Trends in Wadden Sea Fish Fauna, Part II: Dutch Demersal Fish Survey (DFS)

Shallow waters along the North Sea coast provide nursery areas for juveniles of several fish species, including commercially exploited species, and natural habitat for resident species and seasonal visitors. These areas have gone through major changes in the last decades due to climate change and human activities, which will likely result in changes in the abundance and species composition of the fish fauna in coastal waters

Studies on breeding shorebirds at Medusa Bay, Taimyr, in summer 2001

In the Summer of 2001 a combined Dutch-Russian expedition took place to the Willem Barentz field station at Medusa Bay near Dikson in north-western Taimyr. The expedition was organized by Alterra, the Working Group for International Waterbird and Wetland Research (WIWO) and the Agricultural Department of the Dutch Embassy in Moscow. The results obtained by the Alterra team are presented in this report. Subjects of study generally concerned breeding biology of arctic breeding shorebirds, especially aspects related to timing of breeding and adult body condition. This report's purpose is not to discuss the findings thoroughly but merely to summarize the research questions addressed and present all basic information collected during the 2001 season. Topics included are spring arrival and autumn departure of waders from the tundra, breeding phenology, nest success, biometrics of adult waders, chick growth rate, return rates of adult shorebirds, and seasonal and weather-related variation in arthropod availability. Where useful, results are compared with data collected in a previous expedition in 2000. More elaborate analyses and discussion of the data will be made elsewhere

Onderzoeksagenda duurzame garnalenvisserij

Op 13 mei 2009 hebben het Ministerie van LNV, de gezamenlijke Producentenorganisaties voor de garnalenvisserij in Nederland, en de natuurorganisaties Stichting de Noordzee en de Waddenvereniging het belang onderschreven van een gezamenlijk traject naar een verduurzaming van de garnalenvisserij. Hiertoe hebben zij een aantal afspraken ondertekend als start voor het opstellen van deze “Agenda naar een Duurzame garnalenvisserij”. Deze beleidsagenda kent een aantal korte termijn afspraken (t/m 2010) en voor de langere termijn (t/m 2020) wordt een transitietaakstelling neergezet. Eén van de afspraken voor de korte termijn is dat het noodzakelijk is dat er in 2009 een concrete onderzoeksagenda inclusief uitvoeringsprogramma wordt opgesteld. De opstelling van deze onderzoeksagenda hangt samen met de het opstarten van onderzoek dat door LNV als voorwaarde opgenomen is in de NB-wetvergunning voor de garnalensector, en is tevens een voorwaarde in het Beheer en Managementplan (BMP) dat de garnalensector heeft opgesteld om te voldoen aan de criteria van MSC (Marine Stewardship Council)-certificering. Volgend uit het BMP MSC-certificering is reeds een Onderzoeksvoorstel opgesteld door de Kopgroep MSC Garnalen (27 maart 2009) waarin een inventarisatie van lopend en benodigd onderzoek wordt gepresenteerd. Daarnaast moet de onderzoeksagenda ondersteunend zijn aan de nog te maken langere termijn afspraken gericht op de verduurzaming van de garnalensector in 2020

Eggs in the freezer: energetic consequences of nest site and nest design in Arctic breeding shorebirds

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 diameter 2 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

Mechanisms promoting higher growth rate in arctic than in temperate shorebirds

We compared prefledging growth, energy expenditure, and time budgets in the arctic-breeding red knot (Calidris canutus) to those in temperate shorebirds, to investigate how arctic chicks achieve a high growth rate despite energetic difficulties associated with precocial development in a cold climate. Growth rate of knot chicks was very high compared to other, mainly temperate, shorebirds of their size, but strongly correlated with weather-induced and seasonal variation in availability of invertebrate prey. Red knot chicks sought less parental brooding and foraged more at the same mass and temperature than chicks of three temperate shorebird species studied in The Netherlands. Fast growth and high muscular activity in the cold tundra environment led to high energy expenditure, as measured using doubly labelled water: total metabolised energy over the 18-day prefledging period was 89% above an allometric prediction, and among the highest values reported for birds. A comparative simulation model based on our observations and data for temperate shorebird chicks showed that several factors combine to enable red knots to meet these high energy requirements: (1) the greater cold-hardiness of red knot chicks increases time available for foraging; (2) their fast growth further shortens the period in which chicks depend on brooding; and (3) the 24-h daylight increases potential foraging time, though knots apparently did not make full use of this. These mechanisms buffer the loss of foraging time due to increased need for brooding at arctic temperatures, but not enough to satisfy the high energy requirements without invoking (4) a higher foraging intake rate as an explanation. Since surface-active arthropods were not more abundant in our arctic study site than in a temperate grassland, this may be due to easier detection or capture of prey in the tundra. The model also suggested that the cold-hardiness of red knot chicks is critical in allowing them sufficient feeding time during the first week of life. Chicks hatched just after the peak of prey abundance in mid-July, but their food requirements were maximal at older ages, when arthropods were already declining. Snow cover early in the season prevented a better temporal match between chick energy requirements and food availability, and this may enforce selection for rapid growth.

Zeldzame vissen in het IJsselmeergebied : jaarrapport 2002

In deze rapportage wordt een overzicht gegeven van de vangsten in de periode 1994 t/m 2002, waarbij voor de hele periode een selectie gemaakt is van de vissers die gedurende de laatste twee jaren de bemonstering uitgevoerd hebben. Van negen zeldzame soorten (waaronder vijf rode lijstsoorten) presenteren we verspreiding in de ruimte en tijd, lengtefrequentieverdelingen, rijpheidsstadia en geslachtsverhoudingen

Overzicht Wadvisserij Deelproject A bijvangst garnalenvisserij Eindrapportage

In 2009 hebben het Ministerie van LNV, de gezamenlijke Producentenorganisaties voor de garnalenvisserij in Nederland, en de natuurorganisaties Stichting de Noordzee en de Waddenvereniging het belang onderschreven van een gezamenlijk traject naar een verduurzaming van de garnalenvisserij. Daarnaast wil de Nederlandse garnalenvisserij in aanmerking komen voor een Marine Stewardship Council (MSC) label. Hiervoor moet inzicht verkregen worden in de bijvangst in de Nederlandse garnalenvisserij

Modelling population effects of juvenile offshore fish displacement towards adult habitat

Recent studies of fish distribution patterns highlight shifts in the spatial distributions of particular life-stages. Focus has thus far been on changes in habitat use and possible drivers for these changes. Yet, small-scale shifts in habitat use of certain life stages may have profound consequences on population dynamics through changes in resource use and competition. To explore this, a conceptual stage-structured model was developed with 3 stages and 2 resources and allowing a move of large juveniles from the shallow to the deep habitat. Large juveniles compete with small juveniles in shallow waters and with adults in deeper waters. Alternative stable states occur, with one state dominated by small juvenile biomass and the other dominated by adult biomass.The model results show for both states that while large juvenile biomass responds to a change in time spent in the deep habitat, the biomass of small juveniles and adults is barely affected. Between the 2 states there is a profoundly different population response to increased fishing mortality. In the adult biomass dominated state, adult biomass is hardly affected while juvenilebiomass increases until population collapse, with increased fishing. In the small juvenile dominated state, adult and small juvenile biomass decrease, and large juvenile biomass increases. This state persists at much higher fishing mortality than the adult biomass dominated state. This study highlights that safeguarding nursery functions in a changing environment requires monitoring of juvenile life-stages in a range of habitats and a spatially adaptive management strateg

Memo: Naar een Rijke Visstand - Inventarisatie

Inventarisatie naar de bestaande kennis over (1) de huidige toestand van de visgemeenschap in de Waddenzee en Noordzeekustzone (2) alsmede naar het staande en toekomstige beleid relevant voor dit onderwerp

Klimaatverandering in de Noordzee: gevolgen voor vis

Niet alleen op het land merken we de invloed van de opwarming van de aarde, ook in de zee zijn er grote veranderingen waarneembaar. In hoeverre deze veranderingen toe te schrijven zijn aan klimaatverandering is moeilijk te zeggen. Want behalve het veranderend klimaat zijn er nog andere belangrijke factoren die tegelijkertijd invloed uitoefenen, zoals visserij en eutrofiëring. Aan de hand van veranderingen in de visfauna in de Noordzee zullen we de mogelijke rol van klimaatverandering illustrere