Temperature-dependent metabolic consequences of food deprivation in the European sardine

International audienceAquatic ecosystems can exhibit seasonal variation in resource availability and animals have evolved to cope with the associated caloric restriction. During winter in the NW Mediterranean Sea, the European sardine Sardina pilchardus naturally experiences caloric restriction owing to a decrease in the diversity and quantity of plankton. However, ongoing global warming has had deleterious effects on plankton communities such that food shortages may occur throughout the year, especially under warm conditions in the summer. We investigated the interactive effects of temperature and food availability on sardine metabolism by continuously monitoring whole-animal respiration of groups of control (fed) and food-deprived sardines over a 60-day experiment in winter (12°C) or summer (20°C) conditions under natural photoperiod. In addition, we measured mitochondrial respiration of red muscle fibres, biometric variables and energy reserves of individuals sampled at 30 and 60 days. This revealed that winter food deprivation elicits energy saving mechanisms at whole animal and cellular levels by maintaining a low metabolism to preserve energy reserves, allowing high levels of survival. By contrast, despite energy saving mechanisms at the mitochondrial level, whole animal metabolic rate was high during food deprivation in summer, causing increased consumption of energy reserves at the muscular level and high mortality after 60 days. Furthermore, a 5-day re-feeding did not improve survival, and mortalities continued, suggesting that long-term food deprivation at high temperatures causes profound stress in sardines that potentially impairs nutrient absorption

Measurement and analysis of small pelagic fish condition: A suitable method for rapid evaluation in the field

International audienceAs condition is a key variable in population dynamics (especially for survival, growth and reproduction), the use of well-defined and accurate fish condition indices is capital. In particular, condition indices (morphometric, bioenergetic and biochemical) have never been compared and validated for the European anchovy Engraulis encrasicolus, the European pilchard Sardina pilchardus and the European sprat Sprattus sprattus. The accuracy of two indirect methods, the morphometric relative condition index Kn and the bioenergetics index determined with the Distell Fish Fatmeter was investigated by comparing with a direct measure of relative lipid content carried out with a thin layer chromatography-flame ionization detector. Estimations from the fatmeter correlated quite well with the relative lipid contents of all species, regardless of the reproductive period (R2 = 0.69 for anchovy, R2 = 0.75 for sprat and R2 = 0.48 for sardine). Kn correlated more poorly with relative lipid content (R2 = 0.22 for anchovy and R2 = 0.41 for sardine, ns for sprat), especially during the reproductive period, pointing out the difficulty for such an index to precisely reflect changes in fat allocation. During the reproductive period, changes in Kn could reflect other processes, such as changes in protein content. Therefore, these different types of commonly used indices do not reflect exactly the same type of energy stores. The high repeatability of the fatmeter was brought to light, so that only one measurement on each fish side may be necessary to evaluate the relative lipid content of a small pelagic fish. Finally, fatmeter measurements were not affected by freezing storage up to one month for anchovy (R2 = 0.66) and sardine (R2 = 0.90), making it possible to use frozen samples of both commercial and scientific survey. In contrast, the freezing storage for sprat should be avoided. Based on this study, the Fatmeter appears to be a suitable indirect method to assess condition and fat content of sardine and anchovy on a large number of individuals

Temperature-dependent metabolic consequences of food deprivation in the European sardine

International audienceAquatic ecosystems can exhibit seasonal variation in resource availability and animals have evolved to cope with the associated caloric restriction. During winter in the NW Mediterranean Sea, the European sardine Sardina pilchardus naturally experiences caloric restriction owing to a decrease in the diversity and quantity of plankton. However, ongoing global warming has had deleterious effects on plankton communities such that food shortages may occur throughout the year, especially under warm conditions in the summer. We investigated the interactive effects of temperature and food availability on sardine metabolism by continuously monitoring whole-animal respiration of groups of control (fed) and food-deprived sardines over a 60-day experiment in winter (12°C) or summer (20°C) conditions under natural photoperiod. In addition, we measured mitochondrial respiration of red muscle fibres, biometric variables and energy reserves of individuals sampled at 30 and 60 days. This revealed that winter food deprivation elicits energy saving mechanisms at whole animal and cellular levels by maintaining a low metabolism to preserve energy reserves, allowing high levels of survival. By contrast, despite energy saving mechanisms at the mitochondrial level, whole animal metabolic rate was high during food deprivation in summer, causing increased consumption of energy reserves at the muscular level and high mortality after 60 days. Furthermore, a 5-day re-feeding did not improve survival, and mortalities continued, suggesting that long-term food deprivation at high temperatures causes profound stress in sardines that potentially impairs nutrient absorption

Average and variability maps and area classification for anchovies, sardines and sprats.

<p>Average and variability maps and area classification for anchovies, sardines and sprats.</p

Annual maps of relative biomass between anchovies and sardines.

<p>Annual maps of relative biomass between anchovies and sardines.</p

Annual (black) and mean (red) modelled variograms of anchovies, sardines and sprats.

<p>The red dotted lines correspond to the 95% confidence interval of the mean variogram deduced from 500 simulations.</p

Main PELMED survey features from 2003 to 2012.

<p>Biomasses are indicated in tons, nm stands for nautical mile.</p><p>Main PELMED survey features from 2003 to 2012.</p

Annual maps of centres of gravity and inertia of patches for anchovies (in green), sardines (in blue) and sprats (in black).

<p>Annual maps of centres of gravity and inertia of patches for anchovies (in green), sardines (in blue) and sprats (in black).</p

Variability in size at maturity of European anchovy (Engraulis encrasicolus) within the Mediterranean Sea

WOS:000739856200001International audienceSize at first sexual maturity (L50) represents an important life history trait in the development of management measures providing fundamental information to avoid the exploitation of younger individuals. L50 is known to display variability due to fishing pressure, geographical gradient and environmental features. In this study, in order to investigate L50 variability among areas of the Mediterranean and Black Sea, maturity ogives of anchovy (Engraulis encrasicolus) were estimated by considering samples collected during the anchovy spawning period in the framework of the MEDiterranean International Acoustic Survey (MEDIAS) program. Anchovy size and sexual maturity data from several Geographical Sub-Areas (GSA) – i.e., Northern Spain, Gulf of Lion, Tyrrhenian Sea, Strait of Sicily, Adriatic Sea and Black Sea – were gathered according to a standard methodological protocol. Maturity ogives were estimated by means of a logistic regression taking into account total length, condition factor, sex and GSA. Obtained results evidenced a significant effect of condition factor, fish in better condition reaching maturity earlier, as well as differences in L50 values among areas and between sexes, with males reaching the maturity at lower length than females. Even though the obtained L50 estimates are relative to the spawning period only, the observed variability at the Mediterranean basin scale highlights the importance to explicitly consider the habitat peculiarities in order to provide management advices based on an ecosystem approach to fishery