Feeding & growth
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  Growth
  The section on feeding & growth is divided into growth, considered here, and DIETS, PREY CAPTURE, and PREY HANDLING & DRILLING, considered in other sections. Growth of octopuses and squids are considered in separate subsections below
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Octopuses

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Research study 1
 

photograph of octopus Enteroctopus dolfleini at the Seaside Aquarium, Oregon
Enteroctopus dofleini
is the largest octopus species in the world.   Its average live mass at maturity is 16kg at just under 3yr of age.  However, much larger specimens have been collected for aquarium display (25-3kg live mass), and anecdotal records include individuals of 96-232kg, collected in Haida Gwaii, British Columbia. 

 

 

 

 

Enteroctopus dolfleini of about 3m tentacle spread crawling
in a tank at the Seaside Aquarium, Oregon

 
Research study 2
 

Growth of tagged octopuses1 Enteroctopus dofleini in shallow-water (2-15m) populations on the west coast of Vancouver Island, British Columbia is highly seasonal (see graph on Left).  A period2 of fast growth is associated with warmer surface-water temperatures in summer (12-13oC), while a graph showing growth of octopuses Enteroctopus dolfleini on the west coast of Vancouver Island, British Columbiaslow period is associated with cooler temperatures in late winter/spring (7-8oC).  There is no reliable way to age3 an octopus.  Other results show that there is no difference in growth rates between sexes or different locations. graph showing crab availability for octopuses on the west coast of Vancouver Island, British Columbia at different times of year

Low temperatures in winter/spring affect not just feeding rates of the octopuses, but also availability of prey in the habitat.  For example, trapping data on crabs Cancer productus suggest that their availability to octopuses may be low in winter, also contributing to the low growth rate at that time (see graph on Right). The authors note that their study is one of the first showing detailed growth in an octopus species in the field.  Robinson & Hartwick 1986 J Zool, Lond, Lond 209: 559.

NOTE1  211 octopuses are tagged and 87 are recaptured (41%), some individuals up to 8 times.  Size range is 2-20kg with a 3:1 ratio of females to males

NOTE2  note that individuals captured more often have proportionally greater representation in the graph

NOTE3  of the potentially “ageable” hard parts in an octopus, the beak does display growth lines but these apparently do not correlate with age. The statoliths (concretions of calcium carbonate within the balance organs, or statocysts, that grow in size as the animal grows) are soft and chalk-like and do not display growth lines. The situation in squids, however, may be different, as squids Rossia pacifica have been aged by counts of lines in the statoliths (see Research Study 7 below)

 
Research study 3
 

graph showing size of Octopus bimaculoides and reproductive state at different agesphotograph of Octopus bimaculoides courtesy Roger Hanlon, Woods Hole Marine Laboratory, MassachusettsGrowth of octopuses Octopus bimaculoides in laboratory culture in Galveston Laboratory, Texas is shown in the graph. Males develop an hectocotylus by about 5mo from hatching (160d), mate at 8mo (320d), and the females begin laying eggs at about 12.5mo (380d).  An additional 3mo of brooding gives a life-span of about 15mo in the laboratory. Males appear to live at least as long as the females.  Before the experiment was terminated after 404d the octopuses had grown from a hatchling live mass of 0.07g to a mean size of 619g.  From their data the authors estimate that in the waters of Santa Barbara eggs would hatch in mid-summer and, with the lower temperatures over autumn and winter (12-15oC), may not be large enough to spawn until the following summer.  Thus, the estimated life span at the northern part of O. bimaculoides’ range would be about 2yr.  However, in the warmer waters at the southern-most limit of distribution, life spans may be closer to 1yr.  Forsythe & Hanlon 1988 Mar Biol 98: 369. Photo of Octopus bimaculoides courtesy Roger Hanlon, Woods Hole Marine Laboratory, Massachusetts.

NOTE  this intertidal/subtidal southern-California species is distributed from Santa Barbara, California to San Quintin, Baja California

NOTE  eggs collected near Los Angeles are divided into 2 portions, and cultured at 18oC and 23oC.  Only data for the former culture are shown here

 
Research study 4
 

graph of live mass of various octopuses and squids with ageIs large size in cephalopods such as Enteroctopus dofleini a product of longer lifespan? or of faster growth?  As for the first question, a plot of size against age for 17 species in 7 families of coleoid cephalopods does show a significant relationship (see graph on Left).  However, when size is plotted graph showing live masses against age in "degree days" for various cephalopodsagainst a different expression of age, that is, “physiological age”, an even better relationship is obtained (see graph on Right).  “Physiological age” is defined by the authors in “degree days”, that is, average temperature in degrees Celsius times days of age, thus taking into account the effect of different water temperatures during development.  Species growing in colder water generally take longer to mature and, thus, their final sizes are greater.  As for the second question, the authors of the study could find no evidence to support the idea that large size in cephalopods results from faster growth.  Wood & O’Dor  2000 Mar Biol 136: 91.

NOTE  included in the graphs are Family Octopodidae (octopuses), Family Sepiidae (cuttlefishes), Families Idiosepiidae and Sepiolidae (sepiolids), Family Loliginidae (loligo squids), Family Ommastrephidae (omastrephid squids), and Family Thysanoteuthidae (thysanoteuthid squids).  Another SubClass, Nautiloidea, which includes several species of shelled Nautilus, is not represented in these presentations. Their inclusion, presumably owing to the large shell, skews the relationships considerably

 
Research study 5
 

photograph of a dead octopus being eaten by a sunflower star Pycnopodia helianthoidesSenescence before dying occurs as a natural process in octopuses.  In males it begins after mating, and in females while brooding and after the eggs hatch.  Typical symptoms include loss of appetite, retraction of skin around the eyes (through shrinking of the rest of the body from lack of food), uncoordinated and undirected behaviour, and appearance of white skin lesions.  The authors note that senescent individuals exhibiting these characters and behaviours in the wild will quickly attract the attention of predators.  In Enteroctopus dofleini, senescence may last a month or more in males, and longer in females.  Anderson et al. 2002 J Applied Anim Welfare Sci 5: 275.

 


Post-senescent (actually, dead) octopus Enteroctopus dolfleini
being eaten by a sunflower star Pycnopodia helianthoides 0.5X

 
Research study 6
 

graph showing live mass/mantle length relationship in octopuses Octopus bimaculatus in the Gulf of CaliforniaStudy on growth of soft-bodied organsisms, such as octopuses, in the field is hampered by uncertainty over the relationship between size (mass, length) and age.  For this reason the old tried-and-true “indirect” method of length-frequency analysis is not usually recommended in fisheries studies on octopuses, yet it is a simple low-cost, easy-to-apply technique that may often be the only alternative in areas where facilities or knowledge of other techniques are lacking.  To shed light on the matter, a consortium of length-frequency histograms for octopuses Octopus bimaculatus during a 12mo period in the Gulf of California Mexican researchers compares growth-rate data for Octopus bimaculatus in Bahia de Los Angeles, Gulf of California obtained from length-frequency analysis, with results from several other growth models widely used in fisheries management.  First, the researchers are able to confirm the reliability of mantle length in octopuses as a measure of size (see graph on Left; correlation R2 = 0.08, P = <0.01).  They then generate length-frequency histograms for a 12mo period in which they follow a single cohort  of octopuses through reproductive maturity, and a second F2 cohort identifiable in August (see histograms on Right).  The authors note that this August cohort presumably derives from major egg-laying that they observed 2mo earlier in June (24oC).    The authors seem to think that the overlap in generations seen in Aug-Sept may reflect an “alternation-of-generation” model, in which a large generation alternates with a small generation, but this is not clear in the data.  What the reader sees is a species with an approximate 1.3yr life cycle in which growth predictably declines in summer leading to death in autumn, with the next generation becoming evident in autumn/winter.  The authors note that the growth model described here agrees well with predictions from other fisheries models that also assume a declining growth rate with increasing age (e.g., Gompertz, von Bertalanffy, and logistic).  López-Rocha et al. 2012 J Shellf Res 31 (4): 1173.

NOTE  field studies on cephalopods in which direct methods are used, such as growth lines in statoliths in squids and beaks in octopuses, have also been at least partially successful

 
 

Squids

 
Research study 1
 

graph comparing growth rates in squids Doryteuthis opalescens from statolith lines and mantle lengthsApart from actually keeping squids Doryteuthis opalescens in captivity to assess growth, something that is technically difficult and yielding results that are difficult to compare with wild animals, there are 2 methods of estimating age: modal-size frequencies (dorsal-mantle length) and statolith-ring counts. Results from these methods are compared in a study in Monterey Bay, California, with quite good drawing of statolith of a squid Doryteuthis opalescens showing growth linesagreement The data show that Doryteuthis reaches adult size in about 2yr.  Spratt 1978 p.35 In, Biological, oceanographic, and acoustic aspects of the market squid, Doryteuthis (Loligo) opalescens Berry 185pp. State of California, Dept Fish Game, Fish Bull 169.

NOTE  the author is able to “calibrate” the rings to some extent by examining statoliths from squids cultured to 2mo of age by other researchers.  Thus, 55mm mantle-length individuals have about 36 rings in their statoliths

 
Research study 2
 

photograph of Rossia pacifica courtesy Roland Anderson and Seattle AquariumCollections of stubby squids Rossia pacifica at Burrows Bay, Washington indicate the presence of 2 overlapping generations.  Growth in laboratory culture of 7 specimens collected in summer 1983 is shown in the graph. These animals died in spring of the following year (1984) but one pair out of the 7produced 2 batches of eggs, leading to the presence of hatchlings by autumn of that year.  These data indicate a life-span of about 2yr.  Summers 1985 Vie Milieu 35: 249. Photo of Rossia pacifica courtesy Roland Anderson and Seattle Aquarium.

NOTE  temperatures of 6-13oC

 
Research study 3
 

Counts of daily growth lines in statoliths of reproductively mature (45-90mm mantle length) stubby squids Rossia pacifica in the Bering Sea give an estimated life-span of only 4-5mo.  This is in marked contrast to estimates of 2yr obtained from animals raised in laboratory culture Note also that the laboratory-cultured animals in Research Study 2 above reach a maximum of only about 40mm mantle length. So, do the differences relate to culture conditions, to growth of field squids at possibly different temperatures than used in culture, or to the reliability of statolith growth-line counts? Arkhipkin 1995 Sarsia 80: 237.

 
Research study 4
 

drawings of suitable fish and crustacean foods for hatchling squids Doryteuthis opalescens in culturegraph showing growth of squids Doryteuthis opalescents from hatchingAfter a decade of attempts, and with progressive modification to rearing facilities including improved water quality, greater rearing space, and provision of a greater diversity of living foods, researchers at the University of Texas are able to culture west-coast squids Doryteuthis opalescens from egg to reproductive adults.  Hatchlings of about 3mm mantle length are not strong swimmers, but provision of ample living food of appropriate size, including small crustaceans, fish eggs and, later, larval fishes (the drawings on the Left are to scale), supports good growth (see graph graph comparing growth rates in several studies of growth in squids Doryteuthis opalescenson Right). The hatchlings are positively phototactic and swim at the water furface.  After about 190d in culture at 15oC mating occurs in head-to-head fashion. Females mate with more than one male.  Egg masses are laid from Day 196 to Day 238 and a number of these later hatch.  Growth rates in laboratory culture are much faster than those recorded in other field studies (see graph lower Right). Yang et al. 1986 Fish Bull 84: 771; see also Yang et al. 1983 Aquaculture 31: 77.

NOTE  freshly laid egg masses are obtained from spawning grounds in Monterey Bay, California

 
Research study 5
 

graph comparing growth of squids Doryteuthis opalescens from different studies using statolith-ring dataAnother estimate of age in squids Doryteuthis opalescens uses ring counts of statoliths (see Research Study 1 above) and compares the results with growth data from squids in culture.  The 2 sets of data show good agreement (see graph on Left) and indicate that reproductive maturity is attained in less than a year in the field, just as it is in culture. The author remarks that differences in size evident in the graph may owe to the propensity of D. opalescens to mature precociously in culture.  Jackson 1994 Bull Mar Sci 54: 554.

NOTE  statoliths are obtained from reproductively mature squids purchased at a fish market in Moss Landing, California and captured near Monterey Point the previous evening.  After removal and drying, the statoliths are mounted in plastic cement, and ground and polished by hand, respectively, on carborundum and wet felt with alumina powder.  The data on growth in culture are from Yang et al. 1986 Fish Bull 84: 771 (see Research Study 4 above).

 
Research study 6
 

graph showing growth of squids Doryteuthis opalescens in cultureBy chance, a 2-yr study on population structure of squids Doryteuthis opalescens in the Channel Islands, California coincided with one of the strongest El Niño events ever recorded (1997-98), followed by record cool La Niña conditions commencing in summer 1998.  The researchers use statolith increments to determine age of sub-sections of the population.  The validity of the statolith-increment method for estimating age in squids is confirmed by data from hatchlings reared in the laboratory for 54d. Results from field sampling show that the oldest males and females are 257 and 225d, respectively, with no distinct hatching period being discernible.  Squids that experience an El Niño grow slower and end up smaller than ones that experience La Niña.  The authors suggest that the metabolic responsiveness of squids (“live fast, die young”) make them useful “ecosystem recorders” for general monitoring of effects of oceanographic conditions.  Jackson & Domeier 2003 Mar Biol 142: 925.

NOTE  mean temperatures in January and August 1998 are 21-24% higher than temperatures on comparable dates in 1999

 
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