CalCOFI Reports, Vol. 11, 1967 - California Cooperative Oceanic ...

REPORTS VOLUME XI, 1 JULY 1963 TO 30 JUNE 196613ithe sediment, for example a high contribution ofland-derived detritus during a pronounced rainyseason, then a yearly lithologic pattern may be preserved.The existence of anaerobic conditions within thesediments must also contribute towards the preservationof organic remains. Anaerobic bacteria are unableto effect the breakdown of organic matter as completelyas aerobic bacteria, and complex organic moleculesare relatively immune from bacterial attack.Furthermore, anaerobic sediments appear to have arelatively high pH of about 8.0 thus insuring thepreservation of inorganic carbonates and apatites,the latter being an important constituent of fish bonesand scales, the former of fish otoliths.The core samples used for this study were fourcores obtained in the east central part of the basin,34' 14' N; 119" 58' W, at a depth of 570 meters.The cores average 90 em in length and have a combinedarea of 90 em2. The report of Emery and Bray(1962) provides the basis for estimating the age atthe bottom of these cores at about 1000 years. Thetime equivalent of 1 em, the subsampling distance,is then roughly ten years. For the purposes of thispaper it will be assumed that a constant rate ofsedimentation has prevailed. Preliminary examinationsof laminae (yearly lithologic patterns) presentin these sediments indicate this is a reasonable assumption.The general procedure used in recovering fish scalesand other coarse debris from sediment was the follow-ing. The core was exposed and the main lithologicfeatures noted. The core was then cut into one centimeterthick slices parallel to the stratification. Theindividual slices were placed in a 10 percent hydrogenperoxide solution for about one half hour in orderto disaggregate the sediment. The resulting slurrywas wet-screened through 0.5 and 0.06 millimetermesh screens. Material such as scales, bones, and otoliths,was retained almost exclusively on the coarserscreen. The scales were manually picked under a lowpowerbinocular microscope and were permanentlymounted on glass slides. Identification was made bycomparison with a reference collection of scales assembledfrom the Scripps Institution of OceanographyFish Collection.The raw data from these cores is a centimeter bycentimeter tabulation of numbers of scales. Threespecies have been identified and counted : the Pacifichake, Merluccius productus, the Pacific sardine,Sardiyaops caerdea, and the northern anchovy, Engraulismordax. In these cores the three speciesaccount for 80 percent of the total scales.By means of the correlation of lithologic patternswithin the cores the data from the four cores havebeen projected into a single composite core. Thisprocedure should emphasize scale abundance patternsover distances greater than the arbitrary sub-samplingdistance of 1 em. On the other hand, correlation errorsshould tend to mask abundance variations occurringat or near this distance. That is to say only abundancevariationi that :ire consistent for equivalent time pe-Numbers of ScalesPacific sardine Northern anchovy Pacific hake0 5 10 15 0 5 10 15 20 0 i0 20 25 30 35ICm30I40E FIFIGURE 2. A plot of numbers of scoles versus the core depth in centimeters. The occurrence of unusually high scale counts at a few centimeterlevels in the case of the Pocific hoke represents o high scale concentration in one of the four cores. In such cases the mean of the three othercores is taken to be more representative of the scale concentration at that level.