Date of Award

1997

Degree Type

Thesis

Degree Name

Master of Science (MS)

Department

Fisheries, Animal and Veterinary Science

First Advisor

Joseph McAlls

Abstract

A study on the distribution of quahog (Mercenaria mercenaria (Linnaeus 1758)) larvae in Narragansett Bay, Rhode Island was conducted during a single summer season in 1995. Samples of the larvae were collected weekly using an electric bilge pump and a 60 um mesh plankton net at two depths (0.3 m and 1.6m) at five sampling stations distributed landward along the West shore, 12.6 kmto 30.6 km from Rhode Island Sound. Three stations were located in the upper estuary, i.e., Upper Bay, and two stations were in the lower estuary, i.e., UpperWest Passage. The temporal distribution of quahog larvae was consistent with moonphase; more larvae were found during neap tides. Early stage larvae, i.e., Dhinge veligers at the age of 1-3 days occurred weekly throughout the period of sample collection and reached peak abundance on June 20. In contrast to the constant occurrence of early stage larvae, late stage larvae, i.e., umbonate veligers, were sometimes absent in the plankton samples. The late stage larvae reached peak abundance on July 7 at all but one station. On the basis of the peak abundances of the two developmental stages, I confirm that the duration of planktonic life of quahog larvae is about 2-3 weeks. Due to high abundances of late stage larvae during this period, the highest intensity of settlement probably occurs in Narragansett Bay around mid July. There was a tendency for a different distributional pattern between the larvae collected from Upper Bay and Upper West Passage stations. Densities of quahog larvae decreased away from the major spawner stock area (Providence River) probably due to the effect of tidal and non-tidal currents and turbulent diffusion. Tidal excursions of 1 - 4.4 km could be responsible for displacing the larvae from the Providence River into as far as Upper Bay in one ebb tide. It is probable that small numbers of larvae might be transported into Upper West Passage due to non-tidal currents. It appears that Upper Bay stations are the areas with relatively higher larval retention than other parts of the Bay.Multiple linear regression analysis indicated that only 20 % of the total variability of quahog larval densities in Narragansett Bay is explained by the independent variables, Le" sampling depths, moon phase, water temperatureand station location.

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