Abstract

In terrestrial environments, nest site selection by birds and mammals is often related to the physical attributes of surrounding vegetation. Similarly, some elasmobranchs use different habitats, including kelps, as oviposition sites. However, habitat features that drive oviposition site selection remain poorly understood. We examined the relationship between kelp morphology (holdfast diameter, number of stripes, and total length) and kelp forest configuration (density, size structure, predator density) with egg presence to identify the factors influencing oviposition choice in the redspotted catshark (Schroederichthys chilensis). We conducted surveys over a latitudinal gradient (19 degrees S to 39 degrees S), encompassing much of the overlap between the kelp, Lessonia trabeculata and S. chilensis in Chile. Eggs were exclusively attached between the upper stipe and basal fronds of Lessonia trabeculata in all sites. At the individual scale, S. chilensis selected larger kelps within a patch, independent of the general population size structure. The number of eggs and clutches was positively associated with stipe length and holdfast diameter. Across all sites, egg-bearing kelps were consistently clustered at a similar depth in the kelp forest rather than being randomly distributed. At the site scale, egg number had a negative correlation with their main predator abundance, Taliepus dentatus, and juvenile kelp density. These results suggest that S. chilensis shows low plasticity in substrate use, as evidenced by non-random, consistent oviposition in kelp morphology along a latitudinal gradient. Our results underscore the need to incorporate kelp size thresholds and the protection of egg-bearing aggregations into harvesting regulations, as overexploitation of L. trabeculata directly threatens the reproductive viability of S. chilensis.