Effects of pile size of artificial reefs on the standing stocks of fishes

Abstract

The relationship between production and reef pile size was analysed using standing stocks of fishes surveyed at three established artificial reef (AR) habitats in the subtropical waters off the northern coast of Taiwan during April–August 1999. For a closer look, the fish assemblage was further divided into visitors and residents, and biomass was used as a parameter to represent production. Visitors were characterised by sporadic occurrences and highly variable school sizes. However, large schools (containing more than 200kg of biomass) occurred only around small AR piles (consisting of less than 15 units of 2-m3 concrete reef). Considering visitors alone, the correlation between biomass and pile size was not significant for the combined data from three sites. Changes in the standing stock of residents followed a clearer trend, and the relationship could be fitted to a sigmoidal equation. This trend shows that collections of the residents tended to increase until the pile reached a size of 20–30 reef units. Thereafter, the increase in biomass slowed, and maximum biomass would eventually be reached only with a further increase in the pile size. Predictions of the efficiency of unit reefs for different pile sizes indicate that a pile consisting of 4–10 units of this type of reef would be most effective in terms of biomass of residents. Nevertheless, a size of 15 units is recommended when the behaviour of visitors is taken into account.