Eve Jourdain

Richard Karoliussen

Jacques Vos

Christelle Stanislav Zakharov

Killer whales (Orcinus orca) feeding on lumpfish (Cyclopterus lumpus) in northern Norway

Keywords: Killer whale, Orcinus orca, Foraging, Feeding behavior, Foraging strategy, Seasonality, Site-47 fidelity 48 49 50 51 52

à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Killer whales (Orcinus orca) feeding on lumpfish (Cyclopterus lumpus) in northern Norway 1 E. Jourdain 1* , R. Karoliussen 1 , J. de Vos 1 , S. E. Zakharov 1 , C. The killer whale (Orcinus orca) is found in all the world's oceans and as a species is 54 generalist, with a wide range of prey documented including fish, marine mammals, 55 cephalopods, reptiles and seabirds [START_REF] Ford | Killer whales Orcinus orca[END_REF]. However, populations have been shown to be 56 prey specialists. For example, in the temperate coastal northeastern Pacific, killer whales feed 57 exclusively on either marine mammals or fish (e.g., [START_REF] Baird | Occurrence and behaviour of transient killer whales: 414 seasonal and pod-specific variability, foraging behaviour, and prey handling[END_REF][START_REF] Ford | Dietary specialization in two sympatric populations of killer whales (Orcinus orca) in Coastal British Columbia and adjacent waters[END_REF], 58 Ford and Ellis 2006). Such prey specialization, including underlying foraging behavior and 59 knowledge about particular prolific feeding areas, are culturally transmitted in the form of 60 learned behavior within groups and persist over time [START_REF] Ford | Dietary specialization in two sympatric populations of killer whales (Orcinus orca) in Coastal British Columbia and adjacent waters[END_REF][START_REF] Riesch | Cultural 528 traditions and the evolution of reproductive isolation: ecological speciation in killer 529 whales?[END_REF]. 61

Resulting ecological and cultural divergences among social groups promote the formation of 62 sympatric socially and genetically isolated ecotypes (Ford andEllis 2014, Foote et al. 2016). 63 Divergent foraging strategies, by creating differences in occurrence and movement patterns as 64 well as social organization, may further play a role in population structuring (Hoelzel et al. 65 2007[START_REF] Morin | Complete mitochondrial genome 507 phylogeographic analysis of killer whales (Orcinus orca) indicates multiple species[END_REF][START_REF] Parsons | Geographic patterns of genetic 523 differentiation among killer whales in the Northern North Pacific[END_REF]. 66 67

In the North Atlantic, two ecotypes of killer whales were proposed based on dietary 68 specialization, Type 1 and Type 2, with nitrogen stable isotope values and tooth wear used as 69 proxies to indicate key prey choice for each type (Foote et al. 2009[START_REF] Foote | Dietary variation within and 453 between populations of Northeast Atlantic killer whales, Orcinus orca, inferred from 454 δ13C and δ15N analyses[END_REF]. Type 1 refers to 70 killer whales from Iceland, Norway, and the North Sea, which rely on the Atlantic herring 71 (Clupea harengus) and/or the Atlantic mackerel (Scomber scombrus) as their main food 72 source(s). In contrast, Type 2 primarily feeds on other cetaceans. However, this simplistic 73 classification seems unlikely to encapsulate the broad-scale diversity of the diet of North 74 Atlantic killer whales. In fact, there is strong evidence for inter-individual variation in the relative proportions of prey types consumed within Type 1 killer whales. For example, some 76 may also prey on pinnipeds, as evidenced by field observations [START_REF] Foote | Movement, site fidelity and 450 connectivity in a top marine predator, the killer whale[END_REF], Vongraven 77 and Bisther 2014, Jourdain et al. 2017[START_REF] Samarra | Prey of killer whales (Orcinus orca) in 531 Iceland[END_REF]). As such, different feeding 78 specializations may exist within populations. Recent studies using ecological tracers were 79 further supportive of inter-individual variation in dietary habits among regions (e.g., Faroe 80

Islands/Denmark vs Greenland; [START_REF] Bourque | Feeding habits of a new Arctic predator: insight 426 from full-depth blubber fatty acid signatures of Greenland, Faroe Islands, Denmark, 427 and managed-care killer whales Orcinus orca[END_REF], within regions [START_REF] Samarra | Intra-population variation 535 in isotopic niche in herring-eating killer whales off Iceland[END_REF], 81 and within social groups (in Greenland, see [START_REF] Bourque | Feeding habits of a new Arctic predator: insight 426 from full-depth blubber fatty acid signatures of Greenland, Faroe Islands, Denmark, 427 and managed-care killer whales Orcinus orca[END_REF]. However, the lack of killer 82 whale identification data and predation records for most regions has impeded our 83 understanding of fine-scale seasonal and/or group-specific prey specializations so far. The 84 potential occurrence of variable foraging strategies and dependence on main and alternative 85 prey resources remains to be investigated further in the North Atlantic. 86 87 Between 1986 and 2005, Norwegian killer whale studies were mainly focused on 88 wintering grounds of the Norwegian Spring Spawning (NSS) stock of the Atlantic herring. At 89 that time these grounds were located in a fjord system (Vestfjord-Ofotfjord-Tysfjord) in the 90 Lofoten region, northern Norway (68°13'N, 15°37'E). Research efforts were focused on 91 photographic identification and investigation of feeding behavior, occurrence patterns, social 92 ecology, and acoustics [START_REF] Similä | Surface and underwater observations of cooperatively feeding 546 killer whales in Northern Norway[END_REF][START_REF] Similä | Occurrence and diet of killer whales in 542 Northern Norway: seasonal patterns relative to the distribution and abundance of 543 Norwegian Spring-Spawning Herring[END_REF][START_REF] Similä | Sonar observations of killer whales (Orcinus orca) feeding on herring 540 schools[END_REF], Domenici et 93 al. 2000[START_REF] Van Parijs | Sounds produced by Norwegian killer 556 whales, Orcinus orca, during capture[END_REF][START_REF] Van Opzeeland | 553 Acoustic behaviour of Norwegian killer whales, Orcinus orca, during carousel and 554 seiner foraging on Spring-Spawning Herring[END_REF]. These studies highlighted killer 94 whales as efficient herring predators using specialized feeding strategies (e.g., Similä and 95 Ugarte 1993). Photo-identification surveys conducted on both wintering and spawning 96 grounds of the NSS herring, combined with satellite tracking of six individual whales tagged 97 in 2000 and 2001, further suggested that some groups may follow the herring's movements for 98 most of the year (Bisther and Vongraven 1995[START_REF] Similä | Occurrence and diet of killer whales in 542 Northern Norway: seasonal patterns relative to the distribution and abundance of 543 Norwegian Spring-Spawning Herring[END_REF], Stenersen and Similä 99 2004), though effective herring-foraging offshore remained largely inconclusive. As a result, and due to lack of evidence for additional prey items, herring has been regarded as the main 101 prey for killer whales in Norwegian waters. This conclusion was further supported by a lack 102 of intra-population variation in stable isotope values from skin samples collected from whales 103 in the NSS wintering grounds [START_REF] Foote | Dietary variation within and 453 between populations of Northeast Atlantic killer whales, Orcinus orca, inferred from 454 δ13C and δ15N analyses[END_REF] Huse et al. 2010, Jourdain andVongraven 2017). From mid-January to mid-February, the 117 herring migrate to the main spawning area located 800-1,000 km south, off the central coast 118 of Norway [START_REF] Dragesund | Variation in migration and abundance of morphological and genetic divergence of sympatric North Atlantic killer whale 448 populations[END_REF], leading to the departure of the winter aggregating killer whales. 119

Research efforts yet maintained throughout the rest of the year in the study area aimed at 120 collecting photo-identification data and predation records. 121 122 Here, we report on a subset of known herring-feeding killer whales showing site-fidelity 123 in a northern Norwegian fjord in spring (March-April), after the herring has departed, for the 124 period 2014-2018. Behavior and predation records were collected over multiple years in order to assess foraging as a predominant function for seasonal use of the area in spring, and to 126 identify the target prey. Group cohesion was investigated with reference to the focal prey and 127 group sizes were compared to winter observations for insights into behavioral adaptations and 128 therefore, indication of seasonal prey switching and specialization for these whales. Beaufort scale 4 or less. We defined an encounter as a sighting of a group of killer whales. A 146 group was defined as all individuals observed in apparent association, acting in a coordinated 147 manner during the observation period and which were within the visual range of the observers 148 (as per [START_REF] Baird | Occurrence and behaviour of transient killer whales: 414 seasonal and pod-specific variability, foraging behaviour, and prey handling[END_REF]. For each encounter, the geographic position (GPS Garmin) was 149 recorded and the whales were systematically photographed using a digital reflex camera and a estimate and cohesion index (see below) were also recorded at five-minute intervals for the 152 majority of surveys. Surveys terminated when the group was lost from sight, travelled away 153 from the study site, or if light and/or sea conditions deteriorated. for the period 2014-2017. Behavior and CI were recorded for 62 h from 48 encounters. 251 Molecular (n=11) and photographic (n=11) evidence enabled positive identification of prey 252 species for 22 predation events from 11 encounter days in 2016-2018. For the period 2014-253 2018, photographs resulted in 276 identifications of 75 distinctively marked individuals (Fig. 254 2). The number of identified individuals per season varied from a minimum of six (in 2014) to 255 a maximum of 42 (in 2018), with a mean of 27 (standard deviation SD=13.3). Poor weather 256 conditions in 2015 and 2017 resulted in lower numbers of encounter days and identifications 257 for these years. Sampling effort is summarized in Table 1. 258 259

Characterization of individual killer whales 260

The 75 identified individuals represent 7.7% of the 971 killer whales identified in the 261 study area [START_REF] Jourdain | Identification catalogue of Norwegian killer whales[END_REF]. Of these, 34 (45.3%) were adult males, 21 (28%) 262 were adult females and 20 (26.7%) were of unknown sex; 61 (81.3%) were encountered at 263 herring wintering grounds on one or multiple years between 2013 and 2018 (unpublished 264 data). Social associations appeared highly variable across encounters, and thus we considered 265 individuals independently. Plotting the cumulative number of newly identified individuals in 266 the period March-April from 2014 to 2018 revealed a steadily decreasing identification rate, 267 suggesting that most distinctive whales using Andfjord in spring had been identified during 268 the study (Fig. 2). 269 270

Sighting frequencies 271

Of 75 individuals, 20 (26.7%) were sighted only once, while 55 (73.3%) were sighted 272 during two or more encounters in March-April from 2014 to 2018. Of these, 40 were seen in 273 multiple years (range=2-4; Fig. 3). Averaging all five spring seasons, individuals were sighted during a mean of 1.8 seasons (SD=0.9; range=1-4) and on 3.7 d (SD=2.7; range=1-12). For 275 individuals sighted on a minimum of two encounter days within each spring season (Fig. 3), 276 mean (minimum) residency varied from 8.3 d (in 2015) to 16 d (in 2018) leading to a mean of 277 11.3 d (SD=6.2; range=2-39; Table 2) throughout the study period. 278 279

Behavioral patterns 280

Foraging (70.3%) and traveling (23.9%) represented the most frequently observed 281 behavioral states, while milling, resting, and socializing accounted for less than 6% of the 282 observations. Group cohesion varied with behavior (X 2 =3,940; df=4; P<0.001). Individuals 283 adopted a tighter group formation when travelling as opposed to scattered over several 284 hundred meters and up to 1 km when foraging. Groups encountered were significantly smaller 285 (Mann-Whitney-Wilcoxon: W=297, P=0.001) in spring (median=8, range=1-30, n=49) than 286 in winter (median=14, range=1-40, n=23; Fig. 4). 287 288

Prey identification 289

Prey fragments from all 11 predation events sampled were identified to be from lumpfish 290 (Cyclopterus lumpus; Table 3). The alignment of the COI fragment was 587 nucleotides long. 291

From the 11 sequences obtained for molecular identification, all BLAST queries resulted in 292 the identification of the lumpfish with 99% to 100% of similarity with the sequence 293 JN311799 [START_REF] Knebelsberger | A reliable DNA barcode reference 492 library for the identification of the North European shelf fish fauna[END_REF]. The new sequences were deposited in GenBank under 294 the accession numbers MF688049 and MH922998-MH923009. 295

Photo and aerial video material enabled unambiguous identification of the lumpfish as the 296 consumed prey for seven and four additional predation events, respectively (Fig. 5, Table 3). 297

Thirteen individual killer whales were confirmed feeding on lumpfish from these 22 predation 298 events, of which five were adult males, three were adult females and five were of unknown sex including three sub-adults (Table 3). Five individuals (NKW-0004, NKW-0572, NKW-300 0712, NKW-0715 and Y093) fed on lumpfish on multiple occasions (range=2-4) during the 301 same encounter. Adult male NKW-0004 was further confirmed to be feeding on lumpfish 302 over two different days, five days apart, in April 2018. 303 304 305 Discussion 306

We have shown that a subset of killer whales seasonally visited Andfjord in March-April 307 of 2014-2018 and remained in the area for several days and up to several weeks. Most of 308 these whales were also encountered at herring wintering grounds in the same years. This 309 further supports the idea that killer whales make adaptive seasonal movements in response to 310 spatial and temporal changes in prey availability in this region [START_REF] Similä | Occurrence and diet of killer whales in 542 Northern Norway: seasonal patterns relative to the distribution and abundance of 543 Norwegian Spring-Spawning Herring[END_REF]. Marked 311 seasonality and predominance of foraging in spring suggests the use of a seasonally reliable 312 food source. All 22 predation events where the prey was identified revealed lumpfish to be the 313 target prey species in March and April. 314 315 The lumpfish is widely distributed throughout the Norwegian Sea [START_REF] Holst | Observations on the distribution of lumpsucker (Cyclopterus Lumpus, L.) in 479 the Norwegian Sea[END_REF]. It 316 remains offshore often at abyssal depths most of the year and migrates to coastal breeding 317 areas from April to July [START_REF] Davenport | Synopsis of biological data on the lumpsucker[END_REF]. Due to dorsal muscles allowing only limited 318 locomotory abilities [START_REF] Davenport | Buoyancy in the lumpsucker Cyclopterus lumpus[END_REF], the lumpfish travels at low swimming 319 speeds (i.e., 0.72 km/h in [START_REF] Mitamura | Movements of lumpsucker females in a 504 Northern Norwegian fjord during the spawning season[END_REF]. Spawning male and female lumpfish are 320 about 28-30 and 40-45 cm in length, respectively [START_REF] Albert | 411 Age-reading of lumpsucker (Cyclopterus lumpus) otoliths: dissection, interpretation 412 and comparison with length frequencies[END_REF]. Spent females may 321 complete spawning over a period of a few weeks and then return to the open ocean, or 322 alternatively may visit adjacent fjords to lay eggs at multiple locations [START_REF] Goulet | Courtship, spawning, and parental care 473 behavior of the lumpfish, Cyclopterus lumpus L., in Newfoundland[END_REF][START_REF] Davenport | Synopsis of biological data on the lumpsucker[END_REF]. These movement patterns suggest seasonal increased availability of the 325 lumpfish nearshore in spring, as supported by exclusive seasonal fishery from April through 326 mid-June for this species [START_REF] Bertelsen | Bestandsutvikling og bestandsstruktur hos rognkjeks og rognkall 417 (Cyclopterus lumpus L.) i Sifjorden i Troms, og maskeseleksjon og fangsteffektivitet 418 ved garn-og rusefiske etter arten. Fiskerikandidatoppgave[END_REF]. 327

328

To the best of our knowledge, the lumpfish has not hitherto been reported as a prey 329 species of Norwegian killer whales, despite previous analysis of 95 stomach contents 330 [START_REF] Christensen | Killer whales in Norwegian coastal waters[END_REF] and observational studies (e.g., [START_REF] Similä | Sonar observations of killer whales (Orcinus orca) feeding on herring 540 schools[END_REF]Ugarte 1993, Similä et al. 331 1996). However, the lumpfish was listed as prey of killer whales off West Greenland where 332 stomachs of 30 harvested killer whales contained only lumpfish [START_REF] Laidre | Reactions of narwhals, Monodon 501 monoceros, to killer whale, Orcinus orca, attacks in the Eastern Canadian Arctic[END_REF], and off 333

Iceland from sporadic predation records [START_REF] Samarra | Prey of killer whales (Orcinus orca) in 531 Iceland[END_REF]. Our results list the lumpfish as 334 prey for killer whales in an additional region of the North Atlantic. Lumpfish repeatedly 335 recorded as prey within single season (n=16 records in 2018) and across years (2016-2018; 336 Fig. 5, Table 3) in this study suggests consistency of this seasonal dietary pattern, likely in 337 response to the increased availability of lumpfish when migrating horizontally towards 338 spawning areas. 339 340 In spring, not only were encountered killer whales and predation records consistent 341 across seasons, but observed foraging behavior was in striking contrast to cooperative herring 342 feeding strategies observed from November to February in the same region (Jourdain and 343 Vongraven 2017). When feeding on herring, killer whales aggregate in a tight group 344 formation for coordinated school-herding, prior to slapping the fish with the underside of their 345 flukes and then individually consuming stunned fish [START_REF] Similä | Sonar observations of killer whales (Orcinus orca) feeding on herring 540 schools[END_REF]Ugarte 1993, Similä 1997). 346

Similar hunting behavior of killer whales feeding on schooling mackerel in the Norwegian 347 Sea in July-August has also been observed [START_REF] Nøttestad | Prey selection of offshore killer whales 517 Orcinus orca in the Northeast Atlantic in late summer: spatial associations with 518 mackerel[END_REF]. In contrast, killer whales 348 foraging on solitary lumpfish [START_REF] Davenport | Synopsis of biological data on the lumpsucker[END_REF] were spread over several hundred meters and more similar to that of killer whales feeding on loose patches of Atlantic salmon in the 351 Lofoten region, Norway [START_REF] Vester | First record of killer whales (Orcinus orca) feeding 559 on Atlantic salmon (Salmo salar) in Northern Norway suggest a multi-prey feeding 560 type[END_REF]. This is in further support of 352 killer whales adapting feeding strategies to behavioral traits of target prey (e.g., Similä and 353 Ugarte 1993[START_REF] Baird | Occurrence and behaviour of transient killer whales: 414 seasonal and pod-specific variability, foraging behaviour, and prey handling[END_REF][START_REF] Samarra | Prey-induced behavioural plasticity of herring-533 eating killer whales[END_REF]. Lumpfish-feeding killer whales 354 also adopted smaller group sizes in spring than when observed at herring wintering grounds 355 (Fig. 4). By maximizing energetic gain, smaller groups could be adaptive to foraging on a 356 scattered prey resource as opposed to highly concentrated wintering herring where a more 357 cooperative foraging strategy is required (Nøttestad andAxelsen 1999, Nøttestad et al. 2002). 358

Our results bring the first robust evidence, featuring individual records of site-fidelity, 359 behavior and predation over several years, for seasonal adaptation and switching between 360 alternative prey resources in Norwegian waters. 361 362

The NSS herring is found in most dense aggregations on its wintering grounds, compared 363 to lower densities due to looser schools on spawning and feeding grounds (Nøttestad et al. 364 1996). The NSS herring is also subject to important changes in fat content throughout its life 365 cycle with the highest rate of energy depletion occurring during the spawning migration. As 366 such, herring fat content is about 22% when entering the wintering area in September and is 367 reduced to eight to 10% after spawning in February-April [START_REF] Slotte | Differential utilisation of energy during wintering and spawning migration in 548 Norwegian Spring-Spawning Herring[END_REF]. As herring both loses 368 fat content and becomes more dispersed in spring, lumpfish with fat content ranging from 369 >8% for gravid females to 20% for males [START_REF] Davenport | Buoyancy in the lumpsucker Cyclopterus lumpus[END_REF] enters the coastal 370 waters to spawn. Some killer whale groups may have diversified their diet and be able to 371 switch to foraging on this alternative, seasonally abundant and apparently relatively 372 nutritious, prey. 373

Our results showed that at least 75 different killer whales have adapted to the seasonality 375 of spawning lumpfish in Andfjord, returning year after year for temporary residence and 376 foraging (Fig. 2 and3, Table 2). This represents 7.7 % of the total number of marked 377 individuals identified in the study area between 2007 and 2018 (Jourdain and Karoliussen 378 2018). This number should be considered as a baseline minimum since it does not include 379 unmarked individuals and calves also observed feeding on lumpfish during this study. 380

Additionally, because this study was entirely based on opportunistic efforts and covered a 381 relatively small area, and because killer whales may temporarily travel away from feeding 382 sites or display group-specific preferences in habitat use, individuals or entire groups may 383 have been undetected [START_REF] Kuningas | Population size, survival and reproductive 498 rates of Northern Norwegian killer whales (Orcinus orca) in 1986-2003[END_REF]. While the lumpfish is a common species along 384 the Norwegian coast with spawning grounds found in multiple regions [START_REF] Davenport | Synopsis of biological data on the lumpsucker[END_REF], 385 Holst 1993) it could very well be part of the diet of killer whales elsewhere and this feeding 386 behavior could be important at the population level. 387 388 Although the NSS herring has long been assumed to be the main prey of killer whales in 389 Norway, recent year-round data collection efforts uncovered persistent dietary specializations 390 on pinnipeds (Jourdain et al. 2017) and on lumpfish (present study) in northern Norway. This 391 highlights the likelihood that killer whale research conducted on a seasonal basis can miss 392

  Data were collected in March -April of 2015 -2018 east of Andøya (Andfjord, 69°19'N, 134 16°08'E; Fig. 1), in Vesterålen region, northern Norway. Because killer whale presence was 135 not known to be regular in the study area at this specific time of year, surveys were largely 136 opportunistic, and effort varied considerably across years. In 2015, surveys were always 137 conducted in response to sightings being reported by locals. In the following years, and based 138 on the 2015 sighting records, land-based watches searched for killer whales on good weather 139 days, as did opportunistic boat surveys, in addition to relying on sighting reports. 140 Supplementary photographs of individual killer whales within the study area with associated 141 date and time data were provided by local wildlife photographers for April-March of 2014-142 2017, and those of high enough quality were accepted for use in the analyses. 143 144 Surveys were conducted on a 20-foot-long aluminum research vessel in sea conditions of 145

154 155

 154 Behavior was divided into five categories (adapted from Ford 1989): (1) Foraging -156 erratic swimming in varying directions, sudden lunges and high-speed swimming, presence of 157 prey fragments and seabirds; (2) Travelling -consistent movement with all group members, 158 in a tight group formation, following the same course at the same speed, while displaying 159 synchronous dives and surfacings; (3) Milling -low speed movement with individuals 160 engaged in frequent changes in direction leading to no directional movement by the group; (4) 161 Resting -low level activity with individuals being stationary lined-up and floating motionless 162 at the surface while displaying coordinated breathings; (5) Socializing -high energy activity 163 in which individuals may physically interact with one another and/or perform aerial displays 164 such as leaps, tail slaps, and spy-hops (defined as vertical half-rise of the body out of the 165 water). Activities displayed by the majority of the whales was considered as the main 166 behavioral pattern for the group. 167 168 Spatial cohesion of the group, often variable throughout encounters, was characterized 169 using a cohesion index (CI) (adapted from Daura-Jorge et al. 2005). Within a group, 170 individuals scattered over distances (visually assessed) greater than 200 m were classified as 171 low cohesion (CI=1), individuals occupying a 60 to 200 m area were classified as 172 intermediate cohesion (CI=2) and individuals aggregated within 50 m were classified as high 173 cohesion (CI=3). Smaller sub-groups, often composed of adult female(s) with offspring, were throughout the study, reducing potential observer-related bias. 176 177 From 2016 onwards, collection of tissue fragments from prey killed and consumed by 178 killer whales was also attempted. Based on the methods developed by Ford et al. (1998), we 179 used speed bursts, directional chases, fast and sharp turns, and head nodding-movements of 180 surfacing whales along with scavenging seabirds as clues to feeding events. Upon detection of 181 such events, the research vessel slowly approached the focal whale, stopped in the fluke print 182 (glassy area visible at the surface as the whale dives and its tail creates an upwelling, as 183 defined by Ford and Ellis 2006) and observers assessed potential presence of prey remains in 184 the water column. Using a long-handled (3 m) fine-mesh net, one observer onboard collected 185 any accessible prey fragments. Because collection was challenged by fast-sinking prey parts 186 and common rough sea state, a professional free-diver assisted in collection of prey remains 187 in April 2018. Upon collection, fragments were placed in a plastic bag and stored in a cooling 188 box while in the field. Ashore, fragments were stored in 1.5 mL vials containing 95% ethanol 189 at -20°C until analysis. 190 191 Whenever a focal whale was observed feeding at close range to the vessel, photographs 192 were also taken in an attempt to visually-identify target prey species. An unmanned aircraft 193 DJI Phantom IV carrying a DJI 1/2.3''CMOS camera was used on three days in 2018 to 194 capture still images and video footage of prey capture events. 195 196 Data processing 197 Killer whales were individually identified based on location and number of notches in the 198 leading and/or trailing edge of the dorsal fin, along with pigmentation pattern of and natural markings occurring on the saddle patch (Bigg 1982). Only individuals displaying one or 200 several unique features were considered as distinctive and effectively catalogued. Calves and 201 other individuals lacking persistent identifying markings were excluded. Individuals with 202 distinctly taller dorsal fins were classified as 'Male' (Olesiuk et al. 1990), adult female-sized 203 individuals repeatedly seen with one calf or older offspring(s) swimming in echelon position 204 throughout the study period were qualified as 'Female' and individuals for which sex was 205 uncertain were qualified as 'Unknown'. Photographs were scored for quality (0 < Q < 2) 206 based upon sharpness, contrast and angle. To minimize misidentification, only excellent 207 quality (Q2) photographic records of distinctive catalogued killer whales were considered in 208 this study. Both left and right-side identification photos were used for ID, but only whales 209 catalogued from the left side were retained for analysis. 210 211Data analysis 212Sighting and behavioral patterns 213To assess site-fidelity patterns, individual sighting records were compared across days 214 and years. Despite sampling biases due to uneven effort throughout seasons and across years, 215 we considered minimum residency to be informative of individuals' site-fidelity periods 216 within seasons. Therefore, the number of days elapsed from the first to the last sighting within 217 each season was calculated for each individual, as compared to the total length of survey 218 period for each given season (as per[START_REF] Weinrich | A shift in distribution 565 of humpback whales, Megaptera novaeangliae, in response to prey in the southern 566 Gulf of Maine[END_REF]. Mean residency values were 219 calculated across individuals per season, excluding individuals not seen, and averaged for the 220 entire study period. 221 222 To investigate seasonal usage of the study area, relative predominance of observed 223 behavioral states was calculated. Further seasonal behavioral characteristics, assumed to be relationship between behavior and cohesion index (CI). Due to low occurrence, records of 226 resting and socializing behaviors were not included in the test. Records of group size 227 collected for this study were compared to group sizes recorded at herring wintering grounds 228 for these same whales in 2015-2018 (S1) using a Mann-Whitney-Wilcoxon test. Statistical 229 tests were performed in R software (R Core Team 2016). 230 231 Molecular and visual prey identification 232 Molecular analyses were conducted on prey tissue samples for identification of target 233 species. Total DNA from 11 samples was extracted from ethanol-preserved samples following 234 standard procedures (Sambrook et al. 1989). A fragment of the cytochrome c oxidase I gene 235 (COI) was PCR-amplified using the GoTaq® G2 Hot Start Colorless Master Mix (Promega) 236 and the primers Pros1Fwd and Pros2Rev (Sparks and Smith 2004) with an annealing step at 237 46°C. Direct sequencing was carried out in both directions at the technical facilities of the 238 Genotyping and Sequencing Platform of the 'Institut des Sciences de l'Evolution de 239Montpellier' (ISEM). Sequences were then aligned in MEGA v7[START_REF] Kumar | MEGA7: Molecular evolutionary genetics 495 analysis version 7.0 for bigger datasets[END_REF] and 240 blasted (https://blast.ncbi.nlm.nih.gov/Blast.cgi) against sequences from the GenBank 241 database (https://www.ncbi.nlm.nih.gov/genbank/). Photographs and video footages of 242 predation events were scanned for visual identification of prey species. 2018, 42 d at sea in March-April resulted in 123.2 h spent with killer 248 whales and 14,170 photographs taken over 51 encounters from a dedicated research vessel.

Figure 1 .Figure 2 .Figure 4 .Figure 5 .

 1245 Figure 1. Location of the study area in northern Norway. Box A corresponds to Andfjord 570

  Figure 2 633

Table 1 .

 1 Sampling effort for the period March-April in 2014-2018 in Andfjord.

	617
		2014	2015	2016	2017	2018	Total
	Dedicated effort by researchers
	Effort days	0	7	11	6	20	44
	Encounter days	0	7	11	4	20	42
	Killer whale encounters	0	7	15	4	25	51
	Hours spent with whales	0	11.7	22.8	8.1	80.6	123.2
	Hours of behavioral sampling	0	6.0	13.7	4.3	38.0	62.0
	Photographs taken	0	2,480	5,080	990	5,620	14,170
	Predation events for which prey remains were collected	0	0	2	0	9	11
	Predation events for which prey were visually identified	0	0	2	2	7	11
	Additionnal photographic contributions
	Encounter days	1	0	3	7	0	11
	Photographs provided	300	0	127	1280	0	1707
	Total
	Encounter days	1	7	14	11	20	53

Table 2 .

 2 Summary of the parameters used to assess minimum residency of killer whales in Andfjord duringMarch-April in 2014-2018. 622 Calculated residency should be considered as minimum values due to opportunistic data collection.

	Identifications		6	41	70	40	119	276
	Distinct individuals		6	29	33	25	42	-
	623
		2014	2015	2016	2017		2018
	Number of encounter days	1	7	14	11		20
	First-to-last encounter period (d)	-	19	32	42		44
	Individuals resighted	-	9	21	8		26
	Residency mean ± SD (min-max)	-	8.3 ± 3.7 (2-14)	10.6 ± 4.8 (3-20)	10.3 ± 6.2 (4-16)	16 ± 10.3 (4-39)
	624
	625
	626

Table 3 .

 3 Summary of predation events for which evidence was collected for identification of the target prey. All resulted in identification of the 627

	628	lumpfish as prey species.
	629
		Events	Season (day/month)	Evidence	ID
		1, 2	2016 (30/4)	Prey fragments	NKW-0712
		3, 4	2016 (30/4)	Photographs	NKW-0712
		5, 6	2017 (12/4)	Photograph	NKW-0572
		7	2018 (5/4)	Prey fragments	NKW-0004
		8-10	2018 (9/4)	Prey fragments	NKW-0004
		11	2018 (9/4)	Photographs	NKW-0912
		12	2018 (11/4)	Photographs	NKW-0079
		13	2018 (12/4)	Prey fragments	NKW-0910
		14	2018 (13/4)	Aerial footage	Unidentified sub-adult
		15	2018 (13/4)	Aerial footage	NKW-0998
		16	2018 (14/4)	Aerial footage	NKW-0908
		17	2018 (15/4)	Aerial footage	Unidentified sub-adult

Norwegian Spring Spawning herring (Clupea harengus L.). Sarsia, 82:97-105.

Acknowledgements

below the surface prior to capture and consumption by adult male killer whale NKW-0572; 594 (B) Adult male killer whale NKW-0712 catching a lumpfish; (C) Adult female-sized killer 595 whale feeding on the carcass of a lumpfish; (D) A subadult killer whale consumed the inner 596 part of a lumpfish before discarding the carcass. 597