Bottom Trawl Surveys - Proceedings of a Workshop Held at Ottawa ...

260
Table 1. Number of stations occupied in each offshore Northeast Fisheries Centre stratum, north of
Cape Hatteras, during the 1980 autumn bottom trawl survey. The number of square nautical miles
(nmi2) in each stratum and the number of (nmi2) represented by each station in these strata are also
presented.
Stratum
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
# of
Stations
7
7
3
3
5
8
3
3
5
8
3
3
9
4
3
10
4'
3
9
6
4
4
5
6
4
5
4
7
8
3
7
5
4
# of
Square Miles
2516
2078
566
188
1475
2554
514
230
1522
2722
622
176
2374
656
230
2980
360
172
2454
1221
424
454
1016
2569
390
1014
720
2249
3245
619
2185
655
861
Square miles/
station
359.43
296.86
188.67
62.67
295.00
319.25
171.33
76.67
304.40
340.25
207.33
58.67
263.78
164.00
76.67
298.00
90.00
57.33
272.67
203.50
106.00
113.50
203.20
428.17
97.50
202.80
180.00
321.29
405.63
206.33
312.14
131.00
215.25
Overall length and weight of each vessel
are significant in determining how the vessel
reacts to sea state. A smaller·and/or lighter
vessel will roll and pitch more than either a
larger or heavier one. Increased vessel motion
is transferred to the bottom trawl via the
trawling warps and can increase variability in
trawl performance.
The NEFC uses the R/V ALBATROSS IV and R/V
DELAWARE II to conduct bottom trawl surveys.
Table 2 lists the autumn surveys each vessel has
participated in since 1g63. During three of
these surveys both ships were used; during three
surveys the DELAWARE II was used; and during the
remaining twelve, the ALBATROSS IV was used.
These ·vessels are both stern trawlers but are
dissimilar in many respects. Some of the more
significant dissimilarities are indicated in
Table 3. In addition to the items indicated in
Table 3, the towing point on the ALBATROSS IV is
higher off the water than the DELAWARE II and
major equipment (e.g., generators) are different
and likely to emit different noises.
The two vessels handle the gear differently
due to different types of winches. The DELAWARE
Stratum
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
# of
Stations
6
4
8
5
5
5
3
6
2
4
5
2
2
4
4
3
3
2
2
2
7
3
2
2
6
4
2
2
5
4
2
2
# of
Square Miles
1766
1097
4069
2108
2560
730
578
1570
156
860
934
150
247
1159
1184
198
1318
243
86
60
2832
555
86
52
2433
1024
281
105
2145
1273
139
60
Square miles I
station
294.33
274.25
508.63
421.60
512.00
146.00
192.67
261.67
78.00
215.00
186.80
75.00
123.50
289.75
296.00
66.00
439.33
121.50
43.00
30.00
404.57
185.00
43.00
26.00
405.50
256.00
140.50
52.50
429.00
318.25
69.50
30.00
II has winches that are driven directly and the
trawl and wire are 'paid out at maximum speed
permitted by the motor. The ALBATROSS IV has
winches with free-spooling drums and wire is
paid out as fast as the setting speed of the
ship. The DELAWARE II, on the other hand, has
sufficient deck area to haul the trawl aboard
without taking a bite, while the ALBATROSS IV
does not have as much deck area and must
retrieve large trawls in bites.
Recognizing that there are significant
differences between these ships, the NEFC
undertook to determine the relative fishing
power of the two vessels during May 1980. The
results indicated no significant difference in
fishing power (Noble, McBride and Byrne, in
preparation). However, this may be a reflection
of the excellent weather conditions during the
experiment. On the other hand, since both
vessels are relatively large, the vessel
differences may be masked by the size of the
gear used relative to ship size. The fishing
power of the R/V ALBATROSS IV and R/V BELOGORSK
was compared during experiments conducted from
1973 to 1g75, In this case, a significant