Nav: Home

Sniffing out sharks

September 14, 2018

A white shark's acute sense of smell is legendary, allowing it to detect a potential meal several miles away -- and giving pause to those of us who work and play in the ocean.

But now humans can sniff them out as well, thanks to a collaboration between researchers from UC Santa Barbara and the U.S. Geological Survey, with colleagues from California State University Long Beach (CSULB) and Central Michigan University (CMU). Through developments in environmental DNA (eDNA), scientists -- and soon, perhaps, any curious individual -- can determine if white sharks have been nearby.

"One of the goals of this research is for a lifeguard to be able to walk down to the shore, scoop up some water, shake it and see if white sharks are around," said Kevin Lafferty, a USGS ecologist and researcher with UCSB's Marine Science Institute (MSI). He is lead author of the new paper "Detecting southern California's white sharks with environmental DNA," published in the journal Frontiers in Marine Science.

The team's results add to a growing body of evidence that white sharks, which had been declining in numbers due to overfishing, have for the last several years been experiencing a comeback along the California coast.

According to CSULB professor, white shark expert and study co-author Chris Lowe, the resurgence is due to the success of state and federal protections from fishing, recovery of marine mammal populations and better fisheries management.

"However, white shark population recovery has co-occurred during a period when more people than ever before are using the coastal ocean for recreation, ultimately increasing the likelihood of interactions," he said. "While sightings of juvenile white sharks have risen considerably along California over the last eight years, there has been no dramatic increase in shark bites on people."

Environmental DNA is genetic material collected from the environment, as opposed to within a living organism. Things animals may leave behind -- such as mucus, feces or shed skin -- contain their genetic signatures, which can be parsed out and identified through genetic sequencing. Scientists can extract and amplify specific genes within the DNA fragments found in water samples, and determine if the DNA contained in those samples is from a specific species.

In Carpinteria, down the coast from UC Santa Barbara, Lowe had been acoustic- and satellite-tracking tagged juvenile sharks at one of several summer/fall nurseries along southern California. Lafferty and Lowe wondered if these sharks were leaving a detectable eDNA plume. Lafferty had little success using eDNA to sample for sharks until eDNA expert and MSI researcher Chris Jerde shared a new protocol he developed with CMU's Andrew Mahon.

"Ten years ago we started working on eDNA," said Jerde, who is a co-author of the paper. "The advances in technology since then have dramatically improved the reliability, portability and widespread application of the method."

Using a new species-specific genetic analysis called digital droplet PCR, CMU biology professor and study co-author Mahon designed specific genetic markers from white shark tissue sent to him by Lowe. Mahon's student, Kasey Benesh, analyzed the water samples and controls blindly. Samples near the shark aggregation matched the genes in the white shark tissue, whereas water samples a mile away did not, confirming that a water sample could sniff out white sharks.

Because eDNA can drift with currents, and sharks can swim long distances in the time it takes eDNA to degrade, the new approach only gives a rough idea about where sharks actually are at a particular moment. Still, "Chris Lowe can now add eDNA to his new white shark monitoring program, which includes real-time acoustic tracking and drone flights," Lafferty said.

For surfers, ocean swimmers and beachgoers, the increase in white shark population may be a cause for concern. Although white sharks don't feed on humans (and juveniles favor rays and other fish), they have certainly been known to bite out of defensiveness, curiosity or mistaken identity, causing grave or lethal injuries. Environmental DNA monitoring could give lifeguards and other people responsible for public safety clues as to when to be extra vigilant, and also help marine biologists understand how well white sharks are recovering in response to protection.

"We can now sample eDNA along the coast to make better maps and seasons for white sharks," Lafferty said, "And if we can do it for white sharks, we can do it for other marine species, too."

Added Lowe, "We can use eDNA not only to determine whether white sharks have been present at a beach, but also to determine if their favorite food is there is well, such as stingrays. Once we are able to better refine and calibrate the methods, another goal will be to integrate eDNA technology into autonomous surface vehicles that can be programmed to move along the coast sampling water and send data into the cloud, along with text alerts to local lifeguards, of the presence of white sharks at a particular location. This technology holds great promise for future, near real-time monitoring."

The result of the scientists' study proves that eDNA sequencing has become a powerful tool for tracking the general movement of single species, as well as for monitoring the biodiversity of a region in real time. Initially a tool to detect the presence of invasive species, such as Asian carp and bullfrogs, eDNA has also been used to detect threatened and endangered species that are often elusive, such as arroyo toads, California red-legged frogs and tidewater gobies.

"New advances in eDNA are allowing for not just a single species to be detected, but instead the DNA for the water sample is screened for all fish species or all amphibian species," Jerde said. "The same technology used to decode the human genome is now used to sequence all the DNA in a water sample. From this we can monitor fish stocks, measure the presence or absence of rare species, and better connect how climate change and pollution are impacting biodiversity."
-end-
This study was made possible with support from UCSB's Marine Biodiversity Observation Network.

University of California - Santa Barbara

Related Dna Articles:

Penn State DNA ladders: Inexpensive molecular rulers for DNA research
New license-free tools will allow researchers to estimate the size of DNA fragments for a fraction of the cost of currently available methods.
It is easier for a DNA knot...
How can long DNA filaments, which have convoluted and highly knotted structure, manage to pass through the tiny pores of biological systems?
How do metals interact with DNA?
Since a couple of decades, metal-containing drugs have been successfully used to fight against certain types of cancer.
Electrons use DNA like a wire for signaling DNA replication
A Caltech-led study has shown that the electrical wire-like behavior of DNA is involved in the molecule's replication.
Switched-on DNA
DNA, the stuff of life, may very well also pack quite the jolt for engineers trying to advance the development of tiny, low-cost electronic devices.
Researchers are first to see DNA 'blink'
Northwestern University biomedical engineers have developed imaging technology that is the first to see DNA 'blink,' or fluoresce.
Finding our way around DNA
A Salk team developed a tool that maps functional areas of the genome to better understand disease.
A 'strand' of DNA as never before
In a carefully designed polymer, researchers at the Institute of Physical Chemistry of the Polish Academy of Sciences have imprinted a sequence of a single strand of DNA.
Doubling down on DNA
The African clawed frog X. laevis genome contains two full sets of chromosomes from two extinct ancestors.
'Poring over' DNA
Church's team at Harvard's Wyss Institute for Biologically Inspired Engineering and the Harvard Medical School developed a new electronic DNA sequencing platform based on biologically engineered nanopores that could help overcome present limitations.

Related Dna Reading:

Who We Are and How We Got Here: Ancient DNA and the New Science of the Human Past
by David Reich (Author)

The Family Tree Guide to DNA Testing and Genetic Genealogy
by Blaine T. Bettinger (Author)

Blueprint: How DNA Makes Us Who We Are (The MIT Press)
by Robert Plomin (Author)

Move Your DNA: Restore Your Health Through Natural Movement Expanded Edition
by Katy Bowman (Author)

Native American DNA: Tribal Belonging and the False Promise of Genetic Science
by Kim TallBear (Author)

The Innovator's DNA: Mastering the Five Skills of Disruptive Innovators
by Jeff Dyer (Author), Hal Gregersen (Author), Clayton M. Christensen (Author)

Darwin Devolves: The New Science About DNA That Challenges Evolution
by Michael J. Behe (Author)

Dinosaur DNA: A Nonfiction Companion to the Films (Jurassic World)
by Marilyn Easton (Author)

DNA: The Story of the Genetic Revolution
by James D. Watson (Author), Andrew Berry (Author), Kevin Davies (Author)

The DNA of Relationships
by Gary Smalley (Author)

Best Science Podcasts 2018

We have hand picked the best science podcasts for 2018. Sit back and enjoy new science podcasts updated daily from your favorite science news services and scientists.
Now Playing: TED Radio Hour

Circular
We're told if the economy is growing, and if we keep producing, that's a good thing. But at what cost? This hour, TED speakers explore circular systems that regenerate and re-use what we already have. Guests include economist Kate Raworth, environmental activist Tristram Stuart, landscape architect Kate Orff, entrepreneur David Katz, and graphic designer Jessi Arrington.
Now Playing: Science for the People

#504 The Art of Logic
How can mathematics help us have better arguments? This week we spend the hour with "The Art of Logic in an Illogical World" author, mathematician Eugenia Cheng, as she makes her case that the logic of mathematics can combine with emotional resonance to allow us to have better debates and arguments. Along the way we learn a lot about rigorous logic using arguments you're probably having every day, while also learning a lot about our own underlying beliefs and assumptions.