Chalk streams and grazing mute swans

The evidence shows that swan grazing can reduce plant abundance, prevent flowering, reduce water depth and reduce fishery value. However, these effects seem to be limited to a small number of sites on larger chalk streams. The results of attempted management have been disappointing, and we currently have no simple effective means of preventing grazing damage. However, our understanding of the effects of swans on the chalk stream ecosystem has been growing rapidly, which gives us hope for future solutions. In particular, combining strategies which improve river condition and move swans away from sensitive areas could offer a way of managing grazing effects

Marginal states of the resistive tearing mode with flow in cylindrical geometry

The linear stability of tearing modes in a cylindrical plasma subject to a sub-Alfvénic equilibrium shear flow along the equilibrium magnetic field is considered. The equations in the resistive boundary layer at the rational surface are solved numerically using a Fourier transform combined with a finite-element approach. The behaviour of the growth rate as a function of the flow and the various parameters (including a perpendicular fluid viscosity) is obtained. Marginal stability curves showing the dependence of the familiar matching parameter Δ' with flow and shear are also given

Basin bifurcations, oscillatory instability and rate-induced thresholds for AMOC in a global oceanic box model

The Atlantic Meridional Overturning Circulation (AMOC) transports substantial amounts of heat into the North Atlantic sector, and hence is of very high importance in regional climate projections. The AMOC has been observed to show multi-stability across a range of models of different complexity. The simplest models find a bifurcation associated with the AMOC `on' state losing stability that is a saddle node. Here we study a physically derived global oceanic model of Wood {\em et al} with five boxes, that is calibrated to runs of the FAMOUS coupled atmosphere-ocean general circulation model. We find the loss of stability of the `on' state is due to a subcritical Hopf for parameters from both pre-industrial and doubled CO${}_2$ atmospheres. This loss of stability via subcritical Hopf bifurcation has important consequences for the behaviour of the basin of attraction close to bifurcation. We consider various time-dependent profiles of freshwater forcing to the system, and find that rate-induced thresholds for tipping can appear, even for perturbations that do not cross the bifurcation. Understanding how such state transitions occur is important in determining allowable safe climate change mitigation pathways to avoid collapse of the AMOC.Comment: 18 figure

Predicting food requirements of overwintering shorebird populations on the Solway Firth. A report to Scottish Natural Heritage and Marine Scotland

In this report we use a recently-developed spreadsheet model to predict the overwinter food requirements of two shorebird species, oystercatcher (Haematopus ostralegus) and red knot (Calidris canutus), within the Solway Firth. The model is based on the energy requirements of the birds together with the energy value of their shellfish food. The model predicts the quantity of shellfish required to maintain high survival rates, and hence avoid significant mortality events within the oystercatcher and knot populations. Knot were assumed to consume 5-14mm cockles (Cerastoderma edule L.), 5-24mm mussels (Mytilus edulis L.) and 8-16 mm tellin (Macoma balthica L.). Oystercatcher were assumed to consume >15mm cockles, 30-60mm mussels and >12mm tellin. The biomasses of invertebrate prey were derived from intertidal surveys of the site. The population sizes of the bird species were derived from Wetland Bird Survey (WeBS) core counts. Predictions were for the winter of 2013-2014. Shellfishing was assumed to exploit >28mm cockles. The food requirements of oystercatcher and knot were predicted for different combinations of food supply. All scenarios assumed that the birds could consume cockles, mussels and tellin. Alternative scenarios assumed that knot and oystercatcher could consume other food from upshore areas, or that oystercatcher could consume food from terrestrial habitats. Cockle and tellin biomasses were estimated within Solway Firth, and at Wigtown Bay, a site outside the area in which bird population sizes were estimated. Further scenarios therefore assumed that birds either could, or could not, consume food from Wigtown Bay. In each scenario the model initially predicted the amount of shellfish biomass not required by the birds. This was then converted into the biomass potentially available for fishing, accounting for the fact that the size range exploited by fishing did not overlap completely with that consumed by the birds. In the case of knot there was no overlap, and so the amount available to fishing was only calculated from the biomass of shellfish not required by oystercatcher. The model predicted that approximately 700 tonnes of >28mm cockles could potentially be exploited by shellfishing during the winter of 2013-2014, after taking into account the food requirements of the birds, excluding cockle and tellin biomass in Wigtown Bay, and assuming that oystercatcher consumed cockles, mussels, tellin and prey from upshore areas and terrestrial habitats. This was considered to be the most realistic scenario given that oystercatcher can potentially feed on terrestrial and upshore habitats, and given the distance between Wigtown and the area in which oystercatcher population size was estimated. The cockle, mussel and tellin surveys did not cover the entire extent of the Solway Firth, not recording cockles or tellin in English waters or mussels or the Scottish side, and so it is likely that a higher biomass of shellfish food is available to the birds in reality. However, without a more extensive survey it is not possible to quantify this. The spreadsheet model’s predictions for the winter of 2007-2008 were also compared with those of a more complex individual-based model that was developed for oystercatcher and knot in the Solway Firth based on shellfish biomass during 2005 to 2007. The individual-based model predicted that knot survival was 100% in all simulations for the winter of 2007-2008, consistent with the prediction of the spreadsheet model that 18038 tonnes of shellfish were not required by the birds during this winter. The spreadsheet model predicted that the oystercatcher population required all of the shellfish food available during the winter of 2007-2008. Similarly, the individual-based model predicted that oystercatcher were relatively sensitive to the amount of biomass removed by fishing during this winter. With a shellfishing Total Allowable Catch (TAC) set at 1000 tonnes there was a predicted reduction in survival and TACs set at 500, 750 and 1000 tonnes were predicted to reduce body mass. The spreadsheet model predicted that birds required all of the food during 2007-2008 and hence that any TAC would reduce survival. This demonstrates that the spreadsheet model is capable of producing broadly similar predictions to the more complex individual model, although the latter is more sensitive when stock levels are more critical

Predicting oystercatcher food requirements on the Dee Estuary. A report to Natural Resources Wales

In UK estuaries conflicts have routinely occurred between economic and conservation interests regarding shellfish such as cockles Cerastoderma edule and mussels Mytilus edulis. The harvest of these species is economically important, but shellfish also constitute the main overwinter food supply of the oystercatcher Haematopus ostralegus. In this report we use a simplified spreadsheet model to predict the overwinter food requirements of oystercatchers in the Dee Estuary and compare the predictions of this model with those of an individual-based model which has been used to advise the setting of Total Allowable Catch in the Dee Estuary over recent years. The models are based on the energy requirements of the birds and the energy value of their shellfish food. The spreadsheet model predicts the amount of shellfish required to maintain high survival rates within the oystercatcher population. The individual-based model predicts how the survival rate within the oystercatcher population is related to the amount of shellfish food and the amount removed by shellfishing. Although more complicated, the individual-based model represents the system in a more realistic way and can simulate specific shellfishing scenarios. The models produced relatively similar predictions, especially when it was assumed that birds fed on upshore and terrestrial food in addition to cockles. As the biomass of cockles has declined since 2008, the models predicted that the amount required by the birds became close to the total available in 2012. The cockle biomass during 2013 was lower than that during 2012 and the spreadsheet model predicted that the birds required virtually all of the cockle stocks available

Towards a simplified approach for assessing bird food requirements on shellfisheries. A report to the Welsh Government.

In northwest Europe conflicts have routinely occurred between economic and conservation interests regarding shellfish such as cockles and mussels. The harvest of these species is economically important, but shellfish also constitute the main overwinter food supply of the oystercatcher Haematopus ostralegus. In this report we describe attempts to produced a simplified modelling approach to predict the quantities of shellfish which need to be left unharvested in order to ensure high overwinter survival of oystercatcher. We review oystercatcher diet and prey selection in order to quantify the dependence of this species on shellfish, and determine the size ranges of shellfish which the birds consume. We also review the food requirements of oystercatchers, based on their energetic needs and the nutritional quality of shellfish. In general the data agree well with those used in previous oystercatcher modelling studies. However, there is a possibility that the daily energy requirements, calculated from an all bird allometric equation, may yield an underestimate of oystercatcher food requirements. A comparison of the physiological food requirements, i.e. the quantity directly consumed, and the ecological food requirements, i.e. the quantity required to avoid high mortality, indicated that the ecological food requirement was between 2.0 and 7.8 times greater, with the value depending on the proportion of cockles Cerastoderma edule and mussels Mytilus edulis in a site. These ratios are calculated from empirical data on oystercatcher survival and the predictions of individual-based models predicting the relationship between mortality rate and the abundance of the food supply. Data from the Burry Inlet indicated that the mean ecological food requirement was 3.3 times greater at this site. We describe a simplified spreadsheet model, which we used to predict the food requirements of the oystercatcher population of the Burry Inlet, and thus the quantity of shellfish which must be left unharvested in order to maintain low mortality rate. The model is based on parameter values derived from the literature reviews in this study, including the energy requirements of the birds, the energy content of shellfish, the minimum size of cockles and mussels consumed, and the ratio of the ecological and physiological requirements. We describe the assumptions and limitations of the model, and compare the model with more detailed individual-based models that can be used to predict the mortality rate of shorebirds in relation to the amount of food available

The Icefield Ranges Research Project 1967

The Icefield Ranges Research Project conducted its seventh field program in the St. Elias Mountains between 15 May and 1 September 1967. Under the broad categories of Earth Sciences and Biological Sciences, studies in 18 disciplines were conducted by more than 38 investigators and their assistants. This figure does not include personnel of the supporting Kluane Lake Activity of the Arctic Institute of North America, nor does it include 8 visiting investigators who took the opportunity to conduct short-term studies or to observe field programs in operation. ..

Conservation in a changing world needs predictive models

Letter From the Conservation Front Lin