directions long before there were any industrial fisheries. The data for that are
anchovy and sardine scale-deposition rates in the sediments of anoxic basins, among
which the Santa Barbara Basin in the southern California Current is the best studied
(Baumgartner et al. 1992). This subsidence basin, just southeast of Point Conception,
California, has a flat-bottomed central pit at 580 m depth that is partly filled with
sediment. This is only very rarely flushed and generally remains anoxic with almost
no benthic macrofauna. Thus, there is little bioturbation, and the sediment retains
visible annual layers or “varves”. These are terrestrial sediment from winter runoff,
alternating with pelagic ooze from summer production. Over the past few thousand
years there have been occasional intervals with bioturbation, and there have been
some slumps. Thus, exact dating by varve counting becomes problematic below about
1100 yr BP, but various corrections give good approximate dating over several
thousand years. There are variations in scale counts between cores, and problems for
deeper levels of inadequate sample volumes (low counts and associated higher
variances). However, by counting only to 10-year resolution and doing some
averaging between cores, the picture emerges (Fig. 17.21) of substantial temporal
variability in both species.
Fig. 17.21 Time-series of (a) sardine and (b) anchovy scale abundance (as deposition
rates) in sediments of the anoxic Santa Barbara Basin from c. 300 CE to the present.
(^) (After Baumgartner et al. 1992.)