(Contributing authors: Walt Golet & Joe Dello Russo, College of Maine; Eric Orbesen & Derke Snodgrass, NOAA Fisheries Southeast Fisheries Science Heart)
Go to most any marquee offshore fishing vacation spot within the Atlantic Ocean—the northeast canyons, Outer Banks, Venice, Bahamas, Ascension Island, Cape Verde, Cape City—and there’s a superb probability one species is on the ‘out there’ listing for at the very least a part of the yr: yellowfin tuna. Like bluefin tuna, the yellowfin tuna is a extremely migratory species that may journey 1000’s of miles throughout ocean basins and is closely fished by each business and leisure fisheries wherever it roams. Nonetheless, when you catch a yellowfin on a bucket-list journey to Ascension Island or within the Gulf of Mexico, Bahamas, or Caribbean, is it from the identical group of fish that we routinely see off the Northeast coast of the USA? Or is it from a very totally different group of fish that can by no means discover their approach into our waters? The solutions to those questions aren’t solely fascinating to ponder, however the truth is are important to the profitable administration of yellowfin fisheries all through the Atlantic Ocean.
Within the Atlantic Ocean, yellowfin are managed by the Worldwide Fee for the Conservation of Atlantic Tunas (ICCAT), a regional fisheries administration group whose mission is to check the populations of tuna and tuna-like species (together with pelagic sharks, marlins, and swordfish), assess inhabitants tendencies, and handle fisheries by way of laws and quotas. As a part of its tasks, ICCAT routinely conducts inventory assessments, which could be regarded as a census of fish populations to guage their general standing—that’s, whether or not they’re overfished (we have now eliminated too a lot of them general) or are experiencing overfishing (the charges at which we’re eradicating them is simply too quick).
In lots of situations, ICCAT conducts separate inventory assessments for distinct teams of fish of a given species which can be considered remoted from each other because of the place they reproduce or spawn; for instance, the japanese and western Atlantic bluefin tuna shares, that are thought to primarily spawn within the Mediterranean Sea and Gulf of Mexico, respectively. Nonetheless, though yellowfin spawn in a number of areas all through the equatorial waters of the Atlantic—together with within the japanese Atlantic off Africa within the Gulf of Guinea and close to Cape Verde and within the western Atlantic throughout the Caribbean Sea and Gulf of Mexico—the yellowfin inventory evaluation is carried out assuming that each one yellowfin within the Atlantic Ocean, from South Africa to Brazil to the Caribbean to the Gulf of Mexico to Canada, are all a part of one interconnected inhabitants. The query is, is that this assumption correct?
Because it seems, the reply to this query just isn’t a easy sure or no, however is sophisticated and a topic of uncertainty amongst scientists and fishery managers. For instance, latest genetic analysis signifies that yellowfin born within the japanese and western spawning areas are genetically distinct, which means that they return to their birthplace for spawning. Nonetheless, typical tagging knowledge additionally demonstrates that yellowfin generally undertake trans-Atlantic migrations between japanese and western spawning areas, which means that particular person fish could spawn in numerous areas all through its lifetime.
In distinction, satellite tv for pc tagging knowledge has revealed {that a} portion of the yellowfin in some areas, together with the Gulf of Mexico, exhibit solely localized actions and could also be resident there all through their lifetime. So as to add to the complexity, otolith (ear bone) microchemistry knowledge from yellowfin captured within the mid-Atlantic Bight and Gulf of Mexico exhibits that fish in these areas originate from all 4 main spawning areas, with the relative contribution of particular person spawning areas being extremely variable between years. Thus, some yellowfin fisheries, like the preferred ones within the US, seem like extremely reliant upon the success of spawning in all the key areas.
With all of the thriller and complexity surrounding the dynamics of the yellowfin inhabitants all through the Atlantic, it’s maybe no shock that the outcomes of the latest yellowfin inventory evaluation (carried out in 2019) have been shrouded in uncertainty, with near-equal chance that the inventory was in good or unhealthy form. To complicate issues, tendencies in general yellowfin biomass during the last twenty years present a gentle decline, and business and leisure fisheries working all through the Atlantic have exceeded the overall allowable yellowfin catch yearly since 2014.
With the yellowfin inventory teetering on the sting of bother and so many questions left to reply about their inhabitants construction, there was a latest push from ICCAT and NOAA Fisheries to be taught extra about yellowfin inhabitants dynamics within the Atlantic Ocean, hoping to enhance our skill to handle this invaluable, worldwide useful resource. As a part of these efforts, a workforce of scientists from the NOAA Fisheries Southeast Fisheries Science Heart, College of Maine, and the Anderson Cabot Heart for Ocean Life on the New England Aquarium has been working to raised perceive how yellowfin caught from the Outer Banks of North Carolina to the Northeast Canyons, within the Gulf of Mexico, and within the Caribbean are related to at least one one other in addition to to spawning areas all through the Atlantic Ocean.
Since 2010, the workforce has deployed over 100 pop-up satellite tv for pc tags in fashionable yellowfin fishing areas just like the Northeast Canyons, Outer Banks, Veracruz, and Curaçao, and tracked the actions of particular person fish for intervals as much as 319 days, or simply over 10 months. Along with the pop-up satellite-tag deployments, the workforce has labored to deploy typical spaghetti tags on yellowfin all through every of those areas as a part of ICCAT’s Atlantic Ocean Tropical Tunas Tagging Program (AOTTP) which is a big, cooperative venture that deployed over 100,000 tags on tropical tunas, comparable to bigeye, skipjack, and yellowfin, all through the Atlantic from 2015 to 2021.
So, what have we realized after almost 15 years of intensive tagging efforts? Effectively, it’s a story of two tags. Wanting solely on the pop-up satellite tv for pc tag knowledge, we’ve realized that yellowfin tagged within the northwest Atlantic don’t appear to be buzzing between areas all that a lot, at the very least not on an annual foundation. Actually, estimated tracks from over 90 pop-up satellite tv for pc tags revealed excessive ranges of residency off the Northeast US, throughout the Gulf of Mexico, and within the Caribbean. For instance, not one of the 26 yellowfin tagged off the Northeast US, from the Outer Banks to the northeast canyons, moved into the Gulf of Mexico or Caribbean Sea—the western Atlantic spawning areas. As a substitute, these fish remained in offshore waters north of the Sargasso Sea and in affiliation with the Gulf Stream for as much as 10 months after launch. Equally, fish tagged within the Caribbean Sea exhibited in depth actions all through the area for as much as 6 months after launch but in addition didn’t transfer towards the Gulf of Mexico or Northeast US. The vast majority of the 50 yellowfin tagged within the Gulf of Mexico additionally remained in that area within the 6 months after launch, with solely 3 fish touring out of the Gulf by way of the Florida Straits and into the Bahamas throughout the fall and spring. These actions represented the best diploma of regional mixing seen within the satellite tv for pc tag knowledge and have been one directional (Gulf to higher Atlantic).
Whereas geographical actions recreated from pop-up satellite-tag knowledge seem disconnected, the place yellowfin prefer to spend their time within the water column is constant throughout tagging areas. Wanting on the vertical distribution of yellowfin permits us to narrate yellowfin actions to oceanographic situations that could be favorable, comparable to heat floor currents just like the Gulf Stream or Gulf of Mexico Loop Present. Should you’ve seen cinematic-quality floor feeds with a popper in hand or quadrupled up whereas floor trolling for yellowfin, you recognize these fish prefer to feed on the floor. Certainly, pop-up satellite-tag knowledge exhibits that yellowfin spend 97% of their time within the higher 200 meters of the water column, and 58% of their time within the higher 50 meters. True to their tropical tuna designation, tagged yellowfin additionally spent 82% of their time in waters hotter than 70F, and 66% of that point was in waters approaching 80F. Whereas heat floor waters are most well-liked, yellowfin are absolutely able to going deep and into chilly water; the deepest a yellowfin went in our dataset was 2,923 ft and the coldest temps skilled have been under 40F.
Collectively, the pop-up satellite-tag knowledge paint an image of resident yellowfin with constant native behaviors however no sturdy connectivity between areas. Nonetheless, knowledge from recaptured yellowfin tagged as a part of the AOTTP paint a considerably totally different image. Since 2018, 5 yellowfin tagged off the Northeast US—two in Veatch Canyon, two within the Hudson Canyon, and one from the Level off Oregon Inlet—have been recaptured off the coast of Africa after being at liberty for 532 to 967 days. These recaptures point out that at the very least a number of the yellowfin we see off the Northeast US migrate again to the coast of Africa to spawn. However, when thought of together with the pop-up satellite-tag knowledge, additionally they inform us that this lengthy migration is maybe not undertaken yearly. As a substitute, it might be that grownup yellowfin make the lengthy trek throughout the pond to spawn solely yearly or two, remaining resident within the Northeast US throughout years once they aren’t fairly able to make the swim. Yellowfin tagged as a part of the AOTTP have additionally but to be recaptured within the Gulf of Mexico or Caribbean Sea, however two yellowfin tagged off North Carolina and recaptured down in Venezuela throughout the mid-90s present proof that there’s at the very least some connection to the Caribbean Sea spawning space. Curiously, though otolith chemistry knowledge has proven that some yellowfin caught off the Northeast US have been spawned within the Gulf of Mexico, no tagging knowledge has proven direct actions between these two areas in both route. Thus, the extent of connection between the 2 hottest yellowfin fishing areas off the US coast stays considerably of a thriller.
Regardless of all we’ve realized about Atlantic yellowfin tuna over the previous decade, maybe the largest factor is that we have to do extra analysis to actually perceive Atlantic yellowfin inhabitants dynamics. Do yellowfin actually return again to their birthplace each time they spawn? How typically do they spawn? Are they spawning each time a tag exhibits them being current in a spawning space? These are among the many many questions that scientists hope to reply with extra tagging analysis, and in addition by way of the ability of ever-advancing chemical and genetic methods. So, the subsequent time you place a stud yellow on deck and take into consideration how nice that first steak goes to style, additionally take into consideration the tens of 1000’s of miles of ocean that fish swam by way of, the place that fish got here from, and what migration paths might need lay forward. The solutions to these questions are key to making sure that extra yellowfin can hit the deck in years to come back.
» For extra info on the AOTTP outcomes and to observe Atlantic yellowfin tuna tag recaptures, try this hyperlink.
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