(full paper is archived in the Miller Library)
Title: Over 20 year stablity in abalone population in an area
inhabited by sea otters
Student Author(s): Stoll, Nicolai
Bugbee, Clarke
Faculty Advisor(s): Pearse, John
Pages: 13
Location: UC Santa Cruz Kelp Forest Ecology Class
Date: Fall 1992
Keywords: HMLR, Haliotis rufescens
Abstract: One of the principle food items of the sea otter
Enhydra lutris at Hopkins Marine Life Refuge, Pacific Grove
CA, and throughout most of their present range is the abalone,
Haliotis spp.(Costa 1978). The sea otter and the abalone
coexisted for thousands of years in equilibrium (the nature of which
is uncertain) on the Pacific coast until the 1800's when otters were
hunted extensively for their fur. By the turn of the century the
otter population had been reduced to near extinction levels. Laws
protecting sea otters helped to revive the population from about 50
animals in 1911 to about 2000 animals off the central California
coast in 1978, with otters returning to Hopkins Marine Life Refuge
sometime in the 1960's. The otter's range in California has extended
to a section of the coastline of about 250 km from Santa Cruz county
to San Luis Obispo county (Hines and Pearse 1982).
Observations of McLean (1962) in the 1950's show that the sea floor
at Hopkins Marine Life Refuge was densely populated with abaloanes
"spaced only a few feet apart". This situation presents a
very good opportunity to study the impact that the return of the
otter has had on an abalone population in an area where otters had
been absent for many decades. Since 1973 there has been a series of
studies (Lowry and Pearse 1973, Cooper et al. 1977, Hines and Pearse
1982) which have examined a particular site at Hopkins Marine Life
Refuge in respect to density, size frequency, mortality and turnover
of the abalone population there. These studies have shown that
although otters have continued to feed actively on abalones, and
abalone size and density initially decreased dramatically, the
population has remained stable since this decline, with high
mortality balanced with high recruitment and growth rates. Abalone
living within the otters range are strictly limited to the protection
of cracks and crevices in rocks and are therefore highly dependent on
substrate topography for maintenance of their population density.
Since 1981 (Hines and Peaarse 1982) there have been no follow up
studies of abalone done at this specific site at Hopkins Marine Life
Station (except Pollard 1992 which studied a nearby site and used
diferent sampling techiques). This study was undertaken to see (1)
if the stability of the abalone population has persisted, (2) if
there has been any change in the size frequency distribution, and (3)
if high turnover rates persist.