Recently Yahoo News on-line reported the following:
Billions of crabs went missing around Alaska. Scientists
now know what happened to them
Rachel Ramirez, CNN
Fri, October 20, 2023 at 2:00 a.m. GMT+8
Billions of snow crabs have disappeared from the ocean
around Alaska in recent years, and scientists now say they know why: Warmer
ocean temperatures likely caused them to starve to death.
The finding comes just days after the Alaska Department of Fish and Game announced the snow crab harvest season was canceled for the second year in a row, citing the overwhelming number of crabs missing from the typically frigid, treacherous waters of the Bering Sea.
The study, published Thursday by scientists at the National Oceanic and Atmospheric Administration, found a significant link between recent marine heat waves in the eastern Bering Sea and the sudden disappearance of the snow crabs that began showing up in surveys in 2021.
“When I received the 2021 data from the survey for the first time, my mind was just blown,” said Cody Szuwalski, lead author of the study and fishery biologist at NOAA. “Everybody was just kind of hoping and praying that that was an error in the survey and that next year you would see more crabs.”
“And then in 2022, it was more of a resignation that this is going to be a long road,” Szuwalski told CNN.
That year was the first the US snow crab fishery was closed in Alaska. Catchers have attributed to the population decline to overfishing, but “overfished” is a technical definition that triggers conservation measures, experts told CNN — it doesn’t actually explain the collapse.
“The big take home for me from the paper, and just the whole experience in general, is that historically, fishery scientists had been very worried about overfishing — this has been our white whale, and in a lot of places we really solved that with management,” Szuwalski said. “But climate change is really throwing a wrench into our plans, our models and our management systems.”
For the study, scientists analyzed what could have triggered the disappearance of the snow crabs beginning in 2020 and boiled it down to two categories: the snow crabs either moved or died.
Szuwalski said they looked north of the Bering Sea, west toward Russian waters and even into deeper levels of the oceans, and “ultimately concluded that it was unlikely that the crabs moved, and that the mortality event is probably a big driver.”
They found that warmer temperatures and population density were significantly linked to higher mortality rates among mature crabs.
The reason behind the mortality event: hungrier crabs.
Snow crabs are cold-water species and found overwhelmingly in areas where water temperatures are below 2 degrees Celsius, though they can function in waters up to 12 degrees Celsius, according to the study. Warmer ocean water likely wreaked havoc on the crabs’ metabolism and increased their caloric needs.
The amount of energy crabs needed from food in 2018 — the first year of a two-year marine heat wave in the region — may have been as much as quadrupled compared to the previous year, researchers found. But with the heat disrupting much of the Bering Sea’s food web, snow crabs had a hard time foraging for food and weren’t able to keep up with the caloric demand.
Other species took advantage of this dire situation, said Kerim Aydin, a co-author of the study and fisheries research biologist with NOAA’s Alaska Fisheries Science Center.
Normally, there is a temperature barrier in the ocean that prevents species like Pacific cod from reaching the crabs’ extremely cold habitat. But during the heat wave, the Pacific cod were able to go to these warmer-than-usual waters and ate a portion of what was left of the crab population.
“This was a huge heat wave effect,” Aydin told CNN. “When the heat wave came through, it just created a huge amount of starvation. Other species may have moved in to take advantage of it, and then when the heat wave passed, things are maybe a bit more back to normal — although the crabs have a long road to getting past that even in normal times.”
Temperatures around the Arctic have warmed four times faster than the rest of the planet, scientists have reported. Climate change has triggered a rapid loss in sea ice in the Arctic region, particularly in Alaska’s Bering Sea, which in turn has amplified global warming.
“2018 and 2019 were an extreme anomaly in sea ice in the Bering Sea, something that we’d never seen before,” Szuwalski said. “There was maybe 4% of the coverage of ice that we’ve historically seen, and to know whether or not that’s going to continue going forward is hard to say.”
What’s happening with Alaska’s crabs is proof the climate crisis is rapidly accelerating and impacting livelihoods, Szuwalski said. He knew this was going to happen at some point, but he “didn’t expect it to happen so soon.”
“This was kind of an unexpected, punctuated change in their populations,” he said. “But I think long term, the expectation is that the snow crab population will move north as the ice recedes and in the eastern Bering Sea, we probably won’t see as much of them anymore.”
Translation
近年來，數十億隻雪蟹從阿拉斯加周圍的海洋中消失，科學家現在表示他們知道原因：海洋溫度升高可能導致它們餓死。
就在這項發現幾天前，阿拉斯加漁獵部宣布連續第二年取消雪蟹收穫季節，理由是大量蟹在通常寒冷、危險的白令海水域中失蹤。
美國國家海洋暨大氣總署的科學家週四發表的這項研究發現，最近白令海東部的海洋熱浪與 2021 年調查中開始出現的雪蟹突然消失之間有顯著關聯。
該研究的主要作者、NOAA 漁業生物學家 Cody Szuwalski 表示： “當我第一次收到 2021 年調查數據時，我大吃一驚” “每個人都希望並祈禱這是調查中的錯誤，明年你會看到更多的蟹” 。
Szuwalski告訴 CNN: 「到了 2022 年，是更多的無奈, 這將是一條漫長的路」。
那一年是美國阿拉斯加雪蟹漁場首次關閉。 捕撈者將蟹群數量下降歸因於過度捕撈，但專家告訴美國有線電視新聞網，「過度捕撈」是一個觸發保護措施的技術定義，它實際上並不能解釋蟹群瓦解的原因。
Szuwalski說: 「這篇論文給我帶來的最大收穫是，從歷史上看，漁業科學家一直非常擔心過度捕撈 - 這就是我們的白鯨，在很多地方，我們確實用管理解決了這個問題」; 「但氣候變化打亂了我們的計劃、我們的模型和管理系統」。
在這項研究中，科學家分析了2020年開始雪蟹消失的原因，並將其歸結為兩類：雪蟹要麼遷移，要麼死亡。
Szuwalski說，他們望向白令海以北、向西到俄羅斯水域，甚至深入海洋深處， “最終得出結論，螃蟹不太可能遷移，死亡事件可能是一個重要的推動因素。”
他們發現，氣溫升高和族群密度與成長螃蟹的死亡率升高有顯著相關。
死亡事件背後的原因是：較飢餓的蟹。
研究表明，雪蟹是冷水物種，絕大多數生活在水溫低於 2 攝氏度的地區，但它們也能在高達
12 攝氏度的水域中生存。 溫暖的海水可能會對螃蟹的新陳代謝造成嚴重破壞，並增加它們的熱量需求。
研究人員發現，2018 年（該地區兩年海洋熱浪的第一年）蟹從食物所需的能量, 可能比前一年增加了四倍。 但由於高溫破壞了白令海的大部分食物網，雪蟹很難覓食，也無法滿足其熱量需求。
該研究的合著者、美國國家海洋暨大氣總署阿拉斯加漁業科學中心的漁業研究生物學家Kerim Aydin說，其他物種趁機利用了這種可怕的情況。
在通常情況下，海洋中存在溫度屏障，阻止太平洋鱈魚等物種到達螃蟹極冷的棲息地。 但在熱浪期間，太平洋鱈魚能夠前往這些比平常溫暖的水域, 並吃掉一部分剩下的螃蟹族群。
Aydin 告訴美國有線電視新聞網：「這是一次巨大的熱浪效應 」; 「當熱浪襲來時，它造成了大量的飢餓。 其他物種可能已經跑進來利用它，然後當熱浪過去時，情況可能會稍微恢復正常 - 即使在正常情況下，螃蟹在這條復常路也有很長的路要走。 」
科學家報告稱，北極周圍的氣溫變暖速度是地球其他地區的四倍。 氣候變遷引發了北極地區海冰的快速流失，特別是阿拉斯加白令海的海冰迅速減少，進而加劇了全球暖化。
Szuwalski說: 「2018 年和 2019 年白令海海冰出現極端異常，這是我們以前從未見過的」; 「冰覆蓋率可能是我們歷史上見過的 4%，很難說這種情況是否會繼續下去」。
Szuwalski說，阿拉斯加螃蟹的情況證明氣候危機正在迅速加劇並影響生計。 他知道這會在某個時候發生，但他「沒想到會這麼快發生」。
他說: 「他們的數目發生了一種意想不到的、斷斷續續的變化」;
「但我認為從長遠來看，隨著冰層消退，雪蟹族群將向北移動，在白令海東部我們可能不會再看到那麼多雪蟹了」。
So, what is happening
with Alaska’s crabs is a proof that climate crisis is rapidly accelerating and
impacting livelihoods. The snow crab population will move north as the ice
recedes in the eastern Bering Sea, we probably will have a new fishing
ground with lesser catches.
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