Distribution and size composition of penaeid prawns, penaeus monodon and penaeus indicus in Saadan Estuarine Area, Tanzania | |
| Author | Mosha, Erastus J. |
| Call Number | AIT Diss. no.AQ-13-02 |
| Subject(s) | Shrimps--Tanzania Shrimp fisheries--Tanzania |
| 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 | Tanzania has two types of prawn fishery: 1) artisanal fishery which centers on the capture of penaeids within estuaries which is not subject to closed season and 2) large - scale commercial prawn fishery operating offshore which is subject to closed season. Artisanal prawn fisher s harvest penaeids in the estuary throughout the year causing growth overfishing and reduction of broodstock which in turn affects the rate of offshore stock recovery. Scientific information on how penaeid prawns are distributed in the estuaries based on International Standards or Codex Alimentarius Commission Grading Systems for Capture and Culture Prawns is scarce, which is an obstacle for fisheries management. This study investigated the distribution and size composition of two major commercial species of prawns in Tanzania, Penaeus monodon and Penaeus indicus in Saadan estuary. Environmental parameters such as water temperature, salinity, substrate particle size and substrate’s organic matter were investigated . The area was divided into 5 transects, each 3.7 km from other and perpendicular to the estuary. Transects were sampled three times per month from January to April 2011 and 2012 respectively, the period t hat represent two main seasons: dry season (January to February) and wet season (March to April) the peak season for prawn fishery in which 815 specimen of prawns were collected and 330 samples of bottom substrates were analyzed. Juveniles were 84.2% in dry season, while sub - adults and adults were 75.5% in wet season. Juveniles, sub adults and adults of Penaeus monodon from 8.33 grams to 250 grams and Penaeus indicus from 8.33 grams to 58 grams and juveniles less than 8.33 grams were caught during the sampling period. Significant difference (p < 0.05) was observed between months and seasons (dry and wet seasons) with more individuals of Penaeus monodon and Penaeus indicus in March and April. In the months of January to February (the dry season) juveniles of less than 8.33 grams dominated the catch by 80.6% and the largest by 20.4% while in March to April the (wet season) the largest size of greater than 8.33 grams dominated the catch by 75.5% and juveniles of less than 8.33 grams by 24.5%. Water temperature, sediment organic matter and grain size distribution showed no correlation ( p > 0.05 ) with prawn distribution. All categories of Penaeus monodon and Penaeus indicus of larger than 8.3 grams and less than 8.3 grams showed a negative correlation (r =0.425, p < 0.05) with salinity in transect C (06 0 04'S ) and D (06 0 06'S ) while the number of juveniles of less than 8.33 gram of Penaeus monodon and Penaeus indicus showed a positive correlation (r=0.435 p < 0.05) with salinity in transect B (06 0 02'S ) . The data of exported processed prawns, harvested by artisanal prawn fishers from estuaries country - wide, noted as F1 generation were collected and based on calculation assuming that F1 generation is not harvested, t he number of individuals of F2 generation of Penaeus monodon and Penaeus indicus was projected. T he number of individuals of F2 generation ranged from 9.8 x 10 10 to 1.5 x 10 11 and 2.7 x 10 11 to 4.2 x 10 11 which in terms of kg is equivalent to a ratio of 1:60 to 1:137 and 1:60 to 1:137 of Penaeus monodon and Penaeus indicus respectively. The study found that salinity affects distribution and the estuary contains all categories of prawns (including breeders) particularly during the peak prawn fishery season of the year, hence, a temporal closure of the estuary from fishing by artisanal prawn fishers is proposed to be implemented from March to April (wet season) to prevent overharvesting of spawners in order to enhance inshore prawn recruitment and stock recovery. |
| Year | 2013 |
| 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) | Gallardo, Wenresti; |
| Examination Committee(s) | Yakupitiyage, Amararatne;Dabbadie, Lionel;Shrestha, Rajendra; |
| Scholarship Donor(s) | Government of Tanzania; |
| Degree | Thesis (Ph.D.) - Asian Institute of Technology, 2013 |