Momma Can You See Me?

Abstract

Is the distribution and behavior of humpback whale (Megaptera novaeangliae) mother-calf pairs related to water clarity in the ‘Au’Au Channel, Maui, HI? North Pacific humpback whales migrate to the warm, shallow waters of Hawaii to birth and raise their calves, before returning to colder, nutrient rich waters in the Alaskan feeding grounds. Mothers and calves prepare for this migration by conserving energy, optimizing calf growth, and avoiding confrontation with adult humpback whales and potential predators. We hypothesized that mothers chose to rest and nurse in areas of high water clarity, to enable them to visualize approaching threats. We observed and categorized the behavior of mother-calf pairs using 15 minute focal-follows. We recorded pod composition (if escort adult humpbacks were present), behavioral interactions, and time and location of calf surfacing behavior. We categorized calf behavior as resting, slow-travel or fast-travel based on the GPS focal-follow data. Water clarity was measured using a 20cm secchi disk after each focal-follow. We measured water clarity, when whales were not present, at 6 inshore and 6 offshore locations using established zigzag transect lines, constructed between waypoints set at 1 minute intervals (Cartwright et al. 2012). Inshore waypoints were set at 0.25km from the shoreline and offshore waypoints were set at the deepest or mid-point of the channel, whichever lay furthest offshore. The density of zooplankton was assessed with a 10m vertical tow using a 12.7cm diameter 153μm mesh plankton net. Humpback whale research was conducted under NOAA NMFS permit #22750-01.

Presentation