Abstract
Anthropogenic alterations to the hydrology of native California watersheds, coupled with the added pressure of non-native species have led to extirpation and reduced abundances of native fishes throughout the State. As a result, significant effort has been applied to the conservation of native California fishes, especially native salmonids, with a significant focus on studying predation and applying management practices to improve overall survival of native fishes. However, the native Sacramento Pikeminnow (Ptychocheilus grandis) is a relatively understudied native piscivore and is frequently associated with predation of juvenile salmonids. California waters are also home to many non-native species, including various species of non-native Black Bass (Micropterus spp.), which pose not only a predation threat to native fishes, but may also negatively impact Sacramento Pikeminnow through increased competition. The goal of this study was to conduct a captive experiment using two co-occurring piscivores in the Dry Creek system, the native Sacramento Pikeminnow, and the non-native Spotted Bass (Micropterus punctulatus) to identify: 1) which of these piscivores exhibit greater predatory traits, i.e., a comparison of the number of prey consumed and the rapidity of predation events; 2) if interspecific competitive interactions occur between the species; and 3) if differing temperatures affect both predation and interspecific competition for both species.
Captive experiments were conducted using a repeated measures design with each fish being tested at 15° C and 25° C. Both single species and multispecies trials were conducted. Single species trials consisted of only one individual being tested (N=15 for Sacramento Pikeminnow and N=18 for Spotted Bass) and multispecies trials involved one individual of each species being tested in the same experimental aquarium (N=8). Single species trials using Chinook Salmon fry were also conducted with Sacramento Pikeminnow (N=14).
The following measurements were recorded for each trial: activity level, time of predation events, and failed attempts. Activity levels measured the number of times the fish crossed over a 5 x 5 cm grid. The time of each predation event was recorded in seconds, and later converted to a predation rank value that factors both the number of prey consumed and how rapidly predation occurred. The number of failed attempts was recorded and included any attempt where the predator both pursued the prey species and made an active attempt to catch the prey. Sacramento Pikeminnow, Spotted Bass, and a limited number of Chinook Salmon fry were collected from the Dry Creek system for experimental trials. Rosy Red Minnows (Pimephales promelas) were also obtained from local feed stores as prey fish for most of the study.
A repeated measures Multivariate Analysis of Variance (MANOVA) was utilized for analyzing the data. Results of the single species trials using Rosy Red Minnows showed only a significant difference in activity level (F = 16.191, df = 1, p < 0.001). Single species trials comparing Rosy Red Minnows and Chinook Salmon fry showed significance for all predation values: “First_Predation” (F = 9.973, df = 1, p = 0.004), “Second_Predation” (F = 8.785, df = 1, p = 0.006), and “Total Predation” (F = 10.722, df = 1, p = 0.003). Multispecies trials showed no statistical significance.
Results of this study did not find a significant difference in predatory traits between Sacramento Pikeminnow and Spotted Bass, and multispecies trials did not provide any evidence of competitive interactions. However, Spotted Bass did exhibit aggressive behavior leading to four out of twelve attempted trials ending due to pikeminnow mortality. Predation values when comparing the two prey species was significantly different, with farm raised Rosy Red Minnows being predated significantly more than wild caught Chinook Salmon.