Otoliths

Otoliths are calcium carbonate balance organs found in bony fishes (i.e., teleosts). Otoliths grow by the continuous deposition of calcium carbonate with no evidence of resorption. During deposition, certain trace elements accumulate within otoliths in proportion to seawater concentrations, although those proportions can vary with temperature and salinity (Campana et al. 1994, Fowler et al. 1995) . Therefore, otolith elemental composition can reflect ambient water conditions at the time of deposition. Studies on otolith microchemistry have documented levels of isolation among populations that were not evident in genetic studies (Campana et al. 1999, Thorrold et al. 2001) . The evolution of genetic population structure depends on the number of migrants entering a population. Realtively few migrants can maintain genetic homoegeneity of populations (Slatkin 1987). Although t is difficult to empircally estimate levels of exchange among marine populations, the success of numerouls managment and conservation efforts depends depends on such information.

An advantage of otolith microchemistry is that it has the potential to generate information about the environment experienced by an individual fish. Such information can provide insight into the extent of mixing among grousp of fish and provide information on relative dispersal distances. Given the large number of coastal species in the NE Pacific of which little or nothing is known regarding larval dispersal and only limited information is available on adult movements, otolith microchemistry has the potential to contribute new and valuable information.

One limitation to the use of geochemical otolith signatures as natural tags is temporal variation in water chemistry; our study and others observe inter-annual site differences in water chemistry (Elsdon and Gillanders 2004, Thorrold et al. 2002) . Although this inhibits the use of chemical information from one year to predict source locations in future years, it is still possible to gain information on the proportion of individuals at a location that came from local vs. distal sources. If otolith elemental signatures are geographically distinct throughout life, relative estimates of dispersal distance and the number of individuals that dispersed short vs. long distances can be made. Such information is needed to develop adequate commercial and recreational harvest regulations for numerous fisheries. Furthermore, efforts to determine the appropriate placement and spacing of marine protected areas for both conservation and fisheries management and the capacity of reserves to replenish over-fished stocks require realistic estimates of migration.