120
J. Nabhitabhata and S. Segawa
cleaning or replacing. Some capsules might be thrown back into the sea and sink
to the bottom, but these have a low chance of hatching (Chindamaikul et al. 1994).
This disadvantage of squid trapping in view of conservation has not been overlooked by the biologists and a primary solution was initiated. In 1990, the Thailand
Department of Fisheries (DOF) launched a research programme on cephalopod culture at the Rayong Coastal Fisheries Research and Development Center (RCRC) in
Rayong Province, about 200 km from Bangkok. One of the activities in this programme was for restocking through aquaculture methods. The RCRC was in a good
location where artisanal squid trapping was popular and this enhanced the possibilities for tackling the mentioned disadvantages. The first step of a possible solution
was to collect the egg capsules before they were discarded. The fishermen were paid
for the live egg capsules they collected at about US$ 0.33 per 1 kg. This payment
was intended to be an additional source of income for the fishermen and, on the
other hand, to raise their awareness of the economic value of natural resources. The
second step was to endorse hatching of those eggs in a hatchery through aquaculture
management. Previous studies revealed that the hatching rate of egg capsules incubated in plastic baskets was 20 % higher than when left at the bottom (Chindamaikul
et al. 1994). The third step was the release of the produced squid seeds back into the
actual fishing grounds in order to maximise restocking efficiency. Unfortunately,
this activity has declined since 2003 because there have been changes in policy of
the Thailand DOF, and the cephalopod hatchery has been shut down.
7.3.2 Methods
7.3.2.1 Hatchery Seed Production
Sepia pharaonis Broodstock Live cuttlefish are collected from traps and maintained in concrete tanks as broodstock. The fisherman maintains the live cuttlefish
in a partition in his boat through which fresh seawater can flow. The cuttlefish can
survive for more than 24 h in this chamber. The body weight of the spawners range
from 400 to 1,500 g at 200–300 mm ML. At landing, the cuttlefish are transported to
the hatchery in a plastic transportation tank of 500-L capacity. They are maintained
in 2 m
3
concrete tanks at a male-to-female ratio of 1:2 (Fig. 7.3). The cuttlefish will
mate in less than an hour after being released into the tank. Pieces of fishing net,
25 mm mesh size, with stone sinkers are put in the tanks as artificial substrates.
Spawning in the tank proceeds within that day or during the next morning.
The females attach their egg capsules in clusters to the artificial substrates. Each
female is able to spawn approximately 1,600 (500–3,000) egg capsules in total.
(Nabhitabhata 1978b, Nabhitabhata and Nilaphat 1999). One female lays eggs in
one cluster (Fig. 7.4) or more every day or every other day if they are interrupted
while spawning. The spawning period can be more than 3 weeks, depending on the
female size, the numbers of eggs produced and her condition. The male escorts and
protects his mate from other males during spawning, but will turn to form a pair
J. Nabhitabhata and S. Segawa
cleaning or replacing. Some capsules might be thrown back into the sea and sink
to the bottom, but these have a low chance of hatching (Chindamaikul et al. 1994).
This disadvantage of squid trapping in view of conservation has not been overlooked by the biologists and a primary solution was initiated. In 1990, the Thailand
Department of Fisheries (DOF) launched a research programme on cephalopod culture at the Rayong Coastal Fisheries Research and Development Center (RCRC) in
Rayong Province, about 200 km from Bangkok. One of the activities in this programme was for restocking through aquaculture methods. The RCRC was in a good
location where artisanal squid trapping was popular and this enhanced the possibilities for tackling the mentioned disadvantages. The first step of a possible solution
was to collect the egg capsules before they were discarded. The fishermen were paid
for the live egg capsules they collected at about US$ 0.33 per 1 kg. This payment
was intended to be an additional source of income for the fishermen and, on the
other hand, to raise their awareness of the economic value of natural resources. The
second step was to endorse hatching of those eggs in a hatchery through aquaculture
management. Previous studies revealed that the hatching rate of egg capsules incubated in plastic baskets was 20 % higher than when left at the bottom (Chindamaikul
et al. 1994). The third step was the release of the produced squid seeds back into the
actual fishing grounds in order to maximise restocking efficiency. Unfortunately,
this activity has declined since 2003 because there have been changes in policy of
the Thailand DOF, and the cephalopod hatchery has been shut down.
7.3.2 Methods
7.3.2.1 Hatchery Seed Production
Sepia pharaonis Broodstock Live cuttlefish are collected from traps and maintained in concrete tanks as broodstock. The fisherman maintains the live cuttlefish
in a partition in his boat through which fresh seawater can flow. The cuttlefish can
survive for more than 24 h in this chamber. The body weight of the spawners range
from 400 to 1,500 g at 200–300 mm ML. At landing, the cuttlefish are transported to
the hatchery in a plastic transportation tank of 500-L capacity. They are maintained
in 2 m
3
concrete tanks at a male-to-female ratio of 1:2 (Fig. 7.3). The cuttlefish will
mate in less than an hour after being released into the tank. Pieces of fishing net,
25 mm mesh size, with stone sinkers are put in the tanks as artificial substrates.
Spawning in the tank proceeds within that day or during the next morning.
The females attach their egg capsules in clusters to the artificial substrates. Each
female is able to spawn approximately 1,600 (500–3,000) egg capsules in total.
(Nabhitabhata 1978b, Nabhitabhata and Nilaphat 1999). One female lays eggs in
one cluster (Fig. 7.4) or more every day or every other day if they are interrupted
while spawning. The spawning period can be more than 3 weeks, depending on the
female size, the numbers of eggs produced and her condition. The male escorts and
protects his mate from other males during spawning, but will turn to form a pair