Elemental fingerprints of otoliths from Hudson River striped bass Morone saxatilis were used to define resident, estuarine, and ocean migratory contingents, which had previously been determined by otolith microprobe analysis of Sr:Ca. Using solution-based inductively coupled plasma mass-spectrometry, 7 metals were quantified in whole otoliths. Discriminant analysis of elements showed a high degree of separation among the 3 migratory contingents. Barium was significantly higher in otoliths from the freshwater resident group, while Sr and Na were significantly lower in comparison to mesohaline and ocean contingents. Identification of contingents by the bulk chemistry method indicated that divergent migratory patterns persist over lifetimes for Hudson River striped bass.

Chemical signatures in the otoliths of teleost fishes represent natural tags that may reflect differences in the chemical and physical characteristics of an individuals' environment. Otolith chemistry of Atlantic bluefin tuna (Thunnus thynnus) was quantified to assess the feasibility of using these natural tags to discriminate juveniles (age 0 and age 1) from putative nurseries. A suite of six elements (Li, Mg, Ca, Mn, Sr and Ba) was measured in whole otoliths using solution‐based inductively coupled plasma mass spectrometry. Otolith chemistry of age‐1 T. thynnus collected from the two primary nurseries in the Mediterranean Sea and western Atlantic Ocean differed significantly, with a cross‐validated classification accuracy of 85%. Spatial and temporal variation in otolith chemistry was evaluated for age‐0 T. thynnus collected from three nurseries within the Mediterranean Sea: Alboran Sea (Spain), Ligurian Sea (northern Italy), and Tyrrhenian Sea (southern Italy). Distinct differences in otolith chemistry were detected among Mediterranean nurseries and classification accuracies ranged from 62 to 80%. Interannual trends in otolith chemistry were observed between year classes of age‐0 T. thynnus in the Alboran Sea; however, no differences were detected between year classes in the Tyrrhenian Sea. Age‐0 and age‐1 T. thynnus collected from the same region (Ligurian Sea) were also compared and distinct differences in otolith chemistry were observed, indicating ontogenetic shifts in habitat or elemental discrimination. Findings suggest that otolith chemistry of juvenile T. thynnus from different nurseries are distinct and chemical signatures show some degree of temporal persistence, indicating the technique has considerable potential for use in future assessments of population connectivity and stock structure of T. thynnus.

Otolith chemistry of juvenile Pacific bluefin tuna Thunnus orientalis was measured to assess differences in composition among 3 nursery areas in the North Pacific Ocean: East China Sea, Sea of Japan and the Pacific Ocean off Shikoku. Six elements (Li, Mg, Ca, Mn, Sr and Ba) were measured in whole otoliths using solution-based inductively coupled plasma mass spectrometry. Univariate contrasts of T. orientalis otoliths collected in 1994 and 1995 indicated that concentrations of 5 elements (Li, Mg, Ca, Mn, Sr) differed among nurseries. Concentrations of Ca and Sr were significantly higher in the Pacific Ocean than in either marginal sea (East China Sea or Sea of Japan) nursery, while concentrations of Li, Mg and Mn were higher in fishes inhabiting marginal seas. Discriminant analysis showed clear separation of elemental fingerprints between Pacific Ocean and marginal sea nurseries, and to a lesser degree separation between the 2 marginal sea groups. Temporal stability of the elemental fingerprint was examined over a 3 yr period (1995 to 1997) in the East China Sea. Significant interannual trends were observed for 3 elements (Mg, Mn and Ba); however, elemental fingerprints of T. orientalis from the Pacific Ocean nursery were markedly different from all yearclasses in the East China Sea.

To test the hypothesis that elemental composition of otoliths (sagittae) could be influenced by differences in natural prey type, young-of-the-year bluefish Pomatomus saltatrix were captured immediately after their migration from oceanic waters into mid-Atlantic Bight estuaries and fed either shrimp, Crangon septemspinosa and Palaemonetes spp. or fish Menidia menidia under similar temperature and salinity regimes in two separate 60 day experiments. Unlimited rations of fish and shrimp prey were provided in the first experiment which led to differences in bluefish growth rate between the two prey treatments; fish prey was limited in the second experiment to ensure that growth rates of bluefish in the two prey treatments were similar. Concentrations of seven elements in bluefish otoliths were determined using solution-based inductively coupled plasma mass spectrometry (ICPMS). There was no significant effect of diet on five of the seven elements examined (Na, Mg, K, Ca and Mn). The levels of Sr and Ba in the otoliths of shrimp-fed bluefish, however, were significantly higher than fish-fed bluefish in both experiments. Concentrations of Ba in shrimp-fed bluefish otoliths were double that found in fish-fed bluefish. The results suggest that diet can explain some of the variation in otolith chemistry previously attributed to physical and chemical properties of the water. # 2004 The Fisheries Society of the British Isles