Lethality of Sea Lamprey Parasitism on Lake Sturgeon

Abstract

AbstractParasitism by sea lampreys Petromyzon marinus may contribute to the delayed recovery of imperiled populations of lake sturgeon Acipenser fulvescens in the Great Lakes. Our study objectives were to examine the survival, growth, and condition of four size‐classes of lake sturgeon following a single sea lamprey attack. Lake sturgeon from one of four size‐groups (I: 470‐570 mm fork length; II: 570‐650 mm; III: 650‐760 mm; and IV: 950‐1,500 mm) were individually subjected to a sea lamprey attack in a series of 55 experimental trials. Direct mortality of lake sturgeon, resulting from acute anemia after an attack, was greatest for smaller lake sturgeon (I: 11%; II: 31%; III: 8%; IV: 0%). Similarly, indirect mortality resulting from secondary fungal infection was also size dependent (I: 11%; II: 19%; III: 8%; IV: 0%). No direct relationship was found between attachment duration and host survival; short intense attachments were as likely to result in host mortality as longer attachments. More than 50% of sea lamprey attacks occurred on the ventral surface of the rostrum or pectoral fin axils, and attachment at these locations resulted in the mortality of the host more often than did attachments at other locations. Declines in lake sturgeon growth and condition after an attack were more pronounced for smaller (size‐classes I‐III) than larger (size‐class IV) lake sturgeon hosts. Although much uncertainty remains about the effects of sea lamprey parasitism on lake sturgeon, the levels of mortality observed in this study suggest that the no‐observable‐effect lampricide treatment protocol, which is designed to protect larval lake sturgeon at the expense of increased production of sea lampreys, may not be the optimal strategy for the concurrent rehabilitation of self‐sustaining lake sturgeon populations and sea lamprey control in the Great Lakes.