“During the mid-20th century, killer whales (orcinus orca) frequently scavenged from the carcasses produced by whaling. These carcasses were primarily species of large whale, preferred by killer whales, but which normally sink to the bottom after death, possibly putting the carcass beyond the diving range of killer whales,” they say in their report to the Royal Society’s Biological Letters.<\/p>\n
They said that these carcasses would be clustered together and acoustically marked by loud sounds (including the noise of catcher boat engines and exploding harpoons). They propose that during the course of modern [derestricted] whaling, scavenging by killer whales increased.<\/p>\n
“However, during the 1970’s the numbers of available whale carcasses fell dramatically with the cessation of most whaling (in contrast to a reasonably stable abundance of living whales), and the scavenging killer whales lost an important food source. The decline of scavenging opportunities may have led to increased killer whale predation on large whales, seals, sea lions and sea otters. For some populations of those species, such predation pressure may have seriously affected their numbers, and consequently their roles in ecosystems,” they report.<\/p>\n
Greenland cormorants are diving for fish in the dark so they may have other techniques for spotting prey, according to work by a team led by Dr D Gremillet of the Centre de Ecologie et Physiologie Energ\u00e9tiques in Strasbourg France. They say that since most seabirds are visual hunters one would expect the lack of light would be a problem for predator species wintering at high latitude. The team studied great cormorants (phalacrocorax carbo) from West Greenland, conducting the first year-round recordings of the diving activity in a Polar predator. They found the birds dived every day during the Arctic winter and that half of the dives were conducted in the dark during the Polar night. “Our study underlines the stunning adaptability of great cormorants and raises questions about the capacity of diving birds to use non-visual cues to target fish,” they said.<\/p>\n
Research into 1970s warming in the North Pacific may be a cause for significant change on stocks of Walleye Pollock (theragra chalcogramma), according to a team led by Dr Professor N.C. Stenseth at the University of Oslo. They say “changes in the climatic and biotic conditions of the North Pacific in the late 1970s had profound effects in the recruitment dynamics of walleye pollock in the Gulf of Alaska. During periods characterized by high water temperature and predation, pollock recruitment variability and magnitude were below average, and the year class strength was delayed after the first year of life.” In contrast there was high abundance and variability, and early recruitment control when the scenario was low water temperature and low predation. The team says there is a “need better [to] link the mechanisms of recruitment variability with the incumbent environmental regimes”.<\/p>\n
Paradoxically, another report (about humans)suggest that cold-blooded populations (poikilotherms, such as crustaceans and fish) will increase when the climate warms up. Work by Dr J.M. Drake at the National Center for Ecological Analysis and Synthesis, University of California Santa Barbara, says that climatologists predict that human activities [causing climate warming] will result in increasing fluctuations in rain and temperature. Early theories predicted that fluctuations would result in decreasing population growth rates.<\/p>\n
“Now we know that in some cases growth rates might be increased by environmental fluctuations. This study presents the first evidence that fluctuating temperatures can increase population growth rates in some organisms, particularly cold-blooded animals (poikilotherms). This finding is newsworthy because it is an exception to the rule that environmental fluctuations decrease population growth rates and because an increase in extreme temperatures has been predicted as a consequence of global climate change,” Dr. Drake said.<\/p>\n
Finally, should you haul in a jawless, toothless fish in your net, about 24cm long, you will be interested to know that the latest research shows that it does indeed have dentine (which makes up teeth) and enamel but not in its mouth. According to scientists led by Dr J. Sansom at the University of Bristol, UK, until now the Sacabambaspis janvieri from South America has “assumed a central role in debates on the origins and early evolution of the vertebrates”. Now, new evidence from Bolivia and Argentina has found where the teeth went. It seems the armour scales of Sacabambaspis consisted of discrete layers of “bone, dentine and enameloid and that the sensitive tissue dentine is pervasive throughout primitive armoured fish” they said. The sting in the tail is that the fish dates back between 440-480 million years so its fossil remnant in your net will certainly be too tough for human teeth.<\/p>\n","protected":false},"excerpt":{"rendered":"
“During the mid-20th century, killer whales (orcinus orca) frequently scavenged from the carcasses produced by whaling. These carcasses were primarily species of large whale, preferred by killer whales, but which normally sink to the bottom after death, possibly putting the carcass beyond the diving range of killer whales,” they say in their report to the […]<\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[13],"tags":[],"sponsor":[],"class_list":["post-10614","post","type-post","status-publish","format-standard","hentry","category-analysis"],"acf":[],"_links":{"self":[{"href":"https:\/\/www.worldfishing.net\/icefish-conference\/wp-json\/wp\/v2\/posts\/10614","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.worldfishing.net\/icefish-conference\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.worldfishing.net\/icefish-conference\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.worldfishing.net\/icefish-conference\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.worldfishing.net\/icefish-conference\/wp-json\/wp\/v2\/comments?post=10614"}],"version-history":[{"count":0,"href":"https:\/\/www.worldfishing.net\/icefish-conference\/wp-json\/wp\/v2\/posts\/10614\/revisions"}],"wp:attachment":[{"href":"https:\/\/www.worldfishing.net\/icefish-conference\/wp-json\/wp\/v2\/media?parent=10614"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.worldfishing.net\/icefish-conference\/wp-json\/wp\/v2\/categories?post=10614"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.worldfishing.net\/icefish-conference\/wp-json\/wp\/v2\/tags?post=10614"},{"taxonomy":"sponsor","embeddable":true,"href":"https:\/\/www.worldfishing.net\/icefish-conference\/wp-json\/wp\/v2\/sponsor?post=10614"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}