Downsized: gray whales using an alternative foraging ground have smaller morphology

Area of Science:

• Marine Biology
• Ecology
• Evolutionary Biology

Background:

• Gray whale populations exhibit distinct feeding behaviors and ecological niches.
• The Eastern North Pacific (ENP) gray whale population primarily forages in Arctic/sub-Arctic regions.
• A smaller Pacific Coast Feeding Group (PCFG) forages along the North American coast, with evidence suggesting poorer body condition.

Purpose of the Study:

• To investigate morphological differences (length, skull, and fluke span) between ENP and PCFG gray whales.
• To compare length-at-age growth curves of ENP and PCFG gray whales.
• To understand the adaptive significance of morphological variations in relation to foraging niches.

Main Methods:

• Utilized historical data (1926-1997) for ENP gray whales (strandings, whaling, aerial photogrammetry).
• Collected contemporary data (2016-2022) for PCFG gray whales using non-invasive techniques (photo identification for age, drone photogrammetry for length).
• Employed Bayesian methods to account for uncertainty in morphological measurements and age estimations.

Main Results:

• PCFG and ENP gray whales share similar growth rates.
• PCFG whales attain smaller asymptotic lengths compared to ENP whales.
• PCFG whales possess relatively smaller skulls and fluke spans than ENP whales.

Conclusions:

• Morphological differences suggest PCFG gray whales are adapted to a distinct foraging niche.
• Smaller body size and proportionally reduced cranial and fluke dimensions may facilitate specialized foraging.
• This study highlights a compelling example of adaptation within a gray whale population.