Browsing Peer Reviewed Scientific Papers by Title
Now showing items 98-101 of 101
When good neighbours become good friends: observing small scale structures in fish aggregations using multibeam sonar(EDP Sciences, 2010)Converging results in different scientific fields (behavioural ecology, fisheries biology, acoustic tagging, fisheries acoustics, behavioural modelling) suggest the existence of “micro-groups” inside fish schools. These would comprise a few (5–10) fish maintaining contact during a period long enough to allow individuals to recognise each other. It is hypothesised that they would prefer to share the space with familiar rather than anonymous conspecifics. To evaluate whether acoustic methods could be used to recognise “micro-structures” inside fish schools and help test the “micro-group” hypothesis we analysed acoustic data from anchovy schools off Peru, and gadoids in the North Sea. Data collection used a multibeam sonar (Reson SeaBat 6012). In the Peruvian case study, the sonar was mounted set horizontally on a drifting research vessel and the internal structure of the schools of anchovies was analysed, although individual fish could not be discriminated. In the North Sea case study, the sonar was orientated vertically above a demersal trawl to allow observation of individual fish entering the trawl. Geostatistical analyses were used to evaluate the existence of small spatial structures in anchovy schools. In these schools, “micro-structures” with a scale as small as 0.5 m were observed acoustically. For the gadoids nearest neighbour distance (NDD) measurements were carried out, suggesting that the fish aggregated in small groups (2 to 25 individuals, with an average of 3.7 fish per group) in the trawl catches. The perspectives and limitations of these results are discussed.
Where the lake meets the sea: strong reproductive isolation is associated with adaptive divergence between lake resident and anadromous three-spined sticklebacks(PLoS ONE, 2015)Contact zones between divergent forms of the same species are often characterised by high levels of phenotypic diversity over small geographic distances. What processes are involved in generating such high phenotypic diversity? One possibility is that introgression and recombination between divergent forms in contact zones results in greater phenotypic and genetic polymorphism. Alternatively, strong reproductive isolation between forms may maintain distinct phenotypes, preventing homogenisation by gene flow. Contact zones between divergent freshwater-resident and anadromous stickleback (Gasterosteus aculeatus L.) forms are numerous and common throughout the species distribution, offering an opportunity to examine these contrasting hypotheses in greater detail. This study reports on an interesting new contact zone located in a tidally influenced lake catchment in western Ireland, characterised by high polymorphism for lateral plate phenotypes. Using neutral and QTL-linked microsatellite markers, we tested whether the high diversity observed in this contact zone arose as a result of introgression or reproductive isolation between divergent forms: we found strong support for the latter hypothesis. Three phenotypic and genetic clusters were identified, consistent with two divergent resident forms and a distinct anadromous completely plated population that migrates in and out of the system. Given the strong neutral differentiation detected between all three morphotypes (mean FST = 0.12), we hypothesised that divergent selection between forms maintains reproductive isolation. We found a correlation between neutral genetic and adaptive genetic differentiation that support this. While strong associations between QTL linked markers and phenotypes were also observed in this wild population, our results support the suggestion that such associations may be more complex in some Atlantic populations compared to those in the Pacific. These findings provide an important foundation for future work investigating the dynamics of gene flow and adaptive divergence in this newly discovered stickleback contact zone.
Whole-tree harvesting and grass seeding as potential mitigation methods for phosphorus export in peatland catchments(Elsevier, 2014)Forest clearfelling is potentially a major environmental problem with respect to the degradation of water quality in receiving water courses due to phosphorus (P) release from soil and clearfelling residue stocks. Recent studies have highlighted the need to investigate the performance and benefits of potential mitigation methods such as whole tree harvesting (WTH) and grass seeding. In this study, fifteen plots (0.014 ha each) were constructed in a standing coniferous forest and P concentrations in plot runoff were monitored for one year prior to clearfelling. Following clearfelling three replicates of five forest harvesting management practices/treatments were applied to the plots: brash with grass seeding (Treatment 1), brash (Treatment 2), brash mat/ tree extraction route (Treatment 3), WTH (Treatment 4) and WTH with grass seeding (Treatment 5). These treatments were designed to comparatively assess the benefits of WTH and grass seeding practices on mitigating P released from forested peatlands following clearfelling and to determine the sources and sinks of P following clearfelling operations. Annual average total reactive phosphorus (TRP) concentrations in the plot runoff were < 20 µg L-1 in all treatments before clearfelling, and increased to 79 µg L-1, 160 µg L-1, 335 µg L-1, 50 µg L-1 and 38 µg L-1 in Treatments 1, 2, 3, 4 and 5, respectively, after clearfelling. These results highlight that WTH and grass seeding can be used efficiently as methods to improve water quality, aiding in the protection of the biota residing in the aquatic systems draining peatland catchments.
Winter measurements of biogeochemical parameters in the Rockall Trough (2009–2012)(Copernicus publications, 2013)This paper describes the sampling and analysis of biogeochemical parameters collected in the Rockall Trough in January/February of 2009, 2010, 2011 and 2012. Sampling was carried out across two transects, one southern and one northern transect each year. Samples for dissolved inorganic carbon (DIC) and total alkalinity (TA) were taken alongside salinity, dissolved oxygen and dissolved inorganic nutrients (total-oxidised nitrogen, nitrite, phosphate and silicate) to describe the chemical signatures of the various water masses in the region. These were taken at regular intervals through the water column. The 2009 and 2010 data are available on the CDIAC database.