Cook Inlet Beluga Age and Growth

The Cook Inlet beluga population declined 47 percent from 1994 to 1998. This decline has highlighted the need to gather and understand basic life history information of the population. Teeth from harvested and stranded Cook Inlet belugas, collected from 1992 to 2001, were used to establish growth layer group (GLG)/length curves for female and male Cook Inlet belugas. A total of 372 teeth from 58 whales were cut and analyzed. Teeth from matching left and right jaws were compared and found to give statistically equivalent values. Tooth position in the jaw affected wear and maximum GLG counts. Higher counts occurred in teeth from the posterior of the jaw, with tooth position 8 having the highest average count. Growth curves were developed for female and male belugas. Sexual dimorphism was exhibited, with males being longer than females at equal GLG counts.

Additional refinement of the growth curves was done. Average GLGs at each tooth position varied significantly (p = 0.018). Since tooth position 8 had the highest average GLG, regression equations were developed to adjust GLGs for each tooth position to the maximum value reflected in tooth position 8. Using the “regressed” data 2 set, new growth curves were developed for females and males, raising the adjusted R values from the “nonregressed” model.

It is recommended that teeth selected for ageing should come from the posterior of the jaw, with tooth position 8 giving the highest GLG counts. The regression equations are useful for adjusting tooth position values 1 to 7 to the optimum value reflected in tooth position 8, if tooth 8 is not available. The GLG/length models are useful for predicting GLGs based on length for female and male Cook Inlet belugas greater than 300 cm in length.