Effects of temperature and body size on the swimming speed of larval and juvenile Atlantic cod (Gadus morhua):: Implications for individual-based modelling

The routine swimming speed (S) of three groups of 4, 9 and 32 cm total length (L-T) juvenile cod (Gadus morhua) was quantified in the laboratory at 6 - 10 different temperatures (T) between 3.2 and 16.7 degrees C. At temperatures between 5 and 15 degrees C, mean group S increased exponentially with increasing T (S= a e(bT)) and the effect of temperature (b= 0.082, Q(10)= 2.27) was not significantly different among the groups (over the 8-fold difference in fish sizes of early- and post- settlement juveniles). Differences in mean S among individuals within each group were quite large ( coefficient of variation= 40-80%). Swimming data for juveniles and those collected for groups of 0.4, 0.7 and 0.9 cm standard length (LS) larvae were combined to assess the effect of body size on S. At 8 degrees C, S (mm s(-1)) increased with L-S (mm) according to: S= 0.26L(S) (Phi) -5.28L(S)(-1), where Phi= 1.55L(S)(-0.08). Relative S (body lengths s(-1)) was related to L-S by a dome-shaped relationship having a maximum value (0.49 body lengths s(-1)) at 18.5 - 19 mm L-S corresponding to the sizes of fish at the end of larval-juvenile metamorphosis. Previous larval cod IBM's using a cruise-predator mode likely overestimated rates of foraging (prey searching and encounters) by a factor of similar to 2, whereas foraging rates in pause-travel models are closer to estimates of swimming velocities obtained in this and other laboratory studies.