Diver Observation
This study began in 2005 and the dataset is updated annually.
Data from the initial survey conducted in 2005 are presented in a
separate data table as the methods used differed from the standard protocol
adopted in 2006 and no estimates of fish body lengths were made. Each year,
surveys were conducted between 0900 and 1600 hours (local time) during late
July or early August of each year. Four replicate transects were surveyed in
each of six locations on the forereef (two on each of Moorea's three sides),
six locations on the backreef (two on each of Moorea's three sides), and on
six locations on the fringing reef (two on each of Moorea's three sides) for
a total of 72 individual transects. Transects are permanently marked using a
series of small, stainless-steel eyebolts affixed to the reef. Transects on
the fore reef are located at a depth of approximately 12m, those in the back
reef portion of the lagoons are located at a depth of approximately 1.5m and
those on the fringing reef are located at a depth of approximately 10m.
2005 Surveys only
In 2005, a pair of divers using SCUBA swam side by side, down the center of a 5 m by
50 m transect. One diver estimated the abundance of all fishes throughout the entire water
column from the bottom to the surface from the center of the transect line out to 2.5 m to
the left of the center line, while the other diver estimated the abundances of all fishes
throughout the entire water column from the bottom to the surface from the center of the
transect line out to 2.5 m to the right of the center line. Divers did not attempt to
estimate the sizes of the fishes observed. Data from this initial survey are presented but
should be used with a great deal of caution as divers may have double-counted individuals
moving across the 5 m width of the transect or did not count individuals that they mistakenly
thought had been counted by the other diver.
2006 - 2021 Surveys
From 2006 to 2021, the estimated abundances and body lengths (total body length to greatest
precision possible) of all mobile taxa of fishes (Scarids, Labrids, Acanthurids, Serranids, etc.)
observed on a 5 m by 50 m transect extending from the bottom to the surface of the water column
were recorded by a single diver using SCUBA. After completing the initial survey, the diver then
swam back along a 1 m by 50 m band down the center of the original transect line and recorded the
estimated abundances and body lengths of all non-mobile or cryptic taxa of fishes (Pomacentids,
Gobiids, Cirrhitids, Holocentrids, etc).
2006 - Present Surveys
Beginning in 2022 to provide an increased degree of diver safety, the abundance
and body lengths of fishes on each transect are estimated by a pair of divers using SCUBA.
The lead diver estimates the abundances and body lengths of all mobile taxa of fishes
(Scarids, Labrids, Acanthurids, Serranids, etc.) observed on a 5 m by 50 m transect
extending from the bottom to the surface of the water column, while the second diver
trailing approximately 5 m behind the lead diver estimates the abundances and body
lengths of all non-mobile or cryptic taxa of fishes (Pomacentids, Gobiids, Cirrhitids,
Holocentrids, etc) on a 1 m by 50 m band down the center of the transect.
Locations
Locations for the MCR LTER site annual fish census locations are designated with
four components in a stratified design: 6 sites, 3 habitats, 4 transects, 2 swaths
(1 m or 5 m transect width. This yields 144 unique locations surveyed each year.
The six MCR-LTER sites span the three shores of the roughly triangular island of
Moorea with Sites 1 and 2 on the north-facing shore, Sites 3 and 4 on the south-east-
facing shore, and Sites 5 and 6 on the south-west-facing shore. Sites on a given
side of the island are located at least 3 km apart. At each site, the three habitats
surveyed are the Fringing Reef, the Back Reef area of the lagoon, and Fore Reef.
Within each habitat, there are four, 50 m long transects, each of which is surveyed
twice. Once using a 5 m width to census mobile fishes, and once using a 1 m width to
census semi-cryptic or more sedentary species. Individual transects within a given site
and habitat are positioned end to end parallel to either shore or the barrier reef
and are separated by approximately 5 m.
Caution should be used when analyzing these data as individual transects within a
given site and habitat combination may not be statistically independent of each other.
Dive Conditions
In addition to the biotic data collected, divers also record data on the date
and time each transect was surveyed, wind speed and sea state, swell height in m,
amount of cloud cover in %, and horizontal visibility in m. Dive conditions are
recorded for each dive, which is unique to a habitat at a site for a given year.
Therefore, there are 18 unique dive conditions each year (3 habitats at 6 sites).
Divers
There are four permanent transects established within each of the three habitat
types at each of the six sites arrayed around the island. In 2005, each transect
was censused by a pair of divers, each diver estimated the abundance of all fishes
on half of the 5 m width of the 50 m long transect. From 2006 to 2021, each transect
was censused by a single diver who estimated the abundances and sizes of all mobile
fishes first along a 5 m wide by 50 m long transect and then again along a 1 m wide
transect down the center of the original 5 m wide transect to estimate the abundances
and body sizes of all semi-cryptic and sedentary species. Whenever possible, the same
diver covered the same transect number within each habitat type at each site each
year (The diver censusing Transect 3 has varied over time.). Beginning in 2022, each
transect again was censused by a pair of divers. However, unlike in 2005 when the
divers swam side by side and each diver censused only half of the 5 m wide transect
along the 50 m length, beginning in 2022, The lead diver estimated the abundances
and body lengths of all mobile taxa of fishes (Scarids, Labrids, Acanthurids, Serranids,
etc.) observed on a 5 m by 50 m transect extending from the bottom to the surface of
the water column, while the second diver trailing approximately 5 m behind the lead
diver estimates the abundances and body lengths of all non-mobile or cryptic taxa of
fishes (Pomacentids, Gobiids, Cirrhitids, Holocentrids, etc) on a 1 m by 50 m band
down the center of the transect. Since each diver is counting a different set of
species along the entire width of their transect, there is no potential for double
counting individuals or assuming that an individual has been counted by the other
diver. The diver censusing each transect is identified in the data by their initials.
In 2005, the initials of 2 divers are concatenated.
Reference for fish census protocol
The MCR-LTER annual fish census is based on the 'Fish Belt Transect' method
described in: 'Methods for Ecological Monitoring Of Coral Reefs: A Resource For Managers.
Version 1.', J. Hill and C. Wilkinson, 2004, Australian Institute of Marine Science (AIMS),
Townsville, Australia. 117 p.
