Scientists are studying the diets of the oceans’ top predators as they change in response to their environments. This is because how much and what they eat can affect how ecosystems function.
科學家們正進行研究，當海洋頂級捕食者，在對其環境作出反應時，它們改變的食物。這是因為，它們吃什麼及多少，會影響生態體系如何運作。
And while researchers know that killer whales, also known as orcas, are the oceans’apex predators, our understanding of their diet — particularly the quantity of each species they consume — remains incomplete.
不過，儘管研究人員們知曉虎鯨(也被通稱為逆戟鯨)是海洋的頂級捕食者，人們對其食物的瞭解，特別是消耗之每種物種的數量，仍然不完整。
This is especially true for remote populations that cannot be observed year-round.
對無法全年被觀察的遙遠種群而言，這特別是如此。
But there’s now a way to recreate killer whales’ precise diets by using only a sample of their skin and fat. My research team developed a promising technique that reveals these wild predators’ diets across the North Atlantic Ocean.
不過，目前有一種方法，藉由僅使用虎鯨的皮膚及脂肪樣本，來重現虎鯨的精確食物。我的研究團隊開發了一種，有指望揭露此些野生食肉動物，在北大西洋之食物的技術。
Killer whales are intelligent predators that are known to adopt specific hunting techniques, ranging from carousel feeding — co-operatively herding and then feeding on — herring, to co-operatively creating waves that can dislodge seals from ice floes. As a result, they can hunt nearly any species, from fish to fur seals to blue whales, throughout the world’s oceans.
虎鯨眾所周知，採取涉及從旋轉木馬式(轉盤式)捕食(也就是，合作驅趕，然後捕食)鯡魚，到合作創造波浪來從浮冰中，逐出海豹之特殊狩獵技巧的聰明捕食者。
Depending on their location and evolutionary history, different groups of killer whales have developed different ecotypes — unique diets and lifestyles. The most notorious ecotypes are the transient and resident killer whales in the Eastern North Pacific.
取決於它們的棲地及演化史，不同的虎鯨群已經發展出，不同的生態型。也就是，獨特的食物及生存方式。最聲名狼藉的生態型，是於北太平洋東部，短暫及常駐的虎鯨。
These ecotypes have been extensively studied for decades, as the killer whales inhabit densely populated areas, which allows scientists to observe these individuals year-round.
此些生態型已經被廣泛研究，達幾十年。因為，此些虎鯨棲息於人口稠密的地區，這使科學家們得以全年觀察此些個體。
In these populations, scientists found evidence of “trophic cascades,” the effects of predator consumption on the rest of the food web. Killer whales had top-down effects on the density of kelp forests; the killer whales greatly reduced the sea otter population, which caused the sea urchins — the sea otters’ main food source — to proliferate and decimate the kelp forests.
在這些種群中，科學家們發現了，捕食者消耗對食物網其餘部分之諸多影響的“營養級聯”證據。虎鯨對海帶森林的密度，具有自上而下的影響;此些虎鯨大大減少了海獺種群，這導致海膽(海獺的主要食物來源)增殖而大量毀滅海帶森林。
圖1. 一群在冰島韋斯特曼納埃亞爾群島(Vestmannaeyjar)水域，享用完鯡魚後緩慢前行的虎鯨。(圖援用自原文)
A group of killer whales in Vestmannaeyjar, Iceland, travelling slowly after feasting on herring.
Comparing different groups of killer whales around the world reveals that there is still a lot we don’t know about them. Figuring out what killer whales living in remote parts of the Arctic eat, like in Baffin Bay, Greenland and Arctic Norway, is challenging. Observation of feeding events can be difficult in the unstable waters of the Arctic Ocean.
比較世界各地不同的虎鯨群，揭露了我們有關它們，仍有很多不知曉的事。弄清楚生存於北極遙遠地區(如巴芬灣、格陵蘭島及挪威北極地區)的虎鯨吃什麼，是具挑戰性的。因為，在北冰洋不穩定的水域中，觀察進食活動會是困難的。
Initial studies suggested there were two types of killer whales in the North Atlantic: those that prey on marine mammals, and the other group that eats fish and occasionally seals. However, the lack of data, combined with emerging evidence has led to scientists proposing to retire this classification. It appears that there is a more diverse range of diets in some North Atlantic populations.
諸多初步研究顯示，於北大西洋有兩種虎鯨：那些捕食海洋哺乳動物的虎鯨，及另一群吃魚及偶爾吃海豹的虎鯨。不過，由於缺乏數據，加上不斷出現的證據，已經導致科學家們提議，停止使用此分類。於某些北大西洋的種群中，似乎食物有更多樣化的類別。
Due to the challenge of collecting observation data, researchers have focused their efforts on the chemical signals they can measure inside the killer whales’ skin and blubber. These chemical signals can consist of lipids or stable isotopes which tell us what the whales eat and how they impact the food chain.
由於收集觀測數據的難題，研究人員們已經將他們的精力，集中於能測量虎鯨皮膚及脂肪內的化學信號上。這些化學信號能包括，脂質或能告知我們，鯨魚吃什麼及其如何影響食物鏈的穩定同位素。
Our technique measures the lipid composition in the whale’s fat, and uses a computer program to recreate the most probable proportion of each prey species to an individual’s diet.
我們的技術測量鯨魚脂肪中的脂質成分，並使用一種電腦程式，來重新創建每一獵物物種，對個別食物的最可能比例。
All that is required are multiple lipid “signatures” — that represent the proportion of each fatty acid in the whale’s blubber — from the killer whales and from their potential prey.
所需要的只是，來自代表鯨魚脂肪中，每種脂肪酸比例之虎鯨及其潛在獵物的多重脂質“特徵”。
Samples of killer whale blubber reveal detailed information about their preferred food sources.
虎鯨脂肪樣本透露了，有關其優先食物來源的詳細資訊。
Our open-access research, recently published in the Journal of Animal Ecology, used a technique called quantitative fatty acid signature analysis to reveal the diets of nearly 200 North Atlantic killer whales.
我們最近發表於《動物生態學雜誌》上，開放取用的研究使用了一種，被稱為定量脂肪酸特徵分析的技術，來揭露近200頭北大西洋虎鯨的食物。
We also measured lipid compositions in over 900 prey samples. The results showed a range of feeding strategies across the ocean. In the western part of the North Atlantic, killer whales ate mainly other whales (like large baleen whales, belugas and narwhals); killer whales in Greenland preferred seals and in Norway, they showed a preference for fish like herring.
我們也測量了，900多種獵物樣本中的脂質成分。此些結果顯示了，整個海洋一連串進食的重大適應性變化。在北大西洋的西部部分，虎鯨主要吃食其他鯨魚(如大型鯨鬚鯨、白鯨及一角鯨)；於格陵蘭島的虎鯨更喜歡海豹，而在挪威，它們展現了，對於諸如鯡魚等魚類的偏愛。
Using this technique, scientists can now estimate the exact percentage of different species in each whale’s diets. But what surprised us the most was the level of variation between individual diets within each population.
使用此技術，目前科學家們能估計，於每頭鯨魚之食物中，不同物種的確切百分比。不過，最令我們驚訝的是，在每一種群中，個別食物之間的差異程度。
In the western North Atlantic, individuals focus either on cetaceans — marine mammals like belugas and narwhals — or seals. In the mid-North Atlantic, killer whales would feed on all available prey. And for the most part, eastern North Atlantic killer whales seem to keep to a diet rich in fish. Several individual killer whales in Norway and Iceland supplement fish with marine mammals.
於北大西洋西部，各別種群不是聚焦於鯨目動物(諸如白鯨及獨角鯨等海洋哺乳動物)，就是海豹。在北大西洋中部，虎鯨會以所有可資獲得的獵物為食物。而通常，北大西洋東部，虎鯨似乎固守一種富於魚類的食物。於挪威及冰島，幾種各別的虎鯨，以海洋哺乳動物彌補魚類。
Our study is the first and largest of its kind on killer whales, and our findings encourage us to further investigate killer whale diets at the individual scale. We now know that individuals within the same populations can have different diets.
我們的研究是這類針對虎鯨，首次且規模最大的研究。因此，我們的研究結果鼓舞了我們，進一步研究個體規模的虎鯨食物。目前我們知曉，於相同種群中，個體能有不同的食物。
This not only translates to different contaminant exposures and health risks for these top predators, but also represents different feeding strategies throughout the Arctic Ocean.
這不僅說明了，有關這些頂級捕食者的不同污染物暴露及健康風險，而且也代表了整個北冰洋，不同進食的重大適應性變化。
This approach allows us to measure future shifts in these predators’ diets and understand how they may impact Arctic food webs. Because of climate change, killer whales are progressively moving further into the Arctic.
此方法使我們得以估量，在這些食肉動物之食物中的未來變化，及瞭解它們可能如何影響北極食物網。由於氣候變遷，虎鯨正逐漸地更進一步遷移進入北極。
Their presence and a potential increase in consumption of Arctic species could change the ecosystem dynamics in the North. Further research using this technique on samples collected over an extensive period could allow researchers to detect shifts in the whales’ diets and ecosystem.
它們的存在及在北極物種消耗上的潛在增加，可能改變於北極地區之生態體系的動態。使用此技術針對長時間收集樣本的進一步研究，可能使研究人員們得以發現，在鯨魚食物及生態體系上的諸多變化。
網址：https://theconversation.com/analyzing-the-fat-of-killer-whales-reveals-what-they-eat-203497
翻譯：許東榮
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