Field Notes
U.S. Fish & Wildlife Service
Field Notes Entry   
How Old are the Fishin the Missouri River?
Midwest Region, December 1, 2007
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The Columbia National Fish and Wildlife Conservation Office collected spines and scales from 132 fish as part of the 2008 Sturgeon Season Age & Growth sampling.  Aging structures such as pectoral fin spines and scales are collected from target species identified as blue sucker, sauger and shovelnose sturgeon and sent to designated offices participating in the Pallid Sturgeon Population Assessment project.  Structures are collected until ten fish in each ten millimeter size class are represented or the end collection date is reached.

Typically, any bony part will deposit annual growth rings similar to growth rings in a tree.  When prepared correctly, counting annuli (rings) of spines and scales can be an accurate method for age estimation in fish. 

Scales have traditionally been the structure of choice due to ease of and the non-invasive nature of collection.  However, as fish reach maturity, somatic growth slows and scale annuli become less distinct, thereby producing under-estimates of age. Spines are not commonly used due to the labor-intensive nature of preparation methods.  However, when non-lethal sampling is required, spines are a very useful tool for aging fish. 

Each spine is thinly sectioned using a slow speed saw.  Cross-sections of spine are then mounted to a glass slide then viewed with transmitted light to enhance the growth rings.  The translucent bands are counted by two separate individuals to estimate the age of the fish.  Scales are cleaned with an ultrasonic machine and mounted to glass slides or an impression is extruded on acetate slides, then viewed under a microscope so that annuli rings can be counted.

Pectoral fin spines are removed from shovelnose sturgeon ranging in size from 130mm - 530mm.  Spines from fish larger than 530mm are not collected due to limited capabilities and inaccurate estimates associated with aging older sturgeon.  Shovelnose sturgeon are notoriously difficult to age due to the closely spaced and false annuli found in older fish.

Pectoral fin spines are also collected from blue suckers ranging in size from 100mm - 650mm.  Dorsal fin spines and scales are collected from sauger in all size classes.

We eagerly await the release of 2005-2007 Age & Growth reports for the target species.  The cooperative participation of staff between multiple federal and state agencies supports the "Partnership Goal" of the Fisheries Program Vision for the Future.  The Pallid Sturgeon Population Assessment program also addresses the "Native Species Goal" by monitoring and setting the ground work for recovering the federally endangered pallid sturgeon.  

Contact Info: Patricia Herman, 573-234-2132 x170, Patricia_Herman@fws.gov
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