Guam Long-term Coral Reef Monitoring Program Reef Fish Surveys since 2010

The Government of Guam's Comprehensive Long-term Monitoring at Permanent Sites in Guam project, also known as the Guam Long-term Coral Reef Monitoring Program (GLTMP), is a NOAA-funded project currently coordinated through the University of Guam Marine Laboratory. The program involves the regular, intensive collection of data for a suite of coral reef ecosystem health parameters at high priority reef areas (HPRAs) around Guam, as well as critical support for coral bleaching response and other activities carried out by the multi-partner Guam Coral Reef Response Team. The program currently utilizes a split-panel sampling approach, whereby a mix of permanent and non-permanent sampling stations (one sampling station = one transect) are visited within each HPRA. The HPRAs were selected by an advisory body comprised of reef managers, researchers, and technicians. The locations of the sampling stations within each HPRA are generated randomly using GIS software. Various coral reef surveys are carried out on an annual basis along the seaward slope between 7 and 15 m depth in the Tumon Bay Marine Preserve and in East Agana Bay, while surveys are carried out biennially within the Piti Bomb Holes Marine Preserve, the Achang Reef Flat Marine Preserve, and the eastern side of the Cocos Barrier Reef (Cocos-East). Surveys were also carried at along reef margin (1-2 m) and slope (2-15 m) of Western Shoals, in Apra Harbor, in 2011. The surveys, which are currently conducted by University of Guam Marine Laboratory biologists, and which were supported by NOAA PIRO through 2019, currently include benthic photo transects, stationary point count fish surveys, macroinvertebrate belt transects, and chain-length rugosity surveys. The GLTMP has conducted surveys at the Tumon and East Agana HPRAs since 2010, the Piti HPRA since 2012, and the Achang and Cocos-East HPRAs began in 2014. Surveys for Fouha Bay HPRA began in 2015 with data collections also occurring in 2019 and 2021, but the site has not been re-visited due to shifting management priorities. Baseline data is available for the Western Shoals HPRA from 2011 but this site has not been re-visited.

Fish are a culturally and economically valuable resource for the island of Guam (van Buekering et al., 2007). In recognition of the high value of this resource, reef fish surveys are a key component of the Guam Long-term Coral Reef Monitoring Program. Reef fish assessment surveys have been conducted at high priority reef areas around Guam since August 2010. The monitoring team uses a Stationary Point Count Method, adapted from Ault et al. (2006) and NOAA Fisheries, Coral Reef Ecosystem Division (Williams et al., 2011), to conduct the reef fish surveys. These monitoring data can be used to monitor the status and trends in fish density, biomass, diversity; to explore community structure by functional group and size structure; and examine changes in community structure over time.

IMPORTANT NOTE: Significant changes have been made to the fish SPC survey methodology since its first deployment in 2010. These changes, which are documented in the Data Quality and Lineage sections of this metadata record, must be considered in order to properly analyze these data. Also, please note that the results of a 2020 analysis of the fish SPC data conducted by Dr. Peter Houk of the University of Guam Marine Laboratory indicated that data collected in 2010 and 2011 by one observer did not meet quality assurance standards. In response to the results of this analysis observations recorded by this observer are not included in the dataset submitted to NCEI. However, these data can be made available upon request. More information regarding Dr. Houk's analysis can be found in the Data Quality section of the metadata record. Also note that a recent analysis conducted by the program coordinator showed that there were significant, consistent differences in biomass, density, and species richness values calculated using observations obtained by each of the two main fish observers. It is strongly suggested that any users of these data review the report in which these results are presented (https://www.uog.edu/_resources/files/ml/technical_reports/UOGML_TechRep170_GLTMP_2023.pdf) and reach out to the program coordinator to ensure the data are used appropriately. Please refer to the Supplemental Information section below for a list of important considerations and recommendations for any analysis of these data.

The stated goals of the Guam Long-term Coral Reef Monitoring Program (GLTMP) are to determine the status and trends of selected coral reef ecosystem indicators to inform resource managers' decision-making process, provide managers with early notice of abnormal conditions, provide data to better understand the dynamic nature of the island's coastal ecosystems, allow resource agencies to meet certain legal and Congressional mandates, and measure progress towards performance goals. Benthic cover data collected by the GLTMP at several High Priority Reef Areas around Guam provide documentation of the structure and condition of the benthic communities at these sites; data from multiple visits can be used in time series analyses to determine trends in key ecosystem parameters.

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Reef fish SPC data have been collected at permanent and non-permanent sampling stations within multiple monitoring sites since 2010, including:

Tumon Bay: 2010 (belt: 10 perm, 10 non-perm; SPC: 10 perm, 10 non-perm); 2012 (2 perm, 2 non-perm); 2014 (0 perm, 5 non-perm); 2015 (12 perm, 10 non-perm); 2017 (12 perm, 10 non-perm); 2019 (12 perm, 10 non-perm); 2020 (12 perm, 10 non-perm); 2021 (12 perm, 10 non-perm); 2022 (12 perm, 10 non-perm); 2023 (12 perm, 10 non-perm); 2024 (12 perm, 10 non-perm)

East Agana Bay: 2010 (10 perm, 10 non-perm); 2015 (10 perm, 10 non-perm); 2017 (10 perm, 12 non-perm surveys); 2019 (10 perm, 6 non-perm); 2020 (10 perm, 10 non-perm); 2021 (10 perm, 10 non-perm); 2022 (10 perm, 10 non-perm); 2023 (10 perm, 10 non-perm); 2024 (10 perm, 10 non-perm)

Western Shoals: 2011 (belt: 11 perm, 13 non-perm; SPC: 2 perm, 2 non-perm)

Piti Bay: 2012 (6 perm, 8 non-perm); 2014 (10 perm, 2 non-perm); 2017-2018 (10 perm, 10 non-perm); 2020 (10 perm, 10 non-perm); 2022 (10 perm, 10 non-perm); 2024 (10 perm, 7 non-perm)

Achang: 2014 (8 perm, 3 non-perm); 2018 (10 perm, 10 non-perm); 2021 (10 perm, 10 non-perm); 2023 (10 perm, 10 non-perm)

Cocos-East: 2014 (3 perm, 4 non-perm); 2018 (no fish data collected); 2021 (10 perm, 10 non-perm); 2023 (10 perm, 7 non-perm)

Fouha Bay: 2015 (10 perm); 2019 (10 perm); 2021 (10 perm)

Changes to the survey methodology, interobserver biases, and other issues specific to this dataset must be accounted for during any analysis of these data. A list of considerations and recommendations for analysis is provided below:

Tumon site boundary change: The Tumon site boundaries changed after 2010 due to a significant difference in benthic assemblages detected between the southern and northern halves of the original site. Caution is urged in including data from 2010 in any time series analysis of survey data from the Tumon HPRA.

Significant inter-observer bias: The results of an analysis by Dr. Houk of the U. of Guam Marine Laboratory, as well as a recent analysis conducted by the project coordinator for a recently-released report (see link below), indicated significant interobserver biases that must be considered during any analysis of these data. Observer 1 generally detected a greater number of larger-bodied fishes and a greater number of species, in comparison to Observer 2 (and Observer 4, who assisted with surveys in the Tumon HPRA in 2015). In some instances the mean total fish biomass or species richness for a site calculated using observations obtained by Observer 1 were 2-3 times larger than values calculated using observations obtained by observers 2 or 4. Consideration of these interobserver biases is especially important during time series analyses that include earlier data collected only by Observer 1 and more recent data collected only by Observer 2 (2020-2022). The results of analyses conducted using observations from all observers combined as well as with observations by each observer separately, are presented in the 2023 report availalabe at https://www.uog.edu/_resources/files/ml/technical_reports/UOGML_TechRep170_GLTMP_2023.pdf.

Limited data for 2010 and 2012: Due to staff capacity limitations and the exclusion of observations by a relatively inexperienced fish observer, observations are only available for a small number of sampling stations for the Tumon Bay and East Agana Bay HPRAs for survey years 2010 and 2012.

Size/counts only for food fishes in 2020 and 2021: In order to decrease survey time and maximize efficiency with the very limited staff capacity, beginning in 2020 size and count data were limited to only food fishes (although counts were obtained for a few notable non-food fish taxa). Note that the "full" method was used in 2022 in order to maximize comparability to data obtained during the 2022 NOAA PIFSC RAMP cruise in the Mariana Islands. As a result of the method modifications, total fish biomass cannot be directly compared between 2020/2021 and any previous survey years. Also note that biomass for families that include both food and non-food fishes cannot be directly compared between 2020/2021 and any previous survey years. All species are still listed during the first 5 minutes (e.g., the listing phase), so species richness is still comparable for Instantaneous and Non-Instantaneous observations (but not for the Non-instantaneous 5-10, 10-15, and 15+ observations, which were not collected beginning in 2020). The observation type for the modified method (beginning in 2020) and whether or not a species is a food fish can be found in the dataset.

Recommend using only "Instantaneous" and "Non-instantaneous" observations: Instantaneous data are count/size data for fish species recorded during the 5-min listing phase; they are called "Instantaneous" because the observer does a rapid visual sweep for each species during the subsequent enumeration phase, usually one species at a time in order of the list recorded during the listing phase. "Non-instantaneous" observations are count/size data for species recorded during the listing phase, but which were not detected in cylinder during the visual sweep. In those instances the observer has to recall the count/size from the listing phase, although usually the observers know which fish are unlikely to stick around so the count and size of those taxa are often recorded during the listing phase and denoted as non-instantaneous. The "Non-instantaneous 5-10," "Non-instantaneous 10-15," and "Non-instantaneous 15+" observations are count/size data recorded for species that appear within the cylinder 5-10 min, 10-15 min, and >15 minutes after the listing phase, respectively. These additional observation types were collected beginning in 2014 and were eliminated beginning in 2020 (but were used in 2022).

Account for missing replicates when aggregating data at the sampling station level: For various reasons only a single survey replicate was carried out for some sampling station visits; if the halved total survey area isn't taken into account when calculating biomass per area the sampling station biomass would be half of the true value. This concern is specific to the approach to calculating biomass at the sampling station level that involves summing the biomass (in the "BIOMASS_PER_RECORD_G" field) across both replicates and dividing by the total area of two cylinders (353.4292 m^2) to get the total g/m^2 for that sampling station. If this method is used it is critical that the summed value be divided by the area of a single cylinder (176.714 m^2) for those sampling stations at which only a single replicate survey was conducted. Alternatively, the biomass per unit area (g/m^2) of each observation record can be calculated (e.g., the values in the BIOMASS_PER_RECORD_G_PER_M2 field), summed for each replicate, and the average calculated for the sampling station.

Recommend excluding blennies, gobies, spadefishes, sharks, rays, moray eels, and barracuda (depending on the analysis): GLTMP fish observers were not consistent in recording blennies and gobies; the inclusion/exclusion of these families wouldn't significantly impact total biomass but it could affect density and diversity calculations. Spadefishes were excluded from the analysis conducted for the 2023 report because of the rarity of encountering this group during surveys and how much a single school observed in the Tumon Bay HPRA affected biomass values. Similarly, schools of barracuda and the occasional shark or ray are also uncommon or rare, and having any of these appear in cylinder is exceedingly rare in Guam's waters. The very large biomass a single shark, ray, or barracuda school adds to the total biomass for a given sampling station can obscure trends in the more typically observed taxa; this effect is exacerbated by the generally low biomass seen along much of Guam's west coast, and the rarity of large fishes, which can result in outlier values and large variances that can obscure trends in more common taxa. Moray eels were also excluded from the 2023 analysis because of the likely unreliability of length estimates (most of which were made while only the head was visible).

Raw survey data includes metadata for each survey (where, when, who, area); site characteristics (depth, reef type, habitat, exposure); individual reef fish observations identified to the lowest taxonomic level possible (usually species) including size, count, and observation type; and parameters needed to calculate biomass and density.

While every effort has been made to ensure that these data are accurate and reliable within the limits of the current state of the art, NOAA cannot assume liability for any damages caused by errors or omissions in the data, nor as a result of the failure of the data to function on a particular system. The Guam Coastal Management Program makes no warranty, expressed or implied, nor does the fact of distribution constitute such a warranty.

Tumon Bay

East Agana Bay

Western Shoals

Piti (Tepungan) Bay

Achang

Cocos-East

Fouha Bay

Not applicable

Not applicable

Data can be accessed online via the NOAA National Centers for Environmental Information (NCEI) Ocean Archive.

None

Please cite the Guam Coastal Management Program when using data collected prior to October 2013. Guam Coastal Management Program, Guam Bureau of Statistics and Plans, Government of Guam. Please cite the University of Guam Marine Laboratory when using data collected after (and including) October 2013.

Example citation:

For data collected from 2010 to 2012:

Guam Coastal Management Program (YEAR accessed). Guam Long-term Coral Reef Monitoring Program Reef Fish Surveys since 2010. NOAA's National Center for Environmental Information, https://www.fisheries.noaa.gov/inport/item/47783.

For data collected after 2012:

University of Guam Marine Laboratory (YEAR accessed). Guam Long-term Coral Reef Monitoring Program Reef Fish Surveys since 2010. NOAA's National Center for Environmental Information, https://www.fisheries.noaa.gov/inport/item/47783.

None

None

Observations recorded on data sheets are entered into a data management website that populates a Microsoft SQL Server administered by the University of Guam Office of Information Technology

Observations included in this dataset were made by divers who have been trained, and met minimum standards in identifying species present at the survey location. Small fishes and those cryptic during the day, such as apogonids and holocentrids, are likely undercounted. While some small and/or cryptic taxa, such as most gobies or blennies, are not given high priority in the survey and are usually not reported, some larger-bodied or otherwise notable representatives of those taxa, such as Exalias brevis, Plagiotremus spp., and Valenciennea strigata may be reported.

Observations, including species identification, counts, and cylinder size and fish length estimates were periodically checked for consistency between divers. A 2020 analysis carried out by Dr. Peter Houk of the University of Guam Marine Laboratory detected some interobserver biases involving the two observers whose data comprise this dataset. These biases, which are described in the Bias and Comparability sections below, appear to be related to the detection of more cryptic taxa, such as holocentrids, by the more experienced observer, and the detection of a greater number of larger-sized fish. The latter bias may be related to differences in the degree of accuracy each observer exhibited in estimating cylinder size, but it may also have been an artifact of the survey methodology. No significant differences in the accuracy of species identifications or size estimates were detected between the two observers whose data is included in this dataset. However, observations by two other observers were removed from the dataset following Dr. Houk's study, as it was determined that total biomass and individual size estimates for survey replicates conducted by a relatively inexperienced observer in 2010 and 2011 were consistently higher in comparison to survey replicates carried out by a more experienced observer, and sampling station biomass was consistently lower for survey replicates conducted in 2015 by another observer.

A 2023 analysis of fish observations collected between 2010 and 2022 indicate that the interobserver biases discussed above resulted in a significant discrepancies in mean biomass, density, and diversity values at the site level.

The results of an analysis of the fish SPC dataset (food fish only) carried out in 2020 by Dr. Peter Houk of the University of Guam Marine Laboratory indicated that the size estimates of one observer ("Observer 3") who participated in data collection efforts at the Tumon Bay and East Agana sites in 2010 and at the Western Shoals site in 2011 were consistently different enough from the more experienced observer ("Observer 1") to justify removing these observations from the archived dataset. The removed observations include observations made by Observer 3 in 2010 at all of the surveyed stations in the Tumon and East Agana sites, and in 2011 at most of the sampling stations in the Western Shoals site. The observations made by Observer 3 in 2010 comprised the vast majority of fish SPC data obtained at the Tumon and East Agana sites that year, with data collected by Observer 1 at these sites in 2010 only representing one SPC replicate each at the TUM-16, TUM-18, EAB-10, EAB-16, and EAB-20 sampling stations. The increased availability of Observer 1 for surveys at the Western Shoals site in 2011 allowed this observer to carry out at least one SPC replicate at most of the sampling stations at that site that year. Dr. Houk's analysis also showed that the observations of another observer ("Observer 4") who briefly assisted with surveys of the Tumon Bay site in 2015 were consistently smaller than those carried out by the fish team lead at the same sampling stations. These observations, which were obtained during one replicate SPC survey each at 11 sampling stations in the Tumon site in 2015, were included with the archived dataset, but the clear interobserver biases between observers 1 and 4 should be accounted for in any analysis that utilizes the Tumon 2015 data. Data collected by observer 3 can be made available upon request.

Additionally, Dr. Houk's analysis of the fish SPC data indicated that Observer 1's observations generally included a larger number of species each site, and a greater number of observations of larger-sized fishes, than were recorded by Observer 2. Observer 1, who was the more experienced observer, tended to detect more species of cryptic fishes, such as holocentrids than the less experienced Observer 2. Observer 1's detection of a greater number of larger-bodied species that tended to be more wary of divers could potentially be an artifact of the survey methodology, or of differences in the accuracy of each observer's estimate of the cylinder size. With the departure of Observer 1 from the monitoring program in late 2019, and the resulting reliance on Observer 2 to carry out both replicates at each sampling station in 2020 and 2021 will eliminate inter-observer bias for data collection efforts during those years. However, any comparisons of fish SPC data collected before and after 2020 should account for the interobserver bias between observers 1 and 2 detected in Dr. Houk's analysis.

Lastly, it should be noted that the SPC method employed by the GLTMP is likely biased against larger-bodied species that are harvested and which tend to avoid divers. Larger bodied, harvested fish species such as Lethrinus xanthocheilus, Monotaxis grandoculis, and Macolor spp. are sometimes observed beyond the survey cylinder boundaries, as they appear to maintain at least an 8-10 m distance from divers using open-circuit scuba equipment. It is highly recommended that the GTLMP reef fish SPC survey data be used in combination with data collected using other methods to more accurately assess the status of these and other taxa that are less likely to be detected using this SPC method.

As mentioned in the Bias section above, the results of an analysis of the fish SPC data by Dr. Peter Houk indicated that a more experienced fish observer (Observer 1) consistently reported a greater of number of species, and a greater number of larger-bodied species, than the less experienced fish observer (Observer 2). Any comparison of data collected during the same time period by these two observers must account for these biases, as does any comparison of data collected before 2020 (by both Observer 1 and Observer 2) to data collected during and after 2020 (solely by Observer 2).

Additionally, changes in the fish SPC survey methodology must be taken into account. These changes, which are described in more detail in the Lineage section of the metadata record, include the addition of non-instantaneous observations in 2012; the delineation of different types of non-instantaneous observations from 2015 to 2019; and a major change in methodology beginning in 2020 whereby 1) all species are still listed during the first 5 minutes, 2) only food fishes are counted and sized after 5 minutes, 3) some non-food fishes are counted but not sized after 5 minutes, and 4) non-instantaneous observations are not delineated by timing. [Note that the "full" method was utilized in 2022 in order to maximize comparability of GLTMP reef fish SPC survey data and data obtained by NOAA PIFSC staff (and GLTMP Observer 2) during the 2022 NOAA PIFSC Reef Assessment and Monitoring Program cruise in the Marianas]. While species lists generated during the first 5 minutes of each survey should generally be directly comparable across all years, the shorter total survey time for a single replicate SPC survey beginning in 2020 (~15-25 min compared to ~35-40 min before 2020) will likely include fewer species if additional species recorded after the first 5 minutes are included in the species list. The exclusion of non-food fishes from the counting and sizing portion of the survey beginning in 2020 will prevent direct comparisons of total reef fish biomass for sites surveyed before 2020 and those surveyed during and after 2020. However, abundance, biomass, and length data for those taxa and taxonomic groups surveyed across all years are still directly comparable (but note inter-observer bias described in the Bias section above).

Comparisons of fish data across years should also take into account differences in lunar and tide phase. In addition, it should be noted that beginning in 2015 fish surveys were sometimes carried out during different sampling periods than other surveys (e.g., benthic photo transect, coral quadrat, macroinvertebrate, and rugosity surveys) for a given year. These sampling periods can be found in the Extents section of the metadata for each dataset. Comparisons of data across sites or across years must also take into account differences in environmental and biological aspects of each site. Comparisons for a given site across time should consider any changes to the site boundaries over time. Please refer to the Extents section of this metadata record to for a description of how the Tumon site boundaries shifted after 2010.

Only hard-bottom habitats are surveyed. Surveys are conducted annually to biennially for the Tumon and East Agana sites, but are conducted on a less frequent basis at other sites. In addition, while all permanent sampling stations are generally surveyed each sampling period, surveys are not always conducted at the full set of non-permanent stations for each site during each sampling period. Below is a summary of the number of permanent and non-permanent sampling stations surveyed each year for each site:

Tumon Bay: 2010 (belt: 10 perm, 10 non-perm; SPC: 10 perm, 10 non-perm); 2012 (2 perm, 2 non-perm); 2014 (0 perm, 5 non-perm); 2015 (12 perm, 10 non-perm); 2017 (12 perm, 10 non-perm); 2019 (12 perm, 10 non-perm); 2020 (12 perm, 10 non-perm); 2021 (12 perm, 10 non-perm); 2022 (12 perm, 10 non-perm); 2023 (12 perm, 10 non-perm); 2024 (12 perm, 10 non-perm)

East Agana Bay: 2010 (10 perm, 10 non-perm); 2015 (10 perm, 10 non-perm); 2017 (10 perm, 12 non-perm surveys); 2019 (10 perm, 6 non-perm); 2020 (10 perm, 10 non-perm); 2021 (10 perm, 10 non-perm); 2022 (10 perm, 10 non-perm); 2023 (10 perm, 10 non-perm); 2024 (10 perm, 10 non-perm)

Western Shoals: 2011 (belt: 11 perm, 13 non-perm; SPC: 2 perm, 2 non-perm)

Piti Bay: 2012 (6 perm, 8 non-perm); 2014 (10 perm, 2 non-perm); 2017-2018 (10 perm, 10 non-perm); 2020 (10 perm, 10 non-perm); 2022 (10 perm, 10 non-perm); 2024 (10 perm, 7 non-perm)

Achang: 2014 (8 perm, 3 non-perm); 2018 (10 perm, 10 non-perm); 2021 (10 perm, 10 non-perm); 2023 (10 perm, 10 non-perm)

Cocos-East: 2014 (3 perm, 4 non-perm); 2018 (no fish data collected); 2021 (10 perm, 10 non-perm); 2023 (10 perm, 7 non-perm)

Fouha Bay: 2015 (10 perm); 2019 (10 perm); 2021 (10 perm)

The same method of data collection was used at each of the stations surveyed between 2010 and 2019, with some minor changes over time to refine data collection as described below in the process description. While the core SPC method continues to be utilized, significant changes were implemented in 2020 in order to simplify and shorten the survey. These changes include the exclusion of non-food fishes from the counting and sizing portion of the survey (although certain non-food fishes are still counted but not sized) and the elimination of recording timing (e.g., 5-10 min, 10-15 min, etc.) for non-instantaneous observations of fish taxa that enter the cylinder after the 5 min listing phase of the survey.

All observations entered into the database through the online data entry system are compared against observations recorded on the raw data sheet. Once all database records are verified the quality control process is marked as complete for all observations associated with a given station/sampling period. It should also be noted that the data management system employs hard and soft validation to minimize data entry errors.

University of Guam Marine Lab resources and assets

The Stationary Point Count Survey methodology for reef fishes, employed by the Guam Long-term Coral Reef Monitoring Program since 2010.