Tim Dempster

Tim Dempster
University of Melbourne | MSD · School of BioSciences

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199
Publications
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Publications

Publications (199)
Article
Automation of feeding control for sea-caged Atlantic salmon is important to reduce waste feed. Hydroacoustic appetite-led feeding, or echofeeding, uses echo sound to monitor fish biomass in a defined feeding area. As the fish become satiated and begin to leave the feeding area, the monitored biomass falls, enabling the setting of threshold levels o...
Article
Salmonid aquaculture, producing nearly 3 million tons per year, has expanded across temperate seascapes around the globe in recent decades. Cage technologies used to farm salmonids are thought to have changed in both size and location in coastal environments, yet remarkably little data exists to explain these major developments. Using satellite ima...
Article
Full-text available
Amoebic gill disease (AGD) is a significant health issue for Atlantic salmon farmed in a marine environment. While the disease is currently managed using freshwater or hydrogen peroxide baths, there is a need to develop other treatments. The aims of this study were to examine the effect of salinity (0 ppt and 35 ppt) and temperature (3 °C and 15 °C...
Article
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Advances in tag technology now make it possible to monitor the behavior of small groups of individual fish as bioindicators of population wellbeing in commercial aquaculture settings. For example, tags may detect unusual patterns in fish heart rate, which could serve as an early indicator of whether fish health or welfare is becoming compromised. H...
Article
Structural modification of sea cages is continually changing to counter major production issues associated with commercial salmon farming. For example, snorkels and skirts are added to cages to reduce salmon lice infestations, and submerging cages can reduce salmon-lice encounter rates, minimise the effects of storms or avoid other unsuitable sea s...
Article
In the effort to increase the commercial value of urchin gonads produced via roe enhancement aquaculture, a variety of formulated feeds have been tested to increase gonad production and improve colour and taste. The addition of dried algal supplements to formulated feeds can further enhance gonad quality, but the level of improvement is highly vari...
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Human-induced environmental changes are accelerating biodiversity loss. Identifying which life-history traits increase extinction risk is important to inform proactive conservation. While geographically or numerically rare species are typically more vulnerable, ecological specialization may also increase extinction risk particularly when associated...
Article
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The evolution of pest resistance to management strategies is a major challenge for farmed systems. Mitigating the effects of pest adaptation requires identifying the selective pressures imposed by these strategies. In Atlantic salmon (Salmo salar) aquaculture, barriers are used to prevent salmon louse (Lepeophtheirus salmonis) larvae (copepodids) f...
Article
Natural coastlines are being replaced by artificial structures (pilings, pontoons, breakwaters), with negative environmental impacts, particularly in marinas. Ropes seeded with mussels (Mytilus galloprovincialis) were added to artificial structures in a marina, using aquaculture techniques, to reduce the colonisation of invasive taxa. After 6-month...
Article
Surface‐based cages are the dominant production technology for the marine finfish aquaculture industry. However, issues such as extreme weather events, poor environmental conditions, interactions with parasites, and conflicts with other coastal users are problematic for surface‐based aquaculture. Submerged cages may reduce many of these problems an...
Article
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Light is a fundamental environmental cue which influences the migration of many marine organisms. For the salmon louse Lepeophtheirus salmonis , light is believed to drive the diel vertical migration behaviour of their planktonic larvae. Salmon lice are of critical importance to the salmonid industry due to the damage they cause to wild and farmed...
Article
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Sea-cage fish farming is typically open to the environment, with disease transmission possible between farmed and wild hosts. In salmonid aquaculture, salmon lice (Lepeophtheirus salmonis) infestations cause production losses, reduce welfare for farmed fish, and increase infestation rates for wild fish populations. The high density of hosts in farm...
Article
Ectoparasitic salmon lice (Lepeophtheirus salmonis) present a major challenge to Atlantic salmon (Salmo salar) aquaculture. The demand for effective louse control has produced diverse management strategies. These strategies essentially impose novel selection pressures on parasite populations, driving the evolution of resistance. Here we assess the...
Article
Humans are altering marine ecosystems at unprecedented rates, and these changes can result in animals selecting poor‐quality habitats if the cues they use become misleading. Such “ecological traps” increase extinction risk, reduce ecosystem resilience, and are a consequence of human‐induced rapid environmental change. Although there is growing evid...
Article
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A variety of tagging techniques are now available to monitor fish behaviour, physiology and their environmental experience. Tagging is frequently used in aquaculture research to monitor free-swimming individuals within farmed populations. However, for information gathered from tagged fish to be representative of farmed populations, tagging must not...
Article
Sea urchin gonads (roe) are a prized global sea food commodity, with growing demand driving the need for urchin roe enhancement aquaculture. Effective roe enhancement of urchins using formulated feeds require species‐specific optimization and an understanding of the interactions between key dietary components (e.g. protein, lipid, carbohydrate, ene...
Article
An understanding of behaviour is used in zoos, laboratories and agriculture to reduce stressful aspects of the captive environment for animals. While fish are one of the most cultivated of all vertebrate groups, incorporating their behaviour into production management has proved elusive. Here, we evaluate the current evi- dence base relating to use...
Article
Biodiverse ecosystems are sometimes inherently resistant to invasion, but environmental change can facilitate invasion by disturbing natural communities and providing resources that are underutilised by native species. In such cases, sufficiently abundant native predators may help to limit invasive population growth. We studied native and invasive...
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The systematics of the genus Hannia Vari 1978, endemic to freshwater habitats of remote northwestern Australia, is revised in light of recent collections in the region and a molecular study of the group that identified an undescribed candidate species. A new freshwater fish species (Hannia wintoni sp. nov) is described based on analysis of multiple...
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Amoebic gill disease (AGD), caused by the amoeba Neoparamoeba perurans, has led to considerable economic losses in every major Atlantic salmon producing country, and is increasing in frequency. The most serious infections occur during summer and autumn, when temperatures are high and poor dissolved oxygen (DO) conditions are most common. Here, we t...
Chapter
The natural environment has been altered by anthropogenic actions for several centuries. For example, land clearing, water diversion and abstraction for agriculture have changed aquatic ecosystems, as have inputs from various diffuse and point-source pollution sources. The alteration of natural waterbodies leads to water quality and habitat changes...
Article
The evolution of pesticide resistance has driven renewed interest in non-chemical pest controls in agriculture. Spatial manipulations (physical barriers and fallowing, for example) can be an effective method of prevention, but these too might impose selection and cause rapid adaptation in pests. In salmon aquaculture, various non-chemical approache...
Article
Full-text available
The Atlantic salmon aquaculture industry still struggles with ectoparasitic sea lice despite decades of research and development invested into louse removal methods. In contrast, methods to prevent infestations before they occur have received relatively little research effort, yet may offer key benefits over treatment-focused methods. Here, we summ...
Article
Sea-cage salmon farming creates ideal conditions for ectoparasites such as the salmon louse Lepeophtheirus salmonis, with high lice densities leading to welfare challenges for stock and increasing lice burdens on wild salmonids. New treatments with low environmental impacts and minimal handling are needed to complement existing strategies. Irradiat...
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Aim Despite the influence of sea‐level changes on biogeographic/phylogeographic patterns in freshwater ecosystems being well documented, studies that explicitly link the influence of sea‐level change with speciation are rare. We aim to test the hypothesis that sea‐level changes during the Pliocene and Pleistocene have driven speciation in north‐wes...
Article
Buoyancy regulation is a fundamental process by which pelagic fish maintain their position in the water column in an energy efficient way. Buoyancy has been largely overlooked as an important factor in Atlantic salmon production as salmon have a physostomous swim bladder that they fill by gulping air from the surface. The speed and ease at which th...
Article
Parasitic salmon lice (Lepeophtheirus salmonis) are a severe problem for the Atlantic salmon (Salmo salar) farming industry. To reduce infestations, sea-cages can be submerged, below the depth at which lice are most common, with an underwater air dome being provided to allow salmon to refill their swim bladder and maintain buoyancy. When first tran...
Article
Salmon lice, Lepeophtheirus salmonis are a financial and fish welfare issue for the salmon aquaculture industry. Avoiding the planktonic, mostly surface-dwelling infective stage of lice by holding salmon deep in submerged sea-cages could reduce host-parasite encounter rates, reducing the lice problem. However, submergence, or long-term lack of surf...
Article
The salmon aquaculture industry has adopted the use of invertivorous 'cleaner fishes' (CF) for biological control of sea lice infestations on farmed salmon. At present, ~50 million CF are used annually in Norway alone, with variable success in experimental and industrial contexts. We used a national-scale database of lice counts, delousing treatmen...
Article
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Algal bioremediation can significantly improve the quality of wastewater by assimilating nutrients. However, the efficiency and stability of this approach depends on identifying suitable algae based on their biomass productivity and ability to outcompete less desirable algae. Here, we compare the productivity and competitive ability of three taxa o...
Article
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Invasive vertebrates are frequently reported to have catastrophic effects on the populations of species which they directly impact. It follows then, that if invaders exert strong suppressive effects on some species then other species will indirectly benefit due to ecological release from interactions with directly impacted species. However, evidenc...
Article
Full-text available
Securing the welfare and maximising the lice removal efficacy of ~60 million cleaner fish used each year on salmonid farms is essential to develop a productive and ethical industry with low salmon lice Lepeophtheirus salmonis levels. We tested whether ballan wrasse Labrus bergylta welfare and lice consumption differed depending upon whether they we...
Article
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Stocking cleaner fish to control sea lice infestations in Atlantic salmon farms is widespread and viewed as a salmon welfare-friendly alternative to current delousing control treatments. The escalating demand for cleaner fish (~60 million stocked per year) coupled with evidence of poor welfare and high mortality in sea cages requires that the lice...
Article
The global expansion of aquaculture has raised concerns about its environmental impacts, including effects on wildlife. Aquaculture farms are thought to repel some species and function as either attractive population sinks ('ecological traps') or population sources for others. We conducted a systematic review and meta-analysis of empirical studies...
Article
Finding the ideal density to optimise growth, health and welfare of aquaculture species reared in cage or tank environments allows farmers to produce the best quality product per unit area. Appropriate stocking densities are well known for most major aquaculture species, but limited information exists for the developing sea urchin aquaculture indus...
Article
Full-text available
Sea lice are a critical health issue in most salmonid farming regions. New cage-based technologies can prevent infestations from occurring, such as the ‘snorkel’, which introduces an impermeable barrier that separates salmon lice Lepeophtheirus salmonis from Atlantic salmon Salmo salar in the surface waters where lice are most abundant. While snork...
Article
Methods to prevent parasite infestations in farmed fish are becoming widespread, yet tests of their effectiveness often lack commercial relevance and statistical power, which may lead to technology misuse. Here, we examined salmon louse infestation on Atlantic salmon in triplicate commercial snorkel louse barrier and standard cages over a 12 month...
Article
Background: Sea lice infestations on Atlantic salmon (Salmo salar) farms are a considerable burden on the industry and put wild salmonid populations at risk. Frequent delousing treatments are necessary to keep lice densities below allowable limits, but currently viable treatments have drawbacks in terms of financial cost, animal welfare, or enviro...
Article
Full-text available
To test two prominent, alternate hypotheses that provide explanations for the great accumulation of endemic species in the Kimberley bioregion in north‐western Australia, using an extensively sampled, region wide phylogeny of northern Australia's most species‐rich freshwater fish family, Terapontidae. Specifically, we test whether the Kimberley may...
Article
Salmon lice removal with chemotherapeutants often occurs via bathing in cages or well-boats. These methods of administering chemotherapeutants require handling of fish and can expose fish to suboptimal environments which lead to poor performance and mortality. Post-treatment, the medicines used disperse into the environment with potentially harmful...
Article
Animals that select the best available habitats are most likely to succeed in degraded environments, but ecological change can create evolutionarily unfamiliar habitats that may be under- or over-utilized by native fauna. In temperate coastal waters, eutrophication and grazing have driven a global decline in native seaweeds and facilitated the esta...
Preprint
Animals that select the best available habitats are most likely to succeed in degraded environments, but ecological change can create evolutionarily unfamiliar habitats that may be under‐ or over‐utilized by native fauna. In temperate coastal waters, eutrophication and grazing have driven a global decline in native seaweeds and facilitated the esta...
Article
Full-text available
In trying to deal with the problematic salmon louse Lepeophtheirus salmonis in salmon aquaculture, strategies to better prevent infestations are gaining traction. Successful prevention requires an accurate understanding of the environmental influences that alter the distribution of the planktonic stages of lice in the water column in space and time...
Article
Ballan wrasse (Labrus bergylta) are used extensively as cleaner fish to control salmon lice (Lepeophtheirus salmonis) infestations in the Atlantic salmon (Salmon salar) aquaculture industry. Fish are either cultured or caught in the wild before being transferred to salmon sea cages. Ballan wrasse are a poorly studied species, and fundamental knowle...
Article
Full-text available
Interest in sea urchin roe enhancement aquaculture is growing due to an increased global demand for high-quality roe that is suitable for export to international markets. Yet, fine-tuning of efficient collection methods and improved growing techniques are still key bottlenecks to industry success. Urchins suitable for roe enhancement are generally...
Article
Marine ecosystems are beset by disease outbreaks, and efficient strategies to control dispersal of pathogens are scarce. We tested whether introducing no-farming areas or ‘firebreaks’ could disconnect dispersal networks of a parasitic disease affecting the world's largest marine fish farming industry (∼1000 farms). Larval salmon lice (Lepeophtheiru...
Article
Full-text available
The Australian freshwater fish fauna is very unique, but poorly understood. In the Australian Monsoonal Tropics (AMT) biome of northern Australia, the number of described and candidate species has nearly doubled since the last attempt to analyse freshwater fish species composition patterns and determine a bioregionalisation scheme. Here, we utilise...
Article
Warm water thermal treatments dominate delousing operations in Norwegian Atlantic salmon (Salmo salar) aquaculture for the removal of ectoparasitic salmon lice (Lepeophtheirus salmonis). However, treatments can lead to poor welfare outcomes for fish. Reverse thermal delousing by rapidly reducing ambient temperatures to very low treatment temperatur...
Article
Full-text available
Fouling organisms in bivalve aquaculture cause significant economic losses for the industry. Husbandry strategies to reduce biofouling can involve avoidance, prevention, and treatment. In this way, the type of rope used to collect spat or grow bivalves may prevent or reduce fouling by particularly harmful species but remains largely untested. Furth...
Article
Full-text available
Salmon louse Lepeophtheirus salmonis, a key parasite of salmonids, is managed by multiple methods at both salmon farm- and ecosystem-scale that are informed by an understanding of the abundance and distribution of the infective, planktonic stage of the lice. Dispersal modelling using hydrodynamic models relies on accurately estimating larval depth...
Article
Full-text available
Over the last 2 decades, cleaner fishes have been employed to remove external sea lice parasites from Atlantic salmon Salmo salar in sea cages. Norway, Scotland, Ireland, and the Faroe Islands combined now use ~60 million cleaner fish per year. While small-scale experiments demonstrate the efficacy of cleaner fishes, industrial-scale sea cages have...
Article
Full-text available
Electronic tags are widespread tools for studying aquatic animal behaviour, however tags risk behavioural manipulation and negative welfare outcomes. During an experiment to test behavioural differences of Atlantic salmon Salmo salar in different aquaculture cage types, including ones expected to elicit deeper swimming behaviour, we found negative...
Article
Farming Atlantic salmon (Salmo salar L) in submerged cages may be a way for the industry to avoid surface related problems such as salmon lice and make new farming sites available. However, salmon do not cope with long term submergence and regularly need to access the surface to refill their swim-bladders and maintain buoyancy. We tested how salmon...
Article
Full-text available
With the expansion of Atlantic salmon aquaculture, the economic and ecological impacts of salmon lice (Lepeophtheirus salmonis) has increased. Norway battles this problematic parasite with various control and preventative methods within farms. We analysed two national‐level databases to examine the number of operations reported each year from 2012...
Article
Full-text available
Animals use irruptive movement to avoid exposure to stochastic and pervasive environmental stressors that impact fitness. Beneficial irruptive movements transfer individuals from high stress areas (conferring low fitness) to alternate localities that may improve survival or reproduction. However, being stochastic, environmental stressors can limit...
Preprint
The global expansion of aquaculture has raised concerns about its environmental impacts, including effects on wildlife. Aquaculture farms are thought to repel some species and function as either attractive population sinks (‘ecological traps’) or population sources for others. We conducted a systematic review and meta‐analysis of empirical studies...
Article
Full-text available
The use of farmed and restocked fish to supplement the worldwide human consumption of fish, recreational fishing stocks, and conservation efforts, is growing at a rapid rate. Yet, monitoring the benefits of using hatchery-raised fish for supplementation is lacking, often due to hatcheries not marking or tagging all fish prior to release, despite a...
Article
Full-text available
Sea cage fish aquaculture attracts large aggregations of wild fish that feed on farm waste. Fish that associate closely with farms undergo physiological changes, and captive feeding trials indicate possible negative effects on reproductive fitness. However, little is known about the significance of this phenomenon for reproduction in wild fish over...
Article
Full-text available
Overgrazing by the overabundant native purple urchin Heliocidaris erythrogramma has caused kelp-dominated reefs to shift to urchin barrens throughout southeastern Australia. These areas are characterised by low kelp abundance, low biodiversity and high urchin densities. As purple urchin gonads are a delicacy in many countries, commercial harvest fr...
Article
Full-text available
Understanding the impacts that invasive vertebrates have on terrestrial ecosystems extends primarily to invaders’ impacts on species with which they interact directly through mechanisms such as predation, competition and habitat modification. In addition to direct effects, invaders can also initiate ecological cascades via indirect population level...
Article
Full-text available
Environmental management of coastal aquaculture is focused on acute impacts of organic and nitrogenous wastes close to farms. However, the energy-rich trophic subsidy that aquaculture provides may create cascades with influences over broader spatial scales. In a fjord region with intensive fish farming, we tested whether an ecosystem engineer, the...
Article
Full-text available
Surface environment modification is a potential parasite control strategy in Atlantic salmon sea-cage farming. For instance, a temporary low salinity surface layer in commercial-scale snorkel sea-cages has coincided with reduced amoebic gill disease (AGD) levels after an outbreak. We tested if a permanent freshwater (FW) surface layer in snorkel se...
Article
Freshwater bathing is one of the main treatment options available against amoebic gill disease (AGD) affecting multiple fish hosts in mariculture systems. Prevailing freshwater treatments are designed to be long enough to kill Neoparamoeba perurans, the ectoparasite causing AGD, which may select for freshwater tolerance. Here, we tested whether usi...
Article
The prevalence of unrecognised cryptic species impairs biodiversity estimates, clouds biological research and hinders conservation planning. As the rate of cryptic species detection increases globally, research is needed to determine how frequent cryptic species are, whether they are more common in given management regions, and whether these patter...
Article
Full-text available
Organisms increasingly encounter higher frequencies of extreme weather events as a consequence of global climate change. Currently, few strategies are available to mitigate climate change effects on animals arising from acute extreme high temperature events. We tested the capacity of physiological engineering to influence the intra- and multi-gener...