Life History

Introduction

Cetacean life history studies focus on describing the reproductive and survival characteristics of a species. Describing a species’ life history includes, but is not limited to, determining how long individuals live, the age at which they become sexually mature and first reproduce, how often they breed, how long they nurse their young, where they forage and what they eat. Although life history studies focus on individual variability, the combined data for many individuals provides the information necessary to understand a species’ demography, or their growth rate potential.

Specimen material for life history studies are collected by observers working on fishing boats who sample the animals accidentally killed in gear or from animals found stranded on the beach. Standard data collected in the field for each animal includes documenting species identification with photographs, drawings and written observations, measuring total body length and maximum girth, determining gender as well as recording the specifics of when and where it was sampled. Additional data are collected whenever possible and include detailed morphological measurements and tissue sampling. Standard sampling protocols include collection of skin and/or a sample of internal organ for molecular genetic studies, blubber for contaminant and isotope studies, teeth for aging, gonads for determining state of sexual maturity and reproductive status of females, stomachs for identification of prey species, and the head and post-cranial skeleton for morphological studies.

 

Ovary from a northern right whale dolphin. The small circles are scars of ovulation (corpora albicantia) and the lump to the right is a regressing corpus luteum which pruduces hormones neccessary for pregnancy. The corpus luteum will regress, turning into a corpus albicans. The life history program examines ovaries to determine reproductive status of cetaceans and pinnipeds.

Our life history studies have focused primarily on species impacted by the tuna purse-seine fishery in the eastern tropical Pacific, and the drift and set gillnet boats operating off the coast of California. Our primary species of interest have been the pantropical spotted dolphin, eastern and whitebelly spinner dolphin and short-beaked common dolphin. Currently, we are estimating age-specific life history parameters for the eastern and whitebelly spinner dolphins, and short-beaked common dolphin as well as estimating fetal mortality for the spotted, spinner and common dolphins to better quantify their reproductive potential.

Selected References

Chivers, S.J. 2002. Cetacean Life History. Pages 221-225 in: Perrin, W. F., B. Wursig and J. G. M. Thewissen. Encyclopedia of Marine Mammals. San Diego, CA, USA: Academic Press.

Perrin, W. F. and S. B. Reilly. 1984. Reproductive parameters of dolphins and small whales of the family Delphinidae. Reports of the International Whaling Commission (Special Issue 6): 97-113.

 

Strandings

We coordinate San Diego County strandings for the West Coast Region as part of the National Stranding Network established by the 1972 Marine Mammal Protection Act (MMPA).

Currently, the National Stranding Network is part of the broader Marine Mammal Health and Stranding Response Program (MMHSRP) Although the passage of the MMPA established an official network, stranded cetaceans have been of interest to many people for a long time. In fact, our records for San Diego County date back to the early 1900s.

Data collected from stranded marine mammals provide us information about the species that live off our coast, and help us learn more about the species’ life history. In San Diego County, marine mammal strandings are typically of single animals rather than mass strandings. In fact, there are no records of mass strandings for any species in San Diego County. Most animals tend to be emaciated indicating that they have been ill for some time before stranding. Necropsies sometimes reveal their ailment but not always. When responding to strandings we look for evidence of human interaction, particularly fisheries. In many cases, apparently healthy animals (i.e., not emaciated or showing other signs of ailment) will show evidence of having been entangled in fishing gear.

The three cetacean species that most often strand on our beaches are bottlenose dolphinshort-beaked common dolphin and gray whale. However, over the years we have recorded a dozen or so species stranded on our beaches, and they include the blue whaleDall’s porpoise and the pygmy sperm whale.

Our Stranding Hotline phone number is 858-546-7162. We respond to all reports of marine mammals found dead on San Diego County beaches, and we rely on life guards and citizens to report dead marine mammals. All live marine mammal strandings are handled by Sea World.

Additional information:

Geraci, J. R., and V. J. Lounsbury. 1993. Marine mammals ashore: A field guide for strandings.Texas A&M University Sea Grant College Program Publication TAMU-SG-93-601 (ISBN1-883550-01-7). 305 p.

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Fishery Observer Program


Shortbeak common dolphin


Spotted dolphin

Fishery observer programs provide a unique opportunity to collect data about a species from the habitat in which they live. These programs in conjunction with stranding networks have provided most of the data we have about cetacean species living off California and in the eastern tropical Pacific. Fishery observers are trained to collect biological samples from incidentally killed marine mammals. The suite of data collected includes species identification, gender, and total body length, as well as samples of skin for genetics, gonads for reproductive status determination, stomachs for documenting prey, teeth for age, and the skeleton for morphological studies.

Currently, the Southwest Region monitors the drift gillnet and pelagic longline fisheries. We process biological samples collected from marine mammals, cetaceans and pinnipeds, from the driftnet fishery that operates off the California coast. Observers are placed on about 20% of all fishing trips and are instructed to sample marine mammals that are accidentally killed in gillnets. Recently imposed time/area closures to protect turtle species have resulted in reduced incidental marine mammal takes. Short-beaked common dolphin are the most frequently taken species in the fishery, but since the observer program started in 1990, most of the cetacean species living off the coast have been entangled in gillnets including sperm whales, fin whales and several beaked whale species.

We have also begun to work with the Hawaii region, Pacific Islands Area Office, to incorporate the collection of skin samples from cetaceans entangled or accidentally killed in long line fishing gear. Several cetacean species have been observed entangled in the gear and little is known about these species from that area. We hope that the collection of skin for molecular genetic analyses will at least help us improve our understanding about the impacted species’ population structure.

stained cross section of tooth, below; looking at tooth on the image analyzer

Selected References

Most recent estimates of mortality and description of life history data collected from the California drift gillnet fishery:

Carretta, J.V., S.J. Chivers, and K. Danil. 2005. Preliminary estimates of marine mammal bycatch, mortality, and biological sampling of cetaceans in California gillnet fisheries for 2004. Administrative Report LJ-05-10, available from Southwest Fisheries Science Center, 8604 La Jolla Shores Drive, La Jolla, CA 92037. 17 pp.

Additional information about the California drift gillnet fishery:

Chivers, S. J., Robertson, K. M. and Henshaw, M. D. 1997. Composition of the incidental kill of cetaceans in two California gillnet fisheries: 1990-1995. Rep. int. Whal. Commn. 47:909-15.

Hanan, D. A., Holts, D. B. and Coan, Jr., A. L. 1993. The California drift gillnet fishery for sharks and swordfish. Calif. Dept. of Fish and Game, Fishery Bulletin 175. 95 pp.

Jefferson, T. A., Myrick, Jr., A. C. and Chivers, S. J. 1994. Small cetacean dissection and sampling: A field guide. U. S. Department of Commerce, NOAA-Technical Memorandum-NMFS-SWFSC-198. 46pp.

Julian, F. and Beeson, M. 1998. Estimates of marine mammal, turtle, and seabird mortality for two California gillnet fisheries: 1990-1995. Fishery Bulletin 96:271-284.

 

Last modified: 3/9/2016