The impact of overfishing and El Niño on the condition factor and reproductive success of Peruvian hake, Merluccius gayi peruanus

In this study we examine physiological responses of Peruvian hake (Merluccius gayi peruanus) to changes in their population structure and physical environment during the period 1971–2004. In particular, we assess the relative investment of energy in growth and/or reproduction of small (20–35 cm) and large (35–50 cm) hake. We calculated the (i) condition (Fulton’s K), (ii) gonad and (iii) gut fullness indices for 42,761 female hakes sampled from commercial landings; these indices indicate fish somatic, reproductive and feeding condition, respectively. Using Generalized Additive Models we then examined potential relationships between these indices and sea surface temperature anomalies and date. Drastic energy exhaustion and a decrease in female hake fecundity were observed during El Niño events. The long-term trend showed a general increase in condition factor and a decrease in gonad index for large hake between 1971 and 2004. Small hake exhibited a different trend with an increase in reproductive activity, which was accompanied by an earlier maturation. We hypothesise that the observed low investment of energy in reproduction by large female hake might be related to the lack of large males, due to a sex-selective fishery and the impact of El Niño. We suggest that fishing diminished hake reproductive capacity, modified the sex ratio in favour of females and increased population vulnerability to environmental stress, in particular to the El Niño. The impact of multidecadal variability and predators like the squid, Dosidicus gigas, remain unresolved until longer time series become available.     

Revisiting Peruvian anchovy (Engraulis ringens) trophodynamics provides a new vision of the Humboldt Current system

The Peruvian anchovy or anchoveta (Engraulis ringens) forages on plankton and is a main prey for marine mammals, seabirds, fish, and fishers, and is therefore a key element of the food web in the Humboldt Current system (HCS). Here, we present results from the analysis of 21,203 anchoveta stomach contents sampled during 23 acoustic surveys over the period 1996–2003. Prey items were identified to the genus level, and the relative dietary importance of different prey was assessed by determination of their carbon content. Variability in stomach fullness was examined relative to the diel cycle, the distance from the coast, sea surface temperature, and latitude, using generalized additive models (GAMs). Whereas phytoplankton largely dominated anchoveta diets in terms of numerical abundance and comprised >99% of ingested prey items, the carbon content of prey items indicated that zooplankton was by far the most important dietary component, with euphausiids contributing 67.5% of dietary carbon followed by copepods (26.3%). Stomach fullness data showed that anchoveta feed mainly during daytime between 07h00 and 18h00, although night-time feeding also made a substantial contribution to total food consumption. Stomach fullness also varied with latitude, distance from the coast, and temperature, but with substantial variability indicating a high degree of plasticity in anchoveta feeding behaviour. The results suggest an ecological role for anchoveta that challenges current understanding of its position in the foodweb, the functioning of the HCS, and trophic models of the HCS.     

An application of Iatroscan thin-layer chromatography with flame ionization detection—lipid classes of microorganisms as biomarkers in the marine environment

Iatroscan TLC-FID combines the separatory capabilities of thin-layer chromatography (TLC) (on silica coated chromarods) with the possibility of quantitation by flame ionization detection (FID). It can be used to separate lipid extracts into classes of compounds ranging from neutral to polar products. The rapidity with which this system provides lipid class profiles from small samples makes it particularly useful in oceanographic studies where routine analyses of large numbers of samples are required. Lipid classes were analysed in 4 marine bacterial strains grown on various substrates and 10 microalgae isolated from the marine environment and grown in batch cultures. Data on lipid composition of these microorganisms were obtained and compared to literature data. Results show that ratios between classes of compounds within the different groups of microorganisms were characteristic enough to constitute a good print of bacterial or phytoplankton sources in organic matter in sea water. In a preliminary study, phospholipid classes from a bacterial strain and a microalga were separated. Results show that the determination of ratios between phospholipid classes in organic matter could represent an improvement in the utilization of lipid classes as biomarkers.     

Correlations among the reflectances of vitrinite, chitinozoans, graptolites and scolecodonts

Paleozoic marine sequences sampled in outcrops and wells of northeastern Gaspe Peninsula (Quebec Appalachians) yield kerogen composed in part of vitrinite and zooclasts (chitinozoans, scolecodonts and graptolites) on which reflectance measurements were made.The comparison between means of random measurements show that reflectance of chitinozoans is similar to that of telinite (vitrinite with a cellular texture) and that the reflectance of scolecodonts is significantly lower than that of telinite in the lower range of studied values. At higher reflectivities differences decrease but, at the end of the condensate gas zone reflectancea are not yet identical. As shown by previous studies, reflectance of graptolites is slightly less than that of telinite.Pyrobitumen reflectance is related to the lithology of the host-rock and no generalized correlation can be established between the reflectance of pyrobitumen and that of vitrinite.     

Assessment of wind-forcing impact on a global wind-wave model using the TOPEX altimeter

The study presents assessment of an operational wave model (Wavewatch III), focusing upon the model sensitivity to wind-forcing products. Four wind fields are used to drive the model, including the NCEP/NCAR reanalysis and three other products that assimilate various satellite wind measurements having high spatial resolution, including the QuikSCAT scatterometer. Three wave field statistics: significant wave height, mean zero-crossing wave period, and mean square slope are compared with collocated TOPEX altimeter derivatives to gauge the relative skill of differing wind-forced model runs, as well as to demonstrate an extended use of the altimeter beyond simply supplying wave height for wave model validation and assimilation. Results suggest that model output is critically sensitive to choice of the wind field product. Higher spatial resolution in the wind fields does lead to improved agreement for the higher-order wave statistics.     

Neogene exhumation and relief evolution in the eastern Betics (SE Spain): Insights from the Sierra de Gador

The Betics are a key area to study an orogenic landscape disrupted by late‐orogenic extension. New low‐temperature thermochronology (LTT) data (AHe and AFT) coupled with geomorphic constraints in the Sierra de Gador (Alpujarride complex) are used to reconstruct the cooling history and evolution of relief during the Neogene. We document three stages: (1) a fast cooling event between 23 and 16 Ma associated with the well‐known extensive tectonic exhumation of the Alpujarride unit, (2) a period of slow cooling between 16 and 7.2 Ma related to a planation event and (3) a post‐7.2 Ma surface uplift associated with the inversion of the Alboran domain undetected by LTT. The planation event followed by this late uplift can explain the occurrence of inherited low‐relief surfaces overlain by Tortonian–Messinian platform deposits at the top of the range. Finally, we propose that the Sierra de Gador is a more transient landscape than the nearby Sierra Nevada.