Reproduction and recruitment of American lobster (Homarus americanus) in the Great Bay estuary, New Hampshire.

摘要

The overall goal of this research project was to determine if lobsters reproduce and settle in the Great Bay estuary (GBE), NH. First, I mapped the distribution and abundance of ovigerous lobsters carrying late-stage eggs in the estuary, during May and June of 2015. Ovigerous lobsters were concentrated in Little Bay and adjacent sections of the Piscataqua River, with CPUE in these areas of 0.12 +/- 0.02 lobsters/trap haul. Very few were found in the regions furthest from the coast. Next, egg samples were collected from these lobsters, as well as from ovigerous lobsters captured along the NH coast and their hatch dates were determined based on their stage and the rate of egg development at their respective temperatures. The mean predicted hatching date of eggs carried by GBE lobsters was June-09 +/- 11.8 days (SD), while the mean predicted hatch date of eggs carried by coastal lobsters was July-01 +/- 9.5 days, nearly three weeks later. The GBE eggs most likely hatched three weeks later because of the difference in water temperatures between the two areas. Plankton tows were then conducted to determine if larvae were present in the water column at the time when I predicted that the eggs carried by GBE females would be hatching. The predicted hatch dates for the 35 stage I larvae captured ranged from May-21 through July-19, with a mean predicted hatching date of June-28 +/- 17.9 days. This encompasses almost a two-month period, which is longer than either range of predicted hatch dates from eggs obtained either from estuarine or coastal lobsters. However, the larvae that hatched earliest overlapped with when ovigerous lobsters hatched their eggs in the GBE, indicating that a portion of these larvae originated in the estuary.;Strong tidal currents influence particle transport (i.e., planktonic larvae) in GBE and my next goal was to determine if these currents would retain larvae, or carry them out to the Gulf of Maine. Surface currents were characterized using surface drifters (n=21) deployed near areas with the highest densities of ovigerous lobsters carrying late stage eggs in the GBE, as well as in the Piscataqua River (n=6) to determine if larvae were transported into the GBE from areas near to the coast. Drifter movements were extrapolated over 8-16 days (when larvae develop and settle) and over this time period, drifters released from all three locations were retained in the estuary. In fact, these data suggested that the greatest abundance of juvenile lobsters should be in areas that also had the highest densities of ovigerous females. Finally, to test this prediction and to determine if lobster larvae did, in fact, settle in the GBE, the distribution, abundance and composition (size frequency, sex ratio) of juvenile lobsters in the GBE was assessed using trawls consisting of two pairs of modified ventless traps and two pairs of juvenile collector traps. Sampling occurred at six study sites on a spatial gradient, ranging from the upper Piscataqua River to Great Bay proper. The smallest lobster (38 mm carapace length (CL)) was captured in the Piscataqua River, and the average size of lobsters increased as sites furthest up into the GBE (ranging from 66.51 +/- 0.78 mm CL (SEM) in the river (n=185) to 88.67 +/- 2.82 mm CL, n=2, in Great Bay proper). Only adult lobsters were found at the sites furthest up in the estuary, and the adult sex ratio also became more skewed towards males in these areas. However, the sex ratios of juvenile lobsters were 1:1 at the four sites where they were captured (Fisher's Exact test, p=0.995), indicating that the skewed sex ratios of adult lobsters were likely the result of differential movements of males and females. Taken together, these data provide support for a residential and self-recruiting lobster population in the GBE, although the timing of larvae, as well as the characterization of currents using drifters reinforces that, to an extent, the GBE lobster population is supplemented by adults that migrate into the estuary and larvae originating from coastal lobsters that are carried into the GBE by tidal currents.