[unable to retrieve full-text content]
Tuesday, January 30, 2018
Gone fishin': decorator crabs use other species as fishing rods, study reveals
Mengapa Manusia Takut Kepada Hiu?
Hiu mulai muncul di mata publik saat peluncuran film Jaws pada musim panas 1975. Film tersebut bercerita tentang hiu putih besar yang meneror para penduduk di pinggir pantai. Kehadiran film ini cukup untuk menyuntikkan rasa takut ke dalam hati perenang. Thriller serupa pun mengabadikan hiu sebagai penjahat dan musuh manusia.
Mengapa manusia takut kepada hiu?
Menurut Blake Chapman, ahli biologi kelautan dan peneliti hiu di University of Queensland, rasa takut pada hiu atau galeophobia, bukanlah hal yang irasional. Secara sederhana, ikan predator itu memang sangat menyeramkan. Hiu putih besar contohnya, mereka memiliki mulut memanjang dengan barisan 300 gigi setajam belati yang bisa merobek mangsanya dengan mudah. Mereka juga bisa merasakan medan elektromagetik yang memudahkan untuk menemukan mangsa.
Namun, tidak semua jenis hiu seganas hiu putih besar yang digambarkan dalam film tersebut. Ada lebih dari 465 spesies hiu. Ukurannya pun beragam -- dari yang kerdil 7 inci hingga hiu paus sepanjang 50 kaki. Kebanyakan dari mereka makan ikan, krustasea, moluska, plankton, mamalia laut dan hiu lainnya. Dengan kata lain, manusia tidak berada dalam menu makanan hiu.
(Baca juga: Hiu Miliki Kepribadian Berbeda Satu Sama Lain)
David Ropeik, konsultan persepsi risiko dan pengarang buku How Risky Is It, Really? Why Our Fears Don’t Always Match the Facts, mengatakan kita lebih takut dengan cara membunuh yang bisa dilakukan hiu. Dimakan hidup-hidup oleh hiu sepanjang 15 kaki merupakan cara mati yang amat menderita. Namun, ketakutan belum tentu sesuai fakta. Dan rasa takut pada serangan hiu lebih mengarah pada respons emosional dibanding realita.
Secara keseluruhan, kita takut kehilangan kontrol sebagai manusia. Kita tidak ingin rahang predator tersebut menentukan takdir kematian kita.
Dari mana ketakutan itu muncul?
Rasa takut tidak langsung muncul ketika kita dilahirkan. Itu adalah sesuatu yang berkembang seiring berjalannya waktu. Bayi tidak takut pada ular dan ketinggian, tetapi sebagai orang dewasa, otak kita menjadi lebih sensitif pada stimulans yang menakutkan.
Namun, nenek moyang kita pun memiliki banyak hal untuk ditakuti. Pikirkan kembali bagaimana manusia purba bisa bertahan hidup di habitat primitif. Mereka akan menghindari tebing tinggi dan binatang liar karena tahu kedua hal tersebut mengancam dan bisa membunuhnya. Manusia purba beradaptasi untuk melindungi diri mereka.
“Rasa takut merupakan sesuatu yang kita dapatkan dari nenek moyang. Hiu merupakan binatang buas. Makhluk hidup seperti hewan adalah sesuatu yang rentan menimbulkan rasa takut,” kata Chapman.
Bagaimana mengatasi rasa takut terhadap hiu?
Ada beberapa cara yang bisa dilakukan untuk mengurangi ketakutan pada hiu. Kita bisa memberikan ilusi kontrol pada diri sendiri. Sebab, ketika merasa tidak terkontrol, segala sesuatunya menjadi lebih menyeramkan.
(Baca juga: Hiu Miliki Kepribadian Berbeda Satu Sama Lain)
Untuk melakukannya, kita bisa membaca tentang jenis hiu yang tinggal di perairan yang menjadi tempat berenang kita. Dan pahami apakah mereka termasuk yang mengincar manusia.
Selain itu, untuk menghindari serangan hiu, sebaiknya jangan berenang ketika berdarah atau sedang berbaring di atas papan selancar (hiu biasanya mengincar anjing laut, dan dari bawah, papan selancar tampak seperti hewan tersebut). Kita juga sebaiknya menghindari kegiatan spear fishing atau ‘menombak ikan’ karena itu mengirimkan sinyal elektrik yang menarik perhatian hiu.
Jika diserang hiu, para ahli menyarankan kita untuk melawannya. Chapman merekomendasikan untuk menyasar mata atau insangnya jika memungkinkan.
(Elaina Zachos/National Geographic)
Baca Di sini Bro https://nationalgeographic.co.id/berita/2018/01/mengapa-manusia-takut-kepada-hiuMonday, January 29, 2018
Light pollution from research ship makes Artic zooplankton return to the deep
Zooplankton.
Image credits: Wikipedia.
Scientists discovered that zooplankton from the Arctic is very sensitive to light pollution. Even light coming from research ships can make these small organisms sink back into darkness. Sure, it was previously known that the light of a full moon or the northern lights would make these creatures retread to deeper waters, but the possibility that ship-borne lights bothered them was still under debate.
“We did have a suspicion that this was the case,” said Martin Ludvigsen, a professor in NTNU’s Department of Marine Technology and at the university’s Centre of Autonomous Marine Operations and Systems. “We were able to demonstrate this, and show the significance of the lights from the ship” he added.
Run for the depths!
Zooplankton is the most widespread vertical migratory biomass on Earth (and armed to the teeth). Around the globe, these tiny animals rise to the surface during the night to feed and descend into deeper waters to avoid predators during the day. Research over the last decade shows that the weak moonlight or the northern lights cause zooplankton to retreat to darker waters.
Because of its photosensitivity, scientists have a hard time actually studying zooplankton: if light from their ships shines through to the small animals, any accurate recording of their population in an area becomes highly improbable.
To better understand the effects of light and light pollution on zooplankton, a team of researchers from NTNU, UiT (The Arctic University of Norway), the University of Delaware, and the Scottish Association for Marine Science modified a kayak, equipped it with sensors, a petrol engine, strapped it to a ship, and set out to sea. Once in open waters the kayak, dubbed Jetyak, was sent away from the research vessel and used to measure the depth reached by artificial light, as well as to record plankton thickness via sonar.
The “Jetyak” and a part of the research team.
Photo: Geir Johnsen, NTNU/UNIS
The acoustic data collected by the autonomous Jetyak showed that the layer of zooplankton was far thicker and started from closer to the surface near itself compared to that near the research boat (where the plankton was hiding from light). This effect reached depths of up to 80 meters.
“We were sort of surprised how pronounced this avoidance behavior was,” Ludvigsen said. “It was so clear and so fast. Even when we tried to reproduce this in a small boat and a headlamp, it was really easy to see in the echosounder.”
Photo from the board of the research ship.
Photo: Benjamin Hell
“These findings tell us that zooplankton populations and behavior can be under- or overestimated because these marine organisms respond to light, either by swimming away from it, or sometimes towards it,” said Geir Johnsen, co-author and a marine biologist at NTNU.
The biologist believes that scientists have to undertake their studies under natural conditions if they want to discover what zooplankton is truly doing. This means developing autonomous vehicles equipped to sample the vast seas.
Arctic fauna — ranging from bowhead whales to marine birds, to cod — feeds on zooplankton, particularly those in the genus Calanus. Their high content of fatty acids is what makes them such a filling meal.
Calanus glacialis
Photo: Malin Daase, UiT — The Arctic University of Norway
“Light pollution may disturb zooplankton behavior with respect to feeding, predator-prey relationships and diurnal migration, in addition to their development from juveniles to adults,” Johnsen said.
Global warming also poses a serious threat to the Arctic’s tiny inhabitants — as sea ice cover is growing thinner, or outright melting completely in large areas, zooplankton is rapidly running out of the dark areas they like, Johnsen remarked. Considering how central zooplankton is on the local menus, the Arctic ecosystem may have a lot to suffer.
The paper was published in the journal Science Advances.
Enjoyed this article? Join 40,000+ subscribers to the ZME Science newsletter. Subscribe now!
Like us on Facebook
Hot weather attracts jellyfish swarms
The sweltering hot weather has brought swarms of jellyfish and similar creatures into New Zealand waters.
Jellyfish at Island Bay, Wellington Photo: RNZ/Caitlin Cherry
Swimmers have reported dense swarms of creatures rubbing against their bodies as they move through the water.
Have you had any problems with jellyfish while swimming at the beach? Send your accounts or pictures to: iwitness@radionz.co.nz
Dennis Gordon, who is a marine authority at the National Institute of Water and Atmospheric Research, or NIWA, said many were not real jellyfish but a related species known as salps, which was harmless.
Another species was also harmless - though larger - the 30 centimetre diameter Crystal Jellyfish.
Despite its name, it was not a real jellyfish.
But there was also the Lion's Mane jellyfish, which was red, and has poisonous tentacles several metres long.
Dr Gordon said the species was affected by the weather.
"It's probably a consequence of the warmer temperatures, which speed up growth of plant plankton and that's felt up the food chain to the things that prey on plant plankton - animal plankton, zooplankton - and then the things that prey on these zooplankton - including jellyfishes and fishes."
Dr Gordon said numbers of jellyfish varied depending on tides and currents as well as temperatures.
Swimming today at #OrientalBay? Notice thousands of barrel-like transparent critters? These are #salps, herbivorous zooplankton that feed on phytoplankton (& don’t sting!) and are important for marine ecology and biogeochemistry @niwa_nz#UCMsalpspic.twitter.com/UHQmZN9fzJ
— Moira Decima (@moiradecima) January 28, 2018
Wellington surfer Nick Butcher had an unpleasant encounter with such a fish during an ocean swim off Oriental Bay in Wellington Harbour.
"I was just swimming along, as you do, and then splat - face first into what we call 'the mothership of jellyfish'. It kind of freaked me out and it stung me quite a bit.
"It was definitely a face plunge into it ... and then the sting occurred and I was like,'oh, great'," he said.
Mr Butcher said the sting lasted for two hours but left no mark.
A man who was snorkeling off the northern end of Kapiti Island said he swum through a school of what looked like pink coloured jellyfish.
Steve Woodcock said he was only in the water for a minute and when he returned to the boat he was in agony.
He said he was in pain for the next couple of hours describing it as being similar to wasp stings. Mr Woodcock said the symptoms gradually subsided.
Meanwhile, a plague of jellyfish led officials to issue public warnings at Titahi Bay beach north of Wellington.
The kaitiaki of the beach, Conway Matthews, was on guard this morning when he was advised that a swarm had come through.
"One of the other locals came through and he said he had been stung and there were massive jellyfish in the water."
Mr Matthews said the council decided not to close the beach but told him to let people know about the danger before they went swimming.
Initially, people got out of the sea, but went back in later, believing the stingers had moved on and saying they wanted to escape the searing 28-degree heat.
Porirua City Council was investigating and had taken a picture of a stranded jellyfish, which had been sent for analysis.
Baca Di sini Bro https://www.radionz.co.nz/news/national/349148/hot-weather-attracts-jellyfish-swarmsMonday, January 22, 2018
The feeding habits of sharks uncovered thanks to plankton 'post codes'
Christopher Bird, University of Southampton and Clive Trueman, University of Southampton
Across the globe, sharks have been hit hard by fishing and habitat destruction, which has led to declines in many populations. Marine conservation efforts are increasingly focused on managing particular regions to prevent certain kinds of fishing, or to restore a certain habitat, within their boundaries – things like marine protected areas. So knowing how sharks move around the ocean and use different regions to eat, mate or give birth is particularly important.
In recent years, great advances have been made tracking animals (including sharks) with electronic tags, but it remains very expensive and relatively few animals have been tracked. Not only that, but knowing where a shark is doesn't necessarily tell you why it is there.
We're part of a team of 73 scientists from 21 countries who came together to use chemistry to try a different approach to these burning questions. Our study is published in the journal Nature Ecology and Evolution.
We began by looking at plankton. These tiny plants are found at the bottom of marine food webs and, when they are eaten by animals, the chemical make-up of their tissues is passed on. Eventually, the chemical fingerprint first generated by the plants spreads to all other animals in the food web – including sharks.
What we're interested in is the relative amount of two different carbon isotopes in plankton cells (isotopes are atoms of the same element with slightly different weights). This measurement is useful to us because plankton have different carbon isotope contents across the globe – almost like a chemical post code.
Distribution of shark samples compiled in study. The coloured map represents the different carbon isotope "post codes" found across the globe. Image: Bird & Trueman, Nature Ecology & Evolution, Author provided
By comparing the carbon isotope post codes in sharks to maps showing how the isotopes vary in plankton at the bottom of the food chain, we could test whether sharks had been feeding in the same areas in which they were caught. If the post codes matched, we could say sharks likely fed where they were caught. If they differed, this may have been due to feeding in different post codes or on different types of food.
Five thousand sharks
Our team gathered isotope data on more than 5,000 sharks from 114 species, providing information on a global scale and including more than a fifth of all known shark species. We found that sharks who live in waters close to the coast, such as the great white or reef sharks, had indeed likely been feeding close to where they were caught.
Black-tip reef shark surrounded by fish in a shallow lagoon in the Maldives. Image: Mohamed Shareef/Shutterstock
What's more, we also found that individual sharks within a population specialised on food from different food webs – either eating entirely different species, or the same species but in slightly different habitats with different plants at the base of the food chain. Sharks possibly do this to reduce competition among themselves.
Shark species that occur in the open ocean, however, such as blue or mako sharks, appeared to get most of their food from a specific isotopic post code, no matter where in the world they were caught. Cooler bands of water found in the northern and southern hemispheres provide food for lots of different animals, and it appears oceanic sharks spend a lot of time feeding in these areas, too.
Oceanic sharks appear to get most of their food from food webs in the red shaded regions. Image: Clive Trueman, author provided
These key differences in the way in which sharks feed could be important for attempts to protect them.
For those sharks living close to shore, protective areas need to include the varied food webs in which they feed. Populations of white sharks might include some individuals specialising on seals from one bay and others targeting fish from the next bay. Shark populations may continue to suffer unless management practices protect this wide range of coastal habitats.
The areas of the ocean that we found were important feeding grounds for oceanic sharks are also good feeding grounds for other predatory fish such as tuna, which, in turn, attract lots of human fishing. There are currently no protections for sharks in these regions, and establishing large marine protected areas in parts of the sea that are not used for feeding may do little to conserve oceanic shark populations. Measures to limit shark by-catch in tuna fisheries, such as improved gear technology, may be more effective. These may include magnetic hooks that deter sharks, or having fishing lines that sharks are able to break free from.
Our research is not finished and we still know very little about the deep sea. The task now is to combine chemical methods with other technologies, such as satellite tracking and environmental DNA, to improve our knowledge of fish ecology and ultimately the sustainability of our ocean activities.
__
Christopher Bird, PhD graduate, University of Southampton and Clive Trueman, Associate Professor of Marine Ecology, University of Southampton
This article was originally published on The Conversation. Read the original article.
Baca Di sini Bro https://www.earthtouchnews.com/oceans/sharks/the-feeding-habits-of-sharks-uncovered-thanks-to-plankton-post-codes/Saturday, January 20, 2018
Moeldoko Bangga Mahasiswa Indonesia Makin Aplikatif dengan Kepentingan Petani
TRIBUNNEWS.COM, YOGYAKARTA - Ketua Umum Himpunan Kerukunan Tani Indonesia (HKTI) Jenderal TNI (Purn) Moeldoko menghadiri panen ikan menggunakan teknologi micro bubble generator (MBG) karya mahasiswa Universitas Gajah Mada (UGM).
Dirinya mengaku bangga mahasiswa Indonesia makin aplikatif dengan kepentingan petani.
"Ini ada MBG generator karya mahasiswa UGM yang mampu meningkatkan kualitas dan kuantitas ikan budidaya air tawar. Penemuan ini menjawab hal utama bagaimana manfaatnya bagi petani secara langsung," ungkap Moeldoko didampingi Rektor UGM, Panut Mulyono dan akademika UGM pada syukuran panen ikan Nila Merah kelompok tani Mina Ngeromboko, Sleman, Yogyakarta, Sabtu (20/1/18).
Menurut Moeldoko, jika teknologi aplikatif ini terus dikembangkan, maka tingkat kesejahteraan petani bisa meningkat.
Dikatakannya, proses pertanian rakyat, terutama budidaya ikan air tawar di Yogyakarta yang terbatas lahannya, membutuhkan terobosan agar bisa diterima dalam skala industri.
Teknologi MBG merupakan pembuatan gelembung udara mikro dengan generator kecil. Gelembung ini yang memperkaya oksigen dalam air.
"Teknologi tepat guna ini murah dan telah diuji coba di pertanian air tawar," sambung mantan Panglima TNI ini.
Selain itu, MBG juga bisa menghasilkan panen lebih dari tiga kali setahun. Dari tiga kali panen menjadi empat kali panen. Penggunaan listriknya hemat untuk memutar kincir.
Ditambahkannya, jika disosialisasikan kepada masyarakat, teknologi ini efisien dalam proses budidaya ikan. Maka petani akan mendapat hasil yang maksimal, terjadi peningkatan hasil ikan lebih dari 50 persen. Pakan lebih sedikit, waktu memelihara lebih pendek, ikan lebih cepat besar dan sehat.
"Tantangan penelitian perguruan tinggi itu kan, hasilnya bisa diterapkan pada skala industri agar menguntungkan," kata pria yang baru menjabat Kepala Staf Kepresidenan ini.
Peneliti senior UGM Profesor Rustadi menyebutkan, teknologi MBG yang dikembangkan ini sudah terbukti dapat mengefisienkan pakan, salain jumlah ikan yang hidup lebih banyak.
"Karena MBG itu hasilkan gelombung yang kecil dapat melarutkan oksigen di dalam air, menghilangkan jamur dan merangsang pertumbuhan plankton yang bisa menjadi pakan tambahan ikan," tuturnya.
Rustandi yakin teknologi MBG ini prospektif tidak hanya untuk budidaya ikan tawar, tapi juga di air laut seperti budidaya udang dan ikan yang gunakan jaring apung di laut.
"Kami senang didukung biaya riset oleh HKTI dan komitmen Pak Moeldoko memajukan pertanian air tawar," jelasnya.
Baca Di sini Bro http://www.tribunnews.com/regional/2018/01/20/moeldoko-bangga-mahaiswa-indonesia-makin-aplikatif-dengan-kepentingan-petaniFriday, January 19, 2018
How we uncovered the feeding habits of sharks, thanks to plankton 'post codes'
View photos
Michael Bogner / shutterstock
marine protected areas</a>. So knowing how sharks move around the ocean and use different regions to eat, mate or give birth is particularly important." data-reactid="31">Across the globe, sharks have been hit hard by fishing and habitat destruction, which has led to declines in many populations. Marine conservation efforts are increasingly focused on managing particular regions to prevent certain kinds of fishing, or to restore a certain habitat, within their boundaries – things like marine protected areas. So knowing how sharks move around the ocean and use different regions to eat, mate or give birth is particularly important.
In recent years, great advances have been made tracking animals (including sharks) with electronic tags, but it remains very expensive and relatively few animals have been tracked. Not only that, but knowing where a shark is doesn’t necessarily tell you why it is there.
Nature Ecology and Evolution</a>." data-reactid="33">We’re part of a team of 73 scientists from 21 countries who came together to use chemistry to try a different approach to these burning questions. Our study is published in the journal Nature Ecology and Evolution.
We began by looking at plankton. These tiny plants are found at the bottom of marine food webs and, when they are eaten by animals, the chemical make-up of their tissues is passed on. Eventually, the chemical fingerprint first generated by the plants spreads to all other animals in the food web – including sharks.
What we’re interested in is the relative amount of two different carbon isotopes in plankton cells (isotopes are atoms of the same element with slightly different weights). This measurement is useful to us because plankton have different carbon isotope contents across the globe – almost like a chemical post code.
By comparing the carbon isotope post codes in sharks, to maps showing how the isotopes vary in plankton at the bottom of the food chain, we could test whether sharks had been feeding in the same areas in which they were caught. If the post codes matched we could say sharks likely fed where they were caught. If they differed, this may have been due to feeding in different post codes or on different types of food.
5,000 sharks
Our team gathered isotope data on more than 5,000 sharks from 114 species, providing information on a global scale and including more than a fifth of all known shark species. We found that sharks who live in waters close to the coast, such as the great white or reef sharks, had indeed likely been feeding close to where they were caught.
View photos
Black-tip reef shark surrounded by fish in a shallow lagoon in the Maldives.Mohamed Shareef / shutterstock
Not only that, but we found that within a population, individual sharks specialised on food from different food webs – either eating entirely different species, or the same species but in slightly different habitats with different plants at the base of the food chain. Sharks possibly do this to reduce competition among themselves.
Shark species that occur in the open ocean, however, such as blue or mako sharks, appeared to get most of their food from a specific isotopic post code, no matter where in the world they were caught. Cooler bands of water found in the northern and southern hemispheres provide food for lots of different animals, and it appears oceanic sharks spend a lot of time feeding in these areas, too.
These key differences in the way in which sharks feed could be important for attempts to protect them.
For those sharks living close to shore, protective areas need to include the varied food webs in which they feed. Populations of white sharks might include some individuals specialising on seals from one bay and others targeting fish from the next bay. Shark populations may continue to suffer unless management practices protect this wide range of coastal habitats.
limit shark by-catch in tuna fisheries</a> such as improved gear technology may be more effective. These may include magnetic hooks that deter sharks, or having fishing lines that sharks are able to break free from." data-reactid="83">The areas of the ocean that we found were important feeding grounds for oceanic sharks are also good feeding grounds for other predatory fish such as tuna which, in turn, attract lots of human fishing. There are currently no protections for sharks in these regions, and establishing large marine protected areas in parts of the sea that are not used for feeding may do little to conserve oceanic shark populations. Measures to limit shark by-catch in tuna fisheries such as improved gear technology may be more effective. These may include magnetic hooks that deter sharks, or having fishing lines that sharks are able to break free from.
Our research is not finished and we still know very little about the deep sea. The task now is to combine chemical methods with other technologies, such as satellite tracking and environmental DNA, to improve our knowledge of fish ecology and ultimately the sustainability of our ocean activities.
The Conversation</a>. Read the original article." data-reactid="85">This article was originally published on The Conversation. Read the original article.
The Conversation
Christopher Bird received funding from the National Environmental Research Council (NERC) during his PhD.
Clive Trueman receives funding from the Natural Environment Research Council (NERC).
Subscribe to:
Posts (Atom)