Available at: https://digitalcommons.calpoly.edu/theses/3061
Date of Award
6-2025
Degree Name
MS in Biological Sciences
Department/Program
Biological Sciences
College
College of Science and Mathematics
Advisor
Heather Liwanag
Advisor Department
Biological Sciences
Advisor College
College of Science and Mathematics
Abstract
Northern elephant seals (Mirounga angustirostris) are large, ocean migrating carnivores that have a wide distribution along the west coast of North America. Like other pinniped species, northern elephant seals spend considerable time out at sea foraging and return to land to molt and breed. Northern elephant seals were hunted to near extinction in the late 1800s. Due to conservation efforts they have since rebounded, and they currently occupy 27 known terrestrial breeding colonies. Much literature has documented the recolonization, population dynamics, and dispersion of this species. Currently, Piedras Blancas (San Simeon, California) is the largest mainland breeding colony of northern elephant seals. Though there is one study that describes estimated births at the Piedras Blancas colony from its recolonization in 1992 through 2010, not much else is known about its more recent growth, beach dynamics, or the movement of breeding individuals within the colony.
To better understand the long-term growth patterns at Piedras Blancas, we fit both an exponential and a logistic growth model to female northern elephant seal counts obtained from yearly censuses. We used survey data collected 2017-2025 to visualize total colony abundance by week, and further examined the data by age class presence, seal abundance, and seal density across nine breeding beach locations. Additionally, we investigated female northern elephant seal beach choice during two breeding seasons to determine if individuals were prospecting for optimal beach habitat. To do this, we marked and resighted 121 females and used a logistic regression to examine potential trends relating female beach switching probabilities to variables such as seal density, year, and time of arrival.
When we examined present and historic female elephant seal presence, a logistic growth model conferred a better fit than an exponential model, supporting the notion that the Piedras Blancas colony may be slowing in growth and reaching carrying capacity. Seal abundance and density by breeding beach exhibited patterns that suggested central, protected beaches may be more sought after by elephant seals and that recently colonized northern beaches may offer opportunities for further expansion. Furthermore, we observed female elephant seal movements between breeding beaches, and their timing of arrival may influence the probability of switching beaches. This is a novel observation supporting the idea that female northern elephant seals are exhibiting prospecting behavior when choosing a breeding beach. In summary, the results of this study illuminate the historic and present trends of an important breeding colony and support the possibility of female beach prospecting within a single colony.