (Tegelberg and Smith 1957; Alverson et al. 1960; Pearcy 1970, 1972; Robinson in press). Little is known, however, about the vertical distribution and diel migrations of larval and juvenile shrimp, or at what stage of the life history vertical migration and benthic existence are initiated

A database of chlorophyll a in Australian waters

© The Author(s) 2018. Chlorophyll a is the most commonly used indicator of phytoplankton biomass in the marine environment. It is relatively simple and cost effective to measure when compared to phytoplankton abundance and is thus routinely included in many surveys. Here we collate 173, 333 records of chlorophyll a collected since 1965 from Australian waters gathered from researchers on regular coastal monitoring surveys and ocean voyages into a single repository. This dataset includes the chlorophyll a values as measured from samples analysed using spectrophotometry, fluorometry and high performance liquid chromatography (HPLC). The Australian Chlorophyll a database is freely available through the Australian Ocean Data Network portal (https://portal.aodn.org.au/). These data can be used in isolation as an index of phytoplankton biomass or in combination with other data to provide insight into water quality, ecosystem state, and relationships with other trophic levels such as zooplankton or fish

Larval growth and survival optima for four species of penaeids from Australia, as indicated by their distribution and abundance in the field

Abstract only.Prawn catches from tropical northern Australia are dominated by four species of prawns: Penaeus merguiensis, P. semisulcatus, P. esculentus and P. latisulcatus. Three of the species (P. merguiensis, P. semisulcatus and P. latisulcatus) are widespread throughout the Indo-Pacific, while P. esculentus is endemic to northern and eastern Australia. The species appear, however, to have well defined and limited distribution on a smaller scale. Surveys of the larvae in the Gulf of Carpentaria, northern Australia, have shown both spatial and temporal heterogeneity in the abundance of all four of these species. Assessing the temperatures and salinities in which the larvae were caught may be a realistic indicator of conditions suitable for reproduction, as well as growth and survival of the larvae. Means of these distributions may be deemed optima and ranges indicate tolerances. Most of the larvae of all four species are found in water above 26°C and 31 ppt. However, the mean temperatures and salinities vary significantly between species. P. merguiensis has the lowest salinity optimum (31.8 ppt) and the highest temperature optimum (29.0°C). the other three species are similar for both temperature and salinity optima. P. latisulcatus has the lowest temperature optimum of 27.4°C compared with P. semisulcatus at 27.9°C and P. esculentus at 28.5°C. The salinity optima for these three species are almost indentical at approximately 33.2 ppt. While the ranges of temperatures of all four species are similar (21.5-30.6°C), the ranges of salinities in which the lar-vae are found coincide with the size of the biogeographic distribution of the species. The three widespread species have large salinity ranges: P. merguiensis, 26.2-34.9 ppt P. semisulcatus, 27.8-34.9 ppt: and P. latisulcatus, 28.6-34.9 ppt. The Australian endemic, P. esculentus, has the smallest and highest range, 30.1-34.6 ppt. This apparent inability of P. esculentus to tolerate low salinity water may restrict dispersal during the larval stages