Visual census as a means to estimate standing biomass, length, and growth in fishes.

Abstract

A point-count visual census technique was used, in situ to estimate population size as well as length of individual fish during the summer months off the Canarian Islands of El Hierro in 1989 and Fuerteventura in 1990. These data were used to determine fish standing biomass to assess and monitor the environmental health of the inshore habitat. The standing biomass for parrotfish, Sparisoma cretense. off El Hierro (an island as yet undeveloped by the tourist industry) was 399 - 409 g/100m2 The more heavily developed and populated island of Fuerteventura had a standing biomass of only 209 - 228 g/100m2 for this same species. The length-frequency data indicated parrotfish growth in 1989 may have been an artifact owing to the ability of in situ observers to determine fish length precisely, especially in larger fishes. However, an increase in length was also noted for rainbow wrasse, Coris julis during the same five week period. This suggests that it is possible for observers to determine growth, in situ, when the length classes are small and/or the number of fish observed is large enough to account for increased variability in the data set caused by in situ observation.