NOAA Study Finds Ocean Temperatures Impacting Migration Patterns
In 40 years of fishing the Atlantic, Capt. John Williams has developed a deep understanding of when he can expect certain fish to show up to his fishing grounds off New York and New Jersey. When things change, he notices.
“Thresher sharks and mako sharks are usually a June thing,” said Williams, who runs Blue Chip Sportfishing out of Southside Marina in Point Pleasant Beach, N.J. “Now they’re showing up in May.”
Any experienced saltwater angler knows that fish migrations can vary year-to-year. But just like the fascinating unique catches of wayward single fish — such as the large tarpon recently caught off a Cape Cod beach — more than a single captain’s observations are needed to prove a trend.
Now, the National Oceanic and Atmospheric Administration (NOAA) has put scientific proof behind observations that some saltwater species in the Atlantic are migrating from south to north earlier in the year and making their return trips south later in the year.
Highly Migratory Species on the Move
A recently released study from NOAA looked at catch data over a nearly 20-year period for Atlantic Highly Migratory Species (HMS), a group of 12 fish that includes tunas, billfish and sharks. Catch data can help fisheries managers better understand how the world’s warming climate is impacting recreational fisheries.
“The study reveals that the spatial shifts that appear to be related to increasing water temperatures from Maine through Virginia,” said Lauren Gaches, a spokesperson for NOAA. “Recent studies have found that highly migratory species, among others, are generally shifting northward along the coast and arriving earlier in the year as ocean temperatures warm. It appears that temperature change and prey availability are both factors in these shifts.”
Catches of both small and large bluefin tuna, for example, are shifting northward at a rate of 2.5 to 6.2 miles per year. The study found that for each 1 degree Celsius (1.8 F) increase in water temperature, blue sharks and thresher sharks are shifting northward at rates of 19 to 25 miles.
Bluefin tuna catches off Massachusetts in 2019 were estimated to have occurred 80 days earlier than in 2002. Early blue shark catches were estimated to have occurred 66 days earlier off Connecticut and blue marlin catches were found to be 27 days earlier off New York.
NOAA used a complex approach to analyze data collected through its Large Pelagic Survey, mapping locations and timing of recreational catches of HMS from 2002 through 2019. The survey uses three different ways to collect what it calls “intercepts” — in short, the catch of one of the 12 HMS fish.
The Large Pelagics Intercept Survey collects dockside information from a random sample of private anglers and charter operators. The Large Pelagics Telephone Survey uses random phone surveys of HMS permit holders while the Large Pelagics Biological Survey is another dockside operation designed to collect bluefin tuna tissue samples.
All told, the study looked at 96,606 intercepts on 53,698 trips.
Yellowfin tuna accounted for by far the most intercepts, with 14,326 catches accounting for 22 percent of the total. Giant bluefin were second most prevalent, with 12 percent of the total, while white marlin made up 11 percent of the total.
Increasing Ocean Temps
The warming of the world’s oceans, which cover 70 percent of the earth’s surface, is well documented.
Analyzing data from NOAA’s Optimum Interpolation Sea Surface Temperature, the Climate Change Institute at the University of Maine’s Climate Reanalyzer determined that average sea surface temperature reached an all-time high in the spring of 2023, and has remained near that level since.
The North Atlantic has shown an even more pronounced warming, with temperatures about 2 degrees Fahrenheit higher than normal.
A number of factors can lead to acute changes in ocean temperatures. They include well-known atmospheric conditions such as El Niño and La Niña. But global sea surface temperatures averages are tied to warming air temperatures. And, just as climate models are predicting continued increases in global air temperatures, modeling has shown that average ocean temperatures will continue to rise, too.
Recreational anglers will likely see first-hand the impacts of the changing migratory patterns.
“Shifts in the timing and location of Highly Migratory Species catch have important implications for recreational anglers, including seasonal fishing tournaments and coastal communities that rely on these fisheries,” study lead author Dr. Dan Crear said in a statement from NOAA. “Fishermen may have to travel farther or fish earlier in the year to find certain target species. The species found at a favorite fishing spot may be changing over time, with species typically found farther south becoming more common in northern waters.”
Gaches said NOAA may use the study’s findings to improve the Large Pelagics Survey.
“It will also be considered in ongoing agency climate initiatives such as the Climate, Ecosystem and Fisheries Initiative and the implementation of the NOAA Fisheries Climate Science Strategy,” she added.
Of course changing migration patterns could also lead to management and regulations changes, such as shifting seasons and bag limits. For example, while cobia were not a specific focus of the study, NOAA predicts that by 2050 the fish could spend up to 30 more days per year in the Chesapeake Bay. It’s hard to imagine that such significant changes wouldn’t prompt management changes.
The information is already laying a foundation for an examination of fisheries policies.
“We can start to use this kind of information in fisheries management in a practical way,” Gaches said. “For example, under Draft HMS Amendment 15, NOAA Fisheries is evaluating some aspects of spatial management. One of the main drivers of that effort is that static closed areas should be re-evaluated to make sure they account for potential shifts in species distributions. If an area is closed to fishing in the wrong place at the wrong time, then it could have negative impacts on vulnerable species or certain fisheries.”
While anglers will have to adapt to changes, that is something they are used to doing.
“There could be a lag because the location or pattern that worked for them five or 10 years ago might not work for them today,” Gaches said. “But anglers are very good at finding fish.”
Take Capt. Williams of Blue Chip Sportfishing. Sure, those sharks are consistently showing up in May now instead of June. But when they do arrive, no matter when, he’s ready for them.
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