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Age, growth, Reproductive biology and spawning season of Epinphelus Coioidas in U.A.E. Prepared By: Introduction Arabian Gulf is a semi enclosed body of water, connected to the Indian Ocean through a 65 km. Widestrait of Hormuz on the southern side. Many small and medium fresh water rivers flow in to the northern and eastern Arabian Gulf (Euphereties, Tigris, Karun), where as no such fresh water in flex in the western or southern side. Overall, UAE waters contain a large number of habitats for fish, and a rich and varied fish fauna occurs. Fish species generally found in the Arabian Gulf and elsewhere have been described by White and Barwani (1971) Randal etal (1978) Kuronuma and Abe (1972). The type of sea bottom found in the Arabian Gulf varies, with northern parts being largely silt and mud. The bottom along western side of the Gulf have sandy, coral and rocky bottoms. Eastern side is again more muddy and shallow (Figure 1) Emery (1956) F.A.O. (1981) Last two or three decades have witnessed a tremendous growth in the fisheries sector in the U.A.E. The fish landing has increased from a modest quantity of 64 thousand ton in 1976 to 117 thousand ton in 1999. With this increase in the fishing industry it has become all the more important to study and monitor the state of fish stock. Maximizing marine food supply and resources, use on a continues basis while minimizing biological risk without having a high level of knowledge about the fish, fishing and marine environment is impossible. Epinephelus species is the second largest fish species landed in the emirates. The average price varied from 15-20 Dirhams per kilogram. Because of its importance in the landings and is considered as one of the prime fish species by the local community it was decided to study Epinephelus Coioides in detail. The catch, catch rate, biology, length composition, spawning season, age and growth are some of the parameters studied for this species. The important and commonly occurring fish species in the Serranidac family in U.A.E. waters include the following in the order of their abundance in the landing.
Of all these species E. coioides is the most abandant species in Abu Dhabi and Sharjah. E. diacanthus, E. lalifaceatus are available in Dibba (Fujairah) where as E. chlorostigma, E. bleekari, E. jayakari are abundent in the fish landings of Sharjah. E. arealatus, C. miniatus are landed all over the emirates in small quantities. Material and methods The species composition, catch and effort data were collected from four emirates Abu Dhabi, Sharjah, Ras Al Khaimah, Dibba (Fujerah) and Dibba Al Hosn (Sharjah). The landing statistics and length composition of the fish landed were studied from all these sampling locations, however. The biological samples were purchased from Sharjah fish market, only as the fish samples are available all through out the year and because of convenience. As the biological sampling is confined to Sharjah we will discuss about the catch rate, age, growth of length composition of E. coioides from this sampling location. The fish species caught, quantity and fishing effort expended to catch these fish were obtained by monthly interviews of fishing boat captain or the senior fishermen of the boat from four emirates. While interviewing the captain of the fishing boat another group of researches will measure the length composition of the important fish species studied. On an average 100 - 600 fishes were measured monthly from each fish species studied at various emirates according to the availability. 10-15 fish are also purchased and brought to the laboratory at Umm Al Quwain for detailed study on each visit to the fish market. After each visit the average catch per trap pulled were calculated for each species and the total catch is estimated according to the average number fishing trips made by the boats separately for launch and speed boats. Three types of steel meshed fish traps locally known as Gargoor are used to catch most of the demersal fish in U.A.E. and the gulf. These traps are hemispherical in shape with a mouth opening to enter the fish, but it cannot come out once it entered the trap. Fish bait are used to attract the fish and is tied to the flat bottom of the fish trap either by a bag made up of a nylon webbing or by means of a steel wire, where the fish are hooked and tied. Many varieties of baits are used according to the type of fish species targeted. Bread (kubbose), algae, fresh and salted sardine or even fish cutting waste are used as bait. Normally medium and large Gargoor are used to catch big demersal fish species. The fish length were measured to the nearest centimeter under and weight in gram. The gonadal maturity stages were determined according to the eight scale described in Holden and Rait (1974). Available data on sex and maturity stages of hamoor were used to estimate the duration of spawning season, which was defined as the period during which stage 5 and 6 (ripe and running) gonads occurred. The length-weight relationship were determined using the equation. Total weight = abL , where L is the total length, a and b are regression coefficient. The mean catch rate of hamoor were determined for Sharjah as kilogram per trap pulled for the main fishery ie for launch. The length composition of the fish landed were also observed while making catch and effort interviews. 100-600 fish were measured each month at each sampling locations. 10-30 or more fish samples were purchased from the fish market and brought to the laboratory for detailed study, total length (TL), standard length (SL), for length (FL), total body weight, body girth, sex, gonadal maturity stage, gonad weight, liver weight etc. are observed. In addition to that sagettal otolith (ear stone) and fish scales were also collected for age studies. Assessment of tropical fish stocks is a major problem because the ageing of tropical fish is usually difficult or impossible. Various methods have beenfried to over come these difficulties, Brothers etal (1978) Williams and Bedford (1974) Campana and Neilson (1985) Bed ford (1982) Bagnal (1974) Pannella (1974) Samuel etal (1987) Samuel and Mathew have successfully aged hamoor using otolith in Kuwait. The found that the fish scales, particularly older and bigger fish the marks are difficult to read. The sagettac of hamoor were large and usually their in younger fish and rather thick and heavy in older fish. The shape of Otolith differs in various fish species in hamoor sagettac are elongated avoid about twice as long as width, pointed at the tail end. The nucleus is quite small and opaque zones are generally nather diffused and hyaline zone are wider. In some younger fish, the whole otolith immersed in water against a black background gives good result. Thick otolith are split along the nucleus and slightly burned with the help of a spirit lamp, so as to get the broken edge of the otolith slightly chard. After smearing with Udar wood oil / Almond oil it is viewed in transmitted light. The amount of burning varies according to the type and thickness of otolith. The opaque and hyaline marks could be seen clearly. In transmitted light, the sagettac appeared to be composed of more hyaline than opaque material and light zones pre dominated. Samuel etal (1987) have proved that the marks on hamoor otolith up to the age 10 are of yearly marks. Sampling of old fish on a regular basic was difficult hence it was not validated but the formation of marks scenes to be regular and even. The mean length at age were used to calculate the growth in hamoor. Even though fish are sampled from January 2000, otolith were collected from end April and May onwards. All the samples which are aged were used to calculate the mean length at age. How ever no effort is made to validate the ring formation in hamoor otolith as there is not sufficient number of age group in each month. Result and discussions The mean monthly catch rate of hamoor E.coioides from Sharjah is show in table below:
The monthly mean catch rate ranged between 0.537 kg/trap pulled in December to 1.56 kg/trap pulled in June. The low catch rate observed may be due to the cooler water temperature when fish migrate to warm water in the coastal area, while the high catch rate observed in June could also be due to spawning aggregation. A catch rate of 5-25 kg/hour of fishing was reported in the U.A.E. waters by Sivasubramaniam (1981). However the fishing year used during the above survey was that the engel high opening trawl net. A comparison of catch rate obtained by FAO (1981) and the present study could not be possible to infer weather there is any change in the abundance of this species or change in the catch rate. The result presented above were according to the fish trap, which is most commonly used fishing gear in U.A.E. and the Gulf for catching hamoor. The length, weight, relationship obtained for the fish sampled was given by Total weight = 0.01441 TL 3.02413 with the regression co efficient value of 0.0993. the value obtained by Sivasubramaniam (1981) for area 2 was almost similar, however the sample does not include smaller and bigger fishes than in the present study. As it is required to study all life cycle stages of fish including small and big all through out the year so as to avoid bias in the estimation of parameter values. Figure 2 shows the gonadosomatic index obtained for hamoor. This shows the peak spawning occurred during March-April. How ever the spawning season extends from March to May, when there is a steep fall in the GSI values and followed by a flat curve during which the gonads are inactive. The number mature male sampled during the whole study period was 7 and that of female was 236 with 10 immature fish. This shows that for each mature male fish 34 female fish is present. FAO also found 1:7.5 ratio between male and female. This may be due to sampling the population during the spawning season. The size and age of maturity studied else where in the Gulf shows that hamoor sexually mature at a length of 61 cm. and probably when 5-6 years old. With 95% confidence limit of the mean size at maturity were 57.4 - 65.0 cm. The minimum observed size at maturity were 44 cm. Lee etal (1990). Table 2 - Age distribution of the sampled fish
The above table shows that about 73% of the fish sampled were 4 years or less old, while the rest 27% were 5 years and above old. the age distribution of the fish population show either the number of fish sampled may not be sufficient to get a clear picture of the age structure of the population or there could be a migration of bigger and older fish to else where in the Gulf or to the Gulf of Oman, where bigger and larger fish is occurred in the landings. Figure 3 shows the growth curve obtained for hamoor from the mean length at age. The growth curve of hamoor was obtained by ploting the age against the mean total length of the fish. The standard deviation of the mean were also shown in Figure 3. The standard deviation of mean plotted as could be seen is large in older fish than in smaller fish. During the early stages of life cycle fish growth in hamoor is fast and a steady growth could be observed. Probably up to the age of 6 years old and there after the growth slow & down. Table-3 : Mean length at age of hamoor observed in U.A.E. & Kuwait
Table 3 shows the mean length at age of hamoor sampled from both UAE and Kuwait. One year old hamoor is 26 cm. long and six year old was 72.91 cm. in UAE population. Where as it was 24.96 cm. and 62.82 cm. long for a similar aged fish in Kuwait. The growth rate obtained in UAE is slightly higher than in Kuwait. The mean length observed up to five years old were almost same in both the countries. Probably the length differences observed in the older fishes may be due to the environmental difference between the north and south of the Gulf waters. Earlier studies by Rifat M. Ali and Thomas Cherian, on the hydrographical condition of the coastal waters of Abu Dhabi, Umm Al Quwain and Ras Al Khaimah were studied in 1982 and showed that the surface sea water temperature ranged between 19.6º C and 33.8º C in Abu Dhabi, while it was almost same at Umm Al Quwain, but it was slightly different in Ras Al Khaimah. Figure 4a, 4b, 4c and 4d show the percentage frequency number of hamoor measured at the Sharjah fish market during May-December 2000. The smallest fish measured was 20 cm. total length and the biggest fish was 110 cm. The size measured compares very well with the fish measurement observed in Kuwait. However the biggest fish measured in Kuwait was 130 cm, which is rather very occasional to occur in the landings Mathews and Samuel (1987). The data presented here shows that smaller fishes less than 40 cm. are landed in good quantities. The percentage frequency number of small fish (<40 cm) measured varied from 12.4 to 34% during the study period. Sivasubramaniam (1981) observed during the survey in area 2, which is UAE and adjacent waters hamoor length ranged between 31-98 cm. The result presented here may be a true representative of the hamoor population in UAE waters. More years data has to be obtained from all emirates to study the variation in length of fish landed. Conclusion Fairly large quantities of small sized hamoor is caught and landed in the market. About 12.4 - 34% of the fish measured were less than 40 cm. in length. The spawning season of hamoor occurred during the month of March - May with peak spawning in April and May. The minimum observed size at maturity was 44 cm., this shows that a substantial quantity of immature fish is landed. Growth in hamoor is faster during the early years probably up to six years and then the growth slows down. Maximum age obtained was a 22 years old hamoor 73% of the fish sampled were four years or less old, while the rest were above five years old. there is an urgent need to ban fishing of under sized hamoor to protect the stock and allow the fish to grow above the minimum size at maturity so as to improve the spawning stock of hamoor. References:
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