Nicole Flint

Electronic Tagging Data Supporting Flexible Spatial Management in an Australian Longline Fishery

Despite widespread claims for the importance of electronic tagging and the resulting data for improved management of fished species, there are few examples where this has occurred. In this contribution we describe how pop-up satellite archival tagging data have been incorporated into a habitat prediction model to support spatial management in an Australian longline fishery, specifically through reduction of unwanted bycatch of a quota-managed species, southern bluefin tuna (SBT, Thunnus maccoyii). This model, and its practical application, has evolved over time (2002-present), due to the successful cooperation between scientists, fishery managers and stakeholders. To illustrate this example of successful use of tag data in management, we review the appropriate biology of SBT and its’ interaction with the fishery, the management challenge that tagging and the habitat model helped resolve, and how this approach has been implemented. Discussion of the management costs associated with this management system shows that fine-scale spatial management is a suitable approach for this bycatch issue. We conclude with some general lessons for the application of flexible spatial management approaches, based on management and science constraints.

Sublethal effects of fluctuating hypoxia on juvenile tropical Australian freshwater fish

Hypoxia in freshwater ecosystems of the Australian wet tropics occurs naturally, but is increasing as a result of anthropogenic influences. Diel cycling of dissolved oxygen (DO) concentration (fluctuating hypoxia) is common in the region. Laboratory experiments sought to identify relationships between severity of fluctuating hypoxia and sublethal effects on ventilation, feeding and growth for juvenile barramundi (Lates calcarifer), eastern rainbowfish (Melanotaenia splendida splendida) and sooty grunter (Hephaestus fuliginosus). Fish continued to feed and grow under daily exposure to severe fluctuating hypoxia treatments for several weeks. Ventilation rates increased in a significant direct quadratic relationship with the severity of hypoxia treatments and increasing hypoxia caused ventilatory behaviour changes in all species. Barramundi and rainbowfish attempted aquatic surface respiration and were more tolerant of severe hypoxia than was sooty grunter; barramundi and rainbowfish are also more likely to experience hypoxia in the wild. There was a significant quadratic relationship between growth and minimum DO saturation for barramundi. Although all three species were tolerant of hypoxia, anthropogenic stressors on tropical Australian aquatic ecosystems may increase the frequency and severity of hypoxic conditions causing a concomitant increase in fish kill events.

Reproduction and embryo viability of a range-limited tropical freshwater fish exposed to fluctuating hypoxia

Hypoxia can profoundly affect fish reproduction and larval development, but its effects on fish from tropical Australia are not well understood. In the present study, the effects of diel fluctuating hypoxia on reproduction and embryo viability were investigated for a range-limited tropical freshwater fish, namely the Utchee Creek rainbowfish (Melanotaenia utcheensis). The lethal level for adult rainbowfish after gradual oxygen depletion was ~7% dissolved oxygen (DO) saturation. After 28 days, the reproductive success of adult fish exposed to fluctuating hypoxia treatments was measured by fecundity, gonad health, egg incubation time, egg and larval mortality, viability and size of hatching larvae. Reproduction was impaired in the lowest sublethal treatment (minimum 10% DO saturation each day). No ill effects of parental exposure to diel fluctuating hypoxia on embryos were identified, and minor differences in temperature between aquaria had a greater effect on embryos than parental hypoxia treatments. Similarly, no effects of embryonic exposure to diel fluctuating hypoxia were identified. Utchee Creek rainbowfish appear to be more hypoxia tolerant than temperate species, in keeping with their habitat in warm lowland streams, but they are still susceptible to the increasing frequency and intensity of hypoxia possible with increasing temperature and reduced flow as a result of climate change.

Developing a social, cultural and economic report card for a regional industrial harbour

Report cards are increasingly used to provide ongoing snap-shots of progress towards specific ecosystem health goals, particularly in coastal regions where planners need to balance competing demands for coastal resources from a range of industries. While most previous report cards focus on the biophysical components of the system, there is a growing interest in including the social and economic implications of ecosystem management to provide a greater social-ecological system understanding. Such a report card was requested on the Gladstone Harbour area in central Queensland, Australia. Gladstone Harbour adjoins the southern Great Barrier Reef, and is also a major industrial and shipping port. Balancing social, economic and environmental interests is therefore of great concern to the regional managers. While environmental benchmarking procedures are well established within Australia (and elsewhere), a method for assessing social and economic performance of coastal management is generally lacking. The key aim of this study was to develop and pilot a system for the development of a report card relating to appropriate cultural, social and economic objectives. The approach developed uses a range of multicriteria decision analysis methods to assess and combine different qualitative and quantitative measures, including the use of Bayesian Belief Networks to combine the different measures and provide an overall quantitative score for each of the key management objectives. The approach developed is readily transferable for purposes of similar assessments in other regions.

Use of aquatic plants to create fluctuating hypoxia in an experimental environment

In freshwater systems, dissolved oxygen (DO) saturation frequently fluctuates, falling at night and rising during the day in response to respiration and photosynthesis, respectively, of aquatic biota. Low DO (hypoxia) is a common cause of fish kills in freshwater systems around the world. Laboratory studies on responses of fish to fluctuating DO are currently limited, and require techniques that produce a realistic cycle of DO depletion and replacement. Artificial DO-depletion mechanisms frequently used for hypoxia studies may underestimate the field effects of hypoxia on fish because of the lack of the naturally occurring synergistic effect of lower pH, and seldom allow fish to employ behavioural adaptations to hypoxia, such as aquatic surface respiration. We demonstrate proof-of-principle for an alternative method of creating fluctuating hypoxia in an experimental environment, using the natural rhythms of photosynthesis and respiration of aquatic plants to create realistic conditions. A range of volumes of aquatic macrophytes were used alone and in combination with fish to lower DO saturation in sealed freshwater aquaria, and achieved DO saturations as low as 1.3%. This cost-effective method can be deployed over long periods with minimal effort in comparison to traditional methods of DO reduction.

Embryos of eastern rainbowfish Melanotaenia splendida splendida (Peters, 1866) tolerate fluctuating hypoxia

Hypoxia can have profound sublethal effects on reproduction and embryonic development of some freshwater fish. In the present study, the effects of diel fluctuating hypoxia on embryo viability were investigated for the eastern rainbowfish Melanotaenia splendida splendida, a small-bodied species common in wetlands of tropical Queensland. After daily hypoxic exposure (minimum 5% saturation) from fertilisation until hatch, no effects were found on egg incubation time, egg and larval mortality, and viability and size of hatching larvae. Older life history stages of the species are vulnerable to this level of hypoxia. Embryos of phytolithophilic species are likely exposed to fluctuating dissolved oxygen saturations in their natural habitat, and hypoxia tolerance may be a requirement for fish species that spawn predominantly on submerged plant material.