Browsing by Subject "abundance"

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    Conditioning SMOM using the agreed calendar of observed changes in predator and krill abundance: a further step in the development of a management procedure for krill fisheries in area 48
    (2008) Plagányi, Éva E; Butterworth, Doug S
    The updated version of the Spatial Multi-species Operating Model (SMOM) of krill-predatorfishery dynamics described in an accompanying paper is conditioned using the WG-SAM set of reference observations for Area 48 (the SAM calendar). Results are presented for two implementations of SMOM, one with the time series of krill abundance fixed on input, and the other incorporating an explicit model of krill dynamics. Additional versions of SMOM that may need to be conditioned are discussed. In general the two SMOM implementations are broadly successful in reproducing the direction and timing of observed changes in predator abundance. The main method of conditioning involved estimating a shape parameter (the “steepness”) of the predator-prey interaction formulation. The steepness values estimated suggest that penguins respond sooner than other predators to decreasing levels of krill abundance. Given data on fish catches, the model estimates the starting (1970) fish abundance level, with results suggesting that fish populations in several of the SSMUs are much reduced compared to their 1970 levels. The conditioned operating models presented here constitute a further step towards the development of a spatially-structured Management Procedure (MP) for the krill fishery by contributing to the set of such operating models to be used to simulation test candidate MPs for robust performance. The next step involves agreeing the relative plausibilities (weights) for the different operating models. An outline of suggested future steps in the MP development process is discussed.
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    A Generalized Linear Model applied to the South Cost rock lobster CPUE data to obtain area-specific indices of abundance
    (2008) Glazer, Jean Patricia; Butterworth, Doug S
    Area-disaggregated assessments for South Coast rock lobster are currently being developed. An important input to these assessments is the catch per unit effort (CPUE) data. A Generalized Linear Model (GLM) has been applied to the data to obtain areaspecific standardized indices of abundance for input to the assessment models.
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    An integrated approach for the estimation of abundance through a random-effects model
    (2007) Kitakado, T; Butterworth, Doug S; Okamura, H
    Let Nay be the true abundance in the a-th survey block in the year y, and let Nˆ ay (P) and Nˆ ay (C) denote estimates of Nay obtained from passing-mode and closing-mode surveys respectively. If abundance estimates in different blocks or years include common parameters such as effective search half-width, then any two of them are correlated, and the method following takes this into account.
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    Spectroscopic properties of star-forming host galaxies and type Ia supernova hubble residuals in a nearly unbiased sample
    (2011) D\'Andrea, Chris B; Gupta, Ravi R; Sako, Masao; Morris, Matt; Nichol, Robert C; Brown, Peter J; Campbell, Heather; Olmstead, Matthew D; Frieman, Joshua A; Garnavich, Peter; Jha, Saurabh W; Kessler, Richard; Lampeitl, Hubert; Marriner, John; Schneider, Donald P; Smith, Mathew
    We examine the correlation between supernova (SN) host-galaxy properties and their residuals in the Hubble diagram. We use SNe discovered during the Sloan Digital Sky Survey-II Supernova Survey, and focus on objects at a redshift of z < 0.15, where the selection effects of the survey are known to yield a complete Type Ia supernova (SN Ia) sample. To minimize the bias in our analysis with respect to measured host-galaxy properties, spectra were obtained for nearly all hosts, spanning a range in magnitude of -23 < M{sub r} < -17. In contrast to previous works that use photometric estimates of host mass as a proxy for global metallicity, we analyze host-galaxy spectra to obtain gas-phase metallicities and star formation rates (SFRs) from host galaxies with active star formation. From a final sample of {approx}40 emission-line galaxies, we find that light-curve-corrected SNe Ia are {approx}0.1 mag brighter in high-metallicity hosts than in low-metallicity hosts. We also find a significant (>3{sigma}) correlation between the Hubble Residuals of SNe Ia and the specific SFR of the host galaxy. We comment on the importance of SN/host-galaxy correlations as a source of systematic bias in future deep SN surveys.
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    Winter bird assemblages, species richness and relative abundance at a re-vegetated coal mine in the Middelburg district, Mpumalanga Province, South Africa
    (2005) Little, I T; Little, R M; Jansen, R; Crowe, T M
    Winter bird assemblages, species richness and relative abundance were investigated at six re-vegetated sites within the Middelburg Coal Mine (Mpumalanga, South Africa) and compared with those for a site thought to be representative of un-mined biotope within the nearby Witbank Nature Reserve. Age of site since initiation of re-vegetation had little or no apparent effect on richness or abundance. Adjacency to currently active mining and variation in current land management practices appeared to have much more profound effects. Sites surrounded by active mining had lower richness and abundance. Those with 40% or more land left as fallow and strips of un-mowed grass as well as artificial ponds had higher bird richness and abundance.