Sardine Eggs Research Articles

A STATISTICAL STUDY OF THE ESTIMATION OF ABUNDANCE OF SARDINE (SARDINOPS CAERULEA) EGGS1

The reliability of the estimation of abundance of sardine (Sardinops caerulea) eggs is examined from two points of view. Analysis of egg observations collected on spawning surveys off southern California in 1941 indicates that the counts are consistent with the hypothesis that the egg population is distributed according to the negative binomial contagious distribution. Calculation of 95% confidence limits shows that the cruise estimates are subject to a variation of one‐half or double the estimate on the average. A seasonal estimate is probably subject to wider variation than the cruise estimates. Sardine egg observations collected from a 400 square mile grid of 25 stations off Baja California in 1952 over five days show important time and spatial variations. The coefficient of variation of an estimate of abundance of the egg population within the grid for the five day period from a single observation is estimated to be 31.1. The corresponding coefficient of variation of a sum of 40 counts from the grid is 4.9. The implications of this variability for the design of egg sampling surveys are discussed.

A note on the relations of certain parameters following a logarithmic transformation

The logarithmic transformation has been used in the statistical analysis of certain marine biological data. Parameters calculated from the transformed distributions have been used in the description of the observations, but it appears that some of the mathematical procedures adopted have not been fully understood.Winsor & Clarke (1940) have analysed data from plankton hauls. The problem considered by them was the determination of the variability in numbers of animals caught by repeated hauls through the same body of water. The raw data were characterized by a constant coefficient of variation, i.e. the variability in catch was proportional to the size of the catch. By transformation from the actual numbers caught to their logarithmic values, it was possible to equalize the variances and to apply the method of analysis of variance to esti-mate the variability due to the different sources. Finally, an estimate of the coefficient of variation was obtained from the logarithmic values. Their method of estimation was quoted by Snedecor (1946, p. 451) and was employed by Barnes & Bagenal (1951) in their study of repeated trawl hauls. Barnes & Bagenal also calculated confidence limits for comparison of observations following the method of Silliman (1946) in his work on pilchard eggs. These methods seem to be based on a misunderstanding of the nature of a trans-formation. The formal relation between the variance of such transformed data and the coefficient of variation of the untransformed data follows from the moments of the ‘log-normal’ distribution, given first by Wicksell (1917). From these moments it will be shown that the method given by Winsor & Clarke is mathematically unsound.

The Spawning of Mackerel, Scomber Scombrus L., and Pilchard, Clupea Pilchardus Walbaum, in the Celtic Sea in 1937–39

The distributions of mackerel eggs and young stages, pilchard eggs, the siphonophore Muggiaea atlantica and the chaetognaths Sagitta elegans, S. setosa, S. serratodentata and 5. lyra in the Celtic Sea in March 1939, April, May-June 1937, 1938 and 1939 and July 1937 and 1938 are described, together with notes on the hydrological conditions in April 1937, 1938 and 1939, May-June 1939 and July 1938.Mackerel spawning started in mid-March, rapidly reached a maximum in mid-April, declined gradually through May and June and was very slight at the end of July.The changes in intensity of spawning are accompanied by a continuous shift eastward and slightly northward of the locus of spawning. In March spawning occurred in a small area at the western edge of the Continental Shelf only. In mid-April it was spread over the greater part of the Celtic Sea, with the main activity concentrated in two centres—to the south of Ireland and to the west of the mouth of the English Channel. By May-June it had shifted farther to the east and occupied the central area of the Celtic Sea. In July there was no spawning to the westward of the Scilly Isles.The spawning area of the mackerel appears to be confined to the shallow waters over the Continental Shelf.No mackerel young stages were found in March. Small numbers occurred in April (maximum 174). They were abundant in May-June (maximum 8239), and very scarce in July (maximum 20).The distribution of young stages closely follows the movement of spawning during the season.