Coho Salmon (Oncorhynchus kisutch) fry population dynamics in Carnation Creek

Salmon are keystone species to multiple environments and are heavily relied upon by many different organisms. This study compares the populations of rearing Coho salmon fry (Oncorhynchus kisutch) at pre-established sampling sections of Carnation Creek. This population data was collected during the summer as part of the more extensive Carnation Creek Watershed study, which is the longest continuous study of logging and fish interactions in North America. Lineal density of fish was calculated for all sections within the years 2011 and 2013. The results indicate that section 8 had a significantly higher density than all other sections in 2013 but there was no significant difference among section during 2011, although section 8 had one of the higher lineal densities. This indicates that the conditions at section 8 were the most beneficial to rear Coho salmon fry. The conditions present that could be the major influence include: stream flow rate, food availability, and habitat type. No section’s habitat data was available for this study; therefore no conclusion can be made whether habitat was the cause of this preference. Introduction: Salmon are a keystone species in both freshwater and marine environments in the Pacific Northwest (Miller 1996). They are anadromous fishes that hatch and grow within a freshwater system for up to several years before migrating to the ocean to mature for one to four years, depending on species (Healy 2009, Pinsky et al. 2009, Loring & Gerlach 2010). After growing in marine waters, they return to their native stream to spawn and die (Miller 1996, Healy 2009, Pinsky et al. 2009, Loring & Gerlach 2010). All species of salmon are voracious predators, attacking any food source that will fit in their mouths and they fill a necessary niche as primary predators in multiple ecosystems (Page 2007). On the west coast of Canada there are five species of salmon present: Chinook (Oncorhynchus tshawytscha), Coho (Oncorhynchus kisutch), Sockeye (Oncorhynchus nerka), Chum (Oncorhynchus keta), and Pink (Oncorhynchus gorbuscha) (Hartman et al. 1982, Miller 1996, Jaeger & Mikesell 2002, Pinsky et al. 2009) In the Pacific Northwest, salmon are also essential for the survival of many apex predators, such as bears, sharks, whales, and seals (Miller 1996). These individuals rely on salmon spawning runs as a main source of food (Hocking & Reynolds 2011). Along with providing sustenance to predators, salmon also transport many marine nutrients to the streams when returning to spawn. Decomposition of the spawned out adults supplies many nutrients necessary for riparian areas to thrive, without which a large decline would occur in both salmon predator populations and the overall health of riparian areas (Hocking & Reynolds 2011). Based on the salmon population's effects on the environment and the reliance predators have on salmon, they are a vital component of the Pacific Northwest ecosystem. Salmon are an integral part of the way of life of many first nations groups along the west coast of Canada (Knowler et al. 2003, Healy 2009). The first nation’s people, especially those that live in remote locations where jobs are scarce, fish for salmon in both subsistence and commercial fisheries (Knowler et al. 2003, & Loring & Gerlach 2010). Due to the reliance of small communities on salmon, a poor years return of adult fish negatively affects the local economy as well as the areas ecosystems (Loring & Gerlach 2010). In addition to being a primary food and income source to the natives, salmon are a central part of their culture (Miller 1996). Therefore, a poor salmon run would have both economic and cultural significance to the native people of the Pacific Northwest. The Carnation Creek Watershed project has been in operation since 1970 and is the oldest ongoing salmon fry studies in North America (Hogan et al. 1998, Hartman & Scrivener 1990). Initiated to study the effects of logging on a small, west coast rain forest stream and its impact on the stream's fish populations, the project includes measurement of parameters such as seasonal water levels, precipitation, and stream conditions as well as abundance of rearing salmonid fry (Hartman et al. 1982). Data collected throughout this 43 year-long study includes data from prelogging, logging, and post logging periods (Hartman & Scrivner 1990, Holtby 1988). Coho salmon are the most abundant fish species, but the watershed also contains populations of Rainbow trout (Oncorhynchus mykiss), Cutthroat trout (Oncorhynchus clarkii), two species of sculpin (Cottus aleuticus and Cottus asper), and a small run of chum salmon (Oncorhynchus keta) within its estuarine waters (Hogan et al. 1998). The objective of this particular study is to determine the lineal densities of O. kistuch at pre-established sections along Carnation Creek three times each year for both sample years. The three sampling periods each year will be averaged and compared among each other to see which sections are able to house the highest density of Coho salmon fry. This data indicates the fry’s preference on habitat present at the sections with the largest densities present. However, no section’s habitat data was available; therefore no significant results could be determined on the fry’s preferred habitat choice based solely off the density data. Study site Carnation Creek (49N, 125W) is found on the west coast of Vancouver Island, Canada and drains into Barkley Sound (Figure 1a) (Tschaplinski et al. 1998, Tschaplinski 2012). This remote stream is about 7.8km long and the entire watershed covers approximately 10km 2 (Hartman et al. 1982) (Figure 1b). Anadromous fish, such as O. kisutch fry, only have access to the lower 3.5km of the stream, which consists primarily of pools with rock and gravel substrates connected by riffles. Pools are usually formed around logs and other debris and it is hypothesized that the pools are the preferred habitat for Coho fry, as they have calmer waters and have a higher potential for more cover from high stream flows and predators. (Hartman et al. 1982) It is further hypothesized that the sections with the most pools will have the highest Coho salmon fry populations. Figure 1.a. Carnation Creek’s location on Vancouver Island (top) and b. all study sections located within the watershed (bottom) (Tschaplinski 2012) Methods and Materials: The population survey of Coho salmon fry (Oncorhynchus kisutch), Coastrange sculpin (Cottus aleuticus), Prickly sculpin (Cottus asper), Rainbow trout (Oncorhynchus mykiss), and Cutthroat trout (Oncorhynchus clarkii) within the Carnation Creek watershed was conducted three times each year for the years 2011 and 2013. Sampling occurred during June, August and September and each sampling period ranged from six – ten days in duration. A total of nine sections have been established to sample fish populations and have been sampled every year of the 40 year term of the study. Six of the sections are in anadromous waters, and three sections which are not included in the analysis, are used only by resident cutthroat trout. Figure 2. O. kisutch fry bearing sections in the Carnation Creek watershed The survey of fish populations was accomplished by multiple passes using a combination of seine netting and electrofishing to achieve total removal of fish from each section following procedures developed by Seber and LeCren (1967). The top and bottom end of each section was netted off, and the first pass was made with a seine net. This followed by a pass with an electrofisher, and the combined passes constituted one run. Sampling occurred from the bottom to the top of the section, against the flow of the stream. Two runs were conducted at each seeection, with a third run necessary if the catch of run two was higher than 15% that of run one’s catch. Poor weather conditions, such as rain and high water levels, and large quantities of debris within the stream were the main factors that would require a third run to be completed (Bayley & Herendeen 2000). After processing, the catch was returned from where the fish were caught and the stop nets were removed. Results: Coho salmon fry were the dominant fish species located within Carnation Creek, as shown in Fig 3. Coho fry salmon populations were significantly different between 2011 and 2013, with 2013 having significantly (two-sample T-test; T= 12.01, P= 0.000; P > 0.005) more fish (Fig 4.). Figure 3. Fish count within Carnation Creek show Coho Salmon fry are the most abundant fish species located within the creek.