Geographic intraspecific variation in buoyancy within Antarctic notothenioid fishes

Abstract

AbstractWe investigated intraspecific geographic variation in buoyancy by obtaining percentage buoyancy (%B) measurements for the Antarctic notothenioid speciesPleuragramma antarcticum,Trematomus hansoni,T. bernacchiiandGymnodraco acuticepsfrom both McMurdo Sound in East Antarctica and the South Shetland Islands in West Antarctica. Mean percentage buoyancies in these species ranged from 0.22–0.52% in the neutrally buoyantP. antarcticumto 3.34–3.67% in the benthicT. bernacchii. Dispersion (1 standard deviation) of percentage buoyancy (%B) values around the mean was ± 0.2–0.5 %B units for the entire sample. Although intraspecific differences in mean percentage buoyancy were statistically significant (P < 0.05) inP. antarcticumandT. hansoni, we consider these differences as normal variation without substantive biological significance. The dispersion in buoyancy measurements during adult life reflects the density of the fish and this may be influenced, in both the short- and long-term, by gut contents, nutritional condition, and reproductive state. Mitigation of the effects of these variables is not biologically realistic because they constitute normal aspects of the daily and yearly life cycles. The results of our measurements of buoyancy are consistent with what is known about the ecology of these four species and this is considered in the discussion.