Assessment of Road Culverts as Passage Barriers to Wild and Stocked Trout in Pennsylvania Headwaters

One of the primary threats to brook trout in Pennsylvania is population fragmentation due to habitat alteration. Road culverts in particular can isolate populations by reducing access to upstream spawning habitat. To categorize the degree to which culverts prevent fish movement, watershed managers use physical measurements to classify the passability of the each culvert. The North Atlantic Aquatic Connectivity Collaborative (NAACC) conservatively categorizes culverts as “no AOP (Aquatic Organism Passage)” or “red culverts” when they are considered a barrier to aquatic organisms. The Little Bear Creek watershed, a wild trout stream in the Loyalsock watershed, contains three culverts categorized as “reduced AOP” or “gray culverts” that require further investigation to determine actual organism passage. It is unknown whether these gray culverts are indeed barriers to migratory fish, especially native trout. To measure how passable these culverts are, we tagged 546 wild trout in 2015 and 2016 with passive integrated transponder (PIT) tags, distributed up and downstream of each culvert site and a control site without a culvert. Results show that trout are differences in movements between culvert types, implicating a barrier issue in Little Bear’s tributaries. The only metal corrugated culvert in the watershed, which lies on the upper most extent of Sand Spring Run, has proven to be the most passable of the culverts with an average of 0.85 movements per day. A small box culvert on the lower extent of Sand Spring Run had an average of 0.1 movements per day. The largest culvert, a more recently built box culvert close to the mouth of Red Run, had an average of 0.01 movements per day. None of the movements in Red Run were upstream movements. The barrier-free site on Painter Run resulted in an average of 0.27 movements per day. We will further test for correlations of trout movements with daily stream conditions such as temperature and water level. By “ground-truthing” culvert assessment methods, we anticipate our study will ultimately help watershed managers better prioritize culverts for removal or replacement