A Case Study of Sampling Strategies for Estimating the Length Composition of Commercial Catches: The Sri Lankan Shrimp Trawl Fishery

Crustaceana ◽  
2011 ◽  
Vol 84 (12-13) ◽  
pp. 1581-1591 ◽  
Author(s):  
Gunnar Stefánsson ◽  
M. D. S. T. De Croos
Keyword(s):  
Survey Design ◽  
Total Variance ◽  
Sampling Scheme ◽  
Small Scale ◽  
Sampling Variance ◽  
Length Frequency ◽  
Commercial Catch ◽  
Frequency Distributions ◽  
Trawl Fishery ◽  
Shrimp Trawl

AbstractScientific surveys are expensive and often not feasible for artisanal and small-scale fisheries. Biological samples from the commercial catch are the principal source of information in monitoring these fisheries. A pilot sampling scheme of commercial craft conducted during a four-month period on the artisanal coastal shrimp trawl fishery in Sri Lanka revealed that the length compositions of two short-lived shrimp species (Metapenaeus dobsoni and Parapenaeopsis coromandelica), derived from commercial catches, showed high sampling variance and thus resulted in considerable noise in the length-frequency distributions. An analysis of variance components revealed that the total variance was mainly governed by the variance due to the number of samples. Hence, a more effective survey design was to collect samples from as many fishing craft as possible rather than increasing the sample size. The observed total variance of 0.4 based on measuring 43 109 individuals of M. dobsoni from 4 boats per sampling day (∼300 individuals/sample) in the pilot sampling was revised with the new sampling scheme, which reduced the variance to 0.2 based on measuring only 28 800 individuals from 6 boats per sampling day (∼150 individuals/sample). The length-frequency distributions constructed with the revised sampling scheme resulted in less noise in the monthly progression of modes.

Modelling the spatio-temporal bycatch dynamics in an estuarine small-scale shrimp trawl fishery

2019 ◽  
Vol 219 ◽  
pp. 105336 ◽  
Author(s):  
Gabriela A. Rezende ◽  
Marie-Christine Rufener ◽  
Ileana Ortega ◽  
Vinicius Mendes Ruas ◽  
Luiz Felipe C. Dumont
Keyword(s):  
Small Scale ◽  
Trawl Fishery ◽  
Shrimp Trawl ◽  
Spatio Temporal

scholarly journals Influence of Environmental Knowledge on Small Scale Women Farmers Adoption of Conservation Agriculture Nakuru County, Kenya

2019 ◽  
pp. 1-7
Author(s):  
Eliud Garry Michura ◽  
Anne Jerotich Michura
Keyword(s):  
Survey Design ◽  
Conservation Agriculture ◽  
Environmental Knowledge ◽  
Women Farmers ◽  
Small Scale ◽  
Agricultural Practice ◽  
Conventional Agriculture ◽  
Frequency Distributions ◽  
Bonferroni Test ◽  
Small Scale Farmers

Adoption of any technology especially in agricultural practices depends on environmental dynamics. This paper evaluated the influence of environmental knowledge on women small-scale farmers on adoption of conservation agriculture (CA) in Nakuru County. Kenya as one of the developing countries in Africa faced with numerous problems particularly food insecurity, hunger, poverty, diseases and biodiversity loss as a result of conventional agriculture practiced under poor backdrop of environmental knowledge. To alleviate all these problems mentioned above, the alternative method of agricultural practice should now aim at improving conservation agriculture which was discouraged long time ago. But environmental Knowledge to adopt conservation agriculture is needed as better option for maximum agricultural yields and protection of the environment. It is claimed that, CA adoption in Nakuru County by women small-scale farmers was low and there was inadequate research documentation regarding this claim. To establish the claim whether true or not, find out why CA adoption was low in the study area, the research sampled three sites; Naivasha, Rongai and Njoro selected purposefully for differences in ecological characteristics. The sample size of 360 women farmers were randomly selected from a target population of 120,000 women farmers of which, 120 were selected from each of three Sub Counties.  Descriptive survey design using structured questionnaires; interview schedule, personal observation and focus group discussion were used to collect data. Statistical package for social sciences (SPSS version 20) was used in the data processing and analysis. Descriptive statistics; frequency distributions, means, proportions, percentages and inferential statistics; Chi-square, ANOVA, Bonferroni test at alpha value (p < 0.05) level were employed to test the hypothesis. The findings concluded that knowledge of the environment influenced women small scale farmers’ adoption of CA and that CA adoption uptake was low. Recommendations; Policy and decision makers use the results to develop land and agricultural policies, provide incentives to promote small-scale women farmers, use new emerging technologies to speed up knowledge on adoption of CA in order to boost food security and conservation of the environment in Nakuru County and Kenya.

Reference points for the length-based indicator Lmax5% for use in the assessment of data-limited stocks

2019 ◽  
Vol 76 (7) ◽  
pp. 2125-2139 ◽  
Author(s):  
Tanja Miethe ◽  
Yves Reecht ◽  
Helen Dobby
Keyword(s):  
Life Histories ◽  
Stock Assessment ◽  
Reference Points ◽  
Length Frequency ◽  
Frequency Distributions ◽  
Simulation Tools ◽  
Spawning Potential Ratio ◽  
The Mean ◽  
Commercial Sources ◽  
Length Frequency Data

Abstract In the absence of abundance indices from scientific surveys or commercial sources, reliable length frequency data from sampled commercial catches can be used to provide an indirect assessment of fishing mortality. Length-based indicators are simple metrics which describe length frequency distributions. The length-based indicator Lmax5%, the mean length of the largest 5% of individuals in the catch, combined with appropriately selected reference points, can be used to evaluate the presence of very large individuals in the catch and hence determine exploitation level. Using analytical per-recruit models, we derive reference points consistent with a spawning potential ratio of 40%. The reference points depend on the life history parameters for natural mortality, maturity, and growth (M, Lmat, L∞, k, CVL∞). Using available simulation tools, we investigate the sensitivity of the reference points to errors in these parameters and explore the usefulness of particular reference points for management purposes for stocks with different life histories. The proposed reference points are robust to uncertainty in length at first capture, Lc, and take into account the maturation schedule of a species. For those stocks with high M/k ratios (&gt;1), Lmax5%, combined with the appropriate reference point, can be used to provide a data-limited stock assessment.

Size Distributions and Growth of the Fan-shell Pinna bicolor Gmelin (Mollusca : Eulamellibranchia) in South Australia

1979 ◽  
Vol 30 (1) ◽  
pp. 25 ◽  
Author(s):  
AJ Butler ◽  
FJ Brewster
Keyword(s):  
South Australia ◽  
Adductor Muscle ◽  
Size Distributions ◽  
Limited Data ◽  
Length Frequency ◽  
Age Classes ◽  
Frequency Distributions ◽  
Growth And Survival ◽  
Random Samples ◽  
Variable Success

Fourteen random samples of Pinna bicolor were collected over a period of 31 months from 6 m depth in Gulf St Vincent off Edithburgh, South Australia. The length-frequency distributions suggest that: P. bicolor larvae settle in spring but with variable success; growth of newly settled young is rapid over summer; by age 1 year their modal shell length is about 20 cm; by age 2 it is about 26 cm; they may survive substantially longer than 3 years so that a length-class of mode c. 35 cm is always present and is composed of several age-classes not necessarily equally represented. These suggestions are corroborated by limited data on adductor muscle scars, the development of epibiota on the shells, and the growth and survival of tagged animals over 9 months.

Composition and diversity patterns of megafauna discards in the deep-water shrimp trawl fishery off Brazila

2013 ◽  
Vol 83 (4) ◽  
pp. 804-825 ◽  
Author(s):  
J. A. A. Perez ◽  
B. N. Pereira ◽  
D. A. Pereira ◽  
R. Schroeder
Keyword(s):  
Deep Water ◽  
Diversity Patterns ◽  
Trawl Fishery ◽  
Shrimp Trawl

scholarly journals Actual conditions of discards of by-catch from small-scale trawl fishery in Ariake Sea

2003 ◽  
Vol 69 (3) ◽  
pp. 330-336 ◽  
Author(s):  
YOSHIO HIRAI ◽  
HIDEYUKI NISHINOKUBI
Keyword(s):  
Small Scale ◽  
Ariake Sea ◽  
Trawl Fishery ◽  
By Catch

Application of the otolith weight – age relationship for the pilchard, Sardinops sagax neopilchardus

1995 ◽  
Vol 52 (4) ◽  
pp. 657-664 ◽  
Author(s):  
W. J. Fletcher
Keyword(s):  
Maximum Size ◽  
Steady Increase ◽  
Average Weight ◽  
Fish Length ◽  
Natural Mortality ◽  
Length Frequency ◽  
Age Classes ◽  
Frequency Distributions ◽  
Southwestern Australia ◽  
Sardinops Sagax

Adult pilchard (Sardinops sagax neopilchardus) from southwestern Australia held in fish cages for 1 year showed minimal increase in mean length but a steady increase in mean otolith weight (1.61–1.83 mg); this increase (0.22 mg) closely parallels the previously calculated mean difference between adjacent age classes (0.24 mg). Modes in otolith weight frequency distributions of fishery-caught pilchards, previously suggested as corresponding with separate year classes, generally persisted and progressed through subsequent samples. By contrast, fish length frequency distributions of these samples showed no consistent modal progression. The average weight of otoliths for year classes 2–8 were used to calculate growth rates: following sexual maturity, at age 2, males grew to a significantly smaller maximum size than females (L∞ = 162 and 172 mm respectively). The otolith weight – age relationship, validated by following a cohort of unusually low abundance as it moved through the fishery, indicated that recruitment to the fishery generally began at age 2 but was not complete until age 4. These data have been successfully used in forecasting the catch rate of the fishery up to 2 years in advance and providing an estimate of the rate for natural mortality of 0.43.

An Investigation of Coping Strategies Adopted by Small-Scale Sugarcane Growers in Bungoma County, Kenya

2021 ◽  
Vol 3 (1) ◽  
pp. 89-102
Author(s):  
Protas Fwamba Khaemba ◽  
Philomena Muiruri ◽  
Thomas Kibutu
Keyword(s):  
Coping Strategies ◽  
Survey Design ◽  
Primary Data ◽  
Coefficient Of Determination ◽  
Farm Income ◽  
Small Scale ◽  
Sugarcane Farming ◽  
Income Generating Activities ◽  
Household Heads ◽  
By Products

This paper reports on one of the findings of a study undertaken to investigate the coping strategies used by small-scale sugarcane growers in Bungoma County, Kenya. A descriptive survey design was used. A multi-stage sampling procedure was employed in the selection of the divisions, villages, key respondents, and sugarcane farmers to be interviewed. Primary data were collected using questionnaires from 100 small-scale sugarcane growers’ household heads from Bumula Sub-County. Data were collected during the month of December 2016.  Qualitative data collected were analysed thematically. Quantitative data was analysed using regression in SPSS version 23 and Microsoft Excel. Results from small-scale sugarcane farmers in Bumula Sub-County revealed a declining farmers’ participation in sugarcane farming activities in the area. Coping strategies identified included off-farm income-generating activities, sale of sugarcane by-products and non-contracted cane farming. Significance test qualification was based on a percentage of adjusted R2 and within 0.3 to 0.7 ranges for Beta weight value.  The correlation coefficient (R-value) for the model was 0.362, indicating a moderately positive relationship between variables. The coefficient of determination (R2) was found to be 0.284 (28.4%). Adopted coping strategies accounted for 28.4% variability in the declining farmers’ participation in sugarcane farming. This result suggests the existence of other factors that explain the remaining 71.6% of the variation in the declining farmers’ participation. Farmers should enhance both on-farm and off-farm income-generating activities, sugarcane by-products value addition, and non-contracted cane farming in order to reverse the outcome and result in an enhanced farmers’ participation in sugarcane farming activities by 36.2%

Age, stucture, growth rates and movements of sea mullet, Mugil cephalus L., and Yellow-eye Mullet, Aldrichetta forsteri (Valenciennes), in the Swan-Avon river system, Western Australia

1981 ◽  
Vol 32 (4) ◽  
pp. 605 ◽  
Author(s):  
CF Chubb ◽  
IC Potter ◽  
CJ Grant ◽  
RCJ Lenanton ◽  
J Wallace
Keyword(s):  
Growth Rates ◽  
River System ◽  
First Year ◽  
Length Frequency ◽  
Frequency Distributions ◽  
Using Data ◽  
The Times ◽  
First Year Of Life ◽  
Breeding Seasons ◽  
System 1

The age structure, growth rates and movements of M. cephalus and A forsteri in the Swan-Avon river system have been investigated using data obtained from beach seining and gill netting carried out between February 1977 and June 1980. Length-frequency data and scale readings show that the populations of both species consist predominantly of 0+ and 1 + fish. From the times when the smallest fry (20-30 mm) were present in the lower part of the river system, and from the condition of the gonads of older fish, the breeding seasons of the sea and yellow-eye mullets have been estimated as extending from March to September and from March to August respectively. The bimodality or polymodality exhibited by the length-frequency distributions for the 0 + year classes suggest that in both species groups of individuals spawn at slightly different times. The range of mean total lengths and weights of animals caught in May near the end of the first year of life was 178-222 mm and 64-119 gin M. cephalus and 136-154 mm and 19-30 g in A. forsteri, which shows that the growth of each of these two species of mullet is relatively very rapid in the Swan-Avon river system. 1 + and 2 + fish tend to leave the estuary for varying periods. Although 0+ fish of both species utilized the shallow banks of the estuary throughout the year. the sea mullet moved further upstream and were not as consistently abundant in the lower estuary. Since 0+ yellow-eye mullet 40-100 mm long were also abundant in marine coastal waters between January and May. and sea mullet of comparable age were rarely observed in these regions, it would appear that M. cephalus is the more estuarine-dependent of the two species. Commercial catches of M. cephalus were greater than those of A. forsteri. This feature can be related in part to the much faster growth rate of M. cephalus, which results in a larger proportion of its youngest year classes reaching the minimum legal size for capture prior to the time when they leave the estuary in large numbers.

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