Cannibalism occurs in a wide variety of animals, and persists in many populations despite potential negative effects. Cannibalism is well studied in fishes and much has been published on the foraging behavior of largemouth bass, Micropterus salmoides. Here we report on cannibalism in largemouth bass over a 28-year period from a small (1.5 ha), unexploited, north temperate lake in Michigan’s Upper Peninsula (46.252710°N, 86.504085°W), where they dominate the fish community comprising > 95% of the fish biomass. Paul Lake supports a very high population density of bass which varied in density from a low of 87 (95% CI ± 71, 114) to a high of 457 (95% CI ± 380, 574). The unexploited nature and monospecific population of Paul Lake provides for a unique opportunity to investigate cannibalism. Our study objectives are three fold: 1) to meter cannibalism frequency, 2) to identify the principle cannibal cohort, and 3) which size class of YOYs are cannibalized most. To our knowledge, we know of no other continuous largemouth bass cannibalism records of this length.
We report that the majority of cannibalism takes place from mid-June to early August (DOY 170-230), and that largemouth bass 175-225mm TL are the principle cannibals. They prey most frequently on young-of-the-year (YOY) < 30mm. Segregation between adult and juvenile/subadult largemouth bass results in juveniles/subadults opportunistically preying on pelagic zooplanktivorous YOY bass. Juvenile/subadult bass are pushed into the pelagic zone due to high adult bass density in the littoral zone. YOYs move from the littoral zone to the pelagic to forage on zooplankton. The overlap in habitat use by YOYs and juveniles/subadults allows for opportunistic foraging on YOY bass, something not seen in littoral residing adult bass. Of YOYs consumed, 86% were < 27 mm TL and consumed mainly by juvenile/subadult bass < 260 mm TL. High conspecific largemouth bass density relative to prey abundance in Paul Lake is a possible driver influencing foraging generalization and cannibalistic behaviors of juvenile/subadult largemouth bass. Knowing more about largemouth bass behavior in all stages of its life allows ecosystem managers to assess its value to the ecosystem more accurately. Furthermore, the role of cannibalism in fish population dynamics is key to proper management of sportfishes like the largemouth bass.