Page 2 - Gristina_Gagliano2004

236 M. Gristina, M. Gagliano / Fisheries Research 67 (2004) 235–239
versus modern plastic traps under strict laboratory
conditions.
2. Materials and methods
The experiment was conducted during November
2002 at the Acqua Azzurra fish farm in Marzamemi
(southeastern Sicily). A total of 150 lobsters were ob-
tained from a local fish market in Marsala (SW Sicily)
in November 2002. Individuals were selected based
on appearance (no moulting or damaged specimens)
handled carefully and transferred to shallow, covered
holding tanks with 4 h. Filtered water was supplied via
a flow-through system and kept at a steady tempera-
ture of 18.7–20 ◦C. Individuals were sexed, weighed
and measured (carapace length (CL)) to the nearest
0.1 g and mm, respectively. To avoid size and sex re-
lated biases in catch performance, all individuals used
in the experiment measured 67–90 mm CL (mean =
79 mm, S.D. = 5 mm), resulting in 53% of speci-
mens being female. Initial (on transportation) and sub-
sequent mortality during holding were low (3.33%).
Two types of trap were used (Fig. 1). The traditional
type is a hand-made conical rush trap with irregular
triangular mesh (∼2 cm × 4 cm). The trap dimensions
were approximately 90 cm×65 cm with a 20 cm diam-
eter entrance. The second type is a cylindrical trap of
80 cm ×52 cm constructed of plastic mesh (2 cm mesh
size) and steel ring frames (see Goñi et al., 2001) with
a 21 cm diameter entrance. Each trap was baited with
200 g of frozen bogue (Boops boops). All baits were
weighed before trap deployment and re-weighed the
following morning after recovery to determine whe-
ther lobsters were able to escape after entering the trap.
The experimental tanks were kept outdoors and cov-
ered with a dark cloth to reduce light intensity. Tank
dimensions were 15 m × 1.80 m and filled to a depth
of 1 m (Fig. 2). Constant water flow into the six tanks
was maintained at a rate of 128 ± 13.72 l min−1. Tem-
perature, salinity, and light levels were monitored and
identical for all six tanks during the experimental pe-
riod (18.6–20.6 ◦C and 38 ppt).
Lobsters were deprived of food for 2 days before
being transferred from the holding tanks and randomly
assigned to treatments. Each day one trial was run with
four lobsters released at one end of each experimental
tank. The two trap types were set at the opposite end
(A) 90 cm.
65 c m.
20 c m.
4.6 cm2. 80 cm.
(B) 60 cm.
52 c m.
21 c m.
4 cm2.
Fig. 1. Plastic (A) and rush (B) traps used for the experiments on
catch performance.
of each of the experimental tanks with the entrance
downstream approximately 2.70 m (n = 42) from the
tank wall. Although each experimental tank held both
trap types, each tank was assigned one type on any one
particular day. Individuals captured by the assigned
trap type for that day were counted, sexed and mea-
sured. The same 12 traps were used in all trials. To test
catch performance of the two trap types, we ran three
replicates of each treatment on seven separate days.
During each trial, six experimental tanks were used si-
multaneously. Each trial commenced at 17:00 h (after
sunset) and ran till 09:00 h of the following day. Dur-
ing each trial, the number of individuals caught after
4, 7 and 16 h in each trap was observed and recorded.
This allowed us to verify if any lobster had escaped
after entering the trap.
Data sets (number of individuals per trap, weight of
individuals per trap and amount of bait eaten by lob-
sters entering the trap) were analysed with a two-way