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この数週間、カリフォルニア州北部からオレゴン州の海岸に、北大西洋オキアミ（ツノナシオキアミ）が大量に打ち上がっている。この地域では史上最大の大量死だ。北大西洋オキアミは小さな甲殻類で、北大西洋の食物連鎖で重要な役割を担っている。
その大半は、オレゴン州ニューポートからカリフォルニア州マッキンリービルまでの約400キロメートルに及ぶ海岸に、6月16～18日（米国時間）の間に打ち上げられた。レッドウッド国立公園の生物学研究者デビッド・アンダーソン氏はAP通信に対して、打ち上がった大量のオキアミによって、同公園の海岸にはピンク色の長い帯ができたと語っている。
カリフォルニア州のシーグラント公開講座との共同調査を主導している海洋生物学者ジョー・タイバルツィ（Joe Tyburczy）氏によると、広範囲に見られた今回のオキアミ大量死は、交尾期に大きな群れを形成したところを、風向きの大きな変化によって海岸に打ちつけられたものである可能性があるという。
タイバルツィ氏が、カリフォルニア州サンタローザの地元紙「プレス・デモクラット」紙に語ったところによると、今年はオキアミの数が通常より多く、また、西海岸沖の水域の酸素レベルがとりわけ低かった。これらの要因によって、異常に大量のオキアミが、海面からすぐのところを泳ぐようになった可能性がある。その場所だと、強風で海岸に押し出される危険性が出てくるのだという。
オレゴン州とカリフォルニア州で死んでいたオキアミを調査したところ、その大半が、受精卵をもつメスであることがわかった。このことは、交尾期の群れを形成した後で海岸に打ち上げられたという説に信憑性を与えている。
[Aaron Sankin(English) 日本語版：緒方亮/ガリレオ]
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Problems Of The Ocean
Overfishing(01 of09)
Many marine scientists consider overfishing to be the worst impact humans are having on the oceans. The Food and Agriculture Organization estimates that over 70% of the world’s fish species have been entirely exploited or depleted. By capturing fish faster than they can reproduce, we are harming entire ecosystems that interact with those species, from the food they eat to the predators that eat them. These losses make the ecosystems more vulnerable to other disturbances, such as pollution. A complete overhaul of fishing policies, requiring global cooperation, is needed to achieve a sustainable system. (credit:AP)
Irresponsible Fish Farming(02 of09)
Fish farming, or aquaculture, is the growing response to wild fish stocks rapidly depleting. While it sounds like a good idea in theory, it unfortunately has many negative consequences due to poorly managed operations. Nutrient and chemical pollution can occur easily in open-ocean operations when fish feed, excrement, and medication is released into the environment. Farmed fish accidentally released into wild populations can also have destructive effects, such as loss of native stocks, disease transmission, and damaging changes in habitat. Unfortunately, the biggest hindrance to overcoming the challenges of an industry that supplies nearly 50% of the world’s fish food supply is that it currently remains relatively unregulated. (credit:AP)
Ghost Fishing(03 of09)
Ghost fishing is an environmentally harmful issue caused when lost or discarded fishing gear continues to catch fish and other marine life. Often times, the traps trigger a chain-reaction problem when larger predators come to eat the smaller ones that have been ensnared, only to get tangled in the mess themselves. The issue of ghost fishing is most common with passive gear that has been abandoned, and also poses a serious threat to other ocean vessels. Stray gear can be caught in the propeller of a boat, damaging or even disabling it. Many solutions have been offered, such as fishing gear made from biodegradable materials or incentives like the Republic of Korea’s buy-back program, which rewards fisherman for turning in old gear. (credit:AP)
Garbage(04 of09)
This one is the most obvious. It’s astounding how much of our trash finds its way into the ocean. Animals become easily entangled and trapped in our garbage, and it can destroy delicate sea life like coral and sponges. In addition, sea turtles and dolphins often mistake plastic bags for their favorite foods, jellyfish and squids, choking them or clogging their digestive system. If that’s not bad enough, hopefully the bigger-than-Texas trash vortex in the Pacific Ocean and its smaller cousin in the Atlantic will help serve as a wakeup call. (credit:Getty)
Acidification(05 of09)
The ocean absorbs as much as one third of the CO2 emitted worldwide, which keeps us cooler but makes the ocean surface much more acidic. This has the effect of limiting calcium carbonate needed by coral, plankton, and other marine life that use it to build the skeletal frames and shells that protect them. Oceanic acidity has increased by 25% since the industrial revolution, and will eventually destroy much marine life if it increases at this rate. (credit:Getty)
Dead Zones(06 of09)
Dead zones are areas where the sea floor has little to no dissolved oxygen. These areas are often found at the mouths of large rivers, and are caused primarily by fertilizers that are being carried in the runoff. Unfortunately, the lack of oxygen kills many creatures and destroys entire habitats. At our current rate, dead zones will increase by 50% before the end of the century. (credit:Flickr: Sam Beebe / Ecotrust)
Mercury Pollution(07 of09)
Scientists report that our ocean’s mercury levels have risen over 30% the last 20 years, and will increase another 50% in the next few decades. Emissions from coal power plants are the primary culprit, dispensing poisonous mercury that works its way up the food chain, eventually coming to us through the fish we eat. This neurotoxin can alter brain development of fetuses and has been linked with learning problems. (credit:AP)
Offshore Drilling(08 of09)
Offshore drilling continues to be a debate, but it’s clear that proceeding with oil production will only exacerbate the dilemmas of our oceans. The use of fossil fuels is the reason our oceans have been heating up and becoming more acidic, but offshore drilling takes the risks even further. When oil is extracted from the ocean floor, other chemicals like mercury, arsenic, and lead come up with it. Also, the seismic waves used to find oil harm aquatic mammals and disorient whales. In 2008, 100 whales had beached themselves as a result of ExxonMobil exploring for oil with these techniques. Furthermore, the infrastructure projects to transport the oil often create worse problems, eroding the coastline. These realities are another reason (credit:AP)
Shark Finning / Whaling(09 of09)
The destruction of the ocean’s most important predators has significant consequences that ripple down the food chain. 50 to 100 million sharks are killed each year, either as bycatch from fishing vessels or directly hunted for their dorsal fins, used in an expensive soup popular across Asia. When finned, the sharks are thrown back into the water, often still alive and left to bleed to death. Unfortunately, sharks reproduce fairly slowly and don’t have a large amount of offspring, so these actions have long-lasting effects on the delicate ecosystems they help regulate. Despite the 1986 moratorium on many types of whaling, it still continues to be a problem, with some nations like Japan looking for loopholes and lobbying for lax regulations. (credit:AP)