Temperature effects on blood‐oxygen equilibria in relation to movements of the bat ray,Myliobatis Californicain tomales bay, California

In vitro blood‐oxygen binding curves for the bat ray, Myliobatis californica, were constructed at four temperatures (8, 14, 20, and 26°C) to gain insight into the possible adaptations to ambient temperature regimes in Tomales Bay, California. The curves were hyperbolic (mean n50: 1.06) with high affinities (P50: 0.8–3.2 kPa) and large whole blood buffer values (ß: ‐14.25 to ‐16.43 slykes) implying a tolerance to hypoxia and hypercap‐nia while large O2 capacities (CBO2: 3.1–4.1 mmol.L‐1) and Bohr factors (Ø: ‐0.45 to ‐0.52) indicated high activity levels. The temperature effect (?H) was greatest between 14 and 20°C as compared to relatively temperature independent binding between the 8 to 14°C, and 20 to 26°C ranges. The heightened sensitivity between 14 and 20°C parallels a previously‐documented large change in respiratory demand for this same temperature range (Q10 = 6.81). However, the magnitude of the hematological adjustments were small relative to the large increase in metabolic demand and it is likely that increasing cardiac output plays an important role to safeguard oxygen transport as temperature rises. Thus, the movements of rays between warmer and cooler regions of Tomales Bay are not related to their blood oxygen binding characteristics, but may be due to other factors such as increasing assimilation efficiency, minimizing energy expenditure, or social factors.