Hastings Natural History Reservation

18 May, 10 AM - 25 May, 07 AM

Unlike other salmonids, Oncorhynchus mykiss extends its range into the southern Coast Ranges of California, where intermittent streams are ex- tremely prevalent. Juvenile O. mykiss commonly use intermittent habitats in this region, even dur- ing summer. For example, in a 2006 study we found that in early summer (June-July), densities of small fish (FL<10cm) were nearly identical in perennial and intermittent tributaries of the Ar- royo Seco River in Monterey County, just a few weeks prior to the time the streams began drying out. Many fish obviously perished as the streams dried in late summer, but others were able to re- treat to perennial pools. No one has systematically studied the use of intermittent habitats by salmonids, at least to my knowledge, but the literature has some intriguing reports. Erman and Hawthorne (1976) observed a population of rainbow trout (Oncorhynchus mykiss) in which 39-47% of adults entered an intermittent mountain creek to spawn despite the availability of perennial habitat nearby. Ebersole et al. (2006) showed that a creek in Oregon, though nearly dry in midsummer, supported high densities of spawning coho salmon in the fall (Oncorhynchus kisutch). Juveniles in the creek grew rapidly in winter and emigrated as larger smolts, relative to those in perennial creeks nearby. Our study of the Arroyo Seco system suggested that a hydrological mechanism may tend to disproportionately con- centrate spawning habitat into intermittent creeks. The Ebersole study hints that intermittent streams can provide high-quality habitat for juve- niles under some circumstances, especially by supporting higher growth and thus producing juveniles with large body sizes in their first or sec- ond year of life. Large body size appears to pro- vide a distinct survival advantage for juveniles adopting the anadromous life history (Ward et al. 1989, Bond 2006), and the anadromous life history itself provides a distinct fecundity advantage over freshwater residents. This has led some to argue that areas supporting rapid growth in young fish comprise key nursery habitats for anadromous O. mykiss (Bond 2006). The anadromous component is currently at risk of extinction and the focus of various recovery efforts. If intermittent streams support rapid growth of juveniles, they may have an important role to play in recovery efforts, par- ticularly since intermittent streams are so preva- lent in the southern Coast Ranges. A number of possible mechanisms might produce high growth. First, in the Ebersole coho study, the prevalence of spawning adults in the intermittent stream appeared to provide an abun- dant food source (eggs and fry) for yearling fish, and a similar mechanism could be at work for O. mykiss, particularly if intermittency is mechanisti- cally linked to occurrence of spawning habitat. Second, in summer the intermittent creeks tend to concentrate fish, including conspecifics, and may provide abundant (cannibalistic) feeding opportu- nities for larger juveniles. Third, intermittent creeks tend to have greater sun exposure, and hence a potential for high primary productivity supporting a greater food base for the fish. Warmer temperatures could enable faster growth of the fish themselves in a high-productivity sce- nario. Of course intermittent streams also pose greater mortality risks from stress, desiccation, etc. relative to perennial creeks. If any of the above ?high-growth? hypotheses have merit, the habitat would represent a high-risk/high-reward option for juvenile fish. Alternatively, intermittent streams might simply provide high-risk habitats with few benefits to offset the risk; in this case they would function as sink habitat. An interme- diate possibility is that intermittent streams pro- duce high mortality but also rapid-growth survi- vors. These three possibilities have quite different implications for recovery strategies aimed at the fish. We plan to evaluate the role of intermittent creeks in early-life history of O. mykiss via empiri- cal study of such a creek, in a pristine watershed that is inhabited by one of the larger populations of O. mykiss in the central Coast Ranges. The ques- tions raised above will require at least several years to address. Here I describe a plan of study for the initial year (2008), which will focus on de- veloping field methods and addressing some rela- tively straightforward questions about patterns of habitat use. The general plan consists of 1) tagging fish in May using RFID tags; 2) monitoring fish movement over the course of the summer; 3) at least 2 recapture sessions over the course of the summer to estimate survival and growth; 4) de- ployment of a digital temperature sensing unit in late June; and 5) a final recapture session in late August or September, when we will e-fish the re- sidual pools and check dried channels for tags. The goals are to 1) document the scale of move- ment in an intermittent reach in early summer; 2) document patterns of use of perennial pool and intermittent riffle habitat; 3) estimate survival and growth from recaptured fish.

Visit #15337 @Hastings Natural History Reservation

Approved

Under Project # 10052 | Research

NMFS Arroyo Seco / Horse Creek fish tagging, growth, survival study

research_scientist - University of Nevada

Reservation Members(s)

Christine Hatch May 18 - 25, 2008 (8 days)
Christine Hatch May 18 - 25, 2008 (8 days)
Christine Hatch May 18 - 25, 2008 (8 days)

Reserve Resources(s) | Create Invoice

Hastings Cabin 3 May 18 - 25, 2008