Basic HTML Version
Inter. J. of Marine Science 2012, Vol.2, No.4, 24-30
http://ijms.sophiapublisher.com
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life history stages, including spawning aggregations.
Spawning periodicity is also important for practical
fisheries assessments i.e. estimating annual reproductive
output and spawning potential ratios or spawning
stock biomass per recruit (Sadovy et al., 2008).
Similarly, estimates of size at maturity can be used to
improve gear-based management measures (e.g. mesh
size regulations) or market-based measures, such as
minimum size-at-sale. Spawning periodicity is also
used to understand selectivity and assess levels of
growth overfishing. Earlier studies on the reproductive
biology of
S. sutor
had estimated size frequency
distribution of the isolated oocytes, gonad maturity
stages, breeding cycle, length-weight relationship and
condition factor, but information on lunar periodicity
of spawning and size at maturity was lacking (Ntiba
and Jacccarini, 1988; de Souza 1988; Ntiba and
Jacccarini, 1990).
The study was conducted at Msambweni in Kenya's
South Coast (Figure 2). Msambweni is a fishing
settlement located about 70 km south of Mombasa
town. It is experiencing the gradual influence of
urbanization. The study area lies between latitude:
4°30'~4°35'S and longitude: 39°22~39°27' E in the
South Coast region of Kenya (Muthiga and McClanahan,
1987). The study area is basically a low-lying coastal
plain submerged complex (below 30 m contour)
dominated by extensive cover of mangrove forests,
intertidal areas covered with seagrass beds and coral
reef in the shallow water lagoons. The past 30 years
have seen the influx into this area of migrant fishermen
Figure 2 Map of south coast of Kenya showing the fish landing site
Msambweni monitored in the study (Source: Agembe et al., 2010)
who have introduced new fishing practices that have
radically changed the fishery (McClanahan et al.,
2005). The study focused on the main artisanal fisheries
landing site Mkunguni/Msambweni. This study was,
therefore, aimed at determining missing parameters on
spawning periodicity and maturity of
S. sutor
for the
Kenyan south coast area of Msambweni, complementing
a suite of parallel studies on spawning aggregation
based fisheries for this species.
1 Results
A total of 376 samples were collected over 12 months,
including 85 that were collected over four lunar
phases in November and December 2010. Excluded
from the present analysis were 177 individuals that
were either immature, of undetermined sex. Monthly
GSI showed two distinct peaks, one in June and July
and one in November and January, suggested two
distinct spawning periods within the year (Figure 3).
The highest GSI was recorded in November while the
lowest values occurred in April, August and
September
.
The monthly samples which were running
ripe and spent ones are presented in (Figure 4) for
comparison with the Monthly GSI graph (Figure 3)
with highest ripe running fishes peaking November
and January. Minor peaks recorded in June-July
(Figure 4).
Mean GSI by lunar phase (Figure 5) showed High GSI
values occurring during the full moon. This period is
not indicating that maximum spawning occurred that
time. Whereas some were hydrated (high GSI), others
could have just spawned.
A lunar pattern in ovarian development stage was seen
Figure 3 Mean GSI (± standard error) by month over the period
March 2009 ~ March 2010 for
S. sutor
females (n=199); GSI
data were not collected in May and December 2009