Fish News: Some Like it Hot, Part II

A few months ago, our attention was drawn to the fish in Australia that can thrive in warmer temperatures as long as they were spawned in those warmer waters.  This week, scientists have discovered another example of surprising climate adaptation: a hybrid shark!  This new fish subspecies is direct evidence that changing oceans have given rise to uncharted reproductive territory.  Species that normally do not come into contact with one another are not only coexisting, but are actually mating and shaking up the evolutionary genetics of the shark world.  

Distribution of the common blacktip

Interestingly enough, like our last climate change story, this one also comes from James Cook University in Australia.  They've proven that Australian blacktip sharks have been intermingling with the common cosmopolitan blacktip shark.  Hybridization naturally occurs at very low rates and it is uncommon to actually find multiple hybrid generations in significant numbers.  Researchers think that this phenomenon is not simply coincidence or happenstance because these two species have very specific temperature ranges.  One likes it cold, and the other prefers warmer waters, leading experts to believe that these hybrids might have a larger tolerance for temperature extremes.

Not only are these new creatures fascinating local and global shark geneticists, but the situation has caught the attention of Australian resource managers because of its implications for the shark fisheries.  If the hybrids are disproportionally caught, or if they are more vulnerable to predation pressure, or if they reproduce less often, the fisheries will risk miscalculating their allowable catches in any given season.  In other words, these hybrids introduce a large degree of uncertainty into the equation, which generally leads to smaller, more conservative quotas.  At this early stage, everyone will have to hold their breaths to see what happens next!

Stay tuned for more stories of climate adaptation from around the globe.  So far, it looks like fishy things are happening in Australia!