International Journal of Marine Science 2015, Vol.5, No.56: 1-5
2
degree, Poyang lake natural fishery now was in the
over exploitation period. The function of its natural
fishery was recession.
C. nasus
is a kind of mid
small-sized fish with resident and migration ecotypes.
The anadromous population has long been recognized
as very important commercial aquatic products in the
lower reaches of the Yangtze River
．
However, habitat
loss, overfishing, and the
C. nasus
have diminished.
Considering the importance of demography and
population regulation to the theory of sustainable
exploitation (Freckleton et al., 2003), it is surprising
how little we know about the population dynamics of
C. nasus
in Poyang Lake.
C. nasus
play a major role
in food webs and community structure. They
constitute an important component of the freshwater
ecosystems in Poyang Lake.
The objectives of this study were (1) to assess four
important parameters namely growth, natural and
fishing mortality and recruitment of
C. nasus
; and (2)
to compare our results with those obtained in other
studies carried out on
C. nasus
, in order to observe
possible differences effectuated by geographic parameters.
2 Materials and methods
The study was carried out at the Poyang Lake through
the Yangtze River Waterway (116.11-116.20 N and
29.51-29.74 E) for four month, from April to July(
C.
nasus
Only can be fished in reproductive season in the
Poyang Lake through the Yangtze River Waterway,
and our investigation including the whole breeding
season ) three years in a row, 2012-2014. Monthly
random samples of
C. nasus
were caught using
trammel net and barrier net. The annual average
temperature is 16-18
℃
with 240-330 frost-free days.
Precipitation (effectively: rainfall) is around 1340-1780
mm (Leeuw, 2010). This lake is shallow (maximum
depth: 21 m) and is connected to five main rivers,
namely the rivers Ganjiang, Fuhe, Raohe, Xinjiang,
and Xiushui. Waters from these rivers run through
Poyang Lake and discharge in the Yangtze River
through a narrow passage at Hukou. In addition to the
excellent geographical conditions, clear water and
abundant aquatic plants also provide a good habitat
for
C. nasus
survival. Accordingly, Poyang Lake is
seen as one of the major sites suitable for
C. nasus
reproduction in China.
The body length (BL, from the tip of the rostrum to
the end of the tail section) measured along the dorsal
mid-line to the nearest 0.1 cm. The length frequency
data of
C. nasus
analyzed using FiSAT II (FAO-
CLARM Stock Assessment Tools-Version 1.2.2). The
FiSAT routines were followed thoroughly base on the
user’s manual (Gayanilo et al., 1996) and reference
manual (Gayanilo and Pauly, 1997). Bhattacharya’s
method (BM), implemented from the package FiSAT
II (Gayanilo et al., 1996), was used to identify the
modes in the polymodal body length-requency
distributions of the
C. nasus
, and to simulate the Von
Bertalanffy equation: L
t
= L
∞
* [1 − exp(−K*(t − t 0 ))]
to calculate the asymptotic length L
∞
and the growth
parameter K, where, L
t
is the length at age t, L
∞
is gth),
K is the curvature parameter, and t
0
is the initial condition
parameter. K and L
∞
were calculated using the program
Electronic Length Frequency Analysis (ELEFAN). his
method is based on the assumption that the observed
distribution in size classes results from the overlap of
various normal distributions. The process converts
normal distributions into lines that simplify the procedure,
linearization being performed by computing the natural
logarithms of frequencies. Intercepts and slopes of the
regression lines were used to estimate the parameters
of each normal distribution. Given a distribution in
size classes, Bhattacharya’s (1967) method allows for
the iterative computation of regression lines up to the
total decomposition of the overall size-frequency
distribution.
3 Results and discussion
A total of 576
C. nasus
were used in this study. The
length frequency data of
C. nasus
was analyzed in
FiSAT software using various methods to estimate the
growth, mortality and recruitment. For many fishery
resources, growth parameters (L
∞
and K) have been
estimated because these population parameters are
important to describe the species and inputs in several
fishery production models (Hilborn and Walters,
1992). L
∞
is the largest theoretical mean length that a
species could attain in its habitat whereas
k
is the
speed it grows towards their final size.
3.1 Bhattacharya’s plot
By using the Bhattacharya’s method in FiSAT,
C.
nasus
produced one group or cohort at modal length
25.00 ±1.32 cm.
3.2 Growth parameters
A total of 576 were examined and their length-masst
