Spawning interactions among fertile male, female, and sterilized male sea lampreys Petromyzon marinus were examined by placing externally attached radiotransmitters on 4% (52 animals) of the population of sea lampreys that was introduced above a barrier to their passage in the Carp River, which flows into Lake Superior, during 1996 and 1997. Movements and interactions on nests made by sea lampreys were monitored using portable receivers for up to 20 d from the start of nest construction. Four times as many nests from the same number of introduced animals were found in 1996 than in 1997. Two sea lampreys with radio transmitters emigrated from the stream in 1996, and 13 animals emigrated or were missing from the stream in 1997 when a freshet occurred just before spawning. Only three male sea lampreys with transmitters were observed spawning, and these males visited more than one nest. We continuously checked four or more nests each year and observed that each nest was built, altered, or destroyed several times by sea lampreys. We suggest that fertile and sterile male sea lampreys have low fidelity to a nest or to a female and that a nest may contain reproductive products from different parents.
This study examined olfactory sensory neuron morphology and physiological responsiveness in newly hatched sea lamprey, Petromyzon marinus L. These prolarvae hatch shortly after neural tube formation, and stay within nests for approximately 18 days, before moving downstream to silty areas where they burrow, feed and pass to the larval stage. To explore the possibility that the olfactory system is functioning during this prolarval stage, morphological and physiological development of olfactory sensory neurons was examined. The nasal cavity contained an olfactory epithelium with ciliated olfactory sensory neurons. Axons formed aggregates in the basal portion of the olfactory epithelium and spanned the narrow distance between the olfactory epithelium and the brain. The presence of asymmetric synapses with agranular vesicles within fibers in the brain, adjacent to the olfactory epithelium suggests that there was synaptic connectivity between olfactory sensory axons and the brain. Neural recordings from the surface of the olfactory epithelium showed responses following the application of L-arginine, taurocholic acid, petromyzonol sulfate (a lamprey migratory pheromone), and water conditioned by conspecifics. These results suggest that lampreys may respond to olfactory sensory input during the prolarval stage.
Information from the records of the various agencies on control of the sea lamprey (Petromyzon marinus) was summarized from the early approach to control by mechanical or electrical barriers and chemical toxicants. While fish kill has been an inescapable consequence of the program, information available for migratory species has shown no large-scale detrimental effects. The only reportable instance of damage to a resident stream species has been the near loss of the stonecat (Noturus flavus) from tributaries to the southwest corner of Lake Superior, resulting from chemical treatments. Although no similar occurrences were recognized, available documentation proved inadequate to record long-term effects on these vulnerable species. As long as existing control methods continue, no matter the precautions taken, fish populations will be affected. Whether or not this remains a tenable situation is a question for this symposium and the future.Key words: weirs, chemicals, fish kills, sea lamprey, Petromyzon marinus; Catostomus catostomus, Catostomus commersoni, Noturus flavus, Salvelinus fontinalis
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