Relationship between swordfish swimming behaviour and sea surface temperature in the central Mediterranean Sea during the reproductive period

Abstract

Swordfish is the target species for harpoon fishery in the Central Mediterranean Sea (southern Tyrrhenian Sea and Strait of Messina). This is a seasonal fishing activity, carried out in daylight during the swordfish's reproductive period. The relationship between sea surface temperature (SST), catches, Catch per Unit Effort (CPUE) and fish swimming behaviour, recorded by direct observation, was investigated between 1999 and 2008. Data from AVHRR-SST (Advanced Very High Resolution Radiometer–Sea Surface Temperature), the meteorological station and the swordfish daily catch were recorded. A low presence of pairs was observed in the 2003 summer season, corresponding to an anomalous sea surface temperature recorded in the study area. After 2003, an early presence of pairs (in May rather than in June) was recorded. ANOVA and Bonferroni correction showed significant differences of CPUE of pairs between May and June, and June and August (F₃=8.07, P<0.0001). The relationship between immature and mature adult specimens, single and in pairs, four ranges of SST, seven swimming behaviours and five maturity stages was analysed by the multiple correspondence analysis (MCA). Fish in pairs were mainly observed at temperatures over 24°C, showing a well-defined courtship behaviour, i.e. a female route. At lower temperatures, the dominant behaviour was basking in immature fish and breaching in mature fish. A significant relationship between SST and fish behaviour was detected in both immature and mature adult specimens.

Keywords:

• Central Mediterranean Sea
• harpoon fishery
• sea surface temperature
• spawning
• surface swimming behaviour
• swordfish

Published in collaboration with the University of Bergen and the Institute of Marine Research, Norway, and the Marine Biological Laboratory,University of Copenhagen, Denmark

Published in collaboration with the University of Bergen and the Institute of Marine Research, Norway, and the Marine Biological Laboratory,University of Copenhagen, Denmark

Acknowledgements

This study was carried out during research project of ICRAM Institute (actually ISPRA). We thank the harpoon fishermen for theirhelp in providing valuable information on swordfish behaviour.

Notes

Published in collaboration with the University of Bergen and the Institute of Marine Research, Norway, and the Marine Biological Laboratory,University of Copenhagen, Denmark