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.