Chemistry of otoliths from juvenile menhaden Brevoortia patronus: Evaluating strontium, strontium:calcium and strontium isotope ratios as environmental indicators

Laboratory studies were conducted to establish the utility of otolith chemistry for tracing gulf menhaden Brevoortia patronus environmental histories. Menhaden larvae were hatched from eggs and reared to juveniles under constant conditions at 3 temperatures (18, 22, 26°C) and 3 salinities (20, 26, 33.4). Whole otoliths from experimental fish along with their rearing waters were analyzed by ICPMS (inductively coupled plasma mass spectrometry) and TIMS (thermal ionization mass spectrometry) to determine the effects of temperature and salinity on Sr concentration, Sr/Ca and 87Sr/86Sr. A comparison of elemental composition by otolith type revealed significantly lower Sr concentrations and lower Sr/Ca ratios in the asteriscus versus the sagitta and lapillus. X-ray diffraction analyses for each otolith type determined that menhaden sagittae and lapilli are aragonite while their asterisci are vaterite. This suggests the type of calcium carbonate matrix deposited can affect the concentrations of trace elements incorporated into otoliths. In laboratory reared menhaden no significant relationships between Sr concentration or Sr/Ca ratios and temperature, salinity or menhaden growth rate were detected (ANOVA, p = 0.05). We found no indication that 87Sr/86Sr ratios of menhaden otoliths were affected by water temperature. 87Sr/86Sr did reflect the salinity of the rearing water; however, the relationship between Sr isotope ratios and salinity limits the utility of Sr isotope ratios as a precise indicator of salinity to low salinity environments (< 20) or over wide ranges of salinity. A comparison between Sr isotope ratios of menhaden otoliths and menhaden vertebrae, along with an analysis of a vertebra from a reproductive adult bay anchovy Anchoa mitchilli, showed there was no significant difference between otolith and vertebra 87Sr/86Sr ratios, indicating that other bony structures might be suitable for strontium isotope analyses in small individual fish

Seasonal distribution, abundance and diversity of demersal fishes in the inner Ría de Arosa, NW Spain

A year of seasonal trawling was initiated in Ria de Arosa, Spain in an area with mussel rafts and an area without mussel rafts, to assess the effect of the presence of the mussels and their associated fauna on the distribution and abundance of the demersal fishes, The demersal fish cornmunity exhibited a strong resident component comprising greater than 96% of the total catch and was dominated by gobiid species, The dominance of gobies resulted in a fish cornmunity composed of a large number of small fish (x = 0'22 individuals/ m"). There were no overwhelming differences in the fish cornmunities or cornmunity indices of the raft and non-raft areas, although biomass and diversity were generally higher in the raft area and the abundances of several species were significantIy different in the two areas, Seasonal biomass estimates ranged from 1'19 to 2'08 g m -2 (x = 1'69) in the raft area and were highest in September and lowest in January, Biomass in the non-raft area ranged from 0'93 to 2'18 g m-2 (x = 1'45) and were highest in April and lowest in july. Diversity (H) was higher in the raft area (0'94 to 1'39) than in- the non-raft area (0'81 to 1'15), Pooled annual Diversity (H) was 1'41. Similarly, other community indices such as Species Richness (D) and Evenness (J) were generally higher in the raft area, The above biomass and diversity values are moderate when compared with values for other estuarine areas, Small decapods, polychaetes and amphipods dominated the gut contents of the specimens analysed, with the crab, Pisidia longicornis the single most important food itern.Versión del editor2,247

Energetics of winter flounder (Pseudopleuronectes americanus) fed the polychaete, Nereis virens, under experimental conditions

Age class I and II winter flounder, Pseudopleuronectes americanus, were fed the polychaete, Nereis virens, under experimental temperatures of 10 C and 20 C in a filtered (10 μ), temperature-regulated seawater system for periods of 40 days. All the fish grew and there was no significant difference in growth between fish at 10 C and those at 20 C, but growth was significantly different (P < 0.05) between age classes at both temperatures. Age I fish had the higher growth efficiency and mean gross growth efficiencies based on calories were 23.7% and 20.2% for age I and II, respectively. Calculated efficiencies were lowest based on wet weight and generally increased when based on dry weight, carbon, and caloric content.Versión del editor1,546

Fisheries and oceanography off Galicia, NW Spain: Mesoscale spatial and temporal changes in physical processes and resultant patterns of biological productivity

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