Diversity of Fish and Shellfish in Negombo Lagoon Sri Lanka

Negombo lagoon (7' 6'-7" 12' N, 79" 49'-79" 53' E) is one of the most productive lagoons in Sri Lanka. It bears a high level of biodiversity and variations of fish and shellfish diversity was evident from time to time. This study aims to provide an update on fish and shellfish diversity in Negombo lagoon after being subjected to many anthropogenic and development activities in recent past. Three major areas of Negombo lagoon i.e. Kadolkele, Dungalpitiya and Kepungoda located 5 km distance to each other were selected as major sampling sites. Fish and shellfish sampling was done once a month from January to December 2018 using a seine net with 50 mm stretch mesh size. Triplicate samplings were conducted at each site. Salinity and surface water temperature were measured in-situ. Water samples were collected to determine Dissolved Oxygen (DO), pH, Nitrate-N and Orthophosphate. Shannon Weiner’s diversity index (H’), effective number of species (exp.SWI), species richness and species evenness were calculated and compared with respected to each site. A total of 51 species belongs to 33 families were identified during this study. Among them 44 species were finfish and 7 species were shellfish including shrimps and crabs. The highest diversity index and species evenness were recorded from Dungalpitiya site while the lowest was from Kadolkele. High evenness was observed from September to December in all most all the sites and thelowest evenness was evident in May. Species richness varied over the year and the highest and lowest values were recorded in Kepungoda (177.9±10.8) and Kadolkele (92.24±12.3) respectively. A drastic declination of species richness was recorded in June after reporting high species richness from March to May. A significant impact of water quality parameters to the diversity variation was observed in Negombo lagoon. Salinity and DO reported a significant impact to the diversity. Compared to previous studies the diversity of the lagoon habitats has been decreased and these updated information will be useful when designing lagoon management plan which is in the process of developing.Keywords: Negombo lagoon, Fish and shellfish diversity, Diversity indices, Water qualit

Reproductive Biology of the Three Spot Swimming Crab (Portunus sanguinolentus) Occurring in the Coastal Waters off Negombo, Sri Lanka with Novel Approach to Determine the Maturity Stage of Male Gonads

The reproductive biology of Portunus sanguinolentus (Three Spot Swimming Crab) wasinvestigated in the coastal waters off Negombo, Sri Lanka from February 2014 to January2015. Reproductive activity was assessed using macroscopic and microscopic observations ofgonad characteristics, trends of gonad indices, size at first sexual maturity and differences inthe monthly sex ratio. Though P. sanguinolentus females have higher body weight thanmales, carapace length, carapace width or body weight of males and females were notsignificantly different (Mann-Whitney test, p>0.05). Ovigerous females were observedthroughout the year, confirming that they are continuous spawners however, peak spawningwas in October. Percentage Gonadosomatic Index (GSI) of females is significantly higherthan the males (t-test; p<0.05; df=193) and GSI values ranged from 0.02 to 3.69 in males and0.12 to 9.44 in females. Sex ratio of P. sanguinolentus population fluctuated seasonally andsignificantly high male to female sex ratio was observed in October 2014 (χ2 test). Size atfirst sexual maturity (Lm50) was estimated at 9.75 and 8.90 cm (carapace width, CW) formales and females, respectively. Three types of external egg masses; stage I, II and III wereidentified based on colour and size of the berried eggs. The mean diameter (μm) of eggs ineach stage was reported as 253.8±3.19, 281.8±6.79, 316.5±9.78, respectively. The averagefecundity of P. sanguinolentus varied from 2.04×104 to 1.24×106 and it increased withincreasing CW. Present study proposes a new method to identify mature and immature malesby using their external characteristics. Accordingly, in mature males, blue color patches canbe observed on the ventral side of chelar propodus and merus but this colour pattern is notprominent in immature males and absent in mature females.Keywords: Portunus sanguinolentus, Sri Lanka, Chelar propodus, Merus, Size at first sexualmaturit

Temporal Variations in the Abundance and Diversity of Surface Zooplankton in the South Coast of Sri Lanka

Zooplankton have extensively studied in the Indian Ocean, but very few systematic studies have been carried out in the marine waters around Sri Lanka. This study aimed to understand the temporal variations in the abundance and diversity of surface zooplankton in the south coast of Sri Lanka. Surface zooplankton samples were collected at five different locations in the south coast of Sri Lanka in November 2015 (second inter monsoon), December 2015 (Northeast monsoon, NE) and May 2016 (Southwest monsoon SW) using R/V Samuddrika. The vertical hauls of zooplankton were collected from 5 m depth at each station using WP-2 net with 180 μm mesh size and samples were immediately preserved in 5% buffered formalin. At the laboratory, zooplankton were identified to the lowest possible taxon using existing guides, species diversity, abundance (ind/m3), evenness and richness were estimated with respect to three different sampling phases. The data were subjected to hierarchical cluster analysis to identify the similarity between temporal variation and zooplankton abundance. A total of 152 zooplankton species were identified during this study. Species belonging to phylum Arthropoda appeared be the most abundant group and their standing crop (whole time period and sites) was 1906±115 ind/m3. Arthropods occupied nearly 86% of total zooplankton community. Among arthropods, order Poecilostomatoida showed the highest abundance (858±8 ind/m3) followed by phylum Protochordata (~3% and average of 74 ind/m3) chetognaths (2.1%) and mollusks (~1.9%). The highest species abundance was recorded in Novemver (1392±5 ind/m3) and lowest was in May (360±2 ind/m3). Species diversity was also highest in November and lowest in May. Cluster analysis revealed two clearly visible abundance clusters with respect to time. The results indicated that there are significant temporal variations in zooplankton abundance (ANOVA, P<0.05) in the South coast of Sri Lanka.Keywords: Zooplankton, Abundance, Diversity, Cluster analysi

Biology, Fishery, Conservation and Management of Indian Ocean Tuna Fisheries

The focus of the study is to explore the recent trend of the world tuna fishery with special reference to the Indian Ocean tuna fisheries and its conservation and sustainable management. In the Indian Ocean, tuna catches have increased rapidly from about 179959 t in 1980 to about 832246 t in 1995. They have continued to increase up to 2005; the catch that year was 1201465 t, forming about 26% of the world catch. Since 2006 onwards there has been a decline in the volume of catches and in 2008 the catch was only 913625 t. The Principal species caught in the Indian Ocean are skipjack and yellowfin. Western Indian Ocean contributed 78.2% and eastern Indian Ocean 21.8% of the total tuna production from the Indian Ocean. The Indian Ocean stock is currently overfished and IOTC has made some recommendations for management regulations aimed at sustaining the tuna stock. Fishing operations can cause ecological impacts of different types: by catches, damage of the habitat, mortalities caused by lost or discarded gear, pollution, generation of marine debris, etc. Periodic reassessment of the tuna potential is also required with adequate inputs from exploratory surveys as well as commercial landings and this may prevent any unsustainable trends in the development of the tuna fishing industry in the Indian Ocean