Meeting Abstract

P3.53  Thursday, Jan. 6  Heat balance in free-swimming swordfish BERNAL, Diego*; AALBERS, Scott; SEPULVEDA, Chugey; Univ. Massachusetts Dartmouth; Pfleger Institute of Environmental Research; Pfleger Institute of Environmental Research dbernal@umassd.edu

Swordfish are large pelagic predators known for their capacity to undergo extensive diurnal vertical movements and have their aerobic, red locomotor muscle (RM) positioned in close proximity to the vertebrae. Although this RM morphology is also found in tunas and lamnid sharks (which are capable of RM endothermy) it is not known whether the swordfish also has the capacity for RM endothermy. In this study we measured RM temperatures in a wild, free-swimming swordfish to document its capacity for heat balance. A temperature tag was deployed on a basking swordfish using traditional harpoon techniques and preliminary results show the fish remaining predominantly below the thermocline during the day and in the upper mixed layer at night with two brief basking events during the daylight hours. Calculation of the thermal rate coefficients during 6 cooling (diving) and 5 heating (surfacing) events show that the rate of heating (k=0.03) was ~6.5 times faster than that of cooling (k=0.005). During the time the swordfish stayed at depth the RM always remained more than 1.5&degC above ambient and upon returning to the surface quickly warmed and remained at least 0.5&degC above ambient. From this initial deployment, k values during diving appear to be within the range of values documented for some tunas but lower than those for mako sharks (i.e., swordfish cool slower than makos but similar to tunas) while the rates for heating are consistently lower in the swordfish than in both makos and tunas (i.e., swordfish warm slower). However, unlike other tunas and lamnid sharks, swordfish RM appears capable of operating at very low temperatures for prolonged periods of time. Future work will further investigate the swordfish’s RM ability to maintain adequate contractile properties during extended periods in the cool conditions.