Simulation of fishery-induced changes on the reproductive cycle of common sardine, Strangomera bentincki, off central southern Chile

Intense fishing mortality generates changes in marine populations and ecosystems, and an increase in the sensitivity to environmental changes. Fishery-induced demographic changes are the main mechanisms involved due to truncation of age structure of a population trough selective removal of larger and older fish from a population. As a consequence, changes in the seasonal spawning pattern can occur because larger and older fish tend to have a longer and more extensive reproductive activity than smaller and first-time spawners. This is the case of a small pelagic fish, known as the common sardine Strangomera bentincki, which supports an important fish activity off central southern Chile (33°S-41°30′ S). In this paper, fishery-induced changes on the seasonal reproductive cycle of common sardine were simulated through an age-structured population dynamics on a monthly basis. The fishery is dependent on the annual pulse of recruitment and fishing efforts are applied intensively on the juvenile fraction during the first half of each year. Thus, fishing mortality removes fast growing fish or fish recruiting earlier, and thereafter the age structure tends to be truncated, and as a consequence, slow-growing fish or late-recruiting fish could be selected in the population. A delayed peak in the reproductive cycle was observed in the gonadosomatic index during the period 2000–2010, as compared with the period 1993–1999. In addition, a change in the length composition of the catches was observed, supporting the results obtained with simulations. The fishery-induced changes on the reproductive cycle of common sardine can increase the sensitivity of the population to climate variability either matching or mismatching the reproductive cycle with favorable/unfavorable environmental variables for recruitment.