{"id":52607,"date":"2026-10-21T09:24:09","date_gmt":"2026-10-21T13:24:09","guid":{"rendered":"https:\/\/www.ecoticias.com\/en\/?p=52607"},"modified":"2026-10-21T09:24:10","modified_gmt":"2026-10-21T13:24:10","slug":"in-alaskas-bering-sea-snow-tanner-hybrid-crabs-became-13-4-times-more-abundant-after-a-marine-heatwave-wiped-out-billions-of-snow-crabs-and-in-2025-they-made-up-41-7-percent-of-commercial-sized-males","status":"publish","type":"post","link":"https:\/\/www.ecoticias.com\/en\/in-alaskas-bering-sea-snow-tanner-hybrid-crabs-became-13-4-times-more-abundant-after-a-marine-heatwave-wiped-out-billions-of-snow-crabs-and-in-2025-they-made-up-41-7-percent-of-commercial-sized-males\/52607\/","title":{"rendered":"In Alaska’s Bering Sea, snow-Tanner hybrid crabs became 13.4 times more abundant after a marine heatwave wiped out billions of snow crabs, and in 2025 they made up 41.7 percent of commercial-sized males"},"content":{"rendered":"\n

In Alaska’s Bering Sea, snow-Tanner hybrid crabs were 13.4 times more abundant in 2025 than their 1988-2024 average. NOAA Fisheries scientists reported the jump on October 19, 2026, in Proceedings of the National Academy of Sciences<\/a>. It came seven years after the 2018-2019 marine heatwave that wiped out billions of snow crabs. In 2025, hybrids made up 41.7 percent of the commercial-sized males on the survey. Before that year, they had never topped 10 percent.<\/p>\n\n\n\n

Erin Fedewa of the Shellfish Assessment Program at NOAA’s Alaska Fisheries Science Center in Kodiak led the study with eight co-authors. In the agency’s feature story<\/a>, she called the results unprecedented. “We were shocked by the magnitude of the hybrid surge while analyzing data from the 2025 eastern Bering Sea bottom trawl survey,” she said. She added that the team saw at once how it would reach fisheries management.<\/p>\n\n\n\n

Two crabs and their offspring<\/h2>\n\n\n\n

Snow crab (Chionoecetes opilio<\/em>) likes cold water. Tanner crab (Chionoecetes bairdi<\/em>) is a sub-Arctic species that does better as the water warms. On the eastern Bering Sea shelf, winter sea ice sets the boundary between their ranges. Where the two ranges meet, the crabs form a hybrid zone.<\/p>\n\n\n\n

The face gives a hybrid away. NOAA’s comparison chart gives snow crab a horizontal mouth and two green eyes. Tanner crab has an M-shaped mouth and two red eyes. A hybrid has a rounded mouth, and its eyes can be one red and one green, half of each color, or other mixes.<\/p>\n\n\n\n

Co-author Leah Zacher took most of the photos NOAA released, on the 2026 eastern Bering Sea bottom trawl survey. That survey is part of NOAA’s long-running Alaska trawl surveys<\/a>.<\/p>\n\n\n\n

\"NOAA
Snow crab (left), snow-Tanner hybrid (center) and Tanner crab (right): the chart notes a horizontal mouth and green eyes, a rounded mouth and mixed eye color, and an M-shaped mouth and red eyes. (Image: NOAA Fisheries)<\/figcaption><\/figure>\n\n\n\n

The heatwave and the snow crab crash<\/h2>\n\n\n\n

In March and April of the heatwave, sea ice cover stayed below 15 percent, which the paper describes as nearly ice-free. Snow crab numbers fell apart soon after. The authors put that collapse among the most significant mass mortality events ever seen in a marine ecosystem, and the fishery, worth hundreds of millions of dollars a year, shut down in more than one season.<\/p>\n\n\n\n

Heat spikes at sea have done similar damage elsewhere, and marine heatwaves have battered coral reefs<\/a> in several oceans.<\/p>\n\n\n\n

Snow crab bounced back fast once the heat eased. Tanner crab did something different and kept rising until 2025, the highest count in a survey record that starts in 1988. NOAA calls that the less surprising part, given a warm-affinity species. The hybrids were the surprise: their 2025 estimate came close to triple the previous record, and their share of legal-sized males was 13.1 times the long-term average.<\/p>\n\n\n\n

Testing three explanations<\/h2>\n\n\n\n

Fedewa and co-author Emily Ryznar ran the numbers with dynamic structural equation models. NOAA calls the method unique because it tests for cause and effect, not just two lines moving together on a chart. Spring sea ice served as the stand-in for the heatwave, since less ice means warmer water and a reshuffled food web at the same time.<\/p>\n\n\n\n

Could warmth alone have kept more Tanner and hybrid crabs alive? In the Tanner crab model, the direct ice effect came out at 0.03, with a P value of 0.74, so no. In the hybrid model it was -0.01 (P = 0.86). Could adult snow and Tanner crabs have crowded together and mated more? The overlap term was -0.09 (P = 0.45), again no support.<\/p>\n\n\n\n

What did hold up was a chain through snow crab. More ice meant more snow crabs (0.25, P = 0.03), and more snow crabs meant fewer hybrids (-0.31, P < 0.001). NOAA’s reading is that with billions of snow crabs gone, Tanner and hybrid crabs faced less competition and predation and more of their young made it.<\/p>\n\n\n\n

In the paper’s words, this causal pathway accounted for 76 percent of heatwave effects on hybrid crab abundance. “This study marks the first time an increase in hybridization has been attributed to a discrete marine heatwave event,” Fedewa said.<\/p>\n\n\n\n

A crab the quota system never counted<\/h2>\n\n\n\n

On paper, nothing stops a crabber from keeping a big male hybrid. Crews can land it as snow crab in the directed winter fishery. Hybrids used to show up as a small slice of snow crab catches, though, so the federal fishery management plan that sets yearly harvest quotas for Bering Sea crab stocks never counted them.<\/p>\n\n\n\n

\"Three
Three harvestable male snow-Tanner hybrid crabs collected during the 2026 eastern Bering Sea bottom trawl survey. (Photo: NOAA Fisheries \/ Leah Zacher)<\/figcaption><\/figure>\n\n\n\n

Today the rules have no formal way to set a hybrid-specific catch limit. In 2025, NOAA says, state managers answered the first pulse by raising the snow crab harvest limit. They hoped the fleet would target and land hybrids.<\/p>\n\n\n\n

The 2026 survey found even more of them. “Given that we saw even more commercial-sized male hybrids on this year’s eastern Bering Sea bottom trawl survey than in 2025, it’s clear this will continue to be a pressing management challenge for decision makers,” Ryznar said.<\/p>\n\n\n\n

Room to adjust the rules<\/h2>\n\n\n\n

To the authors, the boom highlights “the vulnerability of inflexible management systems to unanticipated ecosystem responses.” They point to extensive work on climate scenarios and adaptation pathways for the Bering Sea. None of it listed more hybridization as a plausible outcome of warming.<\/p>\n\n\n\n

They still see value in scenario planning. But forecasts built on past experience have limits once conditions move outside that range, they argue. The 2018-2019 heatwave was part of a long-term borealization trend, as the Bering Sea turns more sub-Arctic. The same shift has species moving into the Arctic as the ice disappears<\/a>. “Greater flexibility in fisheries management systems will be critical in the coming years,” Fedewa said.<\/p>\n\n\n\n

What is still uncertain<\/h2>\n\n\n\n

Scientists cannot age these crabs. Each survey count also mixes groups of crabs that settled in different years. The authors say this adds substantial uncertainty to the delay between the heatwave and its effects. So they tested delays of 0 to 2, 1 to 3 and 5 to 6 years. The results held each time, but the timing remains an estimate.<\/p>\n\n\n\n

The authors favor release from competition or predation, but they do not say which one mattered more. Their data also end in 2025. For 2026 there is only Ryznar’s word that big male hybrids rose again. How long the boom lasts is still unknown.<\/p>\n\n\n\n

PNAS<\/a> carries the full study, and the data and code sit on Zenodo<\/a>.<\/p>\n\n\n\n

Photo: NOAA Fisheries \/ Leah Zacher<\/p>\n","protected":false},"excerpt":{"rendered":"

In Alaska’s Bering Sea, snow-Tanner hybrid crabs were 13.4 times more abundant in 2025 than their 1988-2024 average. NOAA Fisheries … <\/p>\n

Read more<\/a><\/p>\n","protected":false},"author":1,"featured_media":52604,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"eco_video_url":"","footnotes":""},"categories":[3],"tags":[],"class_list":["post-52607","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-environment","resize-featured-image"],"_links":{"self":[{"href":"https:\/\/www.ecoticias.com\/en\/wp-json\/wp\/v2\/posts\/52607","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.ecoticias.com\/en\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.ecoticias.com\/en\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.ecoticias.com\/en\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.ecoticias.com\/en\/wp-json\/wp\/v2\/comments?post=52607"}],"version-history":[{"count":2,"href":"https:\/\/www.ecoticias.com\/en\/wp-json\/wp\/v2\/posts\/52607\/revisions"}],"predecessor-version":[{"id":52628,"href":"https:\/\/www.ecoticias.com\/en\/wp-json\/wp\/v2\/posts\/52607\/revisions\/52628"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.ecoticias.com\/en\/wp-json\/wp\/v2\/media\/52604"}],"wp:attachment":[{"href":"https:\/\/www.ecoticias.com\/en\/wp-json\/wp\/v2\/media?parent=52607"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.ecoticias.com\/en\/wp-json\/wp\/v2\/categories?post=52607"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.ecoticias.com\/en\/wp-json\/wp\/v2\/tags?post=52607"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}