Geology topics

Crawford W. Revie

Publications and source records attributed to Crawford W. Revie.

3 recordsLinked to original sources

USGS2020

Modeling pathogen dispersal in marine fish and shellfish

Bio-physical models are a useful tool for understanding dispersal and transmission of marine pathogens. While utilized for larval dispersal models, they are only recently being used in epidemiological studies and are currently underutilized by the marine epidemiology field. Bio-physical models are useful for spatial planning and coastal management. For example, they have been used for spatial planning of salmon farm site locations, and to establish early warning networks. Bio-physical modeling can be used to test hypotheses, rather than simply develop them. Model resolution and computation demands must be balanced when making decisions about model parameters. Epidemiological bio-physical models are in their infancy. While they have proven useful so far, future applications of these models can incorporate more aspects of disease dynamics and address many additional questions.

Trends in Parasitology↗

USGS2019

Evaluating the potential for sea lice to evolve freshwater tolerance as a consequence of freshwater treatments in salmon aquaculture

Increasing usage of non-medicinal methods (NMMs) to control sea louse infestations on salmon farms has raised questions about whether sea lice may be able to evolve tolerance of NMMs. Of particular concern is the potential for sea lice to evolve freshwater tolerance as a result of freshwater treatments. Wild trout and some juvenile salmonids swim into freshwater to control infestations and regain ionic balance after disruption by sea lice; freshwater tolerance would compromise this potentially adaptive behavior. Here we evaluated the potential for freshwater tolerance to evolve in the sea louse Lepeophtheirus salmonis. When exposed to low-salinity water, parasitic stages of sea lice are able to osmoregulate through the host, while larval planktonic stages are not. Transcriptomic work suggests that sea lice mount a costly polygenic stress response when exposed to brackish water. The population structure of sea lice is panmictic in both the Pacific and Atlantic, making it conducive to rapid evolutionary responses. It is unknown how much heritable genetic variation these panmictic populations have for freshwater treatments. While usage of freshwater treatments on wellboats is increasing, it is unclear whether the freshwater itself is a strong selective force; during the freshwater exposure, sea lice can die from physical disruption during pumping and filtration on the wellboat. Future studies are advised to quantify the heritable variation in freshwater tolerance in sea louse populations, characterize mechanisms for freshwater tolerance in planktonic and attached sea lice, and assess the risk of freshwater tolerance evolution under different management strategies.

Aquaculture Environment Interactions↗

USGS2019

Modelling sea lice control by lumpfish on Atlantic salmon farms: interactions with mate limitation, temperature, and treatment rules

Atlantic salmon farming is one of the largest aquaculture sectors in the world. A major impact on farm economics, fish welfare, and potentially nearby wild salmonid populations, is the sea louse ectoparasite Lepeophtheirus salmonis . Sea louse infestations are most often controlled through application of chemicals, but in most farming regions sea lice have evolved resistance to the small set of available chemicals. Therefore, alternative treatment methodologies are becoming more widely used. One increasingly common alternative treatment involves the co-culture of farmed salmon with cleaner fish, which prey on sea lice. However, despite their wide use, little is understood about the situations in which cleaner fish are most effective. For example, previous work suggests that a low parasite density results in sea lice finding it difficult to acquire mates, reducing fecundity and population growth. Other work suggests that environmental conditions such as temperature and external sea louse pressure have substantial impact on this mate limitation threshold and may even remove the effect entirely. We use an Agent-Based Model (ABM) to simulate cleaner fish on a salmon farm to explore interactions between sea louse mating behaviour, cleaner fish feeding rate, temperature, and external sea lice pressure. We found that sea louse mating has a substantial effect on sea louse infestations under a variety of environmental conditions. Our results suggest that cleaner fish can control sea louse infestations most effectively by maintaining the population below critical density thresholds.

Diseases of Aquatic Organisms↗