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Seasonal and Interannual Variations of Yellowfin Tuna Catches along the Omani Shelf

Saud Al Jufaili and Sergey A. Piontkovski

Sultan Qaboos University, P.O.Box 34, Muscat 123, Sultanate of Oman E-mails: This email address is being protected from spambots. You need JavaScript enabled to view it.; This email address is being protected from spambots. You need JavaScript enabled to view it.

Yellowfin tuna contributed markedly to Omani catches of the past 30 years. However, artisanal catches vary over seasons and years, and induce economic losses. With this regard, the analysis of seasonal and interannual fluctuations of Yellowfin tuna catches was carried out, based on monthly and annual time series of 20 environmental variables. Data were subjected to the Principle Component Analysis and the Multiple Ridge Regression Analysis. It was shown that catches along the Omani shelf, in 1988-2018, were subjected to a human-induced and environmental forcing subjected to seasonal and interannual variations. Seasonal variations demonstrated a bimodal trend, with a major peak in April and a minor one in October, observed during spring and fall inter-monsoon seasons. Apart from the seasonality of fishing efforts associated with rough weather during the Southwest Monsoon, seasonal variations of catches were statistically related to 9 environmental variables (namely, the wind speed, zonal gradient of sea surface temperature, geostrophic current velocity, dissolved oxygen concentration and sardine catches (an indicator of food for tuna), the amount of mesoscale eddies, mixed layer depth, photosynthetically available radiation, and outgoing longwave radiation ), that explained 71% of observed seasonal variations of the tuna catch. Due to the four-fold increase in fishing efforts, artisanal catches of Yellowfin tuna along the Omani shelf exhibited a two-fold increase over the past three decades. However, the catch per unit of effort did not show statistically confirmed increase for this time range. Interannual variations of catches exhibited an irregular pattern, with several peaks (in 1995, 2004 and 2018, with the later one still not resembled entirely). Statistical analysis implied 8 environmental variables, which modulated these variations: the wind

Seasonal Variations of Plankton Communities in Coastal Waters of Oman

K.A. Al-Hashmi1, S.A.Piontkovski1*, G. Bruss1, W.Hamza2, M.Al-Junaibi2, Yu.Bryantseva3 and E.Popova4

1Sultan Qaboos University, Sultanate of Oman.

2United Arab Emirates University, United Arab Emirates.

3M.G. Kholodny Institute of Botany, Ukraine.,/p>

4Institute of Biology of the Southern Seas, Russia.

The monthly plankton sampling carried out in 2018-2019 has revealed over 190 phytoplankton species inhabiting coastal waters of the Sea of Oman. Diatoms were represented by 130 species, the highest diversity and total abundance of which were associated with the Northeast and Southwest Monsoon periods. Strong correlation was found between the abundance of diatoms, silicate and nitrogen concentrations. The dominance of diatoms was not consistent with previous reports which indicated the dominance of dinoflagellates in the coastal waters of the Sea Oman, in 2006-2017. An increase of diatoms stemmed from strong wind-induced mixing and high concentrations of silicates which level was about four fold less during the previous decade. Only few phytoplankton species formed huge algal blooms in studied regions. The dinoflagellate Noctiluca scintillans leads the list. The bloom development of this species lagged peaks of all the others. Copepods were the most abundant in the zooplankton fraction of plankton community. The abundance of 79 copepod species varied gradually over seasons. The main seasonal difference dealt with the number of carnivores, from genera Labidocera, Sapphirina, Corycaeus, and some others.

A comparison of seasonal variability of Arabian Gulf and the Sea of Oman pelagic ecosystems

Sergey A. Piontkovski,1Waleed M. Hamza,2 Nader M. Al-Abri,3 Saud S.Z. Al-Busaidi,3 and Khalid A. Al-Hashmi1

1Sultan Qaboos University, CAMS, P.O.34, Al-Khod, Sultanate of Oman;

2United Arab Emirates University, P.O. 15551, Al-Ain, United Arab Emirates;

3Marine Fisheries Research Center, Ministry of Agriculture and Fisheries, Bandar Al-Rowdha, Muscat 123,Sultanate of Oman

This overview compares algal blooms and pelagic fisheries of the Arabian Gulf with the Sea of Oman.  The data consist of remotely sensed characteristics, directly sampled and modeled. Elucidated seasonal trends were based on 15-year seasonal means, as well as weekly time series of physical parameters. The environmental characteristics (namely photosynthetically available radiation, atmospheric pressure, temperature, wind, aerosol optical thickness, surface currents, surface temperature, salinity, concentration of dissolved oxygen, nitrates, phosphates, chlorophyll-a, net primary production, phytoplankton, zooplankton biomass, fish larvae abundance, small and large pelagic fish catches) were compared between regions. In Sea of Oman, high concentrations of chlorophyll-a were associated with relatively high concentrations of nitrates and phosphates, as well as kinetic energy of surface currents which exceeded that in Arabian Gulf. The dinoflagellate Noctiluca scintillans is one dominat alga in the Sea of Oman, whereas diatom species are more common in the Arabian Gulf blooms. In general, the phytoplankton and zooplankton species diversity during winter was higher than in summer periods. Catches of small pelagic fish (in particular sardines) in the Sea of Oman exceeded that in the Arabian Gulf. This might be associated, in part, with differences in trophic levels interactions. The turnover rate of the net primary production through zooplankton in Sea of Oman was found to be much higher than in Arabian Gulf waters. 

algal blooms, chlorophyll-a, sardines

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