Reproductive Ecology and Food Habits of the Blacknose Shiner, Notropis Heterolepis, in Northern Illinois

Article excerpt

ABSTRACT.-

Although once broadly distributed in the region, the blacknose shiner, Notropis heterolepis, has declined or has already been extirpated throughout much of the Midwest and little is known about its life history. We describe characteristics of reproductive biology and food habits for a lake population of N. heterolepis in northern Illinois to provide information for conservation and management. Gonado-somatic index scores and ovarian stage of female individuals indicated that multiple clutches of ova were produced over a prolonged period lasting from spring until mid-summer. The number of ova present in a clutch was positively related to standard length. However, this relationship weakened and less ova were present in clutches of larger individuals as the reproductive season progressed. Female individuals ≥34 mm SL were mature and the presence of tubercles on male pectoral fins suggested a similar size at maturity for males. Individuals consumed the greatest number of prey items during morning and night -time periods and consumption was less in summer and fall compared to spring. Cladocerans (Chydoridae and Bosminidae) and ostracods were principal diet contributors. Chydorid cladocerans, which are known to associate with aquatic vegetation, were increasingly selected for when ambient densities of all three principal diet contributors were relatively low. Our results indicate that N. heterolepis utilizes a reproductive strategy that should allow resilience to short term, minor disturbances, but they are likely vulnerable to chronic disturbances. In particular, chronic disturbances that reduce or eliminate aquatic vegetation, an important foraging habitat and nursery habitat, will likely have negative impacts on remaining populations.

INTRODUCTION

The blacknose shiner, Notropis heterolepis Eigenmann and Eigenmann, was broadly distributed in North America in clear, well-vegetated lakes and pool and run habitats in streams within the Atlantic, Hudson Bay, Great Lakes and Mississippi River basins (Page and Burr, 1991). However, N. heterolepis has declined dramatically in southern portions of its range, especially in the Midwestern United States where it is considered at some level of conservation concern in seven states (e.g., Roberts, 2004; Bernstein et al., 2000; Cross and Collins, 2000).

Despite the relatively broad geographic distribution of Notropis heterolepis, little is known about the life history of this fish beyond anecdotal observations and general habitat associations. Forbes and Richardson (1920) reported gravid females as early as 5 June and as late as 1 August in Illinois and similar observations have been made in Wisconsin (Becker, 1983; Cahn, 1927). Qualitative investigations indicated that digestive tract contents of N. heterolepis-were comprised mainly of small crustaceans (Backer, 1983; Cahn, 1927). An age and growth study conducted by Emery and Wallace (1974) revealed that individuals of a Wisconsin glacial lake population did not survive their second winter, although occasional age 2 individuals have been reported elsewhere (Becker, 1983).

The above information is largely anecdotal, but provides a foundation for further study to identify life history characteristics that may be important for management and conservation of this declining species. Our overall objective was to closely examine the natural history of Notropis heterolepis in a northern Illinois lake. We targeted two important components of natural history, reproduction and feeding, and specifically aimed to: (1) describe the reproductive biology and life history strategy of N. heterolepis and (2) quantify diet and feeding patterns. Our results will provide insight into the observed declines of southern populations of N. heterolepis, allow for assessments of how remaining populations will react to environmental stressors and reveal linkages between N. heterolepis, its prey and associated habitats.

STUDY AREA

Most individuals for this study were collected from Leopold Lake, an 11. …