Open Collections

Pozas Franco, Ana Lucía

University of British Columbia

The global population of California sea lions (Zalophus californianus) has declined in the Gulf of California (Mexico), while numbers have increased along the California coastline (U.S.). It is unclear what is behind the divergent population trends, but differences in diets likely play a role. I used diet data to investigate whether the changes in sea lion population numbers that occurred in sea lion numbers from 1980–2020 could be explained by differences or shifts in diet quality — specifically energy density and diet diversity. I also explored whether diet quality in the Gulf of California was affected by increased sea surface temperatures that occurred in 2014. I considered rookeries in California (Channel Islands) to be a single ecological Zone and divided the Gulf of California breeding islands into nine Zones based on geographic proximities and similarities in population trajectories. Years with matching population and diet data within all these Zones were used to test for relationships between measures of diet quality and population changes. My results showed that diet variability and composition differed between the Channel Islands and the Zones within the Gulf of California. In general, sea lions breeding in the Gulf of California consumed a large variety of mostly benthic species and schooling fish, whereas sea lions at the Channel Islands primarily consumed schooling fish and squid. Contrary to expectations, no significant relationships were found between population changes and measures of diet quality across all Zones and times. However, the average energy density of sea lion diets in certain Zones within the Gulf of California declined as sea surface temperatures increased. While my results did not reveal a direct relationship between population changes and diet quality, they demonstrate the significance of considering the influence of environmental heterogeneity on regional population dynamics. My results also highlight the importance of better understanding the ecosystem dynamics of the Gulf of California at small regional scales. Such findings may be key to fully understanding the interplay between environmental changes, diets, and future population trajectories of California sea lions and other pinniped species in geographic locations throughout Mexico and the U.S.

Text

2022-11-24

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/83295

Oceans and Fisheries

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/