INTERANNUAL VARIABILITY IN AMERICAN LOBSTER SETTLEMENT: CORRELATIONS WITH SEA SURFACE TEMPERATURE, WIND STRESS AND RIVER DISCHARGE

INTERANNUAL VARIABILITY IN AMERICAN LOBSTER SETTLEMENT:

CORRELATIONS WITH SEA SURFACE TEMPERATURE,

WIND STRESS AND RIVER DISCHARGE

By Mahima Jaini

Thesis Advisor: Dr. Richard Wahle

An Abstract of the Thesis Presented

in Partial Fulfillment of the Requirements for the

Degree of Master of Science

(in Marine Biology)

May, 2011

Recruitment to benthic marine populations is fundamentally a biophysical problem. Diver-based surveys of American lobster (Homarus americanus) nurseries in New England, USA and Atlantic Canada have given rise to over 20 years of data on annual settlement of young-of-year lobsters. There is considerable interannual variability in the lobster settlement time series, suggesting the role of environmental factors in regulating planktonic larval supply and transport. Here we evaluate statistical correlations between the lobster settlement index and sea surface temperature anomalies (SSTa), wind stress, and river discharge, from satellites and meteorological stations, for three oceanographically contrasting regions: coastal Rhode Island, Midcoast Maine and lower Bay of Fundy. Lobster settlement indices were correlated with environmental metrics for the month of settlement sampling, as well as up to three months prior when larvae are hatched into the water column.

Interannual variability in lobster settlement correlated strongly with SSTa and wind stress, but exhibited a weak association with river discharge. Statistically significant correlations were restricted to the two-month window when larvae and postlarvae are in the water column. In certain cases, spatial associations of SSTa mapped to recognizable oceanographic features on the sea surface. For example, Rhode Island settlement correlated positively with monthly SSTa over Georges Bank for up to two months prior to settlement sampling.  Lobster settlement was strongly coupled with cross-shore stress in the Bay of Fundy and alongshore wind stress in Rhode Island and central Gulf of Maine. Lobster settlement showed a weak correlation with local river discharge for central Gulf of Maine only.

Our analysis revealed SSTa and wind stress to be highly significant correlates of American lobster settlement abundance, at time lags relevant to larval transport and settlement i.e. up to two months prior to settlement sampling. Our results help identify areas of the sea surface of Northwest Atlantic shelf waters that may be of particular value in predicting year-to-year fluctuations in inshore larval settlement.