Predation of archival tagged Dolly Varden, Salvelinus malma, reveals predator avoidance behaviour and tracks feeding events by presumed beluga whale, Delphinapterus leucas, in the Beaufort Sea

Background We report compelling evidence suggesting a predation event of a pop-up satellite archival tagged anadromous Dolly Varden (Salvelinus malma) by a marine mammal during summer in the Beaufort Sea based on abrupt changes in temperature and vertical movements. This observation provides insight on predator avoidance behaviour by Dolly Varden and the predator’s feeding frequency while the tag was ingested. Based on published distribution and ecology information, we presumed the predator was a beluga whale (Delphinapterus leucas). Supplemental satellite telemetry data from previously tagged Dolly Varden and beluga whales were used to determine the extent of spatial and vertical overlap between species in the area where predation occurred. Results Prior to the predation event, depths and temperatures occupied by the tagged Dolly Varden averaged 1.1 m and 3.1 °C, respectively. On July 7, 2020, depths remained shallow apart from a sudden dive to 12.5 m (16:45 UTC) followed by a precipitous increase in temperature from 4.4 to 27.1 °C (16:52 UTC) suggesting predation by an endotherm. Subsequent readings indicated the endotherm had a resting stomach temperature of 36.1 °C. Including the predation event, eight separate feeding events were inferred during the 20-h period the tag was ingested (before presumed regurgitation) based on subsequent declines in stomach temperatures (mean decline to 31.1 °C) that took an average of 24.1 min to return to resting temperature. The predator occupied mainly shallow depths (mean = 2.3 m), overlapping with tagged belugas that spent 76.9% of their time occupying waters ≤ 2.5 m when frequenting the area occupied by tagged Dolly Varden in the Canadian Beaufort Sea in July. Back-calculation based on tag drift and mean displacement by tagged belugas indicated the predation likely occurred west of the Mackenzie Delta. Conclusion Our findings provide new information on both anti-predator behaviour by, and marine predators of, Dolly Varden in the Beaufort Sea. We provide the first estimate of feeding frequency and stomach temperature recovery in a presumed wild beluga, and evidence for shallow foraging behaviour by belugas. Elucidating the likely predator and exploring the extent of overlap between Dolly Varden and beluga whales contributes towards knowledge on the trophic interactions in the Beaufort Sea.

Freshwater early life growth influences partial migration in populations of Dolly Varden (Salvelinus malma malma)

Populations of northern Dolly Varden (Salvelinus malma malma) exhibit partial seaward migration, yet little is known about this phenomenon in Dolly Varden populations. Our study analyzed data from three different Dolly Varden populations in the western Canadian Arctic in order to determine if: (1) differences in size-at-first seaward migration exist between fish that migrate at early and late ages among populations inhabiting different river systems, and (2) annual growth influences anadromous or resident life history choice. Otolith strontium analysis and back-calculation were used to determine age- and size-at-first seaward migration, respectively. Differences in age- and size-at-first seaward migration were determined across river system and migration age. Back-calculated fish lengths were compared using a mixed effect model to determine how early growth influences migratory tactics (early or late aged smolt, or resident). Our results indicate that fish exhibiting faster early growth migrated in earlier years and at smaller sizes than slower growing fish, however size- and age-at first seaward migration varied by river system. Faster growing Dolly Varden tended to become either residents or early smolts, while slower growth was associated with smolting later in life. This is contrary to life history theory where the fastest growing fish in a population should mature as a resident. Our results indicate factors other than growth may be influencing life history ‘decisions’ in Dolly Varden. Future work on growth efficiencies and metabolic rates is needed to assess how they affect migratory behaviours.

Victorian Faddishness: The Dolly Varden from Dickens to Patience

This article addresses the origins and nature of the fad through a case study of the ‘Dolly Varden’ dress. The gown originated in the 1770s as a ‘polonaise’ among continental aristocracy, and experienced a minor revival in the 1840s when Dolly Varden, a character in Charles Dickens’s novel Barnaby Rudge (1841) was depicted wearing it. But it did not become a fad until the 1870s, after a Dickens-owned painting of the character was sold and the gown re-entered the public eye. Having shed its historical or literary connections, the gown was revived again in Gilbert and Sullivan’s comic opera Patience (1881), a well-known send-up of Aesthetic foibles. Often overlooked is the fact that dairy maid Patience – who figures in the opera as a counterpoint to the lovesick maidens wearing high Aesthetic garb – wears a Dolly Varden gown, as faddish as any Aesthetic gown, only slightly outdated. The Aesthetic afterlife of the dress demonstrates the mutability of Victorian fads and the gleeful ignorance of antecedents that typifies fad culture. Facilitated by the material and commercial innovations of the period and fuelled by an insistent presentism, fads are – this article argues – a truly Victorian phenomenon.

Species-specific vulnerability to angling and its size-selectivity in sympatric stream salmonids

In mixed fisheries where multiple species are caught, to manage resources sustainably, knowledge about the species-specific vulnerability to fishing is equally or even more important than knowledge of size-selectivity of the gear. We compared the vulnerability to bait recreational angling in four salmonids in natural streams. The ranking of species-specific angling vulnerability was as follows (from highest to lowest): rainbow trout, white-spotted charr, masu salmon, and Dolly Varden. In all species, larger individuals were more vulnerable to angling, but there were differences in the size-dependence between species. In rainbow trout and Dolly Varden (which have a non-anadromous life-history in the study area) the probability of being caught monotonically increased with body size, while the vulnerability to angling in masu salmon and white-spotted charr (which have an anadromous life-history in the study area) showed a domed shaped pattern. We found that across the species the catch-per-unit effort showed a hyperstable relationship with population density. Therefore, diminishing local populations are prone to collapse, and this collapse would be hard to foresee based on catch rate data alone.