Acoustic instruments
Two SIMRAD scientific echo sounders, EK 400/38 kHz and EK 400/120 kHz were used during the survey for estimation of fish density. The EK 400/38 was coupled to a digital integrator QD as well as to an analog integrator QM. The performance of the instruments will be checked by calibrations on a standard copper sphere in a suitable location in Angola. The details of the instrument settings used are as follows:
|
|
EK 400/38 |
EK 400/120 |
|
Range |
0-100 or |
0-250 0-100 |
|
Transmitter |
High (5000 W Nom) |
High (1250 W Nom) |
|
Bandwith |
3.3 kHz |
3.3 kHz |
|
Pulselength |
0.5 ms |
1 ms |
|
TVG |
20 log R |
20 log R |
|
Attenuator |
20 dB |
0 dB |
|
Rec. gain |
7 |
5 |
|
transducer |
8 × 8 ceramic |
Ceramic 10 cm |
QM settings: Gain 20 dB × 10. Threshold 7
Hydrography
Temperature, salinity and oxygen were sampled at standard depths with Nansen bottles. Oxygen was measured with the Winkler method and salinity determined with an inductive salinometer. Surface temperature was recorded at 4 m depth with a thermograph.
Fishing gear
Bottom trawl: High opening shrimp and fish trawl with net headline 31 m (floatline), foot-rope 47 m, gear with 12 cm diameter roller disks, 40 m sweeps, estimated headline hight 6 m and distance between wings during towing 18-20m.
Pelagic trawl: Type "Harstadtrawl", width about 30m, vertical opening 10 - 15m.
Cod ends of trawls with fine meshed inner lining.
