Warming oceans could cause some fish species to produce too many males – and too few females – to sustain their populations, say scientists in Spain and Oregon.
Time magazine reports that Francesc Piferrer and other scientists working at Barcelona’s Institute of Marine Sciences have proved that rising water temperatures caused some species of fish to produce a disproportionate ratio of males to females, through a mechanism called epigenesis.
Unlike humans, whose sex is determined at fertilization by combinations of chromosomes from their parents, sex differentiation in most fish occurs during embryonic development. And in some species, the trigger that causes some fish to develop ovaries (and thus become female) turns out to be temperature-linked. Piferrer’s research suggests that a 3°C or 4°C temperature increase (roughly 37-39°F) could cause those species to go from a roughly 50-50 male-female ration to 80 percent male – bad news for the species’ survival.
Oregon State University fish biologist Scott Heppell, who studies rockfish and other species with Oregon Sea Grant support, reports that some canary rockfish populations are already showing more males than females. Although there are too many variables, thus far, for scientists to pinpoint the cause, Heppell says “The data shows a skew toward males, and the modeling shows that if this skew is real, then the population is in more trouble.”