Recruitment and Retention of Lobsters in a New England Estuary

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Project Type: 
Research
Project Number: 
R/SSS-3
Inception Date: 
2012
Completion Date: 
2014

Participants:

Winsor Watson UNH - Department of Biological Sciences Principal Investigator
Jason Goldstein UNH - Department of Biological Sciences Researcher
Raymond Grizzle UNH - Jackson Estuarine Lab Collaborator
Joshua Carloni N.H. Fish and Game Department Collaborator
James Manning Northeast Fisheries Science Center Collaborator

Students Involved:

Helen Cheng UNH - Department of Biological Sciences
Tom Langley UNH - Department of Biological Sciences
Colin Whitworth University of New England - School of Medicine
Alysia Campbell UNH - Department of Biological Sciences
Chris Chambers UNH - Department of Biological Sciences
Alicia Franklin UNH - Department of Biological Sciences
Adrienne Moran University of New Hampshire
Elsa Lindgren UNH - Department of Biological Sciences
Liz Morrissey UNH - Department of Biological Sciences
Nate Copp UNH - Department of Biological Sciences
Mark Messina UNH - Department of Biological Sciences
Erika Moretti UNH - Department of Biological Sciences
Tracy Pugh UNH - Department of Biological Sciences
Abstract: 
Estuarine ecosystems such as Great Bay offer a unique opportunity to investigate the behavior, population dynamics and reproductive potential of commercially and ecologically important species such as the American lobster, Homarus americanus. Previous studies have shown that lobster populations in Great Bay are somewhat unique with respect to their sex ratios, seasonal migrations, and movements in response to episodic environmental changes. While some lobsters migrate into, and out of, the estuary, our recent data suggest that there might also be a resident population of lobsters. The overall hypothesis that we plan to test during this project is that the Great Bay estuary has all the necessary elements, from appropriate habitats for all life history stages to reproductive adult lobsters, to create a self-sustaining lobster population in the estuary. The objectives of this two-year study are to: 1) identify and quantify suitable habitat for adult, juvenile and newly settled lobsters using underwater video; 2) deploy drifters that mimic larval trajectories to determine if larvae that hatch in the estuary are retained in the system and; (3) carry out a series of field censuses to quantify the abundance of recently-settled and juvenile lobsters at selected stations within the estuarine system. The results from this study will have potential management implications by identifying essential habitat for all lobster life history stages and demonstrating that a New England estuarine system, such as the Great Bay estuary, is capable of supporting a self-sustaining lobster population.
Objectives: 
The overall goal of this project is to test the hypothesis that lobsters reproduce in Great Bay and release larvae that are retained within the estuary and settle in appropriate habitats. We will test this hypothesis by completing the following specific objectives:
 
Objective 1: Identify and quantify suitable settlement and adult habitats, using underwater video methods.
 
Objective 2: Deploy drifters that mimic larvae to determine if larvae that hatch in the estuary are retained in the system.
 
Objective 3: Conduct field censuses to quantify the abundance of recently-settled and juvenile lobsters using suction sampling, diver surveys and modified ventless traps designed to capture and retain very small juvenile lobsters.
Methodology: 
To identify suitable habitats for various lobster life history stages, video transects will be obtained using equipment borrowed from Dr. Ray Grizzle, as well as equipment we build for this purpose. These videos will be analyzed to determine the percent of the bottom that is covered by habitat appropriate for adult, juvenile and recently settled lobsters. These video surveys will be complemented by diver surveys, as well as by fishing custom-built juvenile lobster collectors in these same areas and other sites within the estuary. Finally, we will deploy "drifters" that are designed to mimic the passive movements of larval lobsters. The drifters will be deployed at various locations within the estuary to determine where lobster larvae that hatch in the estuary might settle after their three week planktonic stages. These drifters will be equipped with satellite transmitters so their trajectories can be followed and mapped in near real-time.
Rationale: 
The American lobster is the most valuable marine resource in New England and is heavily exploited in New Hampshire waters, including the Great Bay estuary, where over 100,000 pounds of lobsters with a value in excess of $500,000 were landed in 2009. Management of this important species throughout its range depends, in part, on identifying different subpopulations, or stocks, as well as determining the source of new recruits for these stocks on both local and regional scales. The results from this study will have potential management implications by identifying essential habitat for the settlement and growth of early-stage lobsters and demonstrating that the Great Bay estuary may support an ecologically and commercially important, self-sustaining, lobster population. Finally, being able to assess the potential larval retention and survival of juveniles in an estuarine system may contribute to the source-sink larval dynamics that are currently being explored on a larger scale with lobster larvae in the Gulf of Maine.
Accomplishments: 

2015

Researchers determine sources of N.H.'s Great Bay lobster recruits for improved species management

In 2015, researchers found that new lobster recruits to N.H.'s Great Bay Estuary come from both estuarine and coastal female lobsters, which will help inform management decisions about the lobsters in the estuary.
Relevance: Adult lobsters are routinely caught in traps in N.H.'s Great Bay Estuary, but little is known about the recruitment and retention of lobsters in the system. Management of lobster populations depends on the proper identification of different subpopulations and the sources of young recruits.
Response: In 2015, N.H. Sea Grant-funded researchers collected lobster larvae in the Great Bay Estuary using plankton tows and demonstrated that larvae can be collected from the time period starting from when eggs are first hatched in the estuary to when coastal eggs stop hatching.
Results: Based on their studies, researchers determined that new lobster recruits to the Great Bay Estuary come from both estuarine and coastal females. This information will help inform management decisions about the lobsters in the estuary.

N.H. Sea Grant researchers determine timing of Great Bay lobster egg hatch for improved species management

Research-based surveys conducted in 2015 indicate that lobster eggs carried by N.H.'s estuarine lobsters hatch earlier than coastal lobsters, which will help inform management decisions about the lobsters in the estuary.
Relevance: Previous research indicates that lobsters migrate into and out of N.H.'s Great Bay Estuary, but recent studies indicate there may also be a resident population within the estuary. Having this information is vital as part of an overall management plan for the species in Great Bay.
Response: In 2015, N.H. Sea Grant-funded researchers documented the locations of female lobsters with late-stage eggs in the estuary and the time period when eggs would hatch in late spring and early summer. Researchers conducted similar studies for coastal lobsters as a comparison.
Results: These surveys indicate that lobster eggs carried by estuarine lobsters hatch about a month earlier than those carried by coastal lobsters. This information will help inform management decisions about lobsters in the estuary.

2013

Modified lobster traps improve selectivity for juveniles, improving the ability to quantify their abundance in N.H.
With funding provided by N.H. Sea Grant, researchers conducted field studies to quantify the abundance of juvenile lobsters — those with a carapace length less than 60 mm — in the Great Bay Estuary and to determine if the bay has a self-sustaining lobster population. In 2013, researchers fished three different trap types — crab traps, standard lobster traps and ventless traps they modified to target juveniles — and determined which led to the highest catch per unit effort (CPUE). Although overall CPUE was highest for the standard traps, the range and average carapace length were smaller in the modified ventless traps, indicating trap selectivity for smaller juvenile lobsters. This research revealed that modified ventless traps are the most appropriate method for capturing juvenile lobsters to quantify their abundance in the estuary.

Adult and juvenile American lobsters inhabit different portions of N.H.’s Great Bay Estuary
Recent surveys indicate that N.H.’s Great Bay Estuary may have a self-sustaining population of American lobsters. N.H. Sea Grant-funded researchers conducted trap surveys in 2013 to sample both adult and juvenile lobsters and determine their abundance in locations throughout the estuary. Their surveys found that mean carapace length of lobsters was smaller at the Little Bay and Piscataqua River locations and larger in Great Bay. This indicates that adult lobsters were found further up into the bay while the juveniles were more prevalent in the lower estuary. These results provide resource managers with a clearer understanding of where lobsters are located within the estuary to improve their management of the fishery.

Surveys reveal male-skewed sex ratio and size differences of American lobsters in N.H.’s Great Bay Estuary
It is known that American lobsters migrate into and out of the Great Bay Estuary, but recent studies show that the bay may hold a resident population. N.H. Sea Grant-funded researchers conducted trap surveys in 2013 to determine the size and sex distribution of lobsters captured in the estuary. Their results indicate that there are more adult male lobsters in Great Bay than female lobsters and the males are larger in size. They also found that there was a slightly higher frequency of juvenile males captured than females, but their sizes were comparable. This research will help resource managers better understand lobster populations and distribution in the estuary.

Presence of blue crabs in N.H.’s Great Bay indicates rapidly changing conditions
With funding provided by N.H. Sea Grant, researchers conducted studies to determine if recruitment and retention of lobsters is taking place in N.H.’s Great Bay Estuary. While conducting field surveys in 2013, researchers found blue crabs in the estuary. This finding suggests that environmental conditions in the estuary are changing faster than the N.H. Seacoast, likely due to wider temperature fluctuations in the estuary. This research demonstrates that the Great Bay Estuary serves as an excellent model system for studying the impact of climate change on mobile species, such as crabs and lobsters.

Presence of female lobsters carrying eggs in N.H.’s Great Bay Estuary indicates likelihood of larval release in system
Recent studies suggest there may be a self-sustaining lobster population in N.H.’s Great Bay Estuary, but little is known about whether female lobsters carrying eggs reside in the estuary and if their eggs hatch while they are residents. In 2013, N.H. Sea Grant-funded researchers conducted surveys from the mouth of the Piscataqua River to Adams Point in Great Bay to determine the presence and distribution of late-stage “eggers” — females lobsters carrying eggs that are close to hatching. Almost all of the eggers were captured in Little Bay and in the lower portions of the estuary. The prevalence of late-stage eggers indicates that lobster larvae are likely being released somewhere within the Great Bay Estuary. This research helps support the hypothesis that the estuary contains a self-sustaining population of lobsters and provides information about the source of lobster larvae in the estuary.

Presence of larva in N.H.’s Great Bay Estuary indicates likelihood of self-sustaining population
American lobsters are known to migrate into and out of N.H.’s Great Bay Estuary. However, it is unknown whether any larvae hatch in the estuary, and if so, whether or not they are retained in the system to help create a resident population. In 2013, N.H. Sea Grant researchers conducted eight plankton tows in two locations within the estuary to determine if lobster larvae were present. One larva was captured and identified as stage one, the first lobster stage after it hatches from an egg. Although additional plankton tows are needed to yield more data, the presence of one larva is a positive sign that larvae are present in the estuary and may be carried up into Great Bay to create a self-sustaining population.

2012

Scuba Surveys, Modified Traps Indicate Resident Population of Lobsters in Great Bay
NHSG-funded researchers conducted studies to determine if there is a resident population of lobsters in the Great Bay Estuary. In 2012 they carried out visual surveys by Scuba divers and trap surveys for juvenile lobsters, using modified lobster traps and crab traps to target smaller lobsters and exclude larger ones that may have moved into the estuary without residing there. Small lobsters (50-60 mm carapace length, a size at which they are incapable of traveling long distances) were observed during the Scuba surveys and captured in the trap surveys, indicating that those lobsters likely settled and grew in the estuary, thus creating their own subpopulation. This research will directly benefit resource managers involved in developing management plans for the lobster fishery both in N.H. waters and in other similar bays and estuaries.

Drifters Lend Support to Theory that Great Bay Has Self-sustaining Lobster Population
Management of lobster populations partially depends on the identification of different subpopulations and the sources of young recruits. Using NHSG funds in 2012, researchers deployed drifters that mimic passive larval movements in the water currents to determine if lobsters that hatch in the Great Bay Estuary are retained in the system. Drifters were released around the time lobster eggs typically hatch in the estuary (May-June). Despite some initial movement out towards the river, all of the 16 drifters stayed within the estuary for three weeks — the length of time lobster larvae stay in the water column before they settle to the bottom — indicating that the larvae that hatch there likely settle out there as well. These results support the theory that Great Bay has a self-sustaining lobster population, thus providing more accurate information to resource managers who develop lobster management plans.

Dive Studies, Underwater Video Indicate Suitable Habitat for all Life Stages of Lobsters in Great Bay
The American lobster is the most valuable marine resource in New England, including the Great Bay Estuary, where over 100,000 pounds of lobsters with a value in excess of $500,000 were landed in previous years. Effective management of this species is based, in part, on determination of subpopulations and the sources of recruits. In 2012, NHSG-funded researchers conducted dive studies and underwater video recording to determine if there is suitable habitat available for both juvenile and adult lobsters in the Great Bay Estuary. Based on these surveys, it appears that there is habitat in the estuary suitable for both the settlement of new recruits and the continued residence of adults. This research will help resource managers involved in developing management plans for the lobster fishery in N.H. waters and in other similar bays and estuaries.

Lobster Research Helps Identify Favorable Locations for Oyster Farming, Spat Settlement
The Great Bay Estuary is home to a variety of aquatic organisms, including horseshoe crabs, lobsters and oysters. In 2012, NHSG-funded researchers conducted studies in the estuary to determine whether or not the lobster populations are self-sustaining. During these studies, researchers also identified areas in the estuary where hydrodynamics and water currents may be favorable to oyster farming or spat settlement. The estuary is home to oyster farms as well as oyster reef restoration sites, so this information will help both farmers and resource managers to plan their project locations for optimal success.

Modified Surface Drifters Indicate Trajectories of Lobster Larvae
Researchers developed/modified estuarine surface drifters to provide information about the trajectories that lobster larvae might take when carried by currents in the Great Bay Estuary. Each drifter was fitted with a light beacon and a top-mounted GPS tracking unit capable of sending real-time positional data via satellite to a lab computer. These drifters were also modified to achieve neutral buoyancy just below the water surface using a combination of floats and weights. Drifters modified for this purpose might also have additional applications, such as allowing lobstermen to determine if lobsters settle in offshore habitats and determining where horseshoe crab larvae might settle in the Great Bay Estuary.

Publications

Available from the National Sea Grant Library (use NHU number to search) or NH Sea Grant

Journal Article

  • Goldstein, J., T. Pugh, E. Dubofsky, K. Lavalli, M. Clancy and W. Watson (2014). A noninvasive method for in situ determination of mating success in female American lobsters ("Homarus americanus"). Journal of Visualized Experiments 84:e50498, February 2014.
  • Jury, S. and W. Watson (2013). Seasonal and sexual differences in the thermal preferences and movements of American lobsters. Canadian Journal of Fisheries and Aquatic Sciences 70(11):1650-1657, November 2013.
  • Goldstein, J. and W. Watson (2015). Seasonal movements of American lobsters in southern Gulf of Maine coastal waters: patterns, environmental triggers, and implications for larval release. Marine Ecology Progress Series 524:197-211, 2015.
  • Goldstein, J. and W. Watson (2015). Influence of natural inshore and offshore thermal regimes on egg development and time of hatch in American lobsters, Homarus americanus. Biological Bulletin 228(1):1-12, February 2015.
  • Pugh, T., M. Comeau, K. Benhalima and W. Watson (2015). Variation in the size and composition of ejaculates produced by male American lobsters, Homarus americanus H. Milne Edwards, 1837 (Decapoda: Nephropidae). Journal of Crustacean Biology 35(5):593-604, 2015.

Thesis/Dissertation

  • Goldstein, J. (2012). The impact of seasonal movements by ovigerous American lobsters ("Homarus americanus") on egg development and larval release. Doctoral Dissertation, University of New Hampshire.
  • Pugh, T. (2014). The potential for sperm limitation in American lobsters ("Homarus americanus") as indicated by female mating activity and male reproductive capacity. Doctoral dissertation, University of New Hampshire.
  • Cheng, H. (2014). The environmental influences on American horseshoe crab (Limulus polyphemus) behavior and distribution in the Great Bay Estuary, New Hampshire U.S.A. Master's thesis, University of New Hampshire.