Territories and territorial defense in juvenile brook charr, Salvelinus fontinalis (Pisces: Salmonidae)

Abstract

The typical territory defended by juvenile brook charr (Salvelinus fontinalis) in a laboratory stream tank was cordate in shape, with the resident stationed at the downstream end facing into the current. Responses by the resident were less aggressive toward intruders at increasing distance from the resident's station. Chases predominated immediately around the station, charges were more frequent further away, and lateral displays were most frequent at the territory perimeter. Defense of the anterior (upstream) area tended to be more aggressive, with equal numbers of charge and chase interactions, while laterally less aggressive and presumably less costly (energetically) charges predominated. These details of territory structure and defense agree with the predictions of an hypothesis of the territory as an economically defensible resource.

Effects of location of food delivery and social status on foraging-site selection by juvenile Atlantic salmon

“…Aggression between fish was greatest when the subordinate fish temporarily moved into an upstream position relative to the dominant. Similar observations have been previously reported for a number of different salmonids (McNicol & Noakes 1981, McNicol et al 1985, Grant et al 1989). For example, Grant et al (1989) found that defense effort by brook charr was significantly greater in an upstream rather than downstream direction.…”

Environmental influences on territoriality of juvenile brook charr, Salvelinus fontinalis, in a stream environment

“…The shape of their territories (Noakes & McNicol 1982) and their defense (McNicol & Noakes 1981) support the hypothesis that territorial defense is determined by energetic costs and benefits (Davies 1978, Dill 1978a). How they respond to changes in costs and benefits of defense should therefore test this hypothesis.…”

“…McFadden (1969) believed that territory size should vary inversely with food abundance, thereby maintaining a fixed level of food intake (Feeding Tub/e 6. Body size (length and weight) and territory sizes of individual juvenile brook charr (adopted from McNicol & Noakes 1981 Slaney & Northcote's (1974) report that territory size of juvenile rainbow trout was smallest at high food abundance and largest at low food abundance appears to support this view. However, in their study immigration into the feeding area was not controlled and was greatest in the area of highest food abundance.…”

“…Two enclosures were placed in each of two channels (5 x 1.3 x 0.5 m deep) of a large (N 120001) laboratory stream tank (details in McNicol 1979). Feeding was accomplished through three plastic tubes in front of the upstream barrier of each enclosure (McNicol & Noakes 1981). Fish were fed commercial trout food (Number 2 trout chow, Martin's Feed Mill, Elmira, Ontario) 0.8-l .O mm diameter pellets (0.017-0.02 particle-size to fish-length ratio).…”

“…Durations of LD and CHS were also recorded. LD, CHG and CHS (in order of increasing aggressive nature) were as previously described (McNicol & Noakes 1981). HT occurred when the aggressor, positioned laterally to a conspecific (usually during LD), would suddenly bend its head towards the conspecific at an angle of about 3040".…”