MEPS 702:153-170 (2022)  -  DOI: https://doi.org/10.3354/meps14203

ABSTRACT: The competitive exclusion principle predicts that species exhibit segregation mechanisms to coexist. In the Humboldt Current System, South American sea lions Otaria byronia (SASL) coexist with South American fur seals Arctocephalus australis (SAFS); however, the existence of temporal and spatial partitioning in foraging strategies remains unknown. To compare foraging strategies, we analyzed locations of 35 adults (18 SASL, 17 SAFS; 4 and 8 females, 14 and 9 males, respectively) equipped with satellite tags in Punta San Juan, Peru (2013-2017). We evaluated (1) distance and duration of foraging trips, (2) utilization distributions (UDs), (3) foraging by hour and (4) association of foraging with environmental variables. Regular interval tracks (every 30 min) were modeled, and residence time was estimated to determine foraging events. Proportion overlap and analysis of similarity compared groups in core areas (50% UD) and home ranges (95% UD). Generalized additive mixed models were built to determine if hour of day and environmental conditions had an effect on foraging. Multiple mechanisms for foraging segregation that explain coexistence were found. Duration and distance between species-sex groups were significantly different, except for trip duration between SASL sexes. SAFS traveled longer distances and duration than SASL, and males traveled longer distances and duration than conspecific females. Female UDs overlapped, while male UDs did not. Core areas between sexes overlapped in SAFS and SASL, but home ranges were significantly different. Hour of day had a significant effect on foraging events in SAFS females and SASL males. Environmental conditions during foraging by SASL and SAFS females reflected coastal and offshore habitats, respectively. However, interspecific segregation was not evident between males.

KEY WORDS: Interspecific segregation · Pinnipeds · Coexistence · Arctocephalus australis · Otaria byronia