Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Earstones Tell Fishes’ Tale of Early Life in the Colorado River Estuary

09.06.2004


Cross-section of the earstone, or otolith, from a totoaba shows the annual rings that researchers use to learn about the fish’s history.


Adult totoaba otolith collected from an Indian midden. Specimen courtesy of Scripps Institute of Oceanography, La Jolla, Calif.


During their tender youth, both the endangered fish species totoaba and the commercially important gulf corvina require the brackish water habitat provided by the shrinking Colorado River estuary, report researchers.

Although overfishing has been implicated in the decline of both species, commercial harvesting isn’t the only reason for the two species’ decline, the finding suggests. Since 1960, diversion of Colorado River water for human uses has greatly reduced the amount of fresh water that reaches the Gulf of California, thereby reducing the brackish-water estuary, the region where river water and ocean water mix.

"It’s the first time that we’ve been able to substantiate that these fish are using Colorado River water," said Kirsten Rowell, the aquatic biologist who led the research team. "We provide evidence that both of these fish need brackish water in their youth, but today the northernmost part of the Gulf of California is more saline than the open ocean."



Rowell, a doctoral candidate in the department of geosciences at the University of Arizona in Tucson, used fish earstones, or otoliths, to decipher where the fish lived during their babyhood.

The chemistry of the almond-sized otoliths documents what type of water the fish lived in during various times in their lives. Otoliths act like the fish version of a flight recorder.

"You are what you swim in," she said, adding "Otoliths are great data loggers."

The team’s research shows that when they’re young’uns, the fish prefer the brackish water provided by the mixing of fresh and ocean water in the estuary at the mouth of the Colorado.

Team member Karl W. Flessa said, "There are two sources of human impact on these species: one is the direct effect of overfishing; the other is the indirect effect of freshwater diversion." Flessa, a professor in UA’s department of geosciences, said, "We don’t doubt that overfishing is or has been a threat to these species. We’re saying that changes to the nursery area are also a threat to these species."

Rowell will present the team’s research at the Gulf of California conference held June 13-16 at the Westward Look Resort in Tucson, Ariz. Her presentation, "Isotopic Logs from the Sea of Cortez: Environmental and Life History Records From Totoaba and Gulf Corvina Otoliths " will be given at 4 p.m. on Monday, June 14, in Colorado River Delta Session. Her coauthors are Flessa and David Dettman, a research scientist in UA’s department of geosciences.

The research was funded in part by the National Science Foundation, the Southern Arizona Environmental Management Society, the Chevron Research Fund and T&E, Inc.

Totoaba macdonaldi was the first commercially important fish in the northern Gulf of California. The fish can live 20-something years and grow to six feet in length. "San Felipe used to be just an ephemeral fishing village for totoaba," Rowell said. "They used to ship them overland to San Francisco and San Diego. It was the first time they tried to use refrigerated cars."

The commercial totoaba fishery crashed in 1975. Overfishing has been blamed for totoaba’s decline. The fish was listed by the United States as federally endangered in 1979. The current size of the totoaba population is unknown.

Gulf corvina, Cynoscion othonopterus, are still fished commercially, although the American Fisheries Society, the professional society of fisheries biologists, has recently identified the species as "vulnerable," because of habitat changes in the fish’s nursery area and heavy fishing pressure in fish’s spawning site.

Estuaries, zones where fresh river water and salty ocean water mix to form brackish water, are known to be nursery areas for many species of marine life, including many fishes.

Both totoaba and gulf corvina spawn in the mouth of the Colorado, according to fishermen’s reports. Rowell wondered whether otoliths from totoaba and gulf corvina could be used to document the fishes’ use of the Colorado River estuary as nursery.

Getting gulf corvina otoliths was fairly easy -- Rowell took them from four fish bought at the market in El Golfo de Santa Clara, Mexico, the little fishing village at the mouth of the Colorado.

Obtaining totoaba otoliths was trickier. Scripps Institute of Oceanography in La Jolla, Calif., loaned Rowell four 1,000-year-old totoaba otoliths that had been collected from an Indian archaeological site near San Felipe, Baja, Mexico.

Otoliths grow in layers, one layer per year of life. Rowell used a dental drill to grind off bits of otolith one layer at a time.

She then analyzed each layer for different forms of oxygen, called isotopes, to see where the fish lived each year of its life. Fresh water has relatively more of the lighter form of oxygen, oxygen-16, so layers with more oxygen-16 represented years that the fish had spent in brackish water. If the layer had more of the other form, oxygen-18, that meant the fish spent that year in the saline ocean water.

Rowell found that the corvina had spent part of their first year of life in brackish water in the mouth of the river, and the totoaba had spent up to their first three years in brackish water.

She said, "It shows these fish chose the brackish water habitat -- and we’ve taken it away."

"The totoaba are endangered for two reasons," she said. "The primary reason is being overfished. The second reason is that their nursery grounds have shrunk drastically. The Colorado River no longer makes it down to the Gulf except in flood years." She added, "My data say that before the dams, totoaba lived in a brackish water estuary for several years."

Rowell said, "Freshwater rivers are part of a larger system -- they don’t just stop at the edge of the continents. Rivers have a large influence on coastal marine ecosystems. These economically important marine fish were affected when we turned off the water upstream."

Mari N. Jensen | University of Arizona
Further information:
http://uanews.org/cgi-bin/WebObjects/UANews.woa/5/wa/SRStoryDetails?ArticleID=9292

More articles from Life Sciences:

nachricht Link Discovered between Immune System, Brain Structure and Memory
26.04.2017 | Universität Basel

nachricht Researchers develop eco-friendly, 4-in-1 catalyst
25.04.2017 | Brown University

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Making lightweight construction suitable for series production

More and more automobile companies are focusing on body parts made of carbon fiber reinforced plastics (CFRP). However, manufacturing and repair costs must be further reduced in order to make CFRP more economical in use. Together with the Volkswagen AG and five other partners in the project HolQueSt 3D, the Laser Zentrum Hannover e.V. (LZH) has developed laser processes for the automatic trimming, drilling and repair of three-dimensional components.

Automated manufacturing processes are the basis for ultimately establishing the series production of CFRP components. In the project HolQueSt 3D, the LZH has...

Im Focus: Wonder material? Novel nanotube structure strengthens thin films for flexible electronics

Reflecting the structure of composites found in nature and the ancient world, researchers at the University of Illinois at Urbana-Champaign have synthesized thin carbon nanotube (CNT) textiles that exhibit both high electrical conductivity and a level of toughness that is about fifty times higher than copper films, currently used in electronics.

"The structural robustness of thin metal films has significant importance for the reliable operation of smart skin and flexible electronics including...

Im Focus: Deep inside Galaxy M87

The nearby, giant radio galaxy M87 hosts a supermassive black hole (BH) and is well-known for its bright jet dominating the spectrum over ten orders of magnitude in frequency. Due to its proximity, jet prominence, and the large black hole mass, M87 is the best laboratory for investigating the formation, acceleration, and collimation of relativistic jets. A research team led by Silke Britzen from the Max Planck Institute for Radio Astronomy in Bonn, Germany, has found strong indication for turbulent processes connecting the accretion disk and the jet of that galaxy providing insights into the longstanding problem of the origin of astrophysical jets.

Supermassive black holes form some of the most enigmatic phenomena in astrophysics. Their enormous energy output is supposed to be generated by the...

Im Focus: A Quantum Low Pass for Photons

Physicists in Garching observe novel quantum effect that limits the number of emitted photons.

The probability to find a certain number of photons inside a laser pulse usually corresponds to a classical distribution of independent events, the so-called...

Im Focus: Microprocessors based on a layer of just three atoms

Microprocessors based on atomically thin materials hold the promise of the evolution of traditional processors as well as new applications in the field of flexible electronics. Now, a TU Wien research team led by Thomas Müller has made a breakthrough in this field as part of an ongoing research project.

Two-dimensional materials, or 2D materials for short, are extremely versatile, although – or often more precisely because – they are made up of just one or a...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Expert meeting “Health Business Connect” will connect international medical technology companies

20.04.2017 | Event News

Wenn der Computer das Gehirn austrickst

18.04.2017 | Event News

7th International Conference on Crystalline Silicon Photovoltaics in Freiburg on April 3-5, 2017

03.04.2017 | Event News

 
Latest News

Scientist invents way to trigger artificial photosynthesis to clean air

26.04.2017 | Materials Sciences

Ammonium nitrogen input increases the synthesis of anticarcinogenic compounds in broccoli

26.04.2017 | Agricultural and Forestry Science

SwRI-led team discovers lull in Mars' giant impact history

26.04.2017 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>