Monitoring and Modelling Bio-Physical Parameters for Hypoxia Hazard in a Coastal Sand Pit

Management of coastal areas requires monitoring and modeling of the anthropogenic drivers and the bio-physical processes affecting water quality. To assess the range of hydrographic conditions controlling oxygen distribution in the bottom layers of sand pits, a multi-year oceanographic survey has been conducted in a coastal area with several extraction pits. Hydrographic data including profiles of temperature, salinity and oxygen were collected and related to local wind conditions and circulation. Moreover, 1D and 3D high-resolution non-hydrostatic ocean models were used to describe turbulent mixing regimes and to obtain the range of wind speeds for which the critical anoxic conditions may occur. It is shown that wind speed appears to control the dynamics of oxygen concentrations, with oxygen depleted zones developing in a short time in low wind speed conditions. Moreover, the depth and the shape of the extraction pit contribute to decrease the mixing of the bottom layers and increase the water retention in the hole increasing the output and the persistence of oxygen depleted zones in the excavated area. The results of the numerical simulations show that the risk of hypoxia at the bottom of the sand pits is associated with higher temperatures and wind speed lower than 5 m/s, which is not infrequent during the summer season. However, the number of consecutive days of oxygen depletion can be considered lower than the danger threshold level assumed in the literature

Development and use of a bioeconomic model for management of mussel fisheries under different nutrient regimes in the temperate estuary of the Limfjord, Denmark

Coastal ecosystems worldwide are under pressure from human-induced nutrient inputs, fishing activities, mariculture, construction work, and climate change. Integrated management instruments handling one or more of these problems in combination with socioeconomic issues are therefore necessary to secure a sustainable use of resources. In the Limfjord, a temperate eutrophic estuary in Denmark, nutrient load reductions are necessary to fulfill EU regulations such as the Water Framework Directive (WFD). The expected outcome of these load reductions is an improved water quality, but also reduced production of the abundant stock of filter-feeding blue mussels, Mytilus edulis. This is expected to have significant economic consequences for the million-euro mussel fishing industry taking place in the Limfjord today. We developed a bioeconomic model that can be used to explore the consequences of load reductions for mussel fishery as practiced today, as well as potential management options, to obtain an economically and ecologically sustainable mussel fishery. Model simulations clearly demonstrate a substantial decrease in mussel production after the nutrient load reductions necessary to obtain the targets in the WFD. With today's practice, the mussel fishery in the Limfjord will not be profitable in a future, less eutrophic estuary. However, model simulations also revealed that mussel fishery can be profitable after implementation of the WFD with a reduction in the total fishing quota, fewer fishing vessels, and a higher fishing quota per vessel

Differential expression of gonadotropin and estrogen receptors and oocyte cytology during follicular maturation associated with egg viability in European eel (Anguilla anguilla)

acceptedVersio

Fangst og bifangst i garnfiskeri efter helt i Ringkøbing Fjord

Ringkøbing Fjord er et opvækstområde for Danmarks største bestand af helt og understøtter et lokalt kommercielt garnfiskeri efter helt. Fjorden er også et opvækstområde for havørreder, som reproducerer sig i fjordens tilløb. Det største tilløb, Skjern Å, der leverer omkring 70% af den samlede årlige udtræk af ørredsmolt, har de seneste 20 år været underlagt en række forvaltningstiltag for at forbedre forholdene for blandt andet laksefiskene i åløbet. Den positive udvikling af miljøet og laksebestanden i åen genfindes dog ikke hos havørredbestanden. I modsætning til laks som opholder sig kortvarigt i fjorden inden de vandrer videre ud i havet, anvender havørreder fjorden som opvækstområde og dermed opholder de sig i fjorden i flere år. Derfor er blikket blevet rettet mod presfaktorer i løbet af ørredernes ophold i fjorden, hvor der blandt andet blev sat fokus på fiskeri med nedgarn i fjorden. Denne rapport omhandler således en undersøgelse af heltfiskeriet i Ringkøbing Fjord, med det formål at belyse bifangst af primært havørreder og dermed bidrage med data til videns-baseret rådgivning af fiskeriforvaltningen i fjorden.DTU Aqua gennemførte forsøgsfiskeri med heltgarn over fire år i 2012, 2014, 2015 og 2017. Dette forsøgsfiskeri blev gennemført for at undersøge fangst og bifangst af henholdsvis helt og primært ørreder på forskellige dybder, med forskellige heltgarn typer, på forskellige tidsperioder i løbet af døgnet eller med forskellige røgtningstidspunkter. Herudover blev der gennemført observatør-ture med det kommercielle fiskeri, hvor ansatte fra DTU Aqua eller Fiskerikontrollen deltog i røgtning af heltgarn og registrerede fangsterne. Endeligt blev der gennemført en spørgeskemaundersøgelse med henblik på at indsamle yderligere oplysninger om heltfiskeriet, her- under fiskeriindsatsen i fjorden.Der blev fanget 22 arter i DTU Aquas forsøgsfiskeri med heltgarn. De hyppigste fangede arter i bifangsten var skrubbe, smelt og sild. Der blev fanget betydelig flere skrubbe end helt i dette fiskeri. Samme mønster blev observeret i det kommercielle heltfiskeri.Det eksperimentelle feltarbejde viste, at bifangsten af ørreder i heltfiskeriet var mere eller mindre konstant uanset fiskerimetode anvendt. Et estimat for den gennemsnitlige bifangst af ørreder i det kommercielle heltfiskeri var 0,52 ørreder per tur.På baggrund af vores resultater var der to tiltag, som kunne reducere bifangst af ørreder uden at påvirke heltfangsten:a) Forbud mod brugen af flydende heltgarn. Vores studie viser dog, at det overvejende anvendte redskab i det kommercielle heltfiskeri allerede i dag er bundstående heltgarn.b) Begrænse det kommercielle heltfiskeri til dybder større end 2 m. Her vil bifangsten af havørred kunne reduceres samtidig mens fangsten af helt optimeres. Vores studie tyder dog på, at det kommercielle fiskeri efter helt primært foregår på dybere van

Chronic CO2 exposure markedly increases the incidence of cataracts in juvenile Atlantic cod Gadus morhua L.

A study was undertaken to test the affect of chronic exposure to elevated dissolved carbon dioxide on juvenile Atlantic cod. The CO2 treatment concentrations were designated as low (1-2 mg L-1, 1000 mu atm), medium (8 mg L-1, 3500 mu atm) and high (18 mg L-1, 8500 mu atm), and the fish were reared at 10 C and 20% salinity. A marked observation at the end of the 55 day trial was that an increase in the incidence of eye lesions correlated with increasing CO2 concentration. Typical lesions included unilateral and bilateral exopthalmos, gas bubbles under the sclera and cataracts, and these were quantified in all fish (n = 757 individuals) using field methods. The most notable difference between CO2 treatments was the prevalence and intensity of lenticular cataracts, which were primarily diffuse rather than nucleated. Nearly 75% of all fish from the high CO2 treatment were found to have some degree of cataractous lesion, compared with 10-13% for the other treatments. The severity of the cataract was most pronounced at the highest CO2 concentration, with many fish presenting complete bilateral cataracts. These data indicate that chronic exposure to high CO2 concentrations can cause cataracts in juvenile Atlantic cod. To our knowledge this is the first report of CO2 as a causative agent or aggravating factor for cataracts. (C) 2012 Elsevier B.V. All rights reserved