Publication Date

Fall 2015

Degree Type


Degree Name

Master of Science (MS)


Moss Landing Marine Laboratories


Scott Hamilton


Fishery Management, Geoduck, Geographic Variation, Life History, Morphology, Panopea generosa

Subject Areas

Zoology; Biology


The Pacific geoduck, Panopea generosa, is an ideal candidate to investigate patterns of life history variation and morphological plasticity in shell shape, as it occurs over a large geographic range, inhabits different marine environments, and experiences intense fishing pressure in some locations (i.e., Mexico and Washington). Six populations were sampled from Washington to Mexico to evaluate evidence for geographic variation in demography, life history, and morphology. Results provided evidence for a latitudinal cline with larger clams occurring in locations characterized by colder water temperature. Age structure and longevity analyses indicated that life expectancy was significantly lowered at intertidal sites compared to subtidal sites, potentially in response to fishing. Von Bertalanffy growth model (VBGM) analyses revealed significant spatial variation in asymptotic lengths across sampling locations. Correlations of climate (temperature and chlorophyll a) and growth parameters indicated that clams reached larger sizes at locations that were cooler and more productive. Morphological analyses revealed significant spatial differences that did not follow a latitudinal pattern, but may be better explained by site-specific habitat differences. Results will aid managers in developing regulations, tuned to the demographic variability present along the eastern Pacific coast.