Diel vertical migration patterns in juvenile cod from the Skagerrak coast

Abstract

We demonstrated a clear year-round diel vertical migration pattern (DVM) of small (26 to 45 cm) Skagerrak coastal cod Gadus morhua on a small geographic scale. Generalized additive models (GAMs) were used to make inferences about depth movements from a large data set of repeated depth measurements of cod fitted with acoustical tags. The general pattern in vertical behaviour was closely linked to sunrise and sunset, and the timing varied with the length of the day. The absolute magnitude of vertical movement was seasonally variable and probably influenced by temperature and food availability. Cod constantly selected deeper residence depths during the day than at night, and during winter than in summer. This study uses flexible models to make generalisations of the varying nature of the diel vertical migration patterns in juvenile coastal cod. KEY WORDS: Diel vertical migration · DVM · Generalized additive models · GAM · Coastal cod · Gadus morhua Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 405: [29][30][31][32][33][34][35][36][37] 2010 DVM as a food driven pattern in prey species may therefore induce a similar vertical migration in the predator species.Explanation (2) is based on the fact that temperature affects the metabolic processes of digesting food and growth (Imsland et al. 2005). Fish can regulate metabolic rate by actively choosing a depth with an optimal ambient temperature (Kristiansen et al. 2001); this 'hunt warm, rest cool' behaviour has been shown in many marine fish species (Sims et al. 2006, Mortensen et al. 2007.Novel technology in data storage tags (DST) and acoustic transmitters with depth sensors have allowed detailed studies of the vertical positions of marine organisms. Given batteries with long lifetimes and good storage capabilities some of these tags may produce 100 000 to 200 000 depth observations from a single fish. Coupled with low cost, this provides the opportunity to acquire large data sets on DVM on aquatic species. Making inferences on 'typical' movement, excluding variable individual effects and abnormal behaviour, may be challenging for large data sets. Generalized additive models (GAM) are ideal for describing patterns in biological data sets with complicated structure. Instead of predefining particular linear or nonlinear functional forms, such models 'let the data tell' by fitting local piecewise polynomials to the data. This makes GAMs more flexible than parametric models as they do not require any a priori definition of the shape of the relationship between predictors and response (Hastie & Tibshirani 1990).In this study, we observed the diel vertical migration of juvenile Atlantic cod Gadus morhua on the Norwegian Skagerrak coast and evaluated the factors influencing vertical movement in coastal cod. We expected the DVM patterns to be affected by the following factors: light intensity, ambient temperature and food availability. These factors exhibit large seasonal variations. We used GAMs as a tool for desc...

Season and site fidelity determine home range of dispersing and resident juvenile Greenland cod Gadus ogac in a Newfoundland fjord

“…data). Similar seasonal movements to deep water have been observed in Atlantic cod (Hanson 1996, Comeau et al 2002, Cote et al 2004, Espeland et al 2010. Importantly, however, plasma antifreeze levels in juvenile cod are significantly higher than in adults during winter conditions (Kao & Fletcher 1988, Goddard et al 1992.…”

Behavioral responses of Atlantic cod to sea temperature changes

“…The upper 5–7 m are composed of rocky bottoms covered by macroalgae or sandy bottoms with eelgrass (Espeland et al. ). The deepest areas (5–40 m) consist mainly of mud flats with sparse vegetation (Espeland et al.…”

“…The deepest areas (5–40 m) consist mainly of mud flats with sparse vegetation (Espeland et al. ). Three channels allow fish to move to and from the bay.…”

Life history of fjord cod from the Skagerrak in the mid-2000s compared to 1905

“…This gear is designed to be set in shallow (about 1 to 5 m) depth, and so bottom depth should be comparable among the samples. In any case, recent telemetry data have shown that cod in the Skagerrak region display a marked diurnal vertical migration pattern, visiting the most shallow (< 5 m) near-shore habitats during nighttime and retreating to deeper habitats during the day (Espeland et al 2010). This pattern is visible for both juvenile cod and larger mature cod.…”