Jérôme Spitz

PREDATOR AND PREY BODY SIZES IN MARINE FOOD WEBS

Knowledge of relationships between predator size and prey size are needed to describe interactions of species and size classes in food webs. Most estimates of predator and prey sizes have been based on dietary studies and apply to small numbers of species in a relatively narrow size range. These estimates may or may not be representative of values for other groups of species and body sizes or for other locations. Marine predator and prey size data associated with published literature were identified and collated to produce a single data set. If predator or prey length of mass were not measured in the original study, the length or mass was calculated using length–mass relationships. The data set consists of 34 931 records from 27 locations covering a wide range of environmental conditions from the tropics to the poles and for 93 types of predator with sizes ranging from 0.1 mg to over 415 kg and 174 prey types with sizes from 75 pg to over 4.5 kg. Each record includes: predator and prey scientific names, c...

Cost of Living Dictates what Whales, Dolphins and Porpoises Eat: The Importance of Prey Quality on Predator Foraging Strategies

Understanding the mechanisms that drive prey selection is a major challenge in foraging ecology. Most studies of foraging strategies have focused on behavioural costs, and have generally failed to recognize that differences in the quality of prey may be as important to predators as the costs of acquisition. Here, we tested whether there is a relationship between the quality of diets (kJ·g−1) consumed by cetaceans in the North Atlantic and their metabolic costs of living as estimated by indicators of muscle performance (mitochondrial density, n = 60, and lipid content, n = 37). We found that the cost of living of 11 cetacean species is tightly coupled with the quality of prey they consume. This relationship between diet quality and cost of living appears to be independent of phylogeny and body size, and runs counter to predictions that stem from the well-known scaling relationships between mass and metabolic rates. Our finding suggests that the quality of prey rather than the sheer quantity of food is a major determinant of foraging strategies employed by predators to meet their specific energy requirements. This predator-specific dependence on food quality appears to reflect the evolution of ecological strategies at a species level, and has implications for risk assessment associated with the consequences of changing the quality and quantities of prey available to top predators in marine ecosystems.

Stable isotopes document the trophic structure of a deep-sea cephalopod assemblage including giant octopod and giant squid.

Although deep-sea cephalopods are key marine organims, their feeding ecology remains essentially unknown. Here, we report for the first time the trophic structure of an assemblage of these animals (19 species) by measuring the isotopic signature of wings of their lower beaks, which accumulated in stomachs of stranded sperm whales. Overall, the species encompassed a narrow range in δ13C values (1.7‰), indicating that they lived in closely related and overlapping habitats. δ13C values can be interpreted in terms of distribution with the more 13C-depleted species (e.g. Stigmatoteuthis arcturi, Vampyroteuthis infernalis) having a more pelagic habitat than the more 13C-enriched, bathyal species (e.g. Todarodes sagittatus and the giant squid Architeuthis dux). The cephalopods sampled had δ15N values ranging 4.6‰, which is consistent with the species spanning approximately 1.5 trophic levels. Neither the giant octopod (Haliphron atlanticus) nor the giant squid reached the highest trophic position. Species δ15N was independent of body size, with large squids having both the highest (Taningia danae) and lowest (Lepidoteuthis grimaldii) δ15N values. Their trophic position indicates that some species share the top of the food web, together with other megacarnivores such as the sperm whale.

Grey seal diet at the southern limit of its European distribution: combining dietary analyses and fatty acid profiles

The north-east Atlantic grey seal, Halichoerus grypus, is widely distributed along the European coastline from northern Russia to France, with the core population centred around Scotland. To date, very little is known of the diet of the species at the southern margin of the species range. However, because grey seal numbers have been increasing over the last few decades in France, the issue of their potential interactions with coastal fisheries is frequently raised. The diet of grey seal in the Molene Archipelago was investigated by combining scat, stomach content and fatty acid analyses, since all three approaches have complementary potentials to reveal feeding habits of a predator. A total of 145 scats mostly of moulting adult males, 14 stomach contents of yearlings and 14 blubber samples from animals of all ages were analysed following standard methodologies. Scats revealed a diet mainly constituted of 50.6% by mass (M) of wrasse, Labridae (mostly Labrus bergylta), 20.7%M conger eel, Conger conger, and 11.9%M sea bass, Dicentrarchus labrax. Stomach contents were made up of 52.3%M cuttlefish, Sepia officinalis, 9.5%M sole, Solea solea, and 9.4 %M conger eel. All these prey are different from the diet observed in core areas. Fatty acid analysis from the blubber confirmed that the diet differed between the Molene Archipelago and one of the Scottish breeding sites. It also showed that most of the interindividual variability was explained by variation in seal body masses, which could be linked to behavioural ontogeny of foraging strategies. Most of the prey species identified in the food of the grey seal in Brittany are also targeted by professional and/or recreational fisheries in the area; additionally, several prey size-ranges also partly overlap with marketed size-ranges for several species.

An assessment of contaminant concentrations in toothed whale species of the NW Iberian Peninsula: Part II. Trace element concentrations

Concentrations of Ag, As, Cd, Co, Cr, Cu, Fe, Hg, Mn, Ni, Pb, Se, V and Zn were investigated in the liver and kidney of the five most common toothed whales off the Northwest Iberian Peninsula (NWIP), specifically common dolphin, long-finned pilot whale, harbour porpoise, striped dolphin and bottlenose dolphin. Differences were observed in the bioaccumulation of the above elements between the five species. The differences are probably related to biological factors such as age and sex and/or to ecological factors specific to each species such as feeding habits or bioavailability of the various elements. However, no significant relationship was observed between element accumulation and sex. Pilot whale and striped dolphin showed the highest concentrations of renal Cd and the highest concentrations of hepatic Hg and Se, while bottlenose dolphin showed the highest concentrations of Hg in kidneys. An analysis of inter-elemental relationships showed strong positive correlations between Hg and Se in the five species, however most individuals have Hg:Se molar ratio less than 1:1 indicating an excess of Se compare to Hg. This result, probably reflect the high proportion of young animals in the sample available for this study and/or that these animals had a good health status. We also observed a positive correlation in striped dolphins between Cd and Cu and between Cd and Zn in kidneys. In addition, comparing with other studies world-wide, the element concentrations (Hg and Cd) found in Iberian toothed whales indicate that these populations are not specially threatened by Hg and Cd exposure in the area.

Large amounts of marine debris found in sperm whales stranded along the North Sea coast in early 2016

30 sperm whales (Physeter macrocephalus) stranded along the coasts of the North Sea between January and February 2016. The gastro-intestinal tracts of 22 of the carcasses were investigated. Marine debris including netting, ropes, foils, packaging material and a part of a car were found in nine of the 22 individuals. Here we provide details about the findings and consequences for the animals. While none of the items was responsible for the death of the animal, the findings demonstrate the high level of exposure to marine debris and associated risks for large predators, such as the sperm whale.

A nutrigenomic approach to detect nutritional stress from gene expression in blood samples drawn from Steller sea lions.

Gene expression profiles are increasingly being used as biomarkers to detect the physiological responses of a number of species to disease, nutrition, and other stressors. However, little attention has been given to using gene expression to assess the stressors and physiological status of marine mammals. We sought to develop and validate a nutrigenomic approach to quantify nutritional stress in Steller sea lions (Eumetopias jubatus). We subjected 4 female Steller sea lions to 3 feeding regimes over 70-day trials (unrestricted food intake, acute nutritional stress, and chronic nutritional stress), and drew blood samples from each animal at the end of each feeding regime. We then extracted the RNA of white blood cells and measured the response of 8 genes known to react to diet restriction in terrestrial mammals. Overall, we found that the genomic response of Steller sea lions experiencing nutritional stress was consistent with how terrestrial mammals respond to dietary restrictions. Our nutritionally stressed sea lions down-regulated some cellular processes involved in immune response and oxidative stress, and up-regulated pro-inflammatory responses and metabolic processes. Nutrigenomics appears to be a promising means to monitor nutritional status and contribute to mitigation measures needed to assist in the recovery of Steller sea lions and other at-risk species of marine mammals.

An assessment of contaminant concentrations in toothed whale species of the NW Iberian Peninsula: Part I. Persistent organic pollutants

Concentrations and patterns of polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs) in the blubber of the five most common toothed whales off the Northwest Iberian Peninsula (NWIP), specifically common dolphin, long-finned pilot whale, harbour porpoise, striped dolphin and bottlenose dolphin, were investigated. The study revealed that differences in PCB and PBDE concentrations among the species are highly dependent on age and sex but also on ecological factors such as trophic level, prey type and habitat. Of the five species studied, bottlenose dolphin and harbour porpoise showed the greatest concentrations of PCBs. Both species exceed the toxic threshold of 17μgg(-1) lipid weight (PCB Aroclor equivalent) for health effects on marine mammals, for 100% and 75% of the individuals tested, respectively. Overall, the PCB and PBDE levels observed in the NWIP toothed whales were of the same order of magnitude or lower than those reported by previous studies in areas of the NE Atlantic. However, they are often higher than those for toothed whales from the southern Atlantic and Pacific Ocean.

From banana fields to the deep blue: Assessment of chlordecone contamination of oceanic cetaceans in the eastern Caribbean

In the French West Indies (Caribbean), the insecticide Chlordecone (CLD) has been extensively used to reduce banana weevil (Cosmopolites sordidus) infestations in banana plantations. Previous studies have shown high CLD concentrations in freshwater and coastal communities of the region. CLD concentrations, however, have not yet been assessed in marine top predators. We investigated CLD concentrations in cetacean blubber tissues from Guadeloupe, including Physeter macrocephalus, Lagenodelphis hosei, Stenella attenuata and Pseudorca crassidens. Chlordecone was detected in all blubber samples analysed, with the exception of four P. macrocephalus. Concentrations (range: 1 to 329 ng·g-1 of lipid weight) were, however, lower than those found in species from fresh and brackish water. Ecological factors (open ocean habitat), CLD kinetics, and cetacean metabolism (high or specific enzymatic activity) might explain low concentrations found in cetacean blubber. Future analyses that include internal organ sampling would help to confirm CLD levels observed in this study.