Peter C. Rothlisberg

Restocking and stock enhancement of marine invertebrate fisheries

1. Introduction 2. Restocking Initiatives 2.1 Giant Clams 2.2 Topshell 2.3 Sea Cucumbers 3. Stock Enhancement Initiatives 3.1 Scallops 3.2 Other Bivalves 3.3 Abalone 3.4 Queen Conch 3.5 Shrimps 3.6 Spiny Lobsters 3.7 Lobsters 3.8 Sea Urchins 4. Overview and Progress Towards a Responsible Approach 4.1 Restocking Initiatives 4.2 Stock Enhancement Initiatives 5. Lessons Learned 5.1 Lessons for Restocking 5.2 Lessons for Stock Enhancement 5.3 Lessons for both Restocking and Stock Enhancement 6. Management of Restocking and Stock Enhancement 6.1 Information to Evaluate the Need for Restocking 6.2 Management of Restocking 6.3 Information to Evaluate the Need for Stock Enhancement 6.4 Management of Stock Enhancement 6.5 Measures to Optimize Social and Financial Benefits of Restocking and Stock Enhancement 6.6 Independent Assessments 7. Other Important Considerations for all Initiatives 7.1 Measuring Success 7.2 Genetic Considerations 7.3 Disease risks 7.4 Other Environmental Impacts Conclusions 8.1 Achievements 8.2 The Responsible Approach 8.3 The Way Forward 8.4 Future Research 8.5 Summary Remarks Acknowledgements References Appendix

A mechanism for near-shore concentration and estuarine recruitment of post-larval Penaeus plebejus Hess (Decapoda, Penaeidae)

Vertical migratory behaviour of post-larval Penaeus plebejus Hess was monitored every 2 h for 96 h during both the full and new moon at three adjacent sites in south-east Queensland, Australia: in the mouth of the Nerang River; 2 km offshore (20 m depth); and 12 km offshore (50 m depth). Coastal currents were also measured at stations 4 and 17 km offshore. At the offshore sites, post-larval abundance peaked during the night. In the mouth of the estuary, peak abundances were variable but were always within 3–4 h of the start of the flood tide, regardless of day or night. Post-larval densities were 10–12 times greater in the mouth of the estuary than offshore. We suggest that this coastal concentration is caused by the post-larvae being trapped inshore by the tide once they become tidally active. Estimates of the effectiveness of this mechanism are consistent with the observations. The variability of the along-shore currents together with the varying distances between estuaries will result in a variable number of tidal cycles over which post-larvae can accumulate in the near-shore zone before being swept into an estuary on the flood tide. This variability is consistent with the observed differences in abundance between successive tidal cycles. The mechanism that initiates the movement of the post-larvae into the estuary may be a response to pressure changes. When the pressure change at the bottom becomes a significant fraction of the total pressure, we suggest that post-larvae change from a diurnal vertical-migration pattern to a tidal vertical migration. This mechanism explains how post-larvae can enter nursery grounds without sensing horizontal gradients in estuarine properties such as salinity. Current speeds and post-larval age estimates were used to calculate across-shelf and along-shore advective trajectories and thereby estimate the proximity of effective spawning areas to nearby nursery grounds. The importance of near-shore spawning, limited advection, and local recruitment may have been underestimated in research on long-distance larval advection and adult migrations of P. plebejus.

Natural diet of larval Penaeus merguiensis (Decapoda : Penaeidae) and its effect on survival

The relationship between Penaeus merguiensis protozoea larvae and their phytoplankton diet was examined using seasonal plankton surveys and in situ rearing experiments. Larval abundance, phytoplankton community structure, and chlorophyll a concentration in Albatross Bay, Gulf of Carpentaria, were monitored monthly for 2 yr. Larval abundance peaked in November (spring) and March (autumn), at which times diatoms were the most abundant group in net samples of phytoplankton and in the guts of larvae. During November 1989 and March 1990, larvae were reared in nylon mesh enclosures positioned throughout the water column at three depths: 0 to 3 m, 3 to 6 m and 6 to 9 m. Overall, larval survival and gut fullness were both higher in November than in March. In both months, larval survival was lower at the surface than at other depths. This correlated with lower chlorophyll a concentrations, but lower total cell densities were not detected. During the in situ experiments, diatoms were the most abundant phytoplankton group in the water column and in the guts of larvae and, therefore, appeared to be the principal diet of larvae. Pigment analysis demonstrated that while gut contents generally reflected the composition of the phytoplankton community, the larvae were not feeding exclusively on diatoms. They also ingested green algae and possibly seagrass detritus. The in situ experiments demonstrated that the predominantly diatom flora in Albatross Bay can provide a nutritionally adequate environment for prawn larvae even at seasonally low levels. It is unlikely, therefore, that starvation is a major cause of mortality of P. merguiensis larvae during either of the biannual peaks in their abundance in Albatross Bay, Gulf of Carpentaria.

Sources of nutrients driving production in the Gulf of Carpentaria, Australia: a shallow tropical shelf system

The tropical Gulf of Carpentaria, Australia, has recently been identified as one of the world’s least impacted marine areas, presenting a unique opportunity to understand the nutrient drivers of productivity. The present study examined the nitrogen (N) sources and transformations in this pristine area and the role of N in fuelling primary productivity, principally based on summer data. The N budget estimates on a whole-of-Gulf basis suggest that river N inputs are unlikely to be major contributors to primary productivity. In the deeper waters of the Gulf, beyond the coastal boundary current, the main source of N is estimated to be N fixation by cyanobacteria, principally the abundant genus Trichodesmium. The present study measured high N fixation rates and depleted δ15N–N ratios in the particulate matter in the water column during a summer bloom. During summer, bottom N concentrations increased and δ15N–N ratios were depleted, suggesting that benthic mineralisation is occurring. It is therefore likely that detrital material from N-rich Trichodesmium is an important contributor to benthic processes. During winter, wind-driven mixing results in N from the bottom waters reaching the euphotic zone, and fuelling primary productivity. Therefore, Trichodesmium has an important direct and indirect role in contributing to primary productivity in this pristine tropical ecosystem.

SPECIFIC IDENTIFICATION AND ASSESSMENT OF DISTRIBUTION AND ABUNDANCE OF EARLY PENAEID SHRIMP LARVAE IN THE GULF OF CARPENTARIA, AUSTRALIA

Methods for obtaining eggs and rearing larvae ofpenaeid shrimp at sea, in remote areas, were developed and used to build a comprehensive larval reference collection for taxonomic purposes. Because of the large amount of morphological variation within species and character overlap between species, a multivariate numerical identification technique, discriminant analysis, was tested using larvae of the four speciesofPenaeus:p. esculentus;P. latisulcatus; P. merguiensis; and P. semisulcatus, in our reference collection. The overall accuracy of the technique is high (>85%) and can be increased by narrowing the range of natural morphological variation considered, at the expense of decreasing the number of larvae positively identified. Application of the technique to the first zoeal larvae in our plankton collections from the Gulf of Carpentaria, Australia, shows discrete, discontinuous larval dis tributions which delimit the spawning activity of the four species to a degree not possible by sampling and histological examination of the adult shrimp.

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 prawns 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 prawns 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.

A Complete Larval Description of Pandalus Jordani Rathbun (Decapoda, Pandalidae) and Its Relation To Other Members of the Genus Pandalus 1)

[Eine vollstandige Beschreibung der Larvenstadien von Pandalus jordani Rathbun wird anhand der im Labor gezuchteten Exemplare als auch von weit von der Oregonkuste (in den Vereinigten Staaten von Nordamerika) eingesammelten Planktonsammlungen, gegeben. Diese Beschreibung wird mit einem vorangehenden, unvollstandigen Bericht verglichen. Einflusse des niedrigen Grades der Entwicklung auf die Ausschlupfung und auf die grosse Zahl der Larvenstadien von P. jordani werden diskutiert und mit anderen Arten der Gattung verglichen. Eine mogliche Beziehung zwischen Variationen in der Geschichte des Larvenlebens und der geographischen Verteilung der Gattung wird untersucht., Eine vollstandige Beschreibung der Larvenstadien von Pandalus jordani Rathbun wird anhand der im Labor gezuchteten Exemplare als auch von weit von der Oregonkuste (in den Vereinigten Staaten von Nordamerika) eingesammelten Planktonsammlungen, gegeben. Diese Beschreibung wird mit einem vorangehenden, unvollstandigen Bericht verglichen. Einflusse des niedrigen Grades der Entwicklung auf die Ausschlupfung und auf die grosse Zahl der Larvenstadien von P. jordani werden diskutiert und mit anderen Arten der Gattung verglichen. Eine mogliche Beziehung zwischen Variationen in der Geschichte des Larvenlebens und der geographischen Verteilung der Gattung wird untersucht.]

Impacts of gold mine waste disposal on a tropical pelagic ecosystem

We used a comparative approach to investigate the impact of the disposal of gold mine tailings into the ocean near the Lihir mine (Niolam Island, Papua New Guinea). We found abundance and diversity of zooplankton, micronekton and pelagic fish to be similar or higher in the mine region compared to the reference site. We also found relatively high trace metal concentrations in lower trophic level groups, especially zooplankton, near the mine discharge, but few differences in tissue concentrations of micronekton, baitfish and pelagic fish between the two regions. Biomagnification of some trace metals by micronekton, and of mercury by fish was evident in both regions. We conclude that ocean mine waste disposal at Niolam Island has a local impact on the smaller and less mobile pelagic communities in terms of trace metal concentrations, but has little effect on the abundance and biodiversity of the local food web.

Over 75 years of zooplankton data from Australia

Zooplankton are the key trophic link between primary producers and fish in pelagic ecosystems. Historically, there are few zooplankton time series in Australia, with no data sets longer than two years prior to 2008. Here we compile 98 676 abundance records of more than 1000 zooplankton taxa from unpublished research cruises, student projects, published literature, and the recent Integrated Marine Observing System (IMOS). This data set covers the entire coastal and shelf region of Australia and dates back to 1938. Most records are for copepods, but there are also data for other taxa such as decapods, chaetognaths, thaliaceans, appendicularians, and cladocerans. Metadata are provided for each record, including dates, coordinates, and information on mesh size and sampling methods. To facilitate analysis across the multiple data sets, we have updated the species names according to the World Register of Marine Species (WoRMS) and converted units to abundance per cubic meter. These data will be valuable for studies of biodiversity, biogeography, impacts of climate change, and ecosystem health. We encourage researchers holding additional Australian zooplankton data to contact us and contribute their data to the data set so we can periodically publish updates.

Preventing Genetic Pollution and the Establishment of Feral Populations: A Molecular Solution

Aquaculture animals that escape from farms have the potential to create major environmental problems. These include establishment of potentially destructive feral populations (e.g., Pacific oysters [Crassostrea gigas] in Australia, Atlantic salmon [Salmo salar] in British Columbia) and genetic contamination of wild stocks. The latter includes introgression of foreign genes into natural populations from both hatchery-reared fish and genetically modified fish and invertebrates. Concern about these environmental and genetic effects has already led to restrictions on aquaculture industry development and is likely to grow as demand for genetically improved stocks escalates to fulfill production objectives. To circumvent these problems, we have developed a genetic construct that, when properly integrated into production-line fish or invertebrates, should render individuals functionally sterile outside of hatchery conditions. In the hatchery, however, provision of a simple repressor compound at a particular life-history stage allows the animals to be bred and reared as normal. We Theresa M. Bert (ed.), Ecological and Genetic Implications of Aquaculture Activities, 103–114. 2007 Springer. 103 are developing this ‘‘Sterile Feral’’ technology for both invertebrate and fish species, and we anticipate practical commercial application within a few years.