4. Results of the fishing experiments, catch compositions and swept area biomass estimates

The results of the fishing experiments are summarized in Table 1 to 4. One should note that most of the fishing forms part of a programme for "swept area" biomass estimation, and for this purpose the trawl stations are positioned in advance more or less randomly with the intention to estimate fish density in each depth strata and not to obtain high catch rates. The catch rates thus do not simulate those of a commercial fishery.

All catches were sampled for composition in weight and numbers by species and size sampling was made of important species, using total length. The complete records of fishing stations are shown in ANNEX II.

The composition of the fish fauna on the shelf north of Benguela changes by depth and a partition in an inner shelf down to 70 m depth and an outer shelf 70-200 m has been used as basis for the analyses. The chatches in the slope from 200 m downward are characterized by the occurance of the deepwater shrimps and have been grouped separately.

Benguela-Palmeirinhas

Table 1 shows the catch rates of successful bottom hauls standardized to kg/hour for the main groups of resources on the two parts of the shelf. Both for the inner- and the outer shelf the highest catch rates were obtained for the demersal species. Sharks and shrimps are scarce. The squids are most abundant on the outer shelf, where the common cuttlefish Sepia officinalis is dominating by some 50 % of the squid chatches. The flying squid Todarodes sagitttus is contributing by some 25 %.

Table 2 shows the catch rates of the pelagic species by families from the two parts of the shelf. The Table include both pelagic and botten hauls. These data are not very meaningful as indices of abundance of these types of fish, but they give an indication of the availability of the various forms. Clupeids were caught in small amount by pelagic trawl on the inner shelf, and 70 % where Sardinella maderensis. The carangids dominate the catches on the whole shelfs, the catches from the inner shelf consisted of some 15 % lookdown, Selene dorsalis, 15 % bumper Chloroscrombrus chrysurus, and the remainder was mainly Cunene horse mackerel. Nearly 100 % of the carangid catches from the outer shelf was Cunene horse mackerel dominated by small sized fish. The hairtails are abundant at some stations (231,237,275, 321) where as scombrides are scare. Most of the barracudas were caught on the inner shelf and consisted of the guachanche species Sphyraena guachancho, and some S. spyraena.

Table 3 shows the catch rates of demersal fish in 63 successful bottom hauls by families and zones. The grunts dominate the catches on the whole shelf and consisted mainly of the bigeye grunt Brachydeuterus auritus. Among the seabreams the red pandora Pagellus bellottii was most abundant and contributed with 60 %, the Angola dentex Dentex angolensis with 20 % of the sparids. The pooled size compositions of the species are shown in ANNEX I.

Table 1. Benguela to Pta. das Palmeirinhas. Catch rates by main groups in bottom trawl hauls, standartized to kg/hour.

INNER SHELF

ST. NO.	DEP.	Pelagic	Demersal	Sharks	Cephalopod	Shrimp	Other
232	38	223.40					3.00
235	40	315.00	1456.00				109.40
239	25	90.72	1197.00			2.52	206.32
244	28	87.60	235.20		3.60		34.80
245	60	70.00	2620.00		2.50	5.00	95.00
250	66		72.00		66.00		81.00
252	25	99.20	73.60		3.20	3.20	50.40
253	60	1641.60	664.60		48.00		163.20
263	62	225.00	309.00		9.00		235.50
264	26	154.80	114.00				91.20
265	33	2.16	62.40		13.20		25.20
269	22	131.20	429.60	2.00	4.80	1.20	63.80
270	38	7.89	122.22		0.32		19.74
272	50	1.50	20.00		6.00		36.80
273	24	9.80	8.20		6.00		11.00
275	49	342.10	1387.06		12.44		55.98
281	37	91.80	414.00		3.60		63.00
284	30	55.60	130.40	6.40	8.00		34.40
288	69	1.40	76.00		17.60		28.60
289	27	27.50	7.20	11.00	3.20		4.40
290	23	1.10	2.40	2.00	8.00		4.40
291	60	9.00	51.60		8.10		20.26
298	50	10.40	0.20		0.30		97.60
299	22	3.60	2.40		7.20		10.60
300	18	0.20	20.40		2.40		36.60
301	66	2113.62	13885.80
305	32	6.40	20.80		3.40		33.00
306	24	91.80	11.20				17.80
311	65	24.20	29.80		9.00		12.80
312	31	6.60	125.00				5.00
315	43		2.60		2.20		3.20
318	28	46.80	2.20				21.20
319	39	14.80	78.00		12.00		31.20
MEAN		178.99	716.09	0.65	7.88	0.36	51.71

OUTER SHELF

ST. NO.	DEP.	Pelagic	Demersal	Sharks	Cephalopod	Shrimps	Other
231	86	2063.27	1296.17				291.08
233	100		262.56		18.00		61.60
234	91	0.50	180.50		15.00		51.50
236	93		467.10		5.40		22.50
240	85	9.60	152.80		18.40		39.20
241	98		105.20		24.80		15.70
242	102	0.26	213.88		23.08		35.76
243	72	9.66	92.46		46.80		49.20
248	189		631.20	46.70	46.70		171.20
249	98	739.00	264.40		64.70		131.00
254	97	2.70	189.80		18.90		27.90
262	105	7.20	296.40		12.00		73.20
271	87	354.00	187.00	4.00			56.00
274	111	299.00	1090.20		23.00		167.90
276	197	20.00	47.50	25.50	6.00		26.00
279	110	150.40	265.80		14.40		41.00
280	78	241.92	3661.02	16.12			80.62
282	73	255.20	1038.40				114.40
283	96	627.90	150.60		18.20		85.80
287	122	1018.78	2185.24		96.50		134.94
292	96	53.90	88.00		15.40		50.60
293	151	4.88	749.82	2.88	40.36		106.38
296	199	1.71	822.00	8.57	2.57		48.87
297	90	12.80	216.00		3.80		9.00
304	80	96.00	60.00		4.00		10.00
307	78	11.44	1080.46				7.62
310	102	765.00	685.00		10.00		32.50
313	79	109.80	444.60		7.20		3.60
314	95	76.80	329.60	4.80			124.00
316	72	146.00	81.00				6.50
317	96	372.80	46.40		9.60		8.00
MEAN		240.34	560.68	3.50	17.57		67.21

Table 2. Benguela to Pta. das Palmeirinhas. Catch rates of main pelagic families in bottom trawl hauls, standardized to kg/hour.

INNER SHELF

ST. NO.	DEP.	Clupeids	carangids	Hairtails	Barracudas	Scombrids	Other
232	38	2.40	100.00		116.00	5.00	3.00
235	40		238.00	77.00			1565.40
237	10	52.50	16.50	645.00	51.00		55.50
238	10	40.05	82.80	85.50	36.90		22.05
239	25		63.00		25.20		1408.36
244	28	1.20	8.40	15.60	12.00		324.00
245	60		45.00	25.00			2722.50
250	66						219.00
251	24			12.92			149.53
252	25		3.20				226.40
253	60		1632.00	9.60			875.80
263	62		225.00				553.50
264	26	7.20	94.80	1.20	48.00		208.80
265	33	0.24	0.72		1.20		100.80
266	15	15.60	50.40	2.00	10.40		67.40
267		14.80	12.40		6.40		28.40
268	23	24.00	627.60	12.00			36.00
269	22	14.20	36.00	26.40	51.60	3.00	501.40
270	38			3.47		4.42	142.28
272	50		1.50				62.80
273	24		6.80			3.00	25.20
275	49		37.32	304.78			1455.48
281	37	10.80	27.00	36.00	18.00		480.60
284	30	3.60	20.00	4.00	28.00		179.20
288	69	0.20	1.20				122.20
289	27		21.50		4.00	2.00	25.80
290	23		1.10				16.80
291	60		0.90	3.30	1.50	3.30	79.96
298	50			10.40			98.10
299	22		2.40		1.20		20.20
300	18		0.20				59.40
301	66	26.74	2086.88				13885.80
305	32		1.00	4.00		1.40	57.20
306	24		72.00	10.20	9.60		29.00
308	7	88.60	14.80		4.80		13.20
311	65		4.60	10.00	2.60	7.00	51.60
312	31		0.60	4.00	2.00		130.00
315	43						8.00
318	28		6.80		40.00		23.40
319	39		6.00	0.80	8.00		121.20
320	15	13.20	14.80	4.40	31.60		52.40
321	10			360.00
MEAN		7.51	132.46	39.70	12. 14	0.69	623.99

OUTER SHELF

ST. NO.	DEP.	Clupeids	carangids	Hairtails	Barracudas	Scombrids	Other
231	86		1588.36	474.91			1587.25
233	100						342.16
234	91		0.50				247.00
236	93						495.00
240	85		9.60				210.40
241	98						145.70
242	102		0.26				272.72
243	72		0.06	3.60	6.00		188.46
248	189						895.80
249	98		739.00				460.10
254	97				2.70		236.60
262	105		2.40	1.20		3.60	381.60
271	87		340.00	8.00		6.00	247.00
274	111		299.00				1281.10
276	197			20.00			105.00
279	110		150.40				321.20
280	78		241.92				3757.76
282	73		162.80	92.40			1152.80
283	96	1.30	624.00	2.60			254.60
287	122		1018.78				2416.68
292	96	1.10	52.80				154.00
293	151		2.88			2.00	899.44
296	199			1.71			882.01
297	90		9.80	3.00			228.80
302	96		86.40				55.20
304	80		94.00			2.00	74.00
307	78		11.44				1088.08
310	102		750.00		15.00		727.50
313	79		55.80	28.80	25.20		455.40
314	95		60.80	16.00			458.40
316	72		140.00	4.00	2.00		87.50
317	96		368.00			4.80	64.00
MEAN		0.08	212.78	20.51	1.59	0.58	630.41

Table 3. Benguela to Pta. das Palmeirinhas. Catch rates of main demersal families in bottom trawl hauls, standardized to kg/hour.

INNER SHELF

ST. NO.	DEP.	Seabreams	Grunts	Croakers	Groupers	Hake	Other
232	38						226.40
235	40	84.00	1274.00	63.00	35.00		424.40
239	25	113.40	1076.04	7.56			299.56
244	28		222.00	13.20			126.00
245	60	85.00	2520.00	15.00			172.50
250	66	52.80			0.60		165.60
252	25	1.60	72.00				156.00
253	60	134.40	480.00		2.20		1900.80
263	62	39.00	255.00		1.50		483.00
264	26		91.20	22.80			246.00
265	33	36.24	2.40		2.16		62.16
269	22	1.00	370.60	58.00			203.00
270	38	62.85			44.53		42.79
272	50	0.40			9.00		54.90
273	24				6.00		29.00
275	49	24.88	1244.00	118.18			410.52
281	37		324.00	90.00			158.40
284	30	5.60	120.00		4.80		104.40
288	69	66.00	0.80				56.80
290	23	0.20	2.20				15.50
291	60	11.10	19.50		1.20		57.16
298	50	0.20					108.30
299	22	1.60	0.80				21.40
300	18	8.40	12.00				39.20
301	66	882.88	12842.40	160.52			2113.62
305	32	20.80					42.80
306	24	10.00	1.20				109.60
311	65	28.60			1.20		46.00
312	31	105.00	20.00				11.60
315	43	2.20					5.80
318	28	0.80			1.40		68.00
319	39	26.00	51.20				58.80
MEAN		56.40	656.29	17.13	3.42		250.63

OUTER SHELF

ST. NO.	DEP.	Seabreams	Grunts	Croakers	Groupers	Hake	Other
231	86	289.63	272.73	655.45	8.73		2423.98
233	100	174.00			3.00		165.16
234	91	55.50					192.00
236	93	259.20		180.00			55.80
240	85	96.80					123.20
241	98	85.60			0.20		59.90
242	102	174.28					98.70
243	72	36.06					162.06
248	189	248.22				93.42	554.16
249	98	156.00				1.80	1041.30
254	97	117.00			2.70		119.60
262	105	30.00				3.60	355.20
271	87	14.00	160.00				427.00
274	111	59.80	9.20				1511.10
276	197					26.00	99.00
279	110	221.80	19.20		12.00		218.60
280	78	88.68	3548.16	24.18			338.66
282	73	96.80	880.00	35.20			396.00
283	96	62.40	13.00	44.00			763.10
287	122	19.00					3416.46
292	96	30.80					177.10
293	151	14.42					889.90
296	199	18.85			651.43	42.86	170.58
297	90	95.00	8.00	107,00	3.80		27.80
304	80	58.00					110.00
307	78	1072.84	7.62	2.00			19.06
310	102	20.00	650.00				822.50
313	79	36.00	360.00	46.80			122.40
314	95		320.00				215.20
316	72	81.00					152.50
317	96	41.60					395.20
MEAN		121.07	201.55	35.31	22.00	5.41	503.97

SLOPE 200-600 M

ST. NO.	DEP.	Hake	Seabreams	Shrimps	Sharks	Cephalopod	Other
246	296	13.80		6.90	29.90	6.90	595.70
247	299	16.10		2.30	2.30		570.40
255	200	68.00		56.00	2.40	8.00	82.40
256	301			6.00		1.60	105.20
257	351	404.30		109.60	11.50		274.00
258	447	384.00		230.40	9.60		45.60
259	351	100.00		119.90	11.40	8.50	559.60
260	300	16.60		20.80		12.50	1249.50
261	200	96.00	7.20	19.20		38.64	556.00
277	396	54.60		159.60	9.60		69.60
278	304	14.54	14.54	18.18		10.90	341.76
285	302	14.80		38.30			995.30
286	448	4.00		23.20	1.00	1.60	16.80
294	451	545.30		17.39	1.55		45.14
295	500	42.00		21.60	1.80		80.40
303	542	18.00		8.40	0.80	1.20	63.60
MEAN		112.00	1.36	53.61	5.12	5.62	353.19

Croakers and groupers made more occasional contributions to the catches. The Canary drum Umbrina canariensis was mainly caught on the outer shelf and contributed with 50 % of the croakers. Some small catches of groupers were obtained both on the inner-and the outer shelf consisting most frequently of the white grouper Epinephelus aeneus, whereas the large catch of this group taken at station number 296 was the dungat grouper Epinephelus goreensis.

Table 3 shows the chatch rates of 16 bottom hauls in the slope. The hake Merluccius polli was caught in the slope with the highest catch rates below 350 m depth. Most of the haules were made by nighttime, but st. nos. 259 and 260 were worked in dayhours. The good catch of shrimps at st. no. 259 consisted mainly of spider shrimp Nematocarcinus africanus and narwal shrimp Parapandalus narval. The deepwater rose shrimp Parapenaeus longirostris was caught in small quanteties in the dayhours. Good catches of the rose shrimp were obtained at st. nos. 257, 258 and 277. The red shrimps of the Aristeidae family were caught at rates up to 38 kg/hour at 450 m depth. The pooled size composition of the samples is shown in ANNEX I.

Table 4 shows the swept area estimates of mean densities by species and depth strata, based on 85 successful random bottom trawl hauls made. The bigeye grunts dominates both the 0-50 and 50-100 m bottom depth zone followed by the red pandora Pagellus bellotti and Dentex angolensis in the 50-100 m zone. The deeper waters (100-200 m) are dominated by the splitfin thinlip Synagrops microlepis. The catchability coefficient applied in the estimation is 1.0.

Table 4. Benguela to Pta. das Palmeirinhas. Swept area estimates of demersal fish densities by species and depth ranges.

Table 5 shows the estimated area of the shelf and the resulting biomasses for all demersal species and separately for the dominating species in each zone.

Table 5. Benguela to Palmeirinhas. Biomass estimates of groups of demersal fish by depth strata. Tonnes.

	Total	0-50 m	50-100 m	100-200 m
Shelf area nm2	4 700	1 750	1 680	1 280
Brachydeuterus auritus	53 000	10 000	41 000	2 000
Synagrops microlepis	17 500			17 500
Pagellus bellottii	6 300		1 400	1 900
All demersal	126 000	19 000	7 000	38 000

The total estimate of demersals amounted to 126 000 tonnes compared to 61000 tonnes obtained in the previous survey in February. In the surveys in 1985-86 the estimated demersal biomass varied between 50 and 100 thousand tonnes with a mean value from six surveys of 70 thousand tonnes.

In the 200-600 m bottom depth zone 15 successful hauls were made. Dominating species were splitfin thinlip Synagrops microlepis, greeneyes Chloropthalmus atlanticus and hake. The areal extension of this zone has been estimated to 1 300 nm². The following biomass figures were obtained:

Splitfin thinlip	4 400 tonnes
Greeneyes	6 300 tonnes
Hake	5 000 tonnes

These estimates are close to the corresponding estimates obtained in the previous survey.

Palmeirinhas - Cabinda

Table 6 shows the catch rates by main groups for the successful hauls in the region, and divided by inner shelf, outer shelf and the slope, as above. The mean catch rate in both inner and outer shelf of the pelagic species are reduced to about half of the values found south of Luanda. For demersal species the mean catch rates are reduced to one third. The catch rates of both pelagic and demersal species are however higher than those obtained in survey I. Sharks and shrimp are indicated to be more abundant on the inner shelf where as squid is more often caught on the outer shelf. The catch rates for all these groups are considerably lower than for the demersal and pelagic groups.

The pelagic group broken down to families are given in Table 7 for the inner and outer shelf. On the outer shelf the main pelagic family is the horsemackerel, with a modal length of 15 cm. See ANNEX I on length frequency distributions. The catch rates of the clupeids on the outer shelf are neglible. It should however be kept in mind that the bottom trawl catches reflects accessibility of pelagic species rather than abundance. For the abundance of pelagic species see section on acoustic estimates.

Table 6. Pta. das Palmeirinhas to Cabinda. Catch rates by main demersal families in bottom trawl hauls, standardized to kg/hour.

INNER SHELF

ST. NO.	DEP.	Pelagic	Demersal	Sharks	Squids	Shrimp	Other
323	60	211.14	594.58		7.20		97.92
324	32	273.60	337.00			16.00	9.60
325	30	60.00	149.60			5.80	12.00
326	59	265.60	824.80				3.20
331	27	166.80	111.60	2.00	2.40	16.60	16.80
332	53	52.00	494.60				10.60
335	65	264.00	1476.00
336	23	32.00	66.40			2.60	47.80
337	32	74.00	172.00			17.80	19.00
340	57	60.00	139.20		2.40		8.40
341	50	60.27	89.72				0.55
344	23	35.70	247.20			3.00	23.60
345	25	534.60	370.60				75.60
346	67	42.60	29.80	12.00	5.20		5.60
349	55	17.60	197.60	2.00	13.20		6.80
550	58	1.80	18.20		14.00		7.80
357	66	257.04	1030.08		4.80		25.20
358	24	259.20	230.40	48.00		9.00	43.20
359	23	371.20	63.40	54.40			9.20
360	65	105.30	367.20				10.80
368	66	44.80	144.00			21.60	29.60
374	41	87.60	171.60			6.00	21.20
382	70	27.00	19.20		11.40		3.60
383	35	17.20	15.60		2.20		5.80
388	18	10.40	21.60		2.40		9.60
389	26	6.20	71.20	16.00			19.00
390	66	14.00	92.50		19.50		7.00
393	82	36.40	168.40			0.20	1.40
394	68	9.00	88.50				3.50
403	63	10.40	91.20			0.40	4.80
404	30	43.20	180.80		0.80	10.40	16.60
409	54	1.80	40.60	9.80	1.00		4.80
410	38	58.40	136.80	8.00		1.20	3.20
411	31	16.00	206.80			35.20	53.10
412	34	7.80	121.80			13.80	50.40
413	13	45.00	179.00			6.00	10.00
416	52	28.00	148.40		0.70	4.00	8.40
MEAN		97.50	240.76	4.11	2.36	4.58	13.53

OUTER SHELF

ST. NO.	DEP.	Pelagic	Demersal	Sharks	Squid	Shrimp&Lob	Other
322	90	564.98	834.74
327	102	429.00	134.20		4.40		6.60
333	91	232.00	302.00				2.00
334	92	162.40	32.90				14.70
342	103	34.00	96.60	4.00	11.00		6.30
343	94	389.20	28.00		15.40		7.00
348	89	7.50	148.40		11.20		4.50
351	91	25.80	55.68		15.00		89.40
356	100	111.60	40.80		0.60		30.00
361	99	594.00	59.40		4.40
366	87	118.40	360.00		3.20		20.80
367	90	63.00	206.50		8.00		6.00
369	71	67.00	123.50			9.00	42.00
373	200	10.40	47.20		0.80	14.40	155.20
375	95	222.00	68.40			2:40	33.60
381	95	10.50	119.50		4.50		3.50
386	99	384.00	86.40		4.80		6.80
387	73	6.60	125.20		2.40		13.40
391	82	403.20	25.90		6.00		8.40
395	100	2.40	40.00		0.80		2.50
396	114	114.10	37.10	24.30	2.80		9.10
399	91	57.00	79.60			0.90	17.40
400	186	32.61	346.44		1.30		16.94
401	119	1.00	136.00				13.50
402	85	3.20	66.60		5.20		4.60
407	112	131.20	284.80				27.20
408	96	33.60	99.60		2.40	0.60	13.80
415	128	75.00	62.70		2.40	0.90	8.10
MEAN		153.06	144.58	1.01	3.81	1.01	20.12

Table 7. Pta. das Palmeirinhas to Cabinda. Catch rates by main pelagic families in bottom trawl hauls, standardized to kg/hour.

INNER SHELF

ST. NO.	DEP.	Clupeids	Barracudas	Carangids	Hairtails	Scombrids	Other
323	60			27.54	183.60	61.20	638.50
324	32	112.80	45.60	19.20	96.00		362.60
325	30	31.20	8.00	11.26	9.60		167.40
326	59		108.80	54.40	102.40		828.00
331	27	43.20	42.00	69.60	12.00		149.40
332	53		15.00	17.00	20.00		505.20
335	65		108.00	156.00			1476.00
336	23	24.40	4.80	2.80			116.80
337	32	36.00	10.00	8.00	20.00		208.80
340	57	1.20	24.00	34.80			150.00
341	50	0.27	40.91	16.36	2.73		90.27
344	23	17.70	1.80	1.20	15.00		273.80
345	25	86.40	414.00	16.20	18.00		446.20
346	67	1.00	5.00	35.20	1.40		52.60
349	55		16.00	1.60			219.60
350	58		0.60	1.20			40.00
357	66		32.64	118.32	106.08	4.80	1055.28
358	24	131.20	32.00	67.20	28.80		330.60
359	23	36.80	6.40	324.80	3.20	8.40	118.60
360	65	0.90	52.20	32.40	19.80		378.00
368	66	1.60		3.20	40.00		195.20
374	41	21.60	1.20	10.80	54.00		198.80
382	70		16.00	6.40	4.60		34.20
383	35		11.00	6.20			23.60
388	18			10.40		1.00	32.60
389	26		3.60	2.60		2.00	104.20
390	66			11.00	3.00		119.00
393	32	1.40	22.00	9.00	4.00	1.40	168.60
394	68		1.00	8.00			92.00
403	63			2.40	8.00		96.40
404	30	8.80	10.40		24.00		208.60
409	54		1.20	0.60			56.20
410	38	8.00	24.00	26.40			149.20
411	31	10.00	1.00		5.00		295.10
412	34	1.20		0.60	6.00		186.00
416	52	1.40	4.20	1.40	21.00		161.50
MEAN		16.03	29.54	30.95	22.45	2.19	270.25

OUTER SHELF