Spawning Microhabitat Selection in Wild-Caught Delta Smelt Hypomesus transpacificus under Laboratory Conditions

Abstract

AbstractVery little is understood about the spawning habitat of endangered delta smelt Hypomesus transpacificus, which hinders ongoing recovery efforts such as wetland habitat restoration and spawning habitat augmentation. To address this, the spawning response of wild-caught H. transpacificus to different substrates and water velocities was examined across three experiments. In experiment 1, spawning response to dead wood, pebble, natural and artificial Schoenoplectus acutus, empty tray, and tank floor at water velocities of 1.4 and 8.8 cm/s was tested. Egg deposition on pebble at 8.8 cm/s velocity (78.1% of 7778 total eggs) was significantly greater than that on all other substrate-velocity combinations. In experiment 2, spawning response to natural S. acutus, dead wood, sand, pebble, cobble, and empty tray at velocities of 8.7 and 15.4 cm/s was tested. Egg deposition on pebble at 15.4 cm/s (61.5% of 36171 total eggs) was significantly greater than that on all substrate-velocity combinations except for sand at 15.4 cm/s. Sand at 15.4 cm/s (22.3%) contained significantly more eggs than all combinations except for pebble at 8.7 and 15.6 cm/s. In experiment 3, egg attachment to natural S. acutus, dead wood, sand, pebble, cobble, and empty tray when exposed to 14.6 cm/s velocity was tested. Egg loss on sand was significantly greater than that on empty tray and pebble, indicating that egg deposition on sand may have been underestimated in experiment 2. Together, these results indicate that H. transpacificus selects pebble and sand at higher water velocities for spawning under certain laboratory conditions. These findings are important, as they provide insight into the potential natural habitats that may be used for spawning and thereby inform ongoing habitat restoration efforts.