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Project ID: 2004AR67B

Title: Otolith Microchemistry of Fresh Water Fish

Project Type: Research

Focus Categories: Hydrogeochemistry, Ecology, Conservation

Keywords: Geochemistry, Fisheries, Hydrobiology, Hydrochemistry, Fish Ecology

Start Date: 02/15/2004

End Date: 12/15/2004

Federal Funds: $23,813

Non-Federal Matching Funds: $47,631

Congressional District: First

Principal Investigator:
Robyn E Hannigan
Arkansas State University


A critical component of the Sustainable Fisheries Act of 1996 is the identification and conservation of habitats considered essential for the survival and subsequent recruitment of marine fish. The issues surrounding the identification and conservation of habitats in freshwater systems is becoming increasingly important given the pressures of land-use, rise in invasive species and decline in endemic aquatic fauna. Given that it is be impractical to conserve all habitats, it is critical to identify and protect areas that contribute disproportionately large numbers of recruits to adult fish populations (i.e. sources) rather than preserve or rehabilitate habitats that may con-tain significant juvenile biomass but produce few recruits (sinks).

It has proven difficult to determine exactly which habitats should be targeted for protection, either for conservation or to meet fishery production goals. Generally by comparing the abundance of juveniles in different habitat types an approximation can be made for the relative importance of different habitats. There are, however, several problems with this generalized approach. These difficulties are tied to difficulties in tagging juvenile fish, sampling bias as well as variable and high mortality rates in some habitats that can bias population estimates. Variable and high mortality preclude accurate estimation of relative survival of juvenile fish and recruitment of these juveniles into the adult population. Indeed, recruitment into the adult population may not be a simple function of juvenile abundance at a single point in time but, rather, the accumulation of periodic mortality events.

We propose to apply a geochemical technique, with demonstrated success in marine environ-ments, to address the identification of essential fish habitat in a fresh water system, the Spring River. This geochemical technique uses the chemical variations preserved in fish otoliths (ear stones) as natural tags of fish movement to and from habitat regions within a watershed. This relatively new technique may be a more effective method for estimating habitat use by juvenile and adult fish. Otoliths form through concentric additions of mineralized tissue around a central nucleus. These additions form daily patterns in almost all fish during the larval and early juvenile stages of life. Because the otolith is acellular, it is physiologically static; in other words, once deposited, otolith material is not resorbed or metabolically reworked to any significant degree. Therefore, otoliths remain unaffected by short-term changes in fish condition, such as starvation, and, consequently, provide an accurate means of determining age and growth. Less well known is the fact that the chemical composition of a given daily increment reflects the chemical composition of the water that passed through the fish’s gills on that same day. Migrations between water masses at some age and/or date will, therefore, be recorded in the chemical composition of the otolith at the appropriate daily increment. Thus, otoliths provide a permanent record of the temporal and spatial history of an individual.

Progress/Completion Report PDF

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