Prolonged baleen hormone cycles suggest atypical reproductive endocrinology of female bowhead whales

Serial measurements of hormone concentrations along baleen plates allow for reconstructions of mysticete whale reproductive histories. We assessed gestation and calving interval in bowhead whales (Balaena mysticetus) by measuring progesterone, oestradiol, corticosterone and nitrogen stable isotope ratios (δ¹⁵N) along baleen of 10 females from the eastern Canada-west Greenland population. Three immature females (body size < 14.32 m) had uniformly low progesterone concentrations across their baleen, while seven mature females (body size ≥ 14.35 m) had repeated, sustained elevations of progesterone indicative of pregnancies. The mean duration of progesterone elevations (23.6 ± 1.50 months) was considerably longer than the approximately 14 month gestation previously estimated for this species. We consider several possible explanations for this observation, including delayed implantation or sequential ovulations prior to gestation, strategies that would allow females to maximize their fitness in variable Arctic conditions, as well as suggest modified criteria defining gestation as a shorter component of the entire progesterone peak. Calving intervals varied within and among individuals (mean = 3.7 years; range = range 2.8-5.7 years), providing population-specific reproductive estimates for growth models used in bowhead whale management and conservation.

Nitrous oxide fluxes in three experimental boreal forest reservoirs

Global atmospheric concentrations of nitrous oxide (N2O), a powerful greenhouse gas, continue to increase. While many sources and sinks have been identified, there is little known about how existing and newly constructed reservoirs, such as those created for hydroelectric production, impact current atmospheric N2O concentrations. We hypothesized that N2O fluxes to the atmosphere would increase because enhanced nutrient availability and increased soil respiration following the flooding of soils during reservoir creation would favor denitrification. Furthermore, we hypothesized that emissions would be linked to the amount of organic carbon contained in the flooded landscape. These hypotheses were tested by creating three experimental reservoirs over boreal upland subcatchments that ranged in the amount of organic carbon stored in soils and vegetation. Diffusive surface N2O fluxes within each reservoir were estimated using surface water concentrations of N2O and the thin boundary layer method. Surface fluxes ranged from -1.0 to -3.5 microg N2O m(-2) d(-1), and water column N2O concentrations indicated that contrary to expectations, the reservoirs were acting as slight sinks for atmospheric N2O. This net consumption of N2O was likely related to an excess of labile carbon and low concentrations of oxygen (O2) and nitrate (NO3-) in the flooded soils. Therefore, it is postulated that reservoir creation by flooding boreal soils will likely have little or no net effect of adding additional N2O to the current greenhouse gas (GHG) atmospheric burden, at least over the short term.