Hi Petr,

I'm not an expert in Alaska Plaice, but I do have some experience with otolith reading methodologies. The maximum age for this species is about 37 years (according to the Alaska Fisheries Science Center). I suspect your preliminary ageing is probably not too far off. However, for this species it's difficult to differentiate "pre-annular checks" from true annuli. You don't describe your technique, but you can improve contrast using a simple "break and burn" technique. The method is described on this webpage:

http://elearning.uaf.edu/cc/otolith/break_burn.htm

and in the attached document. Using this technique, the otoliths are generally described as easy to read, and the reader agreement is relatively high.

Cheers!

Shannon

Hi Shannon,

Thank you for your answer. For preparing of the otolith I have used "break-and-burn method" and viewed it with reflected light.

I have read M.E.Matta's paper. For ageing old fish in the AFSC they use marks nearly the sulcus (fig. 4). If I'll use the area adjacent to the sulcus then I can estimate from 8 years (green) to 17 years (magenta + red dots into the picture in this message).

I've passed this round a couple of colleagues at Cefas, and we all tend to agree with your 13 estimate, however my colleague Mark Etherton comments "there could easily be sub annual bands in this area due to the fast growing nature of most small fish. Not being familiar with the species or its life history, it’s difficult to tell. Having looked at the comments immediately below where they mention reading close to the sulcus I would say it’s not usually a good idea as compressed banding in this area can lead to a mis-interpretation (either over or under ageing)"

Hi Petr,

Based on the photograph it looks like a 12 or 13 to me, although the second annulus is difficult to determine. (I also was unsure whether to count the growth on the edge - what time of year was this fish caught?)

Is there any way you could do a darker burn on the otolith? I think that would help eliminate any potential false rings. I would also check the surface of an intact otolith against the burnt otolith for confirmation of the early years.

I hope this helps.

Cheers,

Beth

Hi Ewan, hi Mary! Thank you for your answers.

Mary,

this fish was caught on September 02, 2013 and it had a total length of 38 cm.

I have tried to burn the otolith more. Maybe a little bit too more, because it began to get destroyed :). This is the resulting photo. Also I put here the photos of the surface of an intact otolith and how it looks now.

You are helping me very much :)

Hi Petr,

Thank you very much for doing the second burn. I consulted with Delsa Anderl, who manages production (routine for stock assessments) age determination of Alaska plaice here at the Alaska Fisheries Science Center, and we agreed on an age estimate of 10 yrs for your otolith. I've attached an annotated version of your photo showing how we aged it, relying on the sulcus area for the early years and then using the outer areas for the later years. (I used Photoshop to brighten the image a bit to enhance the contrast between translucent and opaque growth zones.) The "checkiness" that we generally see in the early years of life is much less pronounced in the sulcus region of this otolith.

Compression of annuli in the sulcus area is generally not a problem in Alaska plaice, even for older fish. (I've attached another couple of photos to illustrate this.) The main thing you'll want to do is to follow the annuli from the sulcus to the dorsal and ventral areas of the cross section. 

You can also try adjusting your burning technique - it takes some practice to learn the optimum amount of time to burn the otoliths, and it's important to not hold them too close to the flame (this will help avoid charring). Finally, you can try adjusting your light sources (assuming you're using fiber optics) to get the best angle for enhancing growth zone contrast. As for viewing surfaces, we typically store our otoliths in a glycerin-thymol solution, which both preserves and clears the otolith. While the break-and-burn method is best for Alaska plaice, viewing the surfaces can sometimes help confirm identification of early annuli. If your otoliths are stored dry (which it looks like might be the case?), you could try soaking them in either glycerin-thymol or ethanol for a few days to help clear them.

One last thing to note is that while we haven't validated absolute ages for Alaska plaice, we have found a very strong relationship between annulus width and year-to-year variation in temperature, which in a way is a corroboration of our age estimates. This species in particular displays a pretty strong positive response to bottom temp, at least in the eastern Bering Sea, so you could also use that as a guide if you happen to have temperature data from the area where you collected your fish.

Please let me know if you have any other questions.

Best,

Beth

Hi Mary,

Thank you very much for so detailed explanation. It is very helpful to me. I have downloaded your paper "Climate-driven synchrony in otolith growth-increment chronologies for three Bering Sea flatfish species" and will try to use this approach for validating my age estimation.

Article Climate-driven synchrony in otolith growth-increment chronol...

Lots of checks! I was going to go with 11 years old with your first image-- great to have Beth weigh in.