2016 Gill Net Sampling Report
Every November the UDWR sends me out to sample Lake Powell fish with gill nets. Our purpose is to understand how fish numbers have changed over time. If we do this survey every year, using the same nets, same locations and same time of year, we are confident that dramatic changes in fish numbers can be determined. While handling and recording our catch we can see if physical condition of the various fish species has changed. We sacrifice fish to determine what they have been eating, and if there are parasites or other anomalies that have developed over time. Sometimes over a thousand fish are handled in highly productive areas, but usually 300 to 500 fish of all sizes are captured during the two day netting event at four different locations.
Over the years we have learned that some species are not good candidates for gill net sampling. Largemouth bass, black crappie, bluegill, and green sunfish are prone to hold up in aquatic vegetation. These species do not often move at night when the nets are hard to see and most of the fish are caught. Therefore, these species are caught in low numbers lakewide. We cannot say that there are low numbers of bass or crappie based on gill net sampling results. All of the sampling techniques used at Lake Powell must be combined to make that statement accurate. Fortunately, bass numbers look strong going into 2017.
Some species tend to move constantly. Striped bass and gizzard shad are sampled most often in gill nets because they cruise the shoreline at night. Number of fish netted is indicative of relative abundance at each netting area. Smallmouth bass are active along the shoreline but are not cruisers. Numbers of smallmouth caught at each netting site are often very similar because they are caught based on feeding and moving behavior which is the same at each netting site. Channel catfish, yellow bullheads, and native fish still residing in Lake Powell are caught in low numbers because of their moving behavior.
When netting results are discussed, fish numbers caught per gill net sampling site is more likely to accurately portray relative abundance of striped bass and gizzard shad. We found that Good Hope Bay once again had high numbers of both species. The Good Hope Bay station represents the productive inflowing water that is high in nutrients and plankton which allows more shad to grow and attracts predatory fish. Striped bass and gizzard shad are consistently found in greatest abundance at Good Hope Bay. That was true again in 2016.
The San Juan station in Neskahi Bay is another productive area which has high numbers of shad and stripers. These numbers are not as high as found at Good Hope Bay but are indicative of high population strength for many species. Smallmouth bass are also well represented.
The Rincon has very clear water during November making the nets less productive as many fish can see and evade the nets. From our netting results it seems that the Rincon would be a very poor fishing area. That was the case while we were sampling in November but that changes dramatically in the spring when smallmouth are found in abundance.
The last netting station is in Wahweap Bay. The area near the dam is surprising because there are many more fish species found in abundance than expected. Nets are set from Wahweap main launch ramp to the back of Lone Rock Bay. Water color and productivity increases in the shallower water near Lone Rock. Surprisingly, Wahweap was in second place lakewide in striped bass numbers. Unfortunately, most of the stripers caught were in poor condition or of small size. Striped bass fishing results this fall have not been worthy of a second place prize for lakewide fishing. Sometimes sampling does not directly relate to sport fishing results.
The surprising statistic is walleye numbers. The three stations downstream from Good Hope returned results of essentially the same numbers of walleye caught. That seems similar to smallmouth being caught in the same numbers due to behavior of the fish around nets. Walleye are not an easy fish to catch in gill nets, but the numbers in Good Hope are six times greater than found at any other location. This anomaly is proven to be true by other sampling results and specifically by angler catch. The northern lake has a much larger population of walleye than the rest of the lake combined.
Another factor shown by our netting is that there are two different striped bass populations. Those long, thin stripers that are easy to catch on bait are found lake wide. Many are located in areas where shad numbers are high. The thin stripers are obviously not feeding on the shad resource even when in close proximity. My guess is that these malnourished stripers no longer have the speed to feed on shad. Most of the adults in poor condition will not survive the winter. It seems more humane to me to euthanize these thin fish when caught, instead of allowing them to starve over a long period of time. Adult stripers in good condition outnumber thin fish caught in nets.
Smaller stripers are in good shape and ready to take over as the dominant predator next spring as soon as shad spawn and food is abundant. Smallmouth bass are abundant and the population will increase in size and length in the spring when shad spawn in April and May.
Crappie and largemouth bass are being treated to abundant cover right now as aquatic weed beds have grown up in the back of many canyons and coves. While brushy cover is now abundant these two populations depend on brushy cover in the springtime so that newly hatched young bass and crappie are able to avoid predation by hiding in thick woody cover as terrestrial vegetation is covered by rising lake water. If the lake comes up fast before the spawn is over, bass and crappie numbers will increase in future years. If the runoff is slow and small then these two species will continue to be low in number in the near future.
In summary, Lake Powell fish are in good shape. They will be much happier in the spring if threadfin shad are able to spawn in huge numbers. That only seems to happen every third year. Threadfin shad had an off year in 2016 and are not scheduled to spawn well until 2018. It would be great if the threadfin spawn happened sooner than expected. Fortunately, gizzard shad adults are now here in big numbers and they do spawn every spring. There will be a shad spawn and all of our game fish will thrive during April and May due to presence of adult gizzard shad. Striped bass numbers will be reduced over winter. The reason stripers are so plentiful is that reproductive success is near 90%. There are plenty of healthy adult stripers to spawn. The success of this species is dependent on the shad food supply being strong enough to support the millions of mouths ready to feed.
Smallmouth bass numbers are well represented by smaller fish. The key to the smallmouth population growing in size and length is dependent on the shad spawn. If smallmouth bass have enough shad to eat in the springtime, all ages of bass will grow in length.
Walleye are strong in number in the northern lake. Mark the dates from April 15th to June 15th on your fishing calendar for a walleye trip. Sign up for the tagged walleye contest before you go so you can win a prize when one of the many walleye caught turns out to be a tagged fish.
Lake Powell fish are in good health and strong numbers. My prediction is that fishing in 2017 will mimic that found in 2016. Bass will spawn in April with the best fishing found before the lake begins to rise. There will be good bait fishing for stripers in the spring before the shad spawn. After the spawn, striper slurps will start followed by boils if shad numbers are high enough. It looks like 2017 will be another great year for high fishing success at Lake Powell. I can’t wait!