Temporal and spatial variations of demersal fishes on the continental shelf of Sri Lanka with special reference to groupers | |
| Author | Athukoorala, Athukoorala Arachchige Sujeewa Hemanthi |
| Call Number | AIT Diss. no.AQ-21-03 |
| Subject(s) | Fisheries--Sri Lanka--Management Grouper fisheries--Sri Lanka--Management |
| Note | A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Aquaculture and Aquatic Resources Management |
| Publisher | Asian Institute of Technology |
| Abstract | The demersal fish are a group of essential seafood species. Groupers are among the most important demersal fish groups belonging to the subfamily Epinephelinae in family Epinephelidae, consisting of about 169 species identified so far in the tropical and subtropical seas. Still, they are rarely studied in Sri Lanka. The main objective of the present research was to assess the current stock status of demersal fish species and the population characteristic changes in grouper resources the last four decades through fishery-independent surveys and fishery-dependent surveys. The author joined the R/V Dr. Fridtjof Nansen (DFN) in 2018 to collect fishery-independent data using a swept area bottom trawl survey with the. In addition, secondary data from the three surveys conducted back in 1978, 1979, and 1980 were used for comparison. A fishery dependent survey was conducted on the southern coast of the country by the interview method. There were 620 species from 137 different families observed. The DFN survey results indicated spatial difference in demersal fish density and diversity. The density was over 76% (9.00 ± 1.08 t/NM2 ), Shannon Weiner's diversity index 1.81±0.12, and the evenness 0.26 ± 0.02 in the East region, compared to the West region with 6.85 ± 1.40 t/NM2 , 1.44 ± 0.10, and 0.18 ± 0.02, respectively. Temporal changes were found in grouper resources. In 2018, the average grouper density was 0.28 ± 0.71 t/NM2 while 0.89 ± 0.20 t/NM2 in 1979, the highest record from 1978-1980. The seafloor depth was negatively correlated with grouper density. The grouper contribution to the total catch was ten times lower in 2018 than in 1979. Grouper distribution around the country showed higher accumulation on the south coast. Fishers confirmed a decline in grouper catch as well as a declining fish body size compared with the past. It was noticed that E. tauvina was absent in fishery-dependent and independent surveys but present in the 1978-1980 surveys. The bottom set long line (BLL) and hook and line (HL) were recorded as commonly used fishing gears. The need to reduce fishing pressure on grouper resources was identified. As control measures, reducing the number of BLL and HL gears is recommended. In addition, fishing area closure, access limits, closed season, and entry limits were recommended as a future management initiative to sustainable utilization and conservation of grouper resources. |
| Year | 2021 |
| Type | Dissertation |
| School | School of Environment, Resources, and Development (SERD) |
| Department | Department of Food, Agriculture and Natural Resources (Former title: Department of Food Agriculture, and BioResources (DFAB)) |
| Academic Program/FoS | Aquaculture and Aquatic Resources Management (AQ) |
| Chairperson(s) | Bhujel, Ram C. |
| Examination Committee(s) | Sasaki, Nophea;Tsusaka, Takuji W. |
| Scholarship Donor(s) | Sri Lanka Council for Agricultural Research Policy |
| Degree | Thesis (Ph.D.) - Asian Institute of Technology, 2021 |