Two acoustic surveys of pelagic fish in Hawke Bay,New Zealand, 1980

The design and execution of two acoustic surveys of Hawke Bay in February and September/October 1980 are described. Though the resulting acoustic data were, for technical reasons, of limited value, they illustrate the information which may be drawn from acoustic surveys. Fish distributions may be rapidly mapped, not only by area, but throughout most of the water column and over time. Qualitative observations on fish distribution may be quantified. The estimation of variance in acoustic surveys is discussed in detail with particular emphasis on the problems of systematic surveys. The role of replicate observations is stressed. Coefficients of variation for relative fish density estimates from the two surveys probably lie between 5 and 30%.     

Exploring the links between health and housing: The limitations of population health surveys

While it is intuitively attractive to link health status and the quality of housing, it is methodologically complex to identify the relative importance of housing because individual characteristics and environmental variables act as confounders. A secondary issue is that the data sets which contain detailed data on health status and environmental variables often contain only limited data on housing. Similarly, housing surveys rarely contain detailed data on health and environmental variables. Respondents from Montreal, Toronto and Vancouver in the public use micro-data files of the 1996/97 cycle of the National Population Health Survey make up the data sets for a series of logistic regression models where health status, allergies, asthma, arthritis, migraines and bronchitis/emphysema act as the dependent variables. Sets of variables which measure housing, the environment (smoking and alcohol consumption) and the socio-economic status of individuals are used as independent variables. The issues of confounders and the limitations of the data are illustrated by the results of the analysis. If we are to go beyond local area surveys and carry out broader analyses of the links between health status and the quality of housing, researchers and data collection agencies will need to re-think the artificial divisions between these two critical aspects of peoples' lives.     

The influence of physical and biological processes on the ichthyoplankton communities in the Gulf of Sirte (Southern Mediterranean Sea)

This paper reports on the first study on the ichthyoplankton community structure in the Gulf of Sirte and its spatial distribution in relation to environmental conditions and zooplankton abundance. The results make an important contribution to the future management of fisheries in this unexplored, but much exploited, area. Biological samples were collected in July 2008 using a Bongo40 net. In total, 1914 larvae were found and 1652 of these were identified. In particular, bathypelagic taxa were the most abundant, followed by demersal, mesopelagic, pelagic and epipelagic taxa. The ichthyoplankton community had a patchwork distribution influenced by oligotrophic conditions, the bottom depth and oceanographical features. The results suggest that environmental forcings were able to transport the ichthyoplankton to productive areas. Indeed, maximum fish egg densities were found in coastal stations in correspondence with the Atlantic Tunisian Current inflow, whereas larvae were mainly concentrated in the east side of the Gulf, probably as a result of advection by the anticyclonic circulation. Additionally, the distribution patterns of the total larvae density and the different assemblages were well matched with the abundance of the zooplankton, probably determining final larval survival, growth and recruitment.