Cefas Historic Secchi Depth Measurements

Secchi depth measurements, collected for studying the effects of the light climate on pelagic fish (e.g. fish school position in the water column compared to the depth of penetration of light); The dataset comprise 470 Secchi depth measurements collected in 1931, 1937, 1946-1950, 1968. The coordinates of each observation were generally not indicated in the logbooks and were derived from the associated station-sheets. Occasionally the exact coordinates were not specified but only the location of the sampling station was indicated; therefore the location name (e.g. Smiths Knoll) was used for deriving approximate coordinates. In other cases, the location was expressed as, for example, ‘4 miles SE of Smiths Knoll’; in such cases approximate coordinates were derived associating coordinates to Smiths Knoll and then using Google Earth for moving 4 miles SE of this position. Times of Secchi depth measurements were not available for each measurements, as well as weather condition description. Secchi depth measurements were converted from fathoms (or feet) into meters.