Atlantic cod (Gadus morhua) is among the fish species maturing and spawning earlier in the “spring” reproductive season, due to higher water temperature. Photo by GRID-Arendal, Flickr.
Fisheries managers and researchers may now predict how early fish will spawn in response to warming waters due to climate change, both in the oceans and in freshwaters.
Mandarin fish mating. Image by Klaus Stiefel, Flickr.
Discounting anthropogenic-induced changes, the seasonally oscillating environments where long-lived fish hatch and grow remain more or less the same throughout the course of their lives. This means that the common explanation that states that fish become sexually active – or spawn for the first time – after experiencing certain environmental stimuli does not properly explain this phenomenon.
For more than 40 years, Dr Daniel Pauly, principal investigator of the Sea Around Us initiative at the University of British Columbia’s Institute for the Oceans and Fisheries, has been collecting evidence to further develop his Gill-Oxygen Limitation Theory, also known as GOLT.
Back in 2010, he presented his findings in a slim book titled Gasping Fish and Panting Squids: Oxygen Temperature and the Growth of Water Breathing Animals, whose second edition has just been released; a Chinese edition will soon follow.
A pair of One-spot Pullers (Chromis hypsilepis) preparing to spawn. Home Bommie, Ulladulla, NSW. Photo by Richard Ling, Flickr, CC BY-NC-ND 2.0.
In over 80 per cent of fish species, the females, including those known as ‘big old fecund females,’ or BOFFS, grow bigger than the males. This long-established fact is difficult to explain with the conventional view of fish spawning being a drain on the ‘energy’ available for growth. If this view were correct, females, which are defined by their larger reproductive effort, would always remain smaller than males.
Fish are expected to shrink in size by 20 to 30 per cent if ocean temperatures continue to climb due to climate change.
A new study by researchers at the University of British Columbia updates previous estimates published in 2013 and provides a deeper explanation of why fish are expected to decline in size.