Estructura y migración del rorcual común del Atlántico nororiental establecido mediante trazadores químicos

[spa] El rorcual común (Balaenoptera physalus) es una de les especies de misticeto más abundante en el Atlántico Norte y es considerada como una especie de alta importancia ambiental por la legislación española. Sin embargo, aún quedan grandes lagunas de conocimiento en la biología de esta especie, especialmente durante el invierno. El objetivo global de esta tesis es la mejor comprensión de la estructura poblacional y las migraciones del rorcual común mediante el análisis de marcadores químicos en tres tejidos diferentes. En el primer capítulo, se analizaron alquenonas en la grasa hipodérmica y en el contenido estomacal de rorcuales de Islandia y del noroeste español. Las alquenonas son moléculas orgánicas producidas por organismos haptófitos que pueden ser usadas para estimar la temperatura del agua donde han sido sintetizadas. Los resultados muestran que estas moléculas pueden ser transferidas a lo largo de la red trófica y ser detectadas tanto en el contenido estomacal de los rorcuales como en la grasa hipodérmica. Mientras la temperatura estimada en el contenido estomacal refleja la temperatura ambiental de los 10 días antes del muestreo, las alquenonas de la grasa hipodérmica parecen reflejar la temperatura del hábitat de los rorcuales durante el invierno. Los rorcuales de las dos áreas estudiadas mostraron una composición de alquenonas bien diferenciada, lo que indica que se trata de poblaciones segregadas. En el segundo capítulo se analizaron los isótopos estables en aminoácidos muestreados en las barbas de ballena. Se observó que el nivel trófico de los rorcuales se vuelve más alto y variable durante el invierno, lo que podría indicar que esta especie complementa su dieta con pescado durante esta época. Además, los valores isotópicos ambientales del invierno sugieren que los rorcuales pasan la época invernal en zonas de emergencia de agua profunda, las cuales pueden sostener una producción primaria mayor que el resto del océano oligotrófico. En el tercer capítulo se midió la consistencia temporal de los isótopos estables en los conos auditivos de los rorcuales. Estos mostraron que los rorcuales son especialistas individuales, es decir los individuos ocupan una porción del nicho poblacional disponible. En conjunto, los stocks estudiados de rorcual común del Atlántico Norte parecen ser más generalistas durante el invierno, pero los individuos parecen migrar y alimentarse en zonas concretas cada año, caracterizadas por una alta producción primaria.[eng] Fin whales (Balaenoptera physalus) is one of the most abundant mysticete species in the North Atlantic, and it is considered a species of high environmental importance by the Spanish legislation. However, large knowledge gaps exist in the biology of this species, especially in winter. The main goal of this thesis is to improve our understanding of the migrations of the fin whale analyzing chemical tracers in three different tissues. In the first chapter, alkenones were analyzed in blubber and the stomach content of the fin whales from Iceland and the NW of Spain. The alkenones are a group of organic molecules produced by some haptophyte species, and may be used to infer the water temperature where they were synthesized. The results show that these molecules can be transferred through the trophic web and detected both in the stomach content and the blubber of the whales. While the temperature estimated in the stomach content reflected the environmental SST 10 days before the sampling date, the alkenones in the blubber reflected the environmental temperature where the fin whales had roamed during winter. In the second chapter, the stable isotopes of amino acids were analyzed in baleen plate samples. The results showed that the trophic level of the individuals were higher and more variable during winter, which could indicate that they were including fish in their diet during the winter season. Furthermore, the baseline isotopic values suggested that the fin whales spent the winter season in zones of deep water emergence, which can support a higher primary production than the oligotrophic ocean. In the third chapter, the temporal consistency of the stable isotopes was measured in the earplugs of fin whales. The results showed that the fin whales are individual specialists, this is, they occupy a small portion of the population isotopic niche. Overall, the fin whale stocks studied in this thesis are more generalist during winter than during summer, however, the individuals tend to migrate and feed in specific zones every year, which are characterized by a high primary production

Histological structure of baleen plates and its relevance to sampling for stable isotope studies

Stable isotope analysis of baleen plates is a widespread technique for studying baleen whales. Typically, subsamples along the growth axis of the baleen plate are extracted and analysed to examine time-related variation in their stable isotope signals. However, baleen plate tissue is composed of two different tissues: a pair of cortex layers flanking an internal medulla. These two histological components exhibit differential development, and their consolidation as a tissue is therefore likely non-synchronic. This could influence stable isotope results because the stable isotope signal may differ in each subsample according to the proportion of the two histological components extracted from the tissue. In this study, stable isotope analysis was combined with optical microscopy examination of fin whale (Balaenoptera physalus) baleen plates to understand the ontogeny of the two histological components. In both of them, the 15N values followed a sinewave pattern along the growth axis of the baleen plate. However, the 15N values of the cortex appeared to be advanced compared to those of the medulla. Additionally, the amplitude of the 15N values in the oscillations was higher in the cortex than in the medulla. The histological examination revealed that these differences are caused by earlier and faster synthesis of the cortex layer compared to that of the medulla. Because the stable isotope ratios of the two layers differ, we propose that in this type of studies only the outer-most part (closest to the surface) of the cortex should be subsampled and analysed. Additionally, to include the most recently formed tissue, this subsampling should start well below the zwischensubstanz, or baleen 'gum'

How do baleen whales stow their filter? A compoarative bioimechanical analysis of baleen bending

Bowhead and right whale (balaenid) baleen filtering plates, longer in vertical dimension (3-4+ m) than the closed mouth, presumably bend during gape closure. This has not been observed in live whales, even with scrutiny of videorecorded feeding sequences. To determine what happens to baleen as gape closes, we conducted an integrative, multifactorial study including materials testing, functional (flow tank and kinematic) testing, and histological examination. We measured baleen bending properties along the dorsoventral length of plates and anteroposterior location within a rack of plates via mechanical (axial bending, composite flexure, compression, and tension) tests of hydrated and air-dried tissue samples from balaenid and other whale baleen. Balaenid baleen is remarkably strong yet pliable, with ductile fringes and low stiffness and high elasticity when wet; it likely bends in the closed mouth when not used for filtration. Calculation of flexural modulus from stress/strain experiments shows baleen is slightly more flexible where it emerges from the gums and at its ventral terminus, but kinematic analysis indicates plates bend evenly along their whole length. Fin and humpback whale baleen has similar material properties but less flexibility, with no dorsoventral variation. Internal horn tubes have greater external and hollow luminal diameter but lower density in lateral relative to medial baleen of bowhead and fin whales, suggesting greater capacity for lateral bending. Baleen bending has major consequences not only for feeding morphology and energetics but also conservation given that entanglement in fishing gear is a leading cause of whale mortality

Temporal consistency of individual trophic specialization in southern elephant seals (Mirounga leonina)

ABSTRACT: Individual specialization can be an advantageous strategy that increases predation success and diminishes intra-population competition. However, trophic specialization can be a handicap in changing environments if the individuals are unable to use different prey or feeding grounds in response to change. Southern elephant seals Mirounga leonina allow us to explore this trade-off as they migrate, returning to haul out on land, for 2 extended periods, to breed and to moult. They fast during both periods, but the energetic cost is higher during the breeding season, leading to a poorer body condition after the breeding fast than after the moulting fast. We analysed the carbon (δ13C) and nitrogen (δ15N) isotopic composition of skin and fur samples from Falkland Islands elephant seals. The isotopic values provided information about the foraging strategy of the seals during the pre-breeding season and pre-moulting season, respectively. We assessed individual specialization as the variation between periods of an individual with respect to the variability of the whole population. The high specialization and the correlation between periods suggest that each animal feeds in a similar region and on similar prey during both feeding migrations. The comparison with data from other populations and particulate organic matter suggests that the Falkland Islands elephant seals fed both on the Patagonian Continental Shelf and in the Southern Ocean. The high specialization among individuals within this species could potentially limit the individual capacity of adaptation in the face of changing conditions or leave those abilities to the few generalist individual

Temporal consistency of individual trophic specialization in southern elephant seals (Mirounga leonina)

ABSTRACT: Individual specialization can be an advantageous strategy that increases predation success and diminishes intra-population competition. However, trophic specialization can be a handicap in changing environments if the individuals are unable to use different prey or feeding grounds in response to change. Southern elephant seals Mirounga leonina allow us to explore this trade-off as they migrate, returning to haul out on land, for 2 extended periods, to breed and to moult. They fast during both periods, but the energetic cost is higher during the breeding season, leading to a poorer body condition after the breeding fast than after the moulting fast. We analysed the carbon (δ13C) and nitrogen (δ15N) isotopic composition of skin and fur samples from Falkland Islands elephant seals. The isotopic values provided information about the foraging strategy of the seals during the pre-breeding season and pre-moulting season, respectively. We assessed individual specialization as the variation between periods of an individual with respect to the variability of the whole population. The high specialization and the correlation between periods suggest that each animal feeds in a similar region and on similar prey during both feeding migrations. The comparison with data from other populations and particulate organic matter suggests that the Falkland Islands elephant seals fed both on the Patagonian Continental Shelf and in the Southern Ocean. The high specialization among individuals within this species could potentially limit the individual capacity of adaptation in the face of changing conditions or leave those abilities to the few generalist individual

Temporal consistency of individual trophic specialization in southern elephant seals (Mirounga leonina)

ABSTRACT: Individual specialization can be an advantageous strategy that increases predation success and diminishes intra-population competition. However, trophic specialization can be a handicap in changing environments if the individuals are unable to use different prey or feeding grounds in response to change. Southern elephant seals Mirounga leonina allow us to explore this trade-off as they migrate, returning to haul out on land, for 2 extended periods, to breed and to moult. They fast during both periods, but the energetic cost is higher during the breeding season, leading to a poorer body condition after the breeding fast than after the moulting fast. We analysed the carbon (δ13C) and nitrogen (δ15N) isotopic composition of skin and fur samples from Falkland Islands elephant seals. The isotopic values provided information about the foraging strategy of the seals during the pre-breeding season and pre-moulting season, respectively. We assessed individual specialization as the variation between periods of an individual with respect to the variability of the whole population. The high specialization and the correlation between periods suggest that each animal feeds in a similar region and on similar prey during both feeding migrations. The comparison with data from other populations and particulate organic matter suggests that the Falkland Islands elephant seals fed both on the Patagonian Continental Shelf and in the Southern Ocean. The high specialization among individuals within this species could potentially limit the individual capacity of adaptation in the face of changing conditions or leave those abilities to the few generalist individual