Biodiversity of commercially important finfish species caught by mid-water and bottom trawls from two different coasts of Arabian Sea: Threats and conservation strategies

This study was conducted to estimate the diversity and the occurrence of commercially important finfish species collected by twenty fish sampling site of Sindh and Baluchistan coasts of the Arabian Sea in Pakistan from January to December 2019. Additionally, physicochemical characteristics of seawater were analyzed from these selected sites and found to be within suitable ranges required for fish growth and survive. A total of 81287 fish individuals were collected and identified as 49 species belonging to 26 families in our study. The most diversified family was Sparidae (13 species) followed by Carangidae and Lutjanidae (4 species), Mullidae, Serranidae, Ariidae (3 species), and Sciaenidae (2 species). The remaining 20 families were represented by only one species. The values of Shannon diversity index calculated for the four selected habitats revealed that high fish diversity was reported at Sonmiani Coast (H'=1.81), while less at Ormara Coast (H'=0.23). Likewise, Evenness index (E) was high at Sonmiani Coast (E=0.50) and less fish diversity was reported at Ormara Coast (E=0.06). Reducing risks to threatened marine species in coastal habitats also requires conservation actions at multiple scales. Thus, it was concluded that our study could be valuable in providing the more information’s regarding to the diversity of finfish species and their occurrence along the Pakistan Coast. Further, to better understand the effects, regular monitoring and conservation measures should be taken to mitigate the influence of anthropogenic activities and protect finfish diversity from further decline

On forecasting cyclone movement using TOVS data

The tracks of three cyclonic storms over Bay of Bengal and one over Arabian Sea during 1998 have been analysed using the TOVS data received at Chennai from NOAA satellites. Midtropospheric warmness between 700 and 400 hPa levels which protrudes about 300 to 700 km ahead of the storm acts as precursor to foreshadow the storm movement and predict the landfall about 6 to 24 hrs in advance. This technique has successfully predicted even the peculiar southward movement of Bay storm (28 November to 7 December, 1996).

Predictive relationships between Indian Ocean sea surface temperatures and Indian summer monsoon rainfall

Monthly sea surface temperature (SST) data of 49 years (1950-98) have been analysed to examine the relationship of SST anomalies in the Indian Ocean with Indian summer monsoon rainfall (ISMR) and to derive useful predictors for long-range forecasts of ISMR. There is significant positive relationship between ISMR and SST anomalies over the Arabian Sea during November to January and also in May. SST anomalies over southeast Indian Ocean during February to March and over North Pacific during May are also positively correlated with ISMR. The composite analysis revealed that in Non-ENSO drought years (1966, 1968, 1974 and 1979) negative SST anomalies are observed over south Indian Ocean from February which slowly spread towards equator during the subsequent months. These negative SST anomalies which persist during the monsoon season may be playing an important role in modulating ISMR especially in non-ENSO years. We have derived two indices, ARBSST (SST anomalies in Arabian Sea averaged over 15o - 25o N, 50o -70o E and November-December-January) and SIOSST (SST anomalies over south Indian Ocean averaged over 15o -30o S, 70o -110o E and February and March) as useful predictors for the long-range forecasts of ISMR. The correlation coefficient (for the period 1950-98) of ARBSST and SIOSST with ISMR is 0.45 and 0.46 respectively which is statistically significant at 99.9 % level. SIOSST index has shown consistently stable relationship with ISMR. However the ARBSST index showed significant correlation with ISMR only after 1976.

A study of evening convective clouds over Kochi and neighbourhood

Radar echoes of 0900 and 1100 UTC over Kochi and 200 km around were studied from 1996 to 1999 along with SST of southeast Arabian Sea and Kochi. The following results are obtained : Monsoon convective cloud tops were lower than Pre-monsoon and Post-monsoon convective cloud tops. (ii) In the mean, monsoon cloud tops gradually increased from 1996 to 1998 and then decreased. (iii) Very large convective activity existed during August 1997 to June 1998 compared to other periods of this study. Seasonally the higher the SST, the higher is convective cloud top. (v) Interannually, large positive SST anomaly coincided with high convective activity and this may be related to then prevailing El Nino.

Behaviour of recurving cyclonic storms in Arabian Sea as a response to atmospheric interactions

During the year 1998, Arabian sea witnessed two distinct and unusual cyc\onic systems. The very severe cyclonic storm of June 1998 was the most severe storm since last fifteen years as far as Arabian Sea systems are concerned; while October 1998 system was unique for, Its unusual and sudden easterly track after almost touching Saudi Arabia coast, (ii) Very high speed of movement and (iii) Interaction and merger with another vortex present in Arabian Sea off Saurashtra coast. This study is an attempt to understand the peculiar behaviour of the systems in Arabian sea which do not intensify beyond cyclone stage or even show a tendency to weaken before crossing coast as a response to atmospheric interactions. All the cyclonic systems in Arabian Sea since 1975 (Satellite era) have been examined in detail and the main findings of the study are : (i) Interaction between cyclonic disturbances of different intensities simultaneously present, appears to be the key factor in determining the further intensification or not of the systems. (ii) Track prediction for the systems upto marginal cyclone stage appears to be governed mainly by middle level atmospheric forcing. (iii) Upper level wind steering is found to be important for movement of systems from severe cyclonic storm stage onwards. The above results have direct relevance to operational cyclone forecasting.

Long term trends in the frequency of monsoonal cyclonic disturbances over the north Indian Ocean

Long term trends in the frequencies of cyclonic disturbances (i.e. depressions and cyclonic storms) and the cyclonic storms forming over the Bay of Bengal and the Arabian Sea during the southwest monsoon season (June-September) have been studied utilizing 110 years data from 1890-1999. There have been significant decreasing trends in both the frequencies but the frequency of cyclonic disturbances has diminished at a faster rate. The trend analysis shows that the frequency of cyclonic disturbances has decreased at the rate of about six to seven disturbances per hundred years in the monsoon season. The frequency of cyclonic storms of monsoon season .has decreased at the rate of , one to two cyclones per hundred years.

Tropical cyclone frequency in the north Indian Ocean in relation to southern oscillation phenomenon

The present paper deals with the influence of Southern Oscillation (SO) on the frequency of tropical cyclones in the north Indian Ocean. The results show that during the negative phase of SO the frequency of tropical cyclones and depressions over the Bay of Bengal and the Arabian Sea diminishes in May which is most important pre-monsoon cyclone month. The correlation coefficient between the frequency of cyclones and depressions and the Southern Oscillation Index (SOI) is +0.3 which is significant at 99% level. Post-monsoon cyclone frequency in the Bay of Bengal during November shows a significant positive correlation with SOl implying that it also decreases during the negative phase of SO. Thus there is a reduction in the tropical cyclone frequency over the Bay of Bengal during both intense cyclone months May and November in EI-Nino/Southern Oscillation (ENSO) epochs. Therefore it would not be correct to say that ENSO has no impact on the cyclogenesis in the north Indian Ocean. It is true that ENSO has no significant impact on the frequency of cyclones in the Arabian Sea. ENSO also seems to affect the rate of intensification of depressions to cyclone stage. The rate of intensification increases in May and diminishes in November in the north Indian Ocean during ENSO. The results are based on the analysis of monthly frequencies of tropical cyclones and depressions and SOI for the 100 year period from 1891-1990.