Environmental Controls on Shrimp Recruitment Dynamics

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Project Type: 
Research
Project Number: 
R/MED-4
Inception Date: 
2004
Completion Date: 
2006
Theme Area: 
Fisheries Resources

Participants:

James Pringle UNH - Ocean Process Analysis Laboratory Collaborator
Lewis Incze University of Southern Maine Collaborator
David Townsend University of Maine Collaborator
Anne Richards National Marine Fisheries Service Collaborator
Jeffrey Runge University of Maine - School of Marine Sciences Principal Investigator
Daniel Schick Maine Department of Marine Resources Co-Principal Investigator
Patrick Ouellet Fisheries and Oceans Canada Co-Principal Investigator

Students Involved:

Erin Gordon-Hobbs UNH - Department of Biological Sciences
Michael Bates UNH - Department of Earth Sciences
Meghan Deeney University of New Hampshire
Brian Parian University of New Hampshire
Abstract: 

This proposal represents the New Hampshire Sea Grant contribution to the initiation of a broader collaboration of U.S. and Canadian researchers to study environmental controls on recruitment dynamics of the northern shrimp, Pandalis borealis, in the Gulf of Maine and coastal waters of eastern Canada. There is a need to study factors influencing the growth and survival of the early life stages of northern shrimp in order to understand the dramatic fluctuations in abundance of northern shrimp that have occurred in the western Gulf of Maine over the past 50 years.

The objectives of this proposal are:

1) Determine the trophic interactions of early larval stages of northern shrimp in the Gulf of Maine and specifically test the hypothesis that the early life stages feed on phytoplankton of the winter-spring bloom and later stages feed on zooplankton

2) In collaboration with the research group from Maine (Incze, Townsend, Schick), observe the physical and biotic conditions and abundance and vertical distribution of northern shrimp larval stages along a transect extending from Portsmouth, NH, across Jeffreys Ledge in an area known to contain an abundance of ovigerous females in spring

3) Coordinate the study of trophic dynamics and environmental controls of shrimp dynamics with a similar study in Canadian waters.

This research lays the groundwork for the design of more sophisticated observational and experimental programs directed toward the long- term goal of developing an understanding of the environmental controls on recruitment into populations of northern shrimp in ways that will be useful in the context of an ecosystem-based management of the fishery.

Objectives: 

1) Determine the trophic interactions of early larval stages of northern shrimp, Pandalis borealis, in the Gulf of Maine. Specifically, test the hypothesis that the early life stages feed on phytoplankton of the winter-spring bloom and later stages feed on zooplankton.

2) In collaboration with the research group from Maine (Incze, Townsend, Schick), observe the physical and biotic conditions and abundance and vertical distribution of northern shrimp larval stages along a transect extending from Portsmouth, NH, across Jeffreys Ledge in an area known to contain an abundance of ovigerous females in spring.

3) Coordinate the study of trophic dynamics and environmental controls of shrimp dynamics with a similar study in Canadian waters (P. Ouellet, Fisheries and Oceans, and L. Fortier, Univ. Laval).

Methodology: 

1) Conduct microscopic examinations of gut contents of shrimp larvae captured during survey transects. In addition, conduct laboratory experiments to measure predation rates of shrimp larval stages on common Gulf of Maine microzooplankton prey and selectivity with respect to common phytoplankton species.

2) In coordination with the Maine group, conduct an oceanographic survey of environmental conditions (salinity, temperature, chlorophyll a, nutrients, zooplankton prey abundance) as well as abundance of larval shrimp stages along the Portsmouth-Jeffreys Ledge transect four times between late January and late March.

3) Coordinate planning, survey and gut content and experimental studies with the Canadian group by holding at least two workshops, one in fall 2003 and one in summer 2004.

Rationale: 

One source of interannual variability in inshore shrimp abundances and commercial fishery landings in the Gulf of Maine is recruitment variability imparted through larval survival processes under environmental and oceanographic controls. This proposal represents the first step in the formation of a collaborative research group involving New Hampshire, Maine and Canadian researchers in the investigation of the hypothesis that larval survival and subsequent recruitment controls shrimp abundance.

We propose that recruitment success in the Gulf of Maine is related to dynamics and variability of the timing and intensity of the winter-spring phytoplankton bloom. Our long-term goal is to develop an understanding of the environmental controls on recruitment into populations of northern shrimp, in ways that will be useful in the context of an ecosystem-based management of the fishery, by development of:

1) Statistical models of shrimp recruitment time series with hydrographic and biological variables specifically identified to have a first order impact on larval shrimp survival

2) Coupled physical-biological models simulating observed interannual differences in winter-spring circulation and larval shrimp trophodynamics and mortality.

Accomplishments: 
The results have been transferred to the Gulf of Maine Ocean Observing System (GoMOOS), now called the Northeast Regional Association of Ocean Observing Systems (NERACOOS). They are in the process of incorporation into the Northern Shrimp Fishery data set. It is anticipated that the ability to predict hatch date from ocean temperature data will have significant benefit for the management of the northern shrimp fishery off the coast of New Hampshire and Maine.
 

1. The influence of water temperature on embryonic development and hatching date of northern shrimp in the Gulf of Maine
 
Management of the northern shrimp fishery in the Gulf of Maine has been problematical, involving restricted seasons and rolling openings. The fishery coincides with the migration of egg-bearing adult shrimp near to the coast in late winter. Ideally, adults should be harvested after the eggs hatch, releasing larvae into the water column, and thereby enhancing the annual pool of potential new recruits into the population.
 
In collaboration with colleagues (A. Richards, NMFS, J. Pringle, UNH, and D. Schick, Maine DMR) we developed an empirical relationship that predicts the timing of hatch from bottom temperature experienced by egg-bearing females during the months immediately following egg extrusion and fertilization in late summer/early fall.
 
2. Transport success of northern shrimp larvae in relation to climate forcing
 
Factors influencing recruitment in the early life stages of northern shrimp include physical controls on dispersal, retention and successful transport of the planktonic larvae to nursery areas. In his master’s thesis research, M. Bates investigated the potential for physical control of recruitment using an individual-based particle dispersal model coupled to a model of the western Gulf of Maine circulation. Particles with larval shrimp attributes (depth distribution and duration in the planktonic stage) were released along the coastal western Gulf of Maine in the broad area where ovigerous females are known to aggregate in late winter.
 
The main result indicates that interannual variability in successful settlement to nursery areas due to physical forcing is on the order of 30% about the median value, suggesting that physical forcing does not exert first order control over recruitment, which fluctuates by a factor of 4 or more in the Gulf of Maine population. Catch and recruitment data show no correlation to settlement success indices produced by the model runs using 20 yr of actual wind data, whether successful transport is determined from particles (simulating larvae) averaged over all of the water column or residing continuously at 15, 25 or 35 m. The results implicate biological factors, such as variation in food supply arising from match or mismatch of the timing of larval hatch with the timing of their spring production of phytoplankton and zooplankton prey or variation in the suite of winter-spring predators, as having important control over relative recruitment strength.
 
3. Biological factors controlling recruitment variability in the Gulf of Maine northern shrimp population: feeding behavior and interannual variation in food supply to the planktonic larval stages.
 
The study of early larval transport conducted by M. Bates suggests that variability in the biological factors determining growth and survival of the planktonic larvae, rather that transport to nursery areas, exerts first-order control of recruitment into the Gulf of Maine northern shrimp population. As part of her master’s research supported by this Sea Grant award, E. Gordon Hobbs provided evidence consistent with the Match-Mismatch hypothesis, yielding new insights into the connections among shrimp larvae, their physical habitat and their prey in the western Gulf of Maine. Her research uncovered three major findings:
 
a. Characterization of habitat of the plankton stages in the western Gulf of Maine
 
Ms. Hobbs conducted a seasonal survey in winter spring of two consecutive years (2005- 2006) stations along a transect off Portsmouth Harbor out to Jeffreys Ledge. The transect was sampled every other week between Jan-May in 2005 and Jan-Mar in 2006. Analysis of abundance of larval shrimp collected during the survey is consistent with the hypothesis that the cross-shelf distribution of shrimp larvae coincides with the distribution of ovigerous females, typically distributed in nearshore water of 30-90 m depth. The larvae were found in water with salinity ranging between 31-32 PSU and temperatures ranging from 1-5 C. These results provide backing data for the physical transport models as well spatial context for analysis of the match of larvae with their planktonic prey.
 
b. Feeding behavior of plankton life stages on phytoplankton and zooplankton prey
 
Offspring from northern shrimp captured in winter in the western Gulf of Maine were reared in the laboratory to investigate feeding behavior of the early larval stages on phytoplankton and zooplankton prey. The laboratory study addressed critical questions about feeding responses of the first larval stage (Stage I) and later, more mature stage III to various phytoplankton taxa and zooplankton prey, both separately and in mixtures.
 
The results represent the first quantitative functional response relationships showing feeding rates of northern shrimp larval stages on phytoplankton and zooplankton prey. Northern shrimp larvae clearly ate diatoms during later as well as early developmental stages, although the older larvae showed selectivity for zooplankton prey. These results provide insight into the mechanisms by which feeding and growth of the planktonic shrimp larvae may be linked to the timing of the spring phytoplankton bloom. The rate measurements determined here contribute to quantifying the match/mismatch hypothesis using models than will generate predictions of climate forced environmental change on recruitment into the Gulf of Maine northern shrimp fisheries
 
c. Timing of appearance of larval shrimp with potential planktonic prey.
 
Phytoplankton and zooplankton samples collected along with northern shrimp larvae at stations on the winter-spring transects off Portsmouth in 2005-2006 provided insight into the composition and variability in the larval shrimp prey field. Analysis of algal pigments in larval shrimp guts indicate that all planktonic developmental stages were feeding on phytoplankton, including diatoms. The potential zooplankton prey field likely consists of unicellular heterotrophs (which were not measured, but are assumed to be correlated in abundance to the phytoplankton biomass) and early life stages of planktonic copepods and meroplankton. The dominant metazoan prey in winter-spring in the western Gulf of Maine include naupliar stages of a relatively small number of species of planktonic copepods (Calanus finmarchicus, Microcalanus pusilus, Oithona similis and Pseudocalanus spp.) as well as nauplius larvae the barnacle, Balanus sp. The barnacle nauplii were especially abundant in Mar-Apr of both years. While it is not known at this time whether shrimp larvae are capable of feeding on Balanus, we include it as a potential prey, and point to the need for additional experiments to determine the feeding behavior of shrimp larvae on Balanus.
 
The interannual comparison of planktonic prey fields for northern shrimp larvae in the western Gulf of Maine revealed significant interannual variation in food availability for shrimp larvae. In 2005, phytoplankton standing stocks were relatively high during the larval shrimp growing season, as were Balanus concentrations, especially during March. Measurements from 2006, on the other hand, revealed a much different food environment for shrimp larvae. Phytoplankton standing stocks and copepod egg production (a proxy for nauplius availability) were relatively low throughout the growing season (up until the end of sampling in April). Apart from one occasion in March, Balanus concentrations were also low relative to 2005. These results indicate very different food environments among years. In general, our findings are consistent with the match-mismatch hypothesis, suggesting first order biological control of northern shrimp recruitment in the Gulf of Maine.

Publications

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

Thesis/Dissertation

  • Bates, M. (2007). Modeling physical controls on northern shrimp ("Pandalus borealis") dispersal, retention and settlement success in the Gulf of Maine. Master's Thesis, University of New Hampshire.
  • Hobbs, E. (2008). Distribution and feeding behavior of early life stages of the northern shrimp, "Pandalus borealis," in relation to the spring phytoplankton bloom in the western Gulf of Maine. Master's Thesis, University of New Hampshire.
Keywords: 
modeling