29 December 2011

LISTENING IN ON DIVING MURRES

Thick-billed murres (Uria lomvia). Credit: Art Sowls, USFWS, via Wikimedia Commons.

There's an exciting new paper in Marine Ecology Progress Series (MEPS) that lets us listen in on diving murres to learn more about their feeding ecology. Specifically:
  1. what prey they catch by day
  2. what prey they catch by night (really exciting!)
  3. and how they might find these prey that exist in patchy distributions

The lead author is Kelly Benoit-Bird, at Oregon State University, whose acoustics work I profiled in The BP Cover-Up, my cover article in Mother Jones last year. You can read about her MacArthur Foundation fellowship here.

Red arrow marks the Pribilof Islands. Credit: Aleut International Association.
  
Research for the MEPS paper was conducted in Bering Sea off the Pribilof Islands, home to some 200 million breeding seabirds, one of the largest concentrations in the North Pacific.

The birds nest here because of the phenomenal seasonal abundance that cranks up in these waters each spring with the return of sunlight.
  
Phytoplankton bloom around the Pribilof Islands, Bering Sea. Credit: NASA image by Jeff Schmaltz, MODIS Rapid Response Team, Goddard Space Flight Center, via the Earth Observatory.

Here's how multiple streams of data were gathered simultaneously as the researchers' boat motored along predetermined 10-kilometer (6.2-mile) long transect lines through the waters around the Pribilofs:

  • An observer with binoculars stood on the bow of the boat, sighting murres flying through the air and/or foraging at the surface
  • A 4-frequency echosounder system was used to provide nearly continuous information from underwater on the presence of zooplankton and fish (identified by their acoustic "signatures")
  • To verify the truth of those acoustic signatures, net tows were made at the the beginning of each transect to capture fish and zooplankton
  • At the start and finish of each transect, a CTD (conductivity, temperature, depth) profile was conducted to a depth of 100 m (328 feet) or to within 5 m (16 ft) of the seafloor in shallower waters; the CTD also gathered data on dissolved oxygen and, through a transmissometer and a fluorometer, different data on the presence of fish and/or zooplankton

Common murres (Uria aalge). Credit: Michael Haferkamp via Wikimedia Commons.
  
This system allowed the team to observe thousands of bubble trails made by diving murres and correlate them with schools of krill, juvenile pollock, and squid—their primary prey.

Some of their findings:

  • Individual diving murres were more likely to be found alone in shallow water (<100 m) during the day
  • Aggregations of birds were more likely to be found in the outer shelf and slope zones (>100m) at night

Why? The authors suggest:

[T]hat murres use different tactics when foraging on prey in different habitats and likely reflects the differences in diet noted during the same time period, with parents feeding their chicks small fish that could be caught near the colony while consuming krill and squid that are primarily accessible in deep waters, far from the colonies at night. There was, however, no significant difference in the rate of bird detections during the day and night, suggesting that both periods are important for foraging despite these different tactics. These results indicate that using only daytime observations of murres as an index of habitat use and foraging activity can significantly skew any results drawn from those data, underestimating the importance of deepwater habitats and making the calculation of accurate energy budgets impossible. 
  
Murres on nests, Pribilof Islands, Alaska. Credit: Allen Shimada NOAA/NMFS/OST/AMD via Flickr.
   
As to how the birds find and track their prey—in deep water, often in the dark—the authors note:

The ability of murres to successfully track the abundance, density, and accessibility of prey that occurred at depths between 10 and 100 m (32 and 328 feet) raises questions about how they gather information to exploit these resources effectively, particularly at night. Birds could be directly detecting the prey using vision or chemosensory mechanisms. However, both would likely be inefficient for deep prey, and vision would not be effective at night when foraging activity is equal to daylight foraging activity.
  
Murre. Credit: christopher.woo via Flickr.
   
Possibilities include:  

  • Birds cue to surface ocean color, which indicates the presence or absence of phytoplankton [see 3rd photo in this post, above]: no correlation was found
  • Birds cue to a physical characteristic, such as temperature: a correlation was found between murres and warmer surface temperature 
Further possibilities revolve around birds cuing to other birds—something that seems obvious if you observe birds at sea... though obvious isn't always correct

While the hypothesis that colonies function as ‘information centers’, where group members can learn the location of food by following successful foragers, has largely been discounted... there have been a number of studies showing that the detection of other predators that are already exploiting a prey patch, a process known as ‘local enhancement’, can be an effective foraging strategy... Local enhancement occurs in another species of murre, but its importance is dependent on the predictability of prey... Substantial experimental and at-sea data suggest that local enhancement works whenever feeding groups are more conspicuous than food patches... which is likely to be the case for the deep prey observed here. The local enhancement hypothesis is supported by the prevalence of aggregation among acoustically observed murres... Whatever the reason for aggregating, murres in groups were spaced in a highly regular pattern with an average of 50 m between individuals, suggesting that, while grouped, birds may be attempting to avoid direct competition, a common cause of uniform spacing between individuals.
 
Patchiness of prey and distribution of birds. Click for larger image. Credit: Benoit-Bird, et al. MEPS. DOI:10.3354/meps09408.
 
The authors conclude:

Using this [fisheries acoustic] technique, we were able to observe the diving depths of individual birds, assess these dives in relation to [prey] patch size, density, depth, and type of prey both day and night, and show that birds on the surface were a good proxy for foraging effort taking place in a given area. The concomitance of these data is made possible by acoustic approaches and provides new insights into the predator−prey relationship. During the breeding season, diving murres in the southeastern Bering Sea show strong selection for prey patches with specific characteristics, and the high degree of overlap between murres and their prey at a range of scales shows effective information gathering about prey by these birds.  
 
Thick-billed murre. Credit: susanvg Susan van Gelder via Flickr.
  
The paper (♥ open access): 

  • Benoit-Bird KJ, Kuletz K, Heppell S, Jones N, Hoover B (2011) Active acoustic examination of the diving behavior of murres foraging on patchy prey. Mar Ecol Prog Ser 443:217-235 DOI:10.3354/meps09408

27 December 2011

NEW ISLAND BORN IN RED SEA

New island born from volcanic eruption. Credit: NASA Earth Observatory.

  
Imagine coming across what some fishers in the Red Sea observed on 19 December—fountains of lava bursting from the surface of the water 30 meters/90 feet into the air.

... Followed four days later by the birth of a new island.

Plate boundaries and volcanoes of Africa. Blue arrow marks location of new island near mouth of Red Sea. Credit: USGS map, modified.

  
The volcanic activity occurred among the Zubair Group of small islands off the west coast of Yemen. From the Earth Observatory page:

Running in a roughly northwest-southeast line, the islands poke above the sea surface, rising from a shield volcano. This region is part of the Red Sea Rift where the African and Arabian tectonic plates pull apart and new ocean crust regularly forms.

Zubair Group on 24 October 2007. Credit: NASA Earth Observatory.
 
And here's what the Zubair Group looked like before the birth of the solstice island.

19 December 2011

TEN GIFTS FOR THE OCEAN

NASA image by Jeff Schmaltz, LANCE/EOSDIS MODIS Rapid Response.
 
What to give that favorite ocean on your list? Here are 10 little presents that say "thanks" in a big way to the  big-wet-deep-dark-mysterious lifegiver to us all.

Credit: DanCentury via Flickr.

  
1) On your next visit to the ocean—or any of its feeder rivers, lakes, streams, or ponds—pick up trash. Every piece of (mostly) plastic you carry away will spare the ocean pollution lethal to life.

Credit: Buzz Hoffman via Flickr
 
2) Report garbage on the beach via this smartphone app to the Marine Debris Tracker project.

Via Project Aware.

  
3) If you're a diver, join an underwater clean-up group, like Project Aware, and feed their Dive Against Debris dataset.

Credit: reuvenim via Flickr.

  
4) Reconsider synthetic fleece. As new research shows, its microfibers wend their way from your washing machine through wastewater treatment plants to become yet more plastic pollution in the ocean.

Credit: Justin Gaurav Murgai via Flickr.

  
5) If you eat ocean animals or plants, consult the Monterey Bay Aquarium Seafood Watch list for what's sustainably fished and what's not. Use its recommendations to double-check the recommendations of the Marine Stewardship Council... the group that "vets" seafood sold at Whole Foods and many other markets and restaurants, but that's been making dubious judgement calls of late.

Credit: colros via Flickr.

  
6) Avoid ocean-based remedies and natural medicines like shark cartilage, fish oil (use flaxseed), coral calcium (leafy green veggies are better), plus ingredients (like dried seahorses) in some "herbal" medicines—or any other stuff taken from the sea that may or may not make you healthier but will sicken the ocean.

Credit: irmiller via Flickr. 


  
7) Use ocean-friendly sunscreen at the ocean, river, lake, stream, or pond where you swim. Up to 600 tons of the stuff gets washed off, or washed downstream, into the ocean ever year, carrying all kind of nasties with it. Plus sunscreen may not be so good for you as you think. Here are tips for some better choices.

Credit: Ryan E. Poplin via Wikimedia Commons

  
8) If you keep a saltwater aquarium, buy only fish certified by the Marine Aquarium Council.

Credit: Lee R Berger via Wikimedia Commons.


  
9) Forgo the purchase of ocean souvenirs—objects or jewelry made of coral, sea shells, nautilus shell, seahorses—anything that had to be killed and removed from the ocean in order for you to take it home.

Credit: NOAA's National Ocean Service via Flickr.

  
10) Learn more about the ocean. Our well-stocked brains and hearts are good for the ocean and all living things.

Credit: JIGGS IMAGES via Flickr.

  
Happy Holidays!

ICE BIRDS

Visions photographiques via Flickr

Bruce McKay~YSP via Flickr

Paeonia via Flickr

andreasmarx via Flickr

Charles Jeffrey Danoff via Flickr

Metrix X via Flickr

cozymax.org at Flickr


hannanik via Flickr

glacierman via Flickr

rene j via Flickr

BaboMike via Flickr

Today is a good day via Flickr

16 December 2011

'JAWS' LIKE YOU'VE NEVER SEEN IT


Shark Song from Whitehouse Content on Vimeo.

CIGARETTE CARD ARCTIC

These views of the Arctic are from cigarette cards issued by the Hassan Oriental Cigarette Company between 1900-1917—during the golden age of  polar exploration

The artist is Albert Operti, an Italian who accompanied Robert Peary on his 1896 Greenland expedition. 










Operti also painted many scenes of expeditions he was not a part of. As best I can deduce, the ship in this picture, Hansa, is the same supply vessel that came to an untimely end off Greenland during the 1869-1870 Second German North Polar Expedition. From Wikipedia:

As the supply ship, the Hansa followed the Germania [exploration ship] until July 19, when [Captain Paul Friedrich August] Hegemann misread a flag signal by [captain of the Germania, Carl] Koldeway and went ahead; the ship disappeared in the fog and got separated. The agreement was to meet in such a situation at Sabine Island. After unsuccessful attempts to get there, Hansa was inescapably stuck in the pack ice by mid-September 1869. During the next month, the ship was slowly milled by the ice and finally sank on October 22 at a position 70°32’N, 21°W approximately 10 km from the East Greenland coast. The crew managed to survive the winter in a shelter built of coal dust briquettes, while drifting on the sea ice southward along the eastern coast of Greenland. In June 1870, the crew got to the coast by boat and reached the Moravian Herrnhut mission at Narsaq Kujalleq (then Frederiksdal/Friedrichsthal) near Cape Farewell, from where they got back to Germany on a Danish ship.



When he wasn't painting the real and imaginary Arctic, Albert Operti was painting other make-believe stuff. From Visions of the North:

Like many panorama and diorama painters of the nineteenth century, when the Arctic was also a popular subject for such entertainments, Operti had a background in theatrical scene painting, and it was with this work that he was chiefly occupied in the middle years of his life, principally with the [New York] Metropolitan Opera. In the last six years of his life he returned to the [American Museum of Natural History], painting diorama backdrops, murals, and friezes for their exhibitions. During this period, he actually lived in quarters provided by the [New York] Explorers Club, and it was there that he died in 1927.

All images courtesy the New York Public Library Digital Gallery.