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The study of fluctuation of large pelagic stock (yellowfin tuna, skipjack tuna, longtail tuna, Narrow-barred Spanish mackerel ) in order to optimum exploitation in the Persian Gulf & Oman sea This study was carried out from 2005-07 in order to acquire some biological characteristics and population dynamic parameters for stock management and responsible fisheries. Thunnus albacares (yellowfin tuna), katsuwonus pelamis (skipjack tuna), Thunnus tonggol (longtail tuna) and scomberomorus commerson (Narrow- barred Spanish mackerel) were sampled. In total, length frequency of 9345 specimens of yellowfin tuna were analyzed. Size range was 37-172 cm. Teleost fishes were the most dominant prey species observed in this study (42%), Occurrence of Potunus Pelagicus was found to be the second (28%).Sthenoteuthis oualaniensis (22%), Natosquilla (5%) and octopus (3%) also were identified in the gut content of the yellowfin tuna. Length of maturity (50%) of yellow fin tuna was estimated 77.2 cm and spawning season was started from May. 8443 specimens of skipjack with size range of 32-90 cm were sampled. 48% of food items were teleost fishes. Squid and shrimp were also identified. Spawning season was begun from June. Growth parameters & fishing mortalities of yellow fin tuna and skipjack tuna were also estimated. Size range if longtail tuna was from 26-125cm Length infinity was estimated 132.3 cm with growth parameter of 0.35 per year. In total 10451 specimens of narrow- barred Spanish mackerel were sampled. Size range was from 20-164 cm. Teleost fishes were the most dominant prey species observed in the study (91.3%). Crustaceans (0.6%) and Indian squid (0.2%) also were identified in the specimens. Length maturity (50%) was estimated 83.6cm.

Collecting of biometric parameters and catch and effort data were made for yellowfin and skipjack tunas from artisanal gillnet and industrial purse seine fisheries during the years 2002-2004 in Oman Sea along Sistan and Balouchestan coastal waters. The previous available data was used for the purpose of better monitoring the resources. The frequency of maturity stages and GSI values obtained from yellowfin showed a spawning period from Febraury to May, peaking in April-May. For skipjack, the data indicated a long spawning period which beganed in December with peaking in April-May. LM50% was obtained as 83.1 and 62.4 for yellowfin and skipjack tunas respectively. Sex ratio by size group showed a predominance of males with larger fish. Analysis of stomach contents showed a significant proportion for the both species. The composion of food contents by occurrence method revealed that fish were the most dominant food items by year for the specise. Presence of squilla, crabs, shrimps (Larval stage), belonging to Peneaidea family, in large quantities were the obivious food items so that they had not been reported by previous studies. Blooming of squilla, Natosquilla investingatoris, in the western Indian Ocean provided a situaition to be observed in large occurrence in yellowfin and skipjack stomach contents. The ratio was more in yellowfin stomachs when compared to skipjack ones which accounted for 38%, 19% and 35% of the total stomachs studied by the study year. The shrimps prey were only observed in skipjack gut contents (with exception of one case in yellowfin stomach) which were the second major component in 2002 and 2003( 24% and 17% respectively). Comparsion of mean length showed a sharp decrease from 1992 to 2004 for the species. Regarding yellowfin the mean length from 93.2 cm FL in 1992 reached to 83.2 cm FL in 2004 and from 64.95 to 58.51 cm FL for skipjack. In spite of decreasing mean length for yellowfin, the value increased in 2004 in comparsin to 2003 which was in agreement with Indian Ocean data. Comparative analysis of length frequency with LM50% indicated that immature fish were the major part of the catch. There are available information on population dynamic parameters. A comparative analysis of CPUE,s (kg/panel.day) from artisanal gillnet fishery for yellowfin and skipjack tunas revealed a decreased value by fishing craft class in 2005 when compared to 1998 data, but increased in 2003. Incraesed trend of the species catchs by fishing craft class was due to incraesed fishing effort. Analysis of the statistical catch and effort data for the study years, irrespective of fishing craft class, showed that total landings of the species have increased 4.4 fold in spite of attaining CPUE to 7% in decrease which was a consequence of increased fishing effort up to 4.7 fold. The CPUE,s (tons / possitive set) from industrial purse seine fishery increased in 2003 and 2004( 39% and 10% respectively),but declined up to 54% in 2005. The trend is in agreement with purse seine fishery data from Indian Ocean where the increased values were attributed by larger size of yellowfin. The purse-seine fishing ground data revealed that the major sets were made in Persian Gulf, wherase a shift towards Oman Sea in eastern part of Sistan and Balouchestan coastal waters is recommanded to be a suitable fishing area for the first half of year and towards offshore waters in Indian Ocean for the second half of year. For attaining a sustainable fishery system, it is recommanded to regulate the gillnet mesh size and introduce longline fishery in the area along with stoping any further increased fishing effort in artisanal gillnet fishery. Iranian Fisheries Science Research Institute Published

In order to come up with the responsible fishing pattern, there was a need to identify some of the biological characteristics and population dynamic parameters of yellowfin tuna, skipjack and longtail tuna in the Persian Gulf and Oman Sea. Occurrence of empty stomach was high in all the specimens obtained from the gill net fisheries. Purple back flying squid was the most dominant prey species observed in the yellowfin tuna study (61% in males and 57% in females). The length of maturity (Lm50%) for yellowfin tuna was estimated 76 cm, 62.5 cm skipjack and 62.5 cm longtail tuna. Length range of skipjack was from 31-100 cm and bony fishes were the most dominant prey species observed in the skipjack. The monthly gonad somatic index was driven higher values after June which could be indicated as spawning period. The catch per unit of effort of three purse seiners (Azadegan 1, 2, 3) was compared in 1998- 2000. The species composition was 47% yellowfin tuna, 51% long tail tuna and 2% skipjack.

The method is used to catching tuna fish in the coastal sistan and balouchestan is gillnet.The amount of tuna catch fish has changed in 75 and it has increased in comparison with 3years ago . Total catch of tuna fish have changed from 18150 ( t ) in 71 to 25932 (t) in 75 and always the most percentage of catch has related to yellow fin tuna. skipjak tuna with 7 .9 percentage and long tail tuna with 5.7 percentage in second and third grad of catch . most of the tuna fishes have cathed in the east landings.only Auxis thazard has cached inthe west landings. studing yellow fin tuna nourishing show which squied is the most abundant itemes in it s stomach the stomach compositions skipjack tuna has had variety and number less than yellow fin tuna so crab and fish are found in it s stomach. The length frequncy of yellowfin tuna compared with age class which presented by( Siva subra maniam., 1971) according to this Comparision more percentage of yellow fin tuna catch is below one years old and % 50 maturation for this species is in 3 age . Comparision the length frequency of longtail tuna and skipjack tuna with age class show which most of them are 4 age and biger than it . To revise mesh size gillnet and area of traditional catch for these species has emphasized. Iranian Fisheries Science Research Institute Published

This study examined yellowfin tuna catch data of a series of gill-net sets including 5 ¾ (Control), 6 ¾ , 7 ¾, 8 ½ and 9 1 /3 in both surface and mid-water catch method. Of the total research Cruises (22 days) done on March and April 2002, 19 and 3 net sets made by surface and mid- water (6 meter depth) method, respectively. According to the obtained data from surface One, 8 ½ mesh size constituted the highest proportion of total fish caught. A comparison of total weight caught by mesh size showed varying differences when tested with a one-way ANOVA.As well as, the results obtained by Duncan test indicated four distinct groups that the fish weight entangled from 8 ½ mesh size accounted for the major one. Analysis of data from 5 ¾ mesh size indicated that 30% of the catch fell out of the net during hauling. There was no significant difference between mean fork length among mesh size when tested with a one- way ANOVA. The results obtained from fish caught in three parts of net (top, middle, down) indicated that fish caught from the middle part were the highest proportion of total fish entangled. Similar to the surface catch method, 8 ½ mesh size caught highest proportion and weight to the total fish entangled in mid-water one. It needs to do further study to obtain the best mesh size for catching yellowfin tuna in surface catch method and depth of water for netting in mid-water catch method as well as to compare both methods. Iranian Fisheries Science Research Institute Published

The coast of the Hormozgan province has been divided into five strata. From west to east, the five geographical strata are, Lengeh, Qeshm Island, Bandar Abbas, Kolahi and Jask. The statistical procedure used in the study takes into consideration four boat type categories that are distinguished on the basis of carrying capacity, 1 ton boats, 1 to 20 tons, 20 to 50 tons more than 50 tons and four gear types; gillnet, trap, hooks, beach seine, with tunas being caught mainly by gillnetters and in minor proportion with lines. No data are available for the Bandar Abbas and Qeshm Island geographical strata. Longtail tuna is dominate species in the tuna catches of the Hormozgan province, followed by the two species of seerfish (Scomberomorus) and by yellowfin tuna. The three main strata; Lengeh, Kolahi, Jask, for which completes sets of catch data is available call be taken as being representative of the three main fishing zones of the Hormozgan province. A thazard is caught in all the three strata both inside and outside the Persian Gulf. Yellow tuna (T. albacares) is caught almost exclusively in the outer stratum of Jask between September and December. Longtail tuna (T. tonggol) shows marked differences in Seasonal trends between the open water stratum of Jask and the western stratum of length. Skipjack tuna (K. pelamis) is only caught in the area between September and March, showing approximately the same trend as yellow tuna. Kawakawa (E. affinis) is mainly caught inside the Persian Gulf. In Jask area the best catches of this species are obtained from June to August. The sudden switch between catches of longtail and Yellowfin in the outer stratum of Jask in August – October, could he partly due to a change in fishing strategy. The increase in tuna catches inside the Persian Gulf during the colder months could be the result or active migration by most of the neritic species toward this area in winter.