Use of a Bar Code Symbology to Produce Multiple Thermally Induced Otolith Marks

Abstract

From 1987 to 1993, the Washington Department of Fisheries mass‐marked over 35 million juvenile salmonids by inducing unique banding patterns into their otoliths by means of short‐term water temperature changes during incubation. All five species of Pacific salmon Oncorhynchus spp. were successfully marked, and several broods of returning adults have demonstrated the persistence of these marks for at least 5 years. Using systematic rules developed in the bar code industry and a marking pattern of six bands and five spaces, we created a method for producing up to 10 different bar codes for marking the otoliths of incubating salmonids. Multiple groups (N) of six bands can produce 10N different codes. Ten unique patterns were decoded, both visually and with the aid of a computerized image‐analysis system combined with a decoding algorithm. Repeated blind tests showed that pattern recognition was virtually error free with both methods. Because the symbology is based upon the relative spacing of bands, the pattern can be discerned along any clear otolith axis; a consistent otolith measurement axis or section plane is not required. As a result, relatively gross, rapid otolith preparation procedures were adequate for accurate pattern recognition. Although the decoding algorithm may result in a failure to decode, the likelihood of misclassifications is small due to restrictive rules in the bar code symbology. Many research and management applications of thermal mass‐marking require the use of a number of unique patterns. This bar code method provides a simple means of organizing information so that multiple unique patterns are easily distinguished. Although demonstrated on chinook salmon Oncorhynchus tshawytscha, this method is applicable to any species for which thermal marking of otoliths is appropriate.

Formation of a Stress-Induced Check Mark on the Otoliths of Juvenile Fishes: Implications for Mesocosm Studies

“…All fishes that were captured and handled in our study displayed check marks on the day of capture, indicating they had experienced significant physiological stress at that time. Deliberate check-mark induction has been achieved through fluctuations in water temperature (Volk et al 1994). Although not our intended purpose, we did expose experimental fish to lower water temperatures, which may have contributed to check formation.…”

An Evaluation of Otolith Thermal Marking at the Feather River Hatchery, California

“…We thermally marked otoliths of Chinook salmon alevins by exposing them to a scheduled series of chilled-water treatments while in their incubation trays at the FRH (Figure 1) (Volk et al 1994). The treatment series were initiated approximately 1 week after hatching.…”

“…The otolith banding patterns we selected followed the "interleaved two of five" bar code symbology, consisting of six bands and five spaces (Palmer 1989;Volk et al 1994). A series of six unique codes were used to indicate the run-type and brood year for all…”

Banks Lake Fishery Evaluation Project Annual Report : Fiscal Year 2008 (March 1, 2008 to February 1, 2009).

“…Briefly, shifts in water temperature experienced from the eyed stage through yolk absorption are used to induce visible bands on the microstructure of otoliths. The bands and spaces between them are organized to produce bar codes on otoliths by following a series of simple rules (Volk et al 1994) that create relatively wide and narrow spaces between the bands. Using the methods described by Volk et al (1994) it is possible to produce hundreds of unique thermal marks.…”

“…The bands and spaces between them are organized to produce bar codes on otoliths by following a series of simple rules (Volk et al 1994) that create relatively wide and narrow spaces between the bands. Using the methods described by Volk et al (1994) it is possible to produce hundreds of unique thermal marks. Marks can be induced into otoliths both before and after hatching.…”