Octopus Abundance Research Articles

Sea-surface temperatures predict targeted visual surveys of octopus abundance

In upwelling systems around the world, octopus abundance is forecast by marine productivity linked to upwelling strength, often indicated by sea-surface temperatures. Climate change may disrupt populations of marine animals that are linked to such temperature-dependent events. We analysed the relationship of the abundance of giant Pacific octopuses (Enteroctopus dofleini) to Gulf of Alaska and Washington State water temperatures. Abundance was measured in targeted visual surveys in Prince William Sound, Alaska, over the period 1995–2016 and from REEF.org diver surveys in Washington State from 2003 to 2019. Octopus counts from both survey programs had significant negative correlations with water temperatures over the previous 2.5–4 years. Water temperature accounted for from 0.41 to 0.71 of the variance (R2) in octopus abundance in eastern Gulf of Alaska waters located in ocean currents up-stream of the survey areas, and up to 0.81 of the variance in Washington State waters. These negative correlations provide a possible predictive index for octopus abundance as measured by targeted visual surveys. These methods may be useful tools in management of octopuses and indicate impacts of climate change on North Pacific coastal marine ecosystems.

Design of experimental food patches to measure foraging intensity for octopus: a case study with the giant Pacific octopusEnteroctopus dofleini

ABSTRACTIn a study of the foraging behaviour of the giant Pacific octopus Enteroctopus dofleini, we designed two types of experimental food patches to measure habitat preferences and perceptions of predation risk. The first patch successfully measured giving-up densities (GUDs), confirmed by octopus prey presence and higher foraging at sites with historically greater octopus presence. However, nontarget foragers also foraged on these experimental food patches. Our second floating patch design successfully excluded nontarget species from subtidal patches, and from intertidal patches at high tide, but allowed for foraging by E. dofleini. The second design successfully measured GUDs and suggested that octopus preferred foraging in a subtidal habitat compared to an intertidal habitat. We ascribe the higher GUD in the intertidal habitat to its higher predation risk relative to the subtidal habitat. The second patch design seems well suited for E. dofleini and, in conjunction with a camera system, could be used to provide behavioural indicators of the octopus's abundance, perceptions of habitat quality and predation risk.

The den ecology and the effects of fishing pressure on the distribution of Octopus cyanea (Octopodidae: Mollusca) in Rodrigues lagoon, Rodrigues, Mauritius

ABSTRACT Octopus cyanea is a species of particular economic importance for coastal regions in the tropical Indo-Pacific, including the Mauritian island of Rodrigues. At present, little is known about their habitat preferences and how this may impact on their abundance from fishing pressure. This study aimed to investigate how the abundance of this octopus and their potential den sites differed between three areas of Rodrigues lagoon, Mauritius which were subjected to differing levels of fishing pressure and in which other marine species competed for the same space. A series of surveys over two months was conducted to measure octopus numbers, counted holes and abundance of selected invertebrates in 1000 m2 belt transects, In total, 503 holes were counted that would be suitable for octopuses, and 17 octopuses were observed within the holes. A highly fished lagoon area, contained the most potential den holes. The other organisms found in the counted holes were fish, including eels, urchins and holothurians. I attribute the seemingly low abundance of octopus compared to previous surveys overall to the time of year and the lack of suitable habitat within these areas. Octopus abundance throughout the lagoon is low despite it being within a Marine Protected Area and does not follow the expected patterns of abundance when subjected to differing levels of fishing pressure, that is, it was expected that more would be found in the best protected area. Application of improved knowledge of octopus biology and habitat preferences could provide better management plans for their protection.

Drivers of octopus abundance and density in an anchialine lake: A 30 year comparison

Anchialine systems are isolated from the sea and often support species' populations distinct from their marine counterparts. Sweetings Pond, an anchialine lake on the island of Eleuthera in The Bahamas was identified as a site of high Caribbean reef octopus, Octopus briareus (Robson, 1929) density, relative to coastal populations. However, observed deterioration in local benthic habitat and increased anthropogenic influence over the last 30 years imply that this octopus population may have undergone density and distribution shifts in response to these changing conditions. Here, we assess the system wide octopus density to provide an updated estimate. We hypothesize that despite depressed habitat availability in the 1980s, it will now support octopus densities less than historical estimates because of increasing human impact on the system. Drivers of abundance were also modelled, testing ecological hypotheses of the relationship between octopus count and prey, habitat coverage, and human disturbance. Octopus briareus were found in 7 of 27 of surveys with a mean survey count of 0.630 ± 1.25 per 900 m2. Octopus density did not vary significantly between sites. Octopus count was predicted to increase with increasing cover of calcareous rubble and the density of a preferred prey species, and intriguingly, counts decreased as a function of natural den abundance. System wide octopus density was comparable to earlier studies from the 1980s (1982 = 717.38 per km2; 1983 = 282.59 per km2; 2019 = 643.81 per km2) with no significant difference between years. Given the ecosystem's unique and closed ecological community and the population dynamics and distribution drivers we present, Sweetings Pond has the potential to act as a ‘natural laboratory’ to explore further questions about marine insular systems and their influence on species populations in terms of ecological and behavioural change.

Abundance prediction and influence of environmental parameters in the abundance of Octopus (Octopus vulgaris Cuvier, 1797) in the Gulf of Cadiz

Understanding the processes that influence octopus abundance is important in order to manage the fishing grounds and offer advice on the exploitation of this important resource. Fluctuations in abundance of exploited stocks may be due to a great variety of factors. However, in short-lived animals such as cephalopods, in which abundance depends on strength of the recruitment, it is well known that population abundance is highly influenced by the environmental conditions.In this study we investigated the relationship between octopus (Octopus vulgaris) catches from the fishery located in the area off the Gulf of Cadiz (Spanish South Atlantic Region) and several hydrographic and oceanographic parameters such as sea surface temperature, surface chlorophyll-a, inorganic surface turbidity and climatic indicators such as the NAO index, rain, WeMoi Index, AMO index and or Guadalquivir River discharges. In addition, a recruitment index was obtained from fishery-independent surveys, which was also used to investigate its effect on annual catches. Results revealed that abundance of octopus showed a significant negative relationship with rain in the previous year as well as a positive effect of the recruitment index.We have obtained a model using the rain and the recruit index to forecast the catches.This model explained a high percentage of variation in annual catches and was used to forecast the next year’s catch providing results within the expected confidence intervals. This represents a potentially useful tool to guide fishery managers since no assessment of the species is currently conducted in the area.

Fine-scale habitat partitioning facilitates sympatry between two octopus species in a shallow Florida lagoon

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 609:151-161 (2019) - DOI: https://doi.org/10.3354/meps12845 Fine-scale habitat partitioning facilitates sympatry between two octopus species in a shallow Florida lagoon Chelsea O. Bennice1,*, Andrew P. Rayburn2, William R. Brooks1, Roger T. Hanlon3 1Florida Atlantic University, Boca Raton, FL 33431, USA 2Independent Consulting Ecologist, Golden, CO 80401, USA 3Marine Biological Laboratory, Woods Hole, MA 02543, USA *Corresponding author: cbennice@fau.edu ABSTRACT: Species coexistence is a critical determinant of biodiversity and community structure, yet resource partitioning mechanisms that facilitate coexistence remain understudied for many taxa, including cephalopods. Octopus vulgaris and Macrotritopus defilippi cohabit a shallow-water lagoon in South Florida. Temporal and spatial distribution as well as habitat association were examined as potential resource partitioning mechanisms to facilitate coexistence between these species. Methods included in situ visual observations, marking locations of octopus-occupied dens, and photoquadrats of octopus dens and surrounding habitats. Den locations were marked year-round for 3 yr to determine consistency of spatial distribution and temporal trends. Octopus abundance was highest during spring and lowest during fall for both species, indicating that temporal partitioning (in terms of seasonality) is likely not a mechanism of coexistence. O. vulgaris and M. defilippi had the highest densities of occupied dens in the same general shallow areas of the lagoon; thus there was no evidence of spatial partitioning. Although octopuses spatially overlapped in the same general area, multiple substrate categories were available, and each species’ den and surrounding habitat was associated with different substrates. O. vulgaris was associated mostly with hard bottom and inhabited hard-structured dens while M. defilippi was associated with soft sandy bottom and inhabited burrows in the sand as dens. Fine-scale habitat partitioning is made possible by this lagoon’s heterogeneous microenvironments, which aid in explaining coexistence of these 2 octopus species. KEY WORDS: Resource partitioning · Cephalopods · Spatial distribution · Seasonal abundance · Den ecology · Habitat heterogeneity Full text in pdf format PreviousNextCite this article as: Bennice CO, Rayburn AP, Brooks WR, Hanlon RT (2019) Fine-scale habitat partitioning facilitates sympatry between two octopus species in a shallow Florida lagoon. Mar Ecol Prog Ser 609:151-161. https://doi.org/10.3354/meps12845 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 609. Online publication date: January 17, 2019 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2019 Inter-Research.

Diversity in the diet of the predator Octopus cyanea in the coral reef system of Moorea, French Polynesia

ABSTRACTThis study examines interactions among behavioural and environmental influences on individual octopus diet. Octopus cyanea were surveyed in July 2014 in Moorea, French Polynesia (17°29ʹ S, 149°50ʹ W) and the diversity of their diets – revealed by prey species remains – were combined with data on octopus personality, habitat complexity, prey size and octopus density to test hypotheses on three different levels: individuals, study sites and population. Diets were more diverse for octopuses that exhibited more approach behaviours during a disturbance test of personality, than for those that were more withdrawn. Octopus diets were more diverse within areas of greater substrate type diversity, suggesting that on a local scale, substrate type diversity influences biodiversity. Octopus diets were also more diverse when prey were smaller and where octopuses were more abundant, suggesting an effect of prey abundance (or conversely of competition among octopuses). For the Moorea population overall, dietary diversity was high (richness = 64 taxa of Bivalvia, Crustacea, and Gastropoda), with low dominance. This study confirms that to better understand the variation in octopus diet we should look from the individuals to populations, taking into account environmental and behavioural factors, such as individual personality, habitat diversity, prey sizes (energy) and octopus abundance.

Sea-surface temperature used to predict the relative density of giant Pacific octopuses (Enteroctopus dofleini) in intertidal habitats of Prince William Sound, Alaska

Productivity linked to upwelling strength is an important environmental factor affecting the production and dynamics of octopus populations. This often takes the form of a negative relationship between octopus abundance and sea-surface temperatures (SST). Enteroctopus dofleini (giant Pacific octopuses) is caught as by-catch in several fisheries, but management for octopuses is data-poor. Visual surveys (in Prince William Sound (PWS) and Puget Sound) showed significant negative correlations of octopus counts with winter SST over the previous 30 months in the waters of eastern Gulf of Alaska, as expected on the basis of life-history parameters. In PWS, local octopus densities varied more than six-fold during the study, and correlations with SST accounted for 48–61% of the variance in counts. Octopus by-catch datasets were not similarly significantly correlated with SST. The negative correlation with SST suggests that octopus populations are influenced by factors regulating marine productivity during larval stages of life history far from the site of recruitment to benthic habitats. Targeted visual surveys for E. dofleini may be more predictable than by-catch statistics, and may be better estimators of variation in octopus abundance.

Environmental and fishery-driven dynamics of the common octopus (Octopus vulgaris) based on time-series analyses from leeward Algarve, southern Portugal

Abstract Dynamic factor analysis was used to explore monthly landings per unit effort (LPUE) series of Octopus vulgaris and environmental variables recorded in the southwest Iberian Peninsula, south Portugal. Despite the large fluctuations in the octopus abundance series, results showed a strong aggregation pattern for the last 3 months of the year, possibly related to the input of new recruits to the fishery. The calculated common trend for the 12 months time-series presented significant correlations with autumn rainfall of the previous year (lag − 1), particularly for the October, November, and December series. Other important correlations were found for the Western Mediterranean Oscillation index (lag − 1), Ekman transport, summer river run-off (lag − 1), horizontal and vertical component of windstress, among others. The main trend describes a moderate steady increase in LPUE during the last 10 years, suggesting that octopus abundance has increased from 1990 to 2010. The strong correlations of the monthly octopus LPUE series, together with the annual life cycle, suggest that after environmentally controlled recruitment, population dynamics is largely fishery driven, resulting in strong seasonality in the landings.

Stock Assessment of the Common Octopus (<i>Octopus vulgaris</i>) in Monastir; the Mid-eastern Coast of Tunisia

The common octopus, ( Octopus vulgaris Cuvier, 1797) is widely distributed through the world. It represents an important resource with high economic value. It is exploited by trawl and by other gears such as trammel net, pots and it is also captured by diving. Although the multitude of assessment techniques, few fisheries cephalopods were well managed. In Tunisia, common octopus ( Octopus vulgaris ) is captured particularly in southern coast and the Sahel defined by three regions (Mahdia, Sousse and Monastir). Our study constitutes the first assessment stock in Monastir situated in the mid of the eastern coasts of Tunisia. Using surplus production models, an under fishing state of Octopus in the East of Tunisia is shown. This study confirms also the necessity of the incorporation of environmental parameters for a better explanation of the variability of common octopus abundance and the importance of these results in the assessment and management of this species.

Wavelet analysis of correlation among Canary Islands octopus captures per unit effort, sea-surface temperatures and the North Atlantic Oscillation

Short-term fluctuations in the octopus catches off the Canary Islands have been attributed to changes in the sea surface temperature (SST) and the North Atlantic Oscillation (NAO) pattern. These results have been found using stationarity assumptions. However, the behavior of environmental systems is not always linear, and environmental time series do not always satisfy the statistical property of stationarity. Wavelet spectral analysis is a methodology which can deal with non-linear, non-stationary and noisy time series. Cross wavelet analysis (wavelet coherence) is applied to investigate the environmental effects (SST, NAO) on octopus abundance fluctuations measured as capture per unit of effort (CPUE) from 1989 to 2007 in the waters of the Canary Islands. A slightly positive correlation exists between NAO and CPUE at lags and leads of a few months. Additionally, a good relationship between SST and CPUE exists on the same seasonal scale, but there is a relatively weak relationship between SST anomalies and the NAO. When the analysis is extended to the interannual scale, the wavelet coherence identifies a statistically significant relationship between CPUE and NAO, but this does not happen when the wavelet coherence between CPUE and SST is computed. These results suggest that fluctuations in octopus catches could be the result of SST fluctuations but in synergy with other unknown environmental variables which are also affected by the NAO pattern.

The role of climatic variability on the short-term fluctuations of octopus captures at the Canary Islands

The effect of temperature on the common octopus life cycle has been well studied. However, how other climatic patterns affect them is poorly understood. The present work emphasises the importance of the temperature on common octopus catches by the small-scale trap fishery off the Canary Islands, and also highlights the effect of the North Atlantic Oscillation (NAO) pattern. As well as an inverse and significant correlation between octopus abundance (measured as CPUE) and Sea Surface Temperature (SST), a direct relationship between abundance and NAO, off the Canary Archipelago, is reported. Using a linear model (lm) with a stepwise procedure, SST is found to be the most important and significant variable in autumn, accounting for 34.21%. Meanwhile, the NAO became more important in spring with 28.64% and a 31.13% of the explained variance in autumn.

Comparison of Tehuelche octopus ( Octopus tehuelchus) abundance between an open-access fishing ground and a marine protected area: Evidence from a direct development species

Marine protected areas (MPAs) have been established during the last few decades for conservation and management purposes. Most studies showing a positive effect of MPAs on abundance or size have focused on species exhibiting a planktonic larval stage. In this study, the impact of an MPA on the local abundance of a direct development species, the Tehuelche octopus Octopus tehuelchus, is evaluated. Octopus abundance (catch per unit of effort) was compared between a traditional fishing ground (El Fuerte) and an MPA in northern Patagonia (Argentina), during one spawning/recruitment period (August–October; pre-fishing) and during the following fishing season (January–April). Abundance in the MPA was twice as high as in El Fuerte during the fishing season, but not during the pre-fishing season. Females were more abundant than males at both sites. Contrary to expectations, mean octopus weight was lower in the MPA than in El Fuerte, which can be explained by higher abundance of recruits. In fact, the ratio recruit/spawner was three times higher in the MPA than in El Fuerte. Removal of brooding females during the brooding season in El Fuerte may affect the survival of the embryos, since females provide parental care. More information on the wide diversity of life history of marine species is needed since the current literature on MPAs is strongly biased towards species exhibiting planktonic stages.

Abundance of <i>Octopus vulgaris</i> on soft sediment

SUMMARY: Until now the distribution and abundance of Octopus vulgaris had been investigated in the main fishing areas of the species only by fishing surveys. The catching efficiency of fishing gear is variable and depends on several aspects of the animal’s behaviour and life history as well as on the type of the gear and the environmental characteristics of the area surveyed. A good alternative for studying the abundance of octopus is by visual census. The population density of O. vulgaris was measured by visual census with scuba diving. The survey was conducted in coastal areas of Greece and on soft sediment. O. vulgaris density ranged from 0 to 6.88 individuals/1000m 2 and the mean density values of this study were much higher than those mentioned in other papers. Octopus density was significantly associated with season. Densities of octopuses lower than 500 g were higher in coarse sediments than in finer ones. The density of large octopuses (> 500 g) increased with depth. Octopuses larger than 200 g tended to dwell deeper during the period of intense thermocline than during the nothermocline period.

Octopus–red grouper interaction in the exploited ecosystem of the northern continental shelf of Yucatan, Mexico

Octopus ( Octopus maya) and red grouper ( Epinephelus morio) are the most important fisheries resources on the northern continental shelf of Yucatan, Mexico, with annual yields fluctuating between 9000 and 16 000 t. Octopus is an important component of the diet of red grouper, particularly when the abundance of octopus increases during summer and autumn in shallow waters. A previous mass-balanced model using the Ecopath program described the main flows of biomass in this ecosystem, with emphasis on the commercially important stocks. In this paper, a dynamic structured model of exploited ecosystems, Ecosim, is used to simulate changes in vulnerability of octopus to predation by the red grouper under three scenarios of fishing mortality ( F): (1) F low and constant; (2) gradual increments in F reflecting historical development of the octopus fishery; and (3) high values of F representing the current state of the fishery. A fourth scenario is also presented, based on scenario 2, to observe biomass patterns of other groups. For all scenarios, when vulnerability of the octopus to predation was reduced, their biomass pattern was inverse to that when their vulnerability to predation increased. A similar behavior was found at high levels of vulnerability when octopus were submitted to high fishing effort. The impact of the combined effect of changes in vulnerability with fishing intensity suggests the presence of important compensatory mechanisms tending to maintain a thermodynamic stability, where growth efficiency and consumption play important roles. Even when fishing intensity appears to produce larger impact on the octopus biomass, vulnerability has an important role when it is reduced and when the stock is submitted to very high levels of exploitation. After simulations, the biomasses of octopus and red grouper exhibited a similar picture to historical catch trends, suggesting that Ecosim could provide useful guidance for fisheries managers.

Effects of octopus predation on motile invertebrates in a rocky subtidal community

Octopus birnaculatus, a common member of intertidal and subtidal communities in southern California, consumes many motile benthic invertebrate species, including snails, chitons, h p e t s , bivalves, and crustaceans. An analysis of octopus d d holes in empty snail shells indicates that 0. bimaculatus is a major s n d predator in the community. The addition of marked snails to a natural reef with unmanipulated octopus densities demonstrated that octopuses can quickly reduce s n d abundances, consuming 24 % of the available snails within 24 d. During 5 yr at 1 site, octopus abundance declined from 40 to 8 octopuses, while total prey abundance increased from 16 to 80 ind m-'. A second site experienced a similar drop in octopus density and increase in prey density over 3 yr. At both sites, snails and hermit crabs showed the greatest increases. Sedentary grazers, bivalves, and crabs and shrimps occurred at low densities throughout, possibly because the abundances of these preferred prey were depressed by octopus predation even during years of low octopus density. In splte of the strong negative association at the 2 sltes between octopus and prey over time, for a single time penod at 15 different s ~ t e s prey densities were not negatively correlated w t h the densities of their predators. However, octopus densities were much higher when they appeared to reduce the abundances of their prey than when the 15 different sites were sampled. I conclude that octopus predation can dramatically reduce prey densities when octopuses are unusually common, but that in most years the abundance of octopuses 1s too low to disrupt the basic patterns of prey abundance that result from other processes. The hghest prey species richness and diversity at the 2 study sites occurred during years of lowest octopus densities. Species richness, chversity and evenness of the prey assemblage were not correlated with octopus, lobster or predatory gastropod abundances at the 15 different locations; when the effects of habitat structure were held constant by partial correlation, seastar abundance was negatively correlated with species nchness and diversity. The relation between predation and species chversity suggests that, when predation is effective in this assemblage, it decreases diversity.

The Plague of Octopus on the South Coast, and its effect on the Crab and Lobster Fisheries.

Until the spring of 1899 the true or common octopus (Octopus vulgaris, L.) had been comparatively rare in the neighbourhood of Plymouth during the past ten or twelve years—i.e. since the opening of the Plymouth Laboratory in 1888. Specimens could only be obtained for the aquarium at long intervals, in spite of the tempting inducements offered to fishermen. As much as ten shillings has more than once been given to fishermen for a specimen of this voracious mollusk. On the other hand, the smaller and less powerful octopod known as Eledone cirrosa was almost always obtainable, and the octopus tank in the aquarium was rarely devoid of several specimens.In the early part of last year (1899) the situation began to change, and we were for the first time able to keep the tank supplied with a number of true octopus, since which date there has been no difficulty in procuring an unlimited number of specimens, either from the professional fishermen or in the ordinary course of our own fishing operations.We noticed this increase in the abundance of octopus before there was any means of judging whether it was a purely local phenomenon, or was observable over a wider area. The first specimens were brought to us in January, and from May onwards they were obtained in increasing abundance. Early in the same year, however (though I have no exact record of the date), a visitor from the Channel Islands informed me that the increase of octopus in those islands was so great as to have already caused much damage to the shell fisheries there, since the octopus entered the pots of the fishermen, and destroyed the crabs and lobsters which had been caught.