Growth and survival rates were determined for 4- to 12-wk-old herring larvae (Clupea harengus) reared at prey densities of 0.03, 0.1, 0.3, 1.0, and 3.0 Artemia nauplii/mL. The time required for food to pass through the gut in relation to prey density was also estimated.The results indicate that significant deleterious effects occur when larvae are reared at the two lowest prey densities. Survival was reduced at 0.03 Artemia/mL and growth was lowered at 0.03 and 0.1 Artemia/mL. Growth depensation leading to size hierarchies was not correlated with prey density. Food passed through the gut more rapidly at high prey densities. The threshold prey density above which changes in numbers of prey have little effect on survival or growth was estimated to lie between 0.1 and 0.3 Artemia/mL, possibly near 0.17 Artemia/mL.Key words: fish larvae, herring, feeding ecology, predator-prey
Coexistence of northern pike Esox lucius and muskellunge Esox masquinongy in the Niagara and St. Lawrence rivers has been hypothesized to depend on segregation during spawning. However, large overlap in the use of spawning areas by these two species occurs in the Thousand Islands section of the upper St. Lawrence Riven In this study, egg collections in Point Marguerite Marsh in the upper river revealed a partial temporal and spatial overlap in egg deposition by northern pike and muskellunge. Northern pike began spawning earlier but overlapped with muskellunge spawning for 2 weeks. May 13-27. Northern pike eggs were collected over a larger area than muskellunge eggs and at all locations where muskellunge eggs were collected. Both species deposited eggs over three dominant genera of vegetation: pond weeds Potamogeton, duckweeds Lemna, and stonewort Chara. Northern pike spawned over a wider range of water depths (0.5-2.6 m) than muskellunge (0.8-1.5 m) and selected habitats with denser, taller vegetative cover. The temporal and spatial overlap of northern pike and muskellunge egg deposition suggests that mechanisms other than spawning segregation permit these two species to coexist in the St. Lawrence River.
Distribution, abundance, and survival of age‐0 muskellunge Esox masquinongy were evaluated at 10 bays in the Thousand Islands section of the St. Lawrence River over a 7‐year period, 1990–1996. Muskellunge fry (24 mm) identified with thermal or oxytetracycline otolith markers were stocked in 1990–1992, 1994, and 1996, and fin‐clipped fingerlings (76 mm) were stocked in the bays in 1994 and 1996. Success of the stockings was evaluated to examine the feasibility of enhancing bays that have natural reproduction (natural) and establishing populations in unused bays (restoration). Most age‐0 muskellunge were found in shallow habitats (<1.5 m), and success of capture by seining decreased with increasing water depth. Estimates of age‐0 abundance by mark–recapture and catch–area were not significantly different. Population density ranged from 0 to 42 muskellunge/ha of nursery habitat, and no significant differences were observed between natural (18.8 fish/ha) and restoration bays (20.5 fish/ha). For all years combined, 67% of fish in natural bays originated from fry stocking, compared with 74% in restoration bays. No significant difference in contribution to age‐0 abundance by origin (fry, fingerling, wild) was observed between natural and restoration bays. No stocking occurred in 1993 and 1995, but wild age‐0 muskellunge were captured in 9 of 10 bays. The presence of wild muskellunge in 4 of 5 restoration bays indicated that these bays were incorrectly characterized as lacking natural reproduction. Survival of stocked fry was relatively low (0–3%), compared with survival of fingerlings (0–35%), but stocked fry contributed more to abundance (over 50%) than wild or fingerling sources. Due to its success, fry stocking should be reconsidered as a useful management tool for enhancing and restoring muskellunge populations.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.