Contribution of anadromous fish to the diet of European catfish in a large river system

Many anadromous fish species, when migrating from the sea to spawn in fresh waters, can potentially be a valuable prey for larger predatory fish, thereby efficiently linking these two ecosystems. Here, we assess the contribution of anadromous fish to the diet of European catfish (Silurus glanis) in a large river system (Garonne, southwestern France) using stable isotope analysis and allis shad (Alosa alosa) as an example of anadromous fish. Allis shad caught in the Garonne had a very distinct marine delta(13)C value, over 8 per thousand higher after lipid extraction compared to the mean delta(13)C value of all other potential freshwater prey fish. The delta(13)C values of European catfish varied considerably between these two extremes and some individuals were clearly specializing on freshwater prey, whereas others specialized on anadromous fish. The mean contribution of anadromous fish to the entire European catfish population was estimated to be between 53% and 65%, depending on the fractionation factor used for delta(13)C

Landscape Ecotoxicology of Coho Salmon Spawner Mortality in Urban Streams

In the Pacific Northwest of the United States, adult coho salmon (Oncorhynchus kisutch) returning from the ocean to spawn in urban basins of the Puget Sound region have been prematurely dying at high rates (up to 90% of the total runs) for more than a decade. The current weight of evidence indicates that coho deaths are caused by toxic chemical contaminants in land-based runoff to urban streams during the fall spawning season. Non-point source pollution in urban landscapes typically originates from discrete urban and residential land use activities. In the present study we conducted a series of spatial analyses to identify correlations between land use and land cover (roadways, impervious surfaces, forests, etc.) and the magnitude of coho mortality in six streams with different drainage basin characteristics. We found that spawner mortality was most closely and positively correlated with the relative proportion of local roads, impervious surfaces, and commercial property within a basin. These and other correlated variables were used to identify unmonitored basins in the greater Seattle metropolitan area where recurrent coho spawner die-offs may be likely. This predictive map indicates a substantial geographic area of vulnerability for the Puget Sound coho population segment, a species of concern under the U.S. Endangered Species Act. Our spatial risk representation has numerous applications for urban growth management, coho conservation, and basin restoration (e.g., avoiding the unintentional creation of ecological traps). Moreover, the approach and tools are transferable to areas supporting coho throughout western North America

RUPTURE NUCLEATION ON AN INTERFACE WITH A POWER-LAW RELATION BETWEEN STRESS AND DISPLACEMENT DISCONTINUITY

Abstract. We consider rupture initiation and instability on a displacement-weakening interface. It is assumed to follow a power-law relation between a component of displacement discontinuity (whether tensile opening in mode I or shear slippage in modes II or III) and the reduction from peak strength of a corresponding component of stress (normal or shear stress) on the interface. That is, the stress decrease from peak strength, as the interface discontinuity develops, is assumed to be proportional to displacement-discontinuity to some exponent n> 0. The study is done in the 2D context of plane or anti-plane strain, for an initially coherent interface which is subjected to a locally peaked "loading " stress which increases quasi-statically in time. We seek to establish the instability point, when no further quasi-static solution exists for growth of the ruptured zone along the interface, so that dynamic rupture ensues. We have previously addressed the case of linear displacement-weakening (n = 1), and proven the remarkable result that for an unbounded solid, the length of the displacement-weakening zone along the interface at instability is universal, in the sense of being independent of the detailed spatial distribution of the locally peaked loading stress. Present results show that such universality does not apply when n differs from 1. Also, if n < 2/3, there is no phase of initially quasi-static enlargement of the rupturin

Do fall additions of salmon carcasses benefit food webs in experimental streams?

Research showing that salmon carcasses support the productivity and biodiversity of aquatic and riparian ecosystems has been conducted over a variety of spatial and temporal scales. In some studies, carcasses were manipulated in a single pulse or loading rate or manipulations occurred during summer and early fall, rather than simulating the natural dynamic of an extended spawning period, a gradient of loading rates, or testing carcass effects in late fall-early winter when some salmon stocks in the US Pacific Northwest spawn. To address these discrepancies, we manipulated salmon carcass biomass in 16 experimental channels located in the sunlit floodplain of the Cedar River, WA, USA between mid-September and mid-December, 2006. Total carcass loads ranged from 0–4.0 kg/m2 (0, 0.001, 0.01, 0.1, 0.5, 1.0, 2.0 and 4.0 kg/m2, n = 2 per treatment) and were added to mimic the temporal dynamic of an extended spawning period. We found little evidence that carcasses influenced primary producer biomass or fish growth; however, nutrients and some primary consumer populations increased with loading rate. These effects varied through time, however. We hypothesize that the variable effects of carcasses were a result of ambient abiotic condition, such as light, temperature and disturbance that constrained trophic response. There was some evidence to suggest peak responses for primary producers and consumers occurred at a loading rate of *1.0–2.0 kg/m2, which was similar to other experimental studies conducted during summer