12. SOME REMARKS ON THE FISHING EXPERIMENTS

Bottom trawl

On the research vessel surveys most of the bottom trawl catches were less than 500 kg/hour. For typical demersal species catch rates of up to 1000 kg/h were obtained for croakers and goatfish, these seemed to be the maximum. Every time the catch rate exceeded this figure the main catch consisted of the small pelagic species. The contributors to the highest catch rates were mainly ponyfish, with catches up to 3300 kg/h by “Dr. Fridtjof Nansen” and 4000 kg/h by “Kattegat”. Table 12.1 gives the catch rates for the commercial Soviet trawlers at Sofala Bank from December 1977 to June 1978. In October-November the vessels fished at Boa-Paz Bank between 50 and 100 m depths. The catch rates in this area were between 1500 and 2000 kg/h.

Table 12.1. Average catch rates of the largest Soviet trawlers at Sofala Bank - December 1977 - June 1978. (kg/trawling hour.)

	25 - 50 m		50 - 100 m
	Catch rate	Trawling hours	Catch rate	Trawling hours
December	763	58	1370	500
January	1726	344	1649	280
February	1587	273	2028	140
March	595	34	1436	127
April	1718	474	1795	88
May	1710	903	2672	80
June	2149	865	2224	84

Pelagic trawl

This gear was only applied by “Dr. Fridtjof Nansen” and “Kattegat”. The maximum catch rate, 4300 kg/h, was obtained on the buccaneer anchovy. This species did not occur in bottom trawls and is only accessible to pelagic trawls or probably also to purse seines. Good catches, up to 2000 kg/h, were also obtained of Indian pellona, Indian driftfish, hairtail, thryssa and sardinella. The horse mackerel and scad, however, which contribute significantly to the bottom trawl catches, seemed to be difficult to catch with the pelagic trawl.

Bottom longline and floating gill-net

Except at the St. Lazarus Bank the catches from these gears were completely dominated by different sharks. The fishing operations were mainly carried out at depths between 50 and 150 m. It will probably be difficult to use these gears for species other than sharks within this depth interval.

Pots

During the last part of Cruise III and throughout Cruise IV of “Dr. Fridtjof Nansen” pots were used in the research fishery. The different pots are described in Chapter 2. A longline system including 5 to 10 pots was used in the pot fishery operation. A buoy line was connected to one end of the setline and no extra anchoring device was applied. The pots usually fished overnight with soaking time from 15 to 30 hours. They were baited with chopped fish in perforated plastic bait containers. A total of 204 pots were lifted during the investigation.

Table 12.2. Catch in pots by depth.

Depth (m)	No. of pots	Total catch (kg)	Catch per pot (kg)	Dominant species (Total catch - kg)
St. Lazarus Bank
15 - 23	22	422	19.2	Lutjanus bohar (189)
				Promicrops lanceolatus (94)
Rest of the coast
15 - 23	35	30	4.4	Epinephelus tauvina (12)
30 - 58	47	83	1.8	Crabs (18)
76 - 122	60	225	3.8	Argyrops spinifer (72), Sharks (41), Sparus major (24)
153 - 200	32	134	4.2	Shovel-nosed lobster (22)
275 - 320	8	4	0.5	Dalatias licha/Shark (4)
Total	204	898	4.4

The pots were set out at depths from 15 to 320 m. The results may be separated into five different depth intervals, as shown in Table 12.2. Off the Mozambican coast, excluding the St. Lazarus bank, an average catch per pot of 5 kg or more was obtained only at six localities, as seen in Table 12.3.

Table 12.3. Localities where the average catch per pot exceed 5 kg.

St. no.	Area	Depth (m)	Total catch (kg)	Catch per pot (kg)	Dominant species
139	Sofala	85	119	24	Seabreams, Snappers
167	Bazaruto	200	40	8	Groupers, Seabreams
153	Delagoa	195	24	5	Seabreams
154	Delagoa	100	26	5	Seabreams
192	Delagoa	180	24	5	Shovel-nosed lobsters
196	Inhaca	167	45	9	Sharks, Seabreams

During the investigation, 30 pots of the RK type were set and lifted. In shallow water no catch was obtained, except for small incidental catches of swimming crab and Delagoa thread-fin bream, Nemipterus delagoae. In deeper waters a few good catches of crustaceans were taken:

Depth 300 - 320 m;	catches of spiny lobster Palinurus delagoae, up to 12 individuals (3 kg) pr. pot.
Depth 200 - 285 m;	catches of shovel-nosed lobster Scyllaridae up to 10 individuals (4 kg) pr. pot.
Depth 320 - 352 m;	Deep-water crab Geryon quingedens, up to 72 individuals (30 kg) pr. pot.

Some sharks (Squalus acanthias and Mustelus manazo) were also caught in these traps in deep water (200-285 m). Twenty of the RQ-type pots were lifted during the investigation. Except for incidental catches of crabs and fish, no catches were obtained in these pots.

The catches with the RF-traps in coastal waters were generally low. However, the catches in the depth interval from 76 to 200 m, especially at the stations listed in Table 12.3, may indicate exploitable resources by pot fishing. The relatively good catches at the St. Lazarus Bank show that pots might be a suitable fishing gear in this area. As the pots were used only in the last part of the “Dr. Fridtjof Nansen” investigation, pot data from the St. Lazarus Bank are restricted to the four pot stations in this area during Cruise IV in April. Relatively high catches by handline during the other cruises, however, give reason to believe that the abundance of the main species was fairly constant throughout the year.

Catch data from the crayfish pots (RK) are scarce. A few good catches of crab Geryon quingedens, spiny lobster Palinurus delagoae in deep water indicate that these species can be fished by pots in relatively high quantities.

Since pots were used only in the last part of the investigation, the catch data are scarce, but the following statements can be made:

- 1) Pots (type RF) have proved to be successful for catching fish at the St. Lazarus Bank. Because of the rough bottom conditions pots and handlines seem to be the best gear for exploiting the fish resources in this area.

- 2) The fish catches by pots on the coast are too low, but a few relatively good catches indicate that further investigations may show that pots might also be successful in capturing higher quantities of fish in some areas. Such investigations should also include exploratory pot fishing with smaller vessels in the very shallow waters of the coral reefs.

- 3) Based on the few good catches of crab and spiny lobster in crayfish pots (RK), exploratory fishing should be carried out in deep water to investigate the possibility of exploiting these resources by pot fishing.