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Age & Growth Program

Otolith Oxygen Isotopes Reveal the Life History of a Yellowfin Sole in the Eastern Bering Sea

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Figure 3. Click image to enlarge.
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Figure 4. Click image to enlarge
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Figure 5. Click image to enlarge.

Otoliths have been widely used to reconstruct various aspects of fish environmental and biological history in marine and freshwater ecosystems. Specifically, oxygen isotopes ratios (δ18O) in fish otoliths, while dependent on the isotopic composition of the ambient water, are inversely related to seawater temperature and may provide a record of a fish’s thermal experience. Yellowfin sole (Limanda aspera) is a common flatfish species in the Bering Sea that is known to undertake a gradual offshore ontogenetic migration until maturity, after which it moves seasonally over the continental shelf for the purposes of spawning and feeding. In a feasibility study, otolith oxygen isotope analysis was conducted with an ion microprobe at the University of Wisconsin-Madison’s Secondary Ion Mass Spectrometer (WiscSIMS) laboratory to explore the life history of a yellowfin sole in the eastern Bering Sea. The ion microprobe has much finer spatial and temporal sampling resolution than conventional acid digestion/gas-source mass spectrometry, allowing otolith δ18O measurements to be taken sub-annually.

Values of δ18O were measured from discrete 10-micron spots along three transects from the otolith core to its edge (Fig. 3). Fish age was estimated by counting growth zones, and calendar year was assigned to each growth zone and all corresponding δ18O spot analyses. Cyclical variations in δ18O values in the juvenile portion of the otolith corresponded with the otolith growth-zone banding pattern and were presumably related to seasonal changes in ambient water δ18O values and temperatures (Fig. 4). The ontogenetic migration from shallow to deeper waters was revealed by increasingly higher δ18O values from age-0 to approximately age-7, which roughly corresponds to the onset of maturity (Fig. 4). In conclusion, the ion microprobe provided high-resolution (sub-annual) records of relative environmental conditions experienced on an individual level and was consistent with population-level studies of yellowfin sole ontogeny (Fig. 5).

This work was completed in collaboration with Ian Orland, John Valley, and Takayuki Ushikubo (University of Wisconsin-Madison), Bryan Black (Oregon State University), and Thomas Helser (AFSC’s Age and Growth (A&G) Program). A future study is being planned to use the ion microprobe as a tool to complement current work by A&G scientist Craig Kastelle on Pacific cod (Gadus macrocephalus) age validation. Because of its fine-scale sampling resolution, the microprobe may be able to elucidate seasonal patterns in otolith δ18O better than conventional methods, thereby resolving several currently inconclusive findings.

By Beth Matta

Age and Growth Program Production Numbers

Species Specimens Aged
Blackspotted rockfish    23
Great sculpin  149
Greenland turbot  574
Kamchatka flounder    24
Northern rockfish   331
Pacific ocean perch 1,001
Rougheye rockfish   226
Shortraker rockfish    19
Southern rock sole   415
Walleye pollock 2,532

Estimated production figures for the Age & Growth Program are presented for 1 January – 31 March 2011. Total production figures were 5,294 with 1,104 test ages and 92 examined and determined to be unageable.

By Jon Short




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