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de la Mare W.K.,Australian Antarctic Division
Canadian Journal of Fisheries and Aquatic Sciences

Catch per unit effort (CPUE) is often the only data available from historical fisheries for inferring distribution and abundance of exploited populations. CPUE underestimates variations in relative abundance when gross effort data are only measured in total operating days. Gross effort includes both searching time and handling time, but only searching time is useful for an index of abundance. A method is developed for estimating searching time by subtracting a maximum likelihood estimate of handling time from the gross effort. An expectation maximization (E-M) algorithm is used to combine maximum likelihood estimates of the handling time with the expected additional operating time due to handling the last catch of each day. Simulation tests show that the estimates of catch per unit of searching time (C/CSW) are much closer to proportionally related to local density than gross CPUE. Estimates of handling time are not unbiased, and some nonlinearity between local density and C/CSW may persist. The methods may be useful for other fisheries where historic gross catch and effort data involve both searching and handling. Source

Alexander S.P.,Australian Antarctic Division | Shepherd M.G.,York University
Atmospheric Chemistry and Physics

Temperature data from the COSMIC GPS-RO satellite constellation are used to study the distribution and variability of planetary wave activity in the low to mid-stratosphere (15ĝ€"40 km) of the Arctic and Antarctic from September 2006 until March 2009. Stationary waves are separated from travelling waves and their amplitudes, periods and small-scale vertical distribution then examined. COSMIC observed short lived (less than two weeks and less than 5 km vertically) but large enhancements in planetary wave amplitudes occurring regularly throughout all winters in both hemispheres. In contrast to recent Arctic winters, eastward wave activity during 2008ĝ€"2009 was significantly reduced during the early part of the winter and immediately prior to the major SSW. The eastward waves which did exist had similar periods to the two preceding winters (∼16ĝ€"20 days). A westward wave with zonal wavenumber two, with distinct peaks at 22 km and 35 km and period around 16ĝ€"24 days, as well as a stationary wave two were associated with the 2009 major SSW. In the Southern Hemisphere, the height structure of planetary wave amplitudes also exhibited fluctuations on short time and vertical scales superimposed upon the broader seasonal cycle. Significant inter-annual variability in planetary wave amplitude and period are noticed, with the times of cessation of significant activity also varying. Source

An estimation strategy for natural mortality, M, using multiple cohorts and multiple years of catch-at-age and aged mark-recapture data was tested using simulation. Alternative fishing selectivity functions of age of dome-shaped versus sigmoidally shaped were applied. Two alternative estimation models were developed both using a Poisson likelihood for annual number of recaptures-at-age and model the population numbersat- age by annual difference equations obtained by integrating an ordinary differential equation (ODE) for within-year population dynamics. The 'fully parametric' BODE model is based on the Baranov ODE while the 'semi-parametric' constant catch ODE (CCODE) model uses a new total mortality ODE with constant within-year catch per unit time and does not estimate annual fishing mortality rates (i.e. the F's) or fishing selectivity function parameters. It removes the actual, considered known, catch-at-age numbers directly from the population. Estimation for the BODE model requires an extra component to the log-likelihood which defines the process error in predicted catch-at-age numbers. Simulations assumed 1 000 releases per year over 12 years with recruitment average of 2 million with annual coefficient of variation (CV) of 0.3 and annual catch of 500 000. Simulations which passed catch-at-age numbers to the estimation algorithm after perturbation by observational error were also carried out for each model in order to investigate the effect on estimation of M. Simulations carried out without observational error showed that when all parameters were jointly estimated and selectivity was domeshaped, estimation of M was unreliable for both models but more so for the BODE model. The reason for this is explained by the confounding of selectivity parameter estimates with that for M. In contrast, when sigmoidally shaped selectivity was simulated, and the functional form of selectivity was correctly specified in the BODE model, both models gave close to unbiased and reasonably precise (CVs of 0.07 to 0.14) estimates of M, but the BODE model estimate was substantially more precise. However, when a minor misspecification of the functional form of selectivity was fitted by the BODE model, in comparison the CCODE model gave superior accuracy. When realistic observational error in catch-at-age numbers was included in simulations and combined with the sigmoidally shaped selectivity function, the bias and imprecision in estimates of M increased by no more than 2% for the CCODE model with no increase detectable for the BODE model. With these caveats, both models can be used to estimate this notoriously difficult parameter with the profile likelihood a useful indicator of the degree of success of estimation, even if some bias remains. Source

Wienecke B.,Australian Antarctic Division
Polar Biology

In 1902, the first breeding colony of emperor penguins was discovered. Over the following decades, the number of known emperor penguin colonies increased steadily and new ones are still being discovered. However, rigorous census work has been carried out at only a few colonies and accurate information on trends in breeding populations is limited to a small number of locations. Thus, the total number of breeding pairs is still unknown as is the size of the global population (breeders, non-breeders, juveniles). The International Union for the Conservation of Nature (IUCN) lists the species' status as 'least concern' and states that although the population trend for emperor penguins has not been quantified, the global population appears to be stable. This review summarises the currently available information on the populations of emperor penguins at known colonies in terms of survey methods, count units used and survey frequency. It examines what is known about the state of various colonies and demonstrates that currently available data are inadequate for a trend assessment of the global population. © 2010 Springer-Verlag. Source

Hogan L.,Australian Antarctic Division
Australian Journal of Agricultural and Resource Economics

In July 2010, the Australian Government announced that, effective from 1 July 2012, the petroleum resource rent tax will apply to all offshore and onshore oil and gas projects (including liquefied natural gas and coal seam gas projects), and a minerals resource rent tax will apply to coal and iron ore projects. State/territory governments mainly apply ad valorem royalties to oil and gas, coal and iron ore projects; these royalty payments will be creditable under the Australian Government's resource rent taxes. This paper argues that a hybrid system allows governments to collect a minimum return to the non-renewable resource through the ad valorem royalty and a share of the rent from higher-profit projects through the rent-based tax. This paper also provides updated and expanded estimates of the potential shortfall in resource taxation revenue over the period 1992-1993 to 2009-2010 by comparing actual revenue with revenue under a range of hypothetical Brown taxes. © 2012 The Author. AJARE © 2012 Australian Agricultural and Resource Economics Society Inc. and Blackwell Publishing Asia Pty Ltd. Source

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