For Egg-Laying Shark Species, Warmers Water Means Earlier Emergence & Weaker Offspring
Baby sharks will emerge from their egg cases earlier and weaker as water temperatures rise, according to a new study that examined the impact of warming oceans on embryos.
About 40% of all shark species lay eggs, and the researchers found that one species unique to the Great Barrier Reef spent up to 25 days less in their egg cases under temperatures expected by the end of the century. The extra heat caused embryonic epaulette sharks to eat through their egg yolks faster and when they were born, the rising temperatures affected their fitness.
EDIT
Researchers monitored 27 epaulette egg cases at the New England Aquarium in Boston. Some were reared in waters at 27C – a current average summer – and two other groups were reared at either 29C or 31C. Because the egg cases are translucent, researchers can see the sharks developing and how quickly they are eating the egg yolk. Warmer temperatures saw them eat the yolk faster.
In normal temperatures, the sharks emerged from the egg cases after 125 days. But in 31C waters, they emerged after 100 days. The researchers also measured the fitness of the baby sharks, and found that it peaked at 29C but then fell sharply at 31C. Lead author Carolyn Wheeler, also at James Cook University, said: “The hotter the conditions, the faster everything happened, which could be a problem for the sharks.” She said the results of the study, published Tuesday in the journal Scientific Reports, presented a “worrying future” because many sharks were already under threat.
EDIT
https://www.theguardian.com/environment/2021/jan/12/baby-sharks-emerge-from-egg-cases-earlier-and-weaker-in-oceans-warmed-by-climate-crisis