Scientists closely tracking the survival of endangered Sacramento River salmon faced a puzzle: the same high temperatures that salmon eggs survived in the laboratory appeared to kill many of the eggs in the river.
(From ScienceDaily)– Now the scientists from NOAA Fisheries and the University of California at Santa Cruz have resolved the puzzle, realizing new insights into how egg size and water flow affect the survival of egg-laying fish. The larger the eggs, they found, the greater the water flow they need to supply them with oxygen and carry away waste.
The results of the study were published in the scientific journal Ecology Letters. NOAA Fisheries is using the findings to improve protection of fish in the Sacramento River.
“Our model, based on a literature search of laboratory studies, predicted that temperatures in the upper Sacramento River since 1996 almost never got warm enough to cause mortality of salmon embryos,” said Benjamin Martin, NOAA Fisheries researcher and lead author of the study. “But data from field studies in the Sacramento River indicated that in some years, temperature-related mortality exceeded 75 percent, for example, in 2014-2015.”
Scientists often use laboratory studies to estimate how species will respond to elevated temperatures. The results from this study reveal that fish may respond to temperature differently in the field than in the lab. Understanding the causes for this difference may help researchers improve their predictions of how temperature affects fish eggs across different environments. “We wanted to know why these salmon eggs have a much lower thermal tolerance in the field compared to the lab,” said Martin. “We hypothesized that the reason salmon eggs die in the river is because they don’t get enough oxygen.”
External temperatures govern the biological processes of salmon eggs and the embryos inside. As the water gets warmer their metabolism increases, demanding more and more oxygen. Unlike juvenile and adult fish, eggs cannot move and don’t have a developed respiratory or circulatory system. Instead they rely on flowing water to supply oxygen and carry away waste products. Winter-run Chinook salmon are especially challenged when it comes to warmer water temperatures because their eggs are atypically large and require more oxygen exchange. Their egg size evolved to take advantage of cold water above Shasta Dam where they once spawned. However, the salmon now spawn in the warmer Sacramento River below the dam.
After further analysis of field data, scientists found a fundamental difference between conditions in the laboratory and conditions that effect eggs in the wild.
Read the full article here: https://www.sciencedaily.com/releases/2016/12/161206142635.htm