679 
Age determined from the daily deposition 
of concentric rings on common octopus 
(Octopus vulgaris ) beaks 
Jose L. Hernandez-Lopez 
Jose J. Castro-Hernandez 
Departamento de Biologia 
Universidad de Las Palmas de Gran Canaria 
Apdo. 550, Las Palmas de Gran Canaria 
Canary Islands, Spain 
E-mail address (for J. J Castro-Hernandez, contact author): |ose|uan.castro@biologia ulpgc.es 
Vicente Hernandez-Garcia 
Sea Fisheries Institute, Research Station 
72-600 Swinoujscie, Poland 
The common octopus ( Octopus vulga- 
ris Cuvier, 1797) is an Atlantic and 
Mediterranean species (Guerra, 1992; 
Mangold, 1998). It is one of the most 
important target species of the North- 
west African fisheries (Hernandez and 
Bas, 1993; Foucher et al., 1998). The 
common octopus catch reported for this 
area in 1994 was 137,844 t, represent- 
ing 47.17% of the total world octopus 
catch. In 1996 it was 156,300 t, repre- 
senting 50.03% of the total world octo- 
pus catch (FAO, 1998). 
Octopus age and growth have been 
determined by laboratory rearing stud- 
ies (Itami et ah, 1963; Nixon, 1969; 
Mangold and Boletzky, 1973; Smale 
and Buchan, 1981; Villanueva, 1995) 
and by field studies (Guerra, 1979; Hat- 
anaka 1979; Pereiro and Bravo de La- 
guna, 1979). Growth rates can be cal- 
culated for animals maintained in the 
laboratory, but comparison with growth 
under natural conditions is question- 
able (Mangold, 1983). In field studies, 
growth and age can be correlated when 
there is clear evidence that a single 
year class from a stable population 
is under consideration, but where the 
spawning season is very long as in 
the common octopus (Mangold, 1983; 
Guerra, 1992), identifying year classes 
is difficult (Guerra, 1979, Hatanaka, 
1979). 
Cephalopod age has been determined 
by several methods: Guerra (1979), 
Pereiro and Bravo de Laguna (1979), 
and others have reported growth and 
age correlations by following a single 
year class from a stable population. 
Concentric rings on statoliths (Young, 
1960), the internal shell, and eye lenses 
(Gongalves, 1993) of Octopus vulgaris 
have been reported. Raya and Hernan- 
dez-Gonzalez (1998) observed marks 
on the internal rostral area of beaks 
from common octopus, possibly related 
to daily growth. 
None of these methods has been val- 
idated for known-age Octopus vulgaris. 
Furthermore, all require fairly complex 
methods for preparing structures pri- 
or to observation under the microscope 
(polishing, embedding in resin, and sec- 
tioning with a diamond, etc.) which 
hinders their application to field stud- 
ies. This paper provides an easy new 
method of determining Octopus vulgar- 
is age based on the upper beak micro- 
structure, validated for the paralarval 
period. 
Material and methods 
The study was carried out on 275 
common octopus ( 164 males and 111 
females) collected between January 
1998 and May 1999, from catches of 
the small-scale fishery off the island 
of Gran Canaria (The Canary Islands, 
central-east Atlantic). 
An additional sample of 27 Octopus 
vulgaris paralarvae was obtained from 
spawning females that deposited and 
incubated egg bunches in plastic bur- 
rows inside a 12,000-L tank. The 
embryonic development took between 
25—30 days at a temperature range of 
19-22°C. Once hatched, the paralarvae 
were transferred to transparent 12-L 
containers with open seawater flow, in 
July 1997 and June and July 1999, and 
reared in the laboratory at 19-22°C 
water temperature and natural pho- 
toperiod. The dates of hatching and 
death of each paralarva were record- 
ed. The bottom was siphoned daily to 
remove dead individuals. During rear- 
ing, paralarvae were fed with recently 
hatched crab zoeae (see Hernandez- 
Garcia et al., 2000). 
Ventral mantle length (VML) was 
measured in both benthic octopus and 
paralarvae to the nearest 0.1 mm. We 
used VML as the body measurement 
because we consider it to be more ac- 
curate than dorsal mantle length. To- 
tal body weight (TW) of benthic octo- 
pus was recorded to the nearest 0.01 g 
(to the nearest 0.0001 g in paralarvae). 
With the exception of the paralarvae, 
all the specimens were sexed. 
The beak of each animal, including 
paralarvae, was removed and stored in 
70% ethyl alcohol. Lower and upper 
beaks were sagittally sectioned with 
scissors to obtain two symmetrical half 
beaks (Fig. 1). The half beaks were 
cleaned with water and the mucus cov- 
ering the inner part of the lateral walls 
was removed by rubbing it softly with 
the fingers (obviously, this operation 
was not necessary in the case of the 
paralarvae beaks). 
By using a stereoscopic microscope, 
the concentric rings in the lateral wall 
of each beak were counted from the 
rostral tip area to the opposite end of 
the lateral wall. Because of the lack 
of pigmentation in paralarvae beaks, 
the concentric rings in their lateral 
wall were more easily counted with a 
microscope. Rings of each beak were 
Manuscript accepted 10 April 2001. 
Fish. Bull. 99:679-684 (2001). 
