James A. Hobbs

Using Trace Elements in Pectoral Fin Rays to Assess Life History Movements in Sturgeon: Estimating Age at Initial Seawater Entry in Klamath River Green Sturgeon

Abstract To investigate the timing of the initial entry of green sturgeon Acipenser medirostris into seawater, we examined the ratios of strontium and barium to calcium in pectoral fin rays via laser ablation-inductively coupled plasma-mass spectrometry. In a reference group of six hatchery fish that was reared 1-2 years in freshwater and 1-3 years in seawater, we found a significant increase in the Sr:Ca ratio, a decrease in the Ba:Ca ratio, and an increase in the Sr:Ba ratio in calcified growth zones during the transition from freshwater to seawater. In 10 wild adults captured in the Klamath River, California, combined evaluation of the Sr:Ca and Ba:Ca ratios provided a clearer understanding of fish movements than the Sr:Ba ratio, probably because wild fish have a more complex life history. The Ba:Ca ratio dropped significantly between growth zones 1 and 2 (ages 0.5-1.5), indicating a transition into saline waters, such as the Klamath River estuary. The Sr:Ca ratio increased slightly in the same locatio...

Otolith Microchemistry Provides Information Complementary to Microsatellite DNA for a Migratory Fish

Abstract We investigated the ability of otolith microchemistry to discriminate natal habitats of the splittail Pogonichthys macrolepidotus, a migratory cyprinid endemic to the San Francisco Estuary, California. Splittails are broadly distributed in the brackish and freshwater portions of the lower estuary and make long-distance upstream migrations during winter to rivers and floodplains for spawning. We found that the ratios of Sr: Ca and 87Sr: 86Sr in the otoliths (ascertained by laser ablation inductively coupled mass spectrometry) of age-0 fish collected from natal habitats significantly varied among four primary spawning rivers. Based on these two constituents, quadratic discriminant function analysis correctly classified 71% of the fish to their natal rivers. Recent work with microsatellite DNA indicates that splittails from these same rivers represent two genetically distinct populations. Thus, integrating data obtained from otolith microchemistry and microsatellite DNA can provide complementary inf...

Retrospective determination of natal habitats for an estuarine fish with otolith strontium isotope ratios

We investigated the ability of strontium isotope ratios ( 87 Sr/ 86 Sr) in otolith cores to record the natal habitats of juvenile delta smelt Hypomesus transpacificus from the San Francisco Estuary, USA. Young delta smelt (<60 days old) were collected during the California Department of Fish and Game 20-mm Survey in May and June of 1999 at several potential natal areas: Napa River, Suisun Marsh, West Delta, North Delta, Central Delta, South Delta and East Delta. The core region of sagittal otoliths was assayed with laser ablation-multicollector inductively coupled plasma mass spectroscopy. The laser ablation technique provided precise estimates of 87 Sr : 86 Sr ratios with relative standard deviation of 0.003% (one sigma). Isotope ratios ranged from 0.7065 to 0.708 and were different among natal habitats. However, natal habitats within the delta region were not discernable among each other, and reflect the mixing of the two major rivers, Sacramento River and San Joaquin River within the delta. We will therefore be able to determine natal habitats for delta smelt by assaying the core region of the otoliths. The application of strontium isotope ratios ( 87 Sr/ 86 Sr) in fish otoliths will greatly improve conservation efforts for this protected species.

From ‘Omics to Otoliths: Responses of an Estuarine Fish to Endocrine Disrupting Compounds across Biological Scales

Endocrine disrupting chemicals (EDCs) cause physiological abnormalities and population decline in fishes. However, few studies have linked environmental EDC exposures with responses at multiple tiers of the biological hierarchy, including population-level effects. To this end, we undertook a four-tiered investigation in the impacted San Francisco Bay estuary with the Mississippi silverside (Menidia audens), a small pelagic fish. This approach demonstrated links between different EDC sources and fish responses at different levels of biological organization. First we determined that water from a study site primarily impacted by ranch run-off had only estrogenic activity in vitro, while water sampled from a site receiving a combination of urban, limited ranch run-off, and treated wastewater effluent had both estrogenic and androgenic activity. Secondly, at the molecular level we found that fish had higher mRNA levels for estrogen-responsive genes at the site where only estrogenic activity was detected but relatively lower expression levels where both estrogenic and androgenic EDCs were detected. Thirdly, at the organism level, males at the site exposed to both estrogens and androgens had significantly lower mean gonadal somatic indices, significantly higher incidence of severe testicular necrosis and altered somatic growth relative to the site where only estrogens were detected. Finally, at the population level, the sex ratio was significantly skewed towards males at the site with measured androgenic and estrogenic activity. Our results suggest that mixtures of androgenic and estrogenic EDCs have antagonistic and potentially additive effects depending on the biological scale being assessed, and that mixtures containing androgens and estrogens may produce unexpected effects. In summary, evaluating EDC response at multiple tiers is necessary to determine the source of disruption (lowest scale, i.e. cell line) and what the ecological impact will be (largest scale, i.e. sex ratio).

Classification of Larval and Adult Delta Smelt to Nursery Areas by Use of Trace Elemental Fingerprinting

Abstract Different environmental conditions among habitats may generate unique elemental patterns within fish otoliths that can be used to trace the life history as well as the potential natal origin of migratory species. We investigated the use of trace elements in otoliths as natural tags for determining the natal origins of larval and adult delta smelt Hypomesus transpacificus within a single estuary. Larval fish were collected at potential natal sites within the San Francisco Bay Estuary—the North, Central, South, and West Delta areas, Suisun Bay, and Napa River—during May–June 1999; adults were collected in November 1999 throughout Suisun Bay. Using laser ablation inductively coupled plasma mass spectrometry, we assayed trace elements from core (natal) regions of the otolith (Sr:Ca, Mg:Ca, and Ba:Ca ratios). Linear discriminant function analysis (LDFA) was 90.9–100% successful at classifying larval fish to their natal habitats (Napa River, Sacramento River, and Delta). Adults of unknown natal origin ...

Life History Diversity in Klamath River Steelhead

AbstractOncorhynchus mykiss exhibits a vast array of life histories, which increases its likelihood of persistence by spreading risk of extirpation among different pathways. The Klamath River basin (California–Oregon) provides a particularly interesting backdrop for the study of life history diversity in O. mykiss, in part because the river is slated for a historic and potentially influential dam removal and habitat recolonization project. We used scale and otolith strontium isotope (87Sr/86Sr) analyses to characterize life history diversity in wild O. mykiss from the lower Klamath River basin. We also determined maternal origin (anadromous or nonanadromous) and migratory history (anadromous or nonanadromous) of O. mykiss and compared length and fecundity at age between anadromous (steelhead) and nonanadromous (Rainbow Trout) phenotypes of O. mykiss. We identified a total of 38 life history categories at maturity, which differed in duration of freshwater and ocean rearing, age at maturation, and incidence...

Contaminant and food limitation stress in an endangered estuarine fish.

The abundance of Delta Smelt (Hypomesus transpacificus), a fish species endemic to the upper San Francisco Estuary (SFE), is declining. Several causes for the population decline have been proposed, including food limitation and contaminant effects. Here, using juvenile Delta Smelt collected from throughout their range, we measured a suite of indices across three levels of biological organization (cellular, organ, individual) that reflect fish condition at temporal scales ranging from hours to weeks. Using these indices, the relative conditions of fish collected from five regions in the SFE were compared: Cache Slough, Sacramento River Deep Water Ship Channel, Confluence, Suisun Bay and Suisun Marsh. Fish sampled from Suisun Bay and, to a lesser extent the Confluence, exhibited relatively poor short-term nutritional and growth indices and morphometric condition, while fish from the freshwater regions of the estuary, and Cache Slough in particular, exhibited the most apparent histopathological signs of contaminant exposure. In contrast, fish from the Suisun Marsh region exhibited higher short-term nutrition and growth indices, and better morphometric and histopathological condition. For instance, fish collected from Suisun Marsh had a mean stomach fullness, expressed as a percentage of fish weight, that was 3.4-fold higher than fish collected from Suisun Bay, while also exhibiting an incidence of histopathological lesions that was 11-fold lower than fish collected from Cache Slough. Thus, our findings support the hypothesis that multiple stressors, including food limitation and contaminants, are contributing to the decline of Delta Smelt, and that these stressors influence Delta Smelt heterogeneously across space.

Living in a Dynamic Environment: Variability in Life History Traits of Age-0 Splittail in Tributaries of San Francisco Bay

Splittail Pogonichthys macrolepidotus is a relatively large cyprinid endemic to the San Francisco Estuary watershed. During late winter and early spring, splittails migrate from the estuary to upstream rivers and floodplains for spawning. During 2002 and 2003, we examined the diet composition, muscle stable isotope signatures (d 13 C and d 15 N), and growth rates of age-0 splittails in the four primary rivers used for spawning. Overall, we found substantial variability in all three traits in spatial and temporal comparisons. Age-0 splittails consumed a variety of prey taxa, consisting almost exclusively of aquatic invertebrates, larval stages of chironomids or copepods generally being the most common. We found that the d 15 N and d 13 C signatures of age-0 splittails significantly varied spatially and temporally (d 15 N range ¼ 6.1- 19.6%; d 13 C range ¼� 36.3 to � 17.5%). Environmental conditions, namely flow and how it manipulates habitat connectivity, appeared to affect d 13 C. Age-0 splittails exhibited substantial variability in growth rate both spatially and temporally. However, this variability was not associated with diet composition or stable isotope signatures, suggesting that food availability and physical habitat conditions were important factors affecting growth rates during our study.

Validation of otolith growth rate analysis using cadmium‐exposed larval topsmelt (Atherinops affinis)

We applied otolith growth rate analysis to an investigation of cadmium (Cd)-exposed larval topsmelt (Atherinops affinis) to determine if growth rate was a more sensitive measure than somatic growth (body wt or length). Topsmelt otoliths, calcareous concretions in the fish inner ear, formed daily increments, and otolith growth was proportional to somatic growth. Nine-day posthatch larval topsmelt were exposed to Cd (0-100 ppb) in seawater for 14 d and fed low or high ration levels in separate experiments. Whereas Cd impaired topsmelt growth and growth rates, the extent of growth reduction was dependent on the ration level. At high ration levels, otolith and somatic growth rates of fish exposed to Cd (50 and 100 ppb) were significantly reduced; however, no differences in final mean weight and only marginal differences in final mean length of Cd-exposed topsmelt were observed. At low ration levels, we detected reductions in both somatic growth as well as otolith and somatic growth rates of topsmelt exposed to Cd (50 and 100 ppb). Otolith growth rate analysis was more sensitive than growth measurements of Cd-exposed topsmelt, because it allowed the detection of small differences in growth rates even when differences in somatic growth were not observed.

Validating Fin Ray Microchemistry as a Tool to Reconstruct the Migratory History of White Sturgeon

AbstractThe objective of this study was to validate the use of fin ray strontium isotope ratios (87Sr:86Sr) via laser ablation (LA) to resolve fine-scale movement patterns in sturgeons (Acipenseridae) during freshwater rearing in early life stages. We conducted a laboratory experiment in which juvenile White Sturgeon Acipenser transmontanus were exposed to two water sources exhibiting distinctive 87Sr:86Sr isotope values (American River and Putah Creek, California) over weekly time periods to understand how water exposure histories are archived in pectoral fin rays. Using LA multicollector inductively coupled plasma mass spectrometry with a laser diameter of 65 µm, we detected distinct shifts in fin ray 87Sr:86Sr values to match a water source in fish that were exposed for 2, 4, 6, and 12 weeks. Fin ray 87Sr:86Sr values matched the new water source after 21.7 d (SD = 7.8; range = 11–36 d) of exposure. The lower limit of this estimate was constrained by the rate of fin ray growth as well as the LA spot siz...