Publication Date:
2021-05-19
Description:
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.
Description:
Iranian Fisheries Science Research Institute
Description:
Published
Keywords:
Monitoring
;
Tuna
;
Yellowfin tuna
;
Skipjsck tuna
;
Coastal waters
Repository Name:
AquaDocs
Type:
Report
,
Refereed
Format:
132pp.
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