scholarly journals Otolith shape differences between ecotypes of Icelandic cod (Gadus morhua) with known migratory behaviour inferred from data storage tags

2017 ◽  
Vol 74 (12) ◽  
pp. 2122-2130 ◽  
Author(s):  
Hlynur Bardarson ◽  
Bruce. J. McAdam ◽  
Vilhjalmur Thorsteinsson ◽  
Einar Hjorleifsson ◽  
Gudrun Marteinsdottir
Keyword(s):  
Data Storage ◽  
Gadus Morhua ◽  
Fourier Transforms ◽  
Function Analysis ◽  
Variable Temperature ◽  
Otolith Shape ◽  
Use Of Data ◽  
Data Storage Tags ◽  
Migratory Strategies ◽  
Definition Of

Otolith shape can be used to identify ecotypes of the Icelandic cod (Gadus morhua) stock. The use of data storage tags has increased our knowledge of the stock structure of Icelandic cod. The profiles of tagged cod reveal different migratory strategies. This has led to the definition of two ecotypes within the cod stock. Frontal ecotypes reside in deep waters during feeding season and express a highly variable temperature profile associated with thermal fronts, while coastal ecotypes stay in shallow waters all year round. In this study, the data storage tag profiles were analysed with cluster analysis, which revealed the existence of an intermediate behaviour that expresses a variable depth profile and feeding migration that is both shorter in time and not as deep. The main objective was to develop a morphological key based on otoliths to distinguish the ecotypes. The shape of the otoliths was extracted with shape measurements and fast Fourier transforms. A discriminant function analysis indicated a difference in morphology between the ecotypes, resulting in successful classification.

Spawning behavior in Atlantic cod: analysis by use of data storage tags

2014 ◽  
Vol 506 ◽  
pp. 279-290 ◽  
Author(s):  
TB Grabowski ◽  
V Thorsteinsson ◽  
G Marteinsdóttir
Keyword(s):  
Data Storage ◽  
Atlantic Cod ◽  
Spawning Behavior ◽  
Use Of Data ◽  
Data Storage Tags

scholarly journals Life under pressure: insights from electronic data-storage tags into cod swimbladder function

2007 ◽  
Vol 64 (7) ◽  
pp. 1293-1301 ◽  
Author(s):  
Jeroen van der Kooij ◽  
David Righton ◽  
Espen Strand ◽  
Kathrine Michalsen ◽  
Vilhjalmur Thorsteinsson ◽  
...  
Keyword(s):  
Data Storage ◽  
Gadus Morhua ◽  
Fish Length ◽  
Pressure Reduction ◽  
Electronic Data ◽  
Data Storage Tags ◽  
Rapid Ascent ◽  
Using Data ◽  
Electronic Tagging ◽  
Negatively Buoyant

Abstract van der Kooij, J., Righton, D., Strand, E., Michalsen, K., Thorsteinsson, V., Svedäng, H., Neat, F. C., and Neuenfeldt, S. 2007. Life under pressure: insights from electronic data-storage tags into cod swimbladder function. – ICES Journal of Marine Science. 64: 1293–1301. The behavioural response of cod (Gadus morhua) to sudden pressure reductions was investigated in a large electronic-tagging experiment using data collected from 141 cod tagged in five different areas of the Northeast Atlantic. More than 40% of cod exhibited a characteristic equilibration behaviour after a rapid pressure reduction caused either by capture before tagging, or by pressure reduction during a rapid ascent from the seabed, or when migrating to deeper water. The equilibration allowed the cod to regain demersal residence. The rate of descent averaged 10 m d−1 (ranging from 2 to 23 m d−1) over periods of less than a day to 1 month. Descent rates for cod on the Icelandic shelf were inversely related to fish length, i.e. smaller fish descended more rapidly, findings consistent with results achieved in the past under laboratory conditions. Modelling of swimbladder volume during equilibration suggested that cod were negatively buoyant for most of the time. The results imply that swimbladder functionality is retained after the probable barotrauma that would follow a large and rapid ascent, and that rates of gas exchange into the swimbladder may be naturally variable. These findings have implications for assumptions on discard mortality, the interpretation of cod behaviour, and its impact on biomass estimates obtained from acoustic surveys.

Reconstructing migrations of individual cod (Gadus morhua L.) in the Baltic Sea by using electronic data storage tags

2007 ◽  
Vol 16 (6) ◽  
pp. 526-535 ◽  
Author(s):  
STEFAN NEUENFELDT ◽  
HANS-HARALD HINRICHSEN ◽  
ANDERS NIELSEN ◽  
KEN H. ANDERSEN
Keyword(s):  
Baltic Sea ◽  
Data Storage ◽  
Gadus Morhua ◽  
The Baltic Sea ◽  
Electronic Data ◽  
Data Storage Tags ◽  
The Baltic

Migration patterns of the Faroe Plateau cod ( Gadus morhua , L.) revealed by data storage tags

2017 ◽  
Vol 195 ◽  
pp. 37-45 ◽  
Author(s):  
Katharina Maj Ottosen ◽  
Martin Wæver Pedersen ◽  
Sólvá Káradottir Eliasen ◽  
Petur Steingrund ◽  
Eyðfinn Magnussen ◽  
...  
Keyword(s):  
Data Storage ◽  
Gadus Morhua ◽  
Migration Patterns ◽  
Data Storage Tags

scholarly journals Use of data storage tags to quantify vertical movements of cod: effects on acoustic measures

2004 ◽  
Vol 61 (7) ◽  
pp. 1062-1070 ◽  
Author(s):  
O. Heffernan ◽  
D. Righton ◽  
K. Michalsen
Keyword(s):  
Data Storage ◽  
Gadus Morhua ◽  
Vertical Movement ◽  
Neutral Buoyancy ◽  
Vertical Movements ◽  
Acoustic Measures ◽  
Depth Data ◽  
Basic Assumptions ◽  
Use Of Data ◽  
Sampling Intervals

Abstract Depth data from archival tagging studies of cod (Gadus morhua) were used in three different analyses with the aim of testing basic assumptions of cod behaviour. Examination of post-release depth profiles from cod tagged in the Barents, North, and Irish Seas revealed that some cod underwent a post-release period of adaptation to increasing depth as they readjusted their buoyancy to its pre-tagging level. This depth adaptation behaviour was characterized by gradually increasing mean depth, and enabled the calculation of neutral-buoyancy compliant descent rates, which were less than 1 m h−1. Estimated rates of vertical movement were shown to be highly dependent upon the frequency at which depth was sampled. Maximum estimated rates of ascent and descent from sampling intervals of 10 or 15 min were inconsistent with the maintenance of neutral buoyancy, but estimates from sampling intervals greater than 1 h were not. Calculation of tilt angles using depth data sampled at 10-s intervals showed that cod were often tilted more than 5° relative to the horizontal, and that this effect was more pronounced at night. These findings suggest that basic assumptions regarding cod physiology and behaviour require revision if the accuracy and precision of acoustic methods are to be improved.

Connectivity among offshore feeding areas and nearshore spawning grounds; implications for management of migratory fish

2017 ◽  
Vol 75 (1) ◽  
pp. 148-157 ◽  
Author(s):  
Jón Sólmundsson ◽  
Ingibjörg G Jónsdóttir ◽  
Stefán Á Ragnarsson ◽  
Björn Björnsson
Keyword(s):  
Data Storage ◽  
Gadus Morhua ◽  
Migratory Fish ◽  
Long Distance ◽  
Migration Patterns ◽  
Spatial Management ◽  
Data Storage Tags ◽  
Low Levels ◽  
Mature Fish ◽  
Migration Pathways

Abstract Knowing movement and structure of fish populations is a prerequisite for effective spatial fisheries management. The study evaluates migration patterns and connectivity of two groups of cod (Gadus morhua) associated with offshore feeding and nursery grounds. This was achieved by investigating (i) migration pathways of cod tagged at the feeding areas, (ii) immigration of cod to the areas based on mark-recapture data covering a period of two decades, and (iii) depth and temperature data from data storage tags (DSTs). Despite undertaking long-distance migrations after attaining sexual maturity, the cod aggregations in the two study areas appear to be largely separated from each other. This conclusion is supported by DSTs, indicating that mature fish associated with the two areas occupy different thermal-bathymetric niches. Low levels of connectivity suggest that effective spatial management in the two study areas would preserve fish of different origin. For the highly migratory adults, however, spatial management would need to focus on migration pathways and the areas where the fish are particularly vulnerable to fishing.

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