Reef fish, as predators or grazers, play an important role in the community dynamics of coral reefs. Coral reefs with intact fish populations and trophic linkages are integral to healthy reefs. We study the abundance, size and distribution of fish populations to understand changes in reef dynamics and help understand how humans affect fish populations through activities such as fishing and habitat modification.

Method

The purpose is to count and quantify the abundance and community composition of key fish species along 30-m long × 2-m wide belt transects and measure the relief of the reef. Fish teams should survey a total of 10 transects/site; more are acceptable.

The main indicators investigated are:

– Fish diversity

– Abundance and size structure

– Key fish species

Fish Abundance and Size

We collect both fish count and size data. Fish abundance is a count of the number of fish in a given area and can be calculated in terms of total fish abundance or in terms of abundance of key fish species or families. Abundance is presented as numbers of fish per unit area or when combined with size data, calculated in terms of fish biomass (total weight of fish per unit area). Total fish biomass gives important information about trophic structure and overall reproductive output of fish on the reef. Commercial fish biomass gives an indication of overall stock status, fishing pressure, habitat conditions, and recruitment success.

What is the most common reef fish we have seen? Striped Parrotfish (Scarus iseri) are the most counted fish species we have observed. Fish in the parrotfish, surgeonfish and grunt families have been seen most often.

Herbivorous Fish

Herbivorous fish are a key indicator group as they are important grazers that keep algae from overgrowing corals. Large-sized parrotfish (>20cm) remove more algae. Parrotfish are at high risk of over exploitation due to fishing.