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Some important parameters collected during the different studies were catch and effort data of the fish during landings in studies related to estimation of fish biomass Jiddawi, 1999. Others were areas fished, weather
conditions, the fishing duration and any other factors that could have an impact on the days fishing such as festival and cultural taboos in fishery descriptive studies Jiddawi and Stanley, 1999.
3.4.2 Instrumentation and techniques of data collection
Sampling techniques varied in the different studies. Whereas in the case of Jiddawi and Stanley 1999, the study involved standing at the landing site and recording details of each, Horst 1999 actually followed the fishermen
as an observer in their fishing boats to assess the performance of the dema trap fishery. In some instances specimen were bought from the fishermen for detailed studies of specific fish. These include the biological and
age and growth studies of the Indian mackerel Rastrelliger kanagurta, Jiddawi, 1999, the biological study of squid Mhitu, 1997 and during the study of the biology of the blue speckled parrotfish Leptoscarus vaigiensis
along the coast of Tanzania, Rubindamayungi, 1983.
Few instruments were employed in fishery studies apart from standard equipment such as the measuring board, the Vernier calipers, weighing scales and portable spring balance. In some several instances the fishing gears
were checked on their efficiency. For example the beach seine net was used as an equipment for catching fish in intertidal areas during the study of the nursery potential of the mangrove ecosystem Muhando and Ngoile, 1995,
Mahika 1992 used grid separators to reduce by catch in the Panaeid fishery. Hydrographical data, such as temperature, salinity and oxygen content were collected using reversible Nankeen water bottles which were
applied in different depths during fish resource surveys. Also, samples from the surface were collected by a buckets Iversen et al., 1985. Fish abundance was investigated acoustically using scientific sounders, integrators
and sonar equipment Iversen et al., 1985. Pelagic trawl hauls were carried out either to identify scattering layers or to investigate the surface layer for fish. Demersal trawl hauls were placed at random in trawlable areas and fish
biomass estimations were made according to the swept area method Anon, 1982, Iversen at al., 1985; 1983; Msumi, 1988.
3.4.3 Sampling frequency and time of collection
Sampling frequency and time of collection varied depending on the study. Data collection in most of the fisheries studies requiring landings data was done normally during the rising tide when the fishermen are returning from
their days fishing. During the monitoring study of the artisanal fisheries of Matemwe and Mkokotoni for example the sampling was done routinely twice during the neap tides and twice during the spring tides in a month due to
the differences in fishing effort and landings during the two tides. Also, monitoring was conducted throughout the year so as to get variations within the months. Within the same study detailed sampling was also done daily to
study fishing performance of selected individual fishermen over the different seasons.
In the case of the nursery potential of mangrove ecosystems study, sampling was conducted during spring tides when the water was low enough to use the beach seine and to be able to get some fish Muhando and Ngoile,
1994. During underwater visual surveys of the fish distribution in algal farms observations and sampling was done during high tides to ensure good visibility and easy observation Svanson and Bergman, 1998. Sampling
was done during the day in case of daytime fishery, when the fishermen normally return from their fishing activities Coleman, 1998. Mgimwa, 1998 and at night in case of night fishing such as for the purse seine fishery
Jiddawi, 1999 and in the Wenge light attracted fishery at Kisakasaka Meyers, 1999.
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3.4.4 Data analysis methods and procedure
In most of the studies, data was analysed using standard procedures for fisheries studies. This ofcourse depended on the aspects that were being examined. For example, Length weight relationship of fish were examined
following Le Cren 1951, e.g. Rubindamayugi, 1983,; Mhitu, 1987; Mgimwa, 1988 and Jiddawi, 1999. Statistical tests were analysed as elaborated in Zar 1984, e.g. Mhitu, 1987, Mgimwa 1988. Growth and Mortality
estimates were done using the Fish Stock assessment programme of FAO, e.g. Jiddawi, 1999.
3.5 Quality, usefulness and reliability of data and information 3.5.1
