The behaviour of sharks

Summary Despite the recent upsurge of interest in shark research, the current status of knowledge of the behavioural repertoire of most species is alarmingly incomplete. Clearly, from the steadily decreasing numbers of sharks caught by commercial and sport fishermen, sharks are highly vulnerable to human exploitation. Although education is making inroads, there is still steady opposition to the enforcement of catch limits and management strategies for most species. Accurate life history and behavioural information is required to enforce management policies. Wetherbee et al. (1990) cited a case in which commercial fishermen accused the spiny dogfish of stripping the commerical and recreational fisheries of their herring and salmon catch. A detailed study of the spiny dogfish diet disproved their claims.Sharks are clearly not mindless eating machines, as they have been labelled in the past. They are intelligent and have complex patterns of movement, space utilization, and social organization. Using a combination of remote and direct observational techniques, the scientific community is beginning to have a more complete understanding of these important apex predators in coral reef and oceanic ecosystems. More importantly, researchers who are interested in pursuing the fascinating field of shark behaviour still have a wide choice of direction.     

Vibrio species associated with mortality of sharks held in captivity

Two urease-positiveVibrio spp. were isolated from a brown shark (Carcharhinus plumbeus) that died in captivity at a national aquarium. Morphological, biochemical, and molecular genetic studies revealed one of the isolates to beV. damsela; the other isolate was unique and has been classified asV. carchariae sp. nov. BothV. damsela andV. carchariae were found to be virulent for spiny dogfish (Squalus acanthias), causing death in less than 18 hours after intraperitoneal injection of ca. 4×10⁶ cells.V. damsela was strongly cytotoxic for Y1 adrenal cell monolayers;V. carchariae exhibited weak cytotoxicity for Y1 cells.V. damsela contained cryptic plasmids and both isolates were urease positive.V. carchariae was able to utilize urea as sole source of carbon and nitrogen.     

Pre-copulatory behaviour of captive sandtiger sharks,Carcharias taurus

Synopsis Three bouts of pre-copulatory behaviour were observed in a captive colony of sandtiger sharks,Carcharias taurus, at Oceanworld Manly, Sydney, Australia. The behaviour occurred 14 rather than 12 months apart. Temperature was very similar to that of local coastal conditions where these animals naturally occur. But the photoperiod was artificial and inflexible. The information recorded in all of these cases was almost identical, giving an insight into a very complex social structure in this essentially colonial animal. Dominance displays occurred between both mature and immature males in addition to aggression towards other objects, e.g. small carcharbinid sharks. Most interesting were the interactions between the males and females, especially those which implicate the possible use of chemical stimulants (pheromones). Copulation was observed on two occasions but was not filmed.     

Thermoregulatory significance of basking behaviour in the raccoon dog (Nyctereutes procyonoides)

1. 1.|The raccoon dogs frequently basked in spring while keeping their dark chest area towards the sun. The importance of this behaviour for the thermal balance was examined by using a cylinder model, and the results were compared with that of the blue fox which has pale chest and no basking behaviour.

2. 2.|With no external radiation source, cooling rates of blue fox and racoon dog models were almost equal, while in the sunshine with the chest area towards the sun, raccoon dog gained and blue fox lost heat.

3. 3.|In the same sunshine, the raccoon dog lost heat if its back area was towards the sun in comparison with the situation when the chest area was towards the sun.

4. 4.|Temperatures at the skin level were much higher for sun-exposed raccoon dogs than blue foxes especially on the chest area.

5. 5.|It is concluded that the hair coat structure of the raccoon dog is especially favourable for trapping heat from the sun, and with postural adjustments the animal takes maximal advantage of this free heat.

Association of Vibrio cholerae with plankton in coastal areas of Mexico

The El Niño event of 1997/1998 provided an opportunity to carry out a field experiment in which the relationship of sea surface temperature and the association of Vibrio cholerae with marine plankton could be assessed in Mexican coastal and estuarine areas. Plankton samples were collected from May 1997 through June 1999. Sites included the Mexican ports of Veracruz, Coatzacoalcos and Frontera in the Gulf of Mexico and Ensenada, Guaymas, Mazatlán, Manzanillo, Acapulco and Oaxaca in the Pacific Ocean. Sampling was also accomplished during two oceanographic cruises in the Yucatan channel of the Caribbean Sea. Bacteriological analyses for V. cholerae serogroups O1 and O139 were carried out. Also, the taxonomic structure of the plankton populations was determined. Vibrio cholerae O1 was detected only in Veracruz samples collected during April, May and June 1999, when La Niña climatic conditions prevailed. It is concluded that V. cholerae O1 in Mexico derives from its marine and estuarine origin and not from sewage contamination. The significant number of Acartia tonsa copepodites and V. cholerae copepodite-positive samples suggests a significant role of this copepod in the occurrence and distribution of V. cholerae in coastal areas of Mexico.     

Body temperature and basking behaviour of Nile crocodiles (Crocodylus niloticus) during winter

The ability to thermoregulate in reptilians is often through behavioural modification. We investigated body temperature (T_b) patterns during winter in the amphibious Nile crocodile (Crocodylus niloticus) and its relationship to basking behaviour at the St. Lucia Crocodile Centre, St. Lucia, South Africa. It was found that crocodiles had no daily plateaus in T_b but rather continuous oscillations in T_b within a range of mean minimum T_b 18.8–19.6 °C to mean maximum T_b 26.9–29.2 °C. Crocodile T_b increased during the day, usually after 10:00 irrespective of body size. Behavioural data showed that the crocodiles usually left the water to bask around 10:00. It is suggested that basking behaviour is important for elevating T_b rather than attaining a preferred T_b. The increased T_b may allow them to perform optimally when they return to water. The basking occurrence has management implications as it suggests that the best time to conduct aerial censuses of the St. Lucia crocodiles is during winter after 10:00 when most of the individuals are basking and hence most easily seen.     

Parturient behaviour of a viviparous skink: evidence for maternal cannibalism when basking opportunity is low

We documented the behaviour of pregnant McCann’s skinks (Oligosoma maccanni) before, during and after parturition. Females were maintained in captivity from early pregnancy under thermal environments differing in basking opportunity (low, mid and high regimes). Thermal regime during pregnancy had little influence on maternal behaviours, including basking behaviour prior to birth and the duration of, and site selection for, labour. The majority of births (78%) occurred in the open and warm areas. Most females (61%; n?=?102 births, n?=?36 females) aided offspring post-birth by biting them free of the enclosing extra-embryonic membrane. Some females from the low regime consumed non-viable offspring, but whether this is a consistent difference among females held under different basking regimes requires further study. Many females (c. 79%) also exhibited a brief transient decrease in control of hind-limbs post-birth. Further studies on other squamates are recommended to shed light on the evolutionary history and possible conservation consequences of maternal behaviour during parturition.     

The energetics of basking behaviour and torpor in a small marsupial exposed to simulated natural conditions

Limited information is available on basking behaviour in torpid mammals and its energetic consequences. We investigated the effects of physiological and behavioural strategies on the energetics of the fat-tailed dunnart (Sminthopsis crassicaudata). Metabolic rate and body temperature during torpor, basking and rest were measured over 24 h in response to simulated environmental conditions: (a) constant ambient temperature (T _a) of 15°C, (b) constant T _a of 15°C with access to a radiant heat lamp, (c) a T _a cycle (range 15–31°C), and (d) a T _a cycle with access to a radiant heat lamp. When a radiant heat source was provided, all dunnarts (n = 16) basked during all measurements, which resulted in energy savings of up to 74% during rest. Overall, torpor was used on 59% of measurements with a maximum duration of 16.2 h and reductions in metabolic rate of 90% compared to normothermic values. Torpid dunnarts actively moved from a shaded area to position themselves under the heat lamp with body temperatures as low as 17.5°C and thereby reduced rewarming costs by 66%. We demonstrated, for the first time in the laboratory, that torpid animals actively move to a heat source to bask, and that this behaviour results in considerable energy savings. Our finding supports the view that basking during normothermia and rewarming from torpor substantially reduces energetic requirements, which may be important for the survival of small dasyurids living on limited resources in the Australian arid zone.     

A note on catches of basking sharks, Cetorhinus maximus (Gunnerus), off Norway and their relation to possible migration paths

The distribution and the times of the main catches of the basking shark, Cetorhinus, maximus (Gunnerus), in the commercial fishery off the coast of Norway during the seasons of 1971, 1972 and 1973 are given and analysed. No easily recognized regularities have been identified from season to season so that it is evident that there is no pattern of migration towards the Norwegian coast comparable to that of the bluefin tuna, Thunnus thynnus L., which once provided a substantial fishery in the same area.     

Annual rhythms of swimming behaviour and seawater adaptation in young baltic salmon,Salmo salar,associated with smolting

Synopsis Sexually immature and sexually mature precocious male Baltic salmon,Salmo salar, parr from Umeälven (Ume river) were tested for rheotactic behaviour and adaptation to seawater before, during, and after the time period for smolt migration. Size of fish at the beginning of the experiment in January was on average 13.5 cm. Rheotactic behaviour was tested in annular stream tanks with photocells to measure upstream and downstream movements. Samples of fish were given a Seawater challenge test at monthly intervals in order to determine their ability to adapt to 20%. saltwater. During spring, both immature and sexually precocious parr became silvery and showed progressive development of downstream-directed movements. In early June the fish exhibited good hypoosmoregulatory ability in 20%. saltwater and swimming was predominantly downstream. During late June and early July there was a marked reversal in swimming behaviour, accompanied by a dramatic change in saltwater adaptation. The fish moved mainly upstream and showed decreasing ability to meet the seawater challenge test. This was accompanied by a loss of silvery coloration. The annual cycle of swimming behaviour and seawater adaptation is discussed in relation to the appearance of a smolt-window, i.e., a critical interval for smolt migration.     

Nature management in coastal areas of Western Europe

The general environmental characteristics of West European coastal dunes and those of salt marshes are outlined. It is pointed out that the dynamical character of the dune system with its interaction between plants and sand in building and degeneration phases has been known for a much longer period of time than generally believed.As to the salt marshes the special significance is discussed of ungrazed marshes; the majority of the marshes having been under a grazing regime for a long time is elucidated.The distinction between internal management is mentioned, i.e. the measures taken to maintain or improve the qualities of an area, versus external management, i.e. the measures to prevent or counteract negative influences from outside the area.Nomenclature follows Heukels & Van Ooststroom (1977).     

Arthropods associated with medicinal plants in coastal South Carolina

Arthropods were sampled from feverfew [Tanacetum parthenium （L.） Schultz- Bip], Echinacea purpurea （L.） Moench, Echinacea pallida （Nutt.） Nutt., Valeriana officinalis L., and St. John＇s wort （Hypericum perforatum L.） during 1998-2001. In addition, arthropods were sampled on tansy （Tanacetum vulgare L.） from 2001-2004. In general, 50-60 arthropod species where collected and identified among all of the medicinal plant species. Among the predators, Orius insidiosus （Say） （Hemiptera： Anthocoridae）, Geocoris punctipes （Say） （Hemiptera： Lygaeidae） and spiders were most abundant from 1998-2004. The three-cornered alfalfa hopper, Spissistilus festinus （Say）, was the most abundant herbivore found from 1998 to 2001. Orius insidiosus and G. punctipes were 3-4 times more abundant on T. parthenium than on any other medicinal plant species. Based on the numbers of predatory arthropods found on T. parthenium, this crop could be suitable as a companion or ＂banker＂ plant to attract and maintain populations of predators, especially O. insidiosus and G. punctipes. Whitefly nymphs attacked by predators with piercing/sucking mouthparts are easily identified using a microscope because of the general appearance of the carcass left by the predators. Thus, populations of predators on T. parthenium suppressed Bemisia tabaci populations on E. purpurea when these crops were planted as companion crops.     

The genetical theory of social behaviour

We survey the population genetic basis of social evolution, using a logically consistent set of arguments to cover a wide range of biological scenarios. We start by reconsidering Hamilton''s (Hamilton 1964 J. Theoret. Biol. 7, 1–16 (doi:10.1016/0022-5193(64)90038-4)) results for selection on a social trait under the assumptions of additive gene action, weak selection and constant environment and demography. This yields a prediction for the direction of allele frequency change in terms of phenotypic costs and benefits and genealogical concepts of relatedness, which holds for any frequency of the trait in the population, and provides the foundation for further developments and extensions. We then allow for any type of gene interaction within and between individuals, strong selection and fluctuating environments and demography, which may depend on the evolving trait itself. We reach three conclusions pertaining to selection on social behaviours under broad conditions. (i) Selection can be understood by focusing on a one-generation change in mean allele frequency, a computation which underpins the utility of reproductive value weights; (ii) in large populations under the assumptions of additive gene action and weak selection, this change is of constant sign for any allele frequency and is predicted by a phenotypic selection gradient; (iii) under the assumptions of trait substitution sequences, such phenotypic selection gradients suffice to characterize long-term multi-dimensional stochastic evolution, with almost no knowledge about the genetic details underlying the coevolving traits. Having such simple results about the effect of selection regardless of population structure and type of social interactions can help to delineate the common features of distinct biological processes. Finally, we clarify some persistent divergences within social evolution theory, with respect to exactness, synergies, maximization, dynamic sufficiency and the role of genetic arguments.     

Occurrence of pathogenic vibrios in coastal areas of France

AIMS: This study was carried out to investigate the occurrence of potentially pathogenic species of Vibrio in French marine and estuarine environments. METHODS AND RESULTS: Samples of coastal waters and mussels collected between July and September 1999 were analysed by culture, using selective media including thiosulphate-citrate-bile salts-sucrose and modified cellobiose-polymixin B-colistin agar. Presumptive Vibrio colonies were isolated and identified using selected biochemical tests. Specific primers based on flanking sequences of the cytolysin, vvhA gene, pR72H DNA fragment and 16S-23S rRNA intergenic spacer region (ISR) were used in a polymerase chain reaction (PCR) to confirm the identification of Vibrio vulnificus, V. parahaemolyticus and V. cholerae, respectively. In this study, V. alginolyticus (99 of 189) was the predominant species, followed by V. parahaemolyticus (41 of 189), V. vulnificus (20 of 189) and non-O1/non-O139 V. cholerae (three of 189). All 20 V. vulnificus isolates showed PCR amplification of the vvhA gene, 16 of which had been isolated from estuarine water. The PCR amplification of the pR72H DNA fragment in 41 V. parahaemolyticus isolates generated two unique amplicons of 387 and 320 bp. The latter, present in 24.4% of these isolates, had not previously been found in V. parahaemolyticus strains examined to date. Amplification of the trh gene in two of the isolates suggested these to be virulent strains. Three strains identified as V. cholerae by amplification of the 16S-23S rRNA ISR were confirmed to be non-cholera (non-O1/non-O139) strains. CONCLUSIONS: The results of this study demonstrated the presence of pathogenic Vibrio species in French coastal waters. Furthermore, the PCR approach proved useful for the rapid and reliable confirmation of species identification. SIGNIFICANCE AND IMPACT OF THE STUDY: These findings indicate the potential sanitary risk associated with the presence of pathogenic Vibrio spp. in cultivated mussels and in the aquatic environment. The PCR can be used to detect pathogenic vibrios directly in environmental samples.     

Relative abundance and size of coastal sharks derived from commercial shark longline catch and effort data

In the north-west Atlantic Ocean, stock assessments conducted for some commercially harvested coastal sharks indicate declines from 64 to 80% with respect to virgin population levels. While the status of commercially important species is available, abundance trend information for other coastal shark species in the north-west Atlantic Ocean are unavailable. Using a generalized linear modelling (GLM) approach, a relative abundance index was derived from 1994 to 2009 using observer data collected in a commercial bottom longline fishery. Trends in abundance and average size were estimated for bull shark Carcharhinus leucas, spinner shark Carcharhinus brevipinna, tiger shark Galeocerdo cuvier and lemon shark Negaprion brevirostris. Increases in relative abundance for all shark species ranged from 14% for C. brevipinna, 12% for C. leucas, 6% for N. brevirostris and 3% for G. cuvier. There was no significant change in the size at capture over the time period considered for all species. While the status of shark populations should not be based exclusively on abundance trend information, but ultimately on stock assessment models, results from this study provide some cause for optimism on the status of these coastal shark species.     

Strategies for regulation of aquaculture site selection in coastal areas

Marine fish farming is a relatively new component in the complex mixture of coastal resource uses in north temperate zone countries. In Western Canada, the Province of British Columbia issues site and operational licences for marine fish farms. Before granting licenses, staff evaluate fish farm applications for their technical feasibility as part of a conflict resolution process. This ensures that aquaculture develops in an environmental responsible manner, and is part of a public accountability process that recognises the interests of conflicting marine resource users. A referral system which solicits input from national and local organisations is part of this licensing process. The Norwegian YS for ordering salmon farming industry development involves partitioning the coast at a national level and developing organic loading maxima for each section of the coast. Within the constraints of this national plan Leaf authorities license aquaculture. This paper describes these different approaches and compares their strengths and weaknesses.