Assessing the Impotance of Cutthroat Trout to River Otters in Yellowstone Lake

Recently-introduced exotic stressors, lake trout (Salvelinus namaycush) and whirling disease (caused by the Myxobolus cerebralis parasite), threaten the native cutthroat trout (Oncorhynchus clarki bouvieri) population in Yellowstone Lake. A reduction in cutthroat-availability may affect fish predators negatively, specially during cutthroat spawning. In this study we examined the importance of spawning cutthroat trout to a fish specialist - the river otter (Lontra canadensis). We measured scent­marking rates at 87 otter latrine sites on Yellowstone Lake and its tributary streams throughout the cutthroat spawning period and identified prey items in scats collected at these sites. Based on fecal deposition rates, otters were more active on spawning streams and less active on Yellowstone Lake during the height of the cutthroat spawning season, with a return to elevated activity on the lake after spawning had ended. Cutthroat trout appeared to be the most common prey item in otter scats throughout the study, based on 515 samples identified to the family­level and 110 samples analyzed to the species-level. Overall, trout occurred in 72% and longnose suckers (Catostomus catostomus) in 43% of otter feces. Suckers were more prevalent than trout in otter scats only on tributary streams, towards the end of the cutthroat spawning run. Introduced lake trout, which inhabit deep water and are largely inaccessible to otters, occurred in less than 5% of otter scats. River otters in the Yellowstone Lake system appear to be highly restricted in their diet and are heavily dependent on cutthroat trout. Our findings suggest that continued declines in the cutthroat trout population could negatively impact otters, potentially disrupting their role in linking the aquatic and terrestrial systems of Yellowstone Lake.

Spawning patterns and interspecific matings of sympatric white (Catostomus commersoni) and longnose (C. catostomus) suckers from the Gouin reservoir system, Quebec

White (Catostomus commersoni) and longnose (C. catostomus) suckers from the Gouin reservoir, Quebec, and a small upstream lake (Lac des Cinq Miles) spawned in the same stream. White suckers numerically dominated the runs in all years; however, abundances of both species decreased eightfold during a year when the reservoir level was lowered for maintenance. Return rates of individuals of both species tagged during the spawning run were poor in the following year, and only a few fish (<0.6%) skipped a year to spawn 2 years later. Although some individuals of both species occurred at all monitored spawning areas, white suckers concentrated their spawning activity over sites with boulders, whereas longnose suckers were most abundant over gravel. Differences in the courtship behaviour of the two species initially discouraged interspecific matings. However, white sucker males ultimately participated in 32% of the female longnose sucker matings, though spawning of male longnose suckers with female white suckers was not observed. White suckers spawned in groups or in pairs, whereas in all instances longnose suckers spawned with two or more males.

Metazoan Parasites, Excluding Monogenea, from Longnose and White Suckers

Seven genera of helminths (two of Digenea, one of Cestoda, and two each of Nematoda and Acanthocephala) and one species of parasitic copepod were recovered from 40 longnose suckers (Catostomus catostomus) and five white suckers (Catostomus commersoni), caught at two localities in Labrador, during August and September 1969. The helminths reported include five new host records.

Age, Growth, and Maturity of the Longnose Sucker Catostomus catostomus, of Western Lake Superior

Studies of age, growth, and maturity were based on 1760 fish collected in western Lake Superior in 1964–65. The body:scale relation was curvilinear and the curve had an intercept of 1.65 inches on the length axis. The weight increased as the 2.85 power of the length. Some fish formed an annulus before May 18 in 1965; all had completed annuli by late September. Longnose suckers grew 3.6 inches the 1st year, reached 12 inches in the 6th year, and 18 inches in the 11th year. Fish from Pikes Bay grew faster than those from Gull Island Shoal. Over 6 years were required for weight to reach 1 lb and nearly 10 years to reach 2 lb. Minimum length at maturity was 10.5 inches for males and 11.5 inches for females. The youngest mature male belonged to age-group IV and the youngest mature female to age-group V. All males were mature at 14.5–14.9 inches (age-group VIII) and all females at 15.0–15.4 (age-group IX).Finclipped longnose suckers returned to spawn in the Brule River in successive years. One fish returned to spawn in 4 successive years. Many of the fish were not recaptured until 2 or 3 years after marking. The time of the Brule River spawning migration depended more on water temperature than on length of day. The average water temperature during the peak of the spawning runs of 1958–64 was 55.4 F. Larval suckers apparently spend little time in the Brule River and adjacent streams and drift downstream to the lake soon after hatching. The number of eggs in the ovaries of eight suckers ranged from 14 to 35 thousand and averaged 24 thousand for fish 13.9–17.7 inches long.

Two New Species of Monogenetic Trematodes (Trematoda: Monogenea) from Nasal Cavities of Catostomid Fishes

Pellucidhaptor catostomi n.sp., recovered from the nasal cavities of longnose suckers, Catostomus catostomus (Forster), and Pellucidhaptor nasalis n.sp., recovered from the same site in white suckers, Catostomus commersoni (Lacépède), are described.