The sand flounder Rhombosolea plebeian (Richardson)si found throughout the shallow coastal regions and inlets of New Zealand. The object of this study was to determine the relationship, if any, between the sand flounders inhabiting the bays and inlets of Banks Peninsula and those fish subject to exploitation by trawlers operating in the offshore deeper waters. The aspects studied were as follows. Age determination was based on the interpretation of otoliths. Serveral methods of treatment were tired, staining providing the most successful. Length frequency distributions were analysed for samples taken between January 1964 and February 1967. The apparent shrinkage of fish after death was investigated, and a correction factor calculated for growth rate studies from tag returns. A trial of four varieties of tags was run concurrently with a tagging programme designed to investigate movement, growth and population dynamics. Spaghetti tags were shown to be superior to Petersen discs. Growth data from tag returns was combined with that from otolith and length frequency interpretations, and seasonal and annual growth rates calculated. A close relationship between inshore and offshore fish was proved, and evidence presented which indicated that two separate populations may be present. Feeding habits were investigated, and the results related to age and locality. Population estimations, survival, recruitment and emigration rates were calculated, and the importance of certain inshore regions to the offshore grounds discussed.