Evaluating age in Octopus vulgaris: estimation, validation and seasonal differences

Abstract

Several internal structures have been used to estimate age in the cephalopod Octopus vulgaris, but with limited accuracy. We estimated age by investigating growth increments (rings) in the upper beaks of octopus collected between 2003 and 2010 in the Bay of Naples, Italy (Mediterranean Sea). To validate the daily periodicity of ring deposition, 'thermal shock marking' was for the first time applied to live octopuses fished between 2009 and 2010; this method produced a mark on the beak corresponding to the day of thermal shock, enabling us to elucidate the relationship between ring number and time elapsed (i.e. ~30 d). In addition, rings were counted in > 700 preserved specimens of O. vulgaris collected between 2003 and 2009, also in the Bay of Naples. The estimated age of of these octopuses ranged from about 70 to 370 d. Specimens with similar body weights had different numbers of rings, confirming the view that body size is a not a good index of age. Additionally, the relationship between body weight and number of rings was affected by sex and season, with the distance between rings clearly correlated to seasonal temperature oscillations. Our data suggest that different cohorts of octopus exist in the Bay of Naples and that temperature has a strong influence on growth. Overall the results demonstrate that growth increments in the upper beak of O. vulgaris provide a reliable method of aging that can be applied to assessing differences in the growth patterns in wild populations, and one that provides a record of environmental influences upon an individual. KEY WORDS: Octopus · Age · Thermal marking · Upper beak · Seasonal variability Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 441: 141-149, 2011 142 Age determination in cephalopods has been based on both indirect and direct methods. Indirect methods are not reliable with cephalopods (e.g. Semmens et al. 2004), mainly because growth in any cephalopod species appears to be affected by a series of both biotic and abiotic factors, leading to large individual variability (Mangold 1983, Forsythe & Van Heukelem 1987, Domain et al. 2000, Belcari et al. 2002. As a consequence, body size (weight and dorsal mantle length) is not a reliable indicator of age. For this reason indirect methods require validation by at least one direct method (Krstuloviç Šifner 2008).Among direct methods, one of the most useful means of age estimation in cephalopods is statolith increment analysis. This method has been systematically applied to squids (Arkhipkin & Laptikhovsky 1994, Jackson 1994, Rocha & Guerra 1999, Arkhipkin 2005, Ikeda & Kobayashi 2010 and to cuttlefish (Raya et al. 1994, Bettencourt & Guerra 2001, Challier et al. 2002. Unfortunately, statolith analysis is not useful here as octopus species, including Octopus vulgaris, lack growth rings in this structure (Young 1960, Lombarte et al. 2006). In the case of O. vulgaris, other internal structures have been analysed over the past 20 yr for direct age determination. ...

Determination of squid age using upper beak rostrum sections: technique improvement and comparison with the statolith

“…S. oualaniensis collected from warm water have the widest increments compared to I. argentinus and O. bartramii that were obtained from cold waters and had thinner increments. In addition, D. gigas from warm waters (Ecuador) have wider increments than those from cold waters (Chile) ( Table 2), as found in beaks of O. vulgaris LWS (Canali et al 2011). Such a pattern is also congruent with the findings in statolith (Villanueva 2000) and in cuttlebone (Chung and Wang 2013).…”

“…Validation of the daily deposition of growth increments in beaks is widely studied in octopod O. vulgaris (Oosthuizen 2003;Canali et al 2011;Perales-Raya et al 2014a, b) and O. maya (Rodríguez-Domínguez et al 2013;Bárce-nas et al 2014). Unfortunately, unlike octopods and sepioids, squid are difficult to rear in the laboratory (Iglesias et al 2014).…”

“…In recent years, laboratory culture and marking have been the most popular validation methods for examining the periodicity of increment formation in sepioid cuttlebone (Bettencourt and Guerra 2001;Chung and Wang 2013) and octopod stylet (Doubleday et al 2006;Hermosilla et al 2010), lenses (Rodríguez-Domínguez et al 2013) and beaks (Oosthuizen 2003;Bárcenas et al 2014). By comparing the increment number with the actual age and elapsed days after marking or between two marks, daily deposition of the growth increments in beaks was validated for two octopods, Octopus vulgaris (Oosthuizen 2003;Canali et al 2011;Perales-Raya et al 2014a, b) and Octopus maya (Rodríguez-Domínguez et al 2013;Bárcenas et al 2014). Nevertheless, unlike sepioid and octopod, squid, especially adult individuals, are difficult to raise in the laboratory (Iglesias et al 2014).…”

Determination of age and growth of the horned octopus <em>Eledone cirrhosa</em> (Cephalopoda: Octopoda) using stylet increment analysis

“…This cannot be established as a general tendency in octopods on the basis of previous studies. Neither Hernandez-Lopez et al (2001) nor Canali et al (2011) found significant differences in lifespan between sexes in O. vulgaris. Conversely, Leporati et al (2008) found significant differences in age by reading O. pallidus stylets, although males were significantly longer-lived than females.…”

“…Particularly in octopods, beaks have provided some positive results in reading growth increments of Octopus vulgaris paralarvae (HernandezLopez et al 2001) and adults (Canali et al 2011, PeralesRaya et al 2010. Stylet Increment Analysis has been applied and daily growth increment deposition has been validated in Octopus vulgaris (Hermosilla et al 2010), Octopus pallidus (Doubleday et al 2006), Octopus maya (Rodríguez-Domínguez et al 2013) and Octopus (cf) tetricus (Leporati and Hart 2014).…”