CRAMP Rapid Assessment. Other Fish Survey Techniques
Numerous methods have been developed for sampling fishes. Method selection depends on the focus of the research and the spatial and temporal scales involved. Accuracy can depend on the number and size of transects and whether transect locations are randomly selected, stratified random (e.g. following depth contours), or fixed. Fixed transects may not be representative of the entire community of interest but allow for more accurate repeated measurements.
Spatial and temporal variability of fishes can be extremely high due to mobility and large home ranges. Many fish species are cryptic, rare or transient. There are also diurnal/nocturnal and seasonal sources of variability. To quantify absolute values for fish populations an extremely large sample size is required especially for heterogeneous habitats. Relative values are often used to determine differences between sites.
Our RATs species abundance estimates were selected to maximize data and statistical comparability, allow for length to biomass conversions, and avoid limitations inherent in some other methods. This method includes two measures of abundance: numerical and biomass. These are both important population parameters that address different aspects of fish community structure. Unlike the belt transect method, species abundance estimates do not require additional survey time to allow for fish equilibrium to occur. The transect line is spooled out as the survey is conducted to avoid fish dispersal. Although additional dive and training time must be allotted to estimate fish length, post processing of data is relatively rapid.
Last Update: 04/21/2008
By: Lea Hollingsworth
Hawai‘i Coral Reef Assessment & Monitoring Program
Hawai‘i Institute of Marine Biology
P.O. Box 1346
Kāne‘ohe, HI 96744