Harem polygyny through resource defense territoriality in the sandperch Parapercis pacifica (Pinguipedidae)

In reef fishes inhabiting sandy rubble habitats, such as sandperches, a mating system with territorial female-type harems has been widely confirmed. However, the mechanisms underlying harem maintenance in species with large territories remain poorly understood. Parapercis pacifica (Pinguipedidae) is a relatively large sandperch with large territorial home ranges. To examine the mating system of the sandperch P. pacifica , we conducted underwater observational surveys on the reefs of Sesoko Island, Okinawa, Japan. Both males and females established intrasexually exclusive home ranges. Females maintained wide foraging areas within their territorial home ranges and occasionally displayed aggressive behaviors towards carnivorous fish species, including female conspecifics and other species, suggesting the importance of food resources. Male territories did not completely encompass female home ranges, which differed from those of other sandperch species. However, male territories primarily covered female shelter nests. During the mating period around sunset, males patrolled their territories and visited female shelter nests, indicating that the nests facilitated sexual encounters. Each male maintained a stable mating relationship with one to four smaller females whose territories overlapped intersexually. Thus, by maintaining a territory that covers resources that facilitate encounters with spatially dispersed females, males of P. pacifica may have an energy-saving tactic for monopolizing polygynous mating.