Grey seal predation impairs recovery of an over-exploited fish stock

Grey seal predation has been blamed by fishers for the decline of Atlantic cod stocks and has led to calls for seal culls. In the West of Scotland, estimates of cod consumption by seals have exceeded reported catches and spawning biomass, focussing attention on the interaction between fishers and seals. Bayesian models making different assumptions about seal predation were used to estimate the size of the West of Scotland cod stock between 1985 and 2005 and the mortalities due to fishing and seal foraging. A simple population model was used to identify the likely direction of cod population change at recent mortality rates. All model configurations suggest that the total mortality of cod has remained fairly stable and high for many years regardless of the assumptions on seal predation. The high mortality explains the long-term decline of the stock. The best-fitting model suggests that mortality due to fishing reduced substantially in the decade up to 2005, but has been replaced by increased seal predation mortality on a smaller cod stock. Given total mortality estimates, the stock is unlikely to recover even at present reduced levels of fishing. Synthesis and applications. Our model offers a method of estimating seal predation mortality as part of routine stock assessments that inform fishery management. The analysis shows that predation by seals can be an important component of the total stock mortality. It also shows that assuming invariant natural mortality, as adopted in many standard fish stock assessments, may lead to incorrect perceptions of fishing mortality, over-estimating the benefits of reducing fishing mortality when there is density-dependent predation. It is essential to consider predation by top predators when formulating appropriate advice for managing the fishery

Gamma-Ray Bursts in Circumstellar Shells: A Possible Explanation for Flares

It is now generally accepted that long-duration gamma ray bursts (GRBs) are due to the collapse of massive rotating stars. The precise collapse process itself, however, is not yet fully understood. Strong winds, outbursts, and intense ionizing UV radiation from single stars or strongly interacting binaries are expected to destroy the molecular cloud cores that give birth to them and create highly complex circumburst environments for the explosion. Such environments might imprint features on GRB light curves that uniquely identify the nature of the progenitor and its collapse. We have performed numerical simulations of realistic environments for a variety of long-duration GRB progenitors with ZEUS-MP, and have developed an analytical method for calculating GRB light curves in these profiles. Though a full, three-dimensional, relativistic magnetohydrodynamical computational model is required to precisely describe the light curve from a GRB in complex environments, our method can provide a qualitative understanding of these phenomena. We find that, in the context of the standard afterglow model, massive shells around GRBs produce strong signatures in their light curves, and that this can distinguish them from those occurring in uniform media or steady winds. These features can constrain the mass of the shell and the properties of the wind before and after the ejection. Moreover, the interaction of the GRB with the circumburst shell is seen to produce features that are consistent with observed X-ray flares that are often attributed to delayed energy injection by the central engine. Our algorithm for computing light curves is also applicable to GRBs in a variety of environments such as those in high-redshift cosmological halos or protogalaxies, both of which will soon be targets of future surveys such as JANUS or Lobster.Comment: 12 pages, 5 figures, Accepted by Ap

Liver and Intestine Transplantation in the United States, 1996–2005

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/72937/1/j.1600-6143.2007.01782.x.pd

Hyper-Accreting Black Holes and Gamma-Ray Bursts

A variety of current models for gamma-ray bursts (GRBs) suggest a common engine - a black hole of several solar masses accreting matter from a disk at a rate 0.01 to 10 solar masses per second. Using a numerical model for relativistic disk accretion, we have studied steady-state accretion at these high rates. Inside a radius ~ 10**8 cm, for accretion rates greater than about 0.01 solar masses per second, a global state of balanced power comes to exist between neutrino losses, chiefly pair capture on nucleons, and dissipation. Energy emitted in neutrinos is less, and in the case of low accretion rates, very much less, than the maximum efficiency factor for black hole accretion (0.057 for no rotation; 0.42 for extreme Kerr rotation) times Mdot c**2. The efficiency for producing a pair fireball along the rotational axis by neutrino annihilation is calculated and found to be highly variable and very sensitive to the accretion rate. For some of the higher accretion rates studied, it can be several per cent or more; for accretion rates less than 0.05 solar masses per second, it is essentially zero. The efficiency of the Blandford-Znajek mechanism in extracting rotational energy from the black hole is also estimated. In light of these results, the viability of various gamma-ray burst models is discussed and the sensitivity of the results to disk viscosity, black hole rotation rate, and black hole mass explored. A diverse range of GRB energies seems unavoidable and neutrino annihilation in hyper-accreting black hole systems can explain bursts up to 10**52 erg. Larger energies may be inferred for beaming systems.Comment: 46 pages, includes 9 figures, LaTeX (uses aaspp4.sty), accepted by The Astrophysical Journal. Additional solutions in Tables and Figs. 4 and 5, minor revisions to text, references adde

Geochemical mapping of the Mariana arc-basin system: Implications for the nature and distribution of subduction components

A new ICP-MS database for glasses from the Mariana Trough, together with published and new ICP-MS data from the Mariana arc, provides the basis for geochemical mapping of the Mariana arc-basin system. The geochemical maps presented here are based on the graphic representation of spatial variations in geochemical proxies for the principal mantle and subduction components. The focus is on three elements with high and similar partition coefficients but different behavior in subduction systems, namely, Ba, Th, and Nb. Two elements with different partition coefficients, Ta and Yb, are used as normalizing factors. Ratio maps (Ta/Yb, Nb/Ta, Th/Ta, Ba/Ta, Ba/Th) provide the simplest petrogenetic insights, subduction zone addition maps based on deviations from a MORB array provide more quantitative insights, and component maps represent an attempt to isolate the different subduction components. The maps shown here indicate the presence of a variably depleted asthenosphere and three added components: a Nb-Th-Ba component, a Th-Ba deep-subduction component, and a Ba-only shallow-subduction component. The asthenosphere entering the system is enriched relative to N-MORB and appears to be focused at three sites within the Mariana Trough. The Nb-Th-Ba component is present mainly in the north of the arc (the Northern Seamount province and northern Central Island Province), the northern edge of the Mariana Trough, and two locations within the Southern Seamount Province. It has a distinctively high Nb/Ta ratio and a moderate enrichment in Th and Ba relative to Nb. Its composition and distribution indicate that it may not be part of the present subduction system but instead originates in mantle lithosphere previously enriched above the subduction zone by addition of small-degree, subduction-modified mantle melts. The Th-Ba component is present throughout the arc and, in minor amounts, in parts of the back-arc basin. The Ba-only component is mainly present in the central part of the arc and at the edges of the back-arc basin. Overall, the geochemical maps provide a new perspective on the geochemical processes that accompany the evolution of an arc basin system from prerifting lithospheric enrichment, through arc-rifting to arc volcanism and back-arc spreadin

Hot plasma in the magnetotail lobes shows characteristics consistent with closed field lines trapped in the lobes

We examine the magnetotail using data from the Hot Ion Analyzer on Cluster 1 during 2001–2009. We develop and utilise an algorithm in order to identify times during which Cluster 1 is in the magnetotail lobe but observes plasma which is hotter than our expectations of the lobe. We analyze the prevailing Interplanetary Magnetic Field (IMF) Bz conditions for our algorithm and a reference algorithm (with no particle energy criteria) and find that the periods we select are, on average, ~2 nT more towards northward IMF. Examining the temperature in the magnetotail for our periods shows that the morphology of the average temperature is consistent with the Milan et al. (2005) model of magnetotail structure during Northward IMF, in which closed field lines are prevented from convecting to the dayside, causing them and the plasma trapped on them to protrude into the magnetotail lobes. We also find evidence that ~0.5% of our identified periods may be driven by direct entry into the magnetosphere from the solar wind

A spatio-temporal statistical model of maximum daily river temperatures to inform the management of Scotland's Atlantic salmon rivers under climate change

Faculty Senate Resolution on the Performing Arts Center, adopted on September 14, 1978