RELATIONSHIP OF CALIFORNIA SARDINE ( SARDINOPS SAGAX ) ABUNDANCE TO CLIMATE-SCALE ECOLOGICAL CHANGES IN THE CALIFORNIA CURRENT SYSTEM

Empirical orthogonal function (EOF) analyses link sardine abundance to large-scale processes of the California Current ecosystem. These analyses of the California fish and invertebrate landings (CACom) detect two patterns of variability (EOF1 and EOF2), which indicate that climate-scale changes in CACom species composition occurred during 1930–2000. California sardine landings are related to EOF1 (nominal correlation coefficient, r ’ > 0.9), linking fluctuations in sardine abundance to many other California Current species. Logetransformed sardine landings are closely related (r ’ > 0.9) to accumulated sea surface temperature anomalies at La Jolla, California and to accumulated equatorial process indices (r ’ ≥ 0.8). We found that the length of time that physical anomalies persist is related exponentially to the effects these physical processes will have on sardine abundance. When the sardine series is extended backward to 1890, using sardine-scale deposition rates as an abundance proxy and the equatorial indices as physical proxies, the relationships between sardine abundance and the physical environment holds (r ’ ≥ 0.8). INTRODUCTION The abundance of California sardines, or pilchards, (Sardinops sagax) off the west coast of temperate North America fluctuates, and in the 1930s and 1940s sardine populations were the source of the largest fishery of the western hemisphere (Marr 1960; Jacobson and MacCall 1995; Norton and Mason 2003). The largest landings of sardines were in California ports, where shore-based landings exceeded 400,000 metric tons (t) in each year from 1934 to 1944. California sardine populations declined sharply in the later 1940s and continued to decline into the early 1970s when annual landings were less than 10 t (Mason 2004). In 1967, a moratorium was placed on the directed California sardine fishery, but 15% by weight was allowed in mixed-species landings. In 1969, landings for dead bait were limited to 227 t, and in 1974 recovery plans were developed to allow a directed fishery of 907 t when the California spawning population was estimated to be more than 18,144 t. Increases in the harvest quota would be allowed if the spawning population continued to increase (Conser et al. 2004). In the late 1970s and 1980s, the California sardine population increased due to environmental changes (Jacobson and MacCall 1995), and their landings increased from 388 t in 1986 to more than 56,000 t in 1999 and 2000 (Mason 2004). California state laws require that all sales of fish and invertebrates from primary harvesters (fishers) to fish dealers include the species (or species groups) and weight landed on the sales receipts. The summaries of these sales receipts for catches within the California Fishers Harvest Environment (CFHE), tabulated by the California Department of Fish and Game, were converted to Internet accessible formats by the Pacific Fisheries Environmental Laboratory (http://www.pfeg.noaa.gov/ products/las.html). These records (CACom) provide information about the availability of the commercially important components of the California Current System (CCS) ecosystem (Norton and Mason 2003, 2004). Empirical Orthogonal Function (EOF) analysis of these records showed that EOF1 and EOF2 explained more than 45% of the variance in composition of 29 species that made up more than 85% of the total CACom landings throughout the 1930–2000 period. When timevarying coefficients (principal components) of these EOFs, C1 and C2, were compared to indices of physical change in the CFHE and to time series representing fishing effort and market factors, they were found to be more closely correlated to the environmental indices than to fishing effort or market indices. Landings composition changes shown by C1 were closely related to persisting anomalous conditions in the CFHE as indicated by several physical environmental data series, including sea surface temperature (SST) measured at La Jolla, California (Norton and Mason 2003). The purpose of this study is to investigate the relationship of sardine landings to the physical and biological environments of the CFHE, which is that part of the CCS extending from the coast of California to 400–600 km offshore between 32.5 ̊ and 42 ̊N latitude (Norton and Mason 2003). We build on the observations that the loge of California sardine landings weight is strongly related to C1 (Norton and Mason 2004) and