DIET OF JUVENILE BURBOT AND INSIGHT INTO GAPE LIMITATION

Abstract

Throughout much of their distribution, Burbot (Lota lota ) populations are declining or have been extirpated.  Burbot in the Kootenai River, Idaho represent one such imperiled population.  In an effort to restore Burbot in the Kootenai River, managers have turned to conservation aquaculture.  However, no appreciable increase in natural recruitment has been observed in the system.  The lack of natural recruitment is believed to be partly due to a deficiency of high-quality prey.  As a result, we sought to i) describe the diet of juvenile Burbot, ii) evaluate the influence of Burbot mouth gape on diet and iii) estimate prey availability at release locations.  Burbot were stocked into two earthen ponds at the Boundary Creek Wildlife Management Area (BCWMA) and sampled weekly to evaluate diet.  Zooplankton were sampled weekly from each pond and from release locations of hatchery-reared Burbot (i.e., Kootenai River, Goat River, Boundary Creek, Deep Creek) to quantify prey availability.  Over the course of the study (~3 months), Burbot primarily fed on Cyclopoida.  Burbot never appeared to be gape limited and exhibited little variability in the size of zooplankton ingested.  Zooplankton densities at stocking locations were relatively low in comparison to BCWMA ponds.  Low zooplankton densities at release sites indicate that alternative management actions may need to be considered to enhance Burbot recruitment in the Kootenai River drainage.