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Reef Fish Monitoring - General Description

Visual censuses of the fish assemblages associated with benthic habitat transects is conducted using a standard 25m x 5m underwater visual belt transect survey method (Brock, 1954; Brock, 1982). Four 25m fish transects are run at each location along the 100m length of the CRAMP fixed benthic transect site. A SCUBA diver swims each transect at a constant speed Eric Brown runs fish transect at Hakioawa during August 2000. Photo by Paul Jokiel.(~ 15 min/transect), identifying all fishes visible within 2.5m to either side of the centerline (125m2 transect area). Standard length (SL) of fish is estimated to the nearest centimeter. Care is taken to avoid disturbing the fishes prior to the census. The fish census team is the first to enter the area before any transect lines are set. The first diver attaches a 25m transect line to the first pin of the transect and swims slowly down the transect corridor while reeling out the transect line and counting fish. At the end of the 25m transect the diver advances 5m to the next pin and continues with the second 25m transect. The process is repeated for the 3rd and 4th transects.

Eric Brown runs fish transect at Hakioawa during August 2000. Photo by Paul Jokiel.

Live wet weight (W) of all fishes recorded in all censuses is subsequently calculated from the visually estimated standard length (SL) using the relation W = a(SL)b. Values of the fitting parameters a and b were derived from previous work of the Hawai‘i Cooperative Fishery Research Unit.


Brock VE (1954) A preliminary report on a method of estimating reef fish populations. Journal of Wildlife Management 18: 297-308.

Brock RE (1982) A critique of the visual census method for assessing coral reef fish populations. Bulletin of Marine Science 32: 269-276.

Fish Survey Technique -- Estimating Fish Length

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

808-236-7440 phone

808-236-7443 fax