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While it is common knowledge that Red Drum (Sciaenops ocellatus) inhabit oligohaline waters (salinity . Growth consequences of oligohaline exposure and the relationship of oligohaline residency with river discharge were also investigated. Oligohaline exposure varied most during years 2 and 3 of life. During this time, 22% (n = 26/120 individuals) of Red Drum were oligohaline residents (≥ 90% of these years spent in oligohaline salinities), 34% (n = 41) were meso-polyhaline residents (< 10% of years 2 and 3 spent in oligohaline waters), and 44% (n = 53) spent time in both oligohaline and meso-polyhaline salinities. Trends in oligohaline residency match putative Red Drum life history. Oligohaline residents were present during years 1–6 of life; however, oligohaline residency peaked during the second year of life (n = 37, 31%) and by year 7 no oligohaline residents remained. Growth of oligohaline resident Red Drum during years 2–3 of life was lower than non-resident fish. However, long-term growth consequences of oligohaline residency were not apparent. The proportion of oligohaline residents during years 2 or 3 of life was positively related to river discharge. This divergence in salinity residency by juvenile Red Drum demonstrates that life history diversity was present in this population and that oligohaline waters provided important nursery habitat for fish that successfully recruited to the adult population.

To use elements as salinity proxies, relationships of elemental concentrations with salinity must be known and vary from freshwater to marine endmembers. To extend these proxies to biogenic carbonates, elements must incorporate into carbonate matrices proportional to environmental concentrations. Therefore, this study quantified calcium (Ca), magnesium (Mg), strontium (Sr), barium (Ba), and manganese (Mn) in Mobile Bay, Alabama from freshwater to marine endmembers. Two smaller drainages (Fowl River and Dog River) were quantified to determine if all freshwater elemental concentrations were consistent. The ratio of elements (Mg, Sr, Ba, Mn) to Ca were also measured in water and Red Drum otolith edges across the salinity gradient. Water Ca, Sr, and Mg had positive relationships with salinity, but Ca and Sr were lower in Fowl River freshwater. Barium exhibited a mid-salinity peak and decreased with further salinity increases. More Ba and Mn were present during low river discharge; however, Mn did not vary with salinity. In both water and otoliths, Sr:Ca increased and Ba:Ca decreased non-linearly with salinity increases, Mn:Ca exhibited no relationship with salinity, and Mg:Ca increased non-linearly in water. These results demonstrate that Sr:Ca and Ba:Ca may be used as salinity proxies within the Mobile Bay estuary and likely other estuaries in the region. However, given non-linearity of element:Ca salinity relationships, variable concentrations among species and estuaries from other studies, and variation in elemental ratios between drainages and flow regimes, species-specific element salinity relationships should be known in the estuary of interest prior to utilizing elemental salinity proxies.

Strontium (Sr), barium (Ba), and their ratios to calcium (Ca) may be used as indirect proxies of salinity in otoliths, given that generally Sr:Ca is positively and Ba:Ca is negatively related to salinity. However, these relationships are non-linear, dependent on water chemistry, and vary among species. To determine if salinity reconstructions in northern Gulf of Mexico estuaries (nGOM) are possible for Red Drum (Sciaenops ocellatus) and Gulf Killifish (Fundulus grandis), and if ratios were similar between species, the relationships of Sr:Ca and Ba:Ca with salinity in water and otoliths were examined. Fishes were held at low (

The Gulf of Mexico greater amberjack (Seriola dumerili) stock has been designated as “overfished” by the National Marine Fisheries Service and is currently under a rebuilding plan. Its fishery in the Gulf of Mexico is dominated by recreational landings, where 75% of the total recreational catch are regulatory discards; as such, uncertainty regarding the post-release mortality rate represents a data deficiency in the stock assessment. To determine post-release mortality, a combination of acoustic and pop-up satellite archival transmitting (PSAT) tags were used to monitor the release fate and depth-use of greater amberjack. Thirty-six greater amberjack were tagged with acoustic transmitters at two sites in the northern GOM and monitored for up to 30 days. Sublegal-sized fish (n = 18) ranged from 591 to 740 mm FL (mean = 674.6 ± 40.6 SE) and legal-sized fish (n = 18) ranged from 768 to 1081 mm FL (mean = 871.3 ± 77.5 SE). All 36 fish were detected in the array after release. Based on examination of time series depth profiles, post-release mortality was estimated to be 18.8% ± 6.9%, strikingly similar to the estimate used in the most recent stock assessment. Stepwise model selection using AIC identified the Cox proportional hazards model containing only release condition as the most parsimonious model to predict post-release mortality. Despite differences in depth between the two tagging sites, fish showed slight, but consistent, size-specific segregation patterns. Our findingsadd to a body of literature demonstrating that biotelemetry is an effective tool in catch and release mortality studies, and provide best practices that can aid in the recovery of this stock.

Many applications of otolith chemistry use the ratios of strontium (Sr) and barium (Ba) to calcium (Ca) as indicators of salinity exposure, because typically, as salinity increases, Sr concentration increases and Ba concentration decreases. However, these relationships are nonlinear, can be confounded by temperature, and investigations of salinity and temperature effects on otolith chemistry produce varied results. To determine the relationships of temperature and salinity on Sr:Ca and Ba:Ca in otoliths, we used free ranging Gulf Killifish (Fundulus grandis) in the northern Gulf of Mexico. This species is ideal because it is euryhaline and exhibits limited movements. Otolith edge Sr:Ca and Ba:Ca ratios were related to the previous 30-day mean salinity and temperature experienced by fish. The best model to describe otolith Sr:Ca was one that included a positive asymptotic relationship for both salinity and temperature. However, the salinity asymptotic maximum was reached at 10 psu and changes in otolith Sr:Ca above 10 psu were indicative of temperature changes. Otolith Ba:Ca exhibited an exponential decreasing relationship with salinity, and an exponential increasing relationship with temperature, and these two models combined best explained otolith Ba:Ca. Above 10 psu, the modeled Ba:Ca ratio continued to decrease demonstrating that this ratio may be indicative of salinity changes beyond this value. Therefore, using both Sr:Ca and Ba:Ca could be beneficial in reconstructing fish environmental histories. Temperature effects on otolith element ratios could confound past salinity reconstructions as well and must be a result of endogenous processes, given that no relationship between temperature and water chemistry existed.

A Correction to this paper has been published: 10.1007/s10641-021-01096-6