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        Long Term Monitoring of Red Abalones - see also Black Abalones further down

Haliotis rufescens (Swainson, 1822)

Haliotis rufescensThe red abalone is California's largest marine snail whose name "rufescens" refers to the animals outer shell color, which is typically red or pink but can vary as the color is strongly influenced by the animals diet.. When red algae dominates the food selected in the abalones diet, the shell that is produced is red outside. This red pigment of the shell, known as rufescine, is a bilin compound, obtained from the red pigment (phycoerythrin) in red algae. Conversely, when brown or green algae dominates the food selected in the abalones diet, the shell that is produced range from aquamarine, green, to white color. A mixed diet of red and brown algae results in a somewhat brownish shell. Mature abalones are sedentary creatures, occupying a permanent position, or scar (crevice), on a rock. They do not roam about grazing on attached algae but live almost exclusively on loose plants that lodge near them or are caught with the animals foot as the plants drift slowly by. In those regions where sea otters are established, most red abalones live only in deep protected crevices, but north and south of the seas otter's present range many occupy relatively open rock faces (Morris, Abbott, & Haderlie 1980).

Studies of red abalone population dynamics were first initiated within the Hopkins marine life refuge (HMLR) in 1972 by John Pearse (University of California, Santa Cruz) and his colleagues. This initial “baseline” study has allowed researchers to examine long-term trends in red abalone densities, size structure, and mortality rates in the absence of human take within the Hopkins Marine Life Refuge. For the initial “baseline” study, a permanent 40 × 40 m plot that included granite outcrops interspersed with sandy channels and patches was established at depths of 7–13 m (Hines and Pearse, 1982). Abalone surveys have been conducted within the permanent plot between 1972–1981 ([Lowry and Pearse, 1973], [Cooper et al., 1977] and [Hines and Pearse, 1982]), and subsequently repeated in 1990 (Pollard, 1992), 1992 (Stoll and Bugbee, 1992, and 2003–2011 (Micheli, et al., 2008).

These continued studies have allowed researchers to examine the long-term trends of the densities, population size structure, and mortality rates of red abalone over a 32-year period within the Hopkins marine life refuge, a no-take marine reserve protected since 1931, and to examine temporal trends in populations in the absence of human take.

Monitoring of the red abalone over this 32-years period has not revealed increasing or decreasing trends in red abalone sizes or abundances over the past three decades, in the absence of harvesting. Despite no increasing trends, protection in the Hopkins marine life refuge (HMLR), has led to persistence of red abalone populations over multiple generations, at average densities of 0.2 individuals/m2. At other locations, within the HMLR and elsewhere (outside the refuge), red abalone densities are lower than at the location where long-term studies were conducted. Red abalone densities at the location where long-term studies were conducted (average 0.03 animals/m2 (Micheli, et al., 2008). These results suggest that continued fishery closure and protection in no-take reserves are effective tools for allowing persistence of abalone populations, though there are no signs of recovery to levels comparable to those preceding fisheries collapse. Such failure to recover is most likely associated with high natural mortality and possibly continued illegal take, but not with processes underlying low abalone population levels elsewhere, including food or habitat limitation, recruitment failure, or disease. Linking current structure and trends to specific processes is a crucial first step towards devising focused strategies for conserving and re-building depleted marine populations (Micheli, et al., 2008).

graph of abalone collection data

References

Cooper et al., 1977 J. Cooper, M. Weiland and A. Hines, Subtidal abalone populations in an area inhabited by sea otters, Veliger 20 (1977), pp. 163–167.

Hines and Pearse, 1982 A.H. Hines and J.S. Pearse, Abalones, shells, and sea otters: dynamics of prey populations in central California, Ecology 63 (1982), pp. 1547–1560

Lowry and Pearse, 1973 L. Lowry and J. Pearse, Abalones and sea urchins in an area inhabited by sea otters, Marine Biology 23 (1973), pp. 213–219. Full Text via CrossRef | View Record in Scopus | Cited By in Scopus (25)

Micheli, F., A. O. Shelton, S. M. Bushinsky, A. L. Chiu, A. J. Haupt, K. W. Heiman, C. V. Kappel, M. C. Lynch, R. G. Martone, R. B. Dunbar and J Watanabe. 2008. Persistence of depleted abalones in marine reserves of central California. Biological Conservation 141: 1078-1090.

Morris, Robert H., Donald P. Abbott, and Eugene C. Haderlie, 1980. Intertidal Invertebrates of California. Stanford University Press, Stanford, CA. 690 pp

Pollard, S. 1992. Red abalone, Haliotis rufescens: relative impacts of the recreational fisheries and sea otter predation on the abundance, size frequency and microhabitat distribution of the red abalone populations in central and northern California. Masters thesis, University of California, Santa Cruz, CA, USA

Stoll, N. and Bugbee, C. 1992. Over 20-year stability in abalone population in an area inhabited by sea otters. Unpublished, Undergraduate Project. Hopkins Marine Station, Stanford University, CA, USA.

Status and trends of black abalone populations within the Hopkins Marine Life Refuge

black abaloneBlack abalone (Haliotis cracherodii) are large herbivorous snails living on rocky shores from Northern California to Baja California Sur. Following large population declines from overexploitation and disease, California fisheries for black abalone were closed in 1993 and in February 2009 this species was listed on the US endangered species list.   Despite the fisheries closure, population recovery of black abalones in central California is hindered by high predation rates, ongoing poaching, and possible recruitment failure (e.g., the Allee effect) where population densities are too low to support viable fertilization (Micheli et al. 2008. Biological Conservation).  Similar to many marine fishes and invertebrates, fecundity of these animals increases with size and therefore removal of large individuals by poachers, predators, or storms may have large impacts on the reproductive output and future persistence of these populations.  Additionally, the possible northern expansion of withering syndrome, a disease that has decimated black abalone populations in southern California, poses yet another threat to the future of central California abalone populations.

graph of densities over timeIn recent years, Dr. Fiorenza Micheli and her students have been examining temporal trends in black abalone densities and size structure within the HMLR.  Collection of abalones in the HMLR has been prohibited since the 1917.  However, surveys conducted in 2002 and 2005 indicated that densities are low and large individuals rare (Micheli et al. 2008).  Through ongoing intertidal surveys, Dr. Micheli is determining whether populations of black abalone are stable or if possible illegal take and other sources of mortality (e.g., predation by sea stars and sea otters, disease, storms or temperature stress) are causing continued removal of large reproductive individuals, lower recruitment (e.g., abundance of juveniles) and decreased total abundances.

Micheli, F., A. O. Shelton, S. M. Bushinsky, A. L. Chiu, A. J. Haupt, K. W. Heiman, C. V. Kappel, M. C. Lynch, R. G. Martone, R. B. Dunbar, and J Watanabe. 2008. Persistence of depleted abalones in marine reserves of central California. Biological Conservation 141: 1078-1090.