Key processes regulating the early life history of Barents Sea polar cod

Abstract

The polar cod (Boreogadus saida) in the Barents Sea is one of the main stocks of this species in the Arctic, reaching a total biomass of almost 2 million tonnes in some years. It has been fluctuating considerably in abundance, and in recent years, it has been at a low level. Only small catches have been taken from the stock over the last four decades, and consequently, the observed variation in abundance must be caused by natural (environmental and/or biological) changes in the ecosystem. Sea temperatures have been rising in the Barents Sea in recent years, possibly causing changes to the living conditions of this true Arctic stock. Consequently, there is a need for investigating how the observed changes might affect polar cod in this area. One important aspect of the environmental impact on the stock is possible effect on the recruitment, which has been varying considerably from year to year. In this modelling study, we thus recreate and analyse the environmental and developmental histories of the observed 0-group individuals in the Barents Sea (young of the year), with emphasis on the importance of ice cover, ice breakup time, maximum temperature, and spawning stock biomass. Our simulations indicate that the environmental conditions experienced by individuals successfully "recruited" to the 0-group are characterized by high ice concentration well into summer, and low temperatures throughout the pelagic juvenile phase, and any perturbations from the Arctic ocean climate typically found in the northern and eastern Barents Sea appears to be detrimental to stock recruitment. In light of the projected warming of the Barents Sea in the next decades and the potential reduction in ice cover, this will entail, the mechanisms investigated herein might lead to future marginalization of polar cod in the Barents Sea.

High gene flow in polar cod (Boreogadus saida) from West‐Svalbard and the Eurasian Basin

“…The exact population sizes during sampling events are not known for all locations, but the literature provides some estimates. Like other gadoids, fecundity is high and ranges from 9000 to 67,000 eggs per female (Gjosaeter et al, 2020;Hop et al, 1995). Nahrgang et al (2014) reported estimates of expected lifetime fecundity of each female, assuming iteroparity (multiple reproductive cycles), to be twice as high in Arctic-influenced fjords compared to Atlantic-influenced fjords (up to 75,000 and 39,000 eggs per female, respectively).…”

Cod movement ecology in a warming world: Circumpolar arctic gadids

“…increase gape size, access to more prey: Bouchard & Fortier, 2011; Mueter et al., 2016; Wong et al., 2013). As long as prey are available for early developing larvae (Gjøsæter et al., 2020), this could provide more time for larval fish to grow during spring and summer to a large enough size to avoid predation from gape (or behavioural) limited predators during the following fall/winter (Bouchard & Fortier, 2011; De Robertis et al., 2017; Kono et al., 2016; LeBlanc et al., 2020). Conversely, excessive outflow could negatively impact circumpolar Arctic gadids near river mouths with, for example, elevated turbidity and eutrophication (i.e.…”

Arctic gadids in a rapidly changing environment

“…Relatively small-scale population structure is also evident in the navaga, with three distinct populations in the White Sea (Maznikova and Orlov 2020), as well as in the saffron The second major theme aims to understand how environmental changes drive the growth and survival of polar cod in the Arctic and their ability to adapt to sea ice loss and rising ocean temperatures. Polar cod can be considered a sentinel species for Arctic changes as the southern limits of their distribution are closely tied to variations in temperature (Marsh and Mueter 2020) and variability in early survival is linked to the timing of sea ice retreat (Bouchard et al 2017;Gjøsaeter et al 2020;LeBlanc et al 2020). Bouchard et al (2017) suggest that polar cod, which are adapted to a narrow range of temperatures, will initially benefit from rising temperatures, but will ultimately be replaced by more southern species as ocean temperatures continue to increase.…”

“…Acoustic surveys suggest large interannual variability in abundance (De Robertis et al 2017), but the effects of interannual variability in environmental conditions in the Chukchi Sea on the abundance of polar cod have not yet been examined. Young polar cod in the Barents Sea typically encounter temperatures well within their physiological tolerance (< 6 °C), but individual-based models suggest that an earlier ice melt, reduced summer ice, and the increasing influence of warmer Atlantic waters negatively affect the survival of polar cod larvae from the major spawning aggregations in the southeast Barents Sea (Gjøsaeter et al 2020). The Barents Sea stock is one of the main stocks of polar cod in the Arctic and has long supported an important fishery in the Russian part of the Barents Sea (Boitsov et al 2013;Hop and Gjøsaeter 2013).…”

“…The Barents Sea stock is one of the main stocks of polar cod in the Arctic and has long supported an important fishery in the Russian part of the Barents Sea (Boitsov et al 2013;Hop and Gjøsaeter 2013). The abundance of this stock has fluctuated widely, is currently at low levels, and is expected to further decline under continued warming (Gjøsaeter et al 2020).…”