Parental care is an important, energetically costly component of the life history of many fishes. Despite this importance, little is known about how different species of fish vary parental care in response to natural nest predator burdens. In this study, underwater videography was used to quantify parental care activity of six species of syntopic nesting male centrarchid fishes in Lake Opinicon, Ontario, in response to natural predators. This approach was used to test the hypothesis that as offspring develop from eggs to wrigglers, parental care activity should decrease or remain static for fish guarding nests with low predator burden and increase for those with high predator burden, reflecting different external risks. Principal components analysis (PCA) was used to derive common aeration and nest defence variables. Aeration and predator defence activity of the fish varied extensively among species. Parental care behaviours indicative of defence and vigilance (e.g., turning, departures, time away from nest, displays) tended to be highest for species that had the most predation attempts, although this was not entirely consistent. There was also a positive relationship between the defence PCA metric and attempted predation. Defence did not vary with stage of offspring development, although interactions between defence and developmental stage were noted for several species. A trade‐off between aeration and defence was not observed. In fact, species that provide high levels of aeration also simultaneously provide high levels of defence. Stage‐specific patterns of defence in this study were less apparent than those documented by studies using responses to staged predator intrusions making it unclear as to the extent that fish were responding to the level of the risk to offspring than to the value of the brood. Therefore, combined use of observational and experimental assessments of parental care investment may be most appropriate for refining current theoretical paradigms.
This study was conducted from 1 May to 9 July 2001 in Lake Opinicon (44°33.30′N, 76°20.00′W), Ontario, the site of much previous research into the reproductive biology, parental care and early life history of centrarchid species [rock bass (Gross & Nowell 1980); pumpkinseed (Colgan & Gross 1977); black crappie (Colgan & Brown 1988); bluegill (Gross 1980); smallmouth bass (Cooke et al. 2002); and largemouth bass (Brown 1984; Colgan & Brown 1988; Cooke et al. 2002)]. All these species spawn throughout the littoral zone of Lake Opinicon (Keast et al. 1978). In this study, all these species can also serve as potential nest predators, but bluegill and pumpkinseed are by far the most abundant and frequent nest predators. Other possible nest predators include yellow perch, Perca flavescens , and brown bullhead, Ameiurus nebulosus . Relative to other lakes in the vicinity, Lake Opinicon has one of the highest burdens of potential nest predators (M.‐A. Gravel, Carleton University, unpublished data). None of the potential nest predators in the lake are sufficiently large that they could consume any of the parental centrarchids engaged in care.
Snorkeling surveys initiated when water temperature was 12 °C were used to locate nesting males. Small underwater cameras (AU‐401; Atlantis, Bergenfield, New Jersey) and time‐lapse recorders (SRT 7072; Sanyo, New York, New York) were used to record parental behaviour from multiple nests (Cooke & Bunt 2004). Although video is preferable to other techniques for quantifying parental care activity, there are some clear limitations. The biggest limitation is that it is only possible to observe the behaviour of the fish when it is within the camera’s field of view. During the later stages of offspring development when fish may begin to patrol larger regions, or during absences when the fish leave the nest to engage predators, it is not possible to assess activity (Hinch & Collins 1991). The placement of the camera also has the potential to alter the behaviour of the parent as well as predators. Previous studies (e.g., Hinch & Collins 1991) used rather large cameras which required a cumbersome support stand. Innovations in camera design provided the opportunity to use a micro camera (roughly the size of a lemon) mounted on a narrow diameter (5 mm) aluminium rod that could be pushed between rocks or into soft substrate without mobilising sediment. Videography was chosen because it enabled the simultaneous monitoring of the parental care activity of nesting fish and predator activity less invasively than had snorkeling or SCUBA been used. Recording gear in a boat anchored at least 25 m from nests was connected to cameras by cables. Cameras were positioned 0.5 m from the nest by a diver and were on a 45° angle on a rod pointing down towards the nest. Ambient light provided illumination, so all video observations were obtained during daylight. Several studies of parental care in centrarchids have determined that activity rates remain unchanged at night (e.g., Hinch & Collins 1991; Cooke et al. 2002), so it was assumed that diurnal observations were also representative of nocturnal activity. Male parental behaviours were recorded between 10:00 and 14:00 h for a 10‐min period during both the egg and wriggler stages. The egg stage is the period between egg deposition and hatching and the wriggler stage is the period from hatching to the fry swimming up (e.g., embryo in nest; Ridgway 1988). Video was only recorded from a given individual once so that it was unnecessary to control for ‘individual’ in analyses (e.g., Steinhart et al. 2005). At the conclusion of a video recording, the snorkeler recorded species and stage of offspring development, and estimated total length of the parental male to the nearest 2 cm (Table 1). In total, 210 individual nests were monitored yielding a sample size of between 12 and 20 nests per species at each stage of offspring development (Table 1), totalling 2100 min of video footage.