Assessing the validity of stylets as ageing tools in Octopus pallidus

Determining the age and growth of wild octopus using stylet increment analysis

“…All 4 of these methods have intrinsic limitations: (1) beak microstructure increment analysis is affected by processes such as feeding that wear down the beak, resulting in inaccurate estimates (Hernández-López & Castro-Hernández 2001); (2) laboratory derived findings are not guaranteed to be transferable to wild populations (Joll 1977, Pecl & Moltschaniwskyj 1999; (3) factors such as tagging mortality, growth reduction due to stress, inability to predict age before the tag date, reliance on consistent recaptures and accurate reporting must all be considered when conducting a tag-recapture study ; and (4) histological quantification of lipofuscin is yet to be validated in animals of known age (Semmens et al 2004). What is required is an accurate and validated method of age determination that uses similar internal structures to those found in teleost fish (otoliths and vertebrae), which does not rely on external features such as beaks and morphometric measurements, avoids the uncertainty of laboratory studies and is not as limited in scope as tagging studies.Two types of hard internal structures are present in octopuses: (1) statoliths (analogous to otoliths), which are small paired calcareous structures associated with sensory epithelia, found in the cranium (Lombarte et al 2006) and (2) stylets, which are paired elongate structures, also referred to as vestigial shells, found in the mantle musculature near the base of the gills (Bizikov 2004, Doubleday et al 2006. Successful age estimates have been achieved for many squid (Jackson 1994) and some cuttlefish (Bettencourt & Guerra 2001, Challier et al 2002 species by counting validated concentric daily increments (growth rings) found in statoliths (Boyle & Rodhouse 2005).…”

“…However, this technique has failed to provide results for octopus due to a lack of growth rings and the morphology of octopus statoliths not possessing the same landmarks as those of squid and cuttlefish, which minimises increment visualisation (Lombarte et al 2006). Stylets, however, do have concentric rings (Bizikov 2004) and have been validated for age estimation by Doubleday et al (2006) using Octopus pallidus of known age reared in captivity. This method of stylet increment analysis showed that increments in O. pallidus are deposited daily and provide results similar in reliability and accuracy to statoliths in squid, and otoliths and vertebrae in teleost fishes.…”

“…Stylets, however, do have concentric rings (Bizikov 2004) and have been validated for age estimation by Doubleday et al (2006) using Octopus pallidus of known age reared in captivity. This method of stylet increment analysis showed that increments in O. pallidus are deposited daily and provide results similar in reliability and accuracy to statoliths in squid, and otoliths and vertebrae in teleost fishes.The present study applied the same ageing techniques as Doubleday et al (2006) on a wild population of the same species, Octopus pallidus. This octopus is a semelparous (authors' unpubl.…”

Species identification of <i>Ommastrephes bartramii, Dosidicus gigas, Sthenoteuthis oualaniensis</i> and <i>Illex argentinus</i> (Ommastrephidae) using beak morphological variables

“…Morphological characteristics of body and hard structures have often been used to identify cephalopod species with close affinities (Roper et al 1984, Jackson 1995, Doubleday et al 2006. Since chitinous beaks have a relatively consistent shape (Smale 1996, Clarke 1996, 1998, Neige and Boletzky 1997 and are more resistant to fragmentation than other hard structures, such as the statolith and inner shell, they have been proven to be valuable for studying cephalopod predators (Lu andIckeringill 2002, Cherel andHobson 2005).…”

Wavelet analysis of correlation among Canary Islands octopus captures per unit effort, sea-surface temperatures and the North Atlantic Oscillation

“…On the other hand, it is assumed that cephalopods, due to their short life cycle, around a year (Boyle and Boletzky, 1996;Hernández-López et al, 2001;Mangold, 1983;Doubleday et al, 2006;Leporati et al, 2008), are good indicators of climatic variability (Sims et al, 2001;Zuur and Pierce, 2004;Solari, 2008;Pierce et al, 2008;Caballero-Alfonso et al, 2010).…”