Survey gear calibration independent of spatial fish distribution

2004 ◽  
Vol 61 (4) ◽  
pp. 636-647 ◽  
Author(s):  
Peter Lewy ◽  
J Rasmus Nielsen ◽  
Holger Hovgård
Keyword(s):  
Gadus Morhua ◽  
Atlantic Cod ◽  
Survey Design ◽  
Fish Distribution ◽  
Simulation Studies ◽  
Conversion Factors ◽  
The Baltic ◽  
Standard Software ◽  
Track Line ◽  
Stock Abundance

Trawl surveys provide important information for evaluation of relative stock abundance fluctuations over time. Therefore, when survey gears or vessels are changed, it is important to compare the efficiency and selectivity of old and new gears and vessels. A method for estimation of conversion factors is developed based on a survey design where paired hauls are taken in the same trawl track line. The method explicitly accounts for changes in fish density caused by trawling disturbance. A generalized linear model for paired hauls catches is analytically derived and the gear conversion and disturbance parameters with their precision are obtained using standard software. Simulation studies carried out additionally showed that the estimated conversion factors were practically unbiased. Because of the independence of the spatial fish distribution, the new method is preferable to the traditional paired hauls design for which it is generally not possible to obtain the statistical properties of the estimated conversion factors. The paper is concluded with suggestions on how to optimize survey design. The method was used to estimate conversion factors for Atlantic cod (Gadus morhua) from Danish gear calibration experiments in the Baltic Sea.

How to validate a length-based model of single-species fish stock dynamics

2006 ◽  
Vol 63 (11) ◽  
pp. 2531-2542 ◽  
Author(s):  
Kasper Kristensen ◽  
Peter Lewy ◽  
Jan E Beyer
Keyword(s):  
Survey Data ◽  
Gadus Morhua ◽  
Negative Binomial ◽  
Atlantic Cod ◽  
Population Level ◽  
Single Species ◽  
Model Complexity ◽  
Fish Stock ◽  
Statistical Hypotheses ◽  
The Baltic

This paper validates a new length-based model of the dynamics of fish stocks or crustaceans by hierarchically testing statistical hypotheses and thereby investigating model complexity. The approach is based entirely on scientific survey data and on determination of the statistical distributions of the number of fish caught per haul in each length class. In our example, the negative binomial distribution is statistically accepted and linked to the population level through the new length-based model. The model is derived from the characteristics of continuous recruitment, individually based growth, and continuous, length-dependent mortality rates. Continuous recruitment with annually varying recruitment peaks and individually based growth was crucial for obtaining a model that could be statistically accepted. Natural mortality was estimated as well by the model. The model was applied to survey data for Atlantic cod (Gadus morhua) in the Baltic. Its simple generic nature, as well as the validation procedure, is useful in studying and understanding life history and stock dynamics.

scholarly journals Mitochondrial Cytochrome b DNA Sequence Variation of Atlantic Cod, Gadus Morhua, from the Baltic and the White Seas

Hereditas ◽  
2004 ◽  
Vol 129 (1) ◽  
pp. 37-43 ◽  
Author(s):  
Einar Árnason ◽  
Pétur Henry Petersen ◽  
Snaebjörn Pálsson
Keyword(s):  
Dna Sequence ◽  
Cytochrome B ◽  
Gadus Morhua ◽  
Sequence Variation ◽  
Atlantic Cod ◽  
Mitochondrial Cytochrome ◽  
Mitochondrial Cytochrome B ◽  
Dna Sequence Variation ◽  
The Baltic

scholarly journals Understanding the release efficiency of Atlantic cod (Gadus morhua) from trawls with a square mesh panel: effects of panel area, panel position, and stimulation of escape response

2014 ◽  
Vol 72 (2) ◽  
pp. 686-696 ◽  
Author(s):  
Bent Herrmann ◽  
Harald Wienbeck ◽  
Junita Diana Karlsen ◽  
Daniel Stepputtis ◽  
Erdmann Dahm ◽  
...  
Keyword(s):  
Escape Response ◽  
Gadus Morhua ◽  
Atlantic Cod ◽  
Mesh Size ◽  
Accumulation Zone ◽  
Trawl Fishery ◽  
Trawl Fishing ◽  
Panel Effects ◽  
The Baltic ◽  
Stimulation Of

Abstract Based on size selectivity data for more than 25 000 cod (Gadus morhua) collected during experimental trawl fishing with six different codends, all of which included a square mesh panel, we investigated the effect on cod-release efficiency based on the size of the square mesh panel area, position of the square mesh panel, and stimulation of the escape response. Based on the results, we were able to explain why the BACOMA codend, applied in the Baltic Sea cod directed trawl fishery, releases juvenile cod efficiently, whereas other designs, including a square mesh panel with similar mesh size, are less efficient. Our main findings reveal that the release efficiency of the square mesh panel in the BACOMA codend depends largely on the overlap of the square mesh panel and the catch-accumulation zone in the codend, where cod do not have the option of just drifting further back in the trawl when proximate to the panel. On the contrary, the reduction in panel size by 50% did not significantly affect the release efficiency when the panel overlapped with the catch-accumulation zone. It was possible to stimulate an escape response for cod to achieve a release through a square mesh panel positioned away from the catch-accumulation zone. Our findings demonstrated that this release was as efficient as for a panel mounted in the catch-accumulation zone of the codend. Devices that stimulate behaviour may improve the release efficiency of cod through square mesh panels in other fisheries where this is a problem.

scholarly journals Transcriptome analysis of gill tissue of Atlantic cod Gadus morhua L. from the Baltic Sea

2015 ◽  
Vol 23 ◽  
pp. 37-40 ◽  
Author(s):  
Magdalena Małachowicz ◽  
Agnieszka Kijewska ◽  
Roman Wenne
Keyword(s):  
Baltic Sea ◽  
Transcriptome Analysis ◽  
Gadus Morhua ◽  
Atlantic Cod ◽  
Gill Tissue ◽  
The Baltic Sea ◽  
The Baltic

Biological indications of contaminant exposure in Atlantic cod (Gadus morhua) in the Baltic Sea

2008 ◽  
Vol 65 (6) ◽  
pp. 1122-1134 ◽  
Author(s):  
Sabine Schnell ◽  
Doris Schiedek ◽  
Rolf Schneider ◽  
Lennart Balk ◽  
Pekka J. Vuorinen ◽  
...  
Keyword(s):  
Baltic Sea ◽  
Organic Contaminants ◽  
Gadus Morhua ◽  
Polychlorinated Biphenyl ◽  
Atlantic Cod ◽  
Human Impacts ◽  
Toxic Substances ◽  
The Baltic Sea ◽  
Contaminant Exposure ◽  
The Baltic

The Baltic Sea is exposed to severe human impacts. Besides eutrophication and overfishing, a variety of chemical contaminants threaten the health of fish. During a cruise in December 2001, Atlantic cod ( Gadus morhua ) were collected in the western and southern Baltic Sea, somatic condition factors were estimated, and different biomarkers of contaminant exposure were analysed. Additionally, various polychlorinated biphenyl congeners and organochlorine pesticides were measured in cod liver as more general indicators of pollution, not necessarily as the causative agents for biomarker signals. In most specimens, hepatic ethoxyresorufin-O-deethylase activity and bile 1-OH pyrene, a common polycyclic aromatic hydrocarbon metabolite, were detectable. Both features indicate an induction of the CYP1A biotransformation system in response to toxic substances. The increased occurrence of DNA adducts in some of the specimens also indicates the presence of genotoxic substances. Acetylcholinesterase was inhibited, an indication of exposure to organophosphates, carbamates, or certain heavy metals, particularly in specimens taken at Wismar Bay and off the Lithuanian coast. In general, spatial differences in the biomarker responses as well as in contaminant loads were found, suggesting differences in physiologically active concentrations and mixtures of organic contaminants in this ecosystem.

scholarly journals An adaptive, integrated “acoustic-trawl” survey design for Atlantic cod (Gadus morhua) with estimation of the acoustic and trawl dead zones

2005 ◽  
Vol 62 (1) ◽  
pp. 93-106 ◽  
Author(s):  
Ian H. McQuinn ◽  
Yvan Simard ◽  
Thomas W.F. Stroud ◽  
Jean-Louis Beaulieu ◽  
Stephen J. Walsh
Keyword(s):  
Gadus Morhua ◽  
Sampling Design ◽  
Atlantic Cod ◽  
Survey Design ◽  
Dead Zone ◽  
Total Biomass ◽  
Trawl Survey ◽  
Acoustic Survey ◽  
Night Time ◽  
Diel Vertical Migrations

Abstract The objectives of this study were to design an operationally efficient groundfish survey integrating both acoustic and trawl methodologies, to measure the changing vertical availability of cod to each method over 24 h and to compare cod-biomass estimates from the two methods within two experimental sub-regions. The two-phased sampling design involved (i) conducting an initial systematic acoustic survey to locate an area of high cod concentrations, (ii) using the acoustic-backscatter information to stratify the sub-regions into density strata for the allocation of trawl hauls, and (iii) conducting a second systematic acoustic survey at the same time as a random-stratified trawl survey. This protocol permitted the optimization of trawl sampling according to population density and the realization of simultaneous trawl and acoustic estimates for direct comparison. These cod showed extensive diel vertical migrations, which affected their availability to the trawl gear at night and the acoustic beam by day. An acoustic dead-zone correction was applied to the acoustic estimates, averaging 4–15% of the biomass for the night-time transects and 11–36% for the daytime transects. The detailed temporal acoustic monitoring of the vertical migrations permitted the quantification of the change in cod availability to the trawl gear. From 6% to 47% of cod were above the effective trawl height at night, while 0–10% of cod were in the “trawl dead zone” by day. Estimated cod densities were very similar between the two methods on a haul-by-haul basis after correcting each method for their respective inherent sampling biases. The total biomass estimates were also comparable between the two methods for one sub-region, although significantly higher from the trawl data for the other. The discrepancies were most likely a result of differences in the sampling density of the two methods.

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.

scholarly journals Using the particle filter to geolocate Atlantic cod (Gadus morhua) in the Baltic Sea, with special emphasis on determining uncertainty

2007 ◽  
Vol 64 (4) ◽  
pp. 618-627 ◽  
Author(s):  
K H Andersen ◽  
A Nielsen ◽  
U H Thygesen ◽  
H -H Hinrichsen ◽  
S Neuenfeldt
Keyword(s):  
Baltic Sea ◽  
Particle Filter ◽  
Gadus Morhua ◽  
Atlantic Cod ◽  
Day Length ◽  
Swimming Velocity ◽  
Spatial And Temporal Variability ◽  
The Baltic Sea ◽  
Time Step ◽  
The Baltic

The use of archival tags on fish gives information of individual behaviour with an unprecedented high resolution in time. A central problem in the analysis of data from retrieved tags is the geolocation, namely the infererence of movements of the fish by comparing the data from the tags with environmental observations like temperature, tide, day length, etc. The result is usually represented as a track; however, the spatial and temporal variability in the precision is often substantial. In this article, the particle filter is applied to geolocate Atlantic cod (Gadus morhua) in the Baltic Sea, leading to a representation of the results as probability distributions for each time step, thus giving an explicit representation of uncertainty. Furthermore, the method is used to estimate the magnitude of the error in the measurements by the tags and the swimming velocity of the fish. The average swimming velocity during a day was estimated to be around 0.20 m·s–1 for fish of ~60 cm length. The method is general and the presentation is formulated to facilitate implementation for different systems where other quantities are observed.

Reconstructing historical stock development of Atlantic cod (Gadus morhua) in the eastern Baltic Sea before the beginning of intensive exploitation

2008 ◽  
Vol 65 (12) ◽  
pp. 2728-2741 ◽  
Author(s):  
Margit Eero ◽  
Friedrich W. Köster ◽  
Brian R. MacKenzie
Keyword(s):  
Baltic Sea ◽  
Gadus Morhua ◽  
Atlantic Cod ◽  
Reference Level ◽  
Stock Size ◽  
Intensive Exploitation ◽  
Spawning Stock ◽  
The 1950S ◽  
The Baltic ◽  
Eastern Baltic

The landings of Atlantic cod ( Gadus morhua ) in the eastern Baltic Sea in the early decades of the 20th century were below 50 thousand tonnes and therefore lower than in recent years at very low stock size. These low landings have largely contributed to a perception that the stock size was also low before the 1950s. In this investigation, we demonstrate that cod spawning stock biomass in the years 1925–1944 fluctuated in a similar range as in the periods from the 1950s to the mid-1970s and from the late 1980s onwards and was in most of these years at least twice as high as at present. Fishing mortality before the 1940s was below 0.2, but reached moderate levels during the Second World War. The stock size before the war may be considered as a reference level of biomass at low fishing impact, providing important information for the management of fisheries and the Baltic ecosystem.

scholarly journals Effects of freezing on length and mass measurements of Atlantic cod Gadus morhua in the Baltic Sea

2019 ◽  
Vol 95 (6) ◽  
pp. 1486-1495 ◽  
Author(s):  
Kate McQueen ◽  
Monica Mion ◽  
Annelie Hilvarsson ◽  
Michele Casini ◽  
Hans J. Olesen ◽  
...  
Keyword(s):  
Baltic Sea ◽  
Gadus Morhua ◽  
Atlantic Cod ◽  
Mass Measurements ◽  
The Baltic Sea ◽  
The Baltic
Sign in / Sign up

Export Citation Format

Share Document