Allegheny River Walleye Western Pennsylvania

Transcription

1 Pennsylvania Fish & Boat Commission Biologist Report Allegheny River Walleye Western Pennsylvania Fall Night Boat Electrofishing Surveys In 2008, Pennsylvania Fish and Boat Commission (PFBC) biologists discontinued all supplemental stockings of Walleye in large rivers. This management decision was made to determine if natural reproduction could serve as the exclusive source of recruitment (recruitment = fish added to the fishable stock each year) for maintaining Walleye fisheries at a quality level for major rivers across the Commonwealth. Under a supplemental stocking strategy, hatchery-reared fry or fingerlings are stocked annually or biennially to contribute to an existing population believed to maintain some degree of natural reproduction. Walleye were the only species historically stocked in the Allegheny River under this strategy. In 2007, the last year they were stocked, Walleye fry were stocked in the Allegheny within the 161-mile reach spanning Lock and Dam (L/D) 6 upstream to Kinzua Dam. On only four occasions were Walleye stocked downstream of L/D 6 in 1976, 1977, 1980, and 1983 in the Emsworth Pool near Pittsburgh. Between 2000 and 2007, Walleye fry were stocked in the Allegheny River; but none between 2008 and In 2008, PFBC biologists began to monitor levels of Walleye natural reproduction by conducting surveys to determine presence and relative abundances of young-of-the-year (YOY, Age 0, or fish less than one year old) cohorts. Adult Walleye were also collected during these surveys, which are conducted every September and October using pulsed DC night boat electrofishing gear at fixed sites on the Allegheny. Six sites are located along the Allegheny River s free-flowing reach at Oil City, President, Tionesta, Tidioute, Starbrick, and the tailwaters of Kinzua Dam; and three sites are situated within the impounded reach at Freeport, Templeton, and East Brady (Figure 1). Area PFBC biologists retained scale samples from all Walleye collected during the surveys. These scales were pressed and read in the laboratory to make an age determination for each fish. Preliminary results reveal that Age 0 Walleye collected from the Allegheny River are all less than 9 inches total length (Photograph 1). For analyses presented in this report, all Walleye collected (aged or not) less than 9 inches in length were considered Age 0. The following account summarizes our findings made over the past six years during surveys of Allegheny River Walleye to monitor levels of natural reproduction, as well as to assess trends in population relative abundances, size structure, age structure, and general fish health over time. Figure 1. The nine Allegheny River fixed sites targeted for YOY Walleye are shown in red. Some sites, like Templeton, were surveyed every year. Starbrick and Tionesta were only surveyed once in Other Allegheny River survey locations (e.g., Smallmouth Bass sites) are depicted in black.

2 Photograph 1. YOY Walleye collected at Freeport in September As part of routine stock assessments of managed Walleye fisheries, PFBC biologists use catch-per-unit-effort (CPUE; expressed herein as number of fish collected per hour of electrofishing) values to estimate population relative abundances as well as to monitor levels of natural reproduction. The CPUE statistic served as the principal evaluation benchmark for both YOY Walleye (< 9 inches) and legal-length Walleye ( 15 inches). Catch data from our Allegheny River targeted Walleye surveys are summarized for both length groups in Table 1 (below). Table 1. Walleye catch summary statistics at nine fixed sites on the Allegheny River from Largest fish collected (year collected) Site Mean CPUE < 9 inches (# YOY fish collected per hour) Freeport Templeton East Brady Oil City President Tionesta Tidioute Starbrick Kinzua Years surveyed inches (2012) 20 inches 27 inches (2010) 31 inches (2012,2013) 30 inches 32 inches 30 inches (2009) 19 inches 24 inches (2010,2011) * * 11.9 Site Mean CPUE 15 inches * * 10.8 (# legal-length fish collected per hour) *Not a true mean (represents only one survey year); presented for comparison purposes. Area PFBC biologists really enjoy collecting trophy-size fish during our electrofishing surveys. More importantly, however, we publicize our trophy observations in our Biologist Reports (like this one in particular) so anglers can find out about the tremendous fishing opportunities that exist in Pennsylvania. Walleye surveys conducted this past fall on the Allegheny River were truly exceptional in this regard. Photographs 2 through 4 tell the story. Photograph 2. Ben Dutko (left; Fish Culturist 2 at our Tionesta State Fish Hatchery), Brian Ensign (center; Area 2 Fisheries Biologist at Tionesta), and Kelly McFarland (right, Fish Culturist 2 at our Tionesta State Fish Hatchery) flaunting a hefty 31-inch; 9-pound, 13-ounce Walleye collected October 2013 at Oil City.

3 Photograph 4. Matthew Odonish (left; Junior Environmental Biology major at Clarion University), Brian Ensign (center), and Michael Odonish (right; Junior Environmental Biology major at Clarion University) presenting the largest Walleye collected by PFBC biologists from the Allegheny River a 32-inch; 12-pound, 10-ounce trophy netted (by Ben Dutko) at Tionesta. Freeman s Allegheny River Walleye record only lasted one day! We also landed 29-inch; 8-pound, 8-ounce and 29-inch; 9-pound, 6-ounce Walleyes that night at Tionesta. These big fish were all found in very fast-moving water near our hatchery. Photograph 3. Area 1 Fisheries Biologist Freeman Johns hoisting a 30-inch; 12-pound, 8-ounce monster Walleye he netted October 2013 at President. That s the biggest Walleye I ve ever handled, he later admitted. At the time, this fish broke the record for the largest Walleye PFBC biologists have collected from the Allegheny River.

4 In 2011, PFBC biologists released A Plan for the Management of Pennsylvania's Inland Walleye Fisheries (herein referred to as our Walleye Plan ). This document proposes strategies to help us make more informed decisions regarding Walleye abundances and updates catch rate objectives in order to achieve our goal of creating high-quality targeted Walleye fisheries. The Walleye Plan presents target catch rates for both YOY Walleye 20 per hour; and legal-length Walleye two per hour. The target catch rates for both YOY cohorts and legal-length fish is based on mean catch rates from fall night boat electrofishing surveys of major Pennsylvania rivers already maintaining high-quality targeted Walleye Fisheries. Figure 2 (below) presents CPUE values for Walleye < 9 inches compared to the Walleye Plan target catch rate for YOY cohorts (of 20 per hour) for all nine Allegheny River fixed sites over the past six years. These YOY catch results are thought-provoking. Over a six-year period, President and Freeport only met the target catch rate once, while Tidioute was the least productive, not meeting our Walleye Plan objective in any surveyed year. Kinzua did not perform that well, either, over four years of surveys. On the other hand, Oil City met or exceeded the target catch rate half of the time, while Templeton performed the best of the sites surveyed meeting or exceeding our expectations for YOY Walleye for all six years. The most productive year for natural reproduction of Walleye in the Allegheny River appeared to be Figure 3 (below) presents CPUE values for Walleye 15 inches compared to the Walleye Plan target catch rate for legal-length fish (of 2 per hour) for all nine Allegheny River fixed sites over the past six years. Although Tidioute and Kinzua were low on YOY numbers depicted in Figure 2, these two sites were on the high end of legal-length Walleye abundances depicted in Figure 3.

5 Because of deeper water, electrofishing efficiencies for adult Walleye are typically lower for the impounded reach of the Allegheny. Subsequently, Freeport and Templeton never met the target catch rate presented in our Walleye Plan. East Brady only met it twice. It was another story for the shallower, free-flowing reach of the Allegheny. Oil City and Kinzua met or exceeded our expectations for legal-length Walleye for all years surveyed. Tidioute met our objective for four of five survey years, and President for half of the time. Tionesta and Starbrick also met the target catch rate this past year. The most productive year for legal-length Walleye in the Allegheny River appears to be 2013 great fishing opportunities exist now! Contemporary research on Walleye genetics by Matt White, Ph.D. (Professor and Chair of the Department of Biological Sciences at Ohio University in Athens) and his colleagues at Ohio University have revealed two different lineages. Characteristic differences were found between the genetically distinct and widely-stocked Lake Erie Walleye strain and native Highlands Walleye strain named after a strain found in the Ohio River, the New and Kanawha rivers in West Virginia, and the Cumberland River in Kentucky. Their goal has been to determine the distribution of the native Highlands strain and to identify those populations of natives that appear to have avoided hybridization with the introduced Lake Erie strain. One of Dr. White s former graduate students, Katie Zipfel, now a Fisheries Biologist with the West Virginia Division of Natural Resources (WVDNR) found that of 73 Walleye collected from the Monongahela River between , only three (4%) were the native Highlands strain. The remaining (96%) Walleye were found to be the introduced Lake Erie strain; most likely a result of previous stockings by the PFBC and WVDNR. All Walleye stocked in the Monongahela were produced from broodstocks known to be derived from the Lake Erie strain (e.g., Walleye from our Linesville State Fish Hatchery). WVDNR biologists feel that the native Highlands Walleye strain, which are adapted to river environments, grow faster, grow larger, and maintain a higher reproductive potential in their rivers than the introduced Lake Erie strain, which are adapted to lake environments. To aid and collaborate with Dr. White in walleye research, during our 2013 surveys of the Allegheny River, we retained fin clips from 155 Walleye collected at L/D 3, Freeport, Templeton, East Brady, Kennerdell, Oil City, President, Tionesta, and Kinzua. These clips were preserved and sent to Ohio University. A very preliminary analysis of Allegheny River Walleye by Dr. White and his students has demonstrated the presence of the native Highlands strain at several locations. Of the fin clips analyzed thus far about half of the 155 samples, all have turned out to be the native strain! The results of Dr. White s studies will give us a clearer picture of the distribution of the native Highlands strain of Walleye in the Allegheny River.

6 Results of our evaluation confirms that natural reproduction of Walleye is occurring in the Allegheny River, and that strong year classes (especially 2010) have developed from this natural reproduction at many of the reaches surveyed. Regardless of the fact that we haven t stocked them since 2007, our Allegheny River s Walleye populations continue to be very productive. Over the past six years, upstream, free-flowing Allegheny River sites have been found to be much more productive than downstream, impounded sites in terms of legal-length and trophy-size Walleye. Based on the preliminary findings of Dr. White, the potential exists that much, if not all of the natural reproduction of Walleye occurring in the Allegheny is a direct result of the native Highlands strain. See you on the river! Bob Ventorini Three Rivers Biologist (Somerset)