Cod migration patterns in relation to temperature: analysis of storage tag data

Abstract

Bivariate time-series of depth (pressure) and temperature with two-hour intervals from 19-data storage tags (DST) attached to adult Northeast Arctic cod (Gadus morhua L.) released from mid-March are analysed. Interplay between migration behaviour, physiological limitation factors, environment, and ecology in the Barents Sea is investigated using geometrical and statistical methods. Thermo-stratification is identified using r(t), the ratio between temperature and depth change over each record interval. Vertical activity, act(a), in relation to physiological limitations to pressure change is measured with the ratio of the daily depth range to the free vertical range. Cycles are detected by spectral analysis. The analysis supports conclusions from large-scale studies. Cod migrate along stable thermal paths until they reach a front area (or feeding ground), where the vertical activity increases and the records of depth, temperature, and r(t) change pattern, level and range. The (semi-) diurnal vertical migration (DVM) occurs seasonally in some fish, mainly in areas with large temperature gradient. In 11 out of 12 tags where DVM is detected, this occurs during summer and autumn. In seven out of 11 tags where semi-diurnal tidal cycles are detected in the temperature series together with a significant reduction in vertical migration, this occurs during April. In some tags diurnal or semi-diurnal cycles appear in both depth and temperature series. International Council for the Exploration of the Sea

Vertical migration in adult Atlantic cod (Gadus morhua)

“…In the Barents Sea, the availability of capelin to cod will vary spatially, seasonally, and interannually. However, seasonal variation in availability of pelagic prey is likely to produce a seasonal pattern in the vertical distribution of cod (Righton et al 2001;Stensholt 2001). The simulation results, not surprisingly, predicted that in the absence of pelagic prey, cod would only utilise the benthic food resources and hence not ascend into the pelagic zone.…”

“…The physical environment varies strongly along the vertical axis, in particular for light level and hydrostatic pressure, but often also with regards to temperature (Stensholt 2001), current speed (Arnold et al 1994;Aglen et al 1999), salinity, and oxygen (Neuenfeldt and Beyer 2003). The temporal and vertical distribution of different kinds of prey (Rose and Leggett 1990;Righton et al 2001) is also likely to impact on behaviour.…”

Vertical movements of North Sea cod

“…Over recent years there has been considerable effort to understand the behaviour of individual cod, for example in Newfoundland (Rose et al 1995), Iceland (Palsson & Throsteinsson 2003), Barents Sea (Stensholt 2001) and the North and Irish Seas (Righton et al 2001, Neat et al 2006. As a step towards achieving this goal, we describe the use of acoustic and DSTs to identify the vertical movements of cod tagged at a range of sites in the North Sea.…”

Anglerfish (Lophius spp) in Nordic waters

“…The recent development of Data Storage Tags (DSTs), where data on external parameters can be logged (depth, temperature and now also light intensity) has resulted in the value of tagging studies becoming more pronounced. Tagging studies using DSTs have been successful on species such as cod (Godø & Michalsen, 2000;Stensholt, 2001;Turner et al, 2002), plaice (Solmundsson et al, 2003), tunas (Block et al, 2001;Schaefer & Fuller, 2002) and salmonids (Walker et al, 2000) and have yielded important information relating to, for example, migration and spawning behaviour and behavioural differences between stocks. Aspects of the information obtained can be directly related to both stock assessment and fisheries management.…”