Effect of environmental variables on the number of births at California sea lion (Zalophus californianus) rookeries throughout the Gulf of California, Mexico

Abstract

1. The 13 California sea lion breeding colonies in the Gulf of California (GoC), Mexico are each characterized by different population growth trends, including a variable number of births. Despite being located in a highly productive marine area, both the species' population and the number of births have declined significantly over the past few decades.2. The goal of this study was to assess the effects of certain environmental variables on the number of births at colonies in three regions (northern, central and southern) of the GoC (1995GoC ( -2018. Data on diet, small pelagic fish catches by fisheries, the density of small pelagic fish schools, remotely sampled values of sea surface temperature and chlorophyll-a concentration and El Niño Southern Oscillation events were collected in order to evaluate whether these variables had an effect on the number of births using correlations and generalized linear models.3. No significant relationships were found between the environmental variables and the number of births. However, the number of births decreased when the sea surface temperature anomalies exceeded 1 C in the northern and central regions of the GoC. Although no significant relationships were found between the small pelagic fish catches and the number of births, positive trends were observed between sardine catches and the number of births during certain periods in the central region. A positive correlation between the density of small pelagic fish schools and the number of births suggests a possible relationship between prey availability and reproductive success in the central region. 4. A Programme of Action for the Conservation of the Species should be promoted by the Federal Government and carried out in order to implement specific management actions. Specifically, surveillance efforts should increase, fishing gear conversion plans should be established and sea lion exclusion devices should be introduced, among other measures.

Lower marine productivity increases agonistic interactions between sea lions and fur seals in Northern Pacific Patagonia

“…Proxies for marine productivity and biomass such as SST and landings of demersal fishes were found to have a strong influence on the number of agonistic interactions between SASL and SAFS. SST drives the mixing regimes of the Pacific Ocean and with those, significant changes in the concentrations and distribution of nutrients and plankton, the base component of oceanic food webs ( Laidre et al 2008 ; Doney et al 2012 ; Pelayo-González et al 2021 ). Therefore, there are significant correlations between the thermal regime of the ocean and the distribution of plankton determined through measurement of chlorophyll concentrations by satellites ( Bouffard et al 2018 ; Hao et al 2019 ).…”

Skull shape and size changes in different subpopulations of the California Sea Lion (Zalophus californianus) in Mexico

“…Sampling locations (numbered): 1, Isla Lobos; 2, San Esteban; 3, Isla Granito; 4, Los Cantiles; 5, El Rasito; 6, Los Machos; 7, Cabo San Lázaro; 8, Isla Santa Margarita. Modified from Pelayo-González et al (2021a). Illustration courtesy of Gustavo De La Cruz-Agüero.…”

“…Differences in life history traits and environmental conditions exist between California sea lions from the Pacific coast of the Baja California peninsula and those from the Gulf of California off of the coast of mainland Mexico (Szteren and Aurioles-Gamboa 2011; López-Arvide 2014; Rosas-Hernández et al 2018; Pelayo-González et al 2021a, 2021b; Hernández-Camacho et al 2021), and geographic isolation between populations may be accelerating their genetic divergence (González-Suárez et al 2009). Previous genetic studies indicated that California sea lions are separated into 5 subpopulations (Fig.…”

“…Currently, about 14% (53,000 individuals) of the species occurs on the Pacific coast of the Baja California peninsula, and only 6% (20,000 individuals) are in the Gulf of California—the remainder occur along the Pacific coast of the United States and Canada. The broader, positive trend in total population size could mask the 1 to 4% annual reduction of Gulf of California colonies (Pelayo-González et al 2021a, 2021b)—a trend that toward the risk of colonies disappearing in the coming decades, especially considering that expected loss of genetic variation in geographic isolated and smaller colonies could add to their risk of extinction (Schramm et al 2009; Rayas-Estrada and Hernández-Camacho 2019).…”

“…Analyses show that most colonies within these subpopulations are experiencing declines in population size, with only a few colonies that are stable and 1 increasing (Elorriaga-Verplancken et al 2015; Hernández-Camacho et al 2021). Recent studies show that birth rates and population totals may be linked to a decrease in prey abundance (Adame et al 2020; Pelayo-González et al 2021a, 2021b).…”