Hot fish seeking cooler water!
All fish, minus opah and some tunas, are cold blooded. Thus, their body temperatures are regulated by the environment around them. Every fish species has an optimal temperature range — not only for survival, but also for growth and reproduction. Fish exhibit control over their thermal environment by seeking waters that are closer to their temperature optimum when waters become too warm or too cool.
High and low temperatures that are lethal for a particular species determines the distribution and abundance of its population. With water temperatures trending upward — the result of climate change — many fish are responding by shifting their latitudinal range, expanding their range, and/or moving to deeper depths.
When we’re talking about climate change, it’s important to make the distinction between weather and climate. Weather refers to the short-term (minutes to months). Climate, on the other hand, is the average of weather over time and space. So, a colder than normal winter is weather, but trends in winter weather over time (decades, for instance) is climate.
Saltwater fish species have an advantage over freshwater fish species in that they are not locked in by land. They can move in response to climate change, and will move if they need to. As fish respond to climate change, they still must get enough to eat, not get eaten, and reproduce. When species move, or expand their range, they temporarily upset the natural order of things. New predators, new prey, new competition for habitat, etc. There will be winners and there will be losers.
A great website, OceanAdapt.rutgers.edu, shows how saltwater creatures in the northeastern United States have responded to changes in water temperatures over the last 50 years. Most dramatic is the range shift of the American lobster, which has moved its center of abundance 3 degrees north in latitude from Long Island to Maine. Also noteworthy is the American fourspot flounder, which has shifted its center of abundance 1.5 degrees north and about 50 feet deeper.
As these species have migrated north in search of cooler waters, some traditionally southern species have expanded up the coast to the waters left behind. Notables include tarpon, today routinely caught off Virginia and Maryland, and mangrove snapper, now being caught in Delaware Bay.
Shifting to the Gulf of Mexico, a 2009 study found that warmer winters over the last 30 years have resulted in mangrove snapper, which were generally uncommon in most Texas estuaries along the Gulf Coast, to experience a remarkable increase in abundance. Their numbers have tripled in some areas and are up 20-fold in others. The authors noted that although they only focused on mangrove snapper, the same climatic forces may apply to common snook, tarpon and African pompano — and further mentioned anecdotal increases in both common snook and tarpon along Texas rock jetty passes in recent years.
Closer to home, we are also seeing fish responding to warmer water temperatures. Common snook have been expanding their range along the Gulf Coast of Florida for at least the last decade. Prior to 2008, snook were almost unheard of around Cedar Key. Snook are now plentiful enough there that they are regularly targeted. Occasional cold winter snaps will likely test this expanded population, but savvy snook should find refuge in the many warm-water springs of that area. Similarly, red and black mangroves are rapidly expanding northward on both the east and west coasts of Florida, again most likely due to rising temperatures and a series of mild winters.
Interestingly, a recent paper published in the journal Science measured four decades of range shifts from marine fish and invertebrate surveys. What they found was that bottom temperature explained more than half of the species shifts — except in the upper Gulf of Mexico, where the coastline prevents poleward (northern) movement. In this Gulf region, species affected by temperature tend to move deeper.
Are we seeing climate impacts to fish in Charlotte Harbor? We don’t really know, but it’s certainly possible, especially considering the population expansions and shifts previously noted. One anecdotal observation is that each year more anglers seem to be reporting bonefish catches in Charlotte Harbor. There have even been reports in Tampa Bay this year. Is it climate change? I can’t say; we don’t yet know.
But we certainly should expect new tropical fish species to appear in Charlotte Harbor as waters continue to warm. Likewise, we should be prepared to lose a few species, as they migrate to cooler waters. As different species shift or expand their geographic range, there will be new interactions: New predators, new prey, and new competition for habitat. These interactions will influence the population size of each species. There will be winners and there will be losers.
Obviously, this is all complicated stuff. But, it’s unfolding before our very eyes. Hopefully, anglers are tuning in.
Rutgers School of Environmental and Biological Sciences. 2017. OceanAdapt.rutgers.edu
Perry, Allison L., Paula J. Low, Jim R. Ellis, John D. Reynolds. 2005. Climate Change and
Distribution Shifts in Marine Fishes, Science Vol 308: 5730, 1912-1915.
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of global climate change on marine and estuarine fishes and fisheries, Reviews in Fish Biology
and Fisheries, Vol 14: 2, 251-275.
Speigel, JanEllen. 2016. Beneath the waves, climate change puts marine life on the move:
Connecticut’s traditional fishing catch is heading north, the ct mirror, 08/29/2016. CTMirror.org
Tolan, James M., and Mark Fisher. 2009. Biological response to changes in climate patterns:
population increases of gray snapper (Lutjanus griseus) in Texas bays and estuaries, Fish. Bull.
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Allen, Mike, and Phil Stevens. 2017. Personal Communication