Migration pattern of juvenile cod (Gadus morhua) on the Swedish west coast

Migratory behaviour of Atlantic cod Gadus morhua: natal homing is the prime stock-separating mechanism

“…Hence, these previous observations give strong support for conclusions made in this study of a migration route between the North Sea/western part of the Skagerrak and the eastern Skagerrak/northern Kattegat along the northern Jutland coast. In addition, a tagging study in the 1980s along the Swedish west coast observed that juvenile cod left the coastal habitats and migrated westwards (Pihl & Ulmestrand 1993). Nielsen et al (2005) argued that the seemingly contradictory existence of reproductive isolation in fish populations which encounter few physical barriers with wide distributions and dispersal of pelagic eggs and larvae, was explained by retention of juveniles.…”

“…An almost total eradication of locally spawning cod aggregations along the Swedish Skagerrak coast has, in some years, resulted in the apparent anomaly of low adult cod abundance coinciding with high juvenile abundance (Svedäng 2003, Svedäng & Svenson 2006. Svedäng (2003) and Cardinale & Svedäng (2004) hypothesised that most juvenile cod along the eastern Skagerrak coast had been passively transported from offshore spawning areas (Munk et al 1999), and the following (unexpected) low abundance of adult cod was due to return migration of juvenile and/or maturing fish which had reached a certain size or age (Pihl & Ulmestrand 1993). This theory was supported by the fact that strong year classes of juvenile cod along both the Norwegian and Swedish Skagerrak coast have been genetically assigned to eastern North Sea cod populations (Knutsen et al 2004).…”

Effects of Altered Offshore Food Webs on Coastal Ecosystems Emphasize the Need for Cross-Ecosystem Management

“…Cod is the dominant larger demersal predator in the area and was subjected to a strong commercial fishery during the decline from 1970s to the 2000s. Juveniles of offshore populations of cod settle in nearshore habitats and the larger individuals predate significantly on gobiids, shore crabs and wrasses (Pihl 1982;Pihl and Ulmestrand 1993;Salvanes and Nordeide 1993). Notably, the catch of cod in the offshore bottom trawl survey was negatively correlated with the catch of mesopredators in the coastal fyke net monitoring program (Pearson's product moment correlation; wrasses [sqrt transformed data] r = -0.61, N = 32, t = 4.24, p \ 0.001; shore crab: r = -0.51, N = 32, t = 3.22, p = 0.003; black goby [sqrt transformed data]: r = -0.64, N = 31, t = 4.58, p \ 0.001; Fig.…”

Movements of Marine Fish and Decapod Crustaceans: Process, Theory and Application

“…Some species, however, undertake seasonal migrations that are strategically placed en route to spawning areas (for fish see, Pihl and Ulmestrand, 1993;Koutsikopoulos et al, 1995;and for crustaceans, Hines et al, 1995). For instance, multiple recapture data from tagged ovigerous lobsters (Homarus americanus), off eastern Canada showed a range of movements, from a few kilometres to 322 km (although most were less than 30 km).…”