| Summary: | In Pennsylvania, two burbot, Lota lota (Linneaus), populations are currently known to exist: a lacustrine population in Lake Erie and an inland population in the Allegheny River headwaters of Warren, McKean, and Potter counties. Because of the known distribution in New York, putative populations may exist in the Genesee and Susquehanna rivers in Pennsylvania. The limited distribution and cryptic ecological requirements of the inland burbot have led to a state classification of endangered (as of 2002 ¡V 2003). The goal of this study was to determine the life history aspects of Pennsylvania¡¦s inland burbot population via five research objectives: 1) determine the historic and current distribution and status; 2) analyze age and size structure; 3) identify important food sources; 4) determine habitat usage; and 5) estimate population densities. During 2002 and 2003, 109 localities were electrofished to determine the current distribution of burbot in the Allegheny, Genesee, and Susquehanna rivers within Pennsylvania and the upper Susquehanna and Allegheny rivers in New York. No burbot were captured from the Susquehanna or Genesee rivers in Pennsylvania nor the Allegheny River in New York. Burbot were captured in the upper Allegheny River in Pennsylvania at 22 localities and the upper Susquehanna River in New York at five localities. Population abundance was estimated using depletion sampling at three sites on Cole Creek, McKean County, Pennsylvania. Burbot density estimates increased from 255 burbot / hectare (95% CI: 162, 485) at the upstream site to 266 burbot / hectare (95% CI: 238, 313) at the middle site to 318 burbot / hectare (95% CI: 257, 405) at the lower site. Inland burbot distribution in Pennsylvania appears to be dictated first by zoogeographical events (e.g., stream capture, glaciation), followed by water quality factors and the presence of sheltering habitat. Burbot were typically captured near boulders, concrete slabs, bridge abutments, and undercut banks. Mean water depths 65 - 80 cm and mean velocities 0.0 - 0.1 m/s were most frequent at capture points. In the upper Allegheny River (summer 2002), mean water temperature and pH were both significantly (Ñ = 0.05) lower at burbot capture sites (n = 23; 17.8oC, pH = 7.29) than at sites where they were absent (n = 48; 20.1 o C, pH = 7.69). Aquatic insects and crayfish were identified as diet staples of burbot less than approximately 200 mm total length (TL). The diet of burbot longer than 200 mm TL was a mixture of aquatic insects, crayfish, and vertebrates; thus, a shift from aquatic insects to vertebrates and crayfish was observed as burbot length increased. Inland burbot from the upper Allegheny River attained a maximum standard length of 370 mm. Mean relative weight (Wr) of the population (Wr = 74) was slightly lower than the proposed target range for North American riverine burbot (Wr = 80 + 5). In conclusion, the inland burbot is a zoogeographic relic of the Pleistocene ice age. Glaciation, a vicariance event, was responsible for their dispersal into the Allegheny and Susquehanna rivers. The resultant isolation of this founder population may have created an avenue for speciation. Conservation of these rare and ecologically unique populations should continue as a management priority within Pennsylvania.
|
|---|