The significance of ‘ear stones’ in unraveling the relationship between sardine’s growth rate and its environment  

Motivated by the questions on early life stage growth, influence of survival on the size of adult fish populations that varies due to environmental forces, and changes in the life-history traits such as size-and-age-maturity of fish populations which happens due to numerous selective pressures from the fishery environment, Alexanra Bagarinao-Regalado, a fisheries biologist and faculty from the Division of Biological Sciences, navigates us through her published study.

The sardine industry in general, has suffered severe fluctuations over the years which were attributed to overexploitation of stocks, but then the unpredictability of the stock and their environment in their early stages are left unnoticed. Knowing the relationship and influence of the environment and the environmental mechanisms to the regulation of growth during the early stages of an organisms’ life appear to show the potential variability in the transition from a juvenile fish to a larger life stage. Determining how the environment affects growth is critical to understand processes influencing annual sardine production. 

Sardinella lemuru is one of the most abundant and exploited sardine species in the Philippines. The growth rate of the sardine larvae during the 2-year period were examined using otolith microstructure analysis. Otoliths, dubbed as “ear stones” can determine the age of the fish. The first measurements of larval growth of S. lemuru in the northern Zamboanga upwelling system covers only the 2011-2012 and 2012-2013 spawning seasons. Upwelling is the cooler but prey-rich period or can be nutrient-rich period where our marine waters are fickle and dynamic. The transition to the juvenile stage can occur within the age of 25 to 37 days where the mean growth varies significantly. In both year-classes, the larvae that were hatched during the upwelling period displayed a faster growth rate. 

While temperature may be important, larval growth rates appear to be driven more by prey abundance. Differences in age and growth rates of young sardines were strongly compatible with fickle oceanographic conditions and larval growth rates appear to be driven more by abundance of prey or food for both years. 

What now? Knowing how the environment affects growth is important in order to be cognizant of what is happening in the process of annual sardine production. An enhanced understanding of the early life history of species could develop indicators of ‘good’ and ‘bad’ years for the local sardine fishery. The results of this study along with its other components contributed to the National Sardine Management Plan of the Philippines.

Find out more about this journal article at https://doi.org/10.3354/meps13930