Egg cannibalism in the northern population of the Argentine anchovy, Engraulis anchoita (Clupeidae)

Abstract

Cannibalism by Engraulis anchoita on their eggs was investigated on the spring spawning ground of the northern population of the species during the 1993–1999 period. Egg distribution was patchy and egg cannibalism was only found in a limited number of fish. The maximum number of eggs found in a single stomach analyzed was 433. This value corresponded to 5.1% of the total number of eggs in the stomach of all fish sampled in 1993. Mean number of anchovy eggs per stomach ranged between 3.9 and 10.0 (mean S.E.: 1.5–5.1) for 1993–1996 and 1.3 (mean S.E.: 0.5) for 1999. Consumption of eggs over a 12-h feeding period represented, on average, 15–33% (mean S.E.: 6.2–20.1) of the total egg mortality within the study area in 1993–1996, but only 2% (mean S.E.: 0.8) in 1999. The mean abundance of copepods in the plankton samples (69,000 copepods/m 2), especially calanoids, in 1999 was higher than in previous years (6000–53,000 copepods/m 2). The same pattern was observed with the number of copepods ingested (400 copepods by fish in the 1993–1996 period and 1200 in 1999). Relationship between consumption rate and density of plankton eggs revealed a marked decrease in the egg cannibalism to low egg density values and an increase of that parameter with the increment of the plankton eggs. There was strong evidence of a decrease in egg cannibalism as copepod density increased. Our results indicate that not only intra-specific predation on anchovy eggs was high, but also anchovy egg cannibalism could be an extra source of energy when the principal food (calanoid copepods) is scarce. In areas where cannibalism was intense, that behavior supplied 91% of the daily energy necessary for reproduction.