Length-weight relationship for the dragonfish, Stichopus cf. monotuberculatus (Holothuroidea)

Length-weight relationships are commonly used to convert length measurements to body weights for data from population surveys, to generate estimates of biomass for stock assessment. These morphometric relationships assess whether increases in body weight are proportional to unit increases in length, providing an insight into growth. Few biological data are available for the nocturnally active sea cucumber, Stichopus cf. monotuberculatus, which is harvested throughout the Indo-Pacific region. This study assessed the morphometric relationships between body length and weight, and basal area and weight for three broad colour variants of S. cf. monotuberculatus at two reefs on the Southern Great Barrier Reef. Preparation of ossicles from the external tissues of the animals validated the species identification. All morphometric relationships were significant and revealed negative allometric growth (exponent, b, range = 2.17-2.42), as found in other holothuroids. Despite some deviance in length-weight relationships between colour types, the largely overlapping data points suggest that a single equation should be appropriate for weight estimation of S. cf. monotuberculatus. Length measurements alone were sufficient for estimating weight (r2 = 0.80) because the addition of width measurements made no tangible improvement to the model fit. The findings indicate that this sea cucumber maintains a relatively consistent shape, with limited contraction of the body. These results will be useful for estimations of weight in future fishery surveys to estimate stock biomass and catch volumes.