The importance of previous year conditions on young-of-the-year fish

Background/Question/Methods

Freshwater organisms are particularly affected by anthropogenic disturbances, including climate change, because of the importance of lakes and rivers to human societies. To monitor natural recruitment and the recovery of the Copper Redhorse (Moxostoma hubbsi) population a nationally endangered species endemic to Québec, a young-of-the year (YOY) survey program was implemented in 1999 in the Richelieu River where it is known to spawn. This seine survey is done in late September almost every year. The program also monitored the abundance of four sympatric redhorses (M. anisurum, macrolepidotum, valenciennesi and carinatum). Since YOY Copper Redhorse hatchery-enhancement program took place in 2004 to rebuild the population, this study, focused on the four sympatric redhorses species. Although a large body of literature suggests that events within a sampling year, such as climate (e.g., water temperature) and hydrology (e.g., water flow) influence how many YOY survive, few studies have focused on how water temperature and flow of the preceding year impact YOY redhorse recruitment success. To study the importance of current and the previous year’s water temperature and flow on YOY species abundance, we relied on joint species distribution models and variation partitioning.

Results/Conclusions

As expected, the current-year climate and hydrology influence the abundance of redhorse YOY. However, the importance of the previous-year climate and hydrology was surprisingly high for all four redhorse species considered. Our results further suggest that there may be specific mechanisms that are crucial to regulate YOY abundance of freshwater fishes, which need to be tested. In this regard, we suggest testing three possible hypotheses. Energy hypothesis: Energy input in an aquatic system resulting from, e.g. warmer winter may influence species reproduction. Resource availability hypothesis: Variation in resources availability through time, e.g. increase water level could bring more abundant food leading to increase in fertility rates. Stress hypothesis: Environmental stress imposed on individuals could influence reproductivity and survival, e.g. a drought. Accordingly, the previous year conditions are most likely related to parents' fecundity or likelihood of becoming fertile parents, while current year conditions influence YOY survival success. Atresia caused by poor spawning conditions could also explain a YOY bloom the next year. Understanding how climate and hydrology affects fish populations will help us to refine and maximize conservation effort and strategies.