Southeast Monsoon Research Articles

Retained fish catches of artisanal fishers is dependent on fishing area, season and fishing gear type: A case study from the south coast of Kenya

The artisanal fishery is one of the sources of livelihood along the Kenya coast. Catches of retained fish of artisanal fishers between two fishing areas on the south coast of Kenya were compared. Artisanal fishers usually retain a portion of their daily catch which is reserved for family consumption while the rest is traded for cash to meet other family needs. This study hypothesized that retained fish catches were influenced by fishing area, fishing gear type and season. Daily fish landings and retained fish catches among artisanal fishers were monitored between August 2020 to July 2021 covering the South East Monsoon (SEM) and North East Monsoon (NEM) in Msambweni and Vanga fishing areas. A total of 60 fishers (30 for each area) were randomly selected and their retained catch monitored on a daily basis. The overall total fish landings were 23.3 tons and 210 tons in Msambweni and Vanga, respectively. The mean catch rate at Msambweni was 3.3 ± 0.12 kg.fisher-1day-1 in the NEM season and 2.2 ± 0.09 kg.fisher-1day-1 in the SEM season. Fish catch rates in Vanga was 8.5 ± 0.28 kg.fisher-1day-1 in the NEM season and 7.9 ± 0.29 kg.fisher-1day-1 in the SEM season. A total of 0.98 tons (only 4.2 %) of fish was retained versus 22.32 tons (95.8 %) not retained by the artisanal fishers in Msambweni, while in Vanga a total of 1.64 tons (only 0.78 %) was retained versus 208.36 tons (99.22 %) not retained. Retained fish catch varied significantly with season and type of fishing gear used (p < 0.05). Among the retained species in Msambweni, Siganus sutor made the highest contribution (53 %), followed by Lethrinus mahsena, (5.08 %). The species Euthynnus affinis and Sphyraena obtusata were mostly retained in Vanga with a contribution of 10.4 % and 10.2 %, respectively. The same retained fish species represented the most abundant species in the overall fish landings, however sizes were significantly smaller than those not retained by fishers (p < 0.05). Results of non-Metric Multidimensional Scaling (nMDS) ordination showed differences in species composition between fishing areas, seasons and fishing gear types with implication on fishers’ retained catches.

Simulated circulation and trajectory analysis in the Makassar Strait

Makassar Strait conveys the main Indonesian Throughflow (ITF) pathway, as part of the global thermohaline circulation transferring heat and freshwater fluxes from the Pacific Ocean to the Indian Ocean. Dynamics and variability of the ITF and the monsoon winds system influence significantly marine ecosystem in the Indonesian Seas. The study aims to analyze sea surface circulation patterns and particle trajectories in the Makassar Strait by developing a simulation of the CROCO’s 1/36º regional general circulation model between 2017-2018. The results revealed the dynamics of near-surface layer (0 – 50 m depth) varied seasonally. The magnitude of surface current was about 0.6 m/s during the peak of northwest monsoon (NWM) flowing northward and reverse southward during the peak of southeast monsoon (SEM). The magnitude of the current intensified up to 1 m/s in the subsurface at Labani Channel and persistent flows to the southward. The thermocline transport volume was maximum during SEM with average transport about -11.00 (±1.54) Sv. The analysis shows that the particles near Balikpapan coast spreaded slowly to the north, then rotating at the center of the strait and spreaded according to the NWM and SEM.

Seasonal variation of mixed layer depth and thermocline thickness from the ctd argo float data in the Southern Makassar Strait

The Makassar Strait (MS) is directly connected to the Sulawesi Sea in the north and the Java Sea and the Flores Sea in the south and is the main route of Indonesia Throughflow(ITF). Hence Stratification of water mass in the MS is influenced by the dynamics of these waters. This study aims to describe seasonal variations of the mixed layer depth and the thermocline thickness, identify ITF water masses, and the occurrence of coastal upwelling in the southern part of the MS. The results show that the North Pacific water origin of North Pacific Subtropical Water (NPSW) and North Pacific Intermediate Water (NPIW) are dominant, with a maximum salinity characteristic of 34.6-34.7 psu in the thermocline layer and a minimum salinity of 34.5 psu in the intermediate layer. However, near-surface fresh Java Seawater appears to be dominant during the northwest monsoon (NWM-DJF) period. Seasonal variation of the mixed layer depth is much deeper (93m) and vertical gradient of temperature and salinity are much stronger due to the presence of fresh Java Sea water advected by the eastward Java Monsoon Current. However, during the southeast monsoon (SEM-JJA) period the mixed layer depth is much shallower and the thermocline layer is much thicker (198 m), Associated with much stronger ITF and upwelled colder water from the upwelling area. The coastal upwelling event during the SEM period in the study are is characterized by an increase of isotherm of 25 °C, isohaline of 34.0 psu, and isopycnal of 22.0 kg/m3 from about 75 m depth to the sea surface layer.

Seasonal variation of some oceanographic parameters in the Arafura Sea – Gulf of Carpentaria

The shallow continental shelf of Arafura Sea-Gulf of Carpentaria borders the Torres Strait in the east and the deep Banda Sea in the west, where the monsoonal winds system controls shelf circulation. This study aims to investigate spatial and temporal variation of shelf circulation, surface temperature (SST), seas surface height (SSH), using the multi-datasets of validated model output and satellite-derived data. The model reproduced well the satellite derived SST and SSH (corr.> 0.98). The northwesterly monsoonal winds are fully developed between December and February (NWM period), but the southeasterly winds are intensified during the southeast monsoon (SEM). During the monsoon breaks, the southeasterly-easterly winds are still dominant. The shelf circulation is coincident with the wind direction. During the NMW period the eastward flows from Banda basin and Timor Sea are dominant, creating a clockwise circulation within the Gulf. In contrast, the westward flow dominates during the SEM period, creating an anti-clockwise circulation in the Gulf. Exchange of water via the Torres Strait is also seen. Spatial pattern of temperature and SSH reveal a dissimilarity between the Gulf and the Arafura Sea (99.9% of explained variance) with dominant periodicity of annual and semi-annual scales.

Simulated circulation and particle trajectory analysis related to the oil spill event in the Karawang Coastal Waters

The Karawang waters are situated at the north coast of West Java Province, where the wind-driven monsoonal current controls significantly the dispersion of oil spill. Here accident of oil spill was happened on 12 July 2019. The present study aims to simulate seasonal circulation and particle trajectory analysis related to oil spill dispersion, by performing a fine-resolution 1/96° coastal circulation model of CROCO. The model is validated SST (Sea Surface Temperature) detected form satellite, sea level, and surface current with high correlation (corr.>0.86). The Sentinel-1A imagery determined initial position of oil spill. Seasonal reversal currents are reproduced well by the model, consistence with past studies. The westward flows along the northern coastal area during the southeast monsoon (SEM) bring colder and saltier seawater. In contrast, the eastward flows during the northwest monsoon period, associated with warmer and fresher seawater. The massless particles related to oil spill dispersions are advected by the current westward along the coastal area. About one week after the accident, the oil spill closed to the Tanjung Karawang waters, where particle trajectories overlay with the observed Sentinel imagery. The model suggested that on 24 July 2019, particle trajectories released from oil spill accident arrived offshore Jakarta Bay.

A Biological‐Parameter‐Optimized Modeling Study of Physical Drivers Controlling Seasonal Chlorophyll Blooms off the Southern Coast of Java Island

AbstractA physical‐biogeochemical model consists of many key parameters; theoretically, 10,000 or more numerical experiments are required to obtain a set of optimal biological parameters. The corresponding computing resources are too expensive when running a three‐dimensional and high‐resolution physical‐biogeochemical model. In this study, we improve the performance of a three‐dimensional physical‐biogeochemical model via the conditional nonlinear optimal perturbation method for southern Java Island, where chlorophyll blooms occur seasonally. Based on the improved model results, we calculated the mixed‐layer nutrient budget, thereby characterizing how each physical process transports nutrients into the surface oligotrophic layer and then stimulates the chlorophyll blooms during the southeast monsoon season. Nutrients that upwell along the submarine slope are found in narrow regions along the coast and spread into most of the study area by local wind‐induced offshore transport. The contribution of nonlinearity (advection) is essential to modulating the upslope movement of nutrients off the coast. If local winds are neglected in the model, onshore transport induced by the pressure gradient force in the zonal direction (alongshore) and subsequent downwelling would be dominant, and chlorophyll blooms would diminish in most regions. The role of the South Java Coastal Current varies under the joint influence of remote and local wind forcings. The Indonesian Throughflow from the Lombok Strait also contributes to surface phytoplankton growth along its path off the south of Java Island.

Flame Atomic Adsorption Spectrophotometer (FAAS) to Assess the Concentration of Heavy Metals (Pb, Cd, Cr, and Zn) in Porites Coral from Ambon Bay, Indonesia

The concentration of metals in coral represents environmental changes, monsoonal variation, and human disturbance. Metals in coral were used as a proxy to evaluate the response of coastal areas to climatic and human stresses. In this study, several metals including lead (Pb), cadmium (Cd), chromium (Cr) and zinc (Zn) in Porites coral taken from Ambon Bay, Ambon Island, Indonesia, were investigated. The history of metals transient in the most populated island in Maluku Province is documented here from measurements of metals concentration from monthly-banded coral that grew in coastal seawater from 2001 to 2009. The concentration of heavy metals in coral samples was measured using Flame Atomic Adsorption Spectrophotometry (FAAS) method. The results showed metals bioaccumulation (average ± STD) were following decreasing order: Pb (0.96 ± 1.58 μg/g) > Cr (0.15 ± 0.34 μg/g)> Zn (0.11 ± 0.26 μg/g) > Cd (0.007 ± 0.016 μg/g). Moreover, all metals content in the coral showed a remarkable rose from 2001 to 2009 and showed relatively high concentrations during the southeast monsoon for Pb and Cd. Based on the statistical analysis, all metals in Ambon Bay coral were impacted by terrestrial input. In addition, Pb and Cd were also impacted by natural processes that may be associated with their biogeochemical cycle and monsoonal variation.

Effect of the Asian monsoon on the northward migration of the brown planthopper to northern South China

AbstractAs wind‐borne migration of insects is strongly influenced by atmospheric circulation and weather systems, the relationships between insect population abundance and meteorological conditions are substantial. The brown planthopper (BPH), Nilaparvata lugens (Stål), is one of the major wind‐borne insects hampering rice production in Asia, and its migration is significantly influenced by the Asian monsoon, a main component of the Asian climate system. However, the degree and mechanisms of the effects of monsoon on BPH migration have been little studied. In this paper, the effect of the Asian monsoon on the northward migration of BPH from the Indochina Peninsula to northern South China (NSC) was investigated based on the BPH light‐trap data and meteorological data for 39 years. The results show that the level of BPH migration in May could indicate the degree of annual pest outbreaks in NSC and that the southeast monsoon was more critical in this northward migration than the previously recognized southwest monsoon. The significance of the southeast monsoon stemmed from the strong effect of South China Sea subtropical high on BPH migration under a unique weather system distribution, the Polar low–Continental low–West Pacific subtropical high pattern. Furthermore, based on the key areas of migration obtained from the composite analysis, the multivariable linear regression prediction model could effectively predict the occurrence of BPH in NSC. These results indicate the importance of interactions between monsoons during BPH northward migration, which reflects the complex relationship between BPH migration and atmospheric motion.

Seasonal Occurrence and Relative Abundance of Marine Fish Larval Families over Healthy and Degraded Seagrass Beds in Coastal Kenya

Seagrass beds provide critical nursery habitats and spawning grounds for new generations of fish. The habitats are under threat from human activities and climate change, and with that, an important ocean service is lost that limits fish production. The present study investigates patterns in the larval occurrence and abundance in seagrass meadows at two locations with varying degrees of seagrass fragmentation. Monthly ichthyoplankton sampling was conducted during the northeast monsoon (NEM) and southeast monsoon (SEM) seasons in 2019 and 2020. A total of 42 larval fish families belonging to 37 genera and 21 species were identified. Dominant families were Labridae (29.5%), Blenniidae (28.7%), Gobiidae (26.0%), Engraulidae (23.3%) and Scaridae (22.3%). Canonical Correspondence Analysis and regression analysis revealed water temperature, dissolved oxygen and pH as the most important abiotic variables driving taxonomic composition of larval assemblages, while zooplankton and chlorophyll-a were the most important biotic factors. Fish larvae were more abundant in healthy seagrass habitats as compared to degraded ones. However, despite some loss in functionality, the degraded sites equally played a role in supporting some species, including Gobiidae and Blenniidae. Seasonality influenced larval abundance at the two sites, with a peak in mean abundance coinciding with the NEM season. Interannual variability in fish larval abundance was observed at both sites, indicating that factors controlling larval production varied between the years. This study demonstrates the important role of seagrass meadows in the replenishment of fish stocks and supportive evidence for their management and conservation.

Bali Strait‘s Potential Fishing Zone of Sardinella lemuru

Catch fluctuation of Sardinella lemuru in the Bali Strait in the period 2007 - 2019 shows a significant decrease. The fishermen of this area demanded information on the Potential Fishing Zone (PFZ) specifically targeted for Sardinella lemuru beyond their traditional. PFZ will be very helpful, especially during the famine years. Identification of a Potential Fishing Zone (PFZ) is highly important for increased fishing yields and also reduced fishing time for fishermen. Bali strait is dominated by Sardinella lemuru and contributes 16,2% of the total small pelagic fishery production in Fisheries Management Area (FMA) 573. Bali Strait also supports the fishing industry in Muncar (Banyuwangi-East Java) and Pengambengan (Jembrana-Bali). This study will produce a special PFZ for Sardinella lemuru that is not yet available in Indonesia by using remotely sensed and observer data. Here, we apply the Empirical Cumulative Distribution Function (ECDF) algorithm approach for Sardinella lemuru detection. ECDF was developed using Sea Surface Temperature (SST) and Chlorophyll-a (Chl-a) data from Aqua MODIS and extracted according to observer data during 2011-2014. PFZ for Sardinella lemuru in Bali strait was affected by 72,8 % Chl-a conditions and 27,2% by SST conditions. The maximum suitable preference for Sardinella lemuru in Bali Strait is Chl-a condition at 0,2 mg/m3 and SST condition at 28,38°C in northwest monsoon, while in southeast monsoon are 0,97 mg/m3 for Chl-a and 25,61°C for SST. ECDF model result has 69,33% accuracy, which shows the result of Sardinella lemuru PFZ has good accuracy.

Characterizing the Distribution Pattern and a Physically Based Susceptibility Assessment of Shallow Landslides Triggered by the 2019 Heavy Rainfall Event in Longchuan County, Guangdong Province, China

Rainfall-induced landslides pose a significant threat to the lives and property of residents in the southeast mountainous and hilly area; hence, characterizing the distribution pattern and effective susceptibility mapping for rainfall-induced landslides are regarded as important and necessary measures to remediate the damage and loss resulting from landslides. From 10 June 2019 to 13 June 2019, continuous heavy rainfall occurred in Longchuan County, Guangdong Province; this event triggered extensive landslide disasters in the villages of Longchuan County. Based on high-resolution satellite images, a landslide inventory of the affected area was compiled, comprising a total of 667 rainfall-induced landslides over an area of 108 km2. These landslides consisted of a large number of shallow landslides with a few flowslides, rockfalls, and debris flows, and the majority of them occurred in Mibei and Yanhua villages. The inventory was used to analyze the distribution pattern of the landslides and their relationship with topographical, geological, and hydrological factors. The results showed that landslide abundance was closely related to slope angle, TWI, and road density. The landslide area density (LAD) increased with the increase in the above three influencing factors and was described by an exponential or linear relationship. In addition, southeast and south aspect hillslopes were more prone to collapse than the northwest­–north aspect ones because of the influence of the summer southeast monsoon. A new open-source tool named MAT.TRIGRS(V1.0) was adopted to establish the landslide susceptibility map in landslide abundance areas and to back-analyze the response of the rainfall process to the change in landslide stability. The prediction results were roughly consistent with the actual landslide distribution, and most areas with high susceptibility were located on both sides of the river valley; that is, the areas with relatively steep slopes. The slope stability changes in different periods revealed that the onset of heavy rain on 10 June 2019 was the main triggering factor of these group‑occurring landslides, and the subsequent rainfall with low intensity had little impact on slope stability.

Assessment of vertical and horizontal distribution of meiobenthos along a salinity gradient in the Tana and Sabaki Estuaries, north coast Kenya

Meiobenthos respond to variability in salinity gradients in estuarine habitats and are thus suitable organisms for ecological studies. The vertical and horizontal distribution of the meiofauna community structure of two major estuaries (Sabaki and Tana) on the north coast of Kenya were compared. The aim was to draw a meiofaunal dataset inventory of the two estuaries and to examine how salinity gradient, seasonality and sediment characteristics influence their structure. Replicate samples were collected from three sampling stations along the salinity gradient of each river estuary. A total of 3,556 individuals belonging to 26 taxa were recorded. Based on seasons and across stations, the upper surface (0-5 cm) layer recorded the highest meiobenthic density (90 ± 42 ind.10 cm-2), followed by 46 ± 23 ind.10 cm-2 (5-10 cm) and 30 ± 8 ind.10 cm-2 in the deepest sediment layer (10-15 cm) studied. The southeast monsoon season recorded the highest mean density (160 ± 22 ind.10 cm-2) compared to the northeast monsoon season (22 ± 12 ind.10 cm-2) for both estuaries. Results of the non-Metric Multidimensional Scaling technique revealed distinct seasonal composition in meiobenthos but not between the estuaries. Results of the 2-way ANOSIM test confirmed no significant differences in meiobenthic composition between the estuaries (p = 0.712). However, seasonal difference was significant (p = 0.001) with higher densities for nematoda (166 ± 99 ind.10 cm-2 and 56 ± 29 ind.10 cm-2) recorded in Tana and Sabaki, respectively during the southeast monsoon season. At least 7 taxa out of a total of 26 were present in both estuaries. Salinity gradient, season and sediment depth were found to influence the meiobenthic densities and taxa composition.

Performance of Regional Climate Model (WRF 4.3) in Medium Range Rainfall Forecast (MRRF) for Tamil Nadu, India

The weather events are highly dynamic and fluctuating for the next few days due to enormous processes carried out by nature and physics and it is even more highly variable in tropics. The Medium Range Weather Forecast is incredibly helpful and trustworthy for agricultural purposes and rainfall is one of the most imminent events determining productivity. The Medium Range Rainfall Forecast (MRRF) given by Weather Research and Forecast model (WRF v 4.3) is verified using forecast verification scores including Ratio of Root Mean Square Error (RMSE) to the standard deviation of the observations (RSR), Nash-Sutcliffe Efficiency (NSE), Percent Bias (PBIAS), Kling-Gupta Efficiency (KGE), and Root Mean Square Error (RMSE). Scores were computed by comparing forecast generated using two microphysics options viz., WRF Single Moment scheme (WSM-3) and Kessler scheme during South West Monsoon (SWM) and North East Monsoon (NEM) of the year 2021 for five different physiographic regions of Tamil Nadu. WSM-3 microphysics scheme outperformed in predicting MRRF for all the five regions and during both the monsoons.

Sea Surface Temperature and Salinity in Lombok Strait Reconstructed From Coral Sr/Ca and δ18O, 1962–2012

Coral geochemical tracers have been used in studies of the paleoclimatology and paleoceanography of the tropics and subtropics. We measured Sr/Ca and oxygen isotope ratios (δ18O) in a coral sample collected from the southern part of Lombok Strait, a significant outlet of the Indonesian Throughflow (ITF) to the Indian Ocean, to reconstruct the historical record of sea surface temperature (SST) and seawater δ18O. Seawater δ18O can be used to approximate sea surface salinity (SSS) because it reflects the balance of evaporation and precipitation. The resulting time series reconstructed SST and SSS, covering the period 1962–2012, shows no clear trend of global warming, although the record includes a large cooling event (~4°C) during 1996–1997. Although neither SST nor SSS shows a systematic relationship with El Niño–Southern Oscillation and Indian Ocean Dipole (IOD), weak but significant correlations are found partly. In addition, the coral data show signals of major IOD and El Niño events in 1994 and 1997, respectively, although climatic trends recorded in the coral are not consistent with those found along the Java-Sumatra coast. To evaluate other influences on the ITF in Lombok Strait, we compared our coral record with coral records from sites in the Java Sea, the southern part of Makassar Strait, and Ombai Strait. During the northwest monsoon (December–January–February), variations in SST and SSS at Lombok Strait site are similar to those at the Java Sea and southern Makassar sites for the period 1962–1995, which suggests that low-salinity water from the Java Sea is carried at least to the southern part of Makassar Strait where it suppresses the ITF upstream from Lombok Strait. However, the SST and SSS records differ at the three sites during the southeast monsoon (June–July–August), indicating that surface conditions in Lombok Strait vary separately from those in the Java Sea. In the longer term, although global warming has been widely identified in the Indonesian Seas, the coral record shows no clear warming trend in the southern part of Lombok Strait, where fluctuations in the ITF may be modulating the distribution of heat in the surface waters of the western Pacific and eastern Indian Ocean.

A Comparison of the Three Upwelling Indices in the South Java Sea Shelf

Abstract Upwelling plays a crucial role in driving cross-shelf circulation between the continental shelf and boundary currents. It is well known that upwelling results in the exchange of heat, nutrients, fish larvae, and other properties. It controls primary productivity, which promotes higher trophic levels and fisheries. Upwelling can be identified by at least three physical variables: wind, sea surface temperature (SST), and chlorophyll-a (Chl-a). The intensity of upwelling can then be calculated using the Upwelling Index (UI), which is based on these three variables. Wind-based UI (UIET), SST-based UI (UISST), and Chl-a-based UI (UICHL) were calculated using satellite-derived and reanalysis data from 2002 to 2017. Those three UIs were analyzed spatially and temporarily to determine the differences in upwelling strength and duration. The most appropriate UI for explaining the South Java upwelling system in our domain was determined through the correlation analysis. The monthly mean climatology of all UI (UIET, UISST, and UICHL) reveals the seasonal variation, which is high during the southeast (SE) monsoon. The strongest correlation between UISST and Chl-a with the smallest lag times suggested that South Java upwelling in our domain can be identified better using SST-based UI (UISST) than through the Ekman mass transport-based UIET, particularly in the east, relevant to the earlier study. Keywords: Chlorophyll-a, Upwelling Indexes, South Java Upwelling

Contrasting vertical distributions of recent planktic foraminifera off Indonesia during the southeast monsoon: implications for paleoceanographic reconstructions

Abstract. Planktic foraminifera are widely used in paleoceanographic and paleoclimatic studies. The accuracy of such reconstructions depends on our understanding of the organisms' ecology. Here we report on field observations of planktic foraminiferal abundances (>150 µm) from five depth intervals between 0–500 m water depth at 37 sites in the eastern tropical Indian Ocean. The total planktic foraminiferal assemblage here comprises 29 morphospecies, with 11 morphospecies accounting for 90 % of the total assemblage. Both species composition and dominance in the net samples are broadly consistent with the published data from the corresponding surface sediments. The abundance and vertical distribution of planktic foraminifera are low offshore western Sumatra and increase towards offshore southern Java and the Lesser Sunda Islands (LSI). Average living depth of Trilobatus trilobus, Globigerinoides ruber, and Globigerina bulloides increases eastward, while that of Neogloboquadrina dutertrei, Pulleniatina obliquiloculata, and Globorotalia menardii remains constant. We interpret the overall zonal and vertical distribution patterns in planktic foraminiferal abundances as a response to the contrasting upper-water-column conditions during the southeast monsoon, i.e., oligotrophic and stratified offshore Sumatra (non-upwelling) vs. eutrophic and well mixed offshore Java–LSI (upwelling). Overall, the inferred habitat depths of selected planktic foraminifera species show a good agreement with those from sediment trap samples and from surface sediments off Sumatra, but not with those from surface sediments off Java–LSI. The discrepancy might stem from the different temporal coverage of these sample types. Our findings highlight the need to consider how foraminiferal assemblages and ecology vary on shorter timescales, i.e., from “snapshots” of the water column captured by a plankton net to seasonal and interannual variability as recorded in sediment traps, and how these changes are transferred and preserved in deep-sea sediments.

Impact of Precipitation over the Productivity of Sugarcane in Major Agro-climatic Zones of Tamil Nadu

Sugarcane is one of the traditional crops grown abundantly across the state of Tamil Nadu due to the lengthening of the period of monsoon and its diversified uses in different agro-based industries. Precipitation, a significant factor for sugarcane cultivation, has an impact on its productivity differs for different agro-climatic zones. A secondary data of district wise precipitation and sugarcane productivity of Tamil Nadu for the 30 years (1985 - 2014) were also collected. The impact of precipitation over the productivity of various crops can be explained by using the Standard Precipitation Indices (SPI) data and applying Principal Component regression (PCR) technique. Initially, SPI, A drought monitoring index, represents a Z-Score, was calculated seasonally for different agro-climatic zones. As there was a severe collinearity between the SPI values of seasons, Principal component regression analysis was used to study the impact of precipitation on the sugarcane productivity by considering the SPI values of four seasons along with time as regressor variables. The study showed that the productivity of sugarcane in Cauvery Delta zone and Western Zone mainly depended upon the precipitation during South west monsoon and North East monsoon periods. However, the productivity of sugarcane in North East zone was mostly dependent on the precipitation of Cold Weather period when compared to all other seasons. Unlikely, North west and Southern zones are not significantly influenced by the precipitation.

Molecular and phylogenetic analysis of Sardinella lemuru Bleeker 1835 at fishing ground Canggu-Bali inferred D-loop mutations of mtDNA

Sardinella lemuru resources are abundant, nutritious, high omega-3 and have high economic value in artisanal fisheries. Its production volume landed for over a decade, but the most significant increase was peak southeast monsoon 2019 at Canggu fishing ground. However, prior-conventional kinship assessments genetically need to be confirmed. These research objectives encompass both molecular identification and genetic relationship of Canggu S. lemuru with the others. Similar morphological samples had collected of ten individuals. Chelex 10% was used for genomic DNA extraction, CRK-CRE primer with Hotstart-50 PCR thermal profile had applied for amplification. 1% agarose electrophoresis and Sanger sequencing had examined for both quantity and quality of D-loop amplicon. Identification using the algorithm of BLASTn. Phylogenetic tree analysis uses the neighbor-joining method. The genetic identity of 10 D-loop Canggu samples was high (97.46%-98.47%) as Philippines S. lemuru (MK579633.1-MK579742.1). The phylogenetic significantly shows low barrier inter-waters from low to moderate genetic distance. Inter-waters samples are very close in intraclade, but it still has a different mutation rate in another clade. Means suggested that Canggu S. lemuru is more diverse in nucleotide base substitutions encouraging high variation. These study results provide needed information that southern translocation occurred among waters, its dispersal connection.

Seasonality in Phytoplankton Species Composition and their Influence on Small Pelagic Fish along the Western Pemba Channel

The influence of phytoplankton biomass on small pelagic fish groups was studied at three sites along the Western Pemba Channel, to assess the contribution of seasonality. Sampling took place at the three sites in the coastal waters of Tanga, Tanzania. The study used in-situ data from July 2016 to January 2017, remotely-sensed chlorophyll-a data from August 2016 to August 2017 and 2019–2020, and small pelagic fish catch data from the same periods as the remotely-sensed data. The dominant groups at all the three sites were diatoms, dinoflagellates, and cyanobacteria, with diatoms having the highest number of species compared to the other two. In comparison to the southeast monsoon season, phytoplankton species and biomass were significantly higher during the northeast monsoon season. The most plentiful fish were anchovies, which had high peaks in both seasons, followed by sardinella, while mackerel had the lowest catch. Chlorophyll-a and anchovy catches showed a positive correlation; however, the relationship was not significant (r = 0.47, df = 11, p = 0.12). Both variables showed the highest peaks in October, while other fish groups showed very weak and insignificant positive or negative correlations. These findings suggest that factors other than phytoplankton biomass contribute to controlling small pelagic fish availability.
 Keywords: Phytoplankton; monsoon seasons; chlorophyll-a; Pemba Channel; small pelagic fish.

Reproductive seasonality and fecundity of the spiny lobsterPanulirus homarus homarus(Linnaeus, 1758) (Decapoda: Achelata: Palinuridae) in Kenya: implications for sustainable management

AbstractThe scalloped spiny lobster Panulirus homarus homarus (Linnaeus, 1758) is one of the most commercially important lobsters exploited in Kenya. Despite its local importance and wide distribution, detailed knowledge on its reproduction in East Africa is lacking. The study reported herein sought to determine its spawning season based on seasonal variations in female gonadosomatic index (GSI), temporal distribution of ovarian maturity stages, and the proportion of ovigerous females in the monthly samples captured off Mambrui, Kenya. The study also assessed size composition, sex ratio, fecundity, and reproductive potential. A total of 2,454 lobsters were collected during the study period (January 2000-December 2001), covering a size range of 26–115 mm carapace length (CL). Neither the overall sex ratio nor the monthly sex distributions deviated significantly from the expected ratio of 1:1, except for a few months when males and females alternately dominated the samples with no discernible seasonal trends. Analysis of the cyclical changes in reproductive activity shows strong spawning seasonality in synchrony with the Northeast monsoon season in both years. Simultaneous breeding of a wide size range of females (54–90 mm CL) commenced in November and intensified over the following months until April. Outside the Northeast monsoon season, only 10 females, out of the total 517 sexually mature females sampled during the 2000 and 2001 Southeast monsoon seasons, bore eggs, and all were large individuals (>66 mm CL) encountered in the 2001 samples. Fecundity was positively and linearly related to female size (CL) and best described by the equation E = 10,400 CL – 472,040 (R2 = 0.929, N = 59). Estimated fecundity varied between 81,000 and 474,000 eggs per spawn in female lobsters (54 mm–91 mm CL). Female lobsters between 66 mm and 80 mm CL contributed 62% of the estimated total egg production of the population. The widespread retention of egg-bearing females in a fishery where the main fishing season falls during the spawning season, can have detrimental effects on the spawning stock abundance and egg production with increased risk of recruitment failure and stock collapse.