Observer effects and training in underwater visual surveys of reef fishes

Aa, Thompson; Bd, Mapstone

doi:10.3354/meps154053

Cited by 145 publications

(116 citation statements)

References 18 publications

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“…As discussed by Brock (1982), dwarf, cryptic and nocturnal species are underestimated by the visual census technique. The visual census technique is widely applied and accepted for fish ecological studies on coral reefs (English et al 1994), although differences in skill and technique of observers can be a source of imprecision and/or bias (Thompson and Mapstone 1997). Therefore the first author (M.A.…”

Section: Discussionmentioning

confidence: 99%

Community structure and biogeography of shore fishes in the Gulf of Aqaba, Red Sea

Khalaf¹,

Kochzius

2002

Helgol Mar Res

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Shore fish community structure off the Jordanian Red Sea coast was determined on fringing coral reefs and in a seagrass-dominated bay at 6 m and 12 m depths. A total of 198 fish species belonging to 121 genera and 43 families was recorded. Labridae and Pomacentridae dominated the ichthyofauna in terms of species richness and Pomacentridae were most abundant. Neither diversity nor species richness was correlated to depth. The abundance of fishes was higher at the deep reef slope, due to schooling planktivorous fishes. At 12 m depth abundance of fishes at the seagrass-dominated site was higher than on the coral reefs. Multivariate analysis demonstrated a strong influence on the fish assemblages by depth and benthic habitat. Fish species richness was positively correlated with hard substrate cover and habitat diversity. Abundance of corallivores was positively linked with live hard coral cover. The assemblages of fishes were different on the shallow reef slope, deep reef slope and seagrass meadows. An analysis of the fish fauna showed that the Gulf of Aqaba harbours a higher species richness than previously reported. The comparison with fish communities on other reefs around the Arabian Peninsula and Indian Ocean supported the recognition of an Arabian subprovince within the Indian Ocean. The affinity of the Arabian Gulf ichthyofauna to the Red Sea is not clear.

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Section: Discussionmentioning

confidence: 99%

Community structure and biogeography of shore fishes in the Gulf of Aqaba, Red Sea

Khalaf¹,

Kochzius

2002

Helgol Mar Res

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“…However, other authors suggested that the variability between divers confounded the analysis of diving census data (Thompson and Mapstone 1997). In this study the variation between the 2 divers was tested and found not to be significantly different (except for C. maenas in October) and to be relatively low (Table 6) compared to the variability between sampling dates.…”

Section: Discussionmentioning

confidence: 99%

Comparison of an enclosure drop trap and a visual diving census technique to estimate fish populations in eelgrass habitats

Bobsien

Brendelberger

2006

Limnology & Ocean Methods

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In shallow vegetated aquatic habitats exceeding 2 m depth, conventional methods to determine fish abundances are of limited success. In this study, the sampling qualities of 2 methods for investigating the fish community associated with the eelgrass Zostera marina were tested: a newly developed enclosure drop trap (ET) operated from the water surface and a visual diving strip transect technique. The construction and the sampling procedure of the enclosure trap are described in detail. Both sampling procedures were performed simultaneously at the same eelgrass sampling site at depths between 2 and 5 m. The comparison revealed deficiencies in relative catch efficiency for both methods. Limitations with respect to bottom-dwelling forms are obvious for the ET and with respect to the Syngnathidae and Gasterosteidae for the visual diving census. Abundance estimates of pelagic, schooling species were highly variable with both methods. Correction coefficients for the different behavioral categories of eelgrass fish were calculated. The fish species composition showed good agreement between the 2 methods, but the number of species on each sampling occasion was consistently higher in the ET catches. The length class frequency distributions estimated by the divers corresponded approximately with direct measurements of fish from the ET catches. The methods complemented one another and can be recommended for simultaneous deployment to get accurate quantitative estimates of eelgrass fish populations. The relative capture efficiency of the enclosure trap can be incorporated to improve abundance measurements of small fish in Zostera marina beds without the help of divers.

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“…Both can be problematic. Training appears to be an effective way to reduce observer bias, at least for some taxa, but probably has less impact on inherent variability within observers' counts (Thompson & Mapstone 1997). It seems plausible that experience level might also be a factor affecting inter-or intra-observer variability (Kulbicki & Sarramegna 1999), but we are not aware of any previous study which has specifically examined this issue.…”

Section: Introductionmentioning

confidence: 89%

Impact of observers experience level on counts of fishes in underwater visual surveys

Williams¹,

Walsh²,

Tissot³

et al. 2006

Mar. Ecol. Prog. Ser.

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Underwater visual surveys are widely used to estimate reef fish abundance. Using data from repeated surveys of coral reef sites on West Hawai'i, we assessed one possible factor driving variation among and within observers' counts, namely the level of observers' previous survey experience. Increasing experience was associated with higher estimates of species richness and of abundance for some but not all taxa, but no systematic change in intra-observer variability. Least experienced observers counted 66 to 71% as many Acanthuridae, Labridae, and benthic Pomacentridae as the most experienced observers, and only 44% as many Holocentridae, those taxa being numerically dominated by small, mobile, or cryptic fishes. In contrast, there was no effect of experience level on counts of more conspicuous or slow-moving taxa: Chaetodontidae, Chromis, and Cirrhitidae. Experience bias is unlikely to be a major problem for survey programs that pool data from multiple observers with broadly similar levels of experience, other than that all sources of difference among observers contribute to increased data variability and consequently lowered statistical power and precision. However, experience bias clearly could be a serious issue for survey or monitoring programs that begin with largely inexperienced survey divers who gain experience and, consequently, tend to count more fish as the program matures. While experience level is not the only factor causing differences among observers, it is relatively easy to recognize and therefore to mitigate. KEY WORDS: Underwater visual survey · Bias · Monitoring · Fish countsResale or republication not permitted without written consent of the publisher

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Observer effects and training in underwater visual surveys of reef fishes

Cited by 145 publications

References 18 publications

Community structure and biogeography of shore fishes in the Gulf of Aqaba, Red Sea

Community structure and biogeography of shore fishes in the Gulf of Aqaba, Red Sea

Comparison of an enclosure drop trap and a visual diving census technique to estimate fish populations in eelgrass habitats

Impact of observers experience level on counts of fishes in underwater visual surveys

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Observer effects and training in underwater visual surveys of reef fishes

Cited by 145 publications

References 18 publications

Community structure and biogeography of shore fishes in the Gulf of Aqaba, Red Sea

Community structure and biogeography of shore fishes in the Gulf of Aqaba, Red Sea

Comparison of an enclosure drop trap and a visual diving census technique to estimate fish populations in eelgrass habitats

Impact of observers experience level on counts of fishes in underwater visual surveys

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Impact of observers experience level on counts of fishes in underwater visual surveys