FISHERIES POPULATION DYNAMICS
IKENWEIWE Bolatito Nafisat
SENIOR LECTURER
DEPARTMENT OF AQUACULTURE AND FISHERIES
MANAGEMENT
UNIVERSITY OF AGRICULTURE, ABEOKUTA
titobola2007@yahoo.com, 08033770265
FISHERIES POPULATION
DYNAMICS
FIS 507
Catch per unit effort
• Calculation for catch per unit effort for the
different fishing gears
• Passive Gears
Gill Net
Traps
Longlines
3
Gill Net
• Catch weight (Kg) = CPUE
No. of bundles
– 1 bundle = 30m by 3m
– Area of 1 bundle = 90m2
– CPUE often decreases with fishing time
4
Traps
• Catch = kg/trap = a
No. of Trap
•
a
x 24= CPUE per trap per day
fishing hours (12hrs)
• Fishing hours (set trap 7.00pm, retrieve by
7.00am = 12 hours =fishing hours)
• This is applicable for all traps such Gura,
bamboo and wire trap.
5
Longlines
• Catch (Weight) X 12
No of lines x fishing time
• This is the CPUE per line per 12 hour period
which represent longline fishing day.
• CPUE in this trap increase with fishing time
6
• Active fishing gears
– Cast Net
– Drift Net
– Dragnet
– Beach seine
– Spears and harpoons
– Trawls and dredges
– Seine nets
– Purse seines
7
Cast Net
• Cast Net in Kg/day
• Catch (weight in Kg) x 24 hours
Fishing time
• Assuming that total fishing hour is 24 hours.
8
Drift Net/ Beach
• Catch (Kg)
No. of Hauls
• This gives the CPUE per haul
• Since there are always ‘n’ number of hauls per day,
• therefore the CPUE will equal CPUE per haul x No of
hauls
• CPUE decreases as number of hauls per day
increases
9
• Dragnet (100m length, 6m depth of Nylon netting
material of 25.5 mm stretched mesh). Beach Seine is
an active fishing gear
• Catch per fleet extrapolated to catch per 1000m2 of
net surface area.
• Area of a fleet =30m long x 3m = 90m2
• 9 mesh nets (1, 11/2, 2, 21/2, 3, 31/2, 4, 5, 7 and 9
inches)
• Therefore 9 x 90m2 = 810m2
• If 810m2 gives ‘x’ weight of fish
• 1m2 will give x/180 weight of fish
10
• Therefore, 1000m2 = (x/180) x 1000 weight of
fish
• X = 10 x 1000
• Where x = sum of all fish caught by all meshes
and this is compared to the weight of fish
caught by sampling boat (Kg) under
commercial catch
11
Capture of Fishes and Examination of
fishes
• Terms
– Total length is defined as the measurement taken
from the anterior-most part of the fish to the end
of the caudal fin rays when compressed dorsoventrally (Anderson and Gutreuter 1983).
12
– Fork length is defined as the measurement taken
from the anterior-most part of the fish to the end
of the median caudal fin rays (Anderson and
Gutreuter 1983).
– Standard length is defined as the measurement
taken from the tip of the lower jaw to the
posterior end of the hypural bone (Anderson and
Gutreuter 1983).
13
1. Total Length
2. Fork Length
3. Standard
Length
4. Head Length
5. Snout Length
6. Caudal
peduncle
7. Fin Rays
8. First Dorsal
9. Second
Dorsal
10.
11.
12.
13.
14.
15.
Pectoral Fin
Pelvic Fin
Anal Fin
Finlet
Caudal Fin
Lateral Fin
16.
17.
18.
19.
Scutes
Opercle
Preopercle
Interopercle
20. Adipose Eyelid
21. Supramaxilla
22. Premaxilla
Source: http://www.texasgulfcoastfishing.com
14
External and Internal Anatomy
Source:http://www.kentuckylake.com
15
Source:http://www.kentuckylake.com
16
Gill Net Setting and Randomization
• Experimental gill nets with graded stretched
mesh sizes 1”, 1½”, 2”, 2½”, 3”, 3½”, 4”, 5” and 7”
inches
• which are equivalent to 25.4, 38.1, 50.8, 63.5,
76.0, 88.5, 101.6, 126.4 and 177.2 millimeters
respectively,
• Should be set for fish stock assessment while
monitoring simultaneously the physico-chemical
parameters at each fish sampling station.
• Each mesh size of the experimental gill net
measuring 30 meters in length and 3 meters
depth will be arranged randomly and joined
together to form a fleet giving a total surface
area of 810m² per fleet.
• The nets will be mounted at 50 % hanging
ratio.
• 1” and 1½” meshes were included in the fleet
in order to catch all small fish species in the
water body.
• Also as fishermen were currently using these
meshes (1” and 1½”) to exploit the fishery,
• their inclusion in the fleet would give a useful
index of abundance in small mesh nets and
• the relative catch per unit effort in relation to
larger mesh nets
Setting of the Experimental Gill Net during sampling hour of 68pm
MARK- RECAPTURE
• Reconnaissance visit will be paid to the lake
(water body)
• Gears to be use must not cause harm or injury to
the fish.
• Some individuals (fishes) will be captured
• Caught fish will be marked/tagged and returned
into the water body unharmed
• Marking or tagging materials must not be harmful
and must be easy to see or detect
• After some days/weeks/months (depending
on the type of research), a second visit will be
paid to the study area
• Fishes are captured for the second time and
sorted into marked and unmarked
• Third, fourth or more visits are can be made
• Mark recapture methods rely on some sort of
representative sample taken at two different
times
• Most commonly used mark-recapture
estimate of population size is the same as the
Lincoln index or Peterson Index which
assumes that:
• The proportion of individuals which are
marked in the population is the same as the
proportion of individuals which are marked in
a recaptured sample.
• M =
N
R
C
– M = total individual marked in the population
– N = Total population size (which we don’t know
but would like to)
– R = Number of marked individuals which are
recaptured
– C = Total number of individuals (marked and
unmarked) which are captured in the second trial
• N =
MC/R
FURTHER READINGS
• Ikenweiwe, N.B, D. Odulate, B. Adigun (2011) Ichthyology
and Limnology: Tools In Fisheries Management Fisheries
Management. United Kingdom. Lap Lambert Academic
Publishing. ISBN: 978-3-8433-9364-5. Available online at
http://dnb.b-nb.de 127 pages
• Ikenweiwe B. and S. Otubusin (2010). Limnology and
Plankton Abundance. Germany. Verlag Publisher. ISBN- 10:
3639253167, ISBN-13: 9783639253160 (Available online at
http://www.researchbooks.org/3639253167/LIMNOLOGYPLANKTON-ABUNDANCE-FISH-PRODUCTION/). 249 pages.
• Ita E. O. and M. Mdaihli (1997). The Current Status Of Fish
Stock And Fisheries In Kainji Lake