scholarly journals Local cod (Gadus morhua) revealed by egg surveys and population genetic analysis after longstanding depletion on the Swedish Skagerrak coast

2018 ◽  
Vol 76 (2) ◽  
pp. 418-429 ◽  
Author(s):  
Henrik Svedäng ◽  
Julia M I Barth ◽  
Anders Svenson ◽  
Patrik Jonsson ◽  
Sissel Jentoft ◽  
...  
Keyword(s):  
North Sea ◽  
West Coast ◽  
Population Genetic ◽  
Gadus Morhua ◽  
Atlantic Cod ◽  
Early Stage ◽  
Population Genetic Analysis ◽  
Swedish West Coast ◽  
The North ◽  
Spawning Areas

Abstract Dramatic and persistent reductions in Atlantic cod (Gadus morhua) are common in many coastal areas. While offshore cod stocks still were abundant and productive, the Swedish west coast showed signs of diminishing adult cod abundance at the beginning of the 1980s, where the local cod component was considered to be extirpated. To survey the present cod spawning activity and stock composition, we initiated egg trawling over two consecutive years (203 hauls in total) in combination with population genetic analyses (425 individually genotyped eggs). Here, we provide evidence of cod spawning at the Swedish Skagerrak coast, suggesting recolonization or that local cod has recovered from a nearly depleted state. Early stage eggs were found inside fjords too far to have been transported by oceanic drift from offshore spawning areas. The cod eggs were genetically similar in early to late life-stages and cluster mainly with the local adult cod, indicating that eggs and adults belong to the same genetic unit. The cod eggs were genetically differentiated from adult North Sea cod, and, to a lesser degree, also from the Kattegat and Öresund cod, i.e. indicating a possible recovery of local coastal stock. The patterns of the genetic structure in the inshore areas are, however, difficult to fully disentangle, as Atlantic cod in the North Sea-Skagerrak area seem to be a mixture of co-existing forms: local cod completing their entire life cycle in fjords and sheltered areas, and oceanic populations showing homing behaviours. The egg abundances are considerably lower compared with what is found in similar studies along the Norwegian Skagerrak coast. Nevertheless, the discovery of locally spawning cod along the Swedish west coast—although at low biomasses—is an encouraging finding that highlights the needs for endurance in protective measures and of detailed surveys to secure intraspecific biodiversity and ecosystem services.

scholarly journals Linking spawning ground extent to environmental factors — patterns and dispersal during the egg phase of four North Sea fishes

2018 ◽  
Vol 75 (3) ◽  
pp. 357-374 ◽  
Author(s):  
Hannes Höffle ◽  
Cindy J.G. Van Damme ◽  
Clive Fox ◽  
Stéphanie Lelièvre ◽  
Christophe Loots ◽  
...  
Keyword(s):  
North Sea ◽  
Gadus Morhua ◽  
Atlantic Cod ◽  
Early Stage ◽  
Distribution Patterns ◽  
Melanogrammus Aeglefinus ◽  
Spawning Grounds ◽  
The North ◽  
Generalized Additive Mixed Models ◽  
Additive Mixed Models

Previous studies have shown that four commercially important demersal species, namely Atlantic cod (Gadus morhua), haddock (Melanogrammus aeglefinus), whiting (Merlangius merlangus), and European plaice (Pleuronectes platessa), spawn in distinct areas across the North Sea. Based on two comprehensive ichthyoplankton surveys in 2004 and 2009, the present study uses generalized additive mixed models to delimit these spawning grounds using the distribution of recently spawned eggs, investigates their relationship to specific environmental conditions, and examines egg dispersal during their development. Results indicate that presence–absence of early stage eggs is more related to temporal and topographic variables, while egg densities are closely linked with hydrography. Egg distribution patterns were relatively consistent during development and only changed near hatching. Compared with historic observations, the location of the spawning grounds appeared stable on the broad scale but centres of egg abundance varied between the surveyed years. Potential effects of long-term climate change and anthropogenic short-term disturbances, such as seismic surveys, on fish reproduction are discussed, pointing out the demand for multispecies studies on these issues.

An "experiment" on effort allocation of fishing vessels: the role of interference competition and area specialization

2007 ◽  
Vol 64 (2) ◽  
pp. 304-313 ◽  
Author(s):  
Jan-Jaap Poos ◽  
Adriaan D Rijnsdorp
Keyword(s):  
North Sea ◽  
Gadus Morhua ◽  
Atlantic Cod ◽  
Seasonal Pattern ◽  
Interference Competition ◽  
Catch Rate ◽  
The North ◽  
Closed Area ◽  
Fishing Vessels ◽  
The North Sea

A temporarily closed area established to protect spawning Atlantic cod (Gadus morhua) in the North Sea allowed us to study the response of the Dutch beam trawl fleet exploiting common sole (Solea solea) and plaice (Pleuronectes platessa). A number of vessels left the North Sea 1 month earlier than the normal seasonal pattern. The vessels that continued fishing in the North Sea were concentrated in the remaining open areas. In the first week after the closure, the catch rate decreased by 14%, coinciding with an increase in crowding of 28%. Area specialisation affected the response of individual vessels because vessels without prior experience in the open areas showed a larger decline in catch rate compared with vessels that previously fished in these open areas and were more likely to stop fishing during the closed period. The decrease in catch rate in response to the increase in competitor density allowed us to estimate the strength of the interference competition.

Movements and distribution of cod (Gadus morhua) in the southern North Sea and English Channel: results from conventional and electronic tagging experiments

2007 ◽  
Vol 87 (2) ◽  
pp. 599-613 ◽  
Author(s):  
David Righton ◽  
Victoria Anne Quayle ◽  
Stuart Hetherington ◽  
Gary Burt
Keyword(s):  
North Sea ◽  
Gadus Morhua ◽  
Atlantic Cod ◽  
English Channel ◽  
Seasonal Movement ◽  
Southern North Sea ◽  
The North ◽  
Fisheries Policy ◽  
The Uk ◽  
Electronic Tags

The sub-structure of Atlantic cod (Gadus morhua) stocks in the North Sea has important consequences for fisheries management as the Common Fisheries Policy moves towards a more regional approach. We investigated the movements, distribution and behaviour of cod in the southern North Sea (ICES IVc) and English Channel (ICES VIId) by re-analysing historic data from conventional tagging experiments, and by conducting new experiments with electronic tags. Cod tagged and released in IVc showed a northwards shift in distribution during the feeding season consistent with a homing migration away from spawning grounds along the coasts of the UK and the Netherlands. In contrast, cod tagged and released in VIId did not exhibit a consistent pattern of seasonal movement. Many cod released in VIId were subsequently recaptured close to their release position, although some moved out of the Channel and into the southern North Sea. Overlap between the recapture areas of cod released in the different management areas was no more than 25% in either the spawning or feeding season. Behavioural data from electronic tags suggest that cod in IVc make use of tidal streams to migrate northwards and eastwards in spring, whereas selective tidal stream transport was rarely exhibited by cod tagged and released in VIId. Overall, the evidence suggests that there are behavioural differences between cod in IVc and VIId that limit the mixing of cod from these two areas during the feeding and spawning seasons.

scholarly journals First record of brown colouration of Atlantic cod (Gadus morhua, L.) from the North Sea

Oceanologia ◽  
2014 ◽  
Vol 56 (1) ◽  
pp. 159-163
Author(s):  
Agnieszka Rybczyk ◽  
Przemysław Czerniejewski ◽  
Joanna Rokicka-Praxmajer
Keyword(s):  
North Sea ◽  
Gadus Morhua ◽  
Atlantic Cod ◽  
First Record ◽  
The North ◽  
The North Sea

scholarly journals Shifts in spawning phenology of cod linked to rising sea temperatures

2017 ◽  
Vol 74 (6) ◽  
pp. 1561-1573 ◽  
Author(s):  
Kate McQueen ◽  
C. Tara Marshall
Keyword(s):  
Climate Change ◽  
North Sea ◽  
Gadus Morhua ◽  
Atlantic Cod ◽  
Size Structure ◽  
Gonadal Development ◽  
Trophic Levels ◽  
Irish Sea ◽  
The North ◽  
The North Sea

AbstractWarming temperatures caused by climate change have the potential to impact spawning phenology of temperate marine fish as some species have temperature-dependent gonadal development. Inter-annual variation in the timing of Atlantic cod (Gadus morhua) spawning in the northern North Sea, central North Sea and Irish Sea was estimated by calculating an annual peak roe month (PRM) from records of roe landings spanning the last three decades. A trend towards earlier PRM was found in all three regions, with estimates of shifts in PRM ranging from 0.9 to 2.4 weeks per decade. Temperatures experienced by cod during early vitellogenesis correlated negatively with PRM, suggesting that rising sea temperatures have contributed to a shift in spawning phenology. A concurrent reduction in the mean size of spawning females excluded the possibility that earlier spawning was due to a shift in size structure towards larger individuals, as large cod spawn earlier than smaller-sized individuals in the North Sea. Further research into the effects of climate change on the phenology of different trophic levels within the North Sea ecosystem should be undertaken to determine whether climate change-induced shifts in spawning phenology will result in a temporal mismatch between cod larvae and their planktonic prey.

Annual and spatial variability in endo- and ectoparasite infections of North Sea cod (Gadus morhua Linnaeus, 1758) larvae, post-larvae and juveniles

2014 ◽  
Vol 59 (2) ◽  
Author(s):  
Foojan Mehrdana ◽  
Qusay Bahlool ◽  
Alf Skovgaard ◽  
Jesper Kuhn ◽  
Per Kania ◽  
...  
Keyword(s):  
Spatial Variability ◽  
North Sea ◽  
Gadus Morhua ◽  
Sea Water ◽  
Atlantic Cod ◽  
The North ◽  
Infection Pressure ◽  
High Prevalence ◽  
Atlantic Cod Larvae ◽  
The North Sea

AbstractA parasitological investigation was performed on a total of 5380 Atlantic cod larvae, post-larvae and small juveniles sampled from the North Sea during a period of five years. The copepod Caligus elongatus (Von Nordmann, 1832) and the nematode Hysterothylacium aduncum (Rudolphi, 1802) were found at a relatively high prevalence of infection (4.6% and 5.2%, respectively). The infection by both parasites showed annual and spatial variability. C. elongatus showed a higher prevalence in 1992 compared to the following years, whereas the prevalence of H. aduncum increased from 1992 to 2001.We observed a relation between parasite distribution and parameters such as latitude and water depth. Adult digeneans (Lecithaster gibbosus and Derogenes varicus) and larval cestodes were also found with lower infection rates. Since changes of infection levels coincided with increasing North Sea water temperature in the studied period, it is hypothesized that temperature may affect parasite population levels. However, it is likely that other environmental factors may contribute to the observed variations. Absence of infection intensities higher than one nematode per fish in small larvae and post-larvae suggests that host survival may be affected by a high infection pressure. The relatively high levels of infection in the younger stages of cod, and the annual/spatial variability of these infections should be considered in the understanding of the early life dynamics of the species.

scholarly journals Spawning grounds of Atlantic cod (Gadus morhua) in the North Sea

2015 ◽  
Vol 73 (2) ◽  
pp. 304-315 ◽  
Author(s):  
José M. González-Irusta ◽  
Peter J. Wright
Keyword(s):  
North Sea ◽  
Gadus Morhua ◽  
Atlantic Cod ◽  
Spawning Grounds ◽  
The North ◽  
The North Sea

scholarly journals Intrastock differences in maturation schedules of Atlantic cod, Gadus morhua

2011 ◽  
Vol 68 (9) ◽  
pp. 1918-1927 ◽  
Author(s):  
Peter J. Wright ◽  
Colin P. Millar ◽  
Fiona M. Gibb
Keyword(s):  
North Sea ◽  
Gadus Morhua ◽  
Atlantic Cod ◽  
Reaction Norm ◽  
The North ◽  
Spatial Differences ◽  
Additive Contribution ◽  
Population Structuring ◽  
The Difference ◽  
Rate Of Decline

Abstract Wright, P. J., Millar, C. P., and Gibb, F. M. 2011. Intrastock differences in maturation schedules of Atlantic cod, Gadus morhua. – ICES Journal of Marine Science, 68: 1918–1927. Differences in maturation schedules from three subpopulations of North Sea cod (Gadus morhua) were examined using the demographic probabilistic maturation reaction norm (PMRN) approach. Declines in maturation probability with size and age were evident within the North Sea cod stock, but the magnitude of decline differed among subpopulations. The difference in the rate of decline led to significant spatial differences in recent times. Changes in maturation probability could not be explained by colonization from adjacent regions indicating a local response to conditions. The greatest decline in maturation probability followed the near collapse of regional spawning biomass during the 1980s and 1990s. A new methodology was developed to integrate the effects of temperature and competitive biomass into the estimation of the PMRN. Temperature had a positive effect on maturation probability, but could only partially explain the decreasing trend in PMRN midpoints. Consequently, regional selection for early maturing genotypes provides the most parsimonious explanation for the declines in maturation probability observed. The difference in maturation probability among North Sea cod subpopulations, and the additive contribution of temperature to the estimation of change, underscores the need to account for population structuring and to incorporate temperature as a covariate in future applications of the PMRN.

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