Current Research Journal of Biological Sciences 2(5): 323-327, 2010
ISSN: 2041-0778
© M axwell Scientific Organization, 2010
Submitted Date: June 29, 2010
Accepted Date: July 31, 2010
Published Date: September 15, 2010
The Mortality, Exploitation Rate and Longevity of Macrobrachium macrobrachion
(Herklots, 1851) in Luubara Creek, Ogoni Land, Niger Delta, Nigeria
1
S.N. Deekae and 2 J.F.N . Abowei
Departm ent of Fisheries and A quatic Environment, Faculty of Agriculture, Riv ers State
University of Science and Technolo gy, Port Harcourt, Rivers State, Nigeria
2
Department of Biological Sciences, Faculty of Science, Niger Delta University, Wilberforce
Island , Am assoma, Bay elsa State, Nigeria
1
Abstract: The mortality, exploitation rate and longevity of Macrobrachium macrobrachion from Lu ubara in
Ogoni land area of N iger D elta, Nigeria was studied for period of two years (January, 2006 - Decem ber, 2007).
Total mortality (Z) estimated for 2006 was 2.60 per year and for 2007 2.80 per year. The estimated average total
mortality (Z) for M. macrobrachion in Luubara creek was 2.75 per year. The natural mortality was 2.04 per year
while the fishing mortality was 0.72 per year. Exploitation rate for M. ma crobrachion in Luubara creek was
0.24 in 2006 while in 2007 it was 0.27 with a mean of 0.25. Male shrimps attained sexual maturity between
11mm and 1 4 mm carapace length at one year plus while female shrimps reach sexual maturity between 8 mm
and 25 mm carapace length and a mean length of 11.2 m m. The longevity estima ted for M. macrobrachion in
Luub ara creek was 1.51 y ears. This shows that it is a short lived species like other shrimps. In both years,
M. macrobrachion in Luubara Creek was under exp loited. Therefore, there is the urgent need to improve its
fishery.
Key words:
Exp loitation rate, longevity, L uubara C reek, Macrobrachium macrobrachion, mortality, Niger
Delta, Nigeria
INTRODUCTION
The fresh water shrimp; Ma crob rach ium
macrobrachion belongs to the Phylum, Arthropoda;
Class, Crustacea; Subclass, Malacostraca; Series,
Eumalacostraca; Order, Decapoda; Suborder, Natantia;
Section, Caridea; Family, Palaemonida; Genus,
Macrobrachium; Sp., M. macrobrachion Pow ell (1980).
It can also be found in low salinity brackish water
(Pow ell, 1985).
The body is divid ed into three m ain divisions: the
head, thorax and abdom en. The h ead and thorax are
joined to form a cephalothorax, which carries the
mandibles, flagella, rostrum and the eyes containing a
stalk and has five pairs of walking legs. The abdomen has
six body segmen ts with the last segment bearing a uropod
or telson. The other five segments bear swimming
apparatus known as swimmerets. A definite feature of
Macrobrachium is that the second walking legs are
modified to form the che lae. Mo st species are
distinctively colored having either blue or brownish
colors. The legs also have definitive features such a s hairs
or furs.
Significant differences exist between the male and
female. Mature males are considerably larger than females
and the second walking leg is much thicker. The
cephalothorax is also proportionally larger in the male
than female while abdomen is narrower in the female. The
genital pores of the male are between the bases of the fifth
walking leg (New and S ingho lka, 1982). The female’s
genital pores situates at the base of the third walking legs.
The pleura of the abdomen are lower and broader in the
female than in the male. The pleura of the female form a
brood chamber in which the eggs are carried between
laying and hatching. A ripe ovige rous female can easily
be identified because the ovaries can be seen as large
orange-colored mass occupying a large portion of the
cephalothorax.
The gear used for collecting the shrimp is loca lly
known as “K ara”. It is cone shaped and has two nonreturn value mechanisms at the center of the trap. The trap
is constructed from either the blades of bamboo plant or
blades of raffia fronds which are woven around three
round frames made from cane. The total length of each
trap was between 0.95 and 1 m w hile the opening aperture
was between 25 and 30 cm. Fresh palm oil fruits were
used as bait to set the trap along the creek lets against the
water current.
Shrimps and p rawns of the genus Ma crob rach uim
and Penaeus are highly cherished by the people of the
Corresponding Author: J.F.N. Abowei, Department of Biological Sciences, Faculty of Science, Niger Delta University,
Wilberforce Island, Amassoma, Bayelsa State, Nigeria
323
Curr. Res. J. Biol. Sci., 2(5): 323-327, 2010
Niger Delta. They are used as condimen ts in the
preparation of food because of their high protein value
(Umoh and Bassir, 1977; Deekae and IdoniboyeObu, 1995). They are highly priced and are in high
demand in the market (Marioghae, 1990). It has been
observed that there is significant reduction of the natural
stock of shrim ps in our coa stal wate rs (Nw osu, 2007).
This may be due to enviro nme ntal degradation w hich is
detrimental to the abundance and life cycle of M.
macrobrachion. Also , there are few fishers n ow to exploit
the available species as a result of rural migration.
The unfriendly fishing methods of local fishers who
use poisons and che micals are affecting the shrimp catch.
Therefore understanding the biology, environmental
parame ters and population structure is essential to
optimize production from the wild. The shrimp
M. macrobrachion is exploited in Luubara creek R ivers
State in large quantities yet there are no reports on the
population biolog y of this species in the area. A study of
the mortality, exploitation of Macrob rachiu m
macrobrachion from Luubara creek provides base line
data for management decision in the management of the
species in the area and similar water bodies.
Mortality can be defined as the death of an organism.
It is a very important aspect of population biology since
it provides information about changes in the population
(Abowei and H art, 2007; Ab owe i and Hart, 2009).
Mortality can be caused by fishing activity (called fishing
mortality) or by natural action (natural mortality) (Abowei
and Davies, 2009; Abow ei et al., 2010). Determining the
cause of death of an individual shrimp is usu ally difficu lt
because it is combination of physical and mental factors,
therefore, we study what happens to a population of
shrimps or fishes of the same age (a cohort) (King, 1995;
Sparre et al., 1989). The decrease in numbers of a year
class (cohort) of shrimp o r fish by death throug h time is
usua lly expressed by means of exponential rates
(Pauly, 198 3).
The three comm only defined rates a ccord ing to
Pauly (198 3) are:
C Natural mortality rate denoted as M . It include s all
deaths due to natural causes like predation, diseases
and old age.
C Fishing mortality rate denoted as F. It is death of fish
or shrim p cau sed by fishing mo rtality.
C Total mortality rate denoted as Z. It is the
com bination of natural mortality and fishing
mortality.
W hen F = 0, then Z = M, Which means that the natural
and total mortality are equal and there is no fishing
activity (or an unexploited stock) taking place. As a
cohort of shrim p increases in size, it is observed that there
will be a decrease in number of survivors w ith time. T his
can b e exp ressed mathema tically as:
(2)
Numbe r of survival after tim e (t)
Original number of fish (or shrimp)
2.7128 (base of natural logarithm (a constant)
Z
t
Instantaneous rate of total mortality
Time (age - usually in units of years)
=
=
It is a decreasing exp onential function and is
therefore called, exponential decay mo del. Th ere is little
work done on the mortality of shrimps in the Niger Delta.
The various methods of estimating mortality of fishes
can also be used for shrimps (Pauly, 1983, 1990;
King, 1995). Specifically, Garcia and Reste (1981) have
listed five different possible approaches for estimating the
mortality rates of shrimps. These are analysis of catch
curves; tagging; analysis of catch per unit effort
relationship; analysis of catch vectors; virtual population
and coho rt analysis and appro ximate methods.
Amo ngst these methods, analysis of the catch curve
seems to be used more frequently (Pauly, 1984;
Sparre, 1987; Jon es and V an Zalinge , 1981; K ing, 1995).
Catch curve can either be age or length based (Sparre and
Venema, 1998). It is used ma inly with tropical fishes and
invertebrates such as shrimps where age of individua ls is
difficult to determine or where on ly length freque ncy data
is available. The length frequencies that are obtained
overtime are pooled together. The lengths are then
converted to ages or relative age s (to) by means of a set of
grow th
parameters
according
to
Sparre and
Ven ema, (199 8).
Exploitation rate allows for determining whether a
stock is over fished or not on the assumption that the
optimal value of E equals 0.5 (Pauly, 1983). A study of
the mortality, exploitation rate and longevity of
Macrobrachium macrobrachion from Luubara creek in
Ogoni Land, Niger D elta, Nigeria; provides information
for management of the species, creek , and similar water
bodies and species.
Pauly (198 3) stated that:
Z=F+M
where;
N0 =
Nt =
e1 =
(1)
MATERIALS AND METHODS
where;
Z = Total Mortality
F = Fishing Mortality
M = N atural M ortality
Study area: The study was carried out in Luubara in
Ogoni land area of N iger D elta, Nigeria was studied for
period of two years (January, 2006 - De cemb er, 2007).
324
Curr. Res. J. Biol. Sci., 2(5): 323-327, 2010
The creek is a tributary of the Imo River and is located
between Longitudes 7º15 ! - 7º32 ! E and Latitudes 4º32!4º37 ! N in the Eastern part of the Niger Delta. The upper
part of the creek extends from Bori and meanders through
W iiyaakara, Luegbo, Duburo and joins the Imo River at
Kalooko .
The creek is divided into two distinct sections
brackish water and freshwater. The brackish water stretch
is between Bane and Kalooko while the freshwater stretch
extends from Bane to Bori. The brackish water area has
the normal mangrove vegetation comprising of trees such
as Rhizophora racemosa, Avecenia africana, Laguncularia
racemosa etc., whereas the freshwater has dense
vegetation comprising of large trees, various palms and
aquatic macrophytes at the low intertidal zone. In
freshwater area are Cocos species, Eliasis species,
Nymph ea species, L emn a species an d Raffia species.
It is characterized by high amb ient temperature
usua lly abou t 25.5 oC an d abo ve; high relative h umid ity
which fluctuates between 60 and 95% and h igh rainfall
averaging about 2500 mm (Gibo, 1988). This high rainfall
often increases the volume of water in the creek hence
providing good fishing opportunity for the residents.
Fishing is one of the major activities going on along the
creek because it is the main water route of the Khana
people in O goni area of the N iger D elta.
The fishes caught in the area include Chrysichthys
auratus, C. nigrodigitatus, Hydroc ynus forskalii, Clarias
gariepinus, Pellonula leonensis, Malapterurus, electricus,
Gymnarchus niloticus, Synodontis nigri Hepsetus odoe,
Hernichrom is, fasciatus, Tilapia zilli, Tilapia guine ensis,
Sarotherodon melanotheron and Eleotris se negalensis
and shellfish (crabs and shrimps) especially Uca tangeri
Callinectes amnicola , Goniopsis pelli, Cardisoma
armatum M. macrobrachion, M . vollenhoveni, M.
equidens, Palaemonetes africanus, Caridina africana and
Desm ocaris tripisnosa.
analy sis after each day’s sampling. The species was
identified by use of the keys of Powell (1980, 1982) and
Holthius (19 80).
For each shrimp the T otal length (the distance from
the tip of the rostrum to the end of telson) and the
carapace length (the distance from the base of rostrum to
the first body segmen t) was measured with a Vernier
caliper to the nearest 0.1mm. The shrimps were then
weighed with an Ohaus balance to the nearest 0.1g.
Measurem ents were taken for each monthly collection and
record ed accordingly.
The catch curve method (Pauly, 1983) was used in
estimating the total mo rtality (Z) of the shrimps. This
method involv ed plo tting the n atural log arithms of the
shrimps in various age grou ps (N ) against their
corresponding relative age t. Z was then obtained from the
slope (b) of the descen ding part of the curve after it has
been fitted with a regression line. The equation of the line
was derived from the equation.
logeN=a+bt
(3)
where;
a
= Intercept
b
= Slope
t
= Relative age
N = Age
Only those values of log eN which pertains to the age
of the shrimps that were identified as fully vulnera ble to
the gear were included in the calculation of the linear
function. Fishing mortality co-efficient (F) was
estima ted as:
F =Z –M
(4)
where;
Z = Total mortality
M = Natural mortality
F = Fishing mortality
Natural mortality (M) w as estimated u sing Pauly’s (1980)
empirical formulae using the mean temperature of
Luu bara creek.
Specimen sampling: The shrimp samples were collected
fortnigh tly from three stations alon g the creek: nam ely
W iiyaakara, Luegbo and Duburo. Selection of the stations
was purposefu lly based on fishing activities, ecological
zonation and accessibility of site. For each station five
fishermen were engaged and three traps were used. At
each station the fisher men set the three sets of traps
against the water current among aquatic macrophytes and
left them overnight. The traps were retrieved the
following day after about twe lve ho urs correspo nding to
another low tide. The shrimps collected at each station
were sorted into male and fema le; females were later
separated into berried (ovigerous) and non-berried
(non-ovigerous). Sampling lasted for twenty-three mon ths
from January 2006 to November 2007. The shrimp
samples were then preserved in 4% formaldehyde and
transported to the RSU ST Fish eries laboratory for
log10M = 0.006-0.279 log10L 4 + 0.6543 log10 K
+0.4643 log10T
where;
m = Natural mortality
L 4 =Assymptotic length (i.e., possible length)
K = G rowth co-efficient
T = Mean temperature of Luubara creek
Note that:
Z=F+M
325
Curr. Res. J. Biol. Sci., 2(5): 323-327, 2010
Tab le 1:
W here F is equal to M, it implies that there was no
fishing activity and exploitation is minimal. The catch
curve method has also been incorporated into the FiSAT
computer programme (Gayanilo and Pauly, 1997) hence
Z w as obtained throug h the comp uter packag e.
Exploitation rate (E) of the shrimps was determined as
suggested by Pauly (1983):
Year
2006
M ale
Fem ale
B. F ema le
Bo th
Mean
2005
M ale
Fem ale
Bo th
Mean
Comb ined
(6)
where;
F = Fishing m ortality co -efficient
Z = To tal mortality co-e fficient
E = Exploitation rate
The total mortality (Z) and the natural mortality (m)
per year w as estim ated from length converted catch
curves.
Estim ates of total m ortality (Z) and natural m orta lity (M )
from length converted catch curves of M. macrobrachion
in Luubara creek (2006 - 2007)
Z
F
M
1.95
2.57
1.32
4.51
2.60
0.01
0.10
0.48
1.99
0.64
1.94
2.87
0.84
2.52
1.94
2.63
2.47
5.61
2.8
2.75
0.16
1.26
1.62
0.80
0.72
2.47
1.22
3.99
2.15
2.04
Tab le 2: Sum mary of to tal mo rtality (Z) and natu ral m ortality (M) and
exploitation rate of M. macrobrachion in Luubara creek
(2006 - 2007)
Year
Z
M
F
E
2006
2.60
1.94
0.64
0.24
2007
2.80
2.15
0.80
0.27
Average
2.75
2.04
0.72
0.25
Z = Total mortality, M = Natural mortality, F = Fishing mortality,
E = Ex ploita tion ra tio
RESULTS
The total mortality (Z) estimated for 2006 was 2.60
per year and for 2007 2.80 per year. The estimated
average total mo rtality (Z) for M. macrobrachion in
Luubara creek was 2.75 per year (Table 1). The natural
mortality was 2.04 per year while the fishing m ortality
was 0 .72 per year.
Exploitation rate for M. macrobrachion in Luubara
creek was 0.24 in 2006 while in 200 7 it was 0.27 with a
mean of 0.25 (Table 2). Male shrimps attained sexual
maturity between 11 and 14 mm carapace length at one
year plus while female shrim ps reach sexual maturity
between 8 and 25 mm carapace length and a mean
length of 11.2 mm. The longevity estimated for
M. macrobrachion in Luubara creek was 1.51 years. This
show s that it is a short lived species like other shrimps.
natural and fishing mortality should be equal (E = F/Z =
0.5). There is therefore an urgent need for the
development of M. ma crobrachion fishery in Lub ara
creek.
Enin (1995) estimated the both the total mortality (Z)
and the fishing mortality (F) of M. macrobrachion in the
Cross River to be 10.6 and 7.2 per year, respectively.
W aribugo (2005) reported that the total mortality (Z)
natural mortality (M) and fishing mortality (F) of
Palaemon maculates in River Nun were 0.5, 0.01 and
0.44 per year, respectively. While Enin (1995) showed
that M. macrobrachion was highly exploited in Cross
River, Waribugo (2005) indicated that P. maculatus was
mod erately fished in the N un rive r.
CONCLUSION
DISCUSSION
C
The estimated total mortality (Z = 2.75 per year) in
this study varies with 10.6 per year obtained by
Enin (1995) on M. macrobrachion. The large difference
may be related to the intensive fishing activity in Cross
River estuary compared to Luubara creek. The natural
mortality (M) recorded in this study was 2.04 per year
compared to 3.36 per year in Cross R iver (Enin, 1995)
while the fishing mortality (F) was 0.72 pe r year in
Luub ara creek com pared to 7.24 p er year in Cross R iver.
The fishing mortality calculated for M. macrobrachion in
Cross River is higher than the value for this study.
This may be due to the intensive exploitation
(E = 0.68) at Cross River (Enin, 1995). In Luubara creek
(present study) the shrimp is under exploited (E = 0.25).
This reference is based on the assumption of
Gulland (1971) that in an optimally exploited stock
C
C
C
Mortality values we re gen erally small and indication
of little or no interference.
M. macrobrachion is a short lived species like other
shrimps.
M. macrobrachion in Luubara Creek is under
exploited.
Therefore, there is the urgent need to im prove its
fishery.
ACKNOWLEDGMENT
W e are grateful to Go d Alm ighty for the strength,
know ledge and w isdom in resea rching and w riting this
article. W e also thank our numerous colleques, friends,
wives and students wh ose name s are too num erous to
mention here due to space but contributed immensely to
the success of this work.
326
Curr. Res. J. Biol. Sci., 2(5): 323-327, 2010
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