Showing papers by "Paul J. B. Hart published in 2000"
TL;DR: The study showed that sticklebacks were less aggressive towards a partner when sharing a common food source with a familiar conspecific, compared to when shares a food sourceWith an unfamiliar Conspecific.
Abstract: In this study, pairs of juvenile sticklebacks either familiar with each other or pairs unfamiliar with each other met to share a food source. The study showed that sticklebacks were less aggressive towards a partner when sharing a common food source with a familiar conspecific, compared to when sharing a food source with an unfamiliar conspecific. The results showed that the aggressive behaviour was built up and broken down gradually depending on how long the two competitors had been together or apart. A decrease in aggressiveness was found after the sticklebacks had been together two weeks, with a further decrease after four weeks together. Conversely there was an increase in aggressiveness after the sticklebacks had been parted for two weeks or four weeks. The chance of food being equally distributed between the competing pairs increased with time spent together and decreased with time parted. The observed decrease or increase in the amount of aggression is discussed as a build-up or a breakdown of rank knowledge or of a co-operative partnership.
122 citations
TL;DR: In this article, the authors examined an area subject to a voluntary agreement between these two sectors of the fishing industry such that some areas are used exclusively by fixed-gear fishers, some are shared seasonally by both sectors, and others are open to all methods of fishing all year.
Abstract: When two commercially important marine species coexist in the same habitat, conflict may arise between different sectors of the fishing industry. A good example of this situation is when fishers using towed bottom-fishing gear (scallop dredges, beam trawls, and otter trawls) operate in the same areas in which fixed-bottom gear (crab pots) are deployed. We examined an area subject to a voluntary agreement between these two sectors of the fishing industry such that some areas are used exclusively by fixed-gear fishers, some are shared seasonally by both sectors, and others are open to all methods of fishing all year. This agreement was enacted to resolve conflict between the two sectors of the industry. An additional possible benefit of this agreement is the protection of the seabed from towed bottom-fishing gear, which is one of the greatest sources of anthropogenic disturbance of seabed habitats worldwide. Previous studies have demonstrated that com- plex emergent epifaunal communities are substantially altered by such activities. This habitat alteration in turn influences closely associated species, some of which may be of commercial importance. We undertook comparative surveys of the benthic habitat and communities within the area covered by the agreement and compared different areas subjected to a range of fishing disturbance regimes. Communities found within the areas closed to towed fishing gears were significantly different from those open to fishing either permanently or seasonally. Abundance-biomass curves demonstrated that the communities within the closed areas were dominated by higher biomass and emergent fauna that increased habitat complexity. Areas fished by towed gear were dominated by smaller-bodied fauna and scavenging taxa. Scallop dredges and beam trawls used on more stable habitats appear to have greater impacts on the environment than lighter otter trawls used in shallower water with less stable sediments. It would appear from our data that conflict management in the form of gear-restriction measures has the added benefit of conserving habitats and benthic fauna sensitive to bottom-fishing disturbance.
113 citations
TL;DR: DNA fingerprinting was used to provide an accurate measure of paternity in a nest-box colony of Jackdaws and revealed no cases of extra-pair fertilisation (EPF) or intra-specific brood parasitism, suggesting fledgling output or survival is likely to be a good measure of individual reproductive success in this species.
Abstract: In this study we used DNA fingerprinting to provide an accurate measure of paternity in a nest-box colony of Jackdaws. The species is a semi-colonial, socially monogamous passerine which establishes long-term pair bonds. Parents raise a single annual brood in which 50% brood reduction is commonplace. However, nest sites are a limited resource, non-breeding adults are also common around colonies and males are frequently separated from their incubating females during the fertile egg-laying period so that opportunities arise for extra-pair copulation. The parentage analysis, however, revealed no cases of extra-pair fertilisation (EPF) or intra-specific brood parasitism. Therefore fledgling output or survival is likely to be a good measure of individual reproductive success in this species. The lack of EPFs is not explained by nesting synchrony and we discuss the relative costs and benefits to females of seeking EPFs; the likelihood that paternal care and a life-history strategy similar to many long-lived non-passerines may also constrain the species to monogamy.
60 citations
TL;DR: A model that simulates the foraging behaviour of tunas in the vicinity of ocean fronts cannot explain why physiological differences exist between and within the different tuna species, but it does show how differences in susceptibility to thermal stress will permit different behaviour.
Abstract: We present a model that simulates the foraging behaviour of tunas in the vicinity of ocean fronts. Stochastic dynamic programming is used to determine optimal habitat choice and swimming speed in relation to environmental variables (water temperature and clarity) and prey characteristics (abundance and energy density). By incorporating submodels for obligate physiological processes (gastric evacuation, standard and active metabolic costs) and sensory systems (visual feeding efficiency), we have integrated into a single fitness-based model many of the factors that might explain the aggregation of tunas at ocean fronts. The modelling technique describes fitness landscapes for all combinations of states, and makes explicit, testable predictions about time- and statedependent behaviour. Enhanced levels of searching activity when hungry and towards the end of the day are an important feature of the optimal behaviour predicted. We consider the model to be particularly representative of the behaviour of the warm-water tunas or Neothunnus (e.g. skipjack, Katsuwonus pelamis, and yellowfin, Thunnus albacares) and for surfacedwelling temperate tunas (e.g. young albacore, Thunnus alalunga), which are often observed to aggregate near fronts. For the bluefin group (i.e. older albacore; northern and southern bluefin, Thunnus thynnus and Thunnus maccoyii), for which extended vertical migrations are a significant and as yet unexplained component of behaviour, the model is able to reproduce observed behaviour by adopting the lower optimal temperature and standard metabolic rate of albacore. The model cannot explain why physiological differences exist between and within the different tuna species, but it does show how differences in susceptibility to thermal stress will permit different behaviour.
52 citations
TL;DR: The hypothesis that fish with the HbI*2/2 genotype have a higher motivation to feed and are better competitors than individuals with the other haemoglobin genotypes and that they will eat a larger share of the prey is tested.
Abstract: To succeed in scramble competition for food an individual fish will have to have characteristics that allow it to respond rapidly to encountered prey. A trait such as metabolic rate, which has a positive effect on oxygen consumption and growth rate, is likely to be positively correlated with the traits that determine the speed of reaction. An important factor underlying metabolic rate may be the transport efficiency of oxygen from the gills to the respiring tissue and this is mediated by the structure of the haemoglobin molecule. In cod, two structures of this molecule exist due to polymorphism at the Hb1* locus. An individual cod may be homozygous (HbI*1/1 or HbI*2/2) or heterozygous (HbI*1/2), Evidence exists in the literature that HbI*2/2 fish have higher growth rate and earlier maturation and higher transport efficiency of oxygen at low temperature. However, no study has examined whether this could be associated with fish behaviour. In a study reported here we designed an experiment to test t...
39 citations
TL;DR: This communication reports on experiments, which studied the variation in competitive performance of juvenile cod and their growth rates and found fish that took the highest share of prey tended to be those that took prey earlier than others.
Abstract: This communication reports on experiments, which studied the variation in competitive performance of juvenile cod (Gadus morhua L.) and their growth rates. The fish were held in groups of five in either summer or winter conditions and tested for their individual response to prey offered sequentially. There was marked individual variability. Fish that took the highest share of prey tended also to be those that took prey earlier than others. In winter conditions these fish were the largest, but in summer conditions size had no effect. There was a positive influence of the indices of competitive performance on individual growth rate but the relationship was not significant
26 citations