PROCEEDINGS OF THE CRUSTACEAN MANAGEMENT WORKSHOP

March 1987
RAF/79/065/WP/34/87

organized by the

Regional Project for the Development and Management of Fisheries in the Southwest Indian Ocean (SWIOP)

The designations employed and the presentation of material in this publication do not imply the expression of any opinion whatsoever by the Food and Agriculture Organization of the United Nations concerning the legal status of any country, territory, city or area or of its authorities or concerning the delimitation of its frontiers or boundaries. The views expressed are those of the authors.

CONTENTS

INTRODUCTION

These are the proceedings of the workshop on crustacean management for countries of the Southwest Indian Ocean region, which took place in Mauritius at the Albion Fisheries Research Centre from 1 - 11 October 1985. The workshop was organised by the FAO/UNDP Regional Project for the Development and Management of Fisheries in the Southwest Indian Ocean (SWIOP), to provide a forum to review the status of resources and fisheries, demonstrate biological and economic analytical methods and levels, and for promoting discussions on the management measures appropriate for the region.

These proceedings consist of the papers presented on the biological and bio-economic aspects of crustacean fisheries including aquaculture, and country statements which were presented by the participants at the workshop. Papers already published elsewhere were not included. Abstracts of all presentations can be found in the Report of the Workshop (RAF/79/065/WP/23/86), which also contains an account of the workshop discussions.

In preparing these proceedings textual amendments of the papers has been minimal. Revision has been restricted to the correction of typographical errors and the like.

THE CRUSTACEAN RESOURCES AND FISHERIES OF THE SOUTHWEST INDIAN OCEAN

by

M.J. Sanders

(FAO ROME)

1. INTRODUCTION

This short paper has been prepared as a background document to the Crustacean Management Workshop. It relates particularly to the crustacea resources of the countries serviced by the Southwest Indian Ocean Project, but also includes reference to the lobster stocks of the St. Paul and New Amsterdam Islands which are exploited from Reunion.

The principal contents are the biomass and potential yield estimates (when available), and some indications of the present state of exploitation. Shrimp, lobster and crabs are treated separately. There is a further distinction between shallow-water crustacea (occuring principally in waters less than 100 m) and deep-water crustacea.

Each country is treated separately except for the Seychelles, Mauritius, Comoros and Reunion, which are considered together within the category 'Islands and Banks'. They all fall within the FAO statistics area code 51 (Figure 1).

2. RESOURCES AND FISHERIES IN MOZAMBIQUE

2.1 Shallow-water shrimp

The shallow-water shrimps occur along almost all the coast of Mozambique. The artisanal fishery operates close to shore in less than 5 m depth and is not well understood. The species Acetes erythraeus is believed to form an important part of the total landings, along with juvenile Penaeid shrimps.

Landings of 4000 tons (believed to be an underestimate) for traps, beach seines and cast nets were determined for 1980 in respect to the most productive grounds adjacent to the Sofala Bank (Brinca and Palha de Sousa, 1984). An additional 400 tons is believed to be landed by the artisanal fishermen using beach seines in Maputo Bay (M.I. Sousa, personal communication).

The main fishery involving industrial and semi-industrial trawlers is operated out to about 25 m depth on the Sofala Bank; between Angoche and the delta of the Zambezi River and between Beira and Chiloane (Figure 2). The landings have been about 8000 tons (whole weight) in recent years compared to 10000 to 12000 tons in 1974 (Brinca and Palha de Sousa, 1984).

The second most productive grounds are in Maputo Bay where a fleet of small-scale trawlers has landed about 300 to 400 tons in recent years (M.I. Sousa personal communication).

Penaeus indicus and Metapenaeus monoceros are by far the most abundant species, each contributing some 45 percent to the landings for the Sofala Bank. Of the others, P. monodon, P. semisulcatus and P. japonicus are the more important.

The first substantial assessment of biomass and potential yield is given in Ulltang, Brinca and Silva (1980) for the Sofala Bank fishery. Using catch per unit effort data for part of the industrial fleet, and an estimate of the area of fishing grounds (17000 km2), the mean biomass was estimated as 5000 tons in 1974-75 and 8000 tons in 1976. The conclusions from yield per recruit analyses were that the effort could be increased by a third (from the 1974-75 level), giving a possible 16 percent increase in yield to 14000 tons.

The most recent and somewhat similar assessment, also for the Sofala Bank fishery, is based on survey and commercial vessel data for the years 1980 up to and including 1983 (Ulltang, Brinca and Sousa; 1985). It was concluded that the 1982 level of fishing effort was about optimal, and that increases beyond this level should be avoided. Also included is a proposal that the effort be controlled indirectly through the administration of an annual fishery quota.

The beginning of the year catches per unit effort were shown to reflect annual recruitment, and also to be useful in forecasting the mean catch per unit effort for the year. It was suggested that this could be used to determine the quota, calculated as the product of the latter and the desired annual fishing effort.

In his review of the resources of Mozambique, Saetre (1984) gives a biomass range of 10000 to 14000 tons; and a potential yield range from 8000 to 13000 tons. These values relate to the stocks exploited by the industrial trawlers on the Sofala Bank.

2.2 Deep-water shrimp

The species of principal commercial important are Haliporoides triarthrus and Aristeomorpha foliacea. They are exploited in water depths from 400 to 700 m. During each of 1983 and 1984 the commercial landings were 1572 tons and 1461 tons (whole weight) respectively (C. Silva, personal communication). This involved the use of four trawlers from the German Dem. Rep. and the part-time use of 18 Spanish and three Soviet trawlers.

The most comprehensive assessment for the shrimps is based on surveys from the F/V ERNST HAECKEL. They were conducted during each of August-September 1980, November-December 1980, January-February 1981 and January-February 1982 (Brinca et al., 1983). Another less comprehensive assessment from the results of surveys undertaken during 1976 and 1977 is given in Saetre and De Paula e Silva (1979).

The determination of biomass from the F.V ERNST HAECKEL survey data involved raising the mean catches per hour by the 'area surveyed/area covered per trawl hour'. The efficiency of the trawl net was assumed to be 100 percent. The values obtained from the data for each survey were generally close to 3000 tons and relate to a total area of about 19755 km2 (Table 1 and Figure 3).

Some 60 percent of this biomass was determined to occur in the survey regions 1, and 20 percent in each of region as 2.1 and 2.2. Separate biomass estimates of about 1000 tons were determined for about 5560 km2 of grounds having depths of 450 to 550 m and between 25° 40' S and 26° 20' S (Table 2). The commercial exploitation of the shrimps occurs principally on these grounds.

The shrimp species most prevalent in the catches during the surveys were H. triarthrus (50 to 60%), A. foliacea (mostly 10 to 20 percent) and Aristeus spp. (about 5%); see Table 3.

The potential annual yield of deep-water shrimps is given as 2000 tons in Saetre (1984) along with the recommendation that there should not be any significant increase in the fishing effort.

2.3 Deep-water lobster

The distribution of Palinurus delagoæ is principally in water depths from 200 to 400 m and is scarce North of 21° S (Figure 4). In recent years, exploitation has principally involved a single Japanese vessel equipped with traps attached to long lines. The landings in each of 1983 and 1984 were 203 tons and 141 tons (whole weight) respectively (C. Silva personal communication). The involvement of this vessel ceased during 1985. An unknown quantity was previously taken from South African trawlers which recommenced operations from the end of 1984.

The surveys judged most useful for an assessment of the lobster stocks were conducted during June-August 1976, October-February 1977 and April-June 1977 from the Soviet trawler F/V AELITA (Budnichenko et al., 1977). The vessel was equipped with a special lobster trawl having a 55 m horizontal opening.

Similar although less comprehensive coverages involved the trawler F/V KATTEGAT from the German Dem. Rep. during October-December 1977, and the Norwegian research vessel R.V. Dr FRIDTJOF NANSEN in August-June 1978, (Anonymous, 1978 and Saetre and Paula e Silva, 1979).

Biomass estimates totalling 709 tons (during summer) and 222 tons (during winter) were determined by the latter authors, principally on the results of the F/V AELITA surveys (Table 4). The efficiency of the trawl nets were assumed to be 100% and the catches per hour raised by the 'area surveyed/area covered per trawl hour' to get the biomass.

Budnichenko et al, (1977) assumed the trawl efficiency to be 33.3% and using the F/V AELITA data alone obtained an estimate for the summer biomass of 1850 tons.

The potential annual yield is suggested as 300 tons by Saetre and de Paula e Silva (1979), based on an extrapolation from nearby Natal where it has been claimed that the potential yield is some 25 percent of the biomass. Another estimate of 400 tons for the potential yield is given in Saetre (1984). These values are not much different from the 335 tons caught in traps during 1981, as reported in Brinca and Palha de Sousa (1983).

The species Metanephrops andamanicus has also been determined as occuring at depths between 300 to 500 m and are most abundant between 350 and 450 m (Saetre and de Paula e Silva, 1979). Within these depths the distribution seems patchy and is apparently localised to the Bazaruto area and the Western slope of the Boa Paz Bank.

In recent years small incidental catches of less than 10 tons have been landed from the Japanese vessel engaged in trap fishing for the deep-water lobster (P. delagoæ). They are apparently not readily caught by trawling, due to the habit of burrowing into the bottom substrate. The quantity landed by trawlers is unknown, but presumed to be small.

There have been no attempts to estimate the population biomass. A 'guesstimate' of a few hundred tons for the potential yield is given in Saetre (1984).

2.4 Deep-water crab

The presence of the deep-water crab (Geryon quinquedens) was established by exploratory pot fishing. Up to 72 individals or 30 kg per pot were obtained in Delagoa Bay in depths of about 350 m (Saetre and de Paula e Silva, 1979). Subsequent commercial fishing has established its presence in depths beyond 1000 m.

Until recently the exploitation of crabs has been as a by-catch from the Japanese vessel engaged in trap fishing for the deep-water lobster (Palinurus delagoæ). The catch during 1984 totalled 1095 tons (whole weight), compared to less than 50 tons in the immediately preceeding years (C. Silva personal communication).

As yet there have been no attempts at estimating the population biomass or potential yield.

2.5 Summary

The crustacea resources of Mozambique are reasonably well known as a consequence of exploratory surveys and investigations of the existing commercial fisheries. As indicated in the following tabular summary, the present landings are generally at or near the estimates of potential yield. Management priority is now being directed towards stabilising the landings at about their present levels.

3. RESOURCES AND FISHERIES IN MADAGASCAR

3.1 Shallow-water shrimp

The industrial exploitation of shallow-water shrimp commenced in 1967, with the principal species in the catches being Penaeus indicus (about 80 to 90% of shrimp catch), Metapenaeus monoceros. Penaeus semisulcatus. Penaeus japonicus and Penaeus monodon. The depth distribution is generally up to 45 m, with much of the fishing being between 4 to 15 m.

Since 1971 the annual landings have been mainly between 4000 to 6000 tons (Table 5). The trawling grounds are divided into seven areas (Figure 5) and in respect to each of these an allowable catch has been evaluated in Ralison (1978).

According to Rey (1982) these are administered as follows:

The regulations also provide for a minimum mesh size in the cod-ends, a maximum total headline length for the twin trawls used by each vessel of 77 m, and a prohibition on trawling within two n. miles of the coast. There is also a closed season applying to the industrial fishery from December 15 to February 15.

There have been a number of comprehensive assessments of the shrimp stocks. Ralison (1978) and Marcille (1978) determined maximum sustainable yields of about 6 000 tons (whole weight) from applying production model analyses to the catch and effort data for 1967 through 1977.

Marcille (1978) also applied analytical (Beverton and Holt) type models to show how the mean size (and hence value) of the shrimps in the catches decreased with increasing fishing effort.

Both considered economic factors to be important. Ralison (1978) determined that the maximisation of fishery profits would occur at roughly half the catch which maximises yields. He also estimated that the fishery profits would be generally negative when the yields were maximised.

In respect to the relationship between the artisanal and industrial fisheries, Marcille (1978) concluded that suppression of the fixed trap fishery in Ambaro Bay could lead to an increase in the trawl catch by 8 to 30 percent (depending on the value of the natural mortality coefficients used in the calculations).

3.2 Shallow-water lobster

Lobster are caught by traditional methods principally in the Tolagnaro region. The species comprising the catches are Panulirus versicolor, ornatus, longipes and penicillatus. Since 1979 a system of collecting lobster for export has operated in this region. The landings in recent years are reported as between 60 and 90 tons (whole weight) (FAO Yearbook of Fishery Statistics). There have been no assessments of potential yields. Management includes a closed season from January 1 to April 30.

3.3 Shallow-water crab

Rey (1982) reports that crabs (Scylla serrata) are purchased from the small-scale fishermen for subsequent export. They are presumably also landed from the shrimp trawlers. The landings during 1983 are reported as 477 tons (whole weight) (FAO Yearbook of Fishery Statistics). This is less than in earlier years (nearly 700 tons in each of 1978 and 1979). There has been no assessment of the potential yields of these crabs.

3.4 Summary

The shallow-water shrimps have been comprehensively studied. Sufficient capacity exists within the fleet to fully realise the potential yield. Management of the industrial trawlers includes licence limitation, supplemented by annual quotas for each coastal region. Consideration is also being given to encouraging a reduction in the fishing effort towards reducing the quantities landed so as to improve profitability. The other crustacea resources contribute little to the total landings.

4. RESOURCES AND FISHERIES IN TANZANIA

4.1 Shallow-water shrimp

Exploratory trawling for shallow-water shrimps has been carried out by the East Africa Marine Fisheries Research Organization (EAMFRO) in 1959 using the R/V MANIHINE and R/V CHERMIN; summarised in Venema (1984). During the period June through December 1968 the R/V SAGAMA MARU of the Kanagawa Prefectural Government of Japan also was used for surveys along the Tanzanian coastline (Kanagawa Prefectural Government, 1969). The Bagamoyo and Rufiji regions were identified as having shrimp fishery potential, and commercial trawling commenced from 1969.

The catch and effort data from the commercial vessels from 1969 through 1971 were used to assess the biomass and potential yield for these grounds. This involved estimating mean annual catches per trawling hour and raising these by 'the area occupied by the stock/area covered per hours trawling' (FAO/IOP, 1979, Appendix 7).

The mean catch rates of a TAIKO MARU trawler using twin-rigged 19 m nets and trawling at a speed of 2 knots varied from 22.3 to 26.4 kg/hr (whole weight) on the Bagamoyo grounds and from 25.4 to 31.8 kg/hr on the Rufiji grounds. The area swept by the trawl during an hour was determined as 0.0851 km2. It was assumed that the trawl nets were 100% efficient. The areas of the two fishing grounds were taken as about 950 km2 and 2880 km2 respectively.

On the basis of these data the biomass were determined as 280 tons for Bagamoyo and 940 tons for Rufiji. Assuming that the natural mortality coefficient was M=3.0 (annual), the potential yield for the grounds combined was determined as 1830 tons (whole weight) from the product of half the biomass and the natural mortality coefficient.

The landings from the commercial trawlers reached about 500 tons (whole weight) in 1970, then declined to abut 200 tons when the joint venture company (New Mwananchi Ocean Products) was disbanded (Table 6; and Bwathondi and Mwaya, 1984). A new company (Tanzanian Fisheries Corporation) was subsequently established but as a consequence of operational difficulties the annual landings from trawling has remained at substantially below 200 tons (tail weight); according to Brownell (1982).

Penaeus indicus, Metapenaeus monoceros, P. monodon, P. semisulcatus and P. latisulcatus are identified as the principal species in the landings, particularly the first two in the trawl landings and the third in the landings by the artisanal fishermen.

The annual landings from the artisanal fishery are reported at between about 250 and 500 tons during the years 1965 through 1972 (FAO/IOP, 1979; Appendix 7). Bwathondi and Mwaya (1984) refer to them being at least equal to the landings from the trawlers. The principal methods include stationary traps, cast nets and seines.

4.2 Shallow-water lobster

Bwathondi (1973) has identified Panulirus ornatus, P. longipes, P. versicolor, P. homarus and P. penicillatus as occuring in Tanzanian waters. The first two are the most abundant, contributing more than 80 percent to the landings (Bwathondi, 1980). The most common fishing method involves the use of a hand-held net and an octopus; the latter is used to flush the lobster so they can be scooped up by the net. They are also caught by traps and gillnets set for catching fish and by divers using spearguns.

The reported landings in the years 1966 through 1975 ranged up to 80 tons (whole weight) (Table 6). Hall (1960) reports 13.56 lb (6.15 kg)/man/day as the mean catch rate by divers for six lightly exploited areas around Zanzibar and 9.98 lb (4.53)/man/day for two more heavily exploited areas.

No assessments of the lobster biomass or potential yields have been undertaken.

4.3 Deep-water lobster

Lobsters identified as Linuparus somniosus and Metanephrops andamanicus were regularly caught in depths of 250 to 320 m at the southern end of the Zanzibar Channel during exploratory surveys with the R/V 'Professor Mesyatsev' (Birkett, 1978; VNIRO, 1978 and Burczynski, 1976). The catch rates ranged up to 50 kg/hr (whole weight). These lobsters have not been subject to commercial exploitation.

4.4 Summary

The crustacea resources are moderately well known; more for the shallow-water shrimps than for the other categories. It seems from the underlying summary table that the shallow-water shrimp are being under-utilized. This is despite attempts over more than 15 years to increase production through he use of industrial and semi-industrial trawlers. The potential to increase the shallow-water lobster landings is unknown. The economic viability for exploiting the deep-water lobster is doubtful.

5. RESOURCES AND FISHERIES IN KENYA

5.1 Shallow-water shrimp

Shallow-water shrimps exist principally in depths out to 25 fathom (46 m) in Ungama Bay and off nearby Sabaki and Mambrui. They are also abundant within the estuaries, the largest being at Mombasa and Kilifi. Commercial trawling occurs mainly in Ungama Bay.

During 1984 seven vessels (including one for transporting catches to Mombasa) landed 294 tons (whole weight) of shrimps and 445 tons of fish (information from Fisheries Department in Mombasa). Commercial operators consider these stocks at or close to full exploitation.

Monthly survey cruises in Ungama Bay with the R/V SHAKWE (during Devember 1969 through February 1971) and cruises with the small F/V FAIRTRY (7.6 m) off nearby Sabaki and Mambrui (during June through November 1970 and in January/February 1971) provided shrimp biomass estimates of between 112 to 353 tons (whole weight) (Brusher, 1974; and Table 7).

The most abundant species in the catches were Penaeus indicus (75 to 90%), Metapenaeus monoceros, P. semisulcatus, P. monodon and P. japonicus.

Surveys were also undertaken in the Mombasa and Kilifi estuaries from April through August 1970 from a small outboard-driven boat (5.3 m) equipped with a 3.2 m trawl. Generally the catch rates were less than 2 kg/hour. This was followed by more intensive surveying in the Kilifi estuary during August-September 1970, when 69 hauls with an 8.2 m trawl provided mean catch rates of 3.6 kg/hour (FAO, 1971).

Penaeus semisulcatus was the principal species in the catches from the Mombasa estuary and P. indicus in respect to the Kilifi estuary. The catches consisted mainly of juveniles.

The exploitation of shrimps (and fish) within the estuaries mainly involves the use of stationary traps. A few fishermen also use trawls from small powered and unpowered boats, and beach seines. Apart from the five species previously mentioned, quantities of Acetes erythraeus are caught seasonally, particularly inthe shallow waters of Malindi Bay.

The landings of shrimps by the artisanal and small-scale fishermen from the estuaries and near-shore during 1984 is reported as 111 tons (information from Fisheries Department in Mombasa).

5.2 Deep-water shrimp

Deep water shrimp identified as mainly Heterocarpus woodmasoni were caught during trawl surveys with the F/V UJUZI from 1979 through 1981 (FAO/UNDP, 1982). They were found most abundant at depths of around 200 fathom (366 m) and offshore from Ungama Bay (Figure 6). The total biomass was determined as 1006 tons (whole weight) and occuring on grounds having a trawlable area of 2952 nm2 (10125 km2).

Highest densities were located offshore from Malindi, where a biomass of 144 tons was determined for an area of 45 nm2 (154 km2). The potential yield from this ground was determined as 108 tons.

An attempt at commercial trawling was undertaken from the Kenya owned F/V KUSI (40 m and 1400 HP) during a 14 month period from January 1978. Priority was directed towards landing shrimp and the catch rates obtained ranged from 0.1 kg/hr to 200 kg/hr (Mutagyera, 1984).

There have been no subsequent attempts at the commercial exploitation of the deep-water shrimp. The desk study reported in FAO/UNDP (1982) concluded that offshore trawling (for fish and/or crustacea) would generally not be profitable.

5.3 Shallow-water lobster

The commercial exploitation of lobsters (mainly Panulirus ornatus) occurs along the entire Kenyan coastline (Figure 7). The main fishing grounds are in the North, around the islands of Lamu, Manda, Pate and Kiwayu (Mutagyera, 1978). Much of the landings come from snorkel divers operating to depth of about 4 fathom (7 m) around coral reefs, and to a lesser extent from the use of trammel nets. During 1984 the landings were reported as totalling 127 tons with about 90 percent from around Lamu (from FAO instituted statistics scheme, Coppola personal communication).

The other much less abundant species include P. homarus and P. dasypus (perhaps the same species and mainly found on the North coast around Lamu) and P. versicolar, P. longipes and P. penicillatus which occur principally along the South coast.

A potential yield estimate of 271 tons (whole weight) was determined from the results of experimental fishing with trammel nets conducted by Japanese fishing experts during 1967-68 (Table 8; and FAO 1971). The estimation procedures are not well described, but it appears that the monthly mean catches per 100 m of net were raised by the length of lobster producing coastline. As such the estimates should be used with great caution.

5.4 Deep-water lobster

The lobster Puerulus angulatus along with small quantities of Metanephrops andamanicus were found in water depths beyond 100 fathom (183 m) mainly offshore from Ungama Bay to Malindi during the trawl surveys with the F/V UJUZI (Figure 8). An overall biomass of 1177 tons (whole weight) was determined as occuring on a trawlable area of 2133 nm2 (7316 km2), from raising the mean catches per haul by the 'area surveyed/area covered per trawl haul' (FAO/UNDP 1982). The efficiency of the trawls was assumed to be 100 percent.

The ground considered likely to have commercial potential was located directly offshore from Ungama Bay; where a mean biomass of 330 tons was determined for an area of 66 nm2 (226 km2). The potential yield for this ground, from the product of half the biomass and an assumed natural mortality coefficient, was determined as 140 ton (FAO/UNDP, 1982).

An unsuccessfull attempt at establishing a commercial fishery involved the F/V AEGINA (60 m length and 1,600 HP). Operations ceased after five weeks during 1981. There have been no subsequent attempts at the commercial exploitation of deep-water lobster.

5.5. Summary

The shallow-water shrimps are claimed to be at or near fully exploited; however this requires substantation through a comprehensive investigation of the commercial fishery. Both the deep-water shrimp and lobster resources are known. Attempts at commercial exploitation of these stocks have so far been unsuccessful.

6. RESOURCES AND FISHERIES IN SOMALIA

6.1. Shallow-water shrimp

Panaeid shrimp are found near the mangrove area south of the River Juba to the Kenya borders. Suitable depth and substrate are claimed to exist over an area of 200 km2 off the mangroves. Based on yields from Kenya, a potential yield estimate for shrimp in Somalia of about 400 tons (whole weight) per year was determined by the White Fish Authority (1979)

Shrimp trawling trials in the Juba estuary by Japanese have been interpreted as indicating potential annual catch rates per vessel of 20 tons (whole weight) of shrimp and 250 tons of fish (comment by S. Larsson in FAO internal report).

An estimate of the 1981 landing of shallow-water shrimp is given as 100 tons (whole weight) in Pecker (1982). This relates to the use of an ex-trawler as a base from which shrimp were purchased from local artisanal fishermen. The total landings from all sources is probably greater.

6.2. Deep-water shrimp

The deep-water shrimp (Heterocarpus spp.) are reported as an important component of the by-catch of the industrial trawlers operating in 200 to 400m depth off the northeast coast of Somalia (Johnsen, 1984). No assessments have been undertaken for these species nor have they been separately identified in the landings statistics.

6.3. Shallow-water lobster

Shallow-water lobster occur along the east and north coasts. A report by the White Fish Authority (1979) refers to the potential yield being not greater than 500 tons (whole weight) annually for the whole coastline. Little information is available concerning the present landings which are taken usually by divers (using octopus bait) and sometimes by cast nets. Pecker (1982) refers to the 1981 catch as 80 tons mainly from the southern coast around Kisimaayu. A similar quantity was reported as being landed from the Southern coast during 1983 by Elmer (1985).

Management includes a prohibition on landing berried females, a minimum weight of 460 grammes, and a minimum total length (eye to end of tail) of 23 cm.

6.4. Deep-water lobster

An assessment of the dep-water lobster (Puerulus carinatus and Puerulus sewelli) resulting from a 30 day cruise on the F/V CUSMAAN GEEDI RAAGE concluded the overall biomass for these species as 639 tons and 1,094 tons respectively (Johnsen, 1984). During the cruise the catches ranged from about 100 to 400 kgs (whole weight) per haul of lobster. Another species Metanephrops andamanicus was also present in small amounts.

Separate biomass estimates were determined for each of the fishing grounds (Figure 9 and Table 9). This involved raising the mean catches per haul by the 'area of the ground/area covered per haul'. The efficiency of the trawl nets was assumed to be 100 percent.

The lobster were caught mainly in the depth range of 250 to 400 m. P. carinatus was generally caught South of 10°N and P. sewelli to the North of 8°N.

Commercial exploitation has been underway since 1973, involving both joint-venture arrangements (Somali-Soviet) and the licensing of foreign trawlers. The joint venture (Somalfish) ended in 1977 at which state some 1,150 tons (whole weight) of lobster (and 3,400 tons of fish) were being landed annually (Table 10). Subsequently, Somalia has acquired a small fleet of trawlers. The annual landings from these and licensed Italian vessels is claimed to have been about 10,000 tons of fish and 1,500 tons (whole weight) of lobster in 1981 (Pecker, 1982).

6.5. Summary

The principal fishery is that involving industrial trawlers catching deep-water lobster (and fish). The small amount of assessment work done so far suggests that the stock of lobster is near or at full exploitation. Confirmation through a more comprehensive investigation is urgently required. The other crustacea are little known and lightly fished.

7. RESOURCES AND FISHERIES OF ISLANDS AND BANKS

7.1 Shallow-water shrimp

Recent unpublished investigations in Mauritius have established the presence of Penaeus latisulcatus, P. canaliculatus, P. semisulcatus and P. monodon. Priority is now being given to developing hatchery rearing techniques as a precurser to encouraging the establishment of a commercial culture industry, particularly based on P. monodon. The landings of shallow-water shrimp from the wild stocks is negligible.

7.2 Deep-water shrimp

A resource of deep-water shrimp is known to exist around each of the Seychelles, Mauritius and Reunion. Encouraging results have been obtained with experimental pot fishing off the Seychelles and a similar investigation is to commence shortly off Mauritius. Low level intermittent exploitation has taken place in recent years at Reunion. Potential yields are unknown, and so far the landings have been negligible (a few tonnes) (FAO Yearbook of Fisheries Statistics). The fishing method is with pots.

7.3 Shallow-water lobster

Almost the entire landings of crustacea at Reunion are the lobster (Jasus paulensis) caught in waters up to 50 m depth adjacent to the St. Paul and New Amsterdam Islands. Landings which were about 900 tons (whole weight) in the early 1950s declined to about 500 tons in 1962, then rose to over 1000 tons in 1972 and 1973. Subsequently the landings have been around 500 to 600 tons (Figure 10).

Recent exploitation has involved the use of a single mothership supported by dories undertaking usually one trip per year of about two months duration. The fishing method involves the use of pots.

The most comprehensive assessment of the stocks is that of Duhamel (1980) based mainly on the catch and effort data available from 1950 to 1978. Applying a Schaefer model gave an estimate for the maximum sustainable yield of 600 tons for the inshore component. Insufficient data was available to allow a similar assessment for the smaller offshore part of the stock.

The fishery is presently managed from Reunion and includes limiting exploitation to the single vessel previously mentioned, and applying an annual catch quota which is presently 600 tons (Anonymous, 1980 and Bertrand, 1985). This regime has been operating since 1975.

In Mauritius the species Panulirus longipes and P. pennicillatus are reported to occur on the outer edge of the fringing reefs (FAO/UNDP, 1983). They are caught by the small-scale fishermen using traps. The landings during 1983 is given as 59 tons (whole weight) (FAO Yearbook of Fisheries Statistics). The potential yield is unknown but thought to be not much different from the present landings.

7.4 Summary

Excepting the shallow-water lobster exploited off St Paul and New Amsterdam Islands, the crustacea make only a minor contribution to the total landings from the Islands and Banks. Potential yields are generally unknown, but are likely to be not much greater than the present landings. Greatest interest is presently directed towards exploiting deep-water shrimp stocks, and shallow-water shrimp culture on Mauritius.

8. CONCLUDING COMMENTS

The annual landings of crustacea within the region seems presently to be about 25000 tons (whole weight) with shallow-water shrimp contributing roughly 80 percent of this amount. The most productive countries are Mozambique and Madagascar, with 65 and 22 percent of the total landings respectively.

According to present knowledge the potential yield is abut 30000 tons annually. This is not much greater than the present landings. Also having in mind that it may not be profitable to realise some of this potential, it is most likely than any future increases in the landings will be small and localised.

In respect to the separate categories of crustacea, the landings of shallow-water shrimp totalled nearly 20000 tons (whole weight) in recent years. Most of this comes from Mozambique and Madagascar, 70 and 25 percent respectively.

In both countries the shrimp are considered to be fully exploited and this is reflected in the management regimes. Increases in the fishing effort are being discouraged through a combination of licence limitation and fishery quotas in the case of Mozambique and Madagascar.

The other producing countries are Tanzania, Kenya and Somalia. With the possible exception of Kenya, the stocks of shallow-water shrimp in these countries are under-utilised. The additional yield from full exploitation in the future is estimated at about 1000-1500 tons (not including production from aquaculture).

Although stocks of deep-water shrimp are likely to occur throughout the region, almost all the present catch of about 1500 t (whole weight) is taken by trawlers operated off Mozambique. Shrimp are also being taken incidentally with the deep-water lobster off Somalia and with pots adjacent to Reunion.

Only in Mozambique are the deep-water shrimp nearing full exploitation. Views are being expressed that the fishing effort directed towards these stocks should not be substantially increased. In the other countries the management aim is to increase the landings subject to economic viability.

The only substantial fishery for shallow-water lobster occurs adjacent to St. Paul and New Amsterdam Islands. This is managed with the annual landings of about 600 t (whole weight) being fixed by quota and the fishing rights to one enterprise.

In all the other countries the lobster are taken by artisanal fishermen. The quantities landed are generally small and limited by the ability of the fishermen to market their catches. Whenever a suitable marketing infrastructure is established adjacent to productive fishing grounds the fishermen have generally responded with increased landings.

Deep-water lobster are caught off Somalia (1500 t whole weight) and Mozambique; (150 t whole weight) and in both places the stocks ares considered to be at or near fully exploited. A small stock is known to exist off Kenya, although apparently in insufficient quantities to justify exploitation. Lobster probably occur elsewhere within the region, however, this will need to be substantiated by surveys.

Due to their lower value the crab resources have received relatively little attention. In the shallow waters they are taken by the artisanal fishermen for local consumption. Small quantities are processed for distant markets, whenever a suitable marketing infrastructure exists.

The substantial landing of deep-water crab in Mozambique during 1984 (1095 tons whole weight) is a recent development based on the use of pots from a single vessel. As yet it is unknown whether catches of this magnitude can be sustained over a number of years.