ABUNDANCE OF PELAGIC FISH DURING THE 19TH AND 20TH 



CENTURIES AS RECORDED IN ANAEROBIC 



SEDIMENT OFF THE CALIFORNIAS 



Andrew Soutar and John D. Isaacs^ 



ABSTRACT 



Anaerobic sediment preserves a chronographic record of the bioclimatological conditions in coastal 

 seas. Of the myriad elements within this record, the accumulation of pelagic-fish debris is of particular 

 interest. The deposition of scales of the Pacific sardine, the northern anchovy, the Pacific hake, the 

 Pacific saury, and the Pacific mackerel in the sediment of the Santa Barbara Basin, Alta California, 

 and the Soledad Basin, Baja California, is generally in accord with available population estimates. The 

 relation between scale deposition and population, when applied to the sedimentary record over the past 

 150 yr, suggests that major pelagic-fish productivity between 1925 and 1970 was substantially below 

 pre-1925 levels. 



Man in his search for an environmental perspec- 

 tive has unearthed a number of natural chrono- 

 graphic records. These include the well-known 

 growth rings of trees (Fritts, 1972), the deposition 

 of annual strata in the snowfields of Greenland 

 and Antarctica (Murozumi et al., 1969), the in- 

 cremental growth of coral and stromatolites 

 (Knutson et al., 1972; Panella et al., 1968), and the 

 formation of annual layers in certain lacustrine 

 and marine sediments (Seibold, 1958). 



Perhaps no richer records exist than those finely 

 laminated deposits encountered beneath the sea 

 in regions of anaerobic sedimentation. A web of 

 circumstance involving productivity and topog- 

 raphy serves to produce and protect such records, 

 but no factor can be more important than the ex- 

 clusion of burrowing animals from the sediment 

 by a persistently low dissolved oxygen concentra- 

 tion in the bottom water. Here such diverse and 

 informative fragments of the air-sea-land system 

 as the tests of the microplankton, skeletal and 

 integument debris from the nekton, air- and 

 river-borne detritus, natural radioisotopes, and 

 more recently, anthropogenic products fall in se- 

 quential association to a common resting place. 

 Undisturbed, these threads of information ac- 

 cumulate to form a remarkable sedimentary 

 chronicle combining the rhythmic pulse of the 

 seasons with the vagaries, trends, and inconsis- 

 tencies of ocean life, chemistry, and currents. 



Of the myriad elements within the anaerobic 

 sediment record, the temporal framework and the 

 distribution of pelagic fish scales at depth in the 

 sediment in the Santa Barbara Basin, Alta 

 California (Figure la), and in the Soledad Basin, 

 Baja California (Figure lb), compose a particularly 

 relevant set — relevant not only in relation to the 

 continuing importance of pelagic fish as a resource 

 off the Californias, but also as a potential indi- 

 cator of long-term productivity and change. Such 

 knowledge of ocean conditions within the broader 

 context of the North Pacific gyre and the Northern 

 Hemisphere climate can aid man in his search for 

 a rational interaction with his environment, guide 

 him toward a wise stewardship of marine re- 

 sources, and aid him in discriminating between 

 those changes that he produces by his interven- 

 tions and those that are a part of the natural order. 



Time in the laminated sediment of the Santa 

 Barbara Basin can be estimated through the se- 

 rial assignment of the year of deposition to each 

 laminae pair (Figure 2a). It was suggested that 

 the regular alternation of sediment density is a 

 direct response to the monsoonal climate affecting 

 southern California (Emery, 1960). Confirmation 

 of this and the laminae pair sequence as a yearly 

 depositional record has come through the correla- 

 tion of regional rainfall and sediment-laminae 

 patterns. 2 As indicated (Figure 3), the essentially 

 random pattern of southern California seasonal 



'Scripps Institution of Oceanography, University of California 

 at San Diego, La JoUa, CA 92037. 



Manuscript accepted June 1973. 



FISHERY BULLETIN; VOL. 72, NO. 2, 1974. 



^Soutar, A., J. D. Isaacs, P. A. Crlll. Recent paleoclimatology 

 and paleoecology of the Santa Barbara Basin. Unpubl. manuscr. 



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