Experimental Investigation of Elemental Incorporation in the Otoliths of Larval and Juvenile Fish: Implications for Use as Environmental Recorders

Innovative techniques for discerning fish stocks, identifying nursery habitats, locating spawning sites, tracing larval transport pathways, and quantifying the degree of population connectivity are required to meet the goals of sustainable management of marine capture fisheries. One of the most promising techniques is the use of elemental signatures in fish otoliths (ear stones), which record valuable life history data and serve as the link between fish and their environment. To validate the assumption that otolith elemental composition is a function of water elemental concentrations, and to address the possible effects of external variables such as temperature and salinity, the composition of the ambient water must be known. Thus, three laboratory experiments were conducted using late larval to early juvenile stage spot (Leiostomus xanthurus) and gray snapper (Lutjanus griseus) to quantify the association between fish otoliths and water elemental composition, test the effects of water temperature and salinity on otolith element incorporation, and assess similarities or differences between species. Strontium/calcium (Sr/Ca) ratios in both L. xanthurus and L. griseus were significantly influenced by temperature. Sr/Ca partition coefficients (DSr) were affected by temperature and salinity in L. xanthurus. Magnesium/calcium (Mg/Ca) ratios and DMg were influenced by otolith precipitation rates in L. xanthurus. DMn for L. xanthurus were significantly affected by both temperature and salinity. Although only barium/calcium (Ba/Ca) ratios in L. griseus otoliths were significantly affected by salinity, DBa in both L. griseus and L. xanthurus were affected by salinity, These results are independent of ontogenetic and diet effects, and represent one of the first attempts at validating minor and trace element incorporation in laboratory reared fish. This work also presents the first comparison of otolith element incorporation between fish species. The results prove that otolith element incorporation is not solely a function of water elemental composition because it is affected by both temperature and salinity and those effects varied uniquely among the elements investigated. This comparison between fish species draws attention to the necessity of validation experiments to interpret species-specific elemental signatures in otoliths

Effect of type of otolith and preparation technique on age estimation of larval and juvenile spot (Leiostomus xanthurus)

Otoliths of larval and juvenile fish provide a record of age, size, growth, and development (Campana and Neilson, 1985; Thorrold and Hare, 2002). However, determining the time of first increment formation in otoliths (Campana, 2001) and assessing the accuracy (deviation from real age) and precision (repeatability of increment counts from the same otolith) of increment counts are prerequisites for using otoliths to study the life history of fish (Campana and Moksness, 1991). For most fish species, first increment deposition occurs either at hatching, a day after hatching, or after first feeding and yolksac absorption (Jones, 1986; Thorrold and Hare, 2002). Increment deposition before hatching also occurs (Barkmann and Beck, 1976; Radtke and Dean, 1982). If first increment deposition does not occur at hatching, the standard procedure is to add a predetermined number to increment counts to estimate fish age (Campana and Neilson, 1985)

Larval abundance of summer flounder (Paralichthys dentatus) as a measure of recruitment and stock status

Summer flounder (Paralichthys dentatus) is one of the most economically and ecologically important estuarine-dependent species in the northeastern United States. The status of the population is currently a topic of controversy. Our goal was to assess the potential of using larval abundance at ingress as another fishery independent measure of spawning stock biomass or recruitment. Weekly long-term ichthyoplankton time series were analyzed from Little Egg Inlet, New Jersey (1989–2006) and Beaufort Inlet, North Carolina (1986–2004). Mean size-at-ingress and stage were similar between sites, whereas timing of ingress and abundance at ingress were not similar. Ingress primarily occurred during the fall at Little Egg Inlet and the winter at Beaufort Inlet. These findings agree with those from earlier studies in which at least two stocks (one north and one south of Cape Hatteras) were identified with different spawning periods. Larval abundance at Little Egg Inlet has increased since the late 1990s and most individuals now enter the estuary earlier during the season of ingress. Abundance at Little Egg Inlet was correlated with an increase in spawning stock biomass, presumably because spawning by larger, more abundant fish during the late 1990s and early 2000s provided increased larval supply, at least in some years. Larval abundance at ingress at Beaufort Inlet was not correlated with spawning stock biomass or with larval abundance at ingress at Little Egg Inlet, further supporting the hypothesis of at least two stocks. Larval abundance at Little Egg Inlet could be used as a fishery-independent index of spawning stock size north of Cape Hatteras in future stock assessments. Larval occurrence at Beaufort Inlet may provide information on the abundance of the stock south of Cape Hatteras, but additional stock assessment work is required

Relationships between Larval and Juvenile Abundance of Winter-Spawned Fishes in North Carolina, USA

We analyzed the relationships between the larval and juvenile abundances of selected estuarine-dependent fishes that spawn during the winter in continental shelf waters of the U.S. Atlantic coast. Six species were included in the analysis based on their ecological and economic importance and relative abundance in available surveys: spot Leiostomus xanthurus, pinfish Lagodon rhomboides, southern flounder Paralichthys lethostigma, summer flounder Paralichthys dentatus, Atlantic croaker Micropogonias undulatus, and Atlantic menhaden Brevoortia tyrannus. Cross-correlation analysis was used to examine the relationships between the larval and juvenile abundances within species. Tests of synchrony across species were used to find similarities in recruitment dynamics for species with similar winter shelf-spawning life-history strategies. Positive correlations were found between the larval and juvenile abundances for three of the six selected species (spot, pinfish, and southern flounder). These three species have similar geographic ranges that primarily lie south of Cape Hatteras. There were no significant correlations between the larval and juvenile abundances for the other three species (summer flounder, Atlantic croaker, and Atlantic menhaden); we suggest several factors that could account for the lack of a relationship. Synchrony was found among the three southern species within both the larval and juvenile abundance time series. These results provide support for using larval ingress measures as indices of abundance for these and other species with similar geographic ranges and winter shelf-spawning life-history strategies

Temperature and salinity effects on magnesium, manganese, and barium incorporation in otoliths of larval and early juvenile spot Leiostomus xanthurus

Author Posting. © Inter-Research, Inter-Research. This article is posted here by permission of Inter-Research for personal use, not for redistribution. The definitive version was published in Marine Ecology Progress Series 293 (2005): 223-232, doi:10.3354/meps293223.The use of otolith chemistry to delineate fish populations and trace migration pathways is premised on a significant correlation between the elemental composition of otoliths and physicochemical properties of the ambient environment. However, few experiments have been rigorously designed to address the effects of temperature and salinity on the elemental composition of otoliths. We examined the effects of temperature and salinity on the incorporation of magnesium (Mg), manganese (Mn), and barium (Ba) in the otoliths of larval and early juvenile spot Leiostomus xanthurus by rearing fish in the laboratory under controlled environmental conditions. L. xanthurus are an estuarine dependent species that traverse varying temperature and salinity regimes throughout their life histories. It is important, therefore, to understand the influence of physicochemical properties of different water masses before attempting to reconstruct important life history transitions based on variations in otolith chemistry. Both [Mg/Ca]otolith and the Mg partition coefficient, DMg, were not significantly affected by either temperature or salinity, but were correlated with otolith precipitation and somatic growth rates. Temperature and salinity had significant interaction effects on DMn, but not on [Mn/Ca]otolith. Finally, DBa was influenced by salinity but not temperature. These results highlight the complex nature of elemental deposition in otoliths, and suggest that both environmental and physiological effects likely influence elemental ratios in fish otoliths.This research was supported by grants from the National Science Foundation to S.R.T. (OCE- 0134998), a grant in aid to G.B.M. from the International Women’s Fishing Association, and a PEO International Women’s Organization Scholar Award to G.B.M

Temperature and salinity effects on strontium incorporation in otoliths of larval spot (Leiostomus xanthurus)

Author Posting. © National Research Council Canada, 2004. This article is posted here by permission of National Research Council Canada for personal use, not for redistribution. The definitive version was published in Canadian Journal of Fisheries and Aquatic Sciences 61 (2004): 34-42, doi:10.1139/F03-143.Temperature dependence of strontium/calcium (Sr/Ca) ratios in foraminiferal calcite and coral aragonite is well established; however, factors controlling Sr/Ca ratios in fish otoliths remain obscure. To assess temperature dependence of Sr/Ca in marine fish otoliths, we reared spot (Leiostomus xanthurus) larvae under controlled temperature (17–26 °C) and salinity (15‰ and 25‰). We found a significant linear relationship between temperature and Sr/Ca ratios, with a sensitivity of approximately 5%·°C–1. Otolith Sr/Ca values were also significantly higher at a salinity of 25‰ vs. 15‰, after accounting for differences in dissolved Sr/Ca ratios in the ambient water, with a sensitivity of approximately 1%/salinity (‰). These observations complicate the use of Sr/Ca ratios to determine temperature histories of spot larvae, because accurate temperature reconstructions are possible only with a priori knowledge of both ambient salinity and dissolved Sr/Ca ratios. Fully marine species residing in oceanic waters will not experience significant salinity variations; therefore, otolith Sr/Ca ratios may be useful recorders of temperature exposure. Otolith Sr/Ca thermometry in coastal fish species that make regular excursions into estuarine waters will be more problematic. Multiple geochemical tracers, including oxygen stable isotopes and other trace elements, may be necessary to accurately reconstruct temperature and salinity histories in these species.This research was supported by grants from the National Science Foundation to S.R.T. (OCE-0134998) and to S.R.T. and C.M.J. (OCE-9876565), a grant in aid to G.B.M. from the International Women’s Fishing Association, and a PEO International Women’s Organization Scholar Award to G.B.M