The use of otolith strontium isotopes (87Sr/86Sr) to identify nursery habitat for a threatened estuarine fish

Abstract

Nursery habitats are larval or juvenile habitats that disproportionately contribute individuals to adult populations of a species. Identifying and protecting such habitats is important to species conservation, yet evaluating the relative contributions of different larval habitats to adult fish populations has proven difficult at best. Otolith geochemistry is one available tool for reconstructing previous habitat use of adult fishes during the early life history, thus facilitating the identification of nursery habitats. In this study, we compared traditional catch surveys of larval-stage longfin smelt (Spirinchus thaleichthys) occurring in habitats of different salinities to corresponding larval-stage salinity distributions of sub-adult/adult longfin smelt estimated using otolith geochemical techniques. This allowed us to evaluate the relative contribution of larvae from waters of various salinities to sub-adult/adult populations of longfin smelt. We used laser ablation MC-ICP-MS on otoliths and an empirically-derived relationship between strontium isotope ratios ( 87 Sr/ 86 Sr) of waters across the estuarine salinity gradient to reconstruct the larval salinity history of longfin smelt. Salinity values from the larval region of sub-adult/adult otoliths (corresponding to standard lengths of ca.10-mm) were compared to corresponding catch distribution of larval longfin smelt (≤ 10-mm) from 4 year-classes (1999, 2000, 2003 and 2006) in the San Francisco Estuary spanning a period when the population underwent a dramatic decline. Though the catch distribution of larval-stage longfin smelt was centered around 4-ppt and did not vary significantly among years, salinity distributions of sub-adult/adult were lower and narrower (ca. 2-ppt), suggesting that lowsalinity habitats disproportionally contributed more recruits relative to both freshwater and brackish water habitats and, therefore, may function as important nursery areas. Furthermore, the relative importance of the low salinity zone (ca. 2-ppt) to successful recruitment appeared greatest in years following the longfin smelt population decline. Our results indicate that otolith strontium isotopes ( 87 Sr/ 86 Sr) are a powerful tool for identifying nursery habitats for estuarine fishes.

Life-history characteristics of eleotrid fishes of the western hemisphere, and perils of life in a vanishing environment

“…Application of some of the modern physical and biochemical methods of determining species relationships are needed to resolve questions of species distributions, as well as analyzing life history patterns (otolith Sr:Ca ratios, 87 Sr/ 86 Sr ratios, biochemical identification of larvae, etc., counting of growth rings on otoliths) as applied by Fitzsimons et al (1990), Radke and Kinzie (1996), Lindstrom (1999), Gillanders (2005, Shen and Tzeng (2008), Tsunagawa and Arai (2008), Hobbs et al (2010), Sponagle (2010) among others. Such information seems essential to determine life cycles of these fishes and to make ironclad cases for the appropriate management of fresh and brackish waters occupied by diadromous/ amphidromous species.…”

Movement patterns and dispersal potential of Pecos bluntnose shiner (Notropis simus pecosensis) revealed using otolith microchemistry

“…Otoliths were then rinsed again with ultrapure water, placed in new 1.5 mL vials, and al- lowed to dry under a class 100 laminar-flow hood. After 48 h dry time, otoliths were mounted sulcus side up, affixed to a microscope slide with Crystalbond (Crystalbond 509, Ted Pella Inc., Redding, California), and sanded using a MTI Corporation UNIPOL 1210 grinding-polishing machine (1200 grit sand paper wetted with ultrapure water) to reveal the core to the edge (Thorrold et al 1998;Hobbs et al 2010).…”

Classification of hatchery and wild fish using natural geochemical signatures in otoliths, fin rays, and scales of an endangered catostomid

“…Most chemical analyses in fish utilize otoliths, primarily because Sr readily substitutes for Ca in their calcium carbonate (CaCO 3 ) matrix (Campana 1999). The incorporation of 87 Sr/ 86 Sr from a fish's surrounding water into their otoliths provides a permanent record of fish origins and movements (provenance) throughout an individual's lifetime (Walther and Thorrold 2006;Barnett-Johnson et al 2010;Hobbs et al 2010), without fractionation by abiotic or biotic processes . In this paper, we used signatures in otoliths to assess the likelihood of natural reproduction of JS in Utah Lake.…”