Table 15.1 summarises the results of the present report. All the abundance estimates, as well as the estimates of annual potential yield, should be regarded more as approximates and guidelines rather than the results of accurate calculations. Both the available data as well as the methods used introduce sources of error. In order to be able to do the abundance and yield calculations, some important assumptions had to be presupposed. It is uncertain to which degree these assumptions are fulfilled. We therefore recommend that any increase in fishing should aim at less than the maximum potential yield presented here, until better assessment data are available. It should also be noted that the stock size presented is the maximum observed.
Table 15.1. Summary of the marine fishery resources of Mozambique. (thousand tonnes).
|
|
Maximum stock size |
Present catch |
Maximum potential yield |
|
|
DEMERSAL FISH |
||||
|
|
St. Lazarus Bank |
10 |
0 |
1 |
|
Rest of the coast |
200 |
30 |
50 |
|
|
PELAGIC FISH |
||||
|
|
Anchovies |
300 |
0 |
300 |
|
Other small pelagics |
300 |
30 |
150 |
|
|
Larger pelagics |
? |
<0.5 |
? |
|
|
Sharks |
? |
2-3 |
? |
|
|
MESOPELAGIC FISH |
1000 |
0 |
1000 |
|
|
CRUSTACEANS |
||||
|
|
Shallow-water shrimps |
16 |
12 |
15 |
|
Deep-water shrimps *) |
0.5-1 |
<0.5 |
? |
|
|
Spiny lobsters |
1 |
<0.1 |
0.3 |
|
|
Crayfish |
0.1-0.5 |
? |
? |
|
|
REEF FISHERIES |
? |
? |
5-10 |
|
|
INSHORE FISHERIES |
? |
7 |
5-10 |
|
*) Includes only the stock south of Bazaruto Island.Demersal fish
The stock of St. Lazarus Bank consists of larger demersal species with slow growth rates. and is dominated by the red snapper. The stock is at present not exploited and the annual potential yield is probably of the order 1000 tonnes. The bank area is unsuitable for trawling and traps and handlines appear to be the most appropriate gears. Fishing could be carried out by rather small boats.
The potential along the rest of the coast is about 50 000 tonnes. The most important species are breams, croakers, grunters and lizard fish and the main fishing area is the Sofala Bank. The catch presented in Table 15.1 consists of the estimated by-catch in the shrimp fishery and the catch from the Soviet trawlers from September 1977 to June 1978. These catches are expected to increase during 1979 due to increased effort and skill of the fishermen. If an increase in the shrimp fishery is also to be expected, the catch will probably reach close to the maximum potential yield. Caution should therefore be shown, and the rate of exploitation of the demersal stock closely followed.
Pelagic fish
The main pelagic species is the buccaneer anchovy at Sofala Bank. This fish, 7-8 cm long, has a very short life cycle and the potential yield will therefore most likely equal the stock size. The abundance is subject to very large seasonal variations, between 30 000 and 300 000 tonnes, and the potential yield suggested therefore presupposes, a theoretical maximum exploitation of the stock which may not be fully achievable in practice. At present it is not exploited, as its behaviour differs somewhat from the other pelagic species in such a way that it does not settle at the bottom during daytime. It is therefore not accessible to bottom trawls. It is easily caught by pelagic trawls and probably also purse seines.
For the other pelagic fish we have suggested a maximum potential annual yield of about 150 000 tonnes. The most important of these species are the scad. the Indian pellona, the larger anchovy and the ponyfish. As for the demersal species the present catch consists of the by-catch from the shrimp fishery as well as catches from the Soviet trawlers from September 1977 to June 1978. This stock is rather lightly exploited and there are possibilities for increased catches.
The group ‘larger pelagic species’ consists mainly of tunas. Spanish mackerel and sharks. The available data offer us no possibilities even to guess at the abundance of these species. The current Soviet long-line investigation will increase the knowledge on the more offshore species. The Spanish mackerel is distributed at depths shallower than 50 m at Sofala Bank and Boa-Paz Bank. It is frequently taken as by-catch when trawling is done on the smaller pelagic species on which it feeds. Spanish mackerel might be an important by-catch in a fishery for the small anchovy. There is also probably a significant resource of sharks, especially off the mouth of the Zambezi River.
Mesopelagic fish
This group consists mainly of lantern fish which inhabit the deeper part of the ocean during daytime and migrate to the surface during night. They are widely distributed in most of the oceans of the world and especially abundant in the northern Indian Ocean. The abundance calculations have been carried out for an area from the continental slope to 30 nautical miles seawards. Though the estimate of about 1 million tonnes seems impressive, this group is not believed to represent any immediate significant resource. The main reason for this is the lack of concentrations and techniques for commercial catches. Some contribution from this group, however, will occur as by-catch in bottom trawl hauls from depths greater than 200 m.
Crustaceans
The estimate of shallow-water shrimps is taken from the assessment carried out by ULLTANG, BRINCA and SILVA, 1979. For further comments on the shallow-water shrimp stock we refer to that report.
The estimate of the deep-water shrimp stock is probably seriously underestimated as the population on the slope of Sofala Bank has not been included. The estimate in Table 15.1 includes only the stock south of Bazaruto Island. The deep-water shrimp off Sofala Bank is exploited by Spanish trawlers and the catch is believed to be some few thousand tonnes annually. Some fishing vessels from the German Democratic Republic started fishing on this stock in October 1978. An improved assessment of the deep-water shrimp will probably be possible at the end of 1979. Caution should be shown in not increasing the effort in the deep-water shrimp fishery before a proper assessment can be made.
The stock of spiny lobsters is probably about 1000 tonnes which is most likely an underestimate. At present no regular all-season fishery is carried out on this stock. Fishing from September to November 1977 and in April-May 1978 gave a total catch of about 30 tonnes. Exploratory fishing by a joint Mozambican and Japanese enterprise is now in progress and will significantly improve the necessary data basis for assessment.
The crayfish stock is believed to be of the order of a few hundred tonnes. No specific fishing is carried out on this stock. The catches are mainly a by-catch of the deep water shrimp fishery, as the area of distribution of these two groups overlaps. The chances of over-exploitation of this stock are considered to be small, due to the habit of crayfish of forming burrows in the bottom and staying there at night. This habit make them less assessible for bottom trawls.
Reef and inshore fishery
The coast between Cabo Delgado and Angoche is edged by coral reefs and thus is unsuitable for trawling. Investigations from other reef areas in the region suggest that an annual potential production of about 5 tonnes/km2 should be expected. This will probably give a potential yield in the range of 5-10 000 tonnes. There is lack of information on the current fishery in the area and thus also the possibilities of increasing the fishery.
By an inshore fishery we mean fishing at depths less than 10 m. If an annual production of about 2 tonnes/km2 is reasonable. the expected potential yield will probably be of the same order as that of the reef fishery. A fishery for shad, a small pelagic fish, is carried out in the bays of Maputo and Beira. The annual catch in Maputo Bay was about 900 tonnes in 1977. For Beira Bay no information is available. As for the reef fishery, there is lack of information on the current fishery carried out in the inshore area.
