The Distribution and Spread of Alien Vascular Plants on Prince Edward Island

Surveys of alien plants at subantarctic Prince Edward Island in 2001 show that the ranges of all three introduced species have increased since the last survey in 1998. Poa annua, the longest-established species, increased its range substantially after 1987, prior to which it was confined to a single site for more than 20 years. It remains largely restricted to sites characterized by intense disturbance by seals and seabirds. Sagina procumbens, the most recently discovered alien plant, has spread even more rapidly (up to 800 m year^?1) and has colonized the west coast of the island (a leap of at least 3 km). Unlike Poa annua, it is not restricted to animal-disturbed areas, although its seeds probably are dispersed by both birds and fur seals. Cerastium fontanum also continues to spread at the island, but remains confined to the western coastal plain, where it occurs mostly on dry feldmark slopes or erosion scars. All three species have expanded their ranges faster than at Marion Island, possibly because of a warmer recent climate and higher densities of seabirds and seals at Prince Edward Island. The ranges of alien plants are likely to continue to expand, with S. procumbens causing considerable changes in the island's terrestrial ecology.     

Relationship between measurements of hake biomass and sea surface temperature off southern Namibia

A good relationship between the variability in measurements of Cape hake Merluccius capensis biomass during winter and summer swept-area research surveys and sea surface temperature off southern Namibia for the years 1983–1990 is presented. The results call into question the hypothesis that hake density is related to biomass and imply that abnormally warm summers could support higher catches, regardless of the state of the stock. A hypothesis that anomalous warm conditions could induce hake to concentrate closer to the sea bed, making them more susceptible to bottom trawling, is presented.     

A note on the length/mass relationship and mass conversion factors for Agulhas sole Austroglossus pectoralis

The relationship between mass and length and the landed mass/whole mass conversion factors for Agulhas sole Austroglossus pectoralis were investigated and compared to the results of an earlier study. Earlier length/mass relationships overestimate the mass of small soles but underestimate that of large soles. The mass conversion factor of the present study also differed from the earlier results.     

Monthly mean sea level variability along the west coast of southern Africa

Principal components analysis was used to examine monthly data on sea level obtained from tide-gauge records from the west coast of southern Africa over the period 1957—1975. After a simple correction had removed the effect of local atmospheric pressure, this statistical analysis revealed the structure of nearshore ocean variability over time periods of months to years. The first principal component, accounting for over 55 per cent of the variability in monthly mean sea level, was a near uniform rise and fall everywhere along the west coast of southern Africa. The spectrum of this large-scale structure showed a strong interannual trend, which correlated well with long-term trends of temperature anomaly over the entire South-East Atlantic, and a high-frequency term, which could not be resolved at a time period of one month. The second principal component showed the contrasting response of the northern and southern sites on a seasonal scale, and it could be correlated with seasonal wind data. These results compared well with similar analysis carried out in the North Pacific Ocean.