MMS ENVIRONMENTAL STUDIES PROGRAM:  ONGOING STUDIES

MMS OCS Region:

Gulf of Mexico

Planning Area:

Gulfwide

Title:

Trophic Aspects of Sperm Whales in the Northern Gulf of Mexico Using Stable Isotopes of C and N:  Geographical and Inter-Annual Variation (GM-06-x15)

Total Cost:  $52,808

Period of Performance:  FY 2006-2009

Conducting Organization:

New Mexico State University

MMS Contact:

Dr. Deborah M. Epperson

Description:
Background:  In the northern Gulf of Mexico, scientific research to understand the distribution, habitat, movements, and genetic aspects of sperm whales has been implemented by various scientists, and has been supported principally by Minerals Management Service and the National Marine Fisheries Service.  However, there is no scientific literature describing trophic aspects of sperm whales in this area and therefore feeding areas have not yet been recognized.  Using stable isotopes, this project will attempt to determine sperm whale trophic levels and evaluate differences by sex and maturation levels.  It will also identify potential prey items, primarily cephalopods.  Sampling cephalopods is difficult due to their mobility and deep-water habitats, and this study will use samples collected from other work in the Gulf to analyze predator-prey relationships.

Objectives:  The objectives of this study are to:

·      determine the trophic level of sperm whales and evaluate differences by sex and maturation,

·      evaluate an inter-annual variation in the trophic position of sperm whales,

·      analyze predator-prey relationships between sperm whales and their potential prey (i.e. cephalopods), and

·      recognize feeding areas of sperm whales in the Northern Gulf of Mexico and evaluate differences between them.

Methods:  Sloughed skin and skin biopsies from free-ranging sperm whales collected in the Northern Gulf of Mexico (NGM) from 2000 to 2005 as part of MMS’s sperm whale research program will be used for data analyses.  In addition, gender data determined through the ZFX/ZFY analysis by Dr. Engelhaupt will be used to evaluate differences between female and male sperm whales.  All sperm whale tissue samples will be used to evaluate their relative trophic position, differences of sex and level of maturation, and inter-annual variation in their trophic position from 2000 to 2005.

To determine a trophic level value of sperm whales and to recognize feeding areas, samples of particulate organic matter (POM) were collected. POM was collected at depth of maximum chlorophyll production by filtering 4 L of seawater through a 0.06 mm screen and then onto pre-combusted (450 C for 24 h) GF/F glass-fiber filters or by filtering 4 L of continuously flowing inboard surface seawater through a pre-combusted 47-mm diameter Whatman GF/F filter.  Each filter was placed in a separate, clean plastic filter container and stored frozen at -20º C.

To evaluate predator-prey relationships between sperm whales and cephalopod species, muscle samples of cephalopod species (at least six species) as the main prey of sperm whales in the NGM will be used.  A minimum of 15 beak and muscle samples by each cephalopod species will be needed in areas where sperm whales have shown to be highly aggregated based on previous Sperm Whale Seismic Study (SWSS) reports (is. Mississippi Canyon, West-Central NGM and Western NGM).

Since stable isotope signatures from muscle can be estimated by using beak tissues, the stable isotope signatures of cephalopod beaks from preserved/frozen collections from the NGM will be used to evaluate predator-prey relationships as a secondary source of information.

To recognize feeding areas of sperm whales in the NGM and evaluate differences between them, isotopic signatures from sperm whales, cephalopods, and POM from each area will be used.  This information will be combined with the latitudinal and longitudinal position where each sample was collected and it will be referred to a geographic isotopic map of the northern NGM. Mesoscale oceanographic features from each area (e.g. Central, Western and West-Central) will be used to discuss potential differences or similarities between these areas.

Products:  Final report and peer-reviewed publications.

Importance to MMS:  The destruction of habitat, seismic operations in deep waters, and other intense noise produced by humans are increasing in the Northern Gulf of Mexico.  However, it is still unclear how these activities may or may not impact sperm whale populations in the Northern Gulf.  This study will significantly contribute to the understanding of how sperm whales use the Northern Gulf of Mexico (e.g. as a feeding area) and how their feeding success can he adversely affected by an increase in human activities.  Examining these aspects is necessary to develop feasible and realistic strategies to protect sperm whales and their habitat while managing the mineral resources on the Outer Continental Shelf.

Current Status:  Ongoing.

Final Report Due:

December 2008

Publications:

None

Affiliated WWW Sites:

None

Revised date:

March 2009

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