Provincetown Center for Coastal Studies

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    Habitat Studies Theory and Technique

     
         

    Left profile of a right whale skim feeding at the surface.
    Left profile of a right whale skim feeding at the surface.
    Note vertical rows of gray baleen hanging from the upper jaw.

     

    During the winter months the wide, shallow bay, protected by the arm of Cape Cod, creates the perfect habitat for blooms of phytoplankton, the basis of a complicated and poorly understood food web. Right whales, searching for food, become part of this habitat. For over a decade, PCCS has looked into the factors that make Cape Cod Bay a critical habitat for right whales. It is hoped that a clearer understanding of the habitat, and threfore the whale, will inform conservation efforts.

    Cape Cod Bay is not the only known feeding ground of right whales but it is the only known habitat where the whales are commonly found feeding at the surface (in the Bay of Fundy, right whales generally feed at depth, making observations of this behavior almost impossible). The unique situation of Cape Cod Bay affords researchers with the opportunity to do fine scale studies of right whale habitat requirements. Using our research vessel Shearwater, regular stations within Cape Cod Bay are monitored for a series of environmental characteristics, including: salinity, ambient light, temperature, phytoplankton and zooplankton. Coupled with sightings of right whales (or the lack of sightings) these environmental factors create an image of how right whales use the Bay.

    What has been found is that right whales feed upon a host of zooplankton species, most notably, the crustaceans called copepods. The occurrence of different copepods is tied to such environmental factors as temperature, salinity and availability of their prey, including phytoplankton and other zooplankton. Since all of these factors change through the season and throughout the Bay, the diversity and density of copepods differs over time and space. This patchiness of copepods affects the movements of feeding right whales. The habitat studies team has begun to define the composition of these patches (their size and density), and their occurrence throughout the Bay.

    Map of habitat stations sampled in Cape Cod Bay

    Map of habitat stations

    sampled in Cape Cod Bay

    This long term sampling of the Bay environment has created some surprisingly precise results. For example, right whales may begin feeding when the density of zooplankton reaches 3,750 organisms per cubic meter of water. In other words, right whales may not bother to open their mouths to filter plankton until that threshold is reached. Further, by using energetics models, right whales may not “break even” (where the whale is gaining more energy from the food than is lost to getting that food) until the density of copepods reaches 6600 organisms per cubic meter. And density is not the only factor. Right whales seem to show a preference for certain species of zooplankton, especially copepods. In particular, certain species of Calanus are favored. Thick patches containing Calanus may sustain aggregations of right whales for days or weeks. When Calanus is not available, right whales may target Centropges and Pseudocalanus or even Oithona and Acartia. Any one of these species may be numerous at different times and different areas over the Bay. The composition can even change throughout the 24 hour cycle (see these abstracts).

    How do these patches form? How do whales find these patches? Why does the composition of zooplankton change from year to year? How would changes in the health of the Bay affect zooplankton and therefor the population of right whales? What is the carrying capacity of the Bay (how many whales can the habitat support)? Only through long term research can we hope to answer such questions. Certainly, these questions are not purely academic; they may go a long way to saving one of the rarest animals on earth.

     

     

     

    Techniques

    Weather permitting, weekly cruises head out to sample the Bay from January through May. A suite of sampling techniques can be used during a field cruise to collect data. To collect oceanographic information - the physical aspects of water – a CTD (Conductivity, Temperature, Depth recorder) is employed. The CTD carries a computer chip that processes and stores information regarding depth, salinity, ambient light and temperature every second. All of these factors affect plankton: every species of plankton has differing tolerances for temperature, salinity, depth and light.

    plankton tow
    Plankton net towed from the stern; orange colored plankton caught in sample bottle.
     

    One of the simplest and most time-honored methods for collecting plankton is the plankton tow. A fine meshed, cone shaped net can be towed through the water, concentrating plankton in a sample bottle at the back end. The net can be towed to sample a distance of surface water (a horizontal tow), or the net can be sunk and raised to sample the plankton throughout the water column (a vertical tow). The use of the plankton tow can create broad scale image of the planktonic community but is limited in that it does not collect environmental data to relate to the samples. Two other techniques can bring the biological and environmental samples together.


    Vertical sampling creates an image of the habitat from the Bay floor to the surface waters using the CTD, a motorized pump and a long spool of hose. The hose, attached to the CTD is set overboard and sunk to the bottom. As it is raised, it is stopped every two meters to sample ten gallons of water. The pump draws water through the CTD (collecting environmental data) and sent, via the hose, to the deck. Onboard the same ten gallons of water that was analyzed by the CTD is sent through small, PVC collecting bottles that strain out a sample of the plankton. This detailed picture of the water column takes into account plankton and the physical properties of the water that sustain them.
     

    sampling techniques
    Seawater can be drawn through a hose by a pump (for vertical sampling) or as the boat travels (for horizontal sampling of the near surface). Short PVC sections outfitted with fine mesh can be held into the flow of the hose at intervals. A zooplankton sample is caught by the mesh and can be transferred to bottles and preserved for counting in the lab.

    To look at the surface community over a long distance, horizontal sampling methods are used. A tall pipe, mounted off the stern of the boat reaches into the first meter of surface water. As the boat runs a transect across a portion of the Bay, water enters the pipe and is pushed onboard through PVC collecting bottles to sample for plankton. The water then passes over the CTD to collect data about temperature and salinity. In this way large areas of the surface of the Bay can be sampled.

    All of these techniques can be used if whales are present (“positive data”) and with no whales present (“negative data”) to understand how the habitat changes over time and space: over hours, over weeks, over years, from the shallow waters, to deep water, from north to south.

    At the end of the cruise the difficult and tedious process of counting begins. Hundreds of samples may be gathered in a season and each sample must be analyzed. Using microscopes and species guides each sample is examined for species and numbers of individuals within the species. All of this information can then be related to the sightings of right whales to create an impression of the habitat.

    Conservation and Research

    PCCS and MA- Division of Marine Fisheries Cooperative Habitat Monitoring and Management

    plankton tow PCCS research team conducts monitoring activities aboard R/V Shearwater.

    PCCS right whale surveillance and monitoring activities are aimed at providing management agencies with information to assist in their time-critical decision making (e.g., amendments to seasonal gear restrictions or the issuance of vessel speed restrictions), intended to mitigate human impacts on right whales in the waters of Cape Cod Bay.  Immediately following research cruises, post-cruise “Preliminary Assessments” and the more lengthy “Habitat Assessments” are distributed electronically to interested managers and colleagues; these documents provide descriptions, analyses and forecasts concerning the interaction of right whales, habitat conditions and potential risks.  Detailed “Special Reports” are also used as a tool for exploring ecological phenomena of particular interest.  To address the need to alert DMF to conditions in Cape Cod Bay deserving immediate management attention, PCCS disseminates critical observations and predictions through a rapid reporting system, or a “Right Whale Risk Alert” document.  Within 12 to 24 hours of receipt of such a document from PCCS, DMF issues “Advisories” to mariners explicitly detailing where right whales are aggregating, and subsequently where there is elevated risk of ship strike in Cape Cod Bay and adjacent waters.  This successful partnership demonstrates how science and management can merge, improving the odds that the North Atlantic right whale will recover from near extinction. 


    This work is made possible by the Massachusetts Division of Marine Fisheries through ongoing support from NMFS and NOAA.

    Research Projects

    Are Right Whales Getting Enough Food?

    The Influence of the Vertical Migration of Zooplankton on the Risk of Entanglement and Ship Strike to Right Whales (Eubalena glacialis)

    The Ecology of Risk

    Distribution and Risk Simulator (DARS)

    For more information about these projects, please contact Karen Stamieszkin.

     

     

     
     
     

    Right whale images taken under NOAA Fisheries permit 633-1763, under the authority of

    the U.S. Endangered Species and Marine Mammal Protection Acts - please request PCCS permission for use.

     


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