The reproductive ecology of Bluegill in Lake Nojiri, Japan, was investigated, revealing that males construct nests in colonies and guard them, thereby effectively reducing brood predation. This specialized reproductive strategy is likely a key factor in the successful establishment of invasive Bluegill in Japan.

Tsukuba, Japan—Bluegill, recognized as aggressive invaders causing significant harm to native species, have been introduced to aquatic systems worldwide, including Japan. Their unique colony spawning involves males constructing nests in close proximity to each other, with each male guarding its own nest. However, these behaviors remain understudied in invaded habitats. To address this gap, we examined spawning behavior and brood predators in Lake Nojiri, Northern Nagano Prefecture, Japan, utilizing underwater video analysis and experimental guarding male removal.

Bluegill were observed spawning in shallow habitats from June through July, with nests occurring in loosely aggregated colonies as well as numerous solitary nests (35%). Males displayed various guarding behaviors, such as rim circling, predator chases, and paternal investment behaviors, such as tail fanning. Removal of guarding males revealed four brood predator species totaling 105 individuals, with conspecific Bluegill constituting >90% of all brood predators. Consistent with the colony spawning theory, nests located closer to other nests with active guarding males experienced reduced brood predation and increased predator arrival time following male removal. Additionally, nests where males exhibited more aggressive guarding before removal showed decreased brood predation later on. These findings suggest that the absence of native brood predators, coupled with the advantages of colony spawning, has likely facilitated the successful establishment of Bluegill throughout Japan. Furthermore, the common guarding male removal management strategy in Japan may be less effective due to the influence of colony spawning.

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Author MIP: Grant-in-Aid for JSPS Fellows (DC: 20J20656, PD: 23KJ0233

Original Paper

Title of original paper:

Male guarding behavior and brood predators of invasive Bluegill (Lepomis macrochirus) in a Japanese Lake

Journal:

North American Journal of Fisheries Management

DOI:

10.1002/nafm.10976

Correspondence

JSPS Research Fellow Miles I Peterson
Sugadaira Research Station, Mountain science center Sugadaira research station, University of Tsukuba

Related Link

Sugadaira Research Station, Mountain science center Sugadaira research station, University of Tsukuba