Fish Bulletin No. 71. Growth of the Sardine, Sardinops caerulea, 1941–42 Through 1946–47
- Author(s): Phillips, Julius B;
- et al.
Starting with the 1941–42 sardine season, a comprehensive age-reading program on the Pacific sardine or pilchard, Sardinops caerulea, was undertaken along the Pacific Coast of North America. These readings were based on scales from fish in the commercial catch with collections made by the Fisheries Research Board of Canada, the Washington State Department of Fisheries, the Fish Commission of Oregon, the California Division of Fish and Game and the U. S. Fish and Wildlife Service. The actual age interpretations were made jointly by the members of the latter two agencies and were published by Felin and Phillips (1948). Tables 1 – 6, reproduced from Felin and Phillips, list the number of fish, mean length and standard error of the mean for each year-class for each season, 1941–42 through 1946–47, by region of catch. In addition, Table 7 lists the number of fish and mean length for each age during the period 1941–42 through 1946–47, combined. In the presentation of figures that follow, no averages have been plotted for any year wherein fewer than 10 fish are represented. The left-hand vertical scale of each figure shows the body length2 in millimeters, while the righthand vertical scale shows the corresponding total length in inches. The horizontal scale at the bottom of each figure lists the actual number of observed rings and also the corresponding approximate age that each ring represents. As age is estimated from the number of annual rings present on the scale, 0-ring fish are those that are in their first year of life before the first winter ring is formed and 1-ring fish are those that have formed one winter ring between late fall and early spring, etc. Thus, a fish which is caught in the winter fishery and shows one annulus well inside the margin of the scale is in its second year of life. Since the commercial sardine fishery along the Pacific Coast is conducted almost entirely during the late summer, fall and winter months, the actual ages of the fish are approximately one year more than that indicated by the number of rings. Even though a second annulus has formed recently during a current winter, for example in a scale that already has one annulus formed during the previous winter, that fish is still referred to as a 1-ring fish, and the second annulus is indicated as "forming" or "new" until the end of that season. The following general observations concerning the life-history of the sardine are reviewed as an aid in interpreting the results of this study: This species ranges from southern Alaska to Cape San Lucas and into the Gulf of California. However, there is strong evidence that sardines found in southern Lower California and the Gulf of California constitute a separate population which rarely intermingles with the northern population but that a considerable, and perhaps variable, amount of interchange takes place throughout the range of the northern population from Alaska to Pt. San Eugenio in central Lower California. Exploratory work indicates that spawning may occur throughout the range of the sardine population, usually 50 to 200 miles offshore, but that the heaviest concentration is off Southern California. In this region, the spawning season extends from about January through June with a peak in April. Important nursery grounds are known off Southern California and Lower California and nursery areas of lesser importance may extend as far north as British Columbia. The young that result from the spring spawning in Southern California waters may remain on the nursery grounds in Southern California and Lower California for six months or a year. In their second year, if not earlier, they exhibit some northward movement and the extent of this northward movement increases year by year, with the largest and oldest fish eventually reaching the waters of the Pacific Northwest. A study of the size composition of samples and of tagging results indicates extensive migrations for a large portion of the stock, the largest and oldest fish undertaking the greatest movements. An influx of large fish into the Pacific Northwest fishery in the summer is followed by the appearance of these large fish in the California fishery in the winter preceding the spring spawning season. (Clark, 1935, 1940, 1947; Clark and Janssen, 1945; Hart, 1934, 1943; Scofield, 1934.)