Testing the implications of a permanent or seasonal marine reserve on the population dynamics of Eastern Baltic cod under varying environmental conditions

In order to test the implications of the establishment of a marine reserve in the Baltic Sea, a spatially disaggregated, discrete time, age-structured model for the Eastern Baltic cod (Gadus morhua callarias L.) stock was constructed. Functional relationships for recruitment and predation mortality were developed by multiple regression analyses. The resultant model output compares well with observed data from the fishery. The model was then applied to simulate stock development over a 50 year time period using different management policies and a variety of environmental conditions. The investigated management policies reduce fishing mortality and range from a moratorium on the Eastern Baltic cod fishery via the establishment of a permanent or a seasonal marine reserve in ICES subdivision 25 to a fishing as usual scenario. The environmental conditions incorporated were based on the size of the reproductive volume (RV) and comprise a best case and a worst case of reproductive conditions, and two more realistic scenarios, where we assumed that a historic series of RV-sizes reoccurs over the simulation period. Our results show a strong dependence of stock dynamics on the environmental conditions. Under prevailing low RV, our model projects stock extinction by the year 2020, if fishing continues as usual. Under the restrictive scenarios, where fishing mortality is reduced either directly or by implementation of a marine reserve, the stock benefits from an increase in stock size and an improved age-structure. A seasonal closure of SD 25 as opposed to a closure of the entire Baltic Sea appears to be sufficient to prevent the Eastern Baltic cod stock from falling below safe biological limits.Baltic cod, management, age-structured model, population dynamics, MPA, environmental variability, reproductive volume

Hot DB White Dwarfs from the Sloan Digital Sky Survey

We present ugriz photometry and optical spectroscopy for 28 DB and DO white dwarfs with temperatures between 28,000K and 45,000K. About 10 of these are particularly well-observed; the remainder are candidates. These are the hottest DB stars yet found, and they populate the "DB gap" between the hotter DO stars and the familiar DB stars cooler than 30,000K. Nevertheless, after carefully matching the survey volumes, we find that the ratio of DA stars to DB/DO stars is a factor of 2.5 larger at 30,000 K than at 20,000 K, suggesting that the "DB gap" is indeed deficient and that some kind of atmospheric transformation takes place in roughly 10% of DA stars as they cool from 30,000 K to 20,000 K.Comment: Accepted by the Astronomical Journal. 34 pages, 10 figures, LaTe

A dusty component to the gaseous debris disk around the white dwarf SDSS J1228+1040

We present Infrared Spectrometer And Array Camera (ISAAC) spectroscopy and ISAAC, UKIDSS, and Spitzer Space Telescope broadband photometry of SDSS J1228+1040-a white dwarf for which evidence of a gaseous metal-rich circumstellar disk has previously been found from optical emission lines. The data show a clear excess in the near- and mid-infrared (IR), providing compelling evidence for the presence of dust in addition to the previously identified gaseous debris disk around the star. The IR excess can be modeled in terms of an optically thick but geometrically thin disk. We find that the inner disk temperatures must be relatively high (similar to 1700 K) in order to fit the spectral energy distribution in the near- IR. These data provide the first evidence for the coexistence of both gas and dust in a disk around a white dwarf, and show that their presence is possible even around moderately hot (similar to 22,000 K) stars