187 
Birthdate analysis and its application to 
the study of recruitment of the Atlanto- 
Iberian sardine Sardina pilchardus 
Federico Alvarez 
Francisco Alemany 
Instituto Espanol de Oceanografia 
Muelle de Poniente s/n. Apdo. 291, 07080 Palma de Mallorca, Spain 
E-mail address: falvarez@ctv.es 
Abstract .—The ages of 217 juve- 
niles from the Atlanto-Iberian sardine 
(Sardina pilchardus ) stock were deter- 
mined by means of counts of daily 
growth rings in otoliths. These juve- 
niles were caught by the commercial 
purse-seine fleet off Galicia (NW Spain) 
between June and November 1992. The 
back-calculated hatching period was 13 
December 1991 to 2 April 1992, with a 
mean date of 2 February and a stan- 
dard deviation of ± 17 days. The origi- 
nal aim of the study was to relate the 
birthdate distribution of the recruits to 
environmental, biological, and physical 
data taken during a series of oceano- 
graphic cruises. Oceanographic cruises, 
carried out between March and July 
1992, covered the spring-spawning area 
of the stock (Cantabrian Sea and coasts 
of Galicia, the supposed area of origin 
for the recruits) but such a relationship 
was not documented because the re- 
sults of the study showed that most 
surviving juveniles were spawned be- 
fore the period considered during the 
oceanographic cruises. However, the 
observed birthdate distribution of the 
recruits, together with hydrographic 
data, does suggest that a larval drift 
from the northern Portuguese coasts to 
the Galician coast took place. Thus, at 
least in 1992, there is evidence to sug- 
gest that the winter-spawning zone, 
located along the coast of northern Por- 
tugal, may have been the area of origin 
for recruits off Galicia, in contrast to 
the previous assumption that these fish 
were spawned in the Cantabrian Sea. 
Manuscript accepted 25 September 1996. 
Fishery Bulletin 95:187-194 (1997). 
The Atlanto-Iberian sardine Sardina 
pilchardus (also known as Euro- 
pean pilchard [Robins et al., 1991]) 
is the dominant coastal pelagic fish 
species along the Atlantic coasts of 
the Iberian peninsula, as much for 
the biomass of the stock as for its 
importance in the pelagic fisheries 
of Spain and Portugal. Landings, 
carried out by purse seiners, reached 
a maximum value for the period 
1975-92 of 214,000 metric tons (t) 
in 1981, and a minimum of 126,000 
t in 1992. In the same period, the 
estimated biomass of the spawning 
stock varied between 160,000 t in 
1976 and 510,000 t in 1985 (Anony- 
mous 1 ). An analysis of the abun- 
dance trend of the stock (Pestana, 
1989) suggests that, in the short 
term, catches are dependent on re- 
cruitment, characteristic of short- 
lived pelagic species (Ulltang, 1980). 
In recent years more intensive 
work has been done on document- 
ing the oceanographic characteris- 
tics for the area of distribution of 
the Atlanto-Iberian sardine stock. 
Among these, the most noticeable 
is the seasonal upwelling that af- 
fects the west coast of the Iberian 
peninsula (Fiuza, 1984; Lavin et al., 
1991; Cabanas et al., 1992). Numer- 
ous studies have also been carried 
out on the biological aspects of the 
species, such as areas and periods 
of reproduction (Re et al., 1990; 
Lopez-Jamar et al., in press; Cunha 
and Figueiredo 2 ; Garcia et al. 3 ; Sola 
et al. 4 ), frequency of spawning 
(Perez et al., 1992a), batch fecun- 
dity (Perez et al., 1992b), and lar- 
val growth (Re, 1983; Alemany and 
Alvarez 5 ), as well as the spatial dis- 
tribution by age classes, of which 
the latter suggests a northward dis- 
placement of early age groups as 
they grow (Porteiro et al. 6 ). In this 
area, the sardine has a protracted 
spawning season that can last prac- 
1 Anonymous. 1993. Report of the Work- 
ing Group on the assessment of mackerel, 
horse mackerel, sardine and anchovy. 
ICES Council Meeting 1993/H:19, 274 p. 
(mimeo). 
2 Cunha, E., and I. Figueiredo. 1988. Re- 
productive cycle of Sardina pilchardus in 
the central region off the Portuguese coast 
(1970/1987). ICES Council Meeting 1988/ 
H:61, 54 p. (mimeo). 
3 Garcia, A., C. Franco, A. Sola, and M. 
Alonso. 1988. Distribution of sardine 
Sardina pilchardus egg and larval abun- 
dance off the Spanish North Atlantic coast 
(Galician and Cantabrian areas) in April 
1987. ICES Council Meeting 1988/H:27, 
8 p. (mimeo). 
4 Sola, A., L. Motos, C. Franco, and A. lago 
de Lanzos. 1990. Seasonal occurrence of 
pelagic fish egss and larvae in the Canta- 
brian sea (VIIIc) and Galicia (IXa), from 
1987 to 1989. ICES Council Meeting 
1990/H:25, 15 p. (mimeo). 
5 Alemany, F., and F. Alvarez. 1992. Re- 
gional growth differences in sardine 
Sardina pilchardus larvae from Canta- 
brian and Galician coasts. ICES Council 
meeting, 22 p. (mimeo). 
6 Porteiro, C., F. Alvarez, and J. A. Per- 
eiro. 1986. Sardine ( Sardina pilchar- 
dus Walb.) stock differential distribution 
by age class in Divisions VIIIc and Ixa. 
ICES Council Meeting 1986/H:20, 13 p. 
(mimeo). 
