Specific elements and isotopes incorporated into the growing surface of the fish otolith reflect the physical and chemical characteristics of the ambient water, although not necessarily in a simplistic manner. Since fish that spend at least part of their lives in different water masses often produces otoliths of different elemental composition, the otolith elemental composition ("elemental fingerprint") can serve as an environmentally induced tag of groups of fish. These tags tend to be physically stable, reproducible, and different among stocks, but are not necessarily stable over long periods. Thus, they do not serve as a proxy for genetic identity. However, the fingerprint is very stable over the short term, making it valuable as a seasonally stable biological tracer of predefined groups of fish. Alternatively, the fingerprint of the otolith core can be used as a marker for groups of fish hatched in different environments. Technological advancements in recent years have made otolith elemental fingerprints a viable, and sometimes preferable, means for distinguishing among fish stocks.