Coastal Atlantic Cod Gadus Morhua Research Articles

Attraction of cod Gadus morhua from coastal spawning grounds to salmon farms

Wild fish aggregate at aquaculture net-pens, but the underlying mechanisms are not fully understood. This study examined how salmon farms attract coastal Atlantic cod Gadus morhua from their inshore spawning grounds. Acoustic receivers were deployed at 5 known cod spawning grounds and 6 salmon Salmo salar farms located at varying distances from these grounds in a mid-Norway study site. Cod were caught at each spawning ground annually from 2017-2019, fitted with acoustic transmitters and released (n = 535). A total of 289 tagged cod (54%) were detected at the salmon farms, with more cod detected at farms closest to the focal spawning grounds and at operational farms. The latter result is likely linked to the availability of feeding opportunities at farm locations. Those cod that were detected by the receivers spent less time at farms farther from their release locations. For the farm-associated cod, 70% were detected for <1 wk at the farms. However, 48 cod spent >1 mo close to the farms, with 1 individual staying 720 d underneath the farm. A total of 135 cod visited 2 or more farms, with farms in proximity more connected in terms of inter-farm movement. Some of the cod utilizing these local spawning grounds likely have considerable dietary input from salmon feed.

Spatial ecology of coastal Atlantic cod Gadus morhua associated with parasite load.

Acoustic tags and receivers were used to investigate the spatial ecology of coastal Atlantic cod Gadus morhua (n = 32, mean fork length: 50 cm, range: 33-80 cm) on the Norwegian Skagerrak coast in 2012. Monthly home ranges (HR), swimming activity and depth use varied considerably among individuals and through the months of June, July and August. HR sizes for the period ranged from 0.25 to 5.20 km2 (mean = 2.30 km2. Two thirds of the tagged G. morhua were infected with black spot disease Cryptocotyle lingua parasites; these fish had larger HRs and occupied deeper water compared with non-infected fish. The infected fish also tended to be more active in terms of horizontal swimming. From an ecological and evolutionary perspective, any environmental change that modifies G. morhua behaviour may therefore also alter the parasite load of the population, and its conservation and fishery status.

New perspectives on fish movement: kernel and GAM smoothers applied to a century of tagging data on coastal Atlantic cod

Tagging-recovery studies have been used successfully on many occasions, and the data analysed in a variety of ways with respect to fish movement. Here we provide a synoptic account of useful statistical techniques for delimiting area utilization and movement patterns of a population of individuals. We focus specifically on kernel smoothing for population utilization distribution and gen- eralized additive models for temporal movement patterns. Furthermore, we use these 2 techniques to re-analyse data from tagging studies on coastal Atlantic cod Gadus morhua, shedding new light on one of the underlying mechanisms determining the population structure of the coastal cod along the Norwegian Skagerrak coast. Cod were found to use small areas. On average 25% of a population used areas smaller than 10 km 2 , while 95% of a population used areas smaller than 160 km 2 . The movements displayed were fjord-limited and predominantly within the bounds of the population's home range. By re-analysing existing data on neutral genetic markers, we show that the cross- distance of the area utilized was smaller than the distance over which pair-wise genetic differences appear.

Spatial scale of genetic structuring in coastal cod Gadus morhua and geographic extent of local populations

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 343:229-237 (2007) - DOI: https://doi.org/10.3354/meps06922 Spatial scale of genetic structuring in coastal cod Gadus morhua and geographic extent of local populations Per Erik Jorde1,2,*, Halvor Knutsen1, Sigurd Heiberg Espeland2, Nils Chr. Stenseth1,2 1Institute of Marine Research, Flødevigen, 4817 His, Norway 2CEES – Centre for Ecological and Evolutionary Synthesis, University of Oslo, PO Box 1066, Blindern, 0316 Oslo, Norway *Email: p.e.jorde@bio.uio.no ABSTRACT: We estimated the spatial scale of genetically distinguishable populations of coastal Atlantic cod Gadus morhua using microsatellite DNA markers. Significant overall heterogeneity in allele frequencies was found among 5 cod samples (n = 493) along a 79 km segment of the Norwegian Skagerrak coast (FST = 0.0013; p = 0.021). Most (3 out of 4) samples separated by less than 30 km were genetically highly similar (FST < 0), whereas more distantly separated samples were typically genetically different. This genetic differentiation pattern indicates a patchy population structure with local coastal cod populations being limited in geographic extent to approx. 30 km or less. The spatial structure is thus on the scale of local fjords, suggesting a role for local topography in shaping population structure. The population structuring of coastal cod is more fine-scaled than hitherto reported, but is consistent with mark–recapture studies and data on egg distributions, and emphasises the need to focus on local populations in the management of marine fishes. KEY WORDS: Spatial scale · Coastal Atlantic cod · Gadus morhua · Local populations · Genetic differentiation · Microsatellites Full text in pdf format PreviousNextCite this article as: Jorde PE, Knutsen H, Espeland SH, Stenseth NC (2007) Spatial scale of genetic structuring in coastal cod Gadus morhua and geographic extent of local populations. Mar Ecol Prog Ser 343:229-237. https://doi.org/10.3354/meps06922 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 343. Online publication date: August 07, 2007 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2007 Inter-Research.