Predation by striped searobin (Prionotus evolans, Triglidae) on young-of-the-year winter flounder (Pseudopleuronectes americanus, Walbaum): examining prey size selection and prey choice using field observations and laboratory experiments

The objective of this study was to describe the diet of young-of-the-year and adult alewife (Alosa pseudoharengus) and rainbow smelt (Osmerus mordax) in nearshore waters coincident with the colonization of Lake Ontario by Dreissena. Laboratory experiments and field observations indicated that alewife and rainbow smelt consumed dreissenid veligers and that the veligers remained intact and identifiable in the digestive tract for several hours. Dreissenid larvae were found in field-caught alewife and rainbow smelt in August 1992, even though veliger densities were low (<0.1/L). Zooplankton dominated the diet of all fish and veliger larvae were <0.1% of the biomass of prey eaten by these fish. Density of veligers and the distribution of settled dreissenids declined from west to east along the south shore of Lake Ontario. Based on veliger consumption rates we measured and the abundance of veligers and planktivores, we conclude that planktivory by alewife and smelt in the nearshore waters of Lake Ontario did not substantially reduce the number of veligers during 1991–1993. However, our results indicate that if the density of veligers in Lake Ontario decreases, and if planktivores remain abundant, planktivory on veliger populations could be significant.

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First Cohort of Young-of-the-year Dungeness Crab, Cancer magister, Reduces Abundance of Subsequent Cohorts in Intertidal Shell Habitat

Canadian Journal of Fisheries and Aquatic Sciences ◽

10.1139/f93-234 ◽

1993 ◽

Vol 50 (10) ◽

pp. 2100-2105 ◽

Cited By ~ 39

Author(s):

Miriam Fernandez ◽

David Armstrong ◽

Oscar Iribarne

Keyword(s):

Laboratory Experiments ◽

Oyster Shell ◽

Field Observations ◽

Dungeness Crab ◽

Cancer Magister ◽

First Instar ◽

Alternative Hypotheses ◽

Young Of The Year

Arrival and settlement of successive cohorts of Dungeness crab, Cancer magister, megalopae were observed in Grays Harbor, Washington, in 1991. The first cohort of megalopae entered the estuary between May 15 and 20 and settled in ("occupied") previously constructed artificial, intertidal oyster shell habitats at densities ranging from 155 to 196 first instar juvenile (J1) crabs∙m−2. Subsequently, a second set of shell habitats was constructed that did not contain crabs of the first cohort ("unoccupied"). Between June 15 and 18, when crabs of the first cohort were a mix of second and third instars, a second cohort of megalopae settled in both occupied and unoccupied shell habitat at respective J1 crab densities of 9–37 and 168–298 crabs∙m−2. The possible roles of cannibalism, competition, and conspecific avoidance are proposed as alternative hypotheses to explain significantly lower density of the second cohort in shell habitats previously occupied by larger conspecifics of the first cohort. Based on laboratory experiments, we suggest that cannibalism is a plausible explanation of our field observations.

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