Challenges for Diadromous Fishes in a Dynamic Global Environment

Abstract

<em>Abstract</em>.-The sea lamprey <em>Petromyzon marinus </em>is a widely distributed anadromous species spawning in coastal rivers and streams throughout the north Atlantic basin. In this paper, we review aspects of sea lamprey migration and ecology that relate to the transport of nutrients and materials to and from freshwater ecosystems and provide an example of a long-term study of a native wild population. Several aspects of lamprey life history (rapid growth in marine phase, many adults spawn in upper reaches of small oligotrophic rivers, all adults die after spawning) suggest that anadromous sea lampreys contribute marine-derived nutrients and materials (MDNM) to freshwater ecosystems. We used long-term (20 years) data on spawner abundance, along with literature-derived concentration values, to estimate the import of nutrients and materials to a spawning reach of the Fort River, a tributary of the Connecticut River in western Massachusetts, USA. Sea lamprey imported as much as 0.26 g of P per square meter of stream, as much as of 20% of the total annual P loading to a similar system where a full P budget has been developed. While the MDNM contribution of sea lamprey may be substantial, other aspects of their life history and habitat use may limit the overall magnitude and direction of lamprey influence on freshwater ecosystems. Spawning requirement for rocky substrate within a narrow size range may limit import at the watershed scale. In addition, marine survival rates of less than ~1% will result in a net export of nutrients and materials via out-migrating juveniles (transformers). While there is currently no information on survival rates in wild anadromous populations, the tight link between adult survival and prey/host fish populations observed in landlocked Great Lakes systems suggests that the ecological role of sea lamprey may be strongly related to the abundance of coastal marine fishes. Further research on adult survival, juvenile dispersal and distribution, and the paths of nutrient and material uptake in spawning streams are necessary to more fully evaluate the role of anadromous sea lamprey in the transport of MDNM.