Basic HTML Version
Inter. J. of Marine Science 2012, Vol.2, No.4, 24-30
http://ijms.sophiapublisher.com
28
Figure 8 Length at 50% maturity (L
50
) for females
Siganus
sutor
from Msambweni, Kenya, sampled between March 2009
and March 2010
In other studies bimodal spawning seasons in
rabbitfishes as well as environmental cues such as
temperature or photoperiod have been reported to
possibly stimulate reproductive activity (Takemura et
al., 2004). These findings suggest that a particular
aspect of the lunar phase triggers synchronization in
the final step of reproductive activity and that the
lunar phase utilized is different among the rabbitfish
species (Takemura et al., 2004).
The estimate of size at maturity in this study was
considerably higher than that reported by earlier
studies in the region (Ntiba and Jaccarini, 1988;
Kamukuru, 2006). This partly relates to the parameter
used with de Souza (1988), for example, reporting
minimum size at maturity rather L
50
maturity. In
addition, prior studies did not use a logistic curve (see
Table 2) (de Souza, 1988; Ntiba and Jaccarini, 1988;
Kamukuru, 2006). Given that most ovaries sampled
from fishes landed before midday were fully hydrated,
and that hydration begins within 12 hours of ovulation
(Sadovy, 1996), spawning in
S. sutor
may be
occurring in the evening.
S. sutor
exhibited protracted
spawning seasons corresponding to the NW monsoon
with peaks in reproductive activity tending towards the
inter-tropical monsoons, particularly October/November.
Although the timing differs, a similar pattern has been
demonstrated before for
S. sutor
in East Africa (Ntiba
and Jaccarini, 1990), and a split spawning season may
be common in areas affected by monsoons (Nzioka,
1979; Sadovy, 1996).
Table 2 Seasonality and minimum size at maturity of
S. sutor
in Kenya from previous studies and the present study
Source and year
Locale/site
Seasonal peaks – GSI
Min size at first maturity
De Souza 1988
(1979~1982)
Mombasa
Oct.~Jan.
24.0 cm TL – males
24.0 cm TL – females
Ntiba and Jaccarini, 1988
Mombasa
Jan./Feb. and May/June
21.7 cm TL-males
Kamukuru, 2006
Dar es Salaam
Dec.~May
22.8 cm TL- females
This study
Msambweni
Nov. and Jan. (>80%)
Jun., Jul. and Oct. (60%~70%)
28.2 cm TL-females (L
50
)
In conclusion, histological analysis of ovaries points
to synchronous development of oocytes with moon
phases, which estimates that their release takes place
over short period of time after the full moon. Or more
specifically, spawning occurred during the last quarter
moon phase. It is worthy to note that sampling only
one month of spawning within one year is limited
evidence for characterizing the spawning periodicity
for the species across a year. It is possible for example,
that the June–July spawning is a different population.
Despite limited sample size, this study contributes to
the state of knowledge about the spawning patterns of
S. sutor
in the Msambweni area, which can guide
future management measures for a species that is
subjected to spawning aggregation fishing. The
management should consider temporal catch and sales
ban inclusive of November-January and June-July.
This study provides further impetus for directing
research to environmental cues in the future.
3 Materials and Methods
To identify seasonal and lunar reproductive periodicity
and size at sexual maturity for
S. sutor
in Msambweni,
southern Kenya, artisanal fishery catches were
sampled during 11 of 13 months (March 2009~March
2010, excluding May and December 2009) at a coastal
landing site. Sampling was stratified, based to reported
reproductive (November-March: Ntiba and Jaccarini,
1988) and non-reproductive periods, with 5 days sampled
per month during the spawning season and 3 days per
month for the remainder of the year. Sampling trips
focused on new moon periods, but included other
lunar phases during one lunar cycle from November to
December 2010. Females were sampled preferentially