These movements have driven tiger sharks ( Galeocerdo cuvier ) out of protected areas, leaving them in a delicate situation of vulnerability to commercial fishing. It is the largest cold-blooded apex predator in tropical and subtropical seas, so they are limited by the need to stay in warm waters. Historically, the northeastern coast of the US has been too cold for tiger sharks, but temperatures have risen significantly in recent years, making it suitable for these rare sharks.
“Annual migrations of tiger sharks have expanded poleward in parallel with rising water temperatures,” says Neil Hammerschlag, lead author of the study and director of the UM Shark Research and Conservation Program. “These results have conservation implications for tiger sharks, as changes in their movements outside protected marine waters may make them more vulnerable to commercial fishing.”
This problem is neither new nor exclusive to tiger sharks. “Ocean warming can be driven by long-term climate change or short-term climate variability such as marine heat waves, and reports of species responses to these climate events are increasing across ecosystems. sailors”, can be read in the article. The answers are varied, but the most common are changes or expansions in its distribution range towards the poles. An example is the severe marine heat waves in the Northeast Pacific, during the period 2014-2016. Poleward range expansions were triggered in a wide range of species, including crustaceans, cnidarians, seabirds, and teleosts. “Climate variability and change are also altering seasonality in the ocean, shifting the annual cycle of surface temperatures towards earlier seasons […] For example, catches of tuna in the Bay of Biscay during their summer migrations towards north reflect that albacore tuna (Thunnus alalunga) and bluefin tuna (Thunnus thynnus) arrive 8 and 14 days earlier than 40 and 25 years ago, respectively”. In the study they argue that the key research priorities in the ecology of climate change are to determine and predict the speed, direction and timing of associated changes in space use and species movements, based on variability and climate change.
Hammerschlag and his team discovered these climate-driven changes by analyzing nine years of satellite tracking data from tiger sharks, which had previously been tagged. The data have been combined with a complementary analysis in the region of nearly forty years of conventional tag and retrieval information provided by the National Oceanic and Atmospheric Administration (NOAA) Cooperative Shark Tagging Program, in addition to temperature data from the sea through satellites. Catches for tagging occurred earlier in the year, off the North American continental shelf (see yellow crosses in image).
“The tiger sharks tracked by satellite in the western North Atlantic between 2010 and 2019, revealed a significant annual variability in the geographical extent and timing of their migration to the latitudes of the north due to warming of the ocean , ” can be read in Abstract of article . This study shows that during the last decade ocean temperatures were the warmest on record. For every degree Celsius of above-average water temperature rise, tiger shark migration extends poleward by more than 400 kilometers. These results may have strong implications for the ecosystem. “Given its role as an apex predator, these changes in the tiger shark’s movements may alter predator-prey interactions, leading to ecological imbalances and more frequent encounters with humans,” says Hammerschlag.
An apex predator is a predator that is at the top of the food chain, meaning it has no natural predators feeding on it. In addition to sharks, Siberian tigers ( Panthera tigris altaica ), Alaskan wolves ( Canis lupus pambasileus ) or Kenyan lions ( Panthera leo massaica ), to name a few, are apex predators. In this case, the problem is not only the northward movement of tiger sharks, but also that “they have occurred earlier in the year, during periods with abnormally high sea surface temperatures,” the article states. It further argues that quantifying changes associated with climate and the use of space and the movements of higher trophic level predators is “particularly important given that they present a relatively high risk of extinction and changes in their distribution could make them more vulnerable to The explotion”. In addition, “it could change the probability of encounters with recreational water users or alter the dynamics of the ecosystem through new trophic cascades.” The tiger shark’s general diet includes teleosts, elasmobranchs, sea turtles, seabirds, and marine mammals.
The study, titled Ocean warming alters the distributional range, migratory timing, and spatial protections of an apex predator, the tiger shark (Galeocerdo cuvier) , was published on January 13, 2022 in the journal Global Change Biology. The authors are Neil Hammerschlag, Laura McDonnell, Mitchell Rider, Ben Kirtman of the UM Rosenstiel School; Garrett Street and Melanie Boudreau of Mississippi State University; Elliott Hazen, Lisa Natanson, Camilla McCandless of NOAA Fisheries; Austin J. Gallagher of Beneath the Waves and Malin Pinsky of Rutgers University.
