When working with length frequency date, we often need to compute the mean weights of the fish in the various classes. This article outlines one of the methods used.
Interacting social and ecological processes shape productivity and sustainability of island small-scale fisheries (SSF). Understanding limits to productivity through historical catches help frame future expectations and management strategies, but SSF are dispersed and unaccounted, so long-term standardized data are largely absent for such analyses.
When different strains or breeds of a particular species are available, the best choice is seldom immediately obvious for producers. Scientists are also interested in the relative performance of different strains because it provides a basis for recommendations to producers and it often stimulates the conduct of work aimed at unraveling the underlying biological mechanisms involved in the expression of such differences. Hence, strain or breed comparisons of some sort are frequently conducted.
Aquaculture pond experiments, like agricultural crop trials, are often designed according to the statistical rules of replication and randomization: several treatments are applied to a number of experimental units (in this case: ponds) after which a certain characteristic (e.g., yield) is measured in every pond. Other factors with a possible effect on the measured characteristic are held at the same constant level as much as possible so as not to disturb treatment effects. Analysis of variance (ANOVA) is used to compare the treatments.
Fish and other aquatic animals contribute to the food security of citizens of developing countries, both as a source of income and as a component of healthy diets, yet fishing is not currently captured in most integrated household surveys. This sourcebook provides essential technical guidance on the design of statistical modules and questionnaires aimed at collecting fishery data at the household level.
Monthly length-frequency data of spiny lobster Panulirus homarus collected from the south coast of Sri Lanka during 1988-1990 were analyzed to estimate von Bertallanfy growth parameters. The asymptotic lengths estimated using Wetherall plots were 322 mm and 315 mm total length for the males and females, respectively. Using o' values of 3.53 for males and 3.61 for females, the growth constant (K) was estimated as 0.21 year super(1) and 0.27 year super(1) for the males and females, respectively.
Parameters and related statistics of the length-weight relationship of the form W=aL super(b) are presented for 72 species of fish caught in the area of the Itaipu Reservoir in Parana, Brazil. The b values varied between 2.34 and 3.35, with the mean b=2.986 (s.d.=0.230) not significantly different from 3.0 (df=7, p=0.05).
Growth parameters and mortality rates were estimated from length-frequency data sampled in 1982, using the FiSAT software, for three coral reef fish species, the surgeon fish (Ctenochaetus striatus), the damselfish (Stegastes nigricans) and the squirrel fish (Sargocentron microstoma) in Tiahura Reef, Moorea Island, French Polynesia.
Empirical relationships were established linking estimates of the instantaneous rate of natural mortality (M), the von Bertalanffy growth parameters, L sub( infinity ) (or W sub( infinity )) and K, and annual mean water temperature in 56 stocks of Mediterranean teleosts fish. It is suggested that these relationships generate for these fish more reliable estimates of M than the widely-used model of Pauly (1980, J. Cons. CIEM 33(3):175-192), which was based on 175 fish stocks, but included only five stocks from the Mediterranean.
Details are given of the modification of Munro's method for the estimation of natural mortality from length-frequency data. An example is given of application of the method using length-frequencies of brown trout (Salmo trutta ) from Vebre River, France, showing the difference between Munro's original method and the proposedmodification.