CCAMLR

Population dynamics of Black-browed and Grey-headed Albatrosses were studied at Bird Island, South Georgia for 17 consecutive years (1975-1991). Over this period almost all the Grey-headed Albatross colonies decreased, at an average rate of 1.8% per annum. Although the total Black-browed Albatross population increased (at 0.8% p.a.), 14 of the 23 colonies (including both study colonies) decreased. Black-browed Albatrosses follow an annual breeding cycle, with over 80% of birds successful in rearing a chick and 75% of those failing to do so returning to breed the next year, 5- 10% of both categories delaying one further year (even when still paired). Grey-headed Albatrosses are essentially biennial,

Estimates are provided for crabeater seal life-history parameters, to be incorporated into a simple model of the functional relationships between krill escapement and crabeater seal demographic performance. The crabeater seal parameters were estimated from seals collected near the Antarctic Peninsula between 1964 and 1990. Average annual survival rate of adults was estimated to be 0.93. Age at sexual maturity was estimated to be 3.8 years. Of 44 annual estimates of historical cohort strength, 16 were judged to represent “ good" years for demographic performance, 18 as "poor" years, and 10 as "bad" years.

This paper presents a simultaneous system-of-equations approach to modeling age-structured populations using trawl survey age/size frequency data. The analysis builds upon a Ricker spawner-recruit structure and provides a cohort-based estimation method that retains the underlying dynamic properties of a delay-difference model. The framework shares a common spawner-recruit function across age-class equations. This exploits the commonality among cohort members and serves as an instrumental variable, lessening the effect of measurement errors in estimation. The dynamic features of the underlying age-structured population are retained through age-specific net survivability and growth parameters that link age-classes. The technique uses multiple observations on a cohort to further mitigate the effect of measurement error and improve overall estimation efficiency. A seemingly unrelated regression estimation method is required to address contemporaneous correlation of errors across age-classes. This framework is applied to trawl survey data for adult male Alaskan king crab, Paralithodes camtschaticus.

In order to assess the abundance of the red crab Geryon quinquedens, two otter-trawl cruises were undertaken in July and September 1978, on the continental slope off South West Africa. A bimodal frequency distribution of female crabs was evident with modal sizes at 7.7 cm and 8.7 cm carapace width, whereas the mode for males was at 11.2 cm. In general. larger animals tended to inhabit shallower water, i.e. size is inversely related to depth. Females preferred shallower water than males. Shell states indicated that males were predominantly in the inter-moult stage while most females were either approaching or had recently completed the moult. From morphometric relationships, it was calculated that, in processing the live material to a cooked frozen product, red crab is subject to a mass loss of about 54 per cent. Analysis of stomach contents by volume showed that only 12 per cent of male stomachs contained 5 per cent or more food and 2 per cent of female stomachs exceeded the 5-per-cent level. Highest crab densities occurred at depths of 472-849 m, whereas unusually high concentrations were encountered during two trawls at water depths of 549 and 590 m. The red crab survives at extremely low levels of dissolved oxygen and tolerates a temperature range of more than 7°C.