Steven E. Campana

Strontium and barium uptake in aragonitic otoliths of marine fish

Abstract Minor and trace element analyses of fish otoliths (ear stones) may provide a high-resolution reconstruction of temperature histories and trace element compositions of aquatic systems where other environmental proxies are not available. However, before otoliths can be used to reconstruct water chemistry, it is essential to validate the assumption that trace metals in otoliths are deposited in proportion to dissolved concentrations in the ambient environment. We show, using a marine fish (Leiostomus xanthurus) reared in the laboratory under controlled experimental conditions, that otolith Sr/Ca and Ba/Ca ratios are deposited in proportion to their respective ratios in ambient waters. Temperature significantly affected Sr incorporation but did not affect Ba incorporation in otoliths. Sr/Ca partition coefficients (DSr) were 0.182 and 0.205 at 20°C and 25°C, respectively. The partition coefficients for Ba/Ca were 0.055 at 20°C and 0.062 at 25°C. A nonlinearity in the relationship between DBa and ambient Ba concentrations suggested that extrapolation beyond the Ba levels used in the experiment was not justified. On the basis of our results, it should be possible to reconstruct Sr/Ca and Ba/Ca levels in environments inhabited by fish based on otolith chemistry. Furthermore, Sr/Ca thermometry may also be possible using fish otoliths, but validation of the temperature dependence of Sr/Ca in otoliths will be required. We believe otoliths represent an excellent, and as yet underused, record of the physicochemical properties of both modern and ancient aquatic environments.

Graphical and Statistical Methods for Determining the Consistency of Age Determinations

Abstract Many laboratories rely on periodic rereading of reference collections of scales or otoliths to ensure that their age readers remain consistent in their age interpretations, both through time and with other age readers. Measures of both systematic difference (bias) and precision are required for this purpose, because measures of bias are not suitable as measures of precision, and vice versa. Using data from an age comparison study of haddock Melanogrammus aeglefinus for demonstration purposes, we evaluated a variety of graphical and statistical approaches for making paired age comparisons from the standpoint of both detecting age differences and assessing precision. Parametric and nonparametric matched-pair tests, regression analysis, analysis of variance, and age difference plots were all capable of detecting systematic over- or underaging. However, only the age bias plot was sensitive to both linear and nonlinear biases. The coefficient of variation (CV = SD/mean) was a robust measure of precisi...

Otolith elemental fingerprints as biological tracers of fish stocks

Specific trace elements incorporated into the growing surface of the fish otolith reflect the physical and chemical characteristics of the ambient water, although not necessarily in a simplistic manner. Since fish which spend at least part of their lives in different water masses often produce otoliths of different elemental composition, the otolith elemental composition (‘elemental fingerprint’) can serve as an environmentally induced tag of groups of fish. On the basis of isotope dilution ICPMS (ID-ICPMS) assays of nearly 2500 dissolved adult cod (Gadus morhua) otoliths, it has become clear that cod otolith elemental fingerprints based on the elements Li, Mg, Mn, Sr and Ba are physically stable, reproducible and consistent between left and right otoliths. Highly significant differences existed among the fingerprints of all of the spawning aggregations, resulting in a characteristic marker for each aggregation. Long-term stability (4–13 years) of the fingerprints for a given spawning group was not evident, indicating that the fingerprint was not a proxy for genetic identity. However, the fingerprint was very stable over the short-term (up to 1 year), suggesting that it could serve as a seasonally stable biological tracer, or natural tag, of pre-defined groups of fish, even during situations of extensive stock mixing. As an illustration of the tracer approach, a maximum likelihood-based stock mixture analysis was applied to feeding (summer) and over-wintering stock distributions, using the fingerprints of the spring spawning aggregations as known-stock reference samples. The results of the summer stock mixture analyses suggested that the mixture analysis was accurate within 1%, while the stock mixture analysis of the over-wintering schools produced stock-specific distributions which would have been difficult to obtain using alternative approaches. While the use of elemental fingerprints as natural tags is not suited to all stock mixing situations, suitability can probably be determined beforehand on the basis of existing environmental and biological information.

Global patterns in marine dispersal estimates: the influence of geography, taxonomic category and life history

We examine estimates of dispersal in a broad range of marine species through an analysis of published values, and evaluate how well these values represent global patterns through a comparison with correlates of dispersal. Our analysis indicates a historical focus in dispersal studies on low-dispersal/low-latitude species, and we hypothesize that these studies are not generally applicable and representative of global patterns. Large-scale patterns in dispersal were examined using a database of correlates of dispersal such as planktonic larval duration (PLD, 318 species) and genetic differentiation (FST, 246 species). We observed significant differences in FST (p<0.001) and PLD (p<0.001) between taxonomic groups (e.g. fishes, cnidarians, etc.). Within marine fishes (more than 50% of datasets), the prevalence of demersal eggs was negatively associated with PLD (R2=0.80, p<0.001) and positively associated with genetic structure (R2=0.74, p<0.001). Furthermore, dispersal within marine fishes (i.e. PLD and FST) increased with latitude, adult body size and water depth. Of these variables, multiple regression identified latitude and body size as persistent predictors across taxonomic levels. These global patterns of dispersal represent a first step towards understanding and predicting species-level and regional differences in dispersal, and will be improved as more comprehensive data become available.

Regulation of calcium and strontium deposition on the otoliths of juvenile tilapia, Oreochromis niloticus

Abstract Radioisotopes of calcium and strontium were used to test for a relationship between the environmental concentrations of each element and their respective deposition rates on the otolith. On the basis of 45 Ca and 89 Sr assays, the rate of strontium deposition on the otolith was influenced by strontium concentrations in the water, while the rate of calcium deposition was affected neither by food nor water calcium concentrations. Thus, the deposition rate of strontium on the otolith at least partially reflects environmental availability, while that of calcium does not. Sources in the water contributed 75% of calcium and 88% of strontium to the sagittae of Nile tilapia, Oreochromis niloticus , with the remainder being provided by the diet.

Habitat Fingerprints for Lake Superior Coastal Wetlands Derived from Elemental Analysis of Yellow Perch Otoliths

Abstract Assessing the ecological importance of coastal habitats to Great Lakes ecosystems requires an understanding of the ecological linkages between coastal and offshore waters. Elemental analysis of fish otoliths has emerged as a powerful technique that can provide a natural tag for determining nursery area affiliation, population structure, and movement of individual fish. Since the elemental composition of fish otoliths reflects some of the environmental conditions under which a fish was reared, otolith chemistry can record differences in ambient water conditions specific to habitats used during a fishs life history. Although few studies have been conducted in freshwaters, trace element analysis of marine fish otoliths has proven useful in identifying the chemical signatures unique to particular spawning and nursery habitats. To examine the utility of this method in freshwater, sagittae were removed from 275 young-of-the-year yellow perch Perca flavescens captured from eight wetlands in western Lak...

Age under-estimation in New Zealand porbeagle sharks (Lamna nasus): is there an upper limit to ages that can be determined from shark vertebrae?

Annual deposition of growth bands in vertebrae has been validated for many shark species, and is now widely regarded as the norm. However, vertebrae are part of the sharks axial skeleton, and band deposition may stop in old sharks when somatic growth ceases. We aged vertebral sections from New Zealand porbeagle sharks (Lamna nasus) under reflected white light and using X-radiographs. Bomb radiocarbon assays supported vertebral age estimates up to ∼20 years, but not at older ages. The results suggest that older porbeagles were under-aged by as much as 50% from vertebral band counts, presumably because band width declined to a point where it became unresolvable. This has important implications for growth studies on other long-lived sharks. Estimated ages at sexual maturity were 8-11 years for males and 15-18 years for females, and longevity may be ∼65 years. New Zealand and North Atlantic porbeagles differ in these parameters, and in length at maturity and maximum length, suggesting genetic isolation of the two populations.

Calcium deposition and otolith check formation during periods of stress in coho salmon, Oncorhynchus kisutch

Abstract 1. 1. Periods of stress can disrupt daily growth increment formation on a fish otolith, producing a check (discontinuity). Calcium-45 was used to monitor calcium deposition on the sagittae of coho salmon, Oncorhynchus kisutch , during periods of check formation. 2. 2. 45 Ca deposition on the otolith continued for 12 hr after transfer from 45 Ca water. 3. 3. Stress applied during 45 Ca immersion reduced 45 Ca deposition. 4. 4. Stress applied immediately after transfer from 45 Ca water had no effect on 45 Ca deposition. 5. 5. Stress indirectly disrupted 45 Ca deposition on the otolith through a reduction in branchial uptake of calcium. 6. 6. Stress did not result in resorption of otolith calcium.

Estimating contemporary early life-history dispersal in an estuarine fish: integrating molecular and otolith elemental approaches

Dispersal during the early life history of the anadromous rainbow smelt, Osmerus mordax, was examined using assignment testing and mixture analysis of multilocus genotypes and otolith elemental composition. Six spawning areas and associated estuarine nurseries were sampled throughout southeastern Newfoundland. Samples of adults and juveniles isolated by > 25 km displayed moderate genetic differentiation (FST ~ 0.05), whereas nearby (< 25 km) spawning and nursery samples displayed low differentiation (FST < 0.01). Self‐assignment and mixture analysis of adult spawning samples supported the hypothesis of independence of isolated spawning locations (> 80% self‐assignment) with nearby runs self‐assigning at rates between 50 % and 70%. Assignment and mixture analysis of juveniles using adult baselines indicated high local recruitment at several locations (70–90%). Nearby (< 25 km) estuaries at the head of St Marys Bay showed mixtures of individuals (i.e. 20–40% assignment to adjacent spawning location). Laser ablation inductively coupled mass spectrometry transects across otoliths of spawning adults of unknown dispersal history were used to estimate dispersal among estuaries across the first year of life. Single‐element trends and multivariate discriminant function analysis (Sr:Ca and Ba:Ca) classified the majority of samples as estuarine suggesting limited movement between estuaries (< 0.5%). The mixtures of juveniles evident in the genetic data at nearby sites and a lack of evidence of straying in the otolith data support a hypothesis of selective mortality of immigrants. If indeed selective mortality of immigrants reduces the survivorship of dispersers, estimates of dispersal in marine environments that neglect survival may significantly overestimate gene flow.

Effects of Hydropeaking on Nearshore Habitat Use and Growth of Age-0 Rainbow Trout in a Large Regulated River

Abstract We evaluated the effects of hourly variation in flow caused by power load following at Glen Canyon Dam (“hydropeaking”) on the nearshore habitat use and growth of age-0 rainbow trout Oncorhynchus mykiss downstream from the dam in the Colorado River, Arizona. Reduction in the extent of hydropeaking is a common element of restoration efforts in regulated rivers, but empirical support for such a practice is limited. Our assessment was based on a comparison of abundance in shoreline areas determined by electrofishing at different flows as well as analysis of otolith microstructure. The catch rates of age-0 rainbow trout in nearshore areas were at least two- to fourfold higher at the daily minimum flow than at the daily maximum, indicating that most age-0 rainbow trout do not maintain their position within immediate shoreline areas when flows are high. A striping pattern, identified by the presence of atypical daily increments formed every 7 d, was evident in over 50% of the 259 otoliths examined in 2...