Seasonal dynamics of spatial distributions and overlap between Northeast Arctic cod (Gadus morhua) and capelin (Mallotus villosus) in the Barents Sea

Abstract

The trophic link between cod (Gadus sp.) and capelin (Mallotus sp.) is important in many panarctic ecosystems. Since the early 2000s, the Northeast Arctic cod stock (G. morhua) in the Barents Sea has increased greatly, and the sea has been exceptionally warm. Such changes have potentially large effects on species distributions and overlap, which in turn could affect the strength of species interactions. Due to its high latitude location, the Barents Sea has strong seasonal variation in physical conditions and interactions. To study drivers of variation in cod-capelin overlap, we use data from two annual surveys run in winter and in autumn of 2004–2015. We first model winter and autumn spatial distributions of mature and immature cod and capelin. We then calculate overlap from model predictions on a grid with similar spatial resolution as the survey data. Our approach allowed us to interpret changes in overlap as species-specific effects of stock size and temperature, while accounting for sampling variation due to sampling time and depth. We found that during winter both species expanded their distribution in response to increased stock sizes, but how strongly and where the expansion occurred varied. The effect of temperature on distributions varied in space, and differed for cod and capelin and for different components of the two species. The results for autumn were clearer and more consistent. Both species expanded their distribution areas as their stock sizes increased. A positive effect of temperature was found in the north-eastern Barents Sea, where temperatures were lowest at the start of the study. Overlap increased and shifted north-eastwards during the study period and remained high despite a decline in the capelin stock. The increased overlap during autumn could mainly be attributed to the shift in cod distribution with increased cod stock biomass.

Nonlinearity in interspecific interactions in response to climate change: Cod and haddock as an example

“…The species composition and abundance of cod prey vary over time in relation to environmental conditions and prey population dynamics (Durant et al., 2014). Cod follows the capelin northward with increase in temperature (Fall et al., 2018). The same increase in temperature positively affects the haddock stock size and lead young haddock northward in the Barents Sea (Landa et al., 2014) sustaining the overlap between the two species.…”

“…Subscript 'h' is for haddock, 'c' for cod and 't' for time/year. Ådlandsvik, and explain the dynamics for NEA cod (Hjermann, Stenseth, & Ottersen, 2004) and northward population displacement in the Barents sea of both cod and haddock (Fall, Ciannelli, Skaret, & Johannesen, 2018;Landa, Ottersen, Sundby, Dingsør, & Stiansen, 2014). Both NAO and sea temperature (ST) are classically used in population dynamics studies for the cod and haddock and well documented as affecting the change of population in the studied system (Frainer et al, 2017;Johannesen et al, 2012), particularly at early life stages (Stige et al, 2010), and other fish (Ottersen, Kim, Huse, Polovina, & Stenseth, 2010).…”

“…Temperature is a regional hydro‐climatic variable potentially affecting the survival and growth of early life stages (Dingsør, Ciannelli, Chan, Ottersen, & Stenseth, 2007; Langangen et al., 2014) as well as their distribution (Hidalgo et al., 2012) and recruitment (Ottersen et al., 2013). In the Barents Sea, the Kola transect temperature is representative of the Atlantic water masses in the south‐central Barents Sea (Ingvaldsen, Loeng, Ådlandsvik, & Ottersen, 2003) and explain the dynamics for NEA cod (Hjermann, Stenseth, & Ottersen, 2004) and northward population displacement in the Barents sea of both cod and haddock (Fall, Ciannelli, Skaret, & Johannesen, 2018; Landa, Ottersen, Sundby, Dingsør, & Stiansen, 2014). Both NAO and sea temperature (ST) are classically used in population dynamics studies for the cod and haddock and well documented as affecting the change of population in the studied system (Frainer et al., 2017; Johannesen et al., 2012), particularly at early life stages (Stige et al., 2010), and other fish (Ottersen, Kim, Huse, Polovina, & Stenseth, 2010).…”

Resource‐driven colonization by cod in a high Arctic food web

“…We assume that high stomach fullness in cod is caused by high encounter rates between individual cod and prey, suggesting that expanding cod could quickly exploit a previously underutilized prey base. During the expansion period of cod, a similar northwards expansion of its main prey capelin (Mallotus villosus) occurred, associated with an increase in population size from a collapsed state in [2004][2005][2006][2007] to substantially higher levels in 2008-2013 (Fall et al, 2018). The cod expansion may, however, only partly be driven by capelin, since capelin are restricted to the northwestern Barents Sea which correspond to our subregions 1, 3, and 4 (Fall et al, 2018), whereas cod mainly increased in subregions 1, 2, and 5 ( Figure 1).…”

Climate Change and New Potential Spawning Sites for Northeast Arctic cod

“…The spawning sites have sustained a coastal fishery for thousands of years and a potential shift in the spatial distribution of the spawning sites is likely to impact current fishing activities. NEA cod has undergone distribution shifts involving most of its life history stages, parallel to the observed ocean warming during the last 3 decades Ingvaldsen et al, 2015;Fall et al, 2018). Considerable expansion of its distribution limits north-and eastwards in the Barents Sea has been observed following increased inflow of warm Atlantic Water into the region (Eriksen et al, 2011;Kjesbu et al, 2014;Fossheim et al, 2015).…”