Major differences between marine and freshwater sys- tems are primarily found in the common marine salts (Campana, 1999:271). Environmental variability, while the very basis for how otoliths can be used in sourcing studies, is at the same time another area of concern. Elemental differences also can be expected with major ontogenetic phase shifts, such as the period of larval meta- morphosis into juvenile stage (Hamilton and Warner, 2009:242 Mugiya and Satoh, 1995 Swearer, 2000). Such differences between studies likely re fl ect species-level variability. (1998:258) found “ lower levels of most elemental and isotopic variables with increasing otolith weight, ” an age-related effect that was not systematic enough to allow for mathematical correction. (2011) were able to correct for the effects of otolith size via regression analysis, with data showing linear relationships however, Thorrold et al.

This latter effect probably is related to the rate of protein synthesis (Kalish, 1989), which in turn affects the rate of crystallization of the otolith (Campana, 1999:2740), which gener- ally slows with age (Chang et al., 2012).

However, differences in Sr:Ca ratios between species, even those habitually occupying the same areas, may be expected, as will be an increase in Sr:Ca with the age of the fi sh (Campana, 1999 Hamilton and Warner, 2009). Sr is recognized as the best marker for source (e.g., Ludsin et al., 2006 Pontual et al., 2000), especially for anadromous fi sh (Campana, 1999 see also Disspain et al., 2015), because: 1) it is the least-regulated element 2) there is a purported lack of a temperature effect on Sr uptake (Campana, 1999) and 3) differences in concentration between fresh and salt water (lower Sr:Ca in the former e Hale and Swearer, 2008 Pontual et al., 2000) can be quite abrupt, (Hamilton and Warner, 2009), re fl ecting the 30 e 35% dif- ference in salinity between the two environments. Obviously, this can vary by species, and may vary seasonally by sex for example, Mendoza- Carranza (2003) found that during the rainy season, male gafftopsail cat fi sh ( Bagre marinus ) in near-shore waters consumed signif- icantly more prey fi sh than did females. 10 e 20% of Ca and Sr for freshwater fi shes e Campana, 1999:267). which drink continually) and from food, although this contribution appears to be relatively low (e.g., ca.

Plash island history