GPS Fish Tracking Case Studies

Star-Oddi and Simrad GPS system (GPS Fish Tracking System)

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Research objectives          
Accessibility (Harden Jones 1968):
Definition: How accessible are the fish for fishery tools, or in other words; variation of differences in catch effort. Of those fish that are available within the area, a portion come within the influence of the gear and are more or less accessible to capture, example:

• When and for how long do the fish stay in the area?
• Measure if the cod are far from the bottom (acting pelagic) and are thereby not accessible for bottom trawl.
• Are fish on bottoms that cannot be fished with bottom trawl, but are accessible for net and line?  With Star-Oddi tags, we are able to estimate, by analysis of data, when it is more likely for the fish to be at the bottom or to be pelagic.
• Analysis of the fish behaviour in depth gives information on accessibility for different fishing gear.
• Vertical distribution, individuals, general trends and stock depth distributions in relation to time (or position).
• Ideal for GPS Fish Tracking

   

Analysing environmental conditions:

• The analysis of environmental conditions on migration routes (GPS Fish Tracking), and in spawning and feeding grounds can easily be done by using stored temperature and depth measurements.
  
  

Analysing growth rate of fish:

• Growth rate can be estimated by comparing fish weight and length between times of tagging and recapture.  By correlating the growth rate with the stored information on the ambient temperature fish were exposed to, researchers have information on modelling growth rate in relation to environmental temperature.

Availability (Harden Jones 1968):
Definition: How much of the whole stock is in the area where fishery or sample fishing is performed, example:

• Migration of large quantities from one area to another.
• Seasonal migration such as to wintering areas and spawning grounds.
• Tags giving geographical positions of fish are an obvious advantage for analysing the availability, as well as analysing migration mechanism, and fish behaviour at given positions. Such data give numerous possibilities of analysis by the researcher and institutes.

Detection of commercially harvested fish/stocks:

• Simrad sonars are installed on a large portion of the fishing fleets.  By having fishing vessels transmit GPS signals through the on-board sonar, coverage of areas can be increased considerably, transmitting positions of commercially available species as well as other fish.

Easy to use on vessels:

• It is possible for researchers, with limited cost, to have vessels transmitting continuous GPS signals, by installing GPS transmitters on vessels that are sailing same/similar routes regularly. This could be performed on lakes, rivers, in channels or ocean areas. To obtain complete coverage, the researcher could use other vessels to cover interesting areas.

Fish behaviour:

• Position, temperature and depth information give access to valuable information on individual fish behaviour.

Ideal for modelling:

• GPS positional information for fish opens new dimensions for researchers in modelling, by allowing them to use GPS information together with recovered environmental information from the tagged fish, such as temperature and depth. Modelling could be used to give managers and researchers new information for making case studies on predicting future behaviour/reaction of fish in relation to change in environmental conditions or even behaviour of stocks.

Migration, distribution and mechanisms:

• GPS tags give researchers improved knowledge on migration routes of commercially exploded fish, information that will improve stock estimates and strengthen the decision process for quotas, contributing to sustainable resource management of fish stocks.
• Improved knowledge on fish migration routes will improve our understanding of mechanism that lie behind orientation and navigation of marine animals, one of nature?s mysteries.
• GPS positions of fish give valuable information on fish migration and distribution. When the GPS sonar is out of range of the tagged fish, the tag still measures and stores temperature and depth information, giving the researcher information on behaviour between positions.
• The measurements give general trends in the depth distribution of individual fish, information that could be used to determine the behaviour of stocks.
• GPS tags give researchers information used in analysing what influences migration, and shoals behaviour, vertically and/or horizontally.

Positioning salmon and anadromous trout and charr:

• It is possible by scanning coastlines, to transmit positions of fish and to analyse coastal migration.
• Make escape tests from fish cages to analyse migration, behaviour, and possible mixing with other fish.

Resource Management:

• Fish position gives researchers information that can be used to analyse migration routes, and to identify spawning and feeding routes. The information can be utilised for ecosystem-based management in selected areas and/or fish stocks with the objective of obtaining sustainable fisheries.

Vulnerability (Harden Jones 1968):
Definition: Vulnerability, related to ?catchability? is the integration of fish and the amount caught with gear which is both available and accessible, for example:

• How large a portion of the fish that is within the range of a tow area is caught.
• It is difficult to analyse fish response to fishing gear and the efficiency of different fishing gear with DST alone. In such cases, one would be able to follow individual fish and their response to the fishing gear.
• Temperature influence on vulnerability / catchability of fish with different fishing gear.