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The potential impacts of skate abundances upon the invertebrate resources and growth of yellowtail flounder (Pleuronectes ferrugineus) on Georges Bank
Abstract
On Georges Bank, skates (F. Rajidae) appear to be replacing depleted populations of economically-important demersal fishes like Atlantic cod (Gadus morhua) and yellowtail flounder (Pleuronectes ferrugineus). Because skates share some food resources with these teleosts, National Marine Fisheries Service biologists are concerned that food resources historically available to demersal fishes are now being consumed by the abundant skates, which could indirectly and negatively impact the growth of demersal species. The main objectives of this study were to estimate the consumptive impact of little skate (Raja erinacea) and winter skate (Raja ocellata) on their invertebrate prey, and to test whether these skates may indirectly impact the growth of yellowtail flounder on Georges Bank. The diet of little skate was comprised mainly of amphipods and decapods on Georges Bank. Both proportions of the two taxa and selection of prey varied depending on season, site, and body length of skates. Seasonal overlap was highest (0.42-0.92) between little skate $<$39 cm and all lengths of yellowtail flounder, indicating little skate could affect yellowtail flounder indirectly through resource competition. The consumptive impact of little skate and winter skate on their benthic prey was determined by estimating the percentage of benthic production consumed by these skate species. Annual consumption ranged from 0.085 kg fish$\sp{-1}$ yr$\sp{-1}$ for little skate 10-19 cm in length to 0.860 kg fish$\sp{-1}$ yr$\sp{-1}$ for skates 50-59 cm, and from 1.186 kg fish$\sp{-1}$ yr$\sp{-1}$ for winter skate 40-49 cm to 5.528 kg fish$\sp{-1}$ yr$\sp{-1}$ for 90-99 cm skates. The percentage of benthic production consumed by little skate and winter skate from 1969 to 1990 ranged from 5% to 15% and 11% to 43%. This indicated only a small to moderate proportion of benthic biomass is consumed by these species. Linear regression and Spearman correlation analyses indicated growth of age 1+ to age 4+ yellowtail flounder was significantly and inversely correlated to its own density, indicating growth of this species is density-dependent. Growth was either not, or positively, correlated to the abundance of skates, groundfishes, and other flounders, suggesting interspecific competition is not an important regulatory mechanism of growth. Therefore, skates appear not to have a measurable impact on the growth dynamics of yellowtail flounder.
Subject Area
Forestry|Ecology|Zoology
Recommended Citation
Nelson, Gary Allen, "The potential impacts of skate abundances upon the invertebrate resources and growth of yellowtail flounder (Pleuronectes ferrugineus) on Georges Bank" (1993). Doctoral Dissertations Available from Proquest. AAI9408322.
https://scholarworks.umass.edu/dissertations/AAI9408322