Radiocarbon From Nuclear Testing Applied to Age Validation of Black Drum, Pogonias cromis

Radiocarbon ((14)C) in the world\u27s oceans increased sharply between 1950 and 1970 as a result of the atmospheric testing of nuclear weapons. Through comparison with the (14)C time series reconstructed from atmospheric measurements and marine carbonates, Kalish, in 1993, used the (14)C concentration measured in fish otolith cores as a means of confirming the annulus-based age estimates for some South Pacific fish species. Here we report the pre-and postbomb (14)C chronology of North Atlantic adult black drum (Pogonias cronis), assumed to be between 15 and 42 yr of age on the basis of otolith annulus counts. According to accelerator mass spectrometry (AMS) assays, (14)C in otolith cores in creased sharply between 1958 and 1964, with a timing and magnitude which was very similar to that of the atmospheric bomb (14)C signal. The correspondence between the two (14)C chronologies indicates that the annulus-based age assignments were accurate on average to within 1-3 yr. Differences between the black drum Delta(14)C chronology and that of other marine carbonates in the North Atlantic are explained by the estuarine habitat of young-of-the-year black drum and by the fact that estuarine Delta(14)C values more closely reflect atmospheric values than surface ocean values. At present, there is no other age-validation technique that can confirm the absolute age of long-lived fish species with comparable levels of accuracy

Bomb Radiocarbon Age Validation for the Long-Lived, Unexploited Arctic Fish Species \u3ci\u3eCoregonus clupeaformis\u3c/i\u3e

The growth rates of freshwater fish in the Arctic would be expected to be very low, but some previous studies of lake whitefish (Coregonus clupeaformis) have reported relatively rapid growth and longevity estimates of less than 15 years. We used bomb radiocarbon chronologies to validate an ageing method based on otolith sections for lake whitefish in both an unexploited Arctic lake (MacAlpine Lake; longevity 50 years) and a lightly exploited temperate population (Lake Simcoe; longevity 49 years). Our results confirm previous suggestions that other ageing methods can seriously underestimate lake whitefish age after ~5–8 years. A Chapman–Robson estimate of instantaneous natural mortality rate (M) of 0.12 in the unfished Arctic lake was one-quarter of that measured in other Arctic lake whitefish populations, and one-third of that predicted by Pauly’s (1980) growth–temperature equation. The high estimates of M reported in other whitefish studies and by Pauly’s equation are almost certainly due to their being based on (incorrect) scale or surface otolith ages. Radiocarbon dating confirms that any attempt at predicting sustainable production for long-lived freshwater fishes like lake whitefish will need to be based on accurate ages derived from otolith sections

Response of Otolith Microchemistry to Environmental Variations Experienced by Larval and Juvenile Atlantic Croaker (Micropogonias Undulatus)

Minor and trace elements incorporated into otoliths during growth may permanently record environmental conditions experienced by fishes. To determine the validity of this approach, we used laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS) to assay sectioned otoliths from juvenile Atlantic croaker (Micropogonias undulatus) collected from each of three sites in the Neuse River, North Carolina, and the Elizabeth River, Virginia. Elemental concentrations at the center of the otoliths did not differ between locations, although both Mg : Ca and Ba : Ca were significantly higher at the edge of otoliths from the Neuse River than from the Elizabeth River. Three of the elements (Mg : Ca, Sr : Ca, and Ba : Ca) showed significant variation across otoliths. Sr : Ca, and to a lesser extent Mg : Ca, showed progressive decreases as the fish moved from offshore spawning sites to estuarine nursery areas. The opposite pattern was shown by Ba : Ca. We hypothesize that these patterns were related to the elemental concentrations within oceanic and estuarine water masses. Although both Sr : Ca and Ba : Ca seem to be useful tracers of offshore-inshore migration of estuarine-dependent species, the sensitivity of the technique to more subtle changes in water chemistry remains to be determined

Atlantic Bluefin Tuna (Thunnus thynnus) Diet in the Gulf of St. Lawrence and on the Eastern Scotian Shelf

The stomach contents of 68 Atlantic bluefin tuna (Thunnus thynnus) landed in Port Hood and Canso, Nova Scotia, in 2010, were analyzed to characterize the diet of bluefin tuna at the two locations. Of the sampled fish, 54 stomachs had contents. Pelagic schooling fish such as herring (Clupea harengus) and mackerel (Scomber scombrus) dominated the diets in both regions. However, a number of rare species, including demersal species, were also observed. Despite the difference in location and the significantly larger size of the Atlantic bluefin tuna landed in Port Hood, the diets of the Atlantic bluefin tuna landed at both sites were similar

A century of fish growth in relation to climate change, population dynamics and exploitation

Marine ecosystems, particularly in high‐latitude regions such as the Arctic, have been significantly affected by human activities and contributions to climate change. Evaluating how fish populations responded to past changes in their environment is helpful for evaluating their future patterns, but is often hindered by the lack of long‐term biological data available. Using otolith increments of Northeast Arctic cod (Gadus morhua) as a proxy for individual growth, we developed a century‐scale biochronology (1924–2014) based on the measurements of 3,894 fish, which revealed significant variations in cod growth over the last 91 years. We combined mixed‐effect modeling and path analysis to relate these growth variations to selected climate, population and fishing‐related factors. Cod growth was negatively related to cod population size and positively related to capelin population size, one of the most important prey items. This suggests that density‐dependent effects are the main source of growth variability due to competition for resources and cannibalism. Growth was also positively correlated with warming sea temperatures but negatively correlated with the Atlantic Multidecadal Oscillation, suggesting contrasting effects of climate warming at different spatial scales. Fishing pressure had a significant but weak negative direct impact on growth. Additionally, path analysis revealed that the selected growth factors were interrelated. Capelin biomass was positively related to sea temperature and negatively influenced by herring biomass, while cod biomass was mainly driven by fishing mortality. Together, these results give a better understanding of how multiple interacting factors have shaped cod growth throughout a century, both directly and indirectly.publishedVersio

Temperature exposure in cod driven by changes in abundance

Animals actively select the most suitable habitat in terms of fitness, much of which is mediated by temperature. We reconstructed population abundance, oxygen isotope and temperature chronologies for the Icelandic and the Northeast Arctic (NEA) cod (Gadus morhua) populations to determine if their temperature selectivity over the last 100 years was driven by rising water temperatures and (or) changes in abundance. Individual annual growth increments from immature and mature life history stages of cod collected in southern Iceland and the Lofoten area (Norway) were micromilled from adult otoliths and then assayed for stable oxygen isotopes (δ18Ootolith). Linear mixed effect models were used to identify and quantify the density-dependent temperature exposure of both cod populations. The results indicated that Icelandic cod migrated into warmer waters with increasing abundance (p < 0.05), whereas NEA cod moved into colder waters (p < 0.001). Our results suggest that thermal preferences and density-dependent effects can be used to forecast potential redistribution scenarios of fish as oceans warm.publishedVersio

Migration Pathways, Behavioural Thermoregulation and Overwintering Grounds of Blue Sharks in the Northwest Atlantic

The blue shark Prionace glauca is the most abundant large pelagic shark in the Atlantic Ocean. Although recaptures of tagged sharks have shown that the species is highly migratory, migration pathways towards the overwintering grounds remain poorly understood. We used archival satellite pop-up tags to track 23 blue sharks over a mean period of 88 days as they departed the coastal waters of North America in the autumn. Within 1–2 days of entering the Gulf Stream (median date of 21 Oct), all sharks initiated a striking diel vertical migration, taking them from a mean nighttime depth of 74 m to a mean depth of 412 m during the day as they appeared to pursue vertically migrating squid and fish prey. Although functionally blind at depth, calculations suggest that there would be a ∼2.5-fold thermoregulatory advantage to swimming and feeding in the markedly cooler deep waters, even if there was any reduced foraging success associated with the extreme depth. Noting that the Gulf Stream current speeds are reduced at depth, we used a detailed circulation model of the North Atlantic to examine the influence of the diving behaviour on the advection experienced by the sharks. However, there was no indication that the shark diving resulted in a significant modification of their net migratory pathway. The relative abundance of deep-diving sharks, swordfish, and sperm whales in the Gulf Stream and adjacent waters suggests that it may serve as a key winter feeding ground for large pelagic predators in the North Atlantic

The reproductive biology of the porbeage shark (Lamna nasus) in the western North Atlantic Ocean

Reproductive organs from 393 male and 382 female porbeagles (Lamna nasus), caught in the western North Atlantic Ocean, were examined to determine size at maturity and reproductive cycle. Males ranged in size from 86 to 246 cm fork length (FL) and females ranged from 94 to 288 cm FL. Maturity in males was best described by an inflection in the relationship of clasper length to fork length when combined with clasper calcification. Males matured between 162 and 185 cm FL and 50% were mature at 174 cm FL. In females, all reproductive organ measurements related to body length showed a strong inflection around the size of maturity. Females matured between 210 and 230 cm FL and 50% were mature at 218 cm FL. After a protracted fall mating period (September–November), females give birth to an average of 4.0 young in spring (April−June). As in other lamnids, young are nourished through oophagy. Evidence from this study indicated a one-year reproductive cycle and gestation period lasting 8–9 months

Potential sources of bias in the climate sensitivities of fish otolith biochronologies

Analysis of growth increments in the hard parts of animals (e.g., fish otoliths) can be used to assess how organisms respond to variability in environmental conditions. In this study, mixed-effects models were applied to otolith data simulated for two hypothetical fish populations with assumed biological parameters and known growth response to environmental variability. Our objective was to assess the sensitivity of environment–growth relationships derived from otolith biochronologies when challenged with a range of realistic ageing errors and sampling regimes. We found that the development of a robust biochronology and the precision of environmental effect estimates can be seriously hampered by insufficient sample size. Moreover, the introduction of even moderate ageing error into the data can cause substantial underestimation of environmental sources of growth variation. This underestimation diminished our capacity to correctly quantify the known environment–growth relationship and more generally will lead to overly conservative conclusions concerning the growth response to environmental change. Careful study design, reduction of ageing errors, and large sample sizes are critical prerequisites if robust inferences are to be made from biochronological data.publishedVersio

Trace Element Signatures in Otoliths Record Natal River of Juvenile American Shad (Alosa Sapidissima)

The elemental composition of fish otoliths may represent a permanent record of the environmental conditions an individual has experienced as trace elements, incorporated into the growing surface of the otolith, reflect the physical and chemical characteristics of the ambient water. We tested the utility of trace element signatures in otoliths as natural tags of the river of origin of juvenile American shad (Alosa sapidissima) collected from the Connecticut, Hudson and Delaware Rivers in August and October 1994. Four elements (K, Mn, Sr, and Ba) showed significant variability among sites within rivers in August, although only Mg showed a significant site effect by October. Four elements (Mg, Mn, St, and Ba) differed significantly among rivers in both months. Linear discriminant functions based on the trace element signatures classified fish to their natal river with ~90% accuracy in both August and October collections. The discriminant function generated from the August data was able to classify fish collected in October successfully with better than 80% accuracy. On the basis of our findings, the river of origin of adult fish could be accurately determined by quantifying the trace element composition of the juvenile portion of their otoliths