With no explanation, label text_A→text_B with either "not_related" or "related".
text_A: The ocean is necessary for the blue whale's existence.
text_B: Marine mammals are aquatic mammals that rely on the ocean and other marine ecosystems for their existence .. aquatic mammals. aquatic mammals. marine ecosystems. marine ecosystems. They include animals such as seals , whales , manatees , sea otters and polar bears .. seals. Pinniped. manatees. Sirenia. They do not represent a distinct taxon or systematic grouping , but rather have a polyphyletic relation due to convergent evolution .. polyphyletic. polyphyly. convergent evolution. convergent evolution. They are also unified by their reliance on the marine environment for feeding .. Marine mammal adaptation to an aquatic lifestyle vary considerably between species .. Both cetaceans and sirenians are fully aquatic and therefore are obligate water dwellers .. Seals and sea-lions are semiaquatic ; they spend the majority of their time in the water , but need to return to land for important activities such as mating , breeding and molting .. mating. mating. breeding. breeding in the wild. molting. molting. In contrast , both otters and the polar bear are much less adapted to aquatic living .. polar bear. polar bear. Their diet varies considerably as well ; some may eat zooplankton , others may eat fish , squid , shellfish , sea-grass and a few may eat other mammals .. zooplankton. zooplankton. While the number of marine mammals is small compared to those found on land , their roles in various ecosystems are large , especially concerning the maintenance of marine ecosystems , through processes including the regulation of prey populations .. marine ecosystems. marine ecosystems. This role in maintaining ecosystems makes them of particular concern as 23 % of marine mammal species are currently threatened .. Marine mammals were first hunted by aboriginal peoples for food and other resources .. aboriginal peoples. aboriginal whaling. Many were also the target for commercial industry , leading to a sharp decline in all populations of exploited species , such as whales and seals .. seals. Pinniped. Commercial hunting lead to the extinction of † Steller 's sea cow and the † Caribbean monk seal .. Caribbean monk seal. Caribbean monk seal. After commercial hunting ended , some species , such as the gray whale and northern elephant seal , have rebounded in numbers ; conversely , other species , such as the North Atlantic right whale , are critically endangered .. whale. whale. gray whale. gray whale. northern elephant seal. northern elephant seal. North Atlantic right whale. North Atlantic right whale. critically endangered. critically endangered. Other than hunting , marine mammals can be killed as bycatch from fisheries , where they become entangled in fixed netting and drown or starve .. bycatch. bycatch. Increased ocean traffic causes collisions between fast ocean vessels and large marine mammals .. Habitat degradation also threatens marine mammals and their ability to find and catch food .. Habitat degradation. Habitat degradation. Noise pollution , for example , may adversely affect echolocating mammals , and the ongoing effects of global warming degrade arctic environments .. Noise pollution. Noise pollution. echolocating. Animal echolocation
related.