Climate warming enhances polar cod recruitment, at least transiently

Abstract

a b s t r a c tPolar cod (Boreogadus saida) is the dominant forage fish in Arctic seas and the main prey of the ringed seal (Pusa hispida), the beluga (Delphinapterus leucas) and several seabird species. Changes in the abundance of polar cod will have cascading effects on arctic marine ecosystems. We tested the hypothesis that an earlier sea ice breakup and warmer sea surface temperatures (SST) in spring-summer result in the higher recruitment of juvenile polar cod in late summer. The density (number m À2 ) and biomass (mg m À2 ) of age-0 polar cod in August and September, estimated by hydroacoustics over 9 years in 9 areas of the Canadian Arctic, were negatively correlated to ice breakup week and positively correlated to SST. The timing of the ice breakup was the main determinant of recruitment, with mean juvenile biomass in September up to 11 times greater for early breakup (late May) than for late breakup (early September). Early ice breakup in spring increased juvenile biomass in August and September by allowing the survival of larvae hatched in winter and spring. Since 1979, ice breakup has occurred earlier by as much as 9.3 days per decade in some areas. We thus forecast a transient increase in polar cod biomass over the first part of the present century. Thereafter, the relaxation of extreme climatic conditions in Arctic seas should harbinger the replacement of the hyper-specialized polar cod by subarctic and boreal forage fish.Crown

Feeding of Greenland halibut (Reinhardtius hippoglossoides) in the Canadian Beaufort Sea

“…A C C E P T E D M A N U S C R I P T most important prey for CBS Greenland Halibut, are associated with sea ice during their larval and juvenile stages (Bouchard & Fortier 2011, Hop & Gjøsaeter 2013. Changes in the abundance of Arctic Cod in response to a warmer Arctic are expected to have important cascading effects on Arctic marine food-webs (Bouchard et al 2017) including Greenland Halibut. For example, Arctic Cod abundances in the CBS were low in 2014 (Majewski et al 2016a), presumably because of low recruitment linked to early ice-off over the previous years (Bouchard et al 2017).…”

“…Changes in the abundance of Arctic Cod in response to a warmer Arctic are expected to have important cascading effects on Arctic marine food-webs (Bouchard et al 2017) including Greenland Halibut. For example, Arctic Cod abundances in the CBS were low in 2014 (Majewski et al 2016a), presumably because of low recruitment linked to early ice-off over the previous years (Bouchard et al 2017).…”

“…Halibut more vulnerable to environmental changes (e.g., change in ice coverage and its impact on pelagic prey abundance or distributions, Bouchard et al 2017). Consequently, the multi-species interactions of Greenland Halibut over large spatial and temporal scales make this species a suitable candidate to study how Arctic food webs respond to environmental changes.…”

Body condition impacts blood and muscle oxygen storage capacity of free-living beluga whales (Delphinapterus leucas)

“…Reductions in body condition of ringed seals, Pusa hispida (Ferguson et al, 2017), and polar bears, Ursus maritimus (Stirling and Derocher, 2012), and mortality events in walrus, Odobenus rosmarus (Fischbach et al, 2009), have similarly been associated with climate-induced loss of sea ice. Reductions in sea ice not only affect habitat use by Arctic whales but have also facilitated the northward migration of temperate species (Bouchard et al, 2017;Falardeau et al, 2014). As a result, beluga whales may have to adopt new foraging strategies to accommodate shifts in prey abundance.…”

Between classical and critical geopolitics in a changing Arctic

“…Attention should also be paid to how changes in water temperatures potentially impact the distribution of living marine resources, such as fish stocks. Such changes are expected to have led species and their prey to migrate northwards due to warmer temperatures (Haug et al, 2017;Bouchard et al, 2017;Christiansen, Mecklenburg, & Karamushko, 2014). For example, in late 2013 mackerel was observed outside Longyearbyen, Svalbard, for the first time (Berge et al, 2015).…”