Occurrence and diet of killer whales in northern Norway: seasonal patterns relative to the distribution and abundance of Norwegian spring-spawning herring

Abstract

Our objectives were to investigate the seasonal occurrence of photoidentified killer whale pods in relation to the distribution of Norwegian spring-spawning herring and whether or not pod-specific differences in the occurrence or diet of killer whales could be demonstrated. In a 4-year study, the killer whales occurred in different areas during the summer and the fall-winter, and these areas coincided with the distribution areas of herring. Killer whales were encountered most frequently during October-January when the whole adult and part of the adolescent stock of spring-spawning herring wintered in the study area. Thirty-nine killer whale pods were identified, and generally the same pods were encountered each year of the study. Differences in the timing and areas of occurrence of pods could be demonstrated. Adult and adolescent herring seemed to be the main prey of the killer whales during both fall-winter and summer. Six new species were added to the list of known prey species of Norwegian killer whales. The present pattern of seasonal occurrence of killer whales in the coastal waters of northern Norway is expected to change as a result of growth in the Norwegian spring-spawning herring stock. Résumé : Nous avions comme objectifs d'étudier l'apparition saisonnière de groupes d'épaulards photo-identifiés relativement à la distribution des harengs norvégiens se reproduisant au printemps, et de déterminer s'il y avait des différences spécifiques aux groupes dans le nombre ou le régime alimentaire des épaulards. Lors d'une étude de 4 ans, les épaulards ont été observés à différents endroits à l'été et pendant la période automne-hiver, et ces endroits correspondaient à l'aire de distribution des harengs. On observait surtout des épaulards durant la période allant d'octobre à janvier lorsque la totalité du stock d'adultes et qu'une partie du stock des adolescents de harengs se reproduisant au printemps passaient l'hiver dans l'aire d'étude. Trente-neuf groupes d'épaulards ont été dénombrés, et ce sont surtout les mêmes groupes qui étaient observés chaque année de l'étude. On a fait état de différences dans les moments et les endroits où les groupes étaient observés. Les harengs adultes et adolescents semblaient constituer la principale proie des épaulards, tant pendant la période automne-hiver qu'à l'été. Six nouvelles espèces ont été ajoutées à la liste des proies connues des épaulards norvégiens. La distribution actuelle des épaulards dans les eaux côtières du nord de la Norvège changera, prévoit-on, à la suite de la croissance du stock de harengs norvégiens se reproduisant au printemps. [Traduit par la Rédaction]

Recent changes in distribution and relative abundance of cetaceans in the Norwegian Sea and their relationship with potential prey

“…A recent study on offshore-feeding killer whales (Orcinus orca) in this system found that they mainly targeted northeast Atlantic mackerel (Scomber scombrus) (Nøttestad et al, 2014b). This was in contrast to the earlier perception that their main prey was the Norwegian spring-spawning (NSS) herring (Clupea harengus) (Sigurjónsson et al, 1988;Similä et al, 1996;Simon et al, 2006). This has been the case at least for the more coastal areas, but no such focused large scale study prior to Nøttestad et al (2014b) had given attention to the offshore areas of this highly productive marine ecosystem.…”

Sex-Specific Patterns in Abundance, Temporary Emigration and Survival of Indo-Pacific Bottlenose Dolphins (Tursiops aduncus) in Coastal and Estuarine Waters

“…Consistent with T. truncatus studies in the USA, similar movements out of study areas occur in winter, most likely in response to fluctuations in prey availability (e.g., Maze and Würsig, 1999;Fazioli et al, 2006;Speakman et al, 2010). Elsewhere, seasonal dolphin movement patterns are also typically linked to prey availability (e.g., Similä et al, 1996;Degrati et al, 2012Degrati et al, , 2013. In Bunbury, "potential dolphin prey" in the Leschenault Estuary, Koombana Bay, and near-shore coastal waters has been studied for seasonal abundance, biomass and calorific content (McCluskey et al, accepted).…”

Meta-ecosystems and biological energy transport from ocean to coast: the ecological importance of herring migration

“…by killer whales Orcinus orca aggregating in the fjords hosting the population of NSS herring during autumn and early winter (Simila et al 1996). NSS herring have used these fjords for overwintering since the mid 1980 s (Holst et al 2002) and with the whales, tourism and whale-safaris have become more important for the region.…”

“…The larvae drift northwards with the Norwegian Coastal Current and immature NSS herring spend the first 3-4 years in the Barents Sea. Adults, eggs and larvae of NSS herring are important food for many species at the coast (Durant et al 2003;Høines and Bergstad 1999;Simila et al 1996;Toresen 1991), and immature NSS herring are important prey in the Barents Sea (Bogstad et al 2000).…”