Lunar, diurnal and tidal periodicity in relation to the prawn abundance and migration in the Godavari estuarine systems

Preliminary investigations to study the lunar, diurnal and tidal periodicity in abundance and migrations of prawns were made in the Bairavapalam distributary of the Goutami branch of the Godavari estuary during the period of November 1961 to July 1962. The study was based on observation of the catches of a stake net (bag net) operated near the mouth of the estuary. Records of the catches were maintained tidewise daily. Comparative estimates of abundance were made on the basis of catch per hour's operation. It was generally observed that the catches were higher during the darker half of the month than in the brighter fortnight. The landings during low tides were generally higher than those during high tides and usually heavier catches were made during nocturnal low tides than during the day low tides. A continuous inward and outward (immigration and emigration) movement of prawns of all size groups was observed in the estuary from November to July. In general, more penaeid prawns were found to be immigrating at dawn than at dusk. Similarly, the number of emigrants was also found to be generally higher during the new moon period than during the full moon. Metapenaeus monoceros showed an almost distinct nocturnal periodicity in migration, while no such periodicity was observed, distinctly, in other species. In the case of Penaeus indicus the movement of migrants was prolonged. In M. brevicornis the migrants were scarce till March and thereafter increased numerically. The migrant forms of Metapenaeus dobsoni continued to be abundant till May with peak periods in January and February. The migratory pattern of Metapenaeus affinis was similar to that of Metapenaeus brevicornis, though the migrants of the former species appeared a month earlier than the latter. Intensive studies over extended areas for longer periods are required to understand clearly the migratory pattern of the various species. The phenomenon of immigration of prawns can be clearly understood only by vital staining or tagging studies. Perhaps the emigrants might be returning with the succeeding changing life. To verify this, laboratory experiments, by vital stains, were conducted. The marked specimens, if released during the low tides on a large scale, may be recaptured during the subsequent high tides and the duration also may be calculated. At least some percentage of the emigrants remains in the sea for maturity and breeding.

Seasonal variability in penaeid prawn larval abundance in the Mandovi and Zuari estuaries, Goa

Seasonal variations in the occurrence and abundance of penaeid prawn larvae in the Mandovi and Zuari estuaries of Goa were studied. Larvae and post-larvae of commercially important species viz. Metapenaeus dobsoni (Miers), M.affinis (H. Milne Edwards). M. Monoceros (Fabricius), Penaeus merguiensis de Man and Parapenaeopsis stylifera (H. Milne Edwards) were recorded in that order of abundance. Protozoea and mysis stages were dominant in surface zooplankton collections while the post-larvae were more in the bottom samples. Based on larval density, M. dobsoni appeared to be a continuous breeder. The active spawning periods in other species were during the late post-monsoon and pre-monsoon seasons varying with the species. Peak recruitment of post-larvae in the estuaries was observed mostly during southwest monsoon months (June to September). Penaeid prawn larval ingression was more in the Zuari estuary compared to the Mandovi estuary. Their numerical abundance gradually decreased towards the upstream areas. The feasibility of large scale collection of penaeid prawn larvae for aquaculture is indicated.

Relative abundance and diel variation of zooplankton from south west coast of India

Relative abundance and diurnal variations of zooplankton from six anchor stations along Kerala coast were investigated. Samples were collected during April-May 1988 at three hour intervals from depths varying between 15 and 40 m from the traditional fishing grounds of Kerala coast. Average biomass values ranged from 45-95 ml 100/mˉ³. Increase in zooplankton at night was discernible at most of the stations and the highest biomass noticed was 131 ml 100/mˉ³. Copepods formed the most abundant group, of which calanoids predominated. A swarm of the hydromedusan species, Aequorea conica, (181/mˉ³) was seen at night. Quantitative and qualitative variations of various zooplankton groups from six stations in relation to selected physicochemical factors are discussed. Maximum fish larvae were observed in the night samples. Relatively high abundance of sardines, carangids and flat fish larvae in the collections is in agreement with the predominance of fish catch from the area of study.

Occurrence and abundance of Acetes shrimps in the Kutubdia channel of Bangladesh coastal water

This investigation was carried out from June ‘89 to May ‘90 and focuses on the occurrence and abundance of Acetes shrimps in the Kutubdia channel. The shrimps of the genus Acetes occurred throughout the year in the area of investigation. Acetes showed a bimodal peak in occurrence, one in late monsoon season (August - September) and other in pre-monsoon season (February - March). But the maximum number of Acetes shrimps was recorded in March (462 individuals/haul). The Acetes population of this channel was dominated by four species, Acetes erythraeus (38.50%), A. indicus (32.98%), A. chinensis (4.48%) and A. japonicus (3.32%).

Species composition and abundance of different Macrobrachium species in a natural habitat of Kalu River near Titvala, Maharashtra State

Juveniles of freshwater prawns caught by the traditional cylindrical bamboo traps operated by the local fishermen in a natural habitat of Kalu River near Titvala were sampled every week during September to December 1991 and 1992, to study the composition and relative abundance of different species and their relationship with hydrobiological parameters. The juvenile catch comprised Macrobrachium rosenbergii, M. idella, M. scabriculum and M. bombayensis. Among these M. rosenbergii was more abundant followed by M. idella. It is also observed that high tide catches are more productive than those of low tides.

Apparent abundance of yellowfin and bigeye tuna in the inshore, off shore and near oceanic ranges around Ceylon

Sri Lanka entered oceanic longline fishery in 1967 and have limited the areas of operation to the central equatorial belt, thus limiting their fishery to the yellowfin and bigeye tunas. Sri Lanka while developing her coastal fishery took a leap into oceanic longlining and in view of her programme for accelerated development of the fishing industry, has to fill the gap between the two fisheries by exploiting the intermediate range (off shore and near oceanic) which would chiefly be for tunas and sharks. The present paper has been prepared in this context, utilizing available data and information on the tuna longline fishery in the inshore (approximately 6-15 miles), off shore (approximately 15-100 miles) and near oceanic (approximately 100-300 miles) ranges (Fig, 1).

Indices and fecundity of a threatened freshwater catfish Mystus montanus

Fecundity of threatened catfish Mystus montanus was estimated from a collection of gravid females, which ranged from 290 to 27,972 according to body length and weight. The relationship between fecundity and BL, BW, GL and GW was analyzed by linear regression, which showed both positive and negative correlation. Gonado-somatic index (GSI), hepato-somatic index (HSI) and spleen-somatic index (SSI) ranged from 0.135 to 21.28, 0.358 to 21.33 and 0.126 to 1.08 in females and the corresponding values for males were 0.17 to 10.68, 0.619 to 3.25 and 1.25 to 2.33 respectively.

Impact of Bashundhara Baridhara Housing Project on the status, abundance and species diversity of fish in Bashundhara Housing lake in Dhaka, Bangladesh

A study on the status of fisheries and environmental impact assessment (EIA) was conducted on Bashundhara Baridhara Housing Project (BBHP), Dhaka, Bangladesh for prediction and measure the effects of housing project related development activities that have already been implemented and planned for future implementation. The project is still under development phase and so far allotted 10,000 plots of different sizes. The study shows that the original water bodies and natural fish production there from have greatly declined due to earth filling carried out for development of land for the housing. The physico-chemical parameters of the existing water body within the project area were found to be suitable for fish farming in the estate. A number of economically important fish species are found available in the existing lake. However, the natural fisheries resources of the existing lake is under great stress due to the changes made in the ecosystem, siltation, construction of building and dumping of house building and household waste materials. This has caused some important fish species of the lake to become critically endangered and vulnerable which have been documented in this paper. Appropriate regulatory and mitigating measures with respect to water management, disposal of construction garbage and other biomedical toxic substances far away from the water bodies are required to be taken to keep the water safe and suitable for fish production as well as for multipurpose use of the lake water.

Size related feeding patterns and electivity indices of silver barb (Barbodes gonionotus Bleeker) from a pond, Bangladesh

The feeding patterns with respect to quality and quantity of food of silver barb, Barbodes gonionotus varied with their size and development. The results indicated that the fish in the size group I (7-25 mm TL) were fairly omnivore with particular liking for rotifera, green and blue-green algae while the size group II (25.1-44 mm TL) and III (44.1-55 mm TL) were omnivore with higher tendency of feeding on debris, aquatic plants, green algae, blue-green algae and rotifera. However, the fish of the size group IV (55.1-80 mm TL) were found to be herbivore with feeding preference for aquatic plants, green and blue-green algae. In all the size groups, debris was the most dominant food item. Feeding preference of the fish showed clear ontogenetic shift. The electivity indices revealed that the fish were selective feeder.

Occurrence and abundance of brachyuran larvae in the Manora Channel (Karachi, Pakistan) during 1993

The present paper investigates the occurrence and abundance of brachyuran larvae in the Manora Channel during August- December 1993. The fortnightly planktonic sampling was carried out in Manora Channel which is bordered by mangroves, during day time from surface and subsurface waters at shallow depth using Bongo net of 300 micron mesh size. Analysis of samples revealed presence of brachyuran larvae of 12 species belonging to 6 families. Of these 4 species are confirmed: Serenella indica, Dotilla blanfordi, Metopograpsus thukuhar and Clistocoeloma lanatum, 2 provisionally identified species are: Pilumnus ?karachiensis and Pinnotheres ?pisum, 2 species are identified upto generic level: Philyra sp. and Pinnotheres sp., and 1 Ocypodid species and 3 Xanthid species are identified upto family level. This study based on identification, occurrence and abundance of brachyuran larvae in the area, also gives percentage composition of brachyuran larvae collected during 1993, in the Manora Channel.

Seasonal dynamics in the occurrence and abundance of Pseudo-nitzschia species in the Maheshkhali channel of the Bay of Bengal, Bangladesh

Occurrence and abundance of Pseudo-nitzschia spp. at the mouth of the Maheshkhali channel of the Bay of Bengal, Bangladesh were studied. Plankton and water samples were collected monthly from the sub-surface water during high tide at daytime from June 2000 to May 2001. Four species of Pseudo-nitzschia, namely P. pungens, P. pseudodelicatissima, P. delicatissima and P. australis were identified and among them the first three were most commonly encountered and they varied seasonally. Pseudo-nitzschia delicatissima was the dominant species during the autumn and winter months, whereas P. pungens was dominant during the summer and spring months. Pseudo-nitzschia pseudodelicatissima exhibited its highest abundance level during the summer. Surface water temperature, salinity, nitrate-nitrogen (N03-N) and phosphate-phosphorus (P04-P) were recorded and their relationship with the occurrence and abundance of Pseudo-nitzschia species were studied. At the mouth of the Maheshkhali channel, Pseudo-nitzschia cell density was highest in late autumn (November) when highest salinity (35 o/oo) and P04-P (3.2 mg/l) concentrations and low temperature (23 °C) were recorded.

Abundance, migration and management of Jatka (juvenile hilsa, Tenualosa ilisha) in the Gajner Beel, Pabna, Bangladesh

Studies on the abundance, migration and management of Jatka (juvenile hilsa, Tenualosa ilisha) were conducted in the Gajner Beel, located at the south-east corner of the Pabna Irrigation and Rural Development Project (PIRDP) in Sujanagar Upazila of Pabna district, Bangladesh. The main Jatka season was found to be extended from mid August to mid October. Veshal/Bandh/Khora Jal (lift net) and Ber Jal (beach seine net) were found as the major gears involved in Jatka fishing. The estimated total amount of Jatka caught from the Beel during the studied season was 46.2 t. The migratory route of Jatka is extended from the Padma and/or Jamuna rivers to the Badai river and then to the Beel through the sluice gate. The possibility of breeding of hilsa in the Beel was nullified. Finally, a community based management plan was suggested for implementation by the Gajner Beel management committee.

Diversity indices of selected macrobenthos in Karanja Creek (District-Raigad), Maharashtra, west coast of India

The diversity indices can be used as a good measure for studying the effect of industrial pollution because industrial wastes and sewage almost always reduce the diversity of natural systems into which they are discharged. A measurement of diversity often provides a better index of pollution than a direct measurement of pollutants. The assessment of macrobenthos diversity with respect to diversity indices reflects the marine population and habitat disturbance, and also serves as an important indicator of environmental conditions. The present study was designed to investigate the diversity indices of selected macrobenthos at two ecologically distinct locations on the Karanja creek (District - Raigad), Maharashtra, west coast of India. Results on various diversity indices like Index of Frequency (F) or Importance Probability (Pi), Index of Dominance (c), Rarity Index (R), Shannon's Index of General Diversity (H¹) Margaf’s Richness Index (R sub(1)) and Evenness Index (e) did not vary significantly. This demonstrates that at present, Karanja creek harbours varied forms of macrobenthic community showing no effect of human disturbance, but in future, measures must be taken for the protection and conservation of macrobenthic community of the creek.

Productivity and seasonal abundance of commercially important fishes of Gobindsagar Reservoir

Fishing experiments with gill nets were carried out at different centres of Gobindsagar reservoir through the years 1964-70. The seasonal abundance of main species of fishes and their zone of distribution were studied. Labeo diplostoma, Labeo bata, Barbus tor and Mystus seenghala are the main fish species of the reservoir. The abundance of the above species were observed to be the highest towards the Lunkhar arm of the reservoir.

Ingression, abundance and settlement dynamics of Penaeid chrimp postlarvae in backwaters and adjacent tidal ponds in Cochin, India

Dynamics of penaeid postlarval ingression and settlement in the backwaters of Cochin were studied. Postlarval recruits were constituted by Metapenaeus dobsoni (70.8-78.4%), Penaeus indicus (17.5-24.6%), M. monoceros (3.8-4.6%) and P. monodon (0.3-0.4%). Their composition varied with location and season. Postlarval abundance and ingression were influenced by diel, tidal, lunar and seasonal factors. Ingression is mainly nocturnal in all species with nearly 84% of the activity during night hours. Abundance and ingression peaked up during high tides at night with major peaks coinciding with spring tides of full and new moon. It also followed a generalized seasonal pattern with two well-defined peaks for all species. It was pre-monsoon followed by post-monsoon for P. indicus and M. monoceros and post-monsoon followed by pre-monsoon for M. dobsoni. Sizes of the recruits were relatively small during pre-monsoon and post-monsoon and large during monsoon.