What is an Otolith and Why Do I Care About It?



Fish otolith

An otolith (inner ear bone) can be found in any animal with a vertebra---mammals, birds, amphibians, fish, etc. Otoliths are sensitive to acceleration and gravity; these organ and bone structures tell the brain how the body is moving in relation to the surrounding environment. We are currently looking at kokanee salmon otoliths to evaluate whether hatchery-reared kokanee are helping us recover the native kokanee population in Lake Sammamish. 

Fisheries scientists have figured out that fish otoliths grow much like the rings of a tree trunk. In the summer, when growth is high, the fish lays down a lot of otolith material. In contrast, during the winter when growth is minimal, the fish lays down very little growth material, resulting in the “ring” pattern. Much like a tree, if you count the “rings” you can determine the age of the fish.

Now, bear with me on this one because what I am about to tell you is kind of hard to believe but it's true . . . .

In the hatchery, the temperature of the water the fish are reared in can be controlled. By controlling the water temperature over a short time period (usually a few weeks), a barcode-type pattern is created in the rings of the otolith. This technique is called marking and is permanent. After the fish’s death, the otolith can be extracted, shaved down, put under a microscope and read. By collecting the fish and reading the otoliths, we can tell how old the fish is, what stream its parents came from, whether the fish strayed from its natal stream. That is really, really cool! And all of this from an inner ear bone about 1-4 millimeters in length!

This is what I and other federal, state, and county biologists are doing in the field and in the lab. We are collecting kokanee from Lake Sammamish streams, spawning them, extracting the otolith, collecting biological information on the fish, and then reading the otoliths to see if marking is present. The marking will assist with the research and progression of the Lake Sammamish kokanee supplementation program. This year we saw a larger kokanee run; this is also the first year that the hatchery-reared supplementation fish were old enough to return to spawn. The information we gather from these otoliths will shed new light on the future of kokanee in Lake Sammamish and the human efforts to save this unique population.
    

--Kira Mazzi, Biological Science Technician

 

Photo credit:  WDFW Otolith Thermal Marking Lab

 

Lake Sammamish Kokanee Partner Celebration



Lake Sammamish kokanee fry

On April 19, 2012, citizens and partners in Lake Sammamish kokanee conservation gathered at Hans Jensen Park in Issaquah, WA to commemorate another successful year of the kokanee supplementation program. This year over 60,000 kokanee fry will be released, which is more than the past two years combined. The juvenile kokanee that are just a few inches long are primarily released at night; however, a few were released at the event to mark the success of this year’s efforts.


Releasing kokanee fry into
Laughing Jacobs Creek

Lake Sammamish kokanee, a landlocked form of sockeye salmon, have greatly declined in recent years and were petitioned for listing under the Endangered Species Act in 2007. Although the USFWS has determined that the species does not warrant listing, we continue to work with the Washington Department of Fish and Wildlife (WDFW), King County, local city governments, Trout Unlimited, Snoqualmie Tribe, and other local entities to rebuild its native population.  



Event attendees

Key elements of the Lake Sammamish kokanee strategic habitat conservation effort include protecting and restoring spawning habitat, reducing kokanee mortality in Lake Sammamish, and providing fish passage in tributary streams. The USFWS has provided funding and technical support for both short-term (supplementation program) and long-term (restoration) efforts and is designed to support these efforts for three kokanee generations (12 years). The supplementation program includes collecting wild spawners and using an innovative system of recirculating incubators at Issaquah Creek State Hatchery to increase egg-to-fry survival rates and maximize imprinting to natal streams.


Robyn Thorson, USFWS

Speakers at this year’s event included Dow Constantine, King County Executive; Robyn Thorson, USFWS Pacific Regional Director; Jim Scott, WDFW Assistant Director; and elected officials from Bellevue, Issaquah, Redmond, and Sammamish.

Click here to see a video of the fry release event.