Coexistence of anadromous and resident life history styles of pond smelt, Hypomesus nipponensis, in Lake Ogawara, Japan, as determined by analyses ofotolith structure and strontium : calcium ratios

Anadromous and resident forms of pond smelt, Hypomesus nipponensis, were fo und to occur in sympatry in Lake Ogawara, Japan. Profiles of Sr: Ca ratios from individuals could be grouped to two patterns (1) a 'resident' pattern with low Sr: Ca ratios from core to edge and (2) an 'anadromous' pattern wi th relatively low Sr: Ca ratios near the core with abrupt increases in rati os at a location approximately 0.3 mm from the core. Spawners smaller than 60 mm standard length (SL) were resident, between 60 to 80 mm were mixed re sident and anadromous, and larger than 80 mm were anadromous. Anadromous in dividuals first migrated after 40 to 82 days from hatching (mean +/- sd, 59 .1 +/- 13.5 d) and 14.6 to 30.9 mm SL (22.2 +/- 5.3 mm). There was no diffe rence in SL between resident and anadromous individuals during age at first migration, suggesting that size may not be the mechanism for divergence of alternative life history styles.