Application and Future Potential of Statolith Increment Analysis in Squids and Sepioids

Abstract

Periodic increments within the squid statolith microstructure are now routinely used to obtain individual age estimates. Validation and culture studies have shown that statolith increments (similar to increments in larval fish otoliths) are produced daily in a number of squid species and in one sepioid. However, sample sizes for validation studies are small and there is need for further, more comprehensive validation experiments. Statolith age analysis has revealed that temperate squids can complete their life cycle in less than 2 yr while tropical species live for less than 8 mo. Obtaining individual age estimates has also facilitated the identification of cohorts by analysing hatch date distributions. Size-at-age analysis has been used for some preliminiary growth modelling, and there is a continued need for more accurate age-based squid growth models. There is now potential to use image analysis systems for increment counts and for width analysis of increments. Future studies should be aimed at obtaining age information from a wider number of species, considering how other features within the statolith microstructure, such as zones, might reflect past habitats, and determining how statolith length or weight measurements might be related to past growth histories.

Spatial and temporal variation in elemental signatures of statoliths from the Patagonian longfin squid (Loligo gahi)

“…Both structures are composed primarily of calcium carbonate and are formed of alternating layers of protein and aragonite that are deposited on a daily basis (Jackson 1994). The chemistry of fish otoliths has been used extensively to reconstruct environmental histories of individuals and as natural tags of stock structure (Campana 1999).…”

“…Squid statoliths are composed primarily of aragonite crystals associated with an organic matrix (Radtke 1983). Alternating layers of protein-rich and organic-poor material are deposited on a daily basis in squid statoliths (Jackson 1994). The presence of validated daily increments confirms that material is deposited in statoliths throughout the life of the squid and provides a method for accurate age estimation of individuals.…”

“…Daily deposition of statolith growth increments has been validated in a number of loliginid species both in captivity (Jackson 1994) and in the wild (Lipinski et al 1998). Statolith microstructure in L. gahi was similar to that of other loliginids, so we assumed that the growth increments within L. gahi statoliths were deposited daily and that the total number of increments in a statolith represented the postembryonic age of squid in days.…”

Influence of temperature and salinity on the trace element incorporation into statoliths of the common cuttlefish (Sepia officinalis)

“…Both structures are composed of calcium carbonate and high molecular proteins. Visible increments are formed of alternating layers of protein and aragonite (Clarke 1978;Kristensen 1980;Jackson 1994). These growth rings are frequently used for age determination since a daily deposition of increments has been validated for several cephalopod species including Sepia officinalis (Bettencourt and Guerra 2001).…”

Measuring selective mortality from otoliths and similar structures: a practical guide for describing multivariate selection from cross-sectional data

“…statoliths, spines), can provide a permanent record of traits such as size, age, and growth (e.g. Campana & Neilson 1985, Jackson 1994). This feature makes it possible to measure selective mortality in the absence of information about individual fates.…”