Observations on the Depth Range of tagged Bluefin Tuna (Thunnus thynnus L.) based on Pressure Marks on the Lea Tag

Abstract

The present paper is an investigation on the depth range of tagged bluefin tuna based on pressure marks on the Lea tag (Figure 1). It was observed that the within season recaptures were without pressure marks, while the pressure marks occur on all the between season recoveries (Table 1). A test of the pressure resistance of the Lea tag showed that the bluefin tuna stock feeding off the Norwegian west coast during the summer does not go below 250 metres depth, whereas the stock seems to have a deeper distribution range during the winter.