Renaud de Stephanis

Individual improvements and selective mortality shape lifelong migratory performance

Billions of organisms, from bacteria to humans, migrate each year and research on their migration biology is expanding rapidly through ever more sophisticated remote sensing technologies. However, little is known about how migratory performance develops through life for any organism. To date, age variation has been almost systematically simplified into a dichotomous comparison between recently born juveniles at their first migration versus adults of unknown age. These comparisons have regularly highlighted better migratory performance by adults compared with juveniles, but it is unknown whether such variation is gradual or abrupt and whether it is driven by improvements within the individual, by selective mortality of poor performers, or both. Here we exploit the opportunity offered by long-term monitoring of individuals through Global Positioning System (GPS) satellite tracking to combine within-individual and cross-sectional data on 364 migration episodes from 92 individuals of a raptorial bird, aged 1–27 years old. We show that the development of migratory behaviour follows a consistent trajectory, more gradual and prolonged than previously appreciated, and that this is promoted by both individual improvements and selective mortality, mainly operating in early life and during the pre-breeding migration. Individuals of different age used different travelling tactics and varied in their ability to exploit tailwinds or to cope with wind drift. All individuals seemed aligned along a race with their contemporary peers, whose outcome was largely determined by the ability to depart early, affecting their subsequent recruitment, reproduction and survival. Understanding how climate change and human action can affect the migration of younger animals may be the key to managing and forecasting the declines of many threatened migrants.

PCB pollution continues to impact populations of orcas and other dolphins in European waters

Organochlorine (OC) pesticides and the more persistent polychlorinated biphenyls (PCBs) have well-established dose-dependent toxicities to birds, fish and mammals in experimental studies, but the actual impact of OC pollutants on European marine top predators remains unknown. Here we show that several cetacean species have very high mean blubber PCB concentrations likely to cause population declines and suppress population recovery. In a large pan-European meta-analysis of stranded (n = 929) or biopsied (n = 152) cetaceans, three out of four species:- striped dolphins (SDs), bottlenose dolphins (BNDs) and killer whales (KWs) had mean PCB levels that markedly exceeded all known marine mammal PCB toxicity thresholds. Some locations (e.g. western Mediterranean Sea, south-west Iberian Peninsula) are global PCB “hotspots” for marine mammals. Blubber PCB concentrations initially declined following a mid-1980s EU ban, but have since stabilised in UK harbour porpoises and SDs in the western Mediterranean Sea. Some small or declining populations of BNDs and KWs in the NE Atlantic were associated with low recruitment, consistent with PCB-induced reproductive toxicity. Despite regulations and mitigation measures to reduce PCB pollution, their biomagnification in marine food webs continues to cause severe impacts among cetacean top predators in European seas.

Genetic differentiation among North Atlantic killer whale populations

Population genetic structure of North Atlantic killer whale samples was resolved from differences in allele frequencies of 17 microsatellite loci, mtDNA control region haplotype frequencies and for a subset of samples, using complete mitogenome sequences. Three significantly differentiated populations were identified. Differentiation based on microsatellite allele frequencies was greater between the two allopatric populations than between the two pairs of partially sympatric populations. Spatial clustering of individuals within each of these populations overlaps with the distribution of particular prey resources: herring, mackerel and tuna, which each population has been seen predating. Phylogenetic analyses using complete mitogenomes suggested two populations could have resulted from single founding events and subsequent matrilineal expansion. The third population, which was sampled at lower latitudes and lower density, consisted of maternal lineages from three highly divergent clades. Pairwise population differentiation was greater for estimates based on mtDNA control region haplotype frequencies than for estimates based on microsatellite allele frequencies, and there were no mitogenome haplotypes shared among populations. This suggests low or no female migration and that gene flow was primarily male mediated when populations spatially and temporally overlap. These results demonstrate that genetic differentiation can arise through resource specialization in the absence of physical barriers to gene flow.

Habitat‐driven population structure of bottlenose dolphins, Tursiops truncatus, in the North‐East Atlantic

Despite no obvious barrier to gene flow, historical environmental processes and ecological specializations can lead to genetic differentiation in highly mobile animals. Ecotypes emerged in several large mammal species as a result of niche specializations and/or social organization. In the North‐West Atlantic, two distinct bottlenose dolphin (Tursiops truncatus) ecotypes (i.e. ‘coastal’ and ‘pelagic’) have been identified. Here, we investigated the genetic population structure of North‐East Atlantic (NEA) bottlenose dolphins on a large scale through the analysis of 381 biopsy‐sampled or stranded animals using 25 microsatellites and a 682‐bp portion of the mitochondrial control region. We shed light on the likely origin of stranded animals using a carcass drift prediction model. We showed, for the first time, that coastal and pelagic bottlenose dolphins were highly differentiated in the NEA. Finer‐scale population structure was found within the two groups. We suggest that distinct founding events followed by parallel adaptation may have occurred independently from a large Atlantic pelagic population in the two sides of the basin. Divergence could be maintained by philopatry possibly as a result of foraging specializations and social organization. As coastal environments are under increasing anthropogenic pressures, small and isolated populations might be at risk and require appropriate conservation policies to preserve their habitats. While genetics can be a powerful first step to delineate ecotypes in protected and difficult to access taxa, ecotype distinction should be further documented through diet studies and the examination of cranial skull features associated with feeding.

Identifying key habitat and seasonal patterns of a critically endangered population of killer whales

ruth esteban, philippe verborgh, pauline gauffier, joan gime’nez, isabel afa’n, ana can~adas, pedro garci’a, jose luis murcia, sara magalha~es, ezequiel andreu and renaud de stephanis CIRCE, Conservation Information and Research on Cetaceans, C/Cabeza de Manzaneda 3, Algeciras-Pelayo, 11390 Cadiz, Spain, GEMA, Grupo de Ecologia Marina Aplicada, Estacion Biologica de Donana, CSIC; C/Americo Vespucio, s/n, 41092, Isla de la Cartuja, Sevilla, Spain, LAST, Laboratorio de SIG y Teledeteccion, Estacion Biologica de Donana, CSIC; C/Americo Vespucio, s/n, 41092, Isla de la Cartuja, Sevilla, Spain, Alnilam Research and Conservation, Candamo 116, 28240 Hoyo de Manzanares, Madrid, Spain, ANSE Asociacion de Naturalistas del Sureste Plaza Pintor Jose Maria Parraga, 11, Bajo, 30002, Murcia, Spain, MAR ILIMITADO Porto da Baleeira de Sagres, 8650-368 Sagres, Portugal, TURMARES (Turismo Maritimo del Estrecho), Avd/Alcalde Juan Nunez 3, 11380 Tarifa, Cadiz, Spain

The role of synchronized swimming as affiliative and anti-predatory behavior in long-finned pilot whales

Synchronized swimming in cetaceans has been hypothesized to play a role in affiliative processes as well as anti-predatory responses. We compared observed variation in synchronized swimming at two research sites in relation to disturbance exposure to test these two hypotheses. This study describes and quantifies pair synchronization in long-finned pilot whales at the Strait of Gibraltar, Spain and Cape Breton, Canada. Synchronization differed depending on the behavioral state and the response is different in the two sites leading to the conclusion that environment can shape the occurrence and magnitude of certain behaviors. We also analyzed intra-population variations in synchronization among 4 social units of Pilot whales in the Strait of Gibraltar and the results of this study confirmed the affiliative role of synchronization and highlighted an influence of disturbance on synchronization. We can conclude that synchronization is a common behavior in long-finned pilot whales that allow for close proximity and rapid coordinated response of individuals, with the multiple functions of showing affiliation and reacting to disturbance.

No effect of satellite tagging on survival, recruitment, longevity, productivity and social dominance of a raptor, and the provisioning and condition of its offspring

Summary The deployment of electronic devices on animals is rapidly expanding and producing leapfrog advances in ecological knowledge. Even though their effects on the ecology and behaviour of the marked subjects are potentially important, <10% of the studies are accompanied by an evaluation of impact, and comprehensive, long-term assessments have been few. Therefore, there is an urgent need to test for impacts, especially for tags that are heavy and deployed for long time periods, such as satellite transmitters. We marked 110 individuals of a medium-sized, migratory raptor, the black kite Milvus migrans, with GPS satellite tags, representing about 4% of the body mass and attached as backpacks through a Teflon harness. Tagged individuals were compared to control animals of similar sex, age and breeding status for a large number of behavioural, condition-related and ecological traits. Despite a sample size two- to threefold greater than most previous assessments that reported significant impacts, there was no detectable difference between tagged and control individuals in key vital rates such as survival probability, longevity, recruitment, age of first breeding, reproductive performance and timing of breeding. Tagged and untagged kites showed similar social dominance during fights over food and a similar capability to provision nestlings, which prevented carry-over effects on the stress levels and condition of their offspring. Synthesis and applications. Radio-marking studies are growing exponentially in the current ‘movement ecology era’, and impact assessments will be ever more important. In principle, tags of up to 4% mass-load can be deployed without apparent harm on some avian soaring species, but impacts should be properly evaluated on a case-by-case basis. Resilient species for which impacts seem weak could be used as early warning systems for trials of new devices: if impacts are observed, they are likely to be even greater on more vulnerable species. Finally, individual fatalities caused by marking should be taken into serious account, but comprehensively evaluated in the light of broader population-level impacts. Future initiatives to minimize tagging impacts could include more stringent licensing criteria enforcing attendance at training courses or incorporation of impact evaluations into study designs, increased availability of training courses for tagging, and enhanced sharing of information through blogs, workshops or specialized journal sections.

Diet of bottlenose dolphins (Tursiops truncatus) from the Gulf of Cadiz: Insights from stomach content and stable isotope analyses

The ecological role of species can vary among populations depending on local and regional differences in diet. This is particularly true for top predators such as the bottlenose dolphin (Tursiops truncatus), which exhibits a highly varied diet throughout its distribution range. Local dietary assessments are therefore critical to fully understand the role of this species within marine ecosystems, as well as its interaction with important ecosystem services such as fisheries. Here, we combined stomach content analyses (SCA) and stable isotope analyses (SIA) to describe bottlenose dolphins diet in the Gulf of Cadiz (North Atlantic Ocean). Prey items identified using SCA included European conger (Conger conger) and European hake (Merluccius merluccius) as the most important ingested prey. However, mass-balance isotopic mixing model (MixSIAR), using δ13C and δ15N, indicated that the assimilated diet consisted mainly on Sparidae species (e.g. seabream, Diplodus annularis and D. bellottii, rubberlip grunt, Plectorhinchus mediterraneus, and common pandora, Pagellus erythrinus) and a mixture of other species including European hake, mackerels (Scomber colias, S. japonicus and S. scombrus), European conger, red bandfish (Cepola macrophthalma) and European pilchard (Sardina pilchardus). These contrasting results highlight differences in the temporal and taxonomic resolution of each approach, but also point to potential differences between ingested (SCA) and assimilated (SIA) diets. Both approaches provide different insights, e.g. determination of consumed fish biomass for the management of fish stocks (SCA) or identification of important assimilated prey species to the consumer (SIA).

Cetaceans of the Moroccan coast: information from a reconstructed strandings database

Cetaceans of Morocco have been poorly studied to date, and only sporadic information comes from scientific cruises for this group. In an attempt to learn more on the occurrence, distribution and relative abundances of cetaceans in Morocco, a stranding database was reconstructed from various sources (stranding reports from state agencies and newspaper clippings). This inventory documented 205 cases of stranding between 1980 and 2009. Most of the strandings and most confirmed cases of interactions with human activity (fishing, for dolphins; collisions, for whales) were reported in the Strait of Gibraltar and adjacent areas from the Atlantic and the Mediterranean. Sixteen species were identified from the stranding database, of which seven species were the most abundant. These were striped dolphins, common dolphins, bottlenose dolphins, fin whales, sei whales, sperm whales and long-finned pilot whales. The fin and sei whales were present throughout the year and stranding of common and striped dolphins were minimal between September and December. The fin, sei and sperm whales seem to be present in Moroccan waters at birth and at different stages of their life cycle. Establishing an observation network of sufficient and sustainable density in Morocco is the most likely way to collect robust data for the calculation of credible population indicators for cetaceans. Monitoring will certainly improve through better collaboration among Moroccan institutions and a greater awareness in Moroccan civil society of environmental issues.

Migration by breeders and floaters of a long-lived raptor: implications for recruitment and territory quality

Animal migration is receiving increasing research attention through ever more sophisticated tracking technologies, but the difficulty of trapping nonbreeding floaters has prevented comprehensive tracking studies of how migration varies in young breeders and floaters and whether this has consequences for recruitment (i.e. the transition from floating to breeding). To fill this gap, we satellite-GPS tracked young black kites, Milvus migrans , which start to breed when 1–7 years old. In the prebreeding migration, floaters departed and arrived later than breeders, travelled faster with fewer days at stopovers, as if in a hurry, and suffered more from cross-winds. Survival, recruitment, the territory quality and offspring production of the first reproductive attempt, as well as eventual longevity, declined rapidly with small departure delays. The high payoffs for small gains in timing set young kites on a race for early arrival: individuals improved their departure through early life and late migrants were progressively removed from the population or lingered as old floaters. As a result, individual improvements and selective mortality caused each cohort to progressively split after 3 years of age between a vanishing tail of late floaters and a body of early travelling individuals that then shaped the migratory traits of the adult population. Thus, migration in early life acted as a demographic bottleneck that filtered the transition to the next stage of the life cycle through a carryover effect that linked events operating on different continents.