Accuracy and precision in stock separation of north-east Arctic and Norwegian coastal cod by otoliths - comparing readings, image analyses and a genetic method

2005 ◽  
Vol 56 (5) ◽  
pp. 753 ◽  
Author(s):  
Erik Berg ◽  
Tuula H. Sarvas ◽  
Alf Harbitz ◽  
Svein Erik Fevolden ◽  
Arnt Børre Salberg
Keyword(s):  
Visual Inspection ◽  
Gadus Morhua ◽  
Atlantic Cod ◽  
Complete Separation ◽  
Arctic Cod ◽  
Genetic Method ◽  
North East ◽  
Accuracy And Precision ◽  
Growth Zones ◽  
The Difference

The distinction between north-east Arctic cod and Norwegian coastal cod, two major groups of Atlantic cod (Gadus morhua L.), has for many years been based on different distance and shape similarities between the two first translucent growth zones in the otoliths, subjectively decided by visual inspection in a binocular. To analyse the certainty of this technique, four independent readers have classified 263 cod otoliths in total from five different geographical areas. For three of the readers, between 82% and 89% of the classification results coincided with independent results based on genetic analyses. Further, 38 cod otoliths, where the readers were certain of the classification (21 north-east Arctic cod and 17 coastal cod) were classified by several image analysis methods. A complete separation was obtained by using the ratio of the circumferences of the two zones, providing a typical ratio of approximately 2 for coastal and 1.5 for north-east Arctic cod. The otolith method for separating the two types of cod has been considered adequately accurate in assessing the two stocks of cod. However, the method is sensitive to subjective interpretation, and action needs to be taken to minimise the difference in interpretation among otolith readers.

scholarly journals The making of a genetic cline: introgression of oceanic genes into coastal cod populations in the North East Atlantic

2021 ◽  
Author(s):  
Per Erik Jorde ◽  
Mats BO Huserbråten ◽  
Bjørghild Breistein Seliussen ◽  
Mari Skuggedal Myksvoll ◽  
Frode B. Vikebø ◽  
...  
Keyword(s):  
Gene Flow ◽  
Gadus Morhua ◽  
Atlantic Cod ◽  
Arctic Cod ◽  
North East ◽  
The North ◽  
Extended Contact ◽  
Pelagic Eggs ◽  
Genetic Cline ◽  
Eggs And Larvae

Coastal Atlantic cod (Gadus morhua) in the Northeast Atlantic has seen a continuous decline since the industrialization of the coastal fishery and management needs to address the spatial and temporal complexities of coexisting cod stocks. Toward that end, genetic analyses and oceanographic modelling of coastal and oceanic cod larval drift patterns were combined to elucidate the mechanisms responsible for an observed genetic cline over a >1500 km stretch along the coast of Norway. The results indicate that the north-south cline in coastal cod represents an extended contact zone between genetically divergent North Sea and North East Arctic cod and is maintained by two-way gene flow: by northward drift of pelagic eggs and larvae and by southward spawning migrations of North East Arctic cod. Computer simulations verify that the genetic cline can be established rapidly if gene flow into coastal populations is substantial. The shape of the cline, on the other hand, was found to be largely insensitive to the total amount of gene flow and therefore carries little information on extent of gene flow into and among coastal populations.

scholarly journals Differences in spawning time of captive Atlantic cod from four regions of Norway, kept under identical conditions

2006 ◽  
Vol 63 (2) ◽  
pp. 216-223 ◽  
Author(s):  
Håkon Otterå ◽  
Ann-Lisbeth Agnalt ◽  
Knut E. Jørstad
Keyword(s):  
Life History ◽  
Genetic Control ◽  
Environmental Conditions ◽  
Gadus Morhua ◽  
Atlantic Cod ◽  
Spawning Period ◽  
Life History Parameters ◽  
Wide Range ◽  
Spawning Time ◽  
The Difference

Abstract Several hundred Atlantic cod (Gadus morhua L.) were collected from selected spawning grounds along the Norwegian coast in March 2002. Four areas or regions that represent a wide range of environmental conditions were chosen for our breeding experiments: Porsangerfjord, Tysfjord, Helgeland, and Øygarden. Cod were transported to Øygarden near Bergen, individually tagged, and kept in sea cages. In both 2003 and 2004, a total of 40 family groups (adult pairs) representing the four regions were monitored for their spawning performance in separate tanks. During the spawning period, the quantity and diameter of eggs were recorded. During 2003, the time of peak spawning differed among groups. It was evident that the broodstock from the Øygarden region spawned about one month earlier than the broodstock collected from the Helgeland region. This also occurred in 2004, two years after the cod were collected, suggesting that the difference has a genetic component. Differences in life history parameters between cod populations, such as spawning cycles as described here, could be adaptive and under genetic control. This must be taken into consideration when assessing precautionary means of overcoming the problem with escapees from future cod mariculture.

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.

scholarly journals The acoustic dead zone: theoretical vs. empirical estimates, and its effect on density measurements of semi-demersal fish

2009 ◽  
Vol 66 (6) ◽  
pp. 1364-1369 ◽  
Author(s):  
L. G. S. Mello ◽  
G. A. Rose
Keyword(s):  
Newfoundland And Labrador ◽  
Gadus Morhua ◽  
Atlantic Cod ◽  
Dead Zone ◽  
Demersal Fish ◽  
Depth Gradient ◽  
Density Measurements ◽  
Acoustic Data ◽  
Empirical Estimates ◽  
The Difference

Abstract Mello, L. G. S., and Rose, G. A. 2009. The acoustic dead zone: theoretical vs. empirical estimates, and its effect on density measurements of semi-demersal fish. – ICES Journal of Marine Science, 66: 1364–1369. The height of the acoustic dead zone, the region near the seabed where fish cannot be resolved acoustically, was calculated both theoretically (DZt) and empirically (DZe). The DZe was based on measurements of depth and trawl geometry from sensors (SCANMAR) mounted on a bottom trawl deployed during a survey off Newfoundland and Labrador in winter 2007. Acoustic data were acquired while trawling, using a 38-kHz echosounder (Simrad EK500) with a hull-mounted transducer. The DZe was calculated as the difference between the trawl-footrope depth and the corresponding acoustically sensed, seabed depth. EK500 and SCANMAR estimates of seabed depth were significantly different. The fish caught were mostly Atlantic cod (Gadus morhua). The estimates of DZe ranged between 2.0 and 3.5 m and were greater than DZt by 0.1–0.9 m in more than half the cases. Three values of acoustically derived cod densities were estimated for each tow, without dead-zone correction and with corrections for DZt and DZe. When compared with DZt corrections, DZe resulted in negative (6–12%) and positive (9–35%) corrections to cod density. A general linear model revealed that the seabed depth gradient, standard deviation of estimated fish density in the dead zone, and wind direction and force explained 85% of the difference between DZt and DZe estimates. These factors affected the detection of the seabed and biased acoustically derived indices of demersal-fish abundance.

scholarly journals Climate change in fish: effects of respiratory constraints on optimal life history and behaviour

2015 ◽  
Vol 11 (2) ◽  
pp. 20141032 ◽  
Author(s):  
Rebecca E. Holt ◽  
Christian Jørgensen
Keyword(s):  
Metabolic Rate ◽  
Life Histories ◽  
Gadus Morhua ◽  
Atlantic Cod ◽  
Standard Metabolic Rate ◽  
Aerobic Scope ◽  
Trade Offs ◽  
Different Temperatures ◽  
The Difference ◽  
Common Trade

The difference between maximum metabolic rate and standard metabolic rate is referred to as aerobic scope, and because it constrains performance it is suggested to constitute a key limiting process prescribing how fish may cope with or adapt to climate warming. We use an evolutionary bioenergetics model for Atlantic cod ( Gadus morhua ) to predict optimal life histories and behaviours at different temperatures. The model assumes common trade-offs and predicts that optimal temperatures for growth and fitness lie below that for aerobic scope; aerobic scope is thus a poor predictor of fitness at high temperatures. Initially, warming expands aerobic scope, allowing for faster growth and increased reproduction. Beyond the optimal temperature for fitness, increased metabolic requirements intensify foraging and reduce survival; oxygen budgeting conflicts thus constrain successful completion of the life cycle. The model illustrates how physiological adaptations are part of a suite of traits that have coevolved.

Spatial and temporal microsatellite variation in spawning Atlantic cod, Gadus morhua, around Iceland

2013 ◽  
Vol 70 (8) ◽  
pp. 1151-1158 ◽  
Author(s):  
Guðni Magnús Eiríksson ◽  
Einar Árnason
Keyword(s):  
Allele Frequency ◽  
Gadus Morhua ◽  
Atlantic Cod ◽  
Genetic Difference ◽  
North Coast ◽  
The South ◽  
Microsatellite Variation ◽  
The North ◽  
Significant Difference ◽  
The Difference

The present study suggests that the observed genetic difference between Atlantic cod, Gadus morhua, off the south and the north coast of Iceland may be caused by natural selection affecting genetic variation at a microsatellite loci (Gmo34). When disregarding this locus from the analysis, no genetic difference was observed between northern and southern Iceland. The methods applied here were very sensitive, and differences as small as FST = 0.0005 are unlikely to go unnoticed. The difference between cod off the south and the north coast of Iceland is thus likely to be smaller than that. Such a small difference is negligible and is not likely to have any biological meaning. Genetic drift was detected by allele frequency comparison among different cohorts (FST = 0.0007, P = 0.0209). A small but significant difference was observed among allele frequency for cod grouped by depth at the south coast of Iceland (FST = 0.0017, P = 0.0002). This difference is very subtle and needs to be interpreted with caution.

scholarly journals Condition indices of Atlantic cod (Gadus morhua) biased by capturing method

2012 ◽  
Vol 69 (10) ◽  
pp. 1781-1788 ◽  
Author(s):  
Mikael Ovegård ◽  
Kim Berndt ◽  
Sven-Gunnar Lunneryd
Keyword(s):  
Gadus Morhua ◽  
Atlantic Cod ◽  
Geographical Area ◽  
Lower Growth ◽  
Fish Stocks ◽  
Underlying Causes ◽  
The Difference ◽  
Condition Indices ◽  
The Baltic ◽  
Size At Age

Abstract Ovegård, M., Berndt, K., and Lunneryd, S-G. 2012. Condition indices of Atlantic cod (Gadus morhua) biased by capturing method. – ICES Journal of Marine Science, 69: 1781–1788. In studies evaluating the condition and general health status of fish stocks, the method used for catching the fish is seldom considered as a factor of importance. In this study, condition indices were compared between cod caught in pots, gillnets, and on hooks in the same geographical area. The results showed that cod (Gadus morhua) caught on baited gear types (pots and hooks) generally displayed a lower condition and an older age (i.e. suggesting a lower growth rate) compared to cod caught in gillnets. It is unclear whether these results merely illustrate divergent behavioural responses in fish originating from one single population, or if these divergent behavioural components represent distinct subpopulations displaying different mean conditions and growth rates. Regardless of the underlying causes, the results not only show that parts of the Baltic cod stock are in extremely poor condition, they also indicate that different gear types used in the same area could target similar-sized conspecifics exhibiting large differences in condition and size-at-age. The potential impact of the difference in condition between the pots and other gear types could hamper the implementation of the cod pot as a potentially seal-safe and sustainable fishing method.

Analysing migrations of Atlantic cod Gadus morhua in the north-east Atlantic Ocean: then, now and the future

2013 ◽  
Vol 82 (3) ◽  
pp. 741-763 ◽  
Author(s):  
S. Neuenfeldt ◽  
D. Righton ◽  
F. Neat ◽  
P. J. Wright ◽  
H. Svedäng ◽  
...  
Keyword(s):  
Atlantic Ocean ◽  
Gadus Morhua ◽  
Atlantic Cod ◽  
East Atlantic ◽  
North East ◽  
The North ◽  
The Future

Diet of harp seals (Phoca groenlandica) in nearshore waters of the northwest Atlantic during 1990 – 1993

1995 ◽  
Vol 73 (10) ◽  
pp. 1805-1818 ◽  
Author(s):  
John W. Lawson ◽  
Garry B. Stenson ◽  
Dave G. McKinnon
Keyword(s):  
Gadus Morhua ◽  
Atlantic Cod ◽  
Stomach Contents ◽  
Clupea Harengus ◽  
Relative Importance ◽  
Northwest Atlantic ◽  
Arctic Cod ◽  
Diet Diversity ◽  
Phoca Groenlandica ◽  
Capelin Mallotus Villosus

The nearshore diet of northwest Atlantic harp seals (Phoca groenlandica) was determined by reconstructing the contents of 1167 prey-containing stomachs (78.3% of 1490) collected from 1990 to 1993. Although harp seals consumed at least 62 species, 6 accounted for most of the mass consumed and their relative importance varied by area. Based on percent wet mass, sculpins (Cottidae) and Arctic cod (Boreogadus saida) were the main components of the diet of older seals (> 1 year old) off Labrador, whereas Arctic cod and Atlantic herring (Clupea harengus) were the main prey of seals from northeastern Newfoundland. A more diverse diet was observed in seals taken off the west coast of Newfoundland, where capelin (Mallotus villosus), herring, Atlantic cod (Gadus morhua), redfish (Sebastes spp.), and Arctic cod were the main species. Redfish and Atlantic cod were important to seals along the south coast of Newfoundland. Eighty percent of fish consumed were less than 18 cm long, smaller than those taken by commercial fisheries. Pups (less than 1 year old) consumed fewer and smaller prey of a less varied assortment. Annual and seasonal variation in the diets was observed in the collection from northeastern Newfoundland. Arctic cod was the major prey consumed throughout the year by seals of all ages, although the relative importance of herring, capelin, and squid (Teuthoidea) increased during the summer. Invertebrates and capelin made up a greater proportion of the diet in 1992, owing to a decline in consumption of Arctic cod. This finding was associated with a decrease in the mass of stomach contents. Diet diversity did not change significantly over the study period.

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