Craig A. Boys

Understanding Barotrauma in Fish Passing Hydro Structures: A Global Strategy for Sustainable Development of Water Resources

ABSTRACTFreshwater fishes are one of the most imperiled groups of vertebrates, and population declines are alarming in terms of biodiversity and to communities that rely on fisheries for their livelihood and nutrition. One activity associated with declines in freshwater fish populations is water resource development, including dams, weirs, and hydropower facilities. Fish passing through irrigation and hydro infrastructures during downstream migration experience a rapid decrease in pressure, which can lead to injuries (barotrauma) that contribute to mortality. There is renewed initiative to expand hydropower and irrigation infrastructure to improve water security and increase low-carbon energy generation. The impact of barotrauma on fish must be understood and mitigated to ensure that development is sustainable for fisheries. This will involve taking steps to expand the knowledge of barotrauma-related injury from its current focus, mainly on seaward-migrating juvenile salmonids of the Pacific Northwest, to...

Emergence of Epizootic Ulcerative Syndrome in Native Fish of the Murray-Darling River System, Australia: Hosts, Distribution and Possible Vectors

Epizootic ulcerative syndrome (EUS) is a fish disease of international significance and reportable to the Office International des Epizootics. In June 2010, bony herring Nematalosa erebi, golden perch Macquaria ambigua, Murray cod Maccullochella peelii and spangled perch Leiopotherapon unicolor with severe ulcers were sampled from the Murray-Darling River System (MDRS) between Bourke and Brewarrina, New South Wales Australia. Histopathology and polymerase chain reaction identified the fungus-like oomycete Aphanomyces invadans, the causative agent of EUS. Apart from one previous record in N. erebi, EUS has been recorded in the wild only from coastal drainages in Australia. This study is the first published account of A. invadans in the wild fish populations of the MDRS, and is the first confirmed record of EUS in M. ambigua, M. peelii and L. unicolor. Ulcerated carp Cyprinus carpio collected at the time of the same epizootic were not found to be infected by EUS, supporting previous accounts of resistance against the disease by this species. The lack of previous clinical evidence, the large number of new hosts (n = 3), the geographic extent (200 km) of this epizootic, the severity of ulceration and apparent high pathogenicity suggest a relatively recent invasion by A. invadans. The epizootic and associated environmental factors are documented and discussed within the context of possible vectors for its entry into the MDRS and recommendations regarding continued surveillance, research and biosecurity are made.

Evaluating migratory fish behaviour and fishway performance: testing a combined assessment methodology

To provide passage for migratory native fish, a series of 14 vertical-slot and lock fishways are being constructed on the Murray River in south-eastern Australia. Three of these vertical-slot fishways, at Locks 7, 9 and 10, have a conservative slope (1V : 32H) and are designed with internal hydraulics suitable for the passage of a broad size range of fish (30–1000 mm long). An assessment of these fishways was performed using a combined trapping survey and passive integrated transponder (PIT) approach to determine fishway effectiveness at passing an entire fish community. Fish were trapped within the three fishways between 2004 and 2006, where a total of 13 626 individuals comprising 13 species were collected from 48 sample days (24 h each). Trapping data revealed that the three fishways successfully passed fish within the target size range, though significantly greater numbers of individuals smaller (10–29 mm long) than the target size range could not ascend. PIT tagging revealed important information on fishway ascent times, descent times, seasonality and diel behaviour of medium and large fish. Although each method alone had advantages and disadvantages, the dual assessment approach was useful as it permitted an assessment of fishway success and also provided insights into migratory fish behaviour.

Influence of Approach Velocity and Mesh Size on the Entrainment and Contact of a Lowland River Fish Assemblage at a Screened Irrigation Pump

Fish screens can help prevent the entrainment or injury of fish at irrigation diversions, but only when designed appropriately. Design criteria cannot simply be transferred between sites or pump systems and need to be developed using an evidence-based approach with the needs of local species in mind. Laboratory testing is typically used to quantify fish responses at intake screens, but often limits the number of species that can studied and creates artificial conditions not directly applicable to screens in the wild. In this study a field-based approach was used to assess the appropriateness of different screen design attributes for the protection of a lowland river fish assemblage at an experimental irrigation pump. Direct netting of entrained fish was used along with sonar technology to quantify the probability of screen contact for a Murray-Darling Basin (Australia) fish species. Two approach velocities (0.1 and 0.5 m.sec−1) and different sizes of woven mesh (5, 10 and 20 mm) were evaluated. Smaller fish (<150 mm) in the assemblage were significantly more susceptible to entrainment and screen contact, especially at higher approach velocities. Mesh size appeared to have little impact on screen contact and entrainment, suggesting that approach velocity rather than mesh size is likely to be the primary consideration when developing screens. Until the effects of screen contacts on injury and survival of these species are better understood, it is recommended that approach velocities not exceed 0.1 m.sec−1 when the desire is to protect the largest range of species and size classes for lowland river fish assemblages in the Murray-Darling Basin. The field method tested proved to be a useful approach that could compliment laboratory studies to refine fish screen design and facilitate field validation.

Perspective: Towards environmentally acceptable criteria for downstream fish passage through mini hydro and irrigation infrastructure in the Lower Mekong River Basin

Tropical rivers have high annual discharges optimal for hydropower and irrigation development. The Mekong River is one of the largest tropical river systems, supporting a unique mega-diverse fish community. Fish are an important commodity in the Mekong, contributing a large proportion of calcium, protein, and essential nutrients to the diet of the local people and providing a critical source of income for rural households. Many of these fish migrate not only upstream and downstream within main-channel habitats but also laterally into highly productive floodplain habitat to both feed and spawn. Most work to date has focused on providing for upstream fish passage, but downstream movement is an equally important process to protect. Expansion of hydropower and irrigation weirs can disrupt downstream migrations and it is important to ensure that passage through regulators or mini hydro systems is not harmful or fatal. Many new infrastructure projects (<6 m head) are proposed for the thousands of tributary stre...

Opening the floodgates to the recovery of nektonic assemblages in a temperate coastal wetland

Tidally active wetlands are important nurseries for fish and crustaceans; however, urban development involving structural flood mitigation has fragmented and destroyed much of this habitat, often leading to losses in fisheries productivity. The present study demonstrated that some of these impacts may be reversible if rehabilitation projects are implemented over a sufficiently long time. The incremental opening of eight floodgates at a temperate coastal wetland in Australia afforded the opportunity to monitor water quality and nekton assemblages in a tidal creek over 11 years, encompassing pre-floodgate opening, opening of one gate, three gates and finally all eight gates. Floodgate opening enhanced both water quality and nektonic assemblages relative to a control creek whose barrier remained in place. A doubling in species richness occurred and many commercially important species increased in abundance, including Metapenaeus macleayi (15 times more), Acanthopagrus australis (62 times more), Liza argentea (10 times more) and Gerres subfasciatus (19 times more). Recovery to a condition similar to unrestricted reference creeks was achieved once all eight gates were opened. The study illustrated that reinstating tidal flushing can recover nursery habitats and enhance populations of economically valuable species.

A piecewise regression approach for determining biologically relevant hydraulic thresholds for the protection of fishes at river infrastructure.

A piecewise regression approach was used to objectively quantify barotrauma injury thresholds in two physoclistous species, Murray cod Maccullochella peelii and silver perch Bidyanus bidyanus, following simulated infrastructure passage in a barometric chamber. The probability of injuries such as swimbladder rupture, exophthalmia and haemorrhage, and emphysema in various organs increased as the ratio between the lowest exposure pressure and the acclimation pressure (ratio of pressure change, R(NE:A) ) reduced. The relationship was typically non-linear and piecewise regression was able to quantify thresholds in R(NE:A) that once exceeded resulted in a substantial increase in barotrauma injury. Thresholds differed among injury types and between species but by applying a multispecies precautionary principle, the maintenance of exposure pressures at river infrastructure above 70% of acclimation pressure (R(NE:A) of 0·7) should protect downstream migrating juveniles of these two physoclistous species sufficiently. These findings have important implications for determining the risk posed by current infrastructures and informing the design and operation of new ones.

How low can they go when going with the flow? Tolerance of egg and larval fishes to rapid decompression

ABSTRACT Egg and larval fish that drift downstream are likely to encounter river infrastructure and consequently rapid decompression, which may result in significant injury. Pressure-related injury (or barotrauma) has been shown in juvenile fishes when pressure falls sufficiently below that at which the fish has acclimated. There is a presumption that eggs and larvae may be at least as, if not more, susceptible to barotrauma injury because they are far less-developed and more fragile than juveniles, but studies to date report inconsistent results and none have considered the relationship between pressure change and barotrauma over a sufficiently broad range of pressure changes to enable tolerances to be properly determined. To address this, we exposed eggs and larvae of three physoclistic species to rapid decompression in a barometric chamber over a broad range of discrete pressure changes. Eggs, but not larvae, were unaffected by all levels of decompression tested. At exposure pressures below ∼40 kPa, or ∼40% of surface pressure, swim bladder deflation occurred in all species and internal haemorrhage was observed in one species. None of these injuries killed the fish within 24 h, but subsequent mortality cannot be excluded. Consequently, if larval drift is expected where river infrastructure is present, adopting design or operational features which maintain exposure pressures at 40% or more of the pressure to which drifting larvae are acclimated may afford greater protection for resident fishes. Summary: Eggs are extremely tolerant to rapid decompression, although larvae may be injured once pressure falls below 40% of the pressure to which they are acclimated.