Cryptic Lineages and a Population Damned to Incipient Extinction? Insights into the Genetic Structure of a Mekong River Catfish

An understanding of the genetic composition of populations across management boundaries is vital to developing successful strategies for sustaining biodiversity and food resources. This is especially important in ecosystems where habitat fragmentation has altered baseline patterns of gene flow, dividing natural populations into smaller sub-populations and increasing potential loss of genetic variation through genetic drift. River systems can be highly fragmented by dams built for flow regulation and hydropower. We used reduced-representation sequencing to examine genomic patterns in an exploited catfish, Hemibagrus spilopterus, in a hotspot of biodiversity and hydropower development- the Mekong River basin. Our results revealed the presence of two highly-divergent coexisting genetic lineages which may be cryptic species. Within the lineage with the greatest sample sizes, pairwise FST values, principal components analysis, and a STRUCTURE analysis all suggest that long-distance migration is not common across the Lower Mekong Basin, even in areas where flood-pulse hydrology has limited genetic divergence. In tributaries, effective population size estimates were at least an order of magnitude lower than in the Mekong mainstream indicating these populations may be more vulnerable to perturbations such as human-induced fragmentation. Fish isolated upstream of several dams in one tributary exhibited particularly low genetic diversity, high amounts of relatedness, and a level of inbreeding (GIS = 0.51) that has been associated with inbreeding depression in other outcrossing species. Our results highlight the importance of assessing genetic structure and diversity in riverine fisheries populations across proposed dam development sites for the preservation of these critically-important resources

Report from the Annual Conference of the British Society of Echocardiography, November 2016, Queen Elizabeth II Conference Centre, London.

Peer reviewedPublisher PD

Report from the Annual Conference of the British Society of Echocardiography, November 2017, Edinburgh International Conference Centre, Edinburgh

No abstract available

Boron diffusion in amorphous silicon-germanium alloys

The effect of Ge alloying on B diffusion in amorphous Si1-x Gex alloys is reported for x=0-0.24. The diffusivity was not observed to exhibit any transient decay. The diffusivity decreases with increasing Ge concentration. The activation energy for B diffusion appears to increase from 2.8 eV for amorphous Si to 3.6 eV for amorphous Si0.76 Ge0.24. It is suggested that, in these alloys, Ge distorts the amorphous Si network thereby increasing B trapping by Si

Fish assemblage responses to flow seasonality and predictability in a tropical flood pulse system

Hydropower dams are looming in the Mekong Basin, affecting river flows that structure aquatic communities. Here, we quantitatively assessed flow seasonality and predictability in three sites located in three rivers displaying a gradient in flow alterations caused by upstream dams and investigated how fish assemblages responded seasonally and inter-annually to this gradient. By analyzing 7-yr daily fish and water monitoring data, we found that dams disturbed the natural flow seasonality and predictability. While the river displaying the lower seasonality-predictability was characterized by a distinct seasonal variation in assemblage composition with high species turnover, rivers with stronger flow seasonality-predictability exhibited broadly similar seasonal patterns in fish assemblage composition with low species turnover and regular annual peaks of fish migration. These results challenge the expectation of higher species turnover in systems displaying higher flow seasonality and predictability and may be partly due to the strong adaptation of fish assemblages to these specific systems. By enhancing our understanding of biological systems in the highly seasonal-predictable and aseasonal-unpredictable environments of the lower Mekong system, these findings suggest that hydropower-related pulsed flows that can mimic as far as possible natural pulsed flows are critical to reduce downstream effects on aquatic organisms

Designing freshwater protected areas (FPAs) for indiscriminate fisheries

Freshwater protected areas (FPAs) are increasingly important for biodiversity conservation, given the intensive use of these systems for water, energy and food production. However, the fisheries benefits of FPAs are not well understood, particularly for indiscriminate fisheries typical of tropical systems. Here we report the results of a model that tests the fisheries effects of no-take protected areas in conditions unique to indiscriminate riverine/floodplain systems. The model has a generalized form applicable to a wide range of systems. We report the results of the general model, as well as those from a specialized form parameterized for the Tonle Sap lake, Cambodia. Both the general and Tonle Sap versions of the model show that FPAs can pay important fisheries benefits, especially where it is difficult to control fishing mortality through gear restrictions or other means. The harvest and profit benefit response curves have similar shapes, with additional FPAs paying high dividends at less than approximately 50% FPA coverage, and then truncating and declining thereafter. In the specific setting of the Tonle Sap of Cambodia, FPAs would pay a large increase in harvest because current FPA coverage is low. It may be counterintuitive to community fisheries managers in Cambodia that the best way to increase harvest is to restrict fishing, but at very high levels of fishing effort, reducing effort or area fished will improve both harvest and profit. In Cambodia, it may make sense to maximize harvest rather than profit because fishers living in poverty need to maximize protein offtake, but the benefits of FPAs remain. Similar considerations may apply in many freshwater and indiscriminate fisheries

Designing freshwater protected areas (FPAs) for indiscriminate fisheries

Freshwater protected areas (FPAs) are increasingly important for biodiversity conservation, given the intensive use of these systems for water, energy and food production. However, the fisheries benefits of FPAs are not well understood, particularly for indiscriminate fisheries typical of tropical systems. Here we report the results of a model that tests the fisheries effects of no-take protected areas in conditions unique to indiscriminate riverine/floodplain systems. The model has a generalized form applicable to a wide range of systems. We report the results of the general model, as well as those from a specialized form parameterized for the Tonle Sap lake, Cambodia. Both the general and Tonle Sap versions of the model show that FPAs can pay important fisheries benefits, especially where it is difficult to control fishing mortality through gear restrictions or other means. The harvest and profit benefit response curves have similar shapes, with additional FPAs paying high dividends at less than approximately 50% FPA coverage, and then truncating and declining thereafter. In the specific setting of the Tonle Sap of Cambodia, FPAs would pay a large increase in harvest because current FPA coverage is low. It may be counterintuitive to community fisheries managers in Cambodia that the best way to increase harvest is to restrict fishing, but at very high levels of fishing effort, reducing effort or area fished will improve both harvest and profit. In Cambodia, it may make sense to maximize harvest rather than profit because fishers living in poverty need to maximize protein offtake, but the benefits of FPAs remain. Similar considerations may apply in many freshwater and indiscriminate fisheries