Variability of northeast Arctic cod (Gadus morhua) distribution on the main spawning grounds in relation to biophysical factors

Abstract

Early life stages may on average gain a survival benefit from the regular return of parent fish to the same spawning grounds. Such areas may have a considerable spatial extent, occupation of which varies between spawning seasons. Northeast Arctic cod (Gadus morhua) is an ideal candidate to pinpoint the most influential biophysical factors in these respects due to its data richness and apparently strong “homing” behaviour. Their main spawning grounds, off northern Norway, are split in two by the Lofoten archipelago, and in the previous decade strong spawning activity was observed on the seaward continental shelf (Yttersida), while in recent years spawning activity in the wide fjord (Vestfjorden), that separates the islands from the Norwegian mainland, has again increased. Time-series of egg distribution were available from the 1980s, 1990s, and 2004–2012. We used several fixed and random factors to construct a statistical model for the distribution of recently spawned eggs, and hence, spawning adults in either area. We show that the most relevant covariates for the spatial distribution of eggs in Vestfjorden are local temperature and bathymetry, while at Yttersida influence affecting the whole stock, like regional ocean climate and age structure appear more important. Therefore, spawning inside the fjord may be constrained by suboptimal environmental conditions. Yttersida may be occupied by fish which have been displaced out of Vestfjorden when preferred conditions there are of limited extent.

Organic Matter Sources in North Atlantic Fjord Sediments

“…The small nonlinear variations between C org /N org and δ 13 C org may simply be caused by factors such as phytoplankton growth rate, cell size, metabolism, variations in 13 C content of the carbon source, and also diagenetic alteration (Hayes, 1993;Laws et al, 1995;Rau et al, 1997;Rullkötter, 2006;Talmy et al, 2014). These findings are in agreement with previous investigations, which show that the three fjords and especially the adjacent shelf areas of the Vestfjord are areas of high marine productivity, probably sustained by the inflow of nutrient-rich Atlantic waters as well as upwelling along the steep side-edges of the Vestfjord (Figure 2; Espinasse et al, 2016;Furnes & Sundby, 1981;Höffle et al, 2014;Similä et al, 1996;Sundby & Solemdal, 1984).…”

“…However, no clear relationship between any grain size fraction and C org and N org was found (r < 0.3, n = 39; grain size data are published in Faust et al, 2017). These findings are in agreement with previous investigations, which show that the three fjords and especially the adjacent shelf areas of the Vestfjord are areas of high marine productivity, probably sustained by the inflow of nutrient-rich Atlantic waters as well as upwelling along the steep side-edges of the Vestfjord (Figure 2; Espinasse et al, 2016;Furnes & Sundby, 1981;Höffle et al, 2014;Similä et al, 1996;Sundby & Solemdal, 1984). Only the inorganic nitrogen fraction is strongly related to the clay fraction (r = 0.8, n = 39) indicating a land-derived origin as suggested earlier (Knies et al, 2007).…”

Ticket to spawn: Combining economic and genetic data to evaluate the effect of climate and demographic structure on spawning distribution in Atlantic cod

“…Results of tagging experiments suggest that fish spawning in Møre overlap with fish spawning in Lofoten at the feeding grounds in the Barents Sea. Finally, density-dependent competition at the spawning grounds (Höffle et al, 2014) may be an important mechanism. Another potential mechanism for the decreasing size toward the south, as mentioned above, could be subpopulation structure (Sundby & Nakken, 2008).…”

“…If, for example, different subpopulations have distinct size structure, the observed patterns in size with distance from the feeding grounds could be a result of these distinct size distributions. Finally, density-dependent competition at the spawning grounds (Höffle et al, 2014) may be an important mechanism. Large fish start their spawning migrations earlier (Bergstad et al, 1987) and may potentially occupy the best spots, forcing smaller and late-arriving individuals to spawn further south.…”

Per Solemdal (1941–2016) – an unconventional marine scientist

“…The extensive time series and experimental data that Per and his colleagues collected still attracts interest and new research questions, e.g. in Höffle et al (2014) on the distribution of spawning cod in Lofoten, the last article with Per as a co-author.…”