English abstract
Due to the paucity of fish larvae research which was conducted in South-west part of Oman Sea (Sohar and Muscat) and fragmentary studies conducted by Marine science and fisheries centre, an extensive regular sampling program has been conducted in Omani coastal waters during three years (in 2013-2015), over six regions located in the Arabian Gulf, Sea of Oman and the western Arabian Sea (namely Khasab, Sohar, Muscat, Ashkarah, Doqum and Salalah regions). Monthly samples were collected from the sea surface (1m). The statistical links between physical, chemical and biological parameters were investigated by the Canonical Correspondence Analysis and Principle Component Analysis.
A total of 4871 fish larvae specimens including 70 families and 89 genera were collected from six different coastal stations and identified in terms of their morphology and morphometric characteristics. The bulk of ichthyoplankton catches over regions were contributed by larvae from 10 families- Mugilidae, Clupeidae, Pomacentridae, Mullidae, Gerreidae, Carangidae, Terpontidae, Sparidae, Sphyraenidae, and Blenniidae. In combined samples from six regions over three years, the highest abundance of fish larvae was observed during the North-east Monsoon (547 ind/100 m®) followed by the Fall Inter monsoon season (428 ind/100 m'). The fish larvae diversity showed a moderate variation over sampling regions. The highest Shannon Winner diversity index (H) estimated for the Ashkarah and Muscat sampling regions was in a region of 1.31while, the lowest values (0.84) were observed in Khasab.
Canonical Correspondence Analysis of the major fish larvae family abundance, temperature, chlorophyll a biomass and zooplankton biomass showed that temperature was the most influential variable. In terms of statistical analysis, the Oman Sea and Arabian Gulf regions sab and Sohar) were different from the other ones. In turn, on the Arabian Sea side, the Doqum region was different from Salalah and Ashkarah. Also, the fish larvae abundance during Spring Inter-monsoon and the South-west Monsoon was statistically different from the Fall Inter-monsoon and the North-east Monsoon seasons.
In terms of the this study, it has shown that the fish larvae abundance and their species composition both could serve as sensible indicators for predicting catches of mature specimens. In particular, it was shown that fish larvae of Clupeidae family (which was the most abundant in Muscat region) were consistent with artisanal sardine landings in the same region. Consequently, data on fish larvae abundance could be treated as sensible indicator for predicting seasonal catch of sardine in Muscat region.
As far as practical recommendations are concerned, current results could serve as the basis for a subsequent regular fish larvae surveys along the Omani coast. Data on fish larvae abundance could be treated as sensible indicator for predicting seasonal catches of sardines in the Muscat region. The approach could be applied for a broad range of regions along the coast and commercially important fish species. Based on the results of this study, sea temperature should be nominated as an essential parameter in ecologically oriented fish larval studies. This will contribute to a better understanding of the seasonality and distribution of fish larvae in Omani waters.
As a recommendation of this study, an extensive regular sampling program should be worked out and enforced, in the nearest future. This program would provide further insights in our understanding of the seasonality of fish larvae dynamics in Omani waters. Based on the results of the pilot study of fish larvae with regard to Noctiluca blooms, more investigation is needed to understand the impact of these blooms on the fish larvae.
