We investigated the ability of trace element and isotopic signatures in otoliths to record the nursery areas of juvenile (young-of-the-year) weakfish Cynoscion regalis from the east coast of the USA. Juvenile C. regalis were captured with otter trawls at multiple sites in Doboy Sound (Georgia), Panllico Sound (North Carolina), Chesapeake Bay (Virginia), Delaware Bay (Delaware) and Peconic Bay (New York), from July to September 1996. One sagittal otolith from each specimen was assayed for Mg/Ca, Mn/Ca, Sr/Ca and Ba/Ca ratios uslng inductively coupled plasma mass spectrometry (ICP-MS), while 6I3C and 6180 values from the other sagittal otohth in the pair were determined using lsotope ratio mass spectrometry (IR-MS). A multivanate analysis of variance determined that there were significant differences in trace element signatures among locations. Bootstrapped 95% confidence ellipses on canonical variates indicated that all 5 locations were significantly isolated in discriminant space. On the basis of these differences, linear &scrirninant function analysis (LDFA) and artificial neural network (ANN) models were used to classify inbvidual fish to their natal estuary with an overall error rate of 37 % for LDFA and 29.6% for ANN. Addtion of 6I3C and 6180 values to the LDFA and ANN models derived from the trace element data resulted in overall error around 10%. We d, therefore, be able to use chemical signatures from the juvenile portion of adult C, reyalis otoliths to accurately classify these fish to their natal estuary.

The distribution and intensity of hypoxia (low dissolved oxygen) in estuaries is increasing worldwide due to cultural eutrophication. This study quantifies the strength of associations between the duration of diel-cycling severe hypoxia (≤2 mg O 2 l −1 ) in bottom water (∼15 cm above bottom) of a shallow (<2 m) coastal lagoon estuary (Delaware, USA) and abiotic environmental variables (water temperature, insolation, tide, streamflow, and wind) and predicts the duration of severe hypoxia given different combinations of these variables. The intensity and spatial extent and dynamics of diel-cycling severe hypoxia events were defined. Vertical variability in dissolved oxygen (DO) concentration during the daytime was also determined. During the summers of 2001-2005, bottom DO data were collected for periods of weeks to months at multiple sites using automated sondes. Multiple linear regression (MLR) and regression tree analysis (RTA) were used to determine the relative importance of the environmental variables in predicting the number of hours of severe hypoxia per day. Key findings of the study were that severe hypoxia events of minutes to hours in duration occurred frequently in all four tributaries sampled, primarily between 0200 and 1000 hours. Severe hypoxia duration and diel-cycling amplitudes of DO concentration increased in the up-tributary direction. Hierarchically, the duration of severe hypoxia was influenced mostly by the mean daily water temperature, then by preceding days' total insolation, percentage of morning hours (02:00 to 10:00 A.M.) ebb tide, and daily streamflow. Collectively, the variables examined by the MLR and the RTA approaches accounted for 62% and 65% of the variability in the duration of severe hypoxia, respectively. RTA demonstrated that daily mean water temperature above 26.3°C and previous day's total insolation below 13.6 kW m −2 were associated with the longest lasting severe hypoxic events (9.56 h). The environmental variables and combinations of conditions that modulate or augment diel-cycling hypoxia presented in this paper enhance understanding of this widespread and growing phenomenon and provide additional insight regarding the extent to which it can impact food webs in very shallow estuarine waters that often serve as nursery habitat.

The trophic ecology and structure of 5 benthic Antarctic fish communities were studied. Two locations at South Georgia Island, one at the South Sandwich Islands, and two at the South Orkney Islands were sampled using a bottom trawl. Specles diversity was low with 13 or fewer species in each community and a pronounced dominance of 3 or fewer species per community. H' diversity values were < 1.3 in all cases and < 0.8 in 3; e evenness values were < 0.6 in all cases and < 0.3 in 3.

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