A note on the extremal properties of the morison equation

The extremal properties of the Morison equation F(t) = X′(t) + X(t)|X(t)|; for the force on a circular pile in a fluid, are derived by means of a Slepian model for the behaviour of X(t) around its local maxima. The behaviour of X′(t) near large maxima of X(t) is almost deterministic, and hence there is a simple relation between the maxima in X(t) and those in F(t).     

Burrowing behaviour of the paddle crab Ovalipes catharus (White, 1843) (Brachyura: Portunidae)

The burrowing behaviour of Ovalipes catharus (White, 1843) is described and compared with that of some other burrowing crabs. O. catharus is a fast, back burrowing crab which makes temporary burrows in soft sand. The average time from initiation of burrowing to complete submergence was 6.5 s, there was no difference between males and females but burrowing time increased significantly with crab size. Similar morphological adaptations are required for burrowing and swimming: streamlined body shape, smooth lightly constructed exoskeleton, and flattened legs. O. catharus has a reversed respiratory current like O. guadulpensis but it differs in its burrowing behaviour. Compared to some other crabs, burrowing in O. catharus is rapid.     

Movement patterns of surf-zone fish species in a subtropical marine protected area on the east coast of South Africa

A long-term mark-recapture study was used to assess the movement patterns of surf-zone fishes in the St Lucia Marine Reserve, a marine protected area within the iSimangaliso Wetland Park, a World Heritage Site on the east coast of South Africa. Between 2001 and 2013, 6 613 fish from 71 species, caught by hook and line, were tagged at four sites within and adjacent to a no-take marine sanctuary area. A total of 1 004 (15.2%) recaptures were made from 17 species. The majority (82.4%) of these species displayed station-keeping behaviour, whereas only three were classified as wider-ranging species, and no species with discernible migratory behaviour was observed. Findings for five species with the highest recapture rates, namely Pomadasys furcatus, Epinephelus andersoni, E. marginatus, Dinoperca petersi and Lutjanus rivulatus, are presented in greater detail. Recapture rates ranged from 7% to 50% and time at liberty from 0 to 3 163 days. Individuals of all five species displayed station-keeping behaviour, with the 95th percentile of intra-study-site movements varying between 200 and 1 025 m (linear distance). However, four of the five species also displayed some ranging behaviour and made exploratory excursions ranging from 3.5 to 125 km, in both northerly and southerly directions. The dominance of station-keeping behaviour suggests that the St Lucia Marine Reserve sanctuary zone provides an important refuge for these species, with some export to adjacent areas.     

Individual Variation in the Covering Behaviour of the Shallow Water Sea Urchin Paracentrotus lividus

Abstract. A number of recent field‐based studies have investigated the possible functions of covering behaviour in a range of echinoid species. Some of these have found important relationships between covering behaviour and environmental factors, such as light (in particular, ultra‐violet light) and covering item availability. However, these studies have often shown considerable within‐species variation, thus making covering functionality both within and between species difficult to interpret. The present study experimentally investigates individual variability in covering behaviour characteristics of the sea urchin Paracentrotus lividus (Lamarck). Data were collected bimonthly over a 1‐year period at Lough Hyne, Ireland, by observing P. lividus in outdoor aquaria. Significant variations in covering behaviour characteristics were observed as a function of individual size and mobility but not as a function of sex. A significant relationship between water temperature, mobility and covering behaviour was also found and is hypothesized to have implications for grazing activity in P. lividus. In contrast to previous field studies of P. lividus at Lough Hyne, no summer ‘peak’ in the proportion of individuals covering was observed. However, there was a significant relationship between local solar radiation and ‘time to first cover’. Overall, these data highlight (i) the ecological significance of individual variation in P. lividus covering behaviour and (ii) the importance of investigating multiple factors as potential determinants of echinoid covering behaviour.     

Cheats in a cooperative behaviour? Behavioural differences and breakdown of cooperative behaviour in aggregating,intertidal littorinids (Mollusca)

Cooperative behaviours result in the evolution of cheats: individuals that benefit from the behaviour without sharing the costs required to generate the behaviour. Normally the proportion of cheats is small, as large numbers of cheats will result in the breakdown of the behaviour. Using empirical and simulation‐derived results we demonstrate a cooperative behaviour (aggregation between two species of intertidal snails that provides a benefit by reducing desiccation stress) that shows many characteristics similar to those of a cooperative system with cheats present. In this system, the high rocky shore littorinid Echinolittorina malaccana forages for longer after high water than Echinolittorina radiata, which stops foraging and begins to form aggregations earlier. Nevertheless, E. malaccana, the ‘cheat’ in this system, still occupies an equal proportion of the most beneficial places in aggregations. Computer simulations demonstrate that up to 65% of individual snails can show the behaviour of E. malaccana before the breakdown of this aggregation behaviour begins to occur through aggregations becoming smaller, and hence less effective against desiccation. The high proportion of ‘cheats’ possible in this cooperative behaviour implies that different selective pressures may act on individuals of different species in multi‐species cooperative behaviours to those acting on individuals engaging in single species cooperative behaviours. Social symbiosis appears to be occurring between the species, but it appears that both mutualistic and parasitic symbioses are occurring.     

Exploring composition and behaviour of fish fauna by in situ observations in the Bari Canyon (Southern Adriatic Sea,Central Mediterranean)

Canyons play a fundamental role in enhancing the abundance and diversity of marine organisms through the transport of organic matter and food resources, the presence of complex physical habitats and the absence of trawl fishing. During four baited lander deployments carried out in the Bari Canyon (Southern Adriatic Sea, Central Mediterranean), at depths of 443–788 m, about 43 h of video records were taken, for a total of 619,200 video frames. A total of 12 benthopelagic fish species (five chondrichthyes and seven osteichthyes) were identified. The blackspot seabream (Pagellus bogaraveo) was the most often observed fish species. The depth of 787 m represents a new depth record for this fish in the Adriatic Sea. Groups of up to 40 individuals of P. bogaraveo were attracted to the bait and were shown in single frames. The individuals were observed both exploring the area and feeding actively on the bait. The European conger (Conger conger) was recorded at each deployment. Clear scavenger behaviour was also observed in this teleost fish and in the shark Etmopterus spinax. The shark species Centrophorus granulosus and Hexanchus griseus, which are considered ‘vulnerable’ on the published IUCN Mediterranean Regional Red List, were also recorded but, although attracted by the bait, they were never seen feeding on it. Other fish species, harvested on fishing grounds, such as Merluccius merluccius, Helicolenus dactylopterus and Polyprion americanus, were also recorded. This study represents the first in situ documentation, at very low impact, of the fish fauna in the Bari Canyon, providing new insights into its small scale distribution and behaviour, the first in situ direct observation of the variable feeding behaviour of P. bogaraveo and its gregarious habits, as well as indicating that this canyon could act as a refuge area for species that are vulnerable to fishing on the open slope.     

Summer distribution of the pelagic copepod Centropages aucklandkus in New Zealand waters

The quantitative distribution of Centropages aucklandicus in summer is described. This coastal species, endemic to New Zealand, is found round the whole country except in the north. It has a northern limit coincident with the 19°c isotherm. Possible factors operating to conserve C. aucklandicus in coastal waters, temperature, salinity, food and behaviour, are discussed.     

Distribution,behaviour and photo-identification of Atlantic humpback dolphins Sousa teuszii off Flamingos,Angola

Atlantic humpback dolphins Sousa teuszii are a priority for research due to their restricted geographic range, narrow ecological niche and the paucity of existing information. The distribution and behaviour of S. teuszii off Flamingos, southern Angola, was investigated during summer and winter 2008 using boat- and shore-based surveys. In all, 71 S. teuszii sightings were recorded, ranging from one to eight animals. Sousa teuszii inhabited shallow, nearshore waters throughout the region, with the exception of southern areas adjacent to fishing villages. Small bays, sheltered waters behind reef-breaks and areas off dry river mouths were used for foraging/feeding behaviour, whereas most travelling occurred along exposed coast. Ten individual S. teuszii were photo-identified. Multiple resightings (and absence of unmarked animals) indicate that all individuals present at the time of the surveys were photocaptured, exhibited high site fidelity and had year-round occurrence. Association indices of 0.77-1.0 indicated strong social affiliation between eight individuals, particularly in winter. Off Flamingos, S. teuszii occurs in small numbers and exhibits high site fidelity to a relatively small stretch of nearshore habitat, making the species vulnerable to local extirpation. Wider-scale surveys and development of a management plan are crucial to ensuring the long-term conservation of S. teuszii off Flamingos.     

Ab initio investigations of the charge transport properties of endohedral M@C20 (M= Na and K) metallofullerenes

Using density functional theory and quantum transport calculations based on nonequilibum Green's function formalism, we investigate the charge transport properties of endohedral M@C₂₀ (M= Na and K) metallofullerenes. Our results show that the conductance of C₂₀ fullerene can be obviously improved by insertion of alkali atom at its centre. Both linear and nonlinear sections are found on the I-V curves of the Au-M@C₂₀-Au two-probe systems. The novel negative differential resistance behaviour is also observed in Na@C₂₀ molecule but not in K@C₂₀.     

Distribution of fouling bryozoans in thenorthern South China Sea

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An unexploited population of oysters,Ostrea lutaria Hutton,from foveaux strait

Settlement of Ostrea lutaria on sand‐cement‐plastered asbestos plates held in steel frames on the bottom of Foveaux Strait was studied from March 1965 to April 1967. Spat mortality over the period of plate exposure (about one month) was very low (maximum of 3 percent) and was greatest shortly after settlement. There was no evidence that mortality was due to predation. Essentially the same seasonal pattern of settlement was observed each year. Eighty to 90 percent of spat settled between mid December and mid February in both summers; settlement occurred as early as October; some was observed as late as July.

Results of field experiments suggest some very tentative conclusions on the settlement behaviour of O. lutaria: (1) The larvae are benthopelagic and remain on the bottom in strong current conditions. (2) Light stimulates swimming of larvae in still water. (3) In still water and low light intensities of the area larvae tend to swim upward toward the light. (4) In still water and dim light of the area larvae settle predominantly on under surfaces. (5) In still water in the absence of light larvae settle predominantly on upper surfaces. (6) Under the conditions of current and light in the multiplate frames used to sample spatfall here, larvae settle mainly on upper surfaces. (7) Larvae tend to crawl up inclined surfaces before settling.

The results indicate that larval behaviour may be changed by small alterations of light intensity and current. The contradictory nature of surface angle preferences found by other workers for various species of Ostrea and Crassostrea may have been due to such small variations caused by the experimental techniques. It is possible that the settlement behaviour of all species of these genera is similar.     

The Activity Rhythm of Blennius sanguinolentus Pallas*

Abstract. In the field, feeding activity of the algivorous Blennius sanguinolentus increased remarkably from morning to late afternoon. Swimming is evenly distributed; other behaviour does not fall into regular daily patterns. No association was found, save in extreme values, between the distribution of any activity and environmental factors measured simultaneously. We suggest that the feeding cycle is an adaptation to the metabolic properties of green algae, the staple diet of B. sanguinolentus. Activity distributions following predictable short-term fluctuations in food quality are expected to be found in other animals.     

Movement patterns of an endangered fishery species,Lithognathus lithognathus (Sparidae), and the role of no-take marine protected areas as a management tool

Understanding movement behaviour is essential for effective management of fishery species. Dart tags were used to study coastal movement patterns of white steenbras Lithognathus lithognathus, an overexploited seabream (Sparidae) in South Africa. In total, 6 962 fish (190–1 080 mm fork length) were tagged throughout the species’ distributional range, in four long-term fish-tagging programmes. The predominant behaviour recorded was residency, with relatively short-ranging movements. More than 60% of the 351 recaptured fish were recaptured within 1 km of their tagging site, some of which were at liberty in excess of three years. Most of the juveniles (93.9%), subadults (71.7%) and adults (64.0%) were recaptured within 10 km. Occasional long-distance movements of up to 800 km were recorded. Recapture distances were positively, but weakly, correlated with fish fork length (n = 257 fish measured at recapture; r² = 0.166, p < 0.001). Low levels of connectivity among coastal areas suggest that large-scale annual spawning migrations, as previously hypothesised for this species, are unlikely, which raises the possibility of multiple spawning sites. Seventy-seven percent of L. lithognathus tagged within three marine protected areas (MPAs) were recaptured within the same MPA, suggesting that area closures provide protection for L. lithognathus through the post-estuarine juvenile, subadult and adult life stages. We confirm that the country’s current network of coastal MPAs plays a vital role in sustaining this species, and suggest that additional closures, or otherwise substantial reductions in catch rates, are necessary for the species’ recovery.     

Early growth rate and feeding of a small group of laboratory-reared saury,Scomberesox saurus scombroides (Pisces: Scomberesocidae)

Sea-spawned saury eggs collected 20 km off the west coast of the Cape Peninsula were hatched in laboratory tanks and the larvae reared. The larvae were fed initially on nauplii of cultured copepods, Tisbe holothuriae Humes and Pseudodiaptomus hessei (Mrázek). Growth rate during the first 47 days post-hatch averaged 0,62 mm·day^?1 (at 18—19°C) and between the 47th and 120th day averaged 0,45 mm·day^?1 (at 14,8—15,5°C). Some observations on feeding behaviour are included.     

Feeding ecology,diet and field-based studies on feeding selectivity of the Cape anchovy Engraulis capensis Gilchrist

Samples collected during four cruises on board R.S. Africana were used to study the trophic ecology and feeding behaviour of Engraulis capensis in the southern Benguela region. Previous work had indicated that this species was a non-selective filter-feeding omnivore, diatoms comprising the bulk of the diet. The results of the present study reveal that anchovies selectively feed on mesozooplankton, especially calanoid copepods and euphausiids. Investigation of the feeding behaviour of the species indicates that raptorial feeding is dominant over filter-feeding and that prey appears to be selected primarily on the basis of size.     

Cleaning symbiosis among New Zealand fishes

These first observations of cleaning symbiosis amongst New Zealand fishes were made between June 1967 and March 1970. Five species of labrid fishes; Halichoeres sp., Coris picta (Bloch and Schneider, 1801), Coris sandageri (Hector, 1884), Pseudolabrus luculentus (Richardson, 1848) and Pseudolabrus miles (= coccineus) (Bloch and Schneider, 1801) are now known to be facultative cleaners. One is an undescribed species and two others are new records for New Zealand. Halichoeres sp. is a more active cleaner than the other four and is almost an obligate cleaner. Observed behaviour indicates that these species are typical temperate zone cleaners.     

Reef fish display station-keeping and ranging behaviour in the Pondoland Marine Protected Area on the east coast of South Africa

This study assessed the role of the Pondoland Marine Protected Area (MPA) in the Eastern Cape province of South Africa by evaluating retention versus ‘spillover’ of exploited fishery species that were tagged in a 400 km² no-take zone of the MPA. From April 2006 to July 2010, 2 124 fish comprising 36 species were tagged in the MPA, with an overall recapture rate of 23%. Findings for four important species (Polysteganus praeorbitalis, Chrysoblephus puniceus, Epinephelus andersoni and Epinephelus marginatus) are presented. Recapture rates ranged from 8% to 60% and time-at-liberty from 0 to 1 390 d. Individuals of all four species displayed highly localised station-keeping behaviour. For all four species, the 95th percentile of intra-study site movements was <750 m (linear distance) and many recaptures were within 250 m of the release site, showing that some fish spend most of their time in the MPA's no-take zone. However, some fish moved beyond the boundary of this zone in a north-easterly direction (range 3–1 059 km), where they would be available to the boat-based fishery in KwaZulu-Natal. The combination of resident individuals with some with ranging behaviour suggests that the MPA can provide a conservation role for these species, while exporting some individuals into nearby fisheries.     

Observations on the predatory behaviour of the sevengill shark Notorynchus cepedianus

Studies on the feeding behaviour of large predatory sharks are inherently problematic because of the size of the animals, the difficulty in observing and handling them and the risks to the investigator. Observations on the feeding behaviour of the sevengill shark Notorynchus cepedianus over a seven-year period revealed this species to display at least four distinct foraging strategies. A particular strategy, or a combination of two or more, was employed depending on the size and type of prey being subdued. The four primary factors that appear to influence prey selection were prey size, availability and density, and scavenging. The behaviour of a prey species influences the predator's foraging and hunting behaviour. The success of the sevengill shark as an apical predator can be attributed, in part, to the feeding strategies it employs to subdue prey.     

Vertical distribution and daily migrations of hyperiid amphipods in the northern Benguela in relation to water column stratification

The vertical distribution and migratory behaviour of hyperiid amphipods were studied in a series of tows carried out during a 48-h sampling period at an oceanic station at the northern edge of the Benguela System during a major penetration by Angola Current waters. A total of 49 species of hyperiid amphipods were collected; of these, Tetrathyrus forcipatus was the most abundant, with densities greater than two individuals per 10 m³. Vibilia armata, Lestrigonus latissimus, L. bengalensis and Paratyphis promontorii were also highly abundant. During the sampling period most species were concentrated in the uppermost 40 m of the water column, though in other regions the vertical distribution of these same species has been reported to be broader. Only a few species were able to migrate through the thermocline. We hypothesize that both the non-migratory behaviour and the aggregation of individuals and species were caused by two primary factors: the existence of a strong thermocline, which hindered the transit of species to deeper layers, and abundant concentrations of gelatinous zooplankton above the thermocline. Hyperiids and the gelatinous zooplankton, particularly medusae and siphonophores, exhibited a close association during the sampling period, suggesting that hyperiids are able to partition their habitat by using the different medusan and siphonophoran species as specific substrates, thereby reducing interspecific competition.