What's Hot in Otolith Research
There is a lot of very exciting research involving otoliths being carried out around the world. Some of the research is focused on the otolith itself, but most of it uses some feature of the otolith as a tool to another end. What follows is our view of the most promising of the up and coming fields in otolith research - the fields that we see as making substantial strides in the near future. There may be others, but these are the fields that we currently have our eyes on:
Otolith Workshop in Iceland: The University of Iceland will be repeating its popular and inexpensive 2-week graduate course on fisheries ecology on May 27 - June 7, 2014. The course includes a 2-day introductory workshop on otolith preparation and ageing methods under the instruction of Steven Campana. The workshop is targeted towards those with little or no ageing experience, but contains something for all skill levels. Ageing exercises will focus on Icelandic species such as cod.
New otolith atlas for the western Pacific: Chien-Hsiang Lin and Chih-Wei Chang have just released their new book, Otolith Atlas of Taiwan Fishes. With photographs and/or SEM images of more than 1000 fish species, this book will provide a much-appreciated reference for otolith workers in the western Pacific.
5th International Otolith Symposium: Mark your calendars! Beatriz Morales-Nin and Audrey Geffen are well underway in their organization of the upcoming 5th International Otolith Symposium. The conference will be held 20-24 October 2014 on the island of Mallorca, Spain, and will include both workshops and oral/poster presentations. If previous Otolith Symposia are any indication, this conference is going to be an amazing opportunity to network with both otolith novices and experts, and learn the very latest approaches to otolith science and application. See you there!
Otolith Workshop in Iceland: The University of Iceland will be repeating its popular and inexpensive 3-week graduate course on fisheries ecology on June 6-18, 2013. The course includes a 3-day basic workshop on otolith preparation and ageing methods under the instruction of Steven Campana. The workshop is targeted towards those with little or no ageing experience, but contains something for all skill levels. Ageing exercises will focus on Icelandic species such as cod.
3D Otolith Scanning: Toni Lombarte and colleagues have announced the development of a 3D scanner for otoliths. The resulting images have very good clarity, and can be rotated in 3D when using the appropriate software.
New Ageing Method for Lobsters, Crabs and Shrimps: Crustaceans don't have otoliths, but the discovery of growth bands in their eyestalks and gastroliths borrowed heavily from previous otolith research. Read all about it in Kilada et al. 2012.
Image and Shape Analysis Software: LASAA at IFREMER in France have developed new image analysis software for calcified structure (TNPC). In addition to providing the normal image acquisition capabilities, this software is reported to allow image enhancement, feature measurement and data extraction. A particularly appealing feature is otolith shape analysis, which is often not available in other software packages.
Stock Mixture Analysis Now Combines Otolith and Genetic Markers: The 2010 paper by Smith and Campana reports the first statistical method for stock mixture analysis which allows the simultaneous consideration of genetic, otolith, meristic and other stock characteristics in a Bayesian framework. An R package (which includes a sample dataset) is available for free download. Mix.Fish for Unix is also available. Installation instructions are also provided.
2009 Otolith Symposium Completed: The Fourth International Otolith Symposium in Monterey, California in Aug 2009 turned out to be a very successful and interesting meeting. With more than 260 attendees representing 35 countries, the opportunities for networking and learning new skills were endless. Plus, of course, the venue was gorgeous! Keep your eyes tuned for news of the next Otolith Symposium in 2014.
Statistical Program for Age Validation based on Edge Analysis: Okamura and Semba (2009) published a paper detailing a statistical program for validating annual growth band formation based on edge analysis (whether or not the growing edge of the otolith or vertebra shows an opaque or translucent zone across the year). To our knowledge, this is the first such statistical analysis that has been developed for analyzing edge-type data, which has usually been analyzed in an ad hoc and non-rigorous manner. The authors have made the R code for this program available at their website.
Symposium Completed: Advances in Fish Tagging and Marking Technology: An international symposium on fish tagging and marking, including biological markers such as otolith elemental fingerprints and genetics, was held 24-28 February 2008 in Auckland, New Zealand. Other sessions included those dealing with acoustic telemetry, archival and satellite tags. A book containing some of the papers has now been published.. It was a good meeting!
New Paleothermometer: Everyone is on the look-out for the ideal paleothermometer; something that can be used to reconstruct temperature history without the confounding effects of salinity or water composition. For use with otoliths, stable oxygen isotopes are usually the best bet, but only if the isotopic composition of the water is known. The 2007 paper by Ghosh et al. presents an alternative based on combinations of stable carbon and oxygen isotopes. It's not a panacea, but it avoids complications due to water composition.
Web-based Otolith Identification Software: Although there now a number of otolith atlases around the world which can be used to identify species based on otolith shape and appearance, the AFORO web site presents the first web-based automated species identification software based on otolith shape. The program uses several mathematical methods of shape analysis (including wavelet analysis), and requires nothing more than uploading a suitably-oriented otolith image on a black background. Species identifications are currently limited mainly to the Mediterranean, but the image database is being expanded to other areas.
Maximum Likelihood Software: With the realization that elemental fingerprints can be used very effectively to separate mixtures of fish coming from different sources, there is increasing demand for the maximum-likelihood based software to separate the group mixtures. Discriminant analysis is not a good option here, since the 'priors' parameter is unknown. In the Statistical Analysis section of this web site, we've released a working copy of the Integrated Stock Mixture Analysis (ISMA) program (written for the S-Plus environment) for use in separating stock mixtures based on elemental fingerprints or other continuous or categorical variables.
Otolith Symposium Completed: The Third International Symposium on Fish Otolith Research and Application in Australia was a tremendous success! A combination of technical workshops, state of the art papers, and a superb venue combined to make this an excellent learning experience for all 300 of the participants (representing 35 countries). A dedicated issue of Marine and Freshwater Research 56 (Issue 5) has now been published containing the symposium proceedings. The volume can be viewed on-line at http://www.publish.csiro.au/nid/126/issue/974.htm
New Otolith Equipment: Several companies around the world have developed new equipment for preparing or interpreting otoliths. No endorsement of any of the following is implied, since we have not used any of them, but some look interesting. For example, Benetec offers an otolith sectioning saw as part of its all-inclusive Otolith Processing Line. For polishing several otoliths at once, South Bay Technology offers a MultiLap Polishing Tool with precise controls over individual otoliths. Finally, Ratoc System Engineering has developed a semi-automated daily increment measurement system.
Photographic Atlas of Fish Otoliths: The otolith collections for this book took nearly 20 years to complete, but the Photographic Atlas of Fish Otoliths of the Northwest Atlantic Ocean has now been published. The book includes light microscopic and SEM images of 580 sagittal otolith pairs representing 288 species and 97 families of fish from the northwest Atlantic. Also included are images of lapilli and asteriscii from most families, and an overview essay of factors affecting otolith shape. The book is available from NRC Research Press.
Otolith Methods: New sections have been added to the Methods page of this web site, expanding the coverage to subjects other than that of otolith microstructure. Currently included are pages on preparation for elemental analysis, decontamination, embedding in epoxy for examination of annuli, and the preparation of thin sections using an Isomet saw. The sections on otolith preparation for microstructure examination have also been completed.
Quality control in production ageing: In an informal survey of fisheries labs around the world, we determined that a minimum of 800,000 otoliths are aged annually, most of which is done in mass production fashion by stock assessment laboratories. Some labs use quality control (QC) protocols and have validated reference collections, while some prefer a riskier life. Two recent reviews thoroughly summarize the do's and don'ts of age validation and quality control. The review paper in J. Fish Biol. (Campana, 2001) focuses on age validation and QC protocols, and perhaps surprisingly, soundly criticizes the oft-used marginal increment method of age validation. Taking a more technical approach, a multi-authored book entitled Manual of Fish Sclerochronology, edited by Panfili et al., includes chapters dealing with a range of applications and methods. A particularly novel aspect of the book is the inclusion of a multimedia DVD and videos concentrated on techniques. The book was published in the fall of 2002, and is available from IRD Editions of IFREMER in France.
Age validation of long-lived fishes using fallout and radiocarbon from nuclear testing: Kalish introduced this field, and now our lab is into it in a big way. To our mind, this is THE best way to validate the ages of long-lived fishes, with none of the assumptions that plague other approaches. And the technology and implementation is only going to get better. Stay tuned!
Elemental fingerprints as natural tags: The original dream that the elemental and isotopic composition of the otolith might serve as the ideal non-genetic stock marker has faded. But what has emerged instead - somewhat unexpectedly - is that the elemental fingerprint works just like a natural tag of a group of fishes, with complete stability over short periods of time. This gives the ability to reliably track the movements of those fish no matter where they go and who they mix with. It's just like a large-scale tagging experiment, but without the time and expense of having to tag them in the first place. In many stock mixing situations, we predict that this will give better discrimination than anything else, including microsatellite DNA!
Stock mixture analyses based on maximum likelihood estimation: The topic may make your eyes glaze over, but if you're using elemental fingerprints to classify fish into groups, you'll want to read up on this approach. Almost everyone in the otolith field has become fixated on discriminant function analysis to classify unknown fish into two or more reference groups, but they don't realize that discriminant analysis can give grossly misleading results when you don't know the answer ahead of time (the priors). Here's one area where the geneticists are way ahead of us - they've been using MLE-based stock mixture analyses for years. For an example, read CJFAS 56:1873-1881 (1999). And stay tuned for an integrated stock mixture analysis capable of handling both elemental fingerprint and DNA data at the same time.
High resolution magnetic sector ICPMS: The best tool for analyzing the elemental composition of an otolith just got better. The magnetic sector ICPMS is able to distinguish between many isobaric interferences and the target element, thus allowing more accurate assays for certain key elements. Is there really as much Fe in otoliths as some have reported, or is the 'Fe' really interference from CaOH? This is the instrument that will tell us the answer!
Probe-based reconstruction of temperature history using oxygen isotopes: Lots of people have used oxygen isotopes in whole otoliths to determine the mean water temperature in which the fish lived, and some have used micromilling techniques to zero in on seasonal or annual temperature histories. The new generation of computer-controlled microsamplers allow even more detailed sampling. Laser or ion probe-based techniques are the next logical step, allowing (in principle) monthly, weekly or even daily temperature histories. It's not quite there yet, but it will be.
Mass-marking using calcium-binding compounds or temperature: It's already here, and it's working great! A number of labs and hatcheries are now routinely mass-marking millions of young fish before release into the wild. Some have already used recapture results to test ecological theory, but the possibilities are virtually untapped. For the first application as a tag of newly-hatched marine fish in the wild, read Nature 402:802-804.
Computer-assisted ageing: the big dream is to have an image analysis system age the otolith for you while you kick back and do nothing. Dream on! Even with the ongoing advances in imaging and artificial intelligence, we are unlikely to see a general purpose, fully automated ageing machine in the near future. On the other hand, the resolution and dynamic range of image analysis systems is improving rapidly, implying that image enhancement will become easier than ever. We should also see reductions in the numbers of otoliths required for routine ageing, due to improvements in quality control and the introduction of maximum likelihood statistical techniques for predicting age based on otolith morphometry.
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