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

Abstract

Climate warming and harvesting affect the dynamics of species across the globe through a multitude of mechanisms, including distribution changes. In fish, migrations to and distribution on spawning grounds are likely influenced by both climate warming and harvesting. The Northeast Arctic (NEA) cod (Gadus morhua) performs seasonal migrations from its feeding grounds in the Barents Sea to spawning grounds along the Norwegian coast. The distribution of cod between the spawning grounds has historically changed at decadal scales, mainly due to variable use of the northern and southern margins of the spawning area. Based on historical landing records, two major hypotheses have been put forward to explain these changes: climate and harvesting. Climate could affect the distribution through, for example, spatial habitat shifts. Harvesting could affect the distribution through impacting the demographic structure. If demographic structure is important, theory predicts increasing spawner size with migration distance. Here, we evaluate these hypotheses with modern data from a period (2000–2016) of increasing temperature and recovering stock structure. We first analyze economic data from the Norwegian fisheries to investigate geographical differences in size of spawning fish among spawning grounds, as well as interannual differences in mean latitude of spawning in relation to changes in temperature and demographic parameters. Second, we analyze genetically determined fish sampled at the spawning grounds to unambiguously separate between migratory NEA cod and potentially smaller sized coastal cod of local origin. Our results indicate smaller spawners farther away from the feeding grounds, hence not supporting the hypothesis that harvesting is a main driver for the contemporary spawning ground distribution. We find a positive correlation between annual mean spawning latitude and temperature. In conclusion, based on contemporary data, there is more support for climate compared to harvesting in shaping spawning ground distribution in this major fish stock in the North Atlantic Ocean.

Wind Intensity Is Key to Phytoplankton Spring Bloom Under Climate Change

“…Opdal and Jørgensen (2015) suggested an alternative, but not contradictive, explanation involving size-selective fisheries. However, Langangen et al (2019) supported the hypothesis of climate-driven shifts based on analysis of more recent data (2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010)(2011)(2012)(2013)(2014)(2015)(2016) during a recovery of cod stock demography. Contrary, there is no indication of temporally varying time of spawning.…”

Climate Change and New Potential Spawning Sites for Northeast Arctic cod

“…In a warmer future climate this relationship could result in a northward migration of the NEA cod and potentially to immigration of other cod populations adapted to other sets of environmental conditions. The center of the geographic distribution and the outer fringes of the main spawning site of NEA cod along the coast of Norway have fluctuated throughout at least the last century, where we have reliable observations showing both interannual variability in the use of specific spawning sites, as well as multidecadal distribution shifts (Opdal et al, 2008;Sundby and Nakken, 2008;Opdal and Jørgensen, 2015;Langangen et al, 2018). The alternative to shifting spawning sites in a warmer future could be an evolutionary change of the local population (Mieszkowska et al, 2009).…”

“…The general physical characteristics such as hydrography, spawning depths and bathymetry at different spawning sites of NEA cod are presented in a number of papers (Bergstad et al, 1987;Ottersen and Sundby, 2005;Righton et al, 2010;Höffle et al, 2014), as well as the large-scale variability in spawning locations (Sundby and Nakken, 2008;Opdal, 2010;Opdal and Jørgensen, 2015;Langangen et al, 2018). Two main hypotheses for the observed large-scale variability in spawning location have been presented, suggesting multidecadal climate variability (Sundby and Nakken, 2008), or demographic processes as main drivers (Opdal and Jørgensen, 2015).…”

Changing how we approach fisheries: A first attempt at an operational framework for ecosystem approaches to fisheries management

“…establishing fisheries management based on spatial fishing units that vary over time, whether rotating or otherwise; Table ‐Migration/Movement/Location.VI). For example, the importance of accounting for changes to migration in spatial management has been reinforced in studies documenting spawning shifts of fishes in the Norwegian and Barents Seas (Langangen et al, , ; Reiss, Hoarau, Dickey‐Collas, & Wolff, ). The reasoning behind this is to allow for spawning, feeding, etc.…”

“…If no decline in range is observed, one could then ask if there is an increase in range. If so, evaluation of the population could lead either to a lowering of buffers to biological reference point (BRP) buffer or an increase in fishing pressure (F) ( Seas (Langangen et al, 2019(Langangen et al, , 2018Reiss, Hoarau, Dickey-Collas, & Wolff, 2009 measure. This is not a concern as long as proposed solutions are explored and it is recognized that this duplicity in fact provides a menu of options; for example, reevaluating stock ID has application for multiple scenarios, and regardless of how one arrived at that point, would be beneficial to execute.…”