Thursday, September 30, 2010

The Magic of Strontium

While I attempt to stay afloat during this seemingly endless torrential downpour Eastern North Carolina is experiencing I decided to finally take the time to write about anadromy and how it can be examined using otolith microchemistry.

Anadromous fish spend most of their adult life in the ocean returning to freshwater to spawn, the classic example of anadromy is Pacific salmon. While it is all well and good to say that a fish moves between salt and freshwater the timing and frequency of these movements can have implications on the management of anadromous species. The goal of tracking migrations between the marine and freshwater environment can be accomplished through traditional mark and recapture studies, however, these lack corresponding age data and fail to provide a complete history of the fishes migrations the way otolith analysis can.

In studies of anadromy, it seems as though the element strontium (Sr) is some sort of miracle element. Although exceptions do exist Sr is typically more highly concentrated in marine waters than freshwaters (Limburg 1995). In addition to showing differences between marine and freshwater environments Sr also incorporates into the otolith quite nicely, perhaps becaucuse Sr is similar in size to Ca, and otolith Sr usually reflects Sr in the ambient water (Campana 1999).

If everything stated previously holds true (there is higher concentrations of Sr in saltwater than freshwater, and Sr is incorporated into the otolith in ratios similar to the ambient water) then the pattern of Sr in an otolith should increase and decrease when a fish moves between saltwater and freshwater. The classic pattern of anadromy can be illustrated by this picture (although this picture may or may not have been for the purpose of investigating anadromy) from Dr. Norman Halden at the Univeristy of Manitoba

The bottom plot shows Sr. The center, or core, of the otolith, representing growth when the fish was young shows low Sr. This pattern could be interpreted as the fish was remaining in a low Sr environment (freshwater). As this fish gets older there are peaks and declines in Sr. This could be interpreted as the fish moving between salt (peaks) and freshwater (declines). This pattern is pretty typical of what you would see from an anadromous fish species. The Sr pattern for a fish that spends its whole life in freshwater would theoretically be relatively flat, without the peaks and declines in Sr.

However, there are limitations to this method and the pattern of Sr is not always clear cut, as I am coming to find out with my own data. Dealing with an anadromous species like river herring I would expect to see a pattern of fluctuating Sr. River herring are born in freshwater (where you would expect low Sr), then move to the ocean (where you would expect high Sr). River herring then move between the ocean and freshwater in order to spawn, therefore, I would expect to see low Sr at the core of the otolith and then fluctuations throughout its life. However, I have not necessarily seen this pattern, and at least in some of the fish I have looked at the pattern appears to be backwards. I think this is pretty interesting, and am still trying to determine if it is the result of instrument error or some natural phenomenon.


Campana, S. (1999). Chemistry and composition of fish otoliths:pathways, mechanisms and applications Marine Ecology Progress Series, 188, 263-297 DOI: 10.3354/meps188263

Limburg, K. (1995). Otolith strontium traces environmental history of subyearling American shad Alosa sapidissima Marine Ecology Progress Series, 119, 25-35 DOI: 10.3354/meps119025

Friday, September 24, 2010


Since the purpose of this blog is to write about otoliths and the research I am doing using otolith microchemistry, I am palnning to write a series of posts on the applications of otolith microchemistry and then attempting to explain how I will be applying these to my research.  However, before I do this, I think I should briefly explain what the heck otoliths are and how otolith chemistry works.

Otoliths or earstones (yes humans have similar structures), used for hearing and balance, are metabolically inert and made of calcium carbonate typically in the form of aragonite, however portions of otoliths can be formed of vaterite or calcite (Campana 1999).  The different forms of calcium carbonate are differentiated by crystal shape, and at this point it is unclear as to why otoliths can occasionally be made of forms other than aragonite (Tomas and Geffen 2003).  Fish have three pairs of otoliths--saggital, lapilli, and asteriscii—but because saggital otoliths are typically the largest they are most often used for research (Campana and Neilson 1985). Otoliths have long been used in fish ageing studies because of the visibility of daily growth increments.  Otoltihs form growth rings, similar to that of a tree, by counting these rings you can make estimates of the fishes age in years, or sometimes in days.

While ageing studies have been quite common in fisheries research, otolith chemistry is a somewhat new field.  Otolith microchemistry relies on the assumption that the chemical composition of the otolith is similar to the chemical composition of the water the fish has lived in, thus acting as a sort of natural tag (Elsdon and Gillanders 2003).  The process in which otoliths are formed is at the moment not completely understood (particularly by me), and at this point in my life the entire process is somewhat over my head but I will take a shot at briefly explaining what I know.  The gills absorb elements from the water and the intestine absorbs elements from food, these elements are then passed into the blood plasma and finally into the endolymph fluid, where they crystallize into the otolith (Campana 1999). 

Because otoliths are made of calcium carbonate the most important element in their formation is…you guessed it, calcium.  Because of this, uptake of other trace elements is correlated to the concentration of calcium in the water.  When high concentrations of calcium are present in the water less trace elements are absorbed than when low concentrations of calcium are present. Elements like, Sr (strontium), Zn (zinc), Pb (lead), Mn (manganese), Ba (barium) and Fe (iron), are less physiologically regulated than other elements and thus are used more often in otolith elemental analysis (Campana 1999).

Because otoliths are metabolically inert (meaning they are not reabsorbed, even during periods of starvation), elements incorporated into the otolith should reflect the environmental history of the fish from its time of hatch to time of death (Elsdon and Gillanders 2003).  In combination with age information, otolith elemental analysis can be used to hypothesize about the environmental conditions a fish has experienced throughout its life.  For example, the center, or core, of the otolith represents otolith growth of juvenile fish, whereas the outer edges of the otolith represent recent, or current, otolith growth just prior to capture (Elsdon and Gillanders 2003).  Therefore, the elemental composition of the center of the otolith gives us an idea of the elemental composition of the water the fish was in when it was born, the elemental composition of the outer edge gives us an idea of the elemental composition of the water the fish was in before it was captured. 

Again the easiest way to visualize this is to think of tree rings.  The innermost rings represent the growth of the tree when it is was very young.  Layers of new wood material form as the tree grows.  The outer most rings represent the newest tree growth.  The same concept is used in otolith chemistry. 

Stay tuned for a post about how otolith chemistry can be used to investigate the movement of anadromous fish!

On these images of river herring otoliths you can see annual rings near the center and near the edges.  The center portion of the otolith represents growth as a juvenile.  The outer portion of the otolith represents the most recent growth.

Campana, S.E., and J.D. Neilson.  1985.  Microstructure of fish otoliths.  Canadian Journal of Fisheries and Aquatic Sciences 42:1014-1032.

Campana, S.E.  1999.  Chemistry and composition of fish otoliths:  pathways, mechanisms and applications Marine Ecology Progress Series 188:263-297. 

Elsdon, T.S. and B.M. Gillanders.  2003.  Reconstructing migratory patterns of fish based on environmental influences on otolith chemistry.  Reviews in Fish Biology and Fisheries 13:219-235.

Tomas, J., and A.J. Geffen. 2003.  Morphometry and composition of aragonite and vaterite otoliths of deformed laboratory reared juvenile herring from two populations.  Journal of Fish Biology 63:1383-1401.

Monday, September 20, 2010

Link fest - check it out!

For those of you interested in otolith science particularly the microchemical aspects of otoliths you should check out

This site was put together by Benjamin Walther.  There is a forum where those working with otoliths or even those who are just interested in otoliths can ask questions and share ideas with other otolith scientists.

I think this site is a great idea and kind of gets at what I am hoping to accomplish with this blog, putting ideas and experiences in otolith research out there and getting feedback from people who may (or may not) be helpful.

Other otolith links of interest

Otolith Research Laboratory
Online otolith manual
The otolith page

Sunday, September 19, 2010

Field work funday!

Over the summer I pretty much had the freedom to conduct field work whenever I wanted with the only limiting factor being weather, which was pretty pleasant and cooperative.  However, since school started up in August I have been limited to conducting field work on weekends and holidays (best labor day ever!).  I don't really mind being out on the water every weekend but I do feel for my crew, having to wake up at 6 am on Sundays isn't easy when you are an undergrad.

With that being said we were off to the field today bright and early!  I, of course, stupidly stayed out until one last night and miraculously was able to wake up at 5 to get things ready (all this while still trying to recover from the debauchery of a week in Pittsburgh).  Once everyone assembled we headed up to Columbia NC to pick up the boat and then made our way to Gum Neck NC to launch in the Alligator River.  The purpose of this trip was to collect water samples from the Alligator, Scuppernong and Roanoke Rivers.  We have been collecting monthly water samples from and upstream and downstream location from these three rivers (plus the Chowan and Perquimans Rivers) since June, and we will continue collecting through October.  We are doing this to examine the elemental composition of the water and compare this to the elemental composition of river herring otoliths.  Presumably the elemental composition of the water should be similar to that of the otolith.  If there are differences in the elemental composition of the water in each river we may be able to classify juvenile river herring to their natal river using the elemental composition of their otoliths.  

We got out onto the Alligator River pretty early, but the wind was already howling, and the waves were building, as they tend to do on a large river like the Alligator.  We were able to brave the conditions and collect our samples, however most of our equipment decided to crap out.  First our YSI (used for recording temperature, dissolved oxygen, and salinity etc.), then our GPS batteries died, and finally a hole burst in our filtering tube (this was easily fixed).  This was the first time things have really gone wrong during my field work, and I should feel lucky because these are relatively minor situations and much worse could have happened. 

Work in the Scuppernong and Roanoke Rivers went fairly smooth.  I would have liked to have been able to record salinity and dissolved oxygen from the rivers though, because we did observe some blue crabs pretty far up in the Scuppernong River, and there was a bass tournament in the Roanoke River so I think it would have been interesting to have some water quality data while that was going on.  Also, I saw my first NC black bear which was very exciting!  I haven't seen a black bear in the wild in probably 10-15 years despite spending a lot of time in the Adirondack Mountains.

Sadly I only have one more month of field work left.

Friday, September 17, 2010

Big ol' AFS Review: Part II

Below is a review of some of the more interesting otolith talks I attended on Wednesday and Thursday while in Pittsburgh for the 140th annual meeting of the American Fisheries Society.


Wednesday was a big day in terms of otolith talks and started bright and early with three heavy hitters in the shad and herring symposium.  First up was Benjamin D. Walther on “Estimating origins of migrating American shad with otoliths chemistry”.  Using a combination of elemental and isotopic ratios this research was able to classify American shad juveniles to natal watersheds along the east coast with 93% accuracy!  This is very interesting and this study currently represents the largest database of otolith chemical signatures.  In addition, the otoliths of adult American shad were examined in an attempt to classify them to natal origins and found these fish to be from a small number of rivers. 

Next up was Sara M. Turner on “Determination of river herring natal origin by otolith microchemical markers”.  The goal here was to use elemental and stable isotope ratios to identify chemical signatures in the otoliths of juvenile river herring that could be used to classify them to their natal river.  This work was mostly being carried out in the Hudson River but I believe fish from Virginia and maybe Massachusetts were also being analyzed.  Migration patterns of juvenile river herring were also examined, which I will discuss more in about two paragraphs.

Following Sara was Banjamin I. Gahagan on “Estimating anadromous river herring natal stream homing rates using otolith microchemistry”.  Again the goal of this project was to utilize elemental signatures (no isotopes here, although he did admit that it would strengthen his analysis) in otoliths to classify juveniles and adults to natal origins.  This work was carried out in a number of watersheds in Connecticut.  Migration patterns of juveniles was also investigated, which I will now discuss.

Both Sara and Ben examined the migration patterns of juvenile river herring and found pretty similar patterns of fish entering what could be interpreted and marine water fairly early in life.  This is indicated by increasing strontium levels in otoliths (higher strontium is associated with saltier water).  This pattern is further backed up by my own findings of juvenile river herring appearing to be found in marine or brackish water at a very young age.  I have mixed thoughts about this finding, the juvenile fish have been collected in what would be classified and fresh to low salinity brackish water (at least mine have anyway).  Most of the strontium profiles show a pattern of increasing strontium, which is consistent with larval river herring being transported downriver into a more saline environment.  However, the fish would then be expected to move back upriver into a lower salinity environment.  Many of the fish I have looked at have an increasing strontium profile but do not show any decrease (unfortunately I don’t know were in the river some of the fish were collected).  It is an interesting situation and it appears that Sara, Ben and myself have all come up with similar findings (even though my own data is pretty meager at this point). 

Also, on Wednesday was Stacy K. Beharry on determining fish origin by mining the otolith.  This research utilized stable isotopes, elemental ratios and varying growth rates to classify spotted sea trout to natal grass beds in the Chesapeake Bay.  The factors that were included the higher the classification rate to natal grass beds (I think classification was somewhere between 85 and 95%).  This data could then be used to attempt to classify adult seatrout to natal grass beds.  I thought this talk went very well, however this research is based on the assumption (this has been demonstrated in the literature somewhere but I’m not sure of where) that juvenile spotted seatrout do not leave natal seagrass beds.  It seems strange to make this assumption, when it would be simple enough to test using a laser scan across the otolith and examining potential habitat shifts.  Migrating juveniles could potentially result in lower classification success. 

Other talks of interest on Wednesday were by; James R. Jackson on movements and habitat use of bowfin in Oneida Lake (which is was really really mad that I missed), Jian Yang on relating otolith Sr:Ca ratios to marine, brackish and freshwater habitat use, Ruth E. Haas-Castro on distinguishing between alewife and blueback herring using scales, Courtney V. Holden on the effects of water temperatures on American eel using otolith isotopic analysis, and Roger A. Rulifson on tidal power development in the Bay of Fundy.


Since we left on Thursday morning I was only able to attend one talk, but it was definitely worth only getting four hours of sleep to hear.  Karin E. Limburg presented the work of Todd A. Hayden entitled Searching for the needle in the haystack:  Identifying natural otolith tags to determine natal origins of the humpback chub in the Grand Canyon.  This work utilized some pretty advanced and very interesting techniques in order to analyze the otoliths of these fish, and was able to decipher migration patterns of these fish. 


I thought the conference was great I had a blast getting to hear about a lot of new things, and talking to some interesting people.  I got to present my research for the first time and from most accounts I did pretty well.  I was kind of bummed that I didn’t get to speak during the shad symposium because I really think I might have gotten some better feedback from that group.  Based on the otolith talks I attended I really think I should consider incorporating stable isotope analysis into my work.  I am unsure about the feasibility of this but I think if I can do it my data analysis would really be strengthened.  

Big ol' AFS Review: Part I

The 140th meeting of the American Fisheries Society in Pittsburgh PA is over and I am sure most people would say it was a huge success.  I met some interesting, and helpful people and reconnected with others who could potentially help me with my research along the way.  I was able to attend a number of talks that dealt with otolith chemistry and its application so I will briefly review some of the most interesting.

The first otolith talk I attended was “Isotopic signatures of otoliths in identification of Pacific hake stocks” was given by Yongwen Gao.  I find this topic pretty interesting because it utilizes otolith chemistry rather than genetic techniques, which have apparently been somewhat ineffective in stock discrimination of marine species.  Essentially the core of Pacific hake otoliths was analyzed for oxygen and carbon isotope ratios and significant differences were found between fish caught on the Washington Coast and fish caught in Georgia Strait, British Columbia, indicating that there are separate stocks of Pacific Hake.  I have read a couple papers on stock discrimination of marine fish using otolith chemistry and it appears to be pretty accurate especially when utilizing stable isotope ratios (this will be a running theme throughout this review).  

I then attended “Using a combination of genetic markers and otoliths chemistry to examine connectivity issues and management implications for spotted seatrout” presented by R. Deborah Overath.  This research wanted to address connectivity of seatrout between coastal and in shore habitats on an area of the Texas coast.  While most of the genetics data was over my head, the otolith data was interesting.  Stable oxygen and carbon isotopes were utilized to classify fish to habitat type.  If I am not mistaken the outer edge of the otolith was used for analysis because the research wanted to focus on classifying trout to their most recent habitat area.  

*Begin Tangent*

One of the interesting things about otoliths is that they accrete calcium carbonate sequentially throughout the entire lifetime of the fish and otolith material is not reabsorbed.  The easiest way to think of how an otolith is formed is to think of tree rings.  If you cut a tree you see growth rings, which allows you to make age estimates.  If you cut an otolith you see similar patterns, so much so that we can even count daily rings in some instances.  However, otoliths are more like rocks than trees, and a more accurate method of visualizing the structure of and otolith is to think of an onion.  Onions are made of layers of material in a spherical shape; this is pretty similar to the arrangement of otolith material.  It is this structural pattern that allows us to examine the life history of a fish from birth to death.   

*End Tangent* 

Using isotope ratios 64% of samples were assigned to their correct region.  This number seems a bit low but I believe the area they were working in was pretty small.  It also appeared that straying of fish occurred between habitats that were adjacent to each other.  Perhaps this research could be useful in examining ranges of fish?  I also think that had elemental ratios been incorporated rather than just stable isotopes, the classification success may have been greater (again this will come up later). 

One of the best talks I attended was by Renee Reilly called “Time series applications in otlith chemistry”.  For the life of me I cannot recall many of the details of this talk.  It dealt with the interpretation of elemental ratios across the entire scan of an otolith, and methods to properly interpret this data.  This research is useful when looking at migration patterns and habitat shifts of fish.  Essentially, it involves looking at a string of data and determining where the significant differences are if there are in fact any.  I really hope this research is published, because it would be very helpful in my own data interpretation.

Also of interest on Monday were talks by; Roger Rulifson on restoring river herring in North Carolina, Anthony Overton on growth and mortality rates of larval river herring in the Tar-Pamlico River, Sarah E. Friedl on mortality estimates of juvenile spot in North Carolina, Johnny E. Moore on site fidelity of sand tiger sharks, and Jordan R. Allison on Walleye reproduction in Lake Michigan.  


As far as I can tell there was really only one talk on Tuesday dealing with otolith chemistry (given by me), and I don’t really want to discuss that any further here.  However, Tuesday was the first day of the Shad and River Herring symposium so I attended many of those talks.  Included in the symposium was the work of Kenneth L. Riley and Samantha M. Binion who both presented on different aspects of river herring work on the Roanoke River.  Both of the talks dealt with early life history of river herring and American shad and were very well done. 

Many of the talks given on the first day of the shad and herring symposium dealt with the removal of dams and the effectiveness of this in restoring populations.  It seemed as though the results were mixed.  Even though spawning habitat was opened up if it was a river with multiple impoundments the amount of habitat opened could be insignificant.  It also seems as though these species may not immediately utilize new upstream habitat.  Many theories were bounced around as to why this may be, I found the most interesting to be “the lack of leader fish hypothesis” (not exactly sure who said this but I know I heard Karin Limburg mention this).  Essentially, while the dam has been in place fish that spawn successfully below the dam have been selected for, once the dam is removed there are no fish that are conditioned to make the longer upstream migration so this habitat is not utilized.  The theory is that younger fish will follow “leader” or older fish into the river to make spawning migrations.  If there are no older fish making these longer spawning runs younger fish will not make them either. 

Also of interest on Tuesday were talks by; Mike Bednarski on population trends of shortnose sturgeon in the Altmaha River (which he nailed!), Daniel W. Cullen on the influence of temperature on monkfish distribution, Elizabeth Fairchild on spawning movements of winter flounder (which was one of my favorite talks).

Keep reading part II for reviews of Wednesday, Thursday and some closing thoughts.

Tuesday, September 14, 2010

Dooms Day!

After staying up until 12:30 am last night (and then being woken up at 2:30 am) to put the finishing touches on my presentation for AFS, I woke up at 6:30 am to load my power point onto the computer.  I then milled around until 8:00 am and went to the room were the Marine Ecology section would be located.  There were two presenters before me that presented very well, one talk was on monkfish, and the other was on flounder.

The whole time I was waiting in the room for my presentation to start my heart was definitely pounding as I had never presented my research before and had never given any presentation in a setting such as a national meeting.  My talk started at 8:40 am, and overall went pretty well.  I feel like I stumbled around in some places and was maybe a little vague in others but for the most part I felt pretty comfortable talking about my research.  To be honest I was probably nervous for nothing.  At the present time I really do not have enough data to do any in depth analysis so most of what I presented on was fairly basic and uncomplicated.  I finished my talk two minutes early which left plenty of time for question but alas there were none, which was disappointing as I was really hoping for some comments and suggestions.

Most of the people I talked to afterward said I did really well although I did talk kind of fast, which I kind of expected to be the situation.  Now that I am through with my talk it really feels like a huge weight has been lifted off my shoulders and I look forward to attending more talks tomorrow particularly a few from the shad and river herring symposium that are very similar to my project and utilized otolith microchemistry.

I will probably have a more in depth post concerning some of the more interesting talks after the conference is finished but until that time if something interesting happens I will try and make a short post.

Sunday, September 12, 2010

AFS Day 1

Well the trip from North Carolina to Pittsburgh was relatively uneventful.  I think we watched about four movies because it took us about 11 hours to make the drive.  Which incredibly is the same amount of time it takes me to drive from NC home to New York. 

After going to bed way to late last night and getting up way to early this morning I attended the continuing education class Basic Fisheries Population Modeling using Excel.  It was a very interesting and useful class and it was good to learn new techniques from a software program that I feel like I've used way to much.  It always helps to have someone walk you through complicated sequences step by step.

Presentations start tomorrow and I am really looking forward to seeing some of them.  And Mike will be here tonight!

Saturday, September 11, 2010

Road Trip!

Today I leave for Pittsburgh PA for the the meeting of the American Fisheries Society.  Eight hours in a van driving through NC, VA and West Virginia will hopefully make for some interesting/hilarious red neck and hilbilly jokes.  While I enjoy going to conferences I have been somewhat dreading this one due to the fact that I will be giving a presentation on what little data I have thus far.  At the very least it should be a good learning experience and I always welcome constructive feedback on my project.  The conference should be a good time and I look forward to meeting up with people I haven't seen in a while.

I will try and post updates from the conference, especially Tuesday after I present, however I am not positive on internet availability so don't expect to much.

Thursday, September 9, 2010

Why the Endolymph?

Who am I?

Well, my name is Dan.  I am currently a biology graduate student in eastern North Carolina.  I am studying nursery habitat and migration patterns of river herring (alewife and blueback herring) in tributaries of the Albemarle Sound.  If you are familiar with the area the tributaries I am focused on are the Chowan River, Scuppernong River, Perquimans River, Alligator River (which you may have driven over on your way to the Outer Banks), and the world famous Roanoke River.

However, more interesting than actually simply studying river herring is the method with which I am utilizing.  I am using a technique called otolith microchemistry.  I won't get into the nitty gritty details right now (just wait) but here is a quick overview.  Bony fish have structures in their heads, in what is essentially their ear, called otoliths.  There are three pairs of otoliths, that help the fish hear and stay balanced in the water.  Otoliths are made of calcium carbonate, however, trace elements, such as strontium, barium, manganese and magnesium, may substitute for calcium in the otolith.  Water bodies and habitats have different ratios of trace elements in the water, and these ratios are often reflected in the otoliths of fish.  This allows us to track habitat usage, natal origins, migratory patterns, and allows for stock discrimination.  It all seems very complicated, and it is, but I hope to break things down enough so that if anyone winds up reading this they don't start bleeding from the ears. 

Anyway, elements come together to form otoliths in the endolymph fluid, located in the endolymph sac, hence the name of the blog.  My goal is to bring many thoughts together into one tangible thingy (aka blog).  While I will try and focus on new and exciting happenings in the world of otoliths, namely my own otolith research, I will also probably post on interesting happenings (if such things exist) in my life, and yes I will probably write a little (probably a lot) about hockey.