A 250-YEAR HISTORY OF PELAGIC FISH ABUNDANCES FROM THE ANAEROBIC SEDIMENTS OF THE CENTRAL GULF OF CALIFORNIA

Abstract

The recent appearance of significant numbers of northern anchovy in the Gulf of California, along with the recent decline in sardine biomass, has prompted the fishing industry, agencies of the Mexican government, and the research community to ask whether similar events have occurred in the past. Are these events connected, and are they part of some long-term pattern? In order to answer such questions, we sampled and counted the fish scales in an 85-cm box core from the anaerobic varved sediments of the central Gulf of California. This core was collected from an area underlying one of the principal sardine spawning regions of the gulf. On the basis of these counts, we reconstructed time series of scale-deposition rates for Pacific sardine, northern anchovy, Pacific mackerel, Pacific hake (or a close variant), and an undifferentiated group of myctophids. The time series are resolved into 10year sample blocks and extend from approximately 1730 to nearly 1980. These reconstructions show a strongly negative association between the presence of sardines and anchovies, with anchovies dominating throughout the nineteenth century, and with only two important peaks of sardine scale deposition-one in the twentieth century and one at the end of the eighteenth century. Both the mackerel and the myctophid group vary more like sardines than like anchovies (with the hake intermediate between anchovies and sardines). This suggests an overall coherent pattern in changing ecosystem structure that operates over a period of about 120 to 140 years. By comparing the sardine and anchovy series from the Gulf of California to information from the California Current, we can examine this variability within a geographic as well as a temporal framework. Reference to the Northern Hemisphere air temperature adds another dimension to our interpretations of the inferred variability. The regional differences and relations to climate suggest that the populations (or stocks) of both species from the dif