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Exploring feeding behaviour patterns of cod (Gadus morhua L) in Öresund using stable isotopes of δ13C and δ15N

Daníelsdóttir, Birna (2013) BION21 20101
Degree Projects in Biology
Abstract
ABSTRACT

The stable isotopes of carbon (13C) and nitrogen (15N) were used to investigate trophic relationships of cod and its prey in Öresund. The diet of cod , Gadus morhua, was studied by analysis of stomach content and stable isotopes of muscle and liver tissues. The present study investigated whether body size or condition was related to stable isotopes of carbon and nitrogen. Gathered from linear regression analysis size based feeding was not present nor did it reveal differences between the tissues. These result and from the mixing model, reveal high degree of diet mixing between benthic and pelagic prey. However comparison of stable isotope data from muscle and liver, displayed their moving in food web across time, demonstrated... (More)
ABSTRACT

The stable isotopes of carbon (13C) and nitrogen (15N) were used to investigate trophic relationships of cod and its prey in Öresund. The diet of cod , Gadus morhua, was studied by analysis of stomach content and stable isotopes of muscle and liver tissues. The present study investigated whether body size or condition was related to stable isotopes of carbon and nitrogen. Gathered from linear regression analysis size based feeding was not present nor did it reveal differences between the tissues. These result and from the mixing model, reveal high degree of diet mixing between benthic and pelagic prey. However comparison of stable isotope data from muscle and liver, displayed their moving in food web across time, demonstrated significant directional change in the food web space. Where over time they shift in their rescource by becoming more omnivorous, gaining with a higher trophic level. (Less)
Abstract
Popular science summary

You are what you eat

In this project I used a method called stable isotope analysis. This method is based on the principle ‘you are what you eat.' To begin whith, isotopes are forms of the same element sharing the same number of electrons but differ from each other in its number of neutrons in the nucleus. For example, stable isotope of 13carbon has one extra neutron then 12carbon. This small and subtle chemical difference and the ratio of these two and can be a very usefule tool for scientist. That is because stable isotope ratios vary among food webs and food sources. Carbon isotopes (13C) reflect the primary producers in the area of feeding and there-fore can be used to determine diet. Nitrogen isotopes... (More)
Popular science summary

You are what you eat

In this project I used a method called stable isotope analysis. This method is based on the principle ‘you are what you eat.' To begin whith, isotopes are forms of the same element sharing the same number of electrons but differ from each other in its number of neutrons in the nucleus. For example, stable isotope of 13carbon has one extra neutron then 12carbon. This small and subtle chemical difference and the ratio of these two and can be a very usefule tool for scientist. That is because stable isotope ratios vary among food webs and food sources. Carbon isotopes (13C) reflect the primary producers in the area of feeding and there-fore can be used to determine diet. Nitrogen isotopes (15N) can be used as an indicator of trophic position in a food web because 15N isotope increases with each trophic level. When an animal feeds, the stable isotopes are incorporated into animal's tissue through its diet. This method can therefore be help-ful to understand food webs, to uncover migratory routes and sometimes it is poss-ible to infer the whereabouts of an animal moving between food webs.

The aim of this project was to utilize the difference in turnover rate in liver and muslce by examining the stable isotope of carbon and nitrogen in muscle and liver of cod in Öresund for different age groups. I wanted to illustrate the feeding patterns of the cod in the area. Furthermore, information gained from stomach contents were compared with stable isotope results. This information, stomach contents (immediate past) as well as δ15N and δ13C of the liver (recent past) and muscle (long-term past), can present indication of individual dietary history integrated over a range of time scales. The goal was to see; (1) if younger individuals are utilizing the same habitat (muslce samples) and as they get older diverge to different feeding grounds (liver samples), (2) are older individuals feeding on different preys over time and does the resources from distinct habitats give them better body condition.

The results showed that the cod clearly displays an omnivorous diet and the generalist feeding includes the spectrum from benthic to pelagic prey and invertebrate to fish. From the results, it is reasonable to say that the cod at the population level are generalist foragers but then the generalist population can be made up of subgroups or specialists, where a separation of three groups where found in muscle samples and these groups show diverging patterns of change in foraging behaviour. These groups, over time, shift in their resources, showing more specialized feeding behavoiur at younger age but then shift to more omnivourous diet as the get older.



Supervisor: Anders Nilsson
Master´s Degree Project in Marine Biology 45 credits, 2013
Department of Biology, Lund University (Less)
Please use this url to cite or link to this publication:
author
Daníelsdóttir, Birna
supervisor
organization
course
BION21 20101
year
type
H2 - Master's Degree (Two Years)
subject
language
English
id
4194907
date added to LUP
2013-12-12 10:55:47
date last changed
2013-12-12 10:55:47
@misc{4194907,
  abstract     = {Popular science summary

You are what you eat

In this project I used a method called stable isotope analysis. This method is based on the principle ‘you are what you eat.' To begin whith, isotopes are forms of the same element sharing the same number of electrons but differ from each other in its number of neutrons in the nucleus. For example, stable isotope of 13carbon has one extra neutron then 12carbon. This small and subtle chemical difference and the ratio of these two and can be a very usefule tool for scientist. That is because stable isotope ratios vary among food webs and food sources. Carbon isotopes (13C) reflect the primary producers in the area of feeding and there-fore can be used to determine diet. Nitrogen isotopes (15N) can be used as an indicator of trophic position in a food web because 15N isotope increases with each trophic level. When an animal feeds, the stable isotopes are incorporated into animal's tissue through its diet. This method can therefore be help-ful to understand food webs, to uncover migratory routes and sometimes it is poss-ible to infer the whereabouts of an animal moving between food webs.

The aim of this project was to utilize the difference in turnover rate in liver and muslce by examining the stable isotope of carbon and nitrogen in muscle and liver of cod in Öresund for different age groups. I wanted to illustrate the feeding patterns of the cod in the area. Furthermore, information gained from stomach contents were compared with stable isotope results. This information, stomach contents (immediate past) as well as δ15N and δ13C of the liver (recent past) and muscle (long-term past), can present indication of individual dietary history integrated over a range of time scales. The goal was to see; (1) if younger individuals are utilizing the same habitat (muslce samples) and as they get older diverge to different feeding grounds (liver samples), (2) are older individuals feeding on different preys over time and does the resources from distinct habitats give them better body condition. 

The results showed that the cod clearly displays an omnivorous diet and the generalist feeding includes the spectrum from benthic to pelagic prey and invertebrate to fish. From the results, it is reasonable to say that the cod at the population level are generalist foragers but then the generalist population can be made up of subgroups or specialists, where a separation of three groups where found in muscle samples and these groups show diverging patterns of change in foraging behaviour. These groups, over time, shift in their resources, showing more specialized feeding behavoiur at younger age but then shift to more omnivourous diet as the get older. 



Supervisor: Anders Nilsson
Master´s Degree Project in Marine Biology 45 credits, 2013
Department of Biology, Lund University},
  author       = {Daníelsdóttir, Birna},
  language     = {eng},
  note         = {Student Paper},
  title        = {Exploring feeding behaviour patterns of cod (Gadus morhua L) in Öresund using stable isotopes of δ13C and δ15N},
  year         = {2013},
}