Gillnetting update Nov 2022

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Dan Keller

UT DWR Fish Biologist
We finished our annual gill-netting survey last week. The fall gill-netting survey has been conducted each November since 1981. The survey is completed at 4 stations including Wahweap Bay (down-lake), Rincon (mid-lake), Red Canyon at Good Hope Bay (up-lake), and the Piute Canyon/Neskahi Canyon area on the San Juan arm. Nets were set for 2 consecutive nights at each location and were checked, with fish being removed and processed each morning. If you’re not familiar with gill-nets picture a nylon volleyball net, except 100 feet long and made from monofilament. Each net has 4 panels with progressively increasing mesh sizes of 0.75”, 1.0”, 1.5”, and 2.0”. Nets were set perpendicular to shore with the terminal end usually reaching a 20-60 ft depth range. We use 10 gill-nets at each location mentioned above. Anyway, I wanted to explain in a bit more detail what I mean when I talk about gill-netting. This survey provides us with very valuable information on the health and population trends of all the fish species at Lake Powell.

Historically, the total catch of fishes has been lowest but most consistent at the Wahweap station. Reduced primary productivity (food in the form of phytoplankton and zooplankton) results in a weaker food chain in the lower lake regions. Since 2003 (post establishment of gizzard shad) the mean total catch from the annual gill-net survey at Wahweap was 205 fish. This year at Wahweap our catch was 471 fish, YES more than double the average! The majority of these fish were Striped Bass (n=215) and Walleye (n=94). This is quite a divergence from the norm, however not too surprising when one considers the far from normal lake level over the past few years. We all anticipated seeing changes in the fishery due to lake level, I must admit, a near record number of fish at Wahweap is not something I would have predicted. The question in my mind now is why are we seeing this influx of fish at Wahweap and how long will it last? It’s also important to acknowledge that as important as gill-netting is to managing a fishery, one year of gill-netting provides only a snapshot in time, one we use to generalize the status of the fishery lake-wide for the entire year. Many variables including water temp, turbidity, presence of forage fish and many other factors can influence gill-net catch rates. More years of data will be needed to determine new trends. With the exception of Wahweap, results at the other 3 stations were similar to previous years. The number of fish was lowest at the mid-lake station at the Rincon. The water clarity at this station is typically high during the annual fall gill-net survey as particulate matter that is migrating down-lake falls out before entering the area. The low turbidity makes the gill-nets more visible, and fish are better able to avoid capture. For comparison of all the stations, we caught 471 fish at Wahweap, 400 at San Juan, 287 at Good Hope and 206 total fish at Rincon. The station at Good Hope Bay has historically collected more fishes than any other station. Being the furthest up-lake station in the gill-net survey it benefits from being the most productive in terms of not only primary productivity, but throughout the food web. This year total catch was lower than average at Good Hope Bay. Good news is the number of Walleye is up however we caught fewer Striped Bass. The low lake elevation puts the Colorado River inflow closer to Good Hope Bay than ever before, resulting in higher sediment loads and increased turbidity. Over time we will likely see a down lake shift in fish behavior and patterns as the reservoir adjusts. Many anglers have commented on boils at Good Hope Bay not following the same patterns as years past, I attribute this to the changing water levels rather than lack of fish. We did well fishing for stripers on Nov 10th near our camp at Red Canyon / Blue Notch. Trolling Norman divers 3.5 – 4 mph was the best method.

During our lake wide monitoring trips over the summer, we noticed the Rincon was the most consistent location for striper boils. The boils did appear to abruptly stop in September indicating reduced shad in the area, additionally when we checked the stomachs of Stripers caught at the Rincon and San Juan the majority were empty, most were still very fat and healthy, however I do wonder if shad numbers have declined to the point that Fall boils were somewhat reduced? Hungry Striped Bass have a tendency to move down lake searching for food. A down lake migration of adult Striped Bass searching for shad could help explain some of the increase of fish we observed at Wahweap this year. We did see a good number of young Striped Bass and Walleye at Wahweap, the presence of these young fish indicates good spawning conditions in the lower lake in recent years, as well as a strong cohort of fish to look forward to catching in the future. Over the past 7 months we have collected a variety of data at the same locations we gill-net including water quality, larval shad, pelagic-shad, zooplankton and more. We will be assessing this data over the winter to better understand changes that are occurring and what factors will drive fish populations in future years.

Most of the sportfish stomachs we checked at Wahweap were stuffed full of shad, this is great news for the health of the fish but can make fishing a challenge. Well fed fish are always harder to catch, however as water temperatures continue to drop Striped Bass will move deeper and be easier to pick up with sonar, a well-placed jigging spoon will get their attention. If you’re not ready to store the fishing tackle for winter just yet I suggest you consider a trip to the back of Wahweap Bay, spooning for Striped Bass should be good this winter. I can’t fail to mention one of our nets at Wahweap caught a 43” striper, we were able to take some quick data and return the impressive fish to the water. If you have never made a late season / winter trip to Lake Powell you’re missing out, it’s a great time to visit the Lake !
 

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