Territories within groups: the dynamic competition of drift-feeding juvenile Chinook salmon in 3-dimensional space

• Published in: Canadian journal of fisheries and aquatic sciences 2023-02, Vol.80 (2), p.346-359
• Main Authors: Neuswanger, Jason R, Rosenberger, Amanda E, Wipfli, Mark S, Hughes, Nicholas F
• Format: Article
• Language: English
• Subjects: Animal behavior; Chinook salmon; Competition; Competition (Biology); Environmental aspects; Fish; Food and nutrition; Home range; Juveniles; Oncorhynchus tshawytscha; Population regulation; Rivers; Salmon; Territorial behavior
• ISSN: 0706-652X; 1205-7533
• DOI: 10.1139/cjfas-2022-0112

Salmonid populations are often regulated by territorial competition among juveniles for food and space. In the canonical view, salmonid territories are spaced horizontally across the river bottom in a two-dimensional mosaic. However, some juveniles instead feed in tight, three-dimensional (3-D) social groups. To investigate whether territoriality is possible within such groups, we applied a new concept--the momentary home range--to quantify the size, exclusivity, and temporal dynamics of 3-D space use by juvenile Chinook salmon (Oncorhynchus tshawytscha) in the Chena River, AK. Individual strategies spanned a broad continuum of exclusivity and stationarity. However, some of the largest, most dominant fish in each group aggressively defended stationary, exclusive feeding spaces and thus were unambiguously territorial. Transient floaters entered and left the group quickly. A majority of fish were not aggressive but nevertheless occupied exclusive, stationary spaces that probably function as territories with regard to resource distribution and population regulation. The presence of territoriality within social groups, in a 3-D configuration, expands the known domain of this important behavior.