6. Comparative bottom trawling

In order to compare catch rate by day/night hauls, 5 night hauls were worked at approximately the same positions as 5 of the day hauls in Table 8. Catch rates by main groups for the respective stations are shown in Table 11. Mean catch rate for the 5 day hauls is estimated at 876 kg/hour and 251 kg/hour for pelagics and demersals respectively, whereas the comparable figures at night are 64 and 200. This means that the catchability of the pelagic species in bottom trawl decreases at night whereas the catchability of bottom fish is less dependant on dayhour. The catchability of all the pelagic families is equally redused at night (Table 12), whereas the other species is little influenced by dayhour except for shrimps which seems to be more vulnerable to the gear at night.

Table 11. COMPARATIVE BOTTOM HAULS. Catch rates by main groups during night- and day-hour, kg/hour. Note that St.no.441 is comparable to 439, see Fig. 2.

NIGHT

ST. NO.	DEP.	Pelagic	Demersal	Shark	Squid	Shrimp	Other
441	22	81.60	119.80			25.00	92.70
442	27	48.70	79.10	4.00		0.60	55.80
443	36	70.40	259.20			0.80	145.60
444	45	105.60	308.00	32.00		1.60	65.60
445	52	17.50	238.00	7.50		4.20	51.00
MEAN		64.76	200.82	8.70		6.44	82.14

DAY

ST. NO.	DEP.	Pelagic	Demersal	Shark	Squid	Shrimp	Other
433	50	82.00	171.60	1.80		6.00	5.60
434	44	2454.40	184.80	41.00			46.40
435	30	1242.00	698.00	50.40			353.60
438	22	337.40	29.90	2.00		0.70	22.20
439	20	267.20	172.80			0.64	73.80
MEAN		876.60	251.42	19.04		1.47	100.32

Table 12. COMPARATIVE BOTTOM HAULS. Catch rates by families for pelagic fish at night- and day-hour, kg/hour.

NIGHT

ST. NO.	DEP.	Sardines	Anchovies	Carangids	Scombrids	Hairtails	Other
441	22	46.60				35.00	237.50
442	27	19.60	0.40	0.90		27.80	139.50
443	36	13.60	2.40	16.00		38.40	405.60
444	45	35.20		22.40		48.00	407.20
445	52	16.00				1.50	300.70
MEAN		26.20	0.56	7.86		30.14	298.10

DAY

ST. NO.	DEP.	Sardines	Anchovies	Carangids	Scombrids	Hairtails	Other
433	50	56.40				25.60	185.00
434	44	1354.20	401.80	205.00	464.60	9.60	291.40
435	30	87.40	9.20	377.20		754.40	1115.80
438	22	60.20	14.00	1.40		261.80	54.80
439	20	55.20	8.00	7.20		196.80	247.24
MEAN		322.68	86.60	118.16	92.92	249.64	378.85

Pooled samples of the size distributions of the most important species are shown in Annex III.

Done at Port of Spain
29 May 1988

Figure 2. Course tracks, fishing stations and hydrographic profiles. Broken cource line indicate rough and uneven bottom

Figure 3. Hydrographic profiles.

TRINIDAD NORTH 23-24.5 1988

TRINIDAD EAST 26-27.5 1988

Figure 4. Distribution of pelagic fish from acoustic system.

Figure 5. Distribution of pelagic fish from acoustic system.