52 research outputs found

    Species richness in North Atlantic fish: Process concealed by pattern

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    International audiencePrevious analyses of marine fish species richness based on presence‐absence data have shown changes with latitude and average species size, but little is known about the underlying processes. To elucidate these processes we use metabolic, neutral and descriptive statistical models to analyse how richness responds to maximum species length, fish abundance, temperature, primary production, depth, latitude and longitude, while accounting for differences in species catchability, sampling effort and mesh size

    Testing for differences in spatial distributions from individual based data

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    Spatial distribution is increasingly studied using individual based telemetric methods in lieu of, or supplementing, surveys. Distributions may be in two- or three-dimensions, or in an abstract space such as depth-temperature space. One of the most basic questions one might address when analyzing these data is whether the distributions of two species, populations, genders, age classes, or other units are different. However due to the inherent differences between survey and telemetric approaches, it is difficult for practitioners to find a simple and easily applied approach to answer this question. In contrast to surveys, telemetry collects a large amount of data about a small number of individuals. Methods must therefore account for the random effects of individual variation in a way not otherwise necessary. We will demonstrate, for example, that tests suitable for detecting differences in distributions from survey data can give false positives (type I errors) when faced with telemetry data. This is essentially because the test treats the large number of data points as a very high n, but in fact the small number of individuals makes the n very small. As a solution, we present a test for differences in distribution based on an existing test for survey data based upon randomizing the data at the level of individuals rather than observations

    Evidence from data storage tags for the presence of lunar and semi-lunar behavioral cycles in spawning Atlantic cod

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    Understanding the environmental processes determining the timing and success of reproduction is of critical importance to developing effective management strategies of marine fishes. Unfortunately it has proven difficult to comprehensively study the reproductive behavior of broadcast-spawning fishes. The use of electronic data storage tags (DSTs) has the potential to provide insights into the behavior of fishes. These tags allow for data collection over relatively large spatial and temporal scales that can be correlated to predicted environmental conditions and ultimately be used to refine predictions of year class strength. In this paper we present data retrieved from DSTs demonstrating that events putatively identified as Atlantic cod spawning behavior is tied to a lunar cycle with a pronounced semi-lunar cycle within it. Peak activity occurs around the full and new moon with no evidence of relationship with day/night cycles

    Kinetic compartment modeling of [11C]-5-hydroxy-L-tryptophan for positron emission tomography assessment of serotonin synthesis in human brain

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    The substrate for the second enzymatic step in serotonin synthesis, 5-hydroxy-L-tryptophan, labeled in the beta-position ([11C]-HTP), was used for positron emission tomography (PET) measurements in six healthy human participants, examined on two occasions. One- and two-tissue kinetic compartment modeling of time-radioactivity curves was performed, using arterial, metabolite-corrected [11C]-HTP values as input function. The availability of unchanged tracer in arterial blood plasma was > or = 80% up to 60 minutes after injection, while [11C]-hydroxyindole acetic acid and [11C]-serotonin accounted for the remaining radioactivity, amounting to < or = 16% and < or = 4%, respectively. Compartment modeling was performed for brain stem, putamen, caudate nucleus, anterior cingulate, white matter, and superior occipital, occipitotemporal, and temporal cortices. The average biologic half-life for plasma-to-tissue equilibrium was 7 to 12 minutes, and the volume of distribution was 0.2 to 0.5 microL.mL(-1). In all regions except white matter, the kinetic compartment model that included irreversible [11C]-HTP trapping showed significantly improved model fits with respect to a one-tissue compartment model. The [11C]-HTP trapping rate constant depended on the estimated tissue availability of the serotonin precursor tryptophan, known to reflect serotonin synthesis in healthy individuals, and correlated with serotonin tissue concentration and synthesis rates reported previously in literature. These findings suggest the use of [11C]-HTP PET measurements to investigate serotonin synthesis

    Temporal analysis of archived samples indicates marked genetic changes in declining North Sea cod (Gadus morhua)

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    Despite increasing evidence that current exploitation rates can contribute to shifts in life-history traits and the collapse of marine fish stocks, few empirical studies have investigated the likely evolutionary impacts. Here, we used DNA recovered from a temporal series of archived North Sea cod (Gadus morhua) otoliths, to investigate genetic diversity within the Flamborough Head population between 1954 and 1998, during which time the population underwent two successive declines. Microsatellite data indicated a significant reduction in genetic diversity between 1954 and 1970 (total number of alleles: 1954, 46; 1960, 42; 1970, 37), and a subsequent recovery between 1970 and 1998 (total number of alleles: 1970, 37; 1981, 42; 1998, 45). Furthermore, estimates of genetic differentiation (F and R ) showed a significant divergence between 1998 and earlier samples. Data are consistent with a period of prolonged genetic drift, accompanied by a replacement of the Flamborough Head population through an increased effective migration rate that occurred during a period of high exploitation and appreciable demographic and phenotypic change. Other studies indicate that diversity at neutral microsatellite loci may be correlated with variability at selected genes, thus compromising a population's subsequent recovery and adaptive potential. Such effects are especially pertinent to North Sea cod, which are threatened by continuing exploitation and rising sea temperatures
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