Residency and depth movements of a coastal group of Atlantic cod (Gadus morhua L.)

Link between vertical and horizontal movement patterns of cod in the North Sea

“…However, it is somewhat surprising that there was not a more marked seasonality, given that the timing of cod spawning is thought to occur mainly over a few months in early spring (Cushing & Dickson 1976). One possibility is that the movements we recorded might not only be associated with migration to spawning grounds before the spawning season in January and February but might also reflect repositioning onto new feeding grounds once spawning is over (Turner et al 2002, Wright et al 2006, Svedäng et al 2007). Similar spatial dynamics are shown in plaice (Hunter et al 2004a), and are typical of migratory fish species that aggregate on spatially restricted spawning grounds before dispersal to widespread feeding grounds (e.g.…”

“…This was particular evident for one of the cod tagged in the Jutland area (Cod 861) and one in the English Channel (Cod 1948). This result suggests that either some cod are resident and therefore spawn and forage in the same locality (as in Neat et al 2006) or they may skip breeding in some years (e.g. Rose 2003).…”

“…Certainly in other taxa, non-annual breeding occurs and is associated with extended periods of time necessary to attain a sufficient body condition to initiate breeding (Hays 2000). There have been previous suggestions that cod sub-stocks in different parts of the North Sea have different dispersal patterns and hence travel different distances to spawning sites (Metcalfe 2006) and have different life-history characteristics (Wright et al 2006). The present results support the contention that there is not a single paradigm of extended travel between spawning and foraging areas for this species, but that movements vary from individual to individual, and sub-stock to sub-stock, consistent with the concept that Atlantic cod behaviour is the result of complex interactions between biological and ecological factors (Righton et al 2001).…”

“…Tags were attached to cod either externally or internally, as described in Neat et al (2006) and Righton et al (2006). The tagged fish varied in size from 48 to 65 cm total length (mean ± SD = 56 ± 5 cm, n = 14).…”

“…There is great concern over the decline in stock sizes for the cod Gadus morhua, particularly in the North Sea and the Grand Banks in the last 20 yr (Myers et al 1997, Christensen et al 2003, Horwood et al 2006. While the understanding of cod movements is increasing (Turner et al 2002, Robichaud & Rose 2004, Neat et al 2006, Svedäng et al 2007, the development of a mechanistic understanding of these movements may allow the availability of cod fishing potential at different spatial and temporal scales (O'Brien et al 2000). Similarly, information on cod depth utilisation (e.g.…”