Pratchett, Morgan S., Baird, Andrew H., Burn, Deborah, Caballes, Ciemon F., Chandler, Josie F., Garing, Madeline, Lang, Bethan J., Levering, Leighton T., Pacey, Kai I., and Doll, Peter C. (2026) Detectability of Pacific crown-of-thorns starfish (Acanthaster cf. solaris) using scooter-assisted large area diver-based (SALAD) surveys in the Northern Great Barrier Reef, Australia. Coral Reefs. (In Press)

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Abstract

Limited detectability of crown-of-thorns starfish (CoTS) undermines the capacity to survey and manage population irruptions, though few studies have considered the factors that influence detectability. This study explores spatiotemporal variation in detectability of CoTS during emerging population irruptions in four regions of the Northern Great Barrier Reef (GBR), by comparing recorded densities based on the number of CoTS sighted to inferred densities that account for distinct sets of feeding scars, which are presumed to indicate the localised occurrence of starfish that cannot be detected. Mean detectability was estimated to be 50.51% (± 1.59SE) across all scooter-assisted large area diver-based (SALAD) surveys where CoTS or feeding scars were recorded (n = 405 surveys), ranging from 29.59% (± 4.22SE) up to 59.46% (± 2.69SE) among regions. Regional differences in detectability correspond with differences in the size of CoTS, whereby larger CoTS tended to be more exposed, and marked differences in the proportion of CoTS recorded feeding. The average exposure increased with size of CoTS, with an asymptote at approximately 60% for CoTS > 500 mm diameter. Proportional exposure of individual CoTS was also strongly affected by feeding, whereby CoTS that were feeding during the day were generally completely exposed. This study reaffirms that limited detectability of CoTS needs to be taken into account when estimating absolute densities using different survey methods. These data also highlight significant limitations of survey methods (e.g. manta tow and towed camera) that rely on visual detection from above to estimate CoTS densities.

Item ID:	91934
Item Type:	Article (Research - C1)
ISSN:	1432-0975
Keywords:	Coral reefs; Disturbance; Management; Surveillance; Sampling
Copyright Information:	This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/.
Funders:	Lizard Island Reef Research Foundation (LIRRF), COTS Control Innovation Program
Date Deposited:	14 May 2026 00:17
FoR Codes:	31 BIOLOGICAL SCIENCES > 3103 Ecology > 310305 Marine and estuarine ecology (incl. marine ichthyology) @ 50% 41 ENVIRONMENTAL SCIENCES > 4104 Environmental management > 410402 Environmental assessment and monitoring @ 50%
SEO Codes:	18 ENVIRONMENTAL MANAGEMENT > 1805 Marine systems and management > 180501 Assessment and management of benthic marine ecosystems @ 50% 18 ENVIRONMENTAL MANAGEMENT > 1805 Marine systems and management > 180503 Control of pests, diseases and exotic species in marine environments @ 25% 28 EXPANDING KNOWLEDGE > 2801 Expanding knowledge > 280102 Expanding knowledge in the biological sciences @ 25%
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