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Not Available Bangladesh J. Zool. 48(1): 189-195, 2020

not available Bangladesh J. Zool. 46(2): 275-280, 2018

Seaweeds are primary producers and among the important marine ecosystem engineers capable of modifying their surrounding abiotic and biotic environments. The southern coast of Bangladesh has an excellent prospect for seaweeds farming due to favorable environmental conditions and natural availability of commercially important species. Through quantitative and qualitative analyses, the present study determines potential contribution of seaweeds toward achieving several targets of United Nations sustainable development goals (SDGs) and the blue economic development in Bangladesh. There are 300 households engaged in seaweeds farming, primarily along the southeast coast, producing 390 tonnes wet weight (= 97.5 tonnes dry weight) of seaweeds per annum with potential applications in food, feed, cosmetics and pharmaceuticals sectors. And the current seaweeds production can be increased yearly at ~50% rate, which is 50 million tonnes (dry weight) from ~5,000 km2 farming area when extrapolated to the year 2050. This may bring a positive change to issues regarding food security, gender equality, economic growth, nutrients removal, carbon sequestration, employment and aquatic environmental health. Overall, the benefits of seaweeds farming could reflect on 26 targets of 8 SDGs and potentially contribute US$0.7 million to the blue economy in Bangladesh.

Tidepools are one of the intertidal habitats providing homes to many marine species. This study investigated the diversity and abundance of tidepool fishes on a rocky shore from Bangladesh. Fish samples were collected from the east and west coasts of St. Martin’s Island between November 2018 and March 2019. There were 441 specimens distributed in 23 species belonging to 20 genera and 14 families. Among those, 11 species represented new records for Bangladesh, namely Allenbatrachus reticulatus, Bathygobius coalitus, Bathygobius curacao, Callogobius hasseltii, Crenimugil crenilabis, Halichoeres nigrescens, Istigobius decoratus, Istigobius ornatus, Ostorhinchus cookii, Siganus sutor and Yongeichthys nebulosus. The most speciose families were Gobiidae (6 species), Pomacentridae (3 species) and Blenniidae (2 species), and in terms of number of individuals, Gobiidae (42%) and Blenniidae (38%) were abundant. The mean abundance of fish in tidepools was decreasing with increasing intertidal elevations (i.e. lower > middle > upper intertidal zones), although the differences were not significant. Moreover, fish abundance and diversity were positively correlated with the surface area of tidepool. Six species were common in the sampling sites, and the east coast of St. Martin’s Island had higher species richness and diversity than the west coast. Temperature (31.8 ± 2.9 °C), salinity (31.8 ± 2.1‰) and pH (8.3 ± 0.1) of the tidepool waters were comparable to those reported for a range of rocky/reef environments across the Asia–Pacific region. This is the first report on tidepool fishes from the northern Bay of Bengal that can be useful for understanding the ecological importance of intertidal zones, and further expanding the knowledge of marine biodiversity and natural history in data-poor regions.

Aquatic habitat connectivity is vital for the continued existence of migratory fish. Using GIS and outranking multicriteria analysis based on hydrometeorological data, this study describes habitat preference of egg, fry, juvenile and adult phases of hilsa shad, Tenualosa ilisha (Hamilton), as well as their spawning areas in the aquatic ecosystems of Bangladesh. The total area studied was 29 484 km2, about 29% of which belonged to the Meghna, Shahbajpur, Tetulia and Ander Manik rivers, and the channels of Sandwip, Kutubdia and Moheshkhali islands, which provide the most suitable habitat for the species. An additional 27% of moderately suitable area was located in other deltaic rivers and inshore waters. The remaining 44% was offshore deeper water, which was least suitable for hilsa. The most suitable area for spawning, eggs, fry, adults and juveniles was 6, 11, 29, 38 and 56% of the area, respectively. The model outputs were validated against field measurements and fishers’ indigenous knowledge with an accuracy level of 92%. Thus, this study provides key information about the location of hilsa at different stages of its life cycle, information useful in understanding its occurrence over a relatively large geographical area. Information of this kind is useful in fishery conservation and management.

A sanctuary is a specific form of protected area and considered to be an important management measure for the conservation and management of fisheries resources. Using socioeconomic and biological indicators, this study investigates the perceptions of fishers towards sanctuaries that were established in the rivers of Meghna and Padma and in inshore waters of Bangladesh since 2005 to protect the declining hilsa ( Tenualosa ilisha ) populations. Both qualitative and quantitative data were collected from six communities adjacent to five hilsa sanctuaries and then analyzed to know the socioeconomic profile of fishers as well as their perceptions of the performance of sanctuaries. The majority of fishers felt that an apparent recent increase in hilsa catch is due to the establishment of sanctuaries. Their perception is well supported by catch statistics that show higher overall hilsa production both from inland and marine waters. However, fishery closure led to substantial economic hardship due to lost income. If the sanctuaries are to function effectively, issues (e.g. lost income) affecting fishers must be addressed by offering compensation schemes so that fishers are able to support their families. The process has to be transparent, inclusive and equitable. There is also a need to support alternative livelihoods for fishers in order to reduce dependence on hilsa fishing. Moreover, fishers must be provided with economic and/or other incentives so as to share responsibilities to protect and manage sanctuaries successfully. Since fishers’ involvement is key to the success of sanctuaries, social acceptance of fish sanctuaries by fishers is a must.

Onshore barrier in the intertidal area is reported to influence coastal geomorphology, sediment dynamics, and erosion and accretion processes. The present study describes sediment texture and deposition pattern, and shore profile of a tidal mudflat located in the Kutubdia Island of Bangladesh. A physical barrier in the form of concrete ring structure was placed on the mudflat of experimental site and the control site was 50 m away without any barrier. The texture of sediment was mostly medium silt (45.3%) in leeward side (= the side facing away from the tide/wave action) of the barrier. Whereas, coarse silt was dominant in the control (35.2%) and seaward side (31.2%), followed by medium silt (25.1% and 29.0%, respectively). The proportion of fine sand was higher in the control (18.4%) and seaward side (16.1%) than that of the leeward side (6.1%). Because of the barrier, there was noticeable sedimentation on mudflat as demonstrated by increased elevation of shore profile in the leeward side, 23.3 cm vs. 3.6 cm in the control. Sediment deposition was, however, varied due to susceptibility to erosion depending on grain size distribution, e.g. the fine deposits had greater erodibility than the sandy deposits. These results suggest that barrier on mudflat could bring a positive change to the sediment profiling and shore morphology, and thus help stabilizing the eroding shoreline.

Oyster reefs have the potential as eco-engineers to improve coastal protection. A field experiment was undertaken to assess the benefit of oyster breakwater reefs to mitigate shoreline erosion in a monsoon-dominated subtropical system. Three breakwater reefs with recruited oysters were deployed on an eroding intertidal mudflat at Kutubdia Island, the southeast Bangladesh coast. Data were collected on wave dissipation by the reef structures, changes in shoreline profile, erosion-accretion patterns, and lateral saltmarsh movement and related growth. This was done over four seasons, including the rainy monsoon period. The observed wave heights in the study area ranged 0.1–0.5 m. The reefs were able to dissipate wave energy and act as breakwaters for tidal water levels between 0.5–1.0 m. Waves were totally blocked by the vertical relief of the reefs at water levels

The availability of suitable freshwater spawning habitat is considered to be a major factor limiting the natural recruitment of anadromous Hilsa shad (Tenualosa ilisha) in the coastal waters of Bangladesh. Against this context, we applied georeferenced habitat database to determine spawning habitat suitability index of Hilsa shad. Landsat imagery and thematic layers were analyzed with ENVI and GIS, and developed a series of GIS models to identify and ranking of suitable spawning grounds. Thus, among the studied 29,484 km2 aquatic ecosystems, only 6% (=1851 km2) area is the most suitable consisting of the rivers Meghna, Shahbazpur, Tetulia and Ander Manik as well as the channel of Sandwip island. Whereas, 20% (=5996 km2) area including river, estuary and near shore water bodies are moderately suitable, and in particular, the offshore deep waters occupying 73% (=21,637 km2) area is least suitable. The model outputs were verified after field data of fishers’ indigenous knowledge with an accuracy level of 87%. This study suggests that necessary measures, such as conservation and management of spawning habitat should be implemented for an increased reproductive and recruitment success that will eventually improve populations of wild Hilsa shad in Bangladesh.

Hilsa shad Tenualosa ilisha comprises the largest and most valuable single fishery of Bangladesh. This study was conducted to identify suitable habitats for Hilsa juvenile in the northern Bay of Bengal along the coast of Bangladesh using Geographical Information Systems (GIS) based Multi-Criteria Evaluation (MCE) of water temperature, dissolved oxygen, pH, salinity, turbidity, current, depth and rainfall. Landsat imagery and 8 thematic layers were analyzed with ENVI and GIS capabilities, and developed as a series of GIS models to identify and prioritize the appropriate habitats for Hilsa juvenile. The study covered 29.484 km2 water body and revealed that 56% (16.388 km2) is the most suitable, 21% (6.054 km2) is moderately suitable and 24% (7.042 km2) is not suitable which was consistent with field verification. The assemblage of marinebrackish-freshwater ecosystems with favourable ecological parameters and rainfall patterns are very much important for supporting juvenile Hilsa in the study area. The results are useful for habitat-specific sanctuary development as the efficient conservation may lead to higher production of adult Hilsa and increase the economic benefit to the fishers.

Site selection is a key factor in any aquaculture operation, affecting both success and sustainability as well as solving land or water use conflicts. This study was conducted to identify suitable sites for carp farming development in urban water bodies (UWBs) of Chittagong, Bangladesh using Geographical Information Systems (GIS) based MultiCriteria Evaluation (MCE) of water, soil and infrastructure database. ASTER imagery and 14 thematic layers were analyzed with ENVI and GIS capabilities, and developed a series of GIS models to identify and prioritize the appropriate UWBs for carp farming. The study identified 487 UWBs occupying 362 ha and revealed 280 ha (77%) is the most suitable, 36 ha (10%) is moderately suitable and 46 ha (13%) is not suitable which was consistent with field verification. The results are encouraging for extension of carp culture and diversify the economic activities of the urban dwellers.

The occurrence of Porpita porpita is reported, for the first time, in the coral island of St. Martin’s located in the southeastern coastal region of Bangladesh. P. porpita was found to occur in the lower littoral zone and beach rock pools, together with molluscan species, and collected during the pre-monsoon season when both water temperature (> 30°C) and salinity (> 30‰) tend to reach a maximum. This study recounts some details on the discovery and description of the species, and thus extends the global distribution and range limits of the genus Porpita.

The species identification, distribution pattern, density and biomass of salt marsh and seagrass plants with some of the ecological parameters were studied in the Bakkhali river estuary, Cox's Bazar, Bangladesh during the first half of 2006. Two salt marsh species ( Spartina sp. and Imperata cylindrica ) and one seagrass species ( Halophila beccarii ) were identified during this investigation, providing the first reports of Spartina sp. and H. beccarii in coastal Bangladesh. Seagrass H. beccarii was found in an accreted area and co-existing with salt marsh, and scattered sparsely in the salt marsh habitat and macroalgae Ulva intestinalis . Flowering and fruiting were recorded from the seagrass H. beccarri during January and February. No flowers and fruits were observed for the salt marsh Spartina sp. during the study period. Results showed that the shoot density of Spartina ranged from 400 to 2875 shoots m −2 with the highest total biomass (165.80 g dry weight (DW) m −2 ) in March. Shoot density of H. beccarii ranged from 2716 to 14320 shoots m −2 in this estuarine coastal environment. The total biomass of seagrass was higher (17.56 g DW m −2 ) in March compared to the other months. The highest H. beccarii above ground (AG) biomass and below ground (BG) biomass were 9.59 g DW m −2 and 9.42 g DW m −2 , respectively. These parameters are comparable with those generally observed for the salt marsh and seagrass species in the other places of the world.