Overfishing & conservation/restocking issues

Most world abalone populations have been overfished, some to virtual extinction.  Commercially viable culture facilities exist in several countries, including the U.S. (California), Australia, New Zealand, China, and Japan. For economic reasons, much of the marketing is done at a "cocktail" size of photograph of strings of juvenile abalone being cultured at the Bamfield-Huu-ay-aht Community Abalone Project at Bamfield, British Columbiaproduct. Main problems being addressed by aquaculturists are disease and development of reliable artificial diets.

NOTE  examination of shell middens on San Clemente Island, California dating from 250-2830yr before present reveals early evidence of overfishing in in this area of California.  As black abalones Haliotis cracherodii became depleted by the islanders, they turned more to harvesting the smaller, but more abundant turban snails Chlorostoma funebralis.  The abalones provided not only a protein-rich food source, but their shells were turned into beads, fishhooks, containers, and ornaments.  In this area H. cracherodii is intertidal and therefore would have been handy for harvesting.  Other abalone species were present, but found only subtidally. Raab 1992 J Ethnobiol 12 (1): 63; see also Braje et al. 2009 Ecol Appl 19 (4): 906 for information on historical fishing for red abalone in the Channel Islands, California

A small pilot-culture facility at the Bamfield Marine Sciences
Centre, British Columbia, known as the Bamfield-Huu-ay-aht
Community Abalone Project (now closed), explored the economic viability
of culturing northern abalone H. kamtschatkana 0.7X

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photograph of a SCUBA-diver removing possible predators from an abalone outplanting site near Bamfield, British Columbia taken from a video

CLICK HERE to see a video of an abalone Haliotis kamtschatkana recolonisation experiment. Part of the mandate of the abalone-culture facility at the Bamfield Marine Sciences Centre, British Columbia is enhancement of natural stocks. The video shows a pilot "outplanting" involving, in order: predator clearance, injection of competent larvae from syringes into rock-crevice habitat, and addition of juveniles from plastic bags into prime coralline-algae habitat. Video courtesy James Mortimer, the Bamfield-Huu-ay-aht community Abalone Project hatchery, and the Department of Fisheries and Oceans, Government of Canada.

NOTE video replays automatically

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Research study 1

map showing collection and study sites for abalone In British Columbia, the 1990 closure of the abalone fishery effectively created a “no-take” abalone reserve out of the entire coastline.  Has the closure resulted in more and bigger abalone?  This was examined 7yr after the closure by comparing the size of abalone in the 7yr coastwide “reserve” with 2 other histograms showing abalone abundances in different types of no-take reserves in southern Vancouver Island, British Columbiaareas: one a no-take government-regulated ecological reserve established 18yr previously (designated "18yr Ecological Reserve"); the other, effectively a no-take reserve created by the prohibition of marine traffic around a coastal prison constructed 39yr previously ("39yr Prison Reserve").  A third set of data from Canadian federal fisheries sources is included. Unfortunately, too few abalone are present in the 7yr coastwide "reserve" sites to graph. The other data show an overall larger size of abalones in the 39yr Prison Reserve than in either the 18yr Ecological Reserve or in the government data. The purple-coloured vertical lines in the graph indicate average lengths of abalone in each area.  Wallace 1999 Conserv Biol 13: 882.

NOTE although not specified, these data probably came from open-coast areas from Vancouver Island north to Haida Gwaii (Queen Charlotte Islands

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What can we conclude from this? Consider the answers provided, then CLICK HERE to see explanations.

Ecological reserves for abalone are effective. 

The British Columbia-wide closure of the fisheries is not effective after 7yr. 

Northern abalone Haliotis kamtschatkana appear to reach an upper size of about 14cm.

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Research study 2

graph showing tonnes of abalone Haliotis kamtschatkana fished in British Columbia from 1952 to 1990

For several decades British Columbia has maintained a modest fisheries for northern (pinto) abalone Haliotis kamtschatkana. Owing to low stock abundance, however, the fishery was closed in 1990, and the only exploitation since then has been poaching.  Some time prior to this, fisheries in Washington and Oregon were closed, as they also were in 1995 and 1996-1997, respectively, in Alaska and California.

Reasons cited by researchers for over-exploitation of stocks of abalone in B.C. include the species’ short larval period (poor dispersal), slow growth, relatively long life, and low and sporadic recruitment.  Campbell 2000 p.41 In, Workshop on rebuilding abalone stocks in British Columbia (ed., Campbell) Can Spec Publ Fish Aquat Sci 130.

NOTE  1 tonne = 1 metric ton = 1000kg - approximately 2200lbs

NOTE  the earlier year, 1996, is cited as the closure date for harvesting of white abalone Haliotis sorenseni in California in a study based in the California Channel Islands – an historic centre of abundance of the species.  Later, an exhaustive search in the area yielded few animals and the species is thought to be on the verge of extinction.  Although harvesting was apparently prohibited during previous spawning seasons, this measure failed to protect an adequate spawning-stock density.  The population never recovered and the survivors are dying of old age.  The authors suggest that as natural recovery is unlikely, a management programme must be implemented if the species is to be restored to viable status.  Davis et al. 1998 J Shellf Res 17: 871.

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Research study 3

graph showing abalone yields from fisheries in California from 1940s to 2000Abalone fisheries have been declining from San Francisco to the Mexican border since the late 1960s.  Despite enhancement procedures that include local-fishery closures, outplanting of hatchery-reared juveniles, transplantation of wild adults, and larval seeding, populations of all 5 species have plummeted. Lack of success in some of these programmes is attributed, in part, to inadequate enforcement and poaching.  However, outplanting of juveniles and larvae has been curtailed owing to parasite and pathogen problems in hatchery stocks.  Future enhancement success will depend on solutions being found to these problems, establishment of meaningful brood-stock aggregations in reserves, and possibly management of sea-otter range expansion.  Tegner 2000 In, Workshop on rebuilding abalone stocks in British Columbia (Campbell, ed.).  Can Spec publ Fish Aquat Sci 130.

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Research study 4

graph showing tonnes of abalone fished in California from 1942-1996

The data in this graph show commercial landings in metric tonnes of the California abalone fishery from 1942-1996 and average annual value.  While the data here include 5 species (red, pink, green, black, and white), over 98% of the commercial landings comprise just 2 species: red, Haliotis rufescens and pink, H. corrugata.  From 1969 to about 1982 pink, green, and white abalone were fished to commercially unsustainable levels in an area from San Francisco Bay south.  White abalones have been fished to virtual extinction.  North of San Francisco Bay red abalone (the only abundant species present) may be fished recreationally, but not by use of SCUBA or surface-supplied air.  Karpov et al. 2000 p.11  In, Workshop on rebuilding abalone stocks in British Columbia (ed., Campbell) Can Spec Publ Fish Aquat Sci 130.


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Research study 5


graph showing population size of sea otters Enhydra lutra in southeastern Alaska from 1968-1998photograph of sea otter Enjhydra lutraIn both Central California and Alaska resurgence in numbers of sea otters Enhydra lutris has had considerable impact on the abalone fisheries.  In southeast Alaska, especially, where sea-otter populations have grown exponentially since their re-introduction in the late 1960s (see graph), scientists consider that the coexistence of commercially viable populations of abalone (H. kamtschatkana) and sea otters is not possible.  Woodby et al. 2000 p.25 In, Workshop on rebuilding abalone stocks in British Columbia (ed., Campbell) Can Spec Publ Fish Aquat Sci 130; see also Watson 2000 In, Workshop on rebuilding abalone stocks in British Columbia (Campbell, ed.).  Can Spec publ Fish Aquat Sci 130.

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Research study 5.1

graph showing commercial harvest of white abalone Haliotis sorenseni in the California Channel Islands from 1955-1997Commercial fisheries of white abalone Haliotis sorenseni in southern California lasted for just a decade before collapsing in the late 1970s (see graph). Later, the species was nominated for and received (May, 2001) status on the US Endangered Species List, the first marine invertebrate to be so designated. At the time of the present review (early 2000s) white-abalone numbers had sunk to such low levels in the Channel Islands, California that it was thought to be heading to extinction1. The present researchers, from Australia and California, suggest that in addition to sub-legal mortality (mortal wounding during catching and measuring of under-sized individuals) and illegal fishing, the species’ proclivity for episodic spawning and its poor fertilisation success in face of ever-decreasing population sizes have likely been instrumental in causing the collapse. Density estimates from submersible2 surveys in the late 1990s place the entire California population size at less that 2,600 individuals. The authors’ recommendations for restoration3 of white-abalone populations include, among other things, a network of enforced marine-protected areas along with careful monitoring of life-history characteristics and population dynamics. Hobday et al. 2001 Rev Fish Biol Fisheries 10: 493. Photograph courtesy NOAA Southwest Fisheries Science Center, La Jolla, California

NOTE1 in 1997 all commercial harvesting of abalone in California (5 species) was closed, as was recreational harvesting south of the San Francisco area

NOTE2 white abalone inhabit fairly deep water, from 30-65m, so surveys using a submersible plus camera are the way to go

NOTE3 an updated summary of the status of white abalone at Tanner Bank in the Channel Islands to year 2010 indicates that while individuals still continue to grow, recruitment is low or non-existent, and population numbers have decreased by about 80%. Also, most individuals observed are “loners”, that is, possibly out of contact with other spawners. If extinction is to be avoided, the past policy of “benign neglect” has to be scrapped. Instead, the authors recommend an immediate programme of population enhancement by outplanting in selected areas laboratory-bred juveniles. Can such a conservation programme work? Let’s hope that we have a chance to see if it does. Stierhoff et al. 2012 Biol Conserv 152: 46.

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Research study 6

map showing historical abundances of abalone species in the Channel Islands, CaliforniaA research consortium from several University and State fisheries institutions in California address the question, “where are the best locations to establish marine protected areas (MPAs) for restoration of endangered white (Haliotis sorenseni), pink (H. corrugata), and green (H. fulgens) populations?”.  To answer this the researchers adopt an obvious, but still clever, approach: use past fishery data to identify what have been the past most productive areas in southern California.  Several species-specific sites are thus identified, all in the Channel Islands (see map).  Overall, if only one site were to be chosen, San Clemente Island would seem to be the best for all 3 species; productivity of pinks, however, is exceptionally high in kelp areas around Santa Barbara Island and in Anacapa Island.  No matter how sensible is the plan, the authors emphasise the need for strict enforcement policies if MPAs are going to work.  Rogers-Bennett et al. 2002 Conserv Biol 16: 1308.

NOTE  the authors also use estimates of egg production to compare efficacies of marine protected areas for abalone restoration, but are not considered heregraph showing historical abundances of pink abalone in the Channel Islands, California

  from 2001 white abalones have been on the federal endangered species list, and blacks and greens seem not far behind.  Commercial and recreational fisheries for all 5 abalone species south of San Francisco have been closed since 1997 (see fisheries data for pink abalone for selected Channel Islands on the Right)


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Research study 7


Where do we go from here?  In addition to enhanced enforcement of anti-fishing legislation and promotion of public awareness, rehabilitation programmes for depleted abalone stocks are now underway in most Pacific-coast States and in British Columbia.  They include establishment of larger and better regulated Marine Protected Areas as refugia, outplanting of hatchery-reared larvae and juveniles, and transplantation of wild adult stocks. Disease, most notably withering syndrome,  has been observed in wild populations of black (Haliotis cracherodii) and red (H. rufescens) abalone south of San Francisco and in farmed red abalone throughout the state.  With regard to plans for more extensive outplanting of hatchery-reared red abalone to replace depleted natural stocks, researchers at Bodega Marine Laboratory have identified the presence of the bacterial pathogen at 2 locations in northern California, both associated with outplantings of hatchery-reared H. rufescens.  Although their results are somewhat tentative, the authors caution that careful attention must be paid to the health of abalone being considered for any such re-stocking schemes.  Friedman & Finley 2003 Can J Fish Aquat Sci 60: 1424.

NOTE  areas where fishing is prohibited and, in time, come to act as a source from which larvae may disseminate and adults be harvested for transplantation.  In theory, the recreational fisheries area in northern California acts as a kind of refugium, because animals below free-diving depth survive and perform broodstock duty for the area

NOTE  caused by a Rickettsia-like bacterium Candidatus Xenohaliotis californiensis

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Research study 8

That even small ecological reserves can be effective in preserving breeding populations of abalone is shown by researchers in La Jolla, California.  The reserve in question, the San Diego-La Jolla Ecological Reserve is one of the oldest “no-take” reserves in California (40yr) and histogram showing larger sizes of green abalone Haliotis fulgens in an ecological reserve in Californiaone of the smallest (about 2km2).  Habitat-specific comparisons using transect data from SCUBA divers and ROV video show that the reserve protects the largest remaining populations of green abalone Haliotis fulgens in the area (see histogram).  Despite these findings, however, the authors note that most fished species have actually declined in numbers within the reserve.  They not only point out the generally limited value of small reserves, but also the limited usefulness of  “inside-outside” comparisons in the absence of baseline historical data.  In the authors’ opinion, the reserve is too small for most species to be self-sustaining.  Parnell et al. 2005 Mar Ecol Progr Ser 296: 39.   

NOTE  these are simply comparisons of what is inside the reserve with what is outside, and are used in the absence of more informative “before and after” data

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Research study 9

As part of a extensive programme of research at the Bodega Marine Laboratory, California on climate change, researchers have re-assessed population statuses of west-coast abalone stocks 30yr after original surveys.  Although particular emphasis in the study is paid to 2 species, the flat abalone Haliotis photograph of abalone Haliotis kamtschatkana juvenilewalallensis and northern abalone H. kamtschatkana, other species are referred to and, overall, the status of west-coast abalone stocks should be of grave concern.  Specifically, stocks of H. walallensis have declined in the Hopkins State Marine Reserve from 32% of the total abalone population in the reserve to only 8%, and the species is common now only in southern Oregon.  A once abundant species, H. kamtschatkana’s numbers have declined 10-fold over the past 30yr in northern California, Washington, and British Columbia despite the absence of fishing pressure.  Conservationists consider abalone a “flagship” or indicator species, and have highlighted in their writings the need for protection of kelp habitats.  The author tentatively suggests that the decline of flat and northern abalone may be “due to the rise in ocean temperatures” over the past 30yr.  Rogers-Bennett 2007 Bull Mar Sci 81: 283.

NOTE  the author remarks that a fisheries has actually been developed for them there

Juvenile northern abalone
Haliotis kamtschatkana

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Research study 10

map showing location of study site in Washington for abalone-abundance investigationDespite a statewide fisheries closure for northern (pinto) abalone Haliotis kamtschatkana in Washington, their abundance in the San Juan Archipelago has declined by almost 80% from 1992 through 2006.  During this time shell lengths have increased by 10mm, which suggests a recruitment failure in response to low population densities.  While a commercial fishery for abalone has never existed in Washington, annual estimates of harvest from a recreational fishery (closed in 1994) range around 40,000.  Threatened or “species-of-concern” status for H. kamtschatkana was proclaimed in 1998 by Washington State, in 1999 by the Canadian government, and in 2004 by the United-States goverment.  Rothaus et al. 2008 Can J Fish Aquat Sci 65: 2703.

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Research study 11

map showing sites for study of black-abalone genetics Natural recovery of an over-fished and/or diseased population of abalone will rely in large part on the extent to which remaining populations can supply larvae.  With this in mind, scientists at the Scripps Institution of Oceanography, La Jolla undertake an interesting research project, and that is to determine the genetic interconnectivity of remaining populations of black abalone Haliotis cracherodii along the central California coast and islands in the southern California Bight (see map).  In other words, have certain  populations historically been a larval source for other now-decimated populations?  Genetic analyses disclose, in fact, significant interpopulation genetic divergence, suggesting restricted larval dispersal.  The results agree with at least 2 previous studies showing restricted gene flow among populations of H. cracherodii. The black abalone Haliotis cracherodii crawlingauthors conclude that natural recovery of decimated populations of black abalone inthis area of California is unlikely to occur in the near future.  Gruenthal & Burton 2008 J Exper Mar Biol Ecol 355: 47.

NOTE  the authors use mitochondrial cytochrome-oxidase subunit one DNA sequences, 4 nuclear microsatellites, and 142 amplified fragment-length polymorphisms

NOTE  with respect to this, see an earlier publication by the same research group: Gruenthal et al. 2007 Mar Biol 152: 1237.

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Research study 11.1
  map showing locations in British Columbia where red abalones Haliotis rufescens have been sightedmap showing location of Athabaskan Island, B.C. where a specimen of red abalone Haliotis rufescens was found in 2010Canadian fisheries scientists at the Pacific Biological Station in Nanaimo (PBS) report in 2010 on the “first” occurrence of red abalone Haliotis rufescens in British Columbia (Athabaskan Island, see map on Right) but, in fact, for several decades the species has been known to occur on the west coast of Vancouver Island. Apparently, red abalone can hybridise with pinto abalone, but genetic analysis confirms the new specimen to be the genuine article. A paper concurrent with the first, also by Canadian scientists, document an additional 5 specimens on islands further north, and with these and ones found in 2008 on the shores of Haida Gwaii by a naturalist beach-walker, the northern limit of distribution of red abalones is extended almost to the Alaska border (see map on Left). The occurrence of rufescens in B.C. is hypothesised to be by kelp-rafting/“conveyor-belting” via northward-flowing currents from natural populations further south in Oregon and California, but could also owe to more local aquacultural activities in B.C./Washington. Campbell et al. 2010 Amer Malac. Bull. 28: 185; Sloan et al. 2010 Can Field-Naturalist 124 (3): 238; Merilees 2008 Victoria Naturalist 65 (3): 11.
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Research study 12

graph showing growth rate of pink abalone Haliotis corrugataThe fishery for pink abalone Haliotis corrugata closed in southern California in 1997.  Growth studies on a population near San Diego, California show that it takes about 19yr to reach legal fishery size.  Based on observed rates of juvenile recruitment to the region, the researchers estimate that the populations within the southern California closure area could take 30yr to recover.  This assumes successful reproduction and an absence of poaching.  Button & Rogers-Bennett 2011 Mar Ecol Progr Ser 431: 151.

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Research study 12.1

A later study on pink abalone Haliotis corrugata provides even more reason to be pessimistic about small-scale restoration efforts. The researchers select a 9m-dia area of kelp bed at Point Loma, California containing 23 individuals and stock it with 23 additional adults (new density = 0.18 . m-2). These 46 and 340 additional white abalone, both adults and juveniles, are then genetically analysed (DNA extraction with typing of 17 microsatellites). After 1yr an assay shows that none of the juveniles within the study area has parents from the original aggregation. The researchers are uncertain whether this owes to lack of successful reproduction or to recruitment of any resulting larvae or juveniles outside of the study area. The data are consistent with Sweepstakes Reproductive Success with its inherent risk of decline in genetic diversity. The authors comment that realistic restoration efforts will require greater density to start, although their results do not allow them to suggest what this would have to be to establish an independent population. Their conclusion is that the Point Loma population is insufficiently populated for long-term viability. Coates et al. 2014 J Exp Mar Biol Ecol 460: 184.

NOTE this new density is close to 0.2 . m-2, estimated by the California Department of Fish and Game to be the minimum spawning density of abalone required for successful reproduction. Average density of white abalone in the general Point Loma area at the time of the study is 0.04 individuals . m-2

NOTE posited about 3 decades ago, this well-tested hypothesis equates the chance of reproductive success of an individual, in this case a marine invertebrate, to winning a sweepstakes, such is the low probability of events necessary to make it happen: proximity of partners, proper current flow, fertilisation, larval survival in the plankton, finding a suitable settlement site, recruiting to an adult population, and so on

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Research study 13

sites in the San Juan Archipelago, Washington used in abalone surveyAn update on the status of northern abalone Haliotis kamtschatkana in the San Juan Archipelago, Washington by a research consortium from California and Washington show that population numbers have declined to less than 10% of those found in 1979. Moreover, no juveniles (<75mm) are recorded in a range of habitats surveyed, suggesting recruitment failure of a magnitude seen in British Columbia over the past 2 decades. The authors offer suggestions regarding microhabitat suitability, especially coralline algae substrata near and under kelp beds, that may enhance future restoration action and restocking programmes. Rogers-Bennett et al 2011 Aquatic Conserv: Mar Freshw Ecosyst 21: 573.

NOTE there are 2 subspecies of H. kamtschatkana on this coast, one in the north (H. kamtschatkana kamtschatkana) and one in the south (H. k. assimilis; from Point Conception south to Baja California). The authors correctly use the northern subspecies name in their paper. However, for convenience here and in other Research Studies that deal with the northern subspecies, this is shortened simply to Haliotis kamtschatkana

NOTE  the assessment is based on a one-time survey of 10 locations in Puget Sound, Washington


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Research study 14

map showing sites where "abalone recruitment modules" are deployed in recruitment study on Haliotis kamtschatkanaAnother update on the status of northern abalones Haliotis kamtschatkana in the San Juan Archipelago done by researchers from the University of Washington and Washington Department of Fish & Wildlife at almost the same time as Research Study 13 above,
underscores the need for immediate implementation of a recovery plan. The study employs an artificial habitat (called an Abalone Recruitment Module; see photograph) to estimate abundances of juvenile abalone. The units are a handy way to find and count juveniles by simple inspection, thus avoiding habitat damage caused by traditional rock-turning methodology of SCUBA-divers. The researchers deploy 66 units at 3 locations and 2 depths (3 & 6m), and check for recruitment 6 times over a 2yr study period (see map). Only 8 recruits are counted by the end of the study, supporting what is known from other investigations that present-day recruitment of the species is seriously limited, and that immediate remedial action is needed. The researchers recommend the establishment of marine protected areas, creation photograph of "abalone recruitment module" for assessment of recruitment of abalones Haliotis kamtschatkana in the San Juan Archipelagoof localised adult aggregations to enhance fertilisation, and augmentation of population numbers through culture and release of genetically diverse and disease-free larvae and juveniles. Bouma et al. 2012 Trans Am Fish Soc 141: 76.

NOTE similar designs and methodologies have been used in other abalone-assessment studies. The open mesh and holes in the sides allow, respectively, larval recruitment and entrance of juveniles

NOTE surveys from 1992-2009 by the Washington Department of Fish & Wildlife indicate a >80% decline in numbers of northern abalone within San Juan Archipelago (see Research Study10 above)

The cinder-block substratum within the modified crab-
trap is conditioned for 10mo in seawater. A laboratory
test with 25 juveniles shows that they will readily and
quickly (80% in a 24h test) move into the novel habitat

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Research study 15

cluster of black turban-shells Chlorostoma funebralis in a tidepoolDespite being a low-ranking food source for humans (small size, tough, and not too tasty), shell remains of black turban-shells Chlorostoma funebralis are recorded in middens in North Channel Islands, California over the past 12,000yr.  The middens also reveal abundant remains of abalone, mussels, and owl limpets.  The researchers credit the popularity of C. funebralis in these regions with their abundance, aggregation, and accessibility during daily tidal cycles.  Apparently, the meat of the shell is hard to tease out “winkle” style, and so most of the shell remains are fragmented, having been crushed in small anvil stones called “turban crackers” by the authors.  The authors provide some size data showing an apparent reduction in shell size through size-selective harvesting, but the data are variable and not convincing.  Percentage representation of black turban shells in 19 middens varying in age from 150-12,000ybp ranges from essentially nil to about 68%. Erlandson et al. 2015 Calif Archaeol 7 (1): 59.



Intertidal aggregations of Chlorostoma funebralis
may number in the several hundreds per square meter,
with maxima reaching 1000 or so. An individual may
grow to 3cm diameter over a life span of about 5yr


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Research study 15.1

Until to just a decade or so ago, commercial fishing for red abalones Haliotis rufescens was a burgeoning industry, and even now red abalones can be fished by free-diving in northern California. Given the apparent past historic abundance of red abalones, what explains their virtual absence in aboriginal middens in northern California dating from about 9000ybp? A first naive answer to this qustion would be that the people artist's impression of what competition between Holocene indigenous peoples and sea otters for a common food resource might have been likefound better and easier food elsewhere, but anthropologists in Davis, California who research the issue suggest a more complex explanation. After examining middens in 43 coastal sites north of San Francisco Bay dating from 9000 to 300ybp, the authors conclude that a combination of factors ranging from lack of adequate boat use, competition with sea otters, and more ready access to alternative food sources such as sea mussels, anadromous fish runs, and terrestrial game such as elk and deer, offer the most likely explanations. Colligan et al. 2015 Calif Archeol 7 (1): 33.

NOTE southern California and Channel Island middens, by contrast, are marked by dense accumulations of H. rufescens shells, so much so that they are referred to as “abalone pavements”

NOTE fish species such as salmon and rainbow trout that swim up rivers to breed in fresh water

Artist's impression of what competition between sea otters
and indigenous peoples of northern California for a common
food resource might have seemed like to the peoples themselves

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Research study 16

graph showing changes in density of octopuses Octopus bimaculatus in a study site after restocking with red abalones Haliotis rufescensWhat effect does restocking of abalones in a conservation programme have on populations of local predators, such as whelks, octopuses, fishes, and lobsters? This question is addressed for red abalones Haliotis rufescens by adding hatchery-reared abalone to two 300m2, sites in a kelp-forest habitat (5 spp. of large kelps) near Los Angeles, California previously occupied by red abalones but now bereft. A third 300m2 site is left as a control. Prior to the stocking as many predators as possible are removed from each of the 2 experimental sites, counted, and relocated >0.5km away. The counting is necessary to ascertain initial densities, but the relocation of the predators seems questionable. At each of several post-stocking counts, predators are again removed (but only whelks, not octopuses, lobsters or fishes). Results after 8mo periodic surveying show that octopuses are the most responsive of the predators, surging into the test plots initially, then returning to pre-stocking levels after 2mo (see Sites 1&2 on graph) None of the other predators show any significant incursion, let alone rebound. Post-stocking analysis of empty and damaged shells reveals highest mortality immediately post-stocking, falling off with time, with octopus predation being the most consistent. Octopus drill-holes are easy to distinguish, but other predatory modes such as chipping/smashing are less easy. This means that testing of a second hypothesis, namely, that different predators through their differing strategies will have unequal effects on the prey abalone, could not be tested. The study has several major shortconings, but offers some insight into the dynamics of restoration strategy involved in reintroduction of a depleted species into previously occupied but now vacant habitat. Hofmeister et al. 2018 Hydrobiologia 813: 123.

NOTE each stocking consists of 1200 small (3.2cm shell length) and 400 large (5.6cm) individuals, all tagged. Sites are located about 2km distance from one another and, by selecting the control site to be at the northernmost end of a linear array, it is almost 4km distant from the furthest treatment site. This seems unusually distant for a control to be sited. The authors actually describe the sites as being 1km apart, which seems still too far. Perhaps a middle position for the control would have given the reader more confidence

NOTE this is questionable because one of the hypotheses to be tested is that predator density will increase following the stocking, but how can density increase when the predators have been removed? And why were the removals continued throughout the study? It seems counterintuitive to the aims of the project. In truth, removals were only partial at best: fishes were obviously exempt, lobsters were not touched at all, and octopuses only desultorily. Of the 4 main predatory organisms, only whelks (Kellet's) appear to have been effectively removed

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