| dc.description.abstract | populationSof penaeid prawn species of Tudor creek were studied with
emphasis on recruitment, the growth of juneniles, and the
emigration of the sub-adults.
Five stations were monitored for surface water temperature,salinity,
~nd pH as well as larval and postlarval penaeid densities. Station
i was at the mouth of the creek and stations 2, 3, 4, and 5 were
respectively located at 2km intervals up the creek roughly midway
between the banks. Also monitored was the settling of postlarvae
and juueniles along the shoreline at stations I, II, III, and
IV using beach seines. The stations I - IV were randomly located
between stations 1 and 4. The castnet fishery catches on the
creek were also monitored.
Over the year, both surface water temperature and salinity
varied least at station 1 (23.5 - 30.00 C and 32.0 - 35.~/aoS),
o and most at station 5 (22.5 - 32.0 C and 10.0 - 35.r:f)/00S). pH
values varied little (7.5 - 8.4) with lowest values upcreek.
Panaeid larvae spawned offshore arrive4in the creek at the late
mysis and early post~arval stages with the water currents. Larval
incidence in samples decreased upcreek. Spring tide night samples had
the highest incidence followed by spring tide day samples and neap
tide night samples.
xvrrr,-
Neap tide day samples had the lowest incidence. Larvae were
concentrated at stations 1 and 2 on neap tides but spread out
over the creek during spring tides. Peak larval counts were
encountered at 2030 hours during the two .2400 hours cycles
studied,
The settling penaeid postlarvae and juveniles favour specific
botton\types. All the common Penaeus species (E. lndicus
f. monodon, and P. semisulcatus) were most abundant in the
beach seine catches at the channel station (stn. IV). This
station had soft silty mud bottom type with mud-mangrove banks
and dense vegetation cover. f. indicus had a size range of 105 -
oJ
21.5 mm carapace length (Cl): P. monodon had a range~1.5 - 29.5 mm
oJ
Cl; and P. semi sulcatus had a range~1.5 - 21.5 mm Cl in the beach
seine catches. The three species recruited intensely into the
creek in distinct cohorts between August and March with peak
recruitment in January for P. indicus; in November for f. monodon
and in December for P. semisulcatus.
In the castnet fishery of the Tudor creek, E. indicus formed
46.3J/o;P. monodon, 42.9 ojoand f. semisulcatus, 40j0by wt of
the catch.
The largest recorded size (L max) in f. monodon in the cast net
catches was smaller in Tudor creek than at Vanga. The
estimated growth curves for this species in Vanga werer
Lt = 71.60 ( 1 - e-l•
lOt
) for femalesi and
Lt 62.88 (1 - e- l.mt) for males
- XIXwhere
Lt is the length (Clmm) at age t ( years).
other population parameters on annual basis for females and males
respectively at Tudor creek~re
(a) total mortality rates, Z
2
7.92 (n = 9, r = 0.988);
2
9.63 (n=7, r = 0.986), and
(b)
(c)
( d)
(e)
natural mortality rates, M 1.49 and 1.46;
fishing mortality rates, F 8.14 and 6.46;
exploitation rates, F/Z = 0.85 and 0.82;
mean selection length, Lc = 13.4 and 12.3 mm Cl;
(f) average relative condition factor, Kn = 0.994 +
0.007 (n= 313) and 0.991 ! 0.004 (n = 209).
Lo9Io transformed weight - length relationships were:
2
(a) Log W = -2.948 + 2.856 Log Cl (n= 367, r = 0.978)
in females;
(b) Log W = - 2.670 + 2.657 Log Cl (n= 298, r2 0.651)
in males; and
(c) Log W = -5.224 + 3.009 Log Tl (n 304,
2
r = 0.940)
in females; and
(d) Log W = -4.924 + 2.862 Log Tl (n = 298, r2= 0.658)
in males (where W is the body weight (gms),Cl is the carapace
length (mm)1Tl is the total length(mm),n is the sample size, and
r2is the coefficient of determination). The total length is related
to the carapace length by the following equations:
(a) Females: Tl 10.775 + 4.373 Cl (n = 367,
2
r = 0.977);
(b) Males: Tl = 8.344 + 4.520 Cl (n 298,
-ll-
The carapace length~ 2~~ of the total body length while the
tail length and weight~ BY~ of the total body length and the
total body weight respectively.
All femaleP. monodon specimens examined for ovarian
development were immature. Emigration as a factor could not be
measured. Tudor creek is therefore a nursery ground for
penaeids especially ~ monodon. | en |
