1. FISHERIES POPULATION DYNAMICS
IKENWEIWE Bolatito Nafisat SENIOR LECTURER DEPARTMENT OF AQUACULTURE AND FISHERIES MANAGEMENT UNIVERSITY OF AGRICULTURE, ABEOKUTA

2. FISHERIES POPULATION DYNAMICS

3. Catch per unit effort
Calculation for catch per unit effort for the different fishing gears
Passive Gears
Gill Net
Traps
Longlines

4. 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

5. 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.

6. 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

7. Active fishing gears Cast Net Drift Net Dragnet Beach seine
Spears and harpoons
Trawls and dredges
Seine nets
Purse seines

8. Cast Net Cast Net in Kg/day
Catch (weight in Kg) x 24 hours Fishing time
Assuming that total fishing hour is 24 hours.

9. 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

10. Dragnet (100m length, 6m depth of Nylon netting material of 25
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

11. Therefore, 1000m2 = (x/180) x 1000 weight of fish
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

12. 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 dorso-ventrally (Anderson and Gutreuter 1983).

13. 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).

14. Source: http://www.texasgulfcoastfishing.com
Total Length
Fork Length
Standard Length
Head Length
Snout Length
Caudal peduncle
Fin Rays
First Dorsal
Second Dorsal
Pectoral Fin
Pelvic Fin
Anal Fin
Finlet
Caudal Fin
Lateral Fin
Scutes
Opercle
Preopercle
Interopercle
Adipose Eyelid
Supramaxilla
Premaxilla
Source:

15. External and Internal Anatomy
Source:

16. Source:

17. 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, and millimeters respectively,
Should be set for fish stock assessment while monitoring simultaneously the physico-chemical parameters at each fish sampling station.

18. 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.

19. 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

20. Setting of the Experimental Gill Net during sampling hour of 6-8pm

21. 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

22. 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

23. 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.

24. M = R N C N = MC/R 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

25. 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: Available online at pages
Ikenweiwe B. and S. Otubusin (2010). Limnology and Plankton Abundance. Germany. Verlag Publisher. ISBN- 10: , ISBN-13: (Available online at pages.
Ita E. O. and M. Mdaihli (1997). The Current Status Of Fish Stock And Fisheries In Kainji Lake

26. THANK YOU