Arctic Cod (Boreogadus saida) as Prey: Fish Length-Energetics Relationships in the Beaufort Sea and Hudson Bay

Although Arctic cod (Boreogadus saida) is widely recognized as an important trophic link to top predators in Arctic marine ecosystems, the challenges of conducting fieldwork in the Arctic make this species difficult to study. We establish some basic relationships to improve prey energetics modeling when only in-field parameters (e.g., fork length) can be measured. We investigated the intraspecific relationships among energy density, fork length, mass, and water content for Arctic cod captured by Black Guillemots and Thick-billed Murres at two sites (Western Beaufort and Hudson Bay). Dry energy density was similar between sites (21.6 – 22.2 kJ g-1) and increased with fork length (Dry EDkJ/g = 0.028 (± 0.01) • Fork Lengthmm + 18.12 (± 1.33). Even though fish lost some water as they were transported to the nest by avian predators, wet energy density also increased with fork length. We suggest that environmental conditions had a similar effect on growth at these two locations although they occur in very different oceanographic regimes. Arctic cod, especially large cod, is one of the most energy-rich prey species in the Arctic. Our results highlight the importance of this valuable prey to Arctic ecosystems and the utility of using seabirds opportunistically as samplers of the marine environment.Même si la morue polaire (Boreogadus saida) est grandement reconnue comme un lien trophique important pour les prédateurs situés en bout de chaîne des écosystèmes marins de l’Arctique, cette espèce est difficile à étudier en raison des défis inhérents à la réalisation de travaux sur le terrain dans l’Arctique. Nous établissons des relations de base afin d’améliorer la modélisation de la valeur énergétique des proies lorsque seuls des paramètres sur le terrain (comme la longueur à la fourche) peuvent être mesurés. Nous avons étudié les relations intraspécifiques qui existent entre la densité d’énergie, la longueur à la fourche, la masse et la teneur en eau de la morue polaire capturée par le guillemot à miroir et le guillemot de Brünnich à deux sites (ouest de Beaufort et baie d’Hudson). La densité d’énergie sèche était semblable entre les sites (21,6 – 22,2 kJ g-1) et augmentait en fonction de la longueur à la fourche (DE sèche EDkJ/g = 0,028 (± 0,01) • longueur à la fourchemm + 18,12(± 1,33). Même si les poissons perdaient de l’eau pendant le transport jusqu’au nid par les oiseaux prédateurs, la densité d’énergie humide augmentait également en fonction de la longueur à la fourche. Nous suggérons que les conditions environnementales avaient un effet similaire sur la croissance à ces deux sites même s’ils se trouvent dans des régimes océanographiques très différents. La morue polaire, surtout celle de grande taille, est l’une des espèces proies les plus riches en énergie de l’Arctique. Nos résultats mettent en évidence l’importance de cette précieuse proie pour les écosystèmes de l’Arctique et l’utilité de se servir des oiseaux de mer de manière opportuniste en guise d’échantillonneurs de l’environnement marin

Central-place Foraging in an Arctic Seabird Provides Evidence for Storer-Ashmole's Halo

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Variability in foraging in response to changing prey distributions in rhinoceros auklets

Variable time budgets and foraging behaviour were observed in a marine diving bird, the rhinoceros auklet Cerorhinca monocerata, in response to intraseasonal and interannual variations in prey abundance and distribution. Few studies have simultaneously measured the spatial dispersal of seabirds at sea, time budgets at sea and prey abundance and distribution. Time budgets and foraging behaviour were determined through visual scans. Prey abundance, estimated hydroacoustically during marine transects, was similar among years, but prey was dispersed over larger spatial areas in 1997 than in 1995 and 1996. Rhinoceros auklets were also dispersed over larger spatial areas in 1997 and fewer mixed-species feeding flocks were formed. In 1997, rhinoceros auklets increased the time spent foraging, decreased the recovery periods between successive dives, and were more strongly associated with prey at larger spatial scales. This suggested that auklets were working hard while foraging but were less successful at locating and maintaining contact with prey when prey was more dispersed. In 1996, there was a period (June 13 to 20) when fish schools were common near the surface, during which auklets spent more time foraging and formed more feeding flocks. This suggested that auklets were working hard to take advantage of this readily available prey. This paper illustrates the importance of behavioural plasticity and time budget flexibility for seabirds living in highly variable environments

Signals from seabirds indicate changing biology of capelin stocks

Key forage species lie at the core of complex marine food webs, providing essential linkages among trophic levels. We examined the interactions of an important forage and commercial fish, capelin Mallotus villosus, and its primary avian predator, the common murre Uria aalge, in the NW Atlantic. Murres are capelin specialists and robust samplers of capelin biology. During the 1990s, the coldest surface-water event in the past 50 to 100 yr occurred in the NW Atlantic (1991), and the eastern Canadian ground-fishery was closed (1992). Concordantly, the biology and behaviour of capelin has undergone very substantial changes. We examined parental food deliveries and production at the world's largest common murre colony on Funk Island off the northeast coast of Newfoundland throughout the 1990s. Murres delayed breeding and delivered smaller and lower quality capelin to their chicks. These changes, corroborated with independent fisheries data, resulted in poor condition of murre chicks, indicating significant effects of changing capelin demographics at higher trophic levels. The diets of the murre chicks indicate that the composition of the capelin population has shifted from high size diversity to mainly smaller capelin. We hypothesize that this change resulted from the elimination of the larger-sized and earlier-spawning genotype and that the NW Atlantic capelin population is exhibiting signs of reduced reproductive potential that likely reflects lower spawning biomass

Predator-prey interactions of common murres (Uria aagle) and fish in the northwest Atlantic : foraging strategies on multiple scales

The Northwest Atlantic ecosystem is currently undergoing changes in species interactions and ocean climate. Capelin (Mallotus villosus ), the dominant forage fish in the ecosystem, is the main prey item of marine birds, mammals and piscivorous fish. In the 1990s, spawning capelin were small, spawned later, shifted their distribution southerly to non-traditional areas compared to historical accounts, and abundance estimates have varied widely. During these changes and divergent biomass estimates, this research was initiated. The focus of this thesis is the multi-scale behavioural interactions of marine predators and prey: a marine diving bird, the common murre ( Uria aalge ), and its main prey species, capelin. This study integrates both colony-based and vessel-based techniques. I showed that some aggregations of capelin are stable in space and time on a number of scales: fine- (1-100 m; minute-hour), coarse- (1-100 km; day-week) meso-scale (100-1000 km; annual), allowing murres to use memory to locate prey at sea during different periods during their annual cycle. Social foraging techniques appeared to be important on fine- and coarse-scales (local enhancement, network foraging) while no evidence was found for social foraging techniques over larger spatial scales (Information Center Hypothesis). Spatial scales at which murres tracked capelin were highly variable, as found in other studies examining predator-prey interactions of mobile organisms. The tracking scales of murres to capelin were smallest during the breeding (0.8-5.1 km) and pre-breeding periods (3.1-8 km), compared to post-breeding (6.0-50.0 km). This variability in spatial associations between predators and their prey was likely due to different energetic requirements, locomotory constraints and search strategies used among these periods. Inter-colony comparisons of provisioning behaviour by murres revealed low feeding rates of chicks at the largest murre colony in eastern Canada relative to a smaller colony, which resulted in the lowest average mass and condition of fledgling murres (191.6 ± 4.0 g) reported in the literature. Density-dependence, both while foraging at sea and rearing chicks at the colony, and prey distribution around the largest colony resulted in additional provisioning constraints relative to a smaller colony and divergent life history strategies at the two colonies. Poorer chick condition, and presumably lower recruitment, may have resulted in a lack of population growth at the larger colony, which contains 85% of the common murres in the Northwest Atlantic. Clearly, common murres interact with their prey over multiple temporal and spatial scales and these behavioural interactions are manifested in demographic parameters

Spatial aggregations of seabirds and their prey on the continental shelf off SW Vancouver Island

We investigated the spatial scales at which seabirds aggregate and associate with prey over the continental shelf off southwest Vancouver Island, British Columbia. Bird densities and hydroacoustic measures of prey abundance were recorded in all seasons from 1993 to 1995 from a vessel moving along fixed strip transects (mean distance 93 km; minimum spatial units 250 m). We used the neighbour K analysis to determine the spatial scale (patch radius) and number of birds (crowding) associated with aggregations of birds. Birds were grouped into 3 guilds: divers (dominated by common murres Uria aalge and other alcids), surface-feeders (dominated by California gulls Larus californicus and other gulls) and shearwaters (mainly sooty shearwaters Puffinus griseus). Flying birds occurred in smaller aggregations spread over a wider area than birds on the water. For birds on the water, patch radii were usually 2 to 8 km, and crowding averaged 574, 143 and 50 birds per patch for surface-feeders, shearwaters and divers, respectively. Patch radii showed few significant differences among bird species and guilds, and remained relatively constant throughout the year for most species, despite large seasonal changes in density and mean crowding. Abundance of prey (small schooling fish and euphausiids) was highest in the upper 10 m, declining progressively with deeper depths and showed marked seasonal trends (mean scores 4 to 5x higher in summer than in winter). Significant associations between birds and prey were usually within patch radii of 2 to 8 km. The appropriate scale to map and monitor seabirds and seabird-prey associations, for oil spill assessments and other reasons, would therefore be 1 to 10 km

Scale-dependent associations of predators and prey: constraints imposed by flightlessness of common murres

We examined the behavioural interactions of a mobile marine predator, the common murre Uria aalge, and its prey in a cold ocean regime in the context of shifting foraging constraints of the predator during various periods of the year. To do this, we explored the scale-dependent distribution patterns of murres in relation to their prey under 2 mobility regimes: (1) during the pre-breeding period when murres can fly and (2) during the post-breeding or moulting period when murres are flightless and are accompanied by flightless juveniles. In addition, we documented for the first time the relative contributions of different prey types in the diets of murres during moult using stable isotopic analysis. Flightless adult and juvenile murres were concentrated on a meso-scale (>100 km) in an area (nursery area) where significantly greater amounts of non-capelin, mainly crustaceans, were located in closely spaced aggregations. Accordingly, flightless murres had variable proportions of fish (capelin Mallotus villosus) and crustaceans in their diet, whereas breeding murres exclusively ate capelin. At fine- and coarse-scales (0.1 to 100 km), murres that could fly during pre-breeding tracked prey at smaller spatial scales (3 to 4 km) than flightless murres (6 to 9 km). We hypothesize that varying mobility regimes and energetic demands (activity levels) of murres during these 2 periods resulted in divergent perceptions of the foraging environment and subsequently in varying tracking scales of prey. This has important implications for the scale of study during different periods of the annual cycle of a predator, when varying constraints and trophic levels may interact to produce diverse behavioural responses to prey distribution and densities

Distributional patterns of a marine bird and its prey: habitat selection based on prey and conspecific behaviour

We examined distributional patterns of a pursuit-diving seabird, the common murre Uria aalge, and its fish prey, capelin Mallotus villosus, within the avian foraging range of the largest murre colony in eastern North America: Funk Island, Newfoundland. During chick-rearing, the foraging habitat was previously partitioned into: (1) a high-quality area, 45 km from the colony where energy-rich capelin schools were found, which were spatially and temporally persistent and (2) a low-quality area, 60 km from the colony where schools were composed of lower-energy capelin that were ephemeral. At the scale of the foraging range (meso-scale: 1 to 100 km), murres were highly clustered into 25% of the surveyed area, with fewer murres in the low-quality relative to the high-quality area. There were tighter associations among murre and capelin aggregations in the low-quality (1.2 ± 0.2 km) relative to the high-quality area (2.6 ± 0.4 km). This likely resulted from the divergent capelin behaviour and, thus, different foraging strategies used by murres to search for (e.g. memory vs local enhancement) and capture prey. At fine spatial scales (250 m2) within foraging areas, murres were found at lower densities (mode: 2 murres), revealing that interference competition among individuals may be important during prey capture. Modeling revealed that at >50 murres per 250 m2 in the high-quality area, a murre would have a >90% chance of increasing its foraging efficiency by switching to forage in the low-quality area. Overall, this scale-dependent aggregative behaviour of murres suggests that cooperative foraging among conspecifics may be important in locating prey at the scale of a foraging range, or murres may simply aggregate in areas of high prey abundance, but competitive interactions among conspecifics become important at the scale of prey capture

Search strategies of a pursuit-diving marine bird and the persistence of prey patches

We explored foraging strategies used by marine animals to search for prey by examining the relative importance of information exchange and memory in a cold ocean environment from 1998 to 2000. Recent technological advances have increased our knowledge of the foraging patterns of marine predators, but few of these studies have concurrently measured prey distribution and behavior. We quantified the arrival and departure behavior of a pursuit-diving, colonial seabird, the Common Murre, Uria aalge, at two colonies on the eastern Newfoundland Shelf through observational techniques. We also measured the distribution, abundance, and behavior of the capelin, Mallotus villosus, the main prey species of murres, within foraging ranges of each colony, using hydroacoustic, vessel-based techniques. Return and departure flight directions of murres did not match at either colony during the same period. This indicated that murres departing colonies did not use information on prey distributions outside of visual range of the colony provided by the flight paths of returning flocks of birds to the colony carrying fish. High-abundance aggregations of capelin were reliably found within specific 2.25-km areas (‘‘hot spots’’) for up to two weeks within the foraging ranges of murres from both colonies (;100 km). This circumstance suggests that murres could use memory to locate hot spots on the coarse scale (1– 100 km) of foraging ranges from both colonies. Specific commuting routes (regular flight paths) of murres toward and away from hot spots were obvious at sea, and feeding murres consistently marked the location of capelin schools within hot spots. These distributions provided excellent conditions for murres to locate capelin schools on both coarse and fine (1–1000 m) scales by cueing to the activities of conspecifics, known as local enhancement. While central-place foraging from breeding colonies, murres likely use a mixture of memory and local enhancement to locate prey, depending on the spatial and temporal resolution of search and current prey conditions. Uncovering such behavioral mechanisms responsible for predator–prey interactions increases our understanding of linkages among trophic levels and, ultimately, ecosystem dynamics

The influence of fish behaviour on search strategies of Common Murres Uria aalge in the Northwest Atlantic

Although distribution patterns of seabirds at sea have been described for decades, it remains difficult to identify the mechanisms underlying these patterns. For instance, researchers focusing on prey dispersion as the primary determinant of seabird distribution have found high variability in the spatial overlap of bird and prey aggregations, partially due to the scale-dependent nature of such associations. We conducted a study to identify how the behaviour of capelin Mallotus villosus, the primary prey species of all vertebrate predators in the Northwest Atlantic, influences the search tactics of Common Murres Uria aalge while acting as central-place foragers during chick-rearing. The study was conducted from 1998-2002 on and around Funk Island, the largest colony of murres in eastern Canada (∼ 400 000 breeding pairs , situated on the northeast coast of Newfoundland. We made direct measurements of (1) the distribution, a bundance and spatial and temporal persistence of capelin aggregations within the foraging range from the colony (∼ 100 km) in combination with (2) bio-physical habitat characteristics associated with capelin aggregations, and (3) individual- and population-level arrival and departure behaviour of murres from the colony. During July of 2000, capelin were found to be persistently abundant within specific 2.25 km blocks of transect ("hotspots"). Further study revealed that capelin persisted in hotspots due to bio-physical characteristics suitable for demersal spawning and for staging areas and foraging areas prior to and after spawning. Directions of return and departure flights of murres measured from the colony did not match during the same observation period (∼ 1h), indicating that murres departing the colony did not use information on prey distribution provided by the flight paths of flocks returning to the colony (Information Center Hypothesis). Specific, commuting routes (regular flight paths) of murres toward and away from capelin hotspots, however, were obvious at sea, and feeding murres consistently marked the location of these hotspots. This provided excellent conditions for murres to locate capelin from memory and by cueing to activities of conspecifics (local enhancement). Hotspots were persistent across years in this region, presumably allowing marine predators to learn the locations of hotspots, resulting in the use of traditional feeding grounds through generations. Hotspots of predators and prey promote energy transfer among trophic levels, a key ecosystem process. Human predators also concentrate fishing activities within these areas and, thus, there is a need to identify hotspots for protection. Persistent hotspots would be particularly amenable to the design of marine protected areas defined by the habitats of marine predators and their prey