A Comprehensive Approach to Understanding Diadromy at the Species Level: Learning from the Spawning Migration of Hickory Shad
Joshua G. Murauskas and Roger A. Rulifson
We consider diadromous fish migrations to include three principal components: demographics of the migrating population—who is migrating, external conditions, and movements—where and when is migration occurring, and, physical or internal changes—what changes do fish experience and why do they occur? Despite extensive work to characterize these components (Harden-Jones 1968; McKeown 1984; Smith 1985; McDowall 1988), synthesis of data at the species level is lacking. This is partially due to the narrow scope of many projects limited by objectives, time, resources, and sampling logistics. This process has led to piecemeal explanations of a multifaceted event for many diadromous fishes. The objective of this extended abstract is to briefly demonstrate how a broader approach to investigating diadromy is not only beneficial, but is needed to understand the whole picture.
Hickory shad Alosa mediocris was selected as a model to examine the collective changes experienced by an iteroparous fish during a spawning migration. This relatively unstudied fish belongs to a recreationally and commercially important family that likely accounts for a majority of diadromous fish along the eastern United States. We sampled fish of a particular run in two consecutive years at various points in their ascent in salt-, brackish, and freshwater in coastal North Carolina to describe our three components of diadromy. Time, location, and water quality data were collected at each capture site. Samples of blood, muscle tissue, gonads, stomach, otoliths, and scales were collected from each fish (Table 1). These data along with length, weight, and spatial-temporal data provided a detailed account of internal and external changes experienced by a population during the spawning migration.