ECOLOGICAL AND FISHERIES MANAGEMENT OF EDKU LAKE 5. EFFICIENCYAND SELECTIVE ACTION OF MONOFILAMENT NYLON TRAMMEL NETS AT EDKU LAKE

ECOLOGICAL AND FISHERIES MANAGEMENT OF EDKU LAKE
5. EFFICIENCYAND SELECTIVE ACTION OF MONOFILAMENT
NYLON TRAMMEL NETS AT EDKU LAKE
BY
A.A. ALSAYES*
“National Institute ofOceanography and Fisheries
Keywords: Edku – Egypt – Management -Nets – Selectivity – Fisheries – Lake
ABSTRACT
There is no fishing gear that may exhibit equal chances for catching all the
sizes of fish. For proper management offisheries in Edku Lake it is
attempted in the present paper to define the selective action oftrammel net
which is the most common fishing gear in this lake.
Monofilament nylon trammel nets with various mesh sizes were
experimentally used for fishing in Edku Lake during the period form Nov.
1999 to March 2001.
Baranov’s and Holt’s methods were used to calculate the selective
factor of trammel net for Oreochromis niloticus, Oreochromis aureus,
Tilapia zillii and Sarotherodon galilaeus. The average lengths and 50%
retention lengths were also calculatedfor the different meshes used.
It was found that although the narrow meshes used were able to catch high
numbers of0 aureus and Tilapia zillii representing 41.21% and 21.03 ofthe
total number offish caught in cases of meshes having 3. 33cm and 3. 85cm
stretched mesh size respectively, their catch comprised only 26.24% and
15.57% ofthe weight offish caught. On the other hand, the wide mesh used
(6.85cm stretched mesh size) was able to catch 10.89% ofthe total number of
fish caught, which comprised 19.99% ofits total weight.
For proper management offisheries in Edku Lake it is recommended
that the monofilament nylon trammel net must not be used with meshes of
the inner layer less than 6.0cm stretched measure.