Fish/Shellfish Research and Management - Management and Conservation
Date Published: April 2015
Number of Pages: 89
Author(s): Kale Bentley, Bryce Glaser, Thomas Buehrens, Jim Byrne, and Stacie Kelsey
The mission of the Washington Department of Fish and Wildlife (WDFW) is to preserve, protect and perpetuate fish, wildlife, and ecosystems while providing sustainable fish and wildlife recreational and commercial opportunities. In the lower Columbia River (LCR), WDFWâ€™s goal is to recover populations of steelhead (Oncorhynchus mykiss), which are listed as threatened under the Endangered Species Act (ESA) in the LCR distinct population segment (DPS), while simultaneously managing rivers for recreational fishing opportunities through harvest of hatchery fish and some catch and release (i.e., non-retention) of wild fish. To meet these goals, WDFW must maintain the impacts these fisheries have on wild stocks of steelhead within levels authorized by the LCR Fisheries Management and Evaluation Plan (FMEP). Currently, the only annually occurring method WDFW uses in the LCR to monitor the impacts of recreational steelhead fisheries is through Catch Record Cards (CRC). However, the CRC system is not designed to capture catch information from non-retention fisheries. Therefore, in 2011, WDFW began steelhead creel surveys in LCR tributaries and has developed a plan for continued implementation on a three-year rotating basis. To date, WDFW has completed three years of steelhead creel surveys on the South Fork Toutle and Washougal rivers. This report provides the first comprehensive analysis of the creel data and had three main objectives.
Our first objective was to estimate monthly, seasonal (summer and winter), and yearly patterns of angler effort and catch for hatchery and wild steelhead. A programmed creel survey was conducted on the South Fork Toutle River from May 2011 through March 2014 and on the Washougal River from April 2011 through March 2014; however, surveys were not performed on the Washougal River from mid-June through October in two of the three years. Over the three years, an estimated 7,991 anglers spent 24,346 hours fishing the South Fork Toutle, caught an average of one steelhead per 7.8 hours fished, and landed a total of 3,395 steelhead. Of the landed fish, 60% were of wild origin and released, 35% were of hatchery origin and harvested, and 5% were either hatchery-run or unidentified-origin and released. In the Washougal River, an estimated 28,640 anglers spent 74,351 hours fishing, caught an average of one steelhead per 17.8 hours fished, and landed a total of 6,366 steelhead. Of the landed fish, 44% were of wild origin and released, 43% were of hatchery origin and harvested, and 13% were either hatchery-run or unidentified-origin and released. Among years, the monthly and seasonal pattern in catch and effort was relatively similar. However, the absolute number of hours fished and steelhead caught varied among years, river-systems, and stocks of steelhead (i.e., summer/winter, hatchery/wild).
Our second objective was to evaluate the feasibility of using CRC estimates of hatchery catch to estimate wild catch based on relative handle rates in the South Fork Toutle and Washougal River fisheries. The performance of this ratio in estimating wild fish catch was of interest because it presents a possible method for estimating wild fish catch during periods when creel surveys do not occur. First, we derived the relationship between the two catch estimates by fitting normal and non-normal probability distribution function regression models to the data and found that a zero-inflated Poisson (ZIP) Bayesian mixture model was most appropriate. Relative to creel methods, the CRC method under-estimated monthly catch when catch was less than 200 fish (observed range of monthly catch = 0 - 407 steelhead). However, the two methods provided similar estimates when monthly catch was approximately >200 fish. Therefore, CRC estimates of hatchery catch needed to be adjusted for their negative bias at low ranges of catch prior to their use in estimating wild fish catch based on relative handle rates. Second, we calculated the ratio of wild fish released to hatchery steelhead harvested from creel surveys (i.e., the expansion factor). During the surveyed time period, there was little temporal overlap in catch of hatchery and wild steelhead in the South Fork Toutle River. Thus, few ratios could be calculated and expansion of CRC for wild fish was not feasible. In contrast, the Washougal River did have high temporal overlap in hatchery and wild catch. Therefore, we estimated the ÂgexpandedÂh monthly catch of wild steelhead by multiplying the adjusted CRC catch estimates by the expansion factor, and compared these estimates of wild catch to creel derived estimates. We found a statistically significant, positive linear relationship in wild steelhead monthly catch as estimated by creel and expanded CRC methods. Although the relationship was relatively weak (r = 0.60), the two estimates of wild catch followed a similar monthly pattern with absolute differences in catch ranging from 1 to 201 steelhead. Overall, expanded estimates of wild catch from CRC was possible in river-systems that had high overlapping catch of wild and hatchery steelhead.
Our final objective was to estimate wild population impact rates resulting from nonretention sport fisheries (i.e., hooking mortality) as well as determining the relationship between gear-type and hooking location for use in studies of non-retention mortality. First, we estimated the total number of hooking mortalities by multiplying our estimated seasonal catch per population by the LCR FMEP defined hooking mortalities of 5% for winter steelhead and 8% for summer steelhead. Second, we estimated total impact rates by dividing the total number of mortalities by the total run size, where run size was equal to escapement plus mortalities. From 2012 - 2014, impact rates on wild winter-run steelhead ranged from 2.4 - 6.9% in the South Fork Toutle and from 5.2 - 10.7% in the Washougal River. These estimated impact rates were less than the expected exploitation rate of <10% as outlined in the LCR FMEP in all years and populations except one (Washougal River in 2012). Although absolute total catch was relatively similar among years and populations, the encounter rate of winter-run steelhead in the Washougal River in 2012 was nearly twice that of other years due to the low run size estimate. This high encounter rate led to the relatively high impact rate. However, impact rates can be influenced by bias in escapement estimates if the assumptions made to calculate escapement are not met. For example, WDFW spawner estimates for steelhead based on redds are not currently adjusted for inter-annual variability in survey conditions (i.e., observer efficiencies, females per redd). Finally, we found that >97% of steelhead caught on jigs, lures, and flies were hooked in either the jaw or tongue, which have very high survival rates. Of all fish caught with bait, which accounted for 25 - 45% of catch depending on season, 92% were caught in the jaw or tongue. Therefore, based on the results of these three years of creel surveys, the steelhead sport fisheries in these tributaries appear to be consistent with the expectations described in the LCR FMEP.
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