Terry A Dick

Arctic cephalopod distributions and their associated predators

Cephalopods are key species of the eastern Arctic marine food web, both as prey and predator. Their presence in the diets of Arctic fish, birds and mammals illustrates their trophic importance. There has been considerable research on cephalopods (primarily Gonatus fabricii) from the north Atlantic and the west side of Greenland, where they are considered a potential fishery and are taken as a by-catch. By contrast, data on the biogeography of Arctic cephalopods are still incomplete. This study integrates most known locations of Arctic cephalopods in an attempt to locate potential areas of interest for cephalopods, and the predators that feed on them. International and national databases, museum collections, government reports, published articles and personal communications were used to develop distribution maps. Species common to the Canadian Arctic include: G. fabricii, Rossia moelleri, R. palpebrosa and Bathypolypus arcticus. Cirroteuthis muelleri is abundant in the waters off Alaska, Davis Strait and Baffin Bay. Although distribution data are still incomplete, groupings of cephalopods were found in some areas that may be correlated with oceanographic variables. Understanding species distributions and their interactions within the ecosystem is important to the study of a warming Arctic Ocean and the selection of marine protected areas.

Foraging ecology of ringed seals (Pusa hispida), beluga whales (Delphinapterus leucas) and narwhals (Monodon monoceros) in the Canadian High Arctic determined by stomach content and stable isotope analysis

Stomach content and stable isotope analysis (δ13C and δ15N from liver and muscle) were used to identify habitat and seasonal prey selection by ringed seals (Pusa hispida; n=21), beluga whales (Delphinapterus leucas; n=13) and narwhals (Monodon monoceros; n=3) in the eastern Canadian Arctic. Arctic cod (Boreogadus saida) was the main prey item of all three species. Diet reconstruction from otoliths and stable isotope analysis revealed that while ringed seal size influenced prey selection patterns, it was variable. Prey-size selection and on-site observations found that ringed seals foraged on smaller, non-schooling cod whereas belugas and narwhals consumed larger individuals in schools. Further interspecific differences were demonstrated by δ13C and δ15N values and indicated that ringed seals consumed inshore Arctic cod compared to belugas and narwhals, which foraged to a greater extent offshore. This study investigated habitat variability and interseasonal variation in the diet of Arctic marine mammals at a local scale and adds to the sparse data sets available in the Arctic. Overall, these findings further demonstrate the critical importance of Arctic cod to Arctic food webs.

Summer foraging behaviour of shallow-diving seabirds and distribution of their prey, Arctic cod ( Boreogadus saida ), in the Canadian Arctic

Productive areas in the Canadian Arctic seasonally provide top predators with accessible and often predictable sources of energy. Arctic cod (Boreogadus saida) aggregate in shallow bays during the summer and are exploited by seabirds and marine mammals. Information concerning how prey is presented to predatory seabirds, and the cues seabirds use to optimize foraging potential, is limited. Hydroacoustic surveys were completed in Allen Bay, Nunavut, to determine the presence, density, abundance, and depth of Arctic cod schools in relation to shallow-diving seabirds. Schools were also documented using standardized protocols to examine the influence of environmental variables, such as wind, ice, tidal states and seabird behaviour. The presence of schools was a significant predictor of the distribution of northern fulmars (Fulmarus glacialis) but not black-legged kittiwakes (Rissa tridactyla). Glaucous gulls (Larus hyperboreus) associated with northern fulmars are likely optimizing chances of stealing Arctic cod. The density, size and depth of schools did not significantly affect the distribution of the seabirds. We speculate that Arctic cod from demersal schools separate to feed at the surface in satellite schools (groups of dispersed fish), thus reducing competition but increasing the risk of predation.

Residency and movement patterns of Arctic charr Salvelinus alpinus relative to major estuaries

Estuarine residency and marine movements of 43 anadromous Arctic charr Salvelinus alpinus (mean ± s.d. fork length = 523 ± 97 mm) were examined using acoustic tracking in inner Frobisher Bay (IFB; 63° N; 68° W), Canada, from July to September 2008 and 2009. A mean ± s.d. migration duration of 63 ± 7 days occurred from late June to early September. Detected S. alpinus were either continuously (maximum 34 days) or intermittently present in estuarine zones, on average residing approximately one third of time tracked and returning once every 9 days. Significantly higher estuarine residency during the final 15 migration days suggested that a transition phase may occur prior to freshwater re-entry. Low travel rates during flood tide suggested individuals staged before accessing intertidal and estuarine zones. Although the two main estuaries were c. 22 km apart, 19% of tagged individuals used both. Individuals remained relatively close to freshwater overwintering systems, although late-migration inter-estuarine movements may have indicated natal homing. Approximately half of the individuals exhibited extra-estuarine travel, mostly during mid-migration, but remained within 3 km of shore ranging < 30 km straight line distance (SLD) of either estuary. It was concluded that IFB S. alpinus (1) spent a significant portion of their migration within or adjacent to the estuaries and (2) had a restricted marine distribution within 30 km SLD of the river mouths.

Observation of common raven (Corvus corax) scavenging Arctic cod (Boreogadus saida) from seabirds in the Canadian High Arctic

The common raven (Corvus corax) is one of the most intelligent avian species, known for its ability to scavenge from humans and other animals. This adaptive nature is critical in habitats where food can be scarce. The Arctic is such an environment, and optimizing associations with sources of prey is important. Large aggregations of Arctic cod (Boreogadus saida) in shallow waters provide a high energetic source for top predators such as seabirds and marine mammals, and consequently potential food sources for ravens. We document, to our knowledge, the first observations of a raven feeding on Arctic cod discarded by seabirds. This report supplements knowledge of ravens to opportunistically meet dietary requirements and the importance of Arctic cod to avian ecology in the Arctic.

Movements and Habitat Use by Lake Sturgeon (Acipenser fulvescens) in an Unperturbed Environment: A Small Boreal Lake in the Canadian Shield

The order Acipenseriformes, belonging to a group of basal Acthopterygian fishes (Choudhury and Dick 1998), has two living families (Acipenseridae and Polyodontidae), 6 genera, and 26 species worldwide (Nelson and Paetz, 1992; Nelson 1994). The Acipenseridae are old with the fossil record of sturgeon like fish dating back 100 million years to the upper Cretaceous (Harkness and Dymond 1961, Fogle 1975, Pearce 1986, Mecozzi 1988, Choudhury and Dick 1998). Fossils of an extinct family, the chondrosteidae, are dated from the lower Jurassic to the lower Cretaceous (Scott and Crossman 1998). Other authors state that sturgeon species are primitive relicts of the Devonian period 300 million years ago (Glover 1961, Ono et al. 1983, Houston 1987). Choudhury and Dick (1998) suggest that acipenserids diversified within a narrow time frame and lapsed into a subsequent long period of morphologica1 stasis. The lake sturgeon has the most local names of al1 North American sturgeon species. These names include: rock, common, red, ruddy, Ohio, stone, shell-back, bony, freshwater, smooth-back, rubbernose, black, dogface, bull-nosed and Great Lakes sturgeon (Harkness and Dymond 1961, Williams and Vondett 1962, Scott and Crossman 1998), Pearce 1986, Mecozzi 1988). The decline of sturgeon populations throughout the world (Bemis and Findeis, 1994) and in North America is well documented. Population numbers plummeted around the turn of the 20th century as a result of over-fishing (Prince, 1905, Dick et al. 1998). The continued decline of populations across Canada is due to a variety of factors including habitat loss, continued fishing pressure in the form of commercial, sport, and subsistence fisheries. Consequently, the Committee on the Status on Wildlife in Canada (COSEWIC) raised major concerns on the status of the species and a report was written for Canada by Dick et al. (2006a). Considerable effort has gone into sturgeon research over the past two decades and since then the understanding of lake sturgeon biology and habitat use has improved, facilitating the possible rehabilitation of some populations. The Manitoba records on lake sturgeon population declines are relatively complete because there are good historical records for lake