Learn About Octopuses & Relatives: Predators

photographs of 2-spot octopus Octopus bimaculatus infested with leech ectoparasite Stibarobdella mooreiLeeches suck the blood of their hosts, but of course are not predators. Still, a report of infestation of 2-spot octopuses Octopus bimaculatus in the Gulf of California with leeches Stibarobdella moorei is of interest, if only for the high incidence of infection and for its occurrence ectoparasitically on octopuses at all. The species S. moorei is more commonly known from sharks and rays, and its presence on octopuses of any kind is apparently a first record. The extent of infestation of a population of octopuses in Bahia de los Angeles is impressive, with 92% of 61 individuals being infested, with a mean of 13 leeches being found on each. No information is available on the biology of the parasite, especially whether they find the thin, blue hemolymph of the mollusc to be a satisfactory alternative to rich vertebrate blood. The authors do not comment on whether any of the parasites appear well-fed or were interrupted in their feeding; certainly, the ones photographed by the authors seem thin enough to suggest that perhaps their presence on the octopuses is only temporary. Lopez-Peraza et al. 2017 Helminthologia 54 (4): 322. Photographs courtesy the authors.

NOTE should your octopus O. bimaculatus be suffering from an infestation of leeches Stibarobdella moorei, the same research group offers a handy suggestion for their removal. Just dip the afflicted octopus in a solution of 0.45ml per liter seawater of clove oil for 2min and stand ready with your collecting net. Lopez-Peraza et al. 2018 Amer Malacol Bull 36 (1): 119.

photograph of SCUBA-diver sitting amongst numerous dead octopuses Enteroctopus dolfleini

Predators of octopuses on this coast include sea otters, seals, sea lions, minks, dogfish sharks, lingcod, wolf eels, salmon, dolphins, cormorants, and several species of whales. There appear to be no invertebrate predators other than other cephalopods, at least not in shallow coastal areas.

Here are a few reports of predation on west-coast octopuses and squids, arranged taxonomically by predator:

Octopuses are harvested for food in many parts of the world. The collection shown here may have been part of past Canadian DFO survey estimates of potential commercial "harvestability" of Enteroctopus dolfleini in British Columbia waters

Research study 1: Cormorants

Examination of regurgitated “morning pellets” by adults and chicks, and reference to literature data on stomach content of 3 species of pelagic cormorants in localities ranging from Alaska to Baja California, discloses only a small dietary reliance on cephalopods (e.g., <1% of 9519 prey items from cormorants in the Farallon Islands, California are cephalopods, likely a mixture of Octopus rubescens and Doryteuthis (Loligo) opalescens). Ainley et al. 1981 The Condor 83: 120.

Research study 2: Sperm whales

drawing of sperm whale courtesy Fiscus et al. 1989 NOAA Tech Rep NMFS 83: 1-18

Stomach-content analyses of a sample of 50 sperm whales Physeter macrocephalus captured by whaling vessels off the coast of Vancouver Island, British Columbia during 1948-49 (B.C. Packers Whaling Station, Quatsino Sound) reveals the presence of squids in about 70% of the stomachs. Two species of squids are listed: the large Moroteuthis robusta (2.5m total length, tentacle tips to mantle tip) and the smaller Gonatus fabricii (max. 0.5m total length). Pike 1950 Progr Rep Fish Res Bd Canada No. 83: 27.

Analyses of stomach contents of 552 sperm whales Physeter macrocephalus harvested at the Del Monte and Golden Gate Whaling Stations, California between 1959-1970 reveal 12 containing beaks of giant squids Architeuthis spp. These particular whales were harvested over the continental slope, but there are many reports of Architeuthis beaks in sperm whales in temperate western zones of the Pacific Ocean. Most of the beaks are dorsal ones, but a matched pair is shown in a photograph in the article. Fiscus & Rice 1974 Calif Fish Game 60: 91.

Stomach contents of 20 sperm whales Physeter macrocephalus caught in the region west of Vancouver Island, British Columbia and processed at the Coal Harbour whaling station in northern Vancouver Island yield several hundred cephalopod beaks, of which 152 are sorted and measured. Thirteen species of cephalopods are identified, of which the giant squid Moroteuthis robusta is found to represent 24% of the total beak number, equivalent fo 62% of the mass of flesh represented by the beaks. Beaks of a smaller squid Berryteuthis magister represent 29% of beak number, equivalent to 18% of total cephalopod flesh consumed by the whales. Clarke & MacLeod 1980 Mar Biol 59: 241.

Examination of stomach contents of 157 sperm whales taken in shore-based commercial harvesting off the coast of California during 1959-1970 reveals the presence of 24 species of cephalopods (based on identification of 2060 beaks representing 1700 individual cephalopods). The most commonly occurring cephalopod prey on the basis of frequency of occurrence in the stomachs is the giant squid Moroteuthis robusta (72%), followed by giant squids Architeuthis spp. (7%), giant octopus Enteroctopus dolfleini (7%), commercial squids Doryteuthis (Loligo) opalescens (<1%), and Humboldt squids Dosidicus gigas (2%). Fiscus et al. 1989 NOAA Tech Rep NMFS 83: 1-18.

A more recent and complete analysis of commercial whaling records from the Coal Harbour whaling station in northern Vancouver Island, British Columbia provide dietary information for 779 sperm whales killed during the period 1963-1967. Giant squids Moroteuthis robusta are the dominant prey for both sexes of whales, along with somewhat lesser amounts of fishes (mostly ragfish and rockfish, but also including dogfish, lamprey, skate, and hake) and a few other squids. Flinn et al. 2002 Mar Mammal Sci 18: 663.

A consortium of researchers from Baja California and southern California has used measurements of stable-isotope ratios to determine trophic relationships between sperm whales Physeter macrocephalus and Humboldt squids Dosidicus gigas. Results show that female and immature male whales appear to feed on squids in the Gulf of California, while adult males do not. The method is non-invasive in that sloughed skin samples of free-ranging whales are all that are needed for analysis, rather than the more commonly used stomach-content or fecal-sample analyses. Ruiz-Cooley et al. 2004 Mar Ecol Progr Ser 277: 275.

NOTE the station operated from 1943-1967. The International Whaling Commission required that a biologist be assigned to the station to collect various types of biological data, including stomach-content analyses. The data analysed by the authors cited here also include fin and sei whales but, as only traces of cephalopod remains are recorded for fin whales and none for sei whales, diets of these whales are not considered here

NOTE the method compares ratios of carbon and nitrogen isotopes (Delta13C and Delta15N) in skin of whales and muscle of squids to determine trophic relationship. Significantly higher values of +1.1% and +2.7% in female and immature whales, respectively, are suggestive of a predator-prey relationship

Research study 3: Seals

An early assessment of diets of harbour seals Phoca richardii by researchers from the US Biological Survey, Washington, DC reveals that individuals in Puget Sound, Washington subsist mainly on fishes (94% by volume), with octopuses (Polypus hongkongensis) and squids comprising most of the remainder (6%). Scheffer & Sperry 1931 J Mammalogy 12 (3): 214.

photograph of a harbour-seal haulout in Barkley Sound, British ColumbiaNOTE the current designation for the harbour seal is Phoca vitulina (Linneaus 1758). There are several subspecies, one of which is Phoca vitulina richardii

NOTE 20% of the 100 stomachs sampled are empty or near empty. Octopuses are found in 4 of 23 stomachs sampled in July, one individual with 4 octopuses; the other, 1 octopus plus beaks of 31 others. Other non-fish prey eaten, but representing only a trace of total diets of the seals, are shrimps, crabs, a snail, and a clam. The designation Polypus hongkongensis is an older synonym used in the past for both species of octopus occuring in Puget Sound: the smaller red octopus Octopus rubescens and the giant Pacific octopus Enteroctopus dolfleini

A recent survey of diets of harbour seals Phoca vitulina in Puget Sound lists the frequency of occurrence of cephalopods as 6-12% in scats collected. Cephalopods listed as being eaten include mainly the Pacific red octopus Octopus rubescens, the armhook squid Berryteuthis magister, the market squid Doryteuthis opalescens, and traces of other squids. The absence of traces of giant octopuses Enteroctopus dofleini in scats in this study is contrary to the 1931 survey and suggests that there may have been misidentification in one or both of the studies. Lance et al. 2012 Mar Ecol Prog Ser 464: 257.

NOTE the original species name given by Linneaus in 1758

NOTE the researchers analyse 1723 scats collected at 23 haul-out areas throughout the San Juan Islands and neighbouring areas of Puget Sound

Examination of stomach contents of 22 dead elephant seals Mirounga angustirostris. in rookeries mostly on San Miguel Island, California revealed the beak remains of 12 different cephalopod species, including several smaller squids, one giant squid Moroteuthis robusta, and 2 different species of octopuses (not identified). Condit & Le Boeuf 1984 J Mamm 65: 281; for world review of seal diets see Klages 1996 Phil Trans: Biol Sci 351: 1045.

Spring and summer stomach lavages of 193 elephant seals at San Miguel Island, California during 1984-1990 reveal the remains of numerous deep-water cephalopod species. Most of the 30 or so cephalopod species identified are epi- or meso-benthic. Much less commonly eaten are shallow-water octopuses, including Octopus rubescens (3% frequency of occurrence in the stomachs), Enteroctopus dolfleini (0.5%), and Octopus bimaculatus (0.5). Antonelis et al. 1994. Chap 11 In, Elephant seals Population ecology, behavior, and physiology (eds. Le Boef & Laws) University of California Press, Berkeley.

NOTE direct intervention of this kind can make the seals sick and, in fact, 6 died, undoubtedly through application of an anaesthetic, ketamine hydrochloride

The photographs below taken at Ogden Point, Victoria, British Columbia in February, 2015 show a harbour seal Phoca vitulina fighting with and eventually killing an octopus Enteroctopus dolfleini that the seal brought to the surface. The entire episode lasts for only a few minutes...it seems to have been a one-sided fight. Photographs courtesy Bob Ianson, Victoria.

photograph 1 in a series of 4 of a harbour seal Phoca vitulina attacking and eventually killing an octopus Enteroctopus dolfleini
photograph 1 in a series of 4 of a harbour seal Phoca vitulina attacking and eventually killing an octopus Enteroctopus dolfleini
photograph 1 in a series of 4 of a harbour seal Phoca vitulina attacking and eventually killing an octopus Enteroctopus dolfleini
photograph 1 in a series of 4 of a harbour seal Phoca vitulina attacking and eventually killing an octopus Enteroctopus dolfleini

Research study 4: Salmon & other fishes

Researchers at the Moss Landing Marine Laboratories, California present results of a large-scale examination of stomach contents of potential fish, seabird, and marine-mammal predators of squids Doryteuthis opalescens in Monterey Bay, California. So many of the species examined, especially fishes, consume Doryteuthis that it would be difficult to rank their importance as predators, but the conclusion of the authors is that, although seasonal in occurrence, squids represent an important component of local food webs (see schematic below Right). Morejohn et al. 1978 p. 67 In, Biological, oceanographic, and acoustic aspects of the market squid, Doryteuthis (Loligo) opalescens Berry 185pp. State of California, Dept Fish Game, Fish Bull 169.schematic showing dominant role played by market squids Doryteuthis opalescens in food webs in Monterey Bay, California

NOTE involving examination of stomach and intestinal contents of 1,928 fishes (86 spp.), 513 seabirds (28 spp.), and 143 marine mammals (9-15 spp.)

NOTE Doryteuthis is found to be eaten by 19 species of fishes, many of economic importance

Examination of stomach contents of 308 chinook salmon Oncorhynhcus tshawytscha from 3 sites in northern California sampled during May-Sept shows that 8% of prey mass is made up of squids Doryteuthis (Loligo) opalescens, along with trace amounts of Octopus rubescens. Hunt et al. 1999 Fish Bull 97: 717.

The main predators of the 2-spotted octopuses Octopus bimaculoides in Catalina Island, California are cabezon, sculpins, moray eels, and marine mammals such as seals and sea lions. In one series of collections octopus prey are found to make up 70% of the gut contents of cabezon Scorpaenichthys marmoratus and sculpins Scorpaena guttata. Ambrose 1988 Malacologia 29: 23.

Research study 5: Sea lions

photograph of Steller sea lions Eumetopias jubatus at Cortez Island, British Columbia

Analysis of many hundreds of scats (feces) of Steller sea lions Eumetopias jubatus collected from haulouts and rookeries in southeast Alaska during 1993-1999 disclose remnants of squids and octopuses (not identified to species) representing between 2-20% frequency of occurrence in the diet. Trites et al. 2007 Fish Bull 105: 234.

Steller sea lions Eumetopias jubatus at Cortez Island, British Columbia