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.
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.
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.