The use of tags or marks for fisheries research or monitoring
Before choosing a method to obtain certain information in fisheries research or monitoring, it is necessary to know about the applicability of different methods.
A few initial guidelines about the usefulness of various tags have been drawn up below.
For practical reasons approaches have been divided into different tag and mark types.
Conventional tags and marks
May be either internal or external tags or external or internal-external marks. As a group of tags and marks they have a wide potential for studying population dynamics, growth, survival, migration, geographical distribution, behaviour as well as management studies and studies of fisheries.
A vast number of types of ID-tags and ways of marking exist.
May be either transmitting or data collecting tags.
Transmitting tags may be transmitting radio waves or/and acoustic tags. They have the ability to give information on the position of the fish, and even for some tags on the physiological status or activity of the fish, in its natural environment with minimal disturbance to the fish. These types of tags have been powerful in studies of migration, behaviour and survival.
Data collecting tags archival or memory tags, generally termed Data Storage Tags (DSTs), are essentially data loggers collecting information of one or more environmental variables from the near environment of the fish. This type of tag is relatively new, but is rapidly developing, with the development of miniature electronics. The tags have proved powerful in collecting long time data series from fish in their natural environment without any disturbance of the fish, and have proved useful in studies or habitat preferences, migration and behaviour.
In most cases it is possible to find a suitable tag or mark that will help obtain the information required there are some limitations to the possible use of tags or marks.
No single type of tag or mark is perfect; each has its advantages and disadvantages.
One major limiting factor is size of fish vs. size of tag. Electronic tags are all relatively large, limiting the sizes of fish they can be applied to, since the ratio of fish/tag size is recommended not to exceed 2.0%.
All external tags have the potential of causing health problems for tagged fish as the application implies penetration of the body and protruding tags may cause continuous irritation and access for microbial infections.
In the same way internal tags needs to be inserted in the fish. The process of applying an internal tag may itself be critical, due to penetrating the skin or otherwise affecting the fish.
In general marks are less intrusive than tags. In some cases it may be possible to use natural biological marks, like e.g. genetic marks, that does not need to be applied to the fish.
Limiting the possible use of tags and marks, is the fact that they may be lost or deteriorate during the period from tagging to recapture, which could result in data misinterpretation.
All tagging or marking of fish involves treatment, which causes disturbance and possibly stress or physical damage. Careful handling procedures throughout the capture and marking process are of highest importance.
The influence of tags on fish health, behaviour and growth is dealt with in detail in the scientific report (LINK) and on this web-site (LINK).
The different types of tags and marks and their use is further evaluated under the section Types of tags and marks (LINK) on this site.