Michael E. Douglas

Predation by Introduced Fishes on Endangered Humpback Chub and other Native Species in the Little Colorado River, Arizona

Abstract Fishes in the Little Colorado River in the Grand Canyon, Arizona, were sampled monthly from July 1991 to June 1995 as part of a study of the ecology of endangered humpback chub Gila cypha. Diets of five introduced predatory fish species were examined. Stomach contents varied among species and were low in diversity and dominated by algae (primarily Cladophora), aquatic insects, and fishes. Humpback chub plus other native species were a significant component of the diet (13.7% frequency of occurrence among 219 of 408 stomachs that contained food). Predation mortality from introduced fishes may significantly affect the native species by depleting numbers and reducing recruitment.

Parsimony Analysis and the Phylogeny of the Plecotine Bats (Chiroptera: Vespertilionidae)

Phylogenetic relationships among the taxa of plecotine bats ( Plecotus, Idionycteris, Barbastella, Euderma , and Corynorhinus ) were examined using 32 characters of the skin and skull. Character states for the hypothetical ancestor were inferred by evaluation of outgroup taxa including 12 species of Myotis , two species of Pipistrellus , and Lasionycteris noctivagans . Cladistic analysis performed using PAUP yielded one most-parsimonious tree. The cladogram indicates that each of the taxa is to be regarded as a genus, which supports the contention that Idionycteris is a distinct genus and argues against the subgeneric designation of Corynorhinus . We thus elevate Corynorhinus to full generic status and limit Plecotus to species of the Palearctic.

Spatiotemporal Variation in Length–Weight Relationships of Endangered Humpback Chub: Implications for Conservation and Management

Abstract The largest population of endangered humpback chub Gila cypha inhabits the lower Little Colorado River (LCR) and the main-stem Colorado River near its confluence with the LCR in Grand Canyon, Arizona. At present, fish in both rivers spawn almost exclusively in the LCR. Flows in the main-stem Colorado River are regulated by Glen Canyon Dam, and water temperature approximates predam winter temperatures year-round. The LCR continues to provide a relatively natural hydrograph and seasonal warming patterns. Length–weight relationships among adult humpback chub from the lower Colorado River basin showed a seasonal pattern of declining condition during spring spawning season followed by recovery of condition during summer through early winter. Fish from the main stem recovered condition more rapidly after reproduction than did fish from the LCR and may have benefited from dam-mediated environmental changes. Grand Canyon Colorado River fish had the greatest weight at length of eight locations sampled in ...

Multivariate Discrimination of Colorado Plateau Gila spp.: The “Art of Seeing Well” Revisited

Abstract Fishery managers have long been troubled by phenotypic variation within and among Colorado Plateau Gila. The problem is twofold. From an historical perspective, there was reticence to investigate fishes long considered as “undesirable.” In a taxonomic sense, there is confusion over within- and among-species variability. We document the former, then clarify the latter by applying discriminant analysis to meristic and morphometric data collected from museum specimens. We test three hypotheses: roundtail chub G. robusta humpback chub G. cypha and bonytail G. elegans are morphologically indistinguishable; juveniles are assignable to species based upon adult characters; and putative hybrids are morphologically intermediate between parental forms. Through the use of meristic characters in a nonparametric discriminant analysis, over 95% of all adults were segregated to species. By using morphometric characters, 97% could be allocated to species. Gila robusta was easily separated from G. cypha and G. ele...

Systematic Status of Bonefishes (Albula spp.) From the Eastern Pacific Ocean Inferred from Analyses of Allozymes and Mitochondrial DNA

Recent molecular evidence suggests that at least eight species of bonefishes (Albuliformes: Albulidae: Albula) are found worldwide (Colborn et al. 2001). Adults of most of these species, including two that are restricted to the eastern Pacific Ocean (Albula sp. A from the Gulf of California and Albula sp. C from the Gulf of Panama), have not been formally described. Because cryptic species of bonefishes are known to occur sympatrically, population genetics data provide an important tool for taxonomic studies on this group. Isozyme analyses conducted on larval, juvenile and adult bonefish from the Guaymas region of the central Gulf of California confirmed that only a single species (Albula sp. A) was present there. In addition, analysis of a segment of the cytochrome b gene from three adult Albula collected from coastal waters of southern California revealed high sequence homology with Albula sp. A, suggesting that the southern California specimens were conspecific with those from Guaymas. However, the southern distributional limit of Albula sp. A, and whether there are regions where Albula sp. A and C occur sympatrically, are unknown. The historical background of the available name Atopichthysesunculus Garman, 1899 [= Albula esuncula (Garman, 1899)], and problems associated with the nomenclature of the two species of eastern Pacific bonefishes, are summarized. The systematic status of the related shafted bonefish, Dixonina (= Albula) nemoptera Fowler, 1911, is also reviewed.

DISCRIMINATING GILA ROBUSTA AND GILA CYPHA: RISK ASSESSMENT AND THE ENDANGERED SPECIES ACT

Several sympatric Colorado River basin cyprinid fishes of the genus Gila are federally protected, yet difficulty in identifying individuals to species has limited recovery efforts. Using five characters easily scored in the field, we quantified morphological variation in G. robusta and G. cypha from eight localities, comparing discriminatory power of these data to that of a previous multivariate truss analysis of the same specimens. Significant between-species differences existed in four characters; three displayed patterns consistent with typological differences between species. Success of post hoc identification of specimens exceeded 70% for these three characters and increased to >82% by incorporating variables into a discriminant function. Nevertheless, potentially diagnostic features were relatively uncorrelated within individuals, and little congruence existed between different characters. Multivariate analyses clearly discriminated between sympatric species pairs despite considerable variation amon...

Multivariate Morphometric Analysis of Striped Bass, White Bass, and Striped Bass × White Bass Hybrids

Abstract Striped bass Morone saxatilis, white bass M. chrysops, and striped bass ♀ × white bass ♂ hybrids have been widely introduced into streams and reservoirs throughout the southeastern USA. Because these taxa often cooccur but are managed differently, distinguishing among them is necessary. Although single morphometric and meristic characters were unreliable discriminators, we could separate the three taxa using sheared principal components analysis and discriminant analysis of multiple characters. Snout and second dorsal spine lengths were greater, and postpectoral and third anal spine lengths were shorter, in striped bass than in white bass and hybrids. Distances between posterior of anal fin and posterior of second dorsal fin, and between orbit and preopercle, were greater in hybrids than in the parental species. White bass were separated from hybrids on the basis of second and third anal spine lengths, orbital lengths, base length of pelvic fin, and eye diameter, all of which tend to be greater i...