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USGS1992

A review of differentiation in Great Lakes ciscoes

Seven species of ciscoes (Coregonus, subgenus Leucichthys) were found in the Great Lakes as recently as the early 1950's. Variation within and among species of Great Lakes ciscoes indicates that much of the divergence occurred within lakes. Following postglacial colonization by perhaps two or three species, population differentiation began with homing and reproduction at different localities and times. Physiological interaction between temperature (depth) and maturation time, as well as behavioral tendencies to home to spawning grounds and mate with related individuals, are the basis of premating reproductive separation. Phenotypic differences between populations indicate that ecological character displacement has been an important mechanism in the divergence. Introgression has obscured morphological species boundaries at the same time as intralacustrine speciation has created local subgroups, providing an unresolvable conflict between species definitions based on morphological and other characters and definitions dominated by inferred reproductive isolation. Species should be considered as the smallest diagnosable units within a phylogenetic framework, in which diagnoses are strictly by derived characters. Ecological and seasonal species could be recognized by application of a trinomial, equivalent to the subspecies trinomial.

Polskie Archiwum Hydrobiologii↗
USGS1992

Status of coregonine fishes in the Laurentian Great Lakes

The post-glacial coregonine assemblage in the Great Lakes included several species of the genera Prosopium and Coregonus. Overfishing, habitat degradation, and competition with various exotic fish species severely reduced coregonine abundance and altered their distribution by the mid to latter part of the 20th century. Most of the original Coregonus species, some which were endemic to the Great Lakes, are now extinct or are extremely rare. The prevailing coregonines are mostly benthic and deep-water species, contrasted to the original assemblage dominated by pelagic, nearshore species. Lake whitefish (Coregonus clupeaformis) populations have recovered and now support record fisheries in Lakes Superior, Michigan, and Huron. Bloaters (C. hoyi) have recovered to dominate the planktivorous fish community in Lake Michigan and are rapidly increasing in Lake Huron. The recent resurgence in some coregonine populations are linked to declines in exotic fish populations and favorable climatic changes. The reduced diversity of the coregonines may explain the dominance of the remaining species. The stability of this simplified coregonine community is uncertain but the existing coregonines have demonstrated resiliency.

Polskie Archiwum Hydrobiologii↗
USGS1992

Morphological cladistic study of coregonine fishes

A cladistic analysis of 50 characters from 26 taxa of coregonine fishes and two outgroup taxa yields a phylogenetic tree with two major branches, best summarized as two genera - Prosopium and Coregonus. Presence of teeth on the palatine, long maxillae, and long supra-maxillae are primitive, whereas loss of teeth, short or notched maxillae, and short supermaxillae are derived traits. P. coulteri and C. huntsmani are morphologically and phylogenetically primitive members of their groups. The widespread species, P. cylindraceum and P. williamsoni are morphologically advanced in parallel with the subgenus Coregonus (whitefishes): they share subterminal mouths, short jaws, and reduced teeth. Prosopium gemmifer parallels the ciscoes, subgenus Leucichthys. The whitefishes, C. ussuriensis, C. lavaretus, C. clupeaformis, and C. nasus are a monophyletic group, the subgenus Coregonus. The subgenus Leucichthys is a diverse, relatively plesiomorphic assemblage, widespread in the Holarctic region. This assemblage includes the inconnu, Stenodus.

Polskie Archiwum Hydrobiologii↗
USGS1998

The role of freshwater habitats for the reproduction of common bream Abramis brama (L.) in a brackish water system

Abundance and biomass data for juveniles and adults, length frequency histograms and the electron microprobe analysis (EPMA) of otoliths were used to indicate density, migration and reproduction of common bream Abramis brama in the Kiel Canal drainage, Germany. The reproduction of common bream was primarily restricted to two types of spawning habitats: one in the Haaler Au, a freshwater tributary and another in shallow, oligohaline portion of the main Canal. Both spawning habitats were morphologically characterized as shallow with submerged vegetation. During April to June concentrations of spawners were observed, whereas age-0 common bream dominated from August through December. The distribution of age-0 common bream was primarily restricted to fresh and oligohaline waters. Outside the spawning season, the distribution of common bream was less obvious. Adult fish were more widely distributed within the Canal, indicating a tolerance for higher salinities. During the spawning season common bream seem to show an exceptional mobility between spawning and feeding habitats, which are denoted by different salinities.

Polskie Archiwum Hydrobiologii↗