Long-time spatio-temporal variations in anchovy (Engraulis ringens) biological traits off northern Chile: an adaptive response to long-term environmental change?

Analyses of the dynamics of exploited marine populations show that population variations and tendencies are as often related to recruitment outcomes as to the anthropogenic effects of fishing. For small pelagic fishes such as sardines and anchovies in particular, environmental variability has been described as one of the primary forcings affecting availability and survival of prerecruitment early life stages. Although less well-documented, the impact of environmental variability on biological features can also be confused with traditional exploitation effects. In order to further our understanding of how the environment affects biological features of small pelagic resources, this work analyses variability of biological traits in anchovy (Engraulis ringens) off northern Chile (18 degrees 21'S-24 degrees 00'S) and the primary environmental variables of the sea surface from 1990 to 2015. The results show significant spatial and temporal heterogeneity in both environmental conditions and anchovy biological traits (weight, length, and maturity), revealing an important relationship between the biological condition of E. ringens and food availability (represented by chlorophyll-a concentrations and average sea level). Our results suggest a heterogeneous population structure, and ametapopulation hypothesis is proposed. Over the last 15 years, anchovy monitoring has revealed greater gonad weights and proportions of mature individuals along with smaller, lighter-weight individuals. Such phenotypic plasticity is an adaptive strategy responding to large-scale environmental changes and is probably associated with diminished food availability. Interannual trends in anchovy biological traits in response to environmental variability and the species' heterogeneous population structure have important implications for population evaluations and diagnoses as well as fishery management.