Birds construct nests for several reasons. For species that breed in the Arctic, the insulative properties of nests are very important. Incubation is costly there and due to an increasing surface to volume ratio, more so in smaller species. Small species are therefore more likely to place their nests in thermally favourable microhabitats and/or to invest more in nest insulation than large species. To test this hypothesis, we examined characteristics of nests of six Arctic breeding shorebird species. All species chose thermally favourable nesting sites in a higher proportion than expected on the basis of habitat availability. Site choice did not differ between species. Depth to frozen ground, measured near the nests, decreased in the course of the season at similar non-species-specific speeds, but this depth increased with species size. Nest cup depth and nest scrape depth (nest cup without the lining) were unrelated to body mass (we applied an exponent of 0.73, to account for metabolic activity of the differently sized species). Cup depth divided by diameter2 was used as a measure of nest cup shape. Small species had narrow and deep nests, while large species had wide shallow nests. The thickness of nest lining varied between 0.1 cm and 7.6 cm, and decreased significantly with body mass. We reconstruct the combined effect of different nest properties on the egg cooling coefficient using previously published quantitative relationships. The predicted effect of nest cup depth and lining depth on heat loss to the frozen ground did not correlate with body mass, but the sheltering effect of nest cup diameter against wind and the effects of lining material on the cooling coefficient increased with body mass. Our results suggest that small arctic shorebirds invest more in the insulation of their nests than large species.
After typological pre-classification of 398 calibration sites, fish-based metric models were used to predict the impact of human activities on river quality in European Western Highlands and Western Plains ecoregions. Calibration sites were grouped into six assemblage types and according to their geomorphology; test sites were assigned to their corresponding assemblage type. Five anthropogenic variables were used to describe the impact level of each site and stepwise discriminant analysis was performed to: (i) avoid redundancy between metrics; (ii) examine how selected metrics discriminated impact classes and (iii) predict ecological status for each site of the given fish type. Globally, this approach predicted the impact class correctly for 64% of sites. The difference between observed and predicted impact was more than one class for only 2.5% of the sites. When validating this approach with an independent data set, differences between observed and predicted impact values never exceeded 2 impact classes, but these differences varied in size among countries. K E Y W O R D S : bioassessment, fish assemblages, predictive models, type-specific approach.
This study investigates the effect of water temperature on the development rate of eggs and larvae, the duration of the endogenous feeding period and its consequences for recruitment of smelt (Osmerus eperlanus) in Dutch lakes IJsselmeer and Markermeer. This study measured temperature-dependent egg and larval development rates as well as mortality rates from fertilization till the moment of absorption of the yolk-sac and from yolk-sac depletion onwards in temperature-controlled indoor experiments. Using multinomial modelling the authors found significant differences in development time of egg development stages under different temperature regimes. Based on historic water temperatures, the model predicted that the larval endogenous feeding period has advanced at a rate of about 2.9 days per decade in a more than 50 year period since 1961, yet there was no change in the duration of the endogenous feeding period. As zooplankton is more responsive to daylight than water temperature cues, a mismatch between the peak of the onset of exogenous feeding of smelt and the peak of zooplankton blooms could lead to high mortality and therefore low recruitment of smelt. Such a mismatch might contribute to a decline in the smelt population in Lake IJsselmeer and Lake Markermeer.
Effecten van mogelijke maatregelen ter beheer van de bestanden van brasem, blankvoorn, snoekbaars en baars in het IJssel-en Markermeer Dit onderzoek is uitgevoerd door Wageningen Economic Research in opdracht van en gefinancierd door het ministerie van Landbouw, Natuur en Voedselkwaliteit, in het kader van het Beleidsondersteunend onderzoeksthema 'Natuurinclusieve visserij' (projectnummer BO-43-023.02-016) , 2019. Effecten van mogelijke maatregelen ter beheer van de bestanden van brasem, blankvoorn, snoekbaars en baars in het IJsselen Markermeer. Wageningen, Wageningen Economic Research, Nota 2019-007. 56 blz.; 19 fig.; 12 tab.; 6 ref.Voor de zegen-en staandwantvisserij op het IJssel-en Markermeer wil het ministerie van Landbouw, Natuur en Voedselkwaliteit een vangstreductie van 36% van blankvoorn en brasem. Deze vangstreductie moet bijdragen aan de instandhouding van de schubvisbestanden blankvoorn, brasem, baars en snoekbaars. Er zijn tien maatregelen onderzocht die kunnen bijdragen aan de 36% vangstreductie. Maatregelen die op korte termijn te implementeren zijn en die goed handhaafbaar zijn, zijn een 36% reductie van de huidige visserij-inspanning en daarnaast een sluiting van de visserij tijdens de periode 1 januari tot 15 maart of een kortere periode daarbinnen. Omdat de staandwantvisserij een gemengde visserij is, leidt geen enkele maatregel tot een proportionele, effectieve maatregel voor alle vier bestanden tegelijk. De genoemde maatregelen leiden tot besommingsverliezen die onevenredig over vissers verdeeld kunnen zijn.The Ministry of Agriculture, Nature, and Food Quality wants to achieve a 36% catch reduction of roach and bream for the gill net and seine fishery on the IJsselmeer and the Markermeer. This catch reduction should contribute to the preservation of the scaly-fish stocks of roach, bream, perch, and pike-perch. Ten measures were researched with the potential to contribute to the 36% catch reduction. The measures which can be implemented in the short term and which are easily enforceable are a 36% reduction of the current fishing effort and a closure of the fisheries during the period of 1 January to 15 March, or a shorter period within that time-span. Because the gill net fishery is a mixed fishery, no measure will lead to a proportional, effective impact for all four stocks. The abovementioned measures will lead to a loss of income which may be unevenly distributed among the fishermen.Trefwoorden: IJsselmeervisserij, reductie visserij, besomming Dit rapport is gratis te downloaden op https://doi.org/10.De gebruiker mag het werk kopiëren, verspreiden en doorgeven en afgeleide werken maken. Materiaal van derden waarvan in het werk gebruik is gemaakt en waarop intellectuele eigendomsrechten berusten, mogen niet zonder voorafgaande toestemming van derden gebruikt worden. De gebruiker dient bij het werk de door de maker of de licentiegever aangegeven naam te vermelden, maar niet zodanig dat de indruk gewekt wordt dat zij daarmee instemmen met het werk van de gebruiker of het gebruik van het we...
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