CCAMLR

The properties of a method for detecting anomalous years in CCAMLR index series are discussed. In simple cases this method involves comparing a standardized residual with a critical value obtained on the assumption that the series being considered consists of random values from a constant normal distribution. This idea is extended to situations (a) where the series values are still normally distributed, but contain a linear trend and autocorrelation, and (b) where the series values are from some other constant distribution. For cases like (a) # is proposed that the standardized deviations from a fitted linear regression line are compared with a critical value that is obtained on the assumption that there is no autocorrelation. This test is shown to have good properties even when autocorrelation is present, at least according to one model For cases like (b) it is proposed that a Box-Cox transformation to normality is applied before testing standardized residuals. This test has good properties for data from a wide range of distributions. Some examples are given to illustrate the performance of the proposed methods under various conditions.

Data on Antarctic petrel Thalassoica antarctica population and demography monitoring at Svarthamaren, Dronning Maud Land from five field seasons between 1991/92 and 1996/97 is presented. The results of the population monitoring show that the number of pairs with chick or egg varied between 55,387-178,240 (mean 119,000). Assuming that about 10 % of the colony is situated in inaccessible parts outside the area covered by the monitoring system the mean number of pairs producing a chick each year is about 132,000. On average 52% of the reproductive fraction of the population breeds each year indicating that the total number of reproductive birds attached to the colony is approximately 510,000 individuals. Annual survival rates varied between 0.871-0.954 (mean 0.924). Our results suggest that a monitoring programme for breeding Antarctic Petrels should include estimation of mortality rates and breeding frequency in addition to the numbers of birds breeding.

Target strength measurements of free swimming krill at 120kHz were made using a single beam monostatic system in a 10 m3 laboratory tank. Krill (grouped according to length classes) swam freely in the tank triggering the data acquisition system when generating a back scattered signal larger than a threshold, determined by the system noise level. Dorsal and ventral target strength estimates were calculated indirectly by deconvolution of the cumulative probability function of echo ensembles of single animal insonifications. For mean length classes in the range [29.6, 36.2] mm the median single-animal target strengths are in the range [-76.7,-71.8] dB. Monte Carlo computer simulations were used to evaluate the effects of varying the ratio of largest to smallest echo amplitudes for a given ensemble, thus enabling the estimation of threshold induced bias in the target strength estimates. The threshold induced bias was then determined for each ensemble of experimental data and used to determine corrections which were in the range of [-0.84, -0.33] dB. An error analysis of the target strength estimates detailing the components due to measurement accuracy and precision, and the indirect signal processing techniques used is also presented.