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The spawning behaviour of bream Abramis brama was studied in 1993, in a harbour on the River Meuse, Belgium. Fish spawned from 22 to 27 April and from 11 to 14 May, when the water temperature rose to 14·5 C. The reproductive behaviour of the bream was studied within a 15 m long part of the harbour using a video camera. Territorial males with tubercles (33-43 cm total length; >5 years old) defended bank areas of diameter 80-150 cm which included spawning substratum, i.e. roots of alder and willow trees and aquatic plants. Water depth ranged from 25 to 50 cm. Non-territorial males without tubercles (24-33 cm; 3-4 years old), remained 2-4 m away from the bank. Aggressive behaviour between males was frequent and, occasionally, males with tubercles were unable to defend a territory. Mature females (25-43 cm; >3 years old), coming from the deeper water of the surrounding area, were followed by non-territorial males before spawning in territories near the bank. 1996 The Fisheries Society of the British Isles

Abstract.-Sexual behaviors in dyadic encounters in the alpine newt, Triturus alpestris alpestris, is described to test whether male behavior is influenced by external cues, that is, female responsiveness. De pending on this factor, a male exhibits one of the two following tactics during the sperm transfer phase.The male either waits for a positive response from the female before initiating sperm transfer ("waiting" tactic), or creeps and deposits a spermatophore in front of a nonresponsive female ("luring" tactic). The sperm transfer success rates of these tactics are 31% and 6%, respectively, and encounter success rates, 64% and 8%, respectively. The success of the second tactic is linked to behaviors that lure the female, notably quiver and distal lure. The same individual can exhibit both tactics, and neither body size nor condition appears to influence the tactic a male exhibits. These tactics can be interpreted as the result of a conditional strategy, that is, a strategy that allows an individual to incorporate information about its ability to obtain fitness through alternative tactics and then express the tactic that maximizes its fitness. More particularly, these tactics are examples of a side-payment strategy, that is, a strategy that allows individuals to achieve small gains by capitalizing on passing opportunities.

Grey seals breed in a wide range of littoral environments and are thus suitable for investigating the mechanisms of behavioural adaptation under environmental influences. However, most studies of grey seal behaviour, energetics and mating strategies only focus on the typical breeding colony of this species: a large (more than 1 000 seals) and dense land-based group. In this study, we measured the activity budget of reproductive individuals in such a typical colony and in three poorly known colonies, considered marginal by their geographic location, their small size (less then 500 individuals) or their environmental characteristics. The variation of activity among the studied colonies appears to be significant and could be shaped by the major environmental differences observed between these colonies (mainly topographical), supporting a previously raised hypothesis (Anderson and Harwood 1985). In one of the marginal colonies studied here, grey seals spend more than 40 % of their breeding time in the water while in others, they stay on land for several weeks of reproduction. This type of difference might influence individuals energy balance and mating strategy. We suggest that the understanding of the grey seal behavioural plasticity is unlikely to be complete without integrating data on marginal populations.Resume. -Se reproduisant dans toute une gamme d'environnements littoraux, le phoque gris pcrmet d'etudier les mecanismes d'adaptation comportementale aux facteurs du milieu. Neanmoins, la plupart des etudes comportementales, energetiques ou du Systeme de reproduction se limitcnt aux colonies les plus typiques de cc phoque : groupe dense de plus de 1 000 individus sur unc portion de cöte. Ici, nous comparons le budget d'activite des reproducteurs dans une colonie typique avec l'activite des reproducteurs dans trois colonies peu connues, considerees commc marginales par leur localisation geographique, leur taille reduite (moins de 500 individus) ou leurs particularites environnementales. Les differences d'activite entre phoques des quatre colonies etudiees semblcnt significativcs et s'expliquent bien par les importantes differences cnvironncmentales entrc colonies (essentiellement topographiques), en accord avec Phypothese d' Andcrson et Harwood (1985). Dans l'une des colonies marginales etudiees ici, les phoques gris en periodc dc reproduction passent plus de 40 % du temps dans 1'eau tandis que dans d'autres sites, ils rcstent emerges pendant plusieurs semaines. Ce type de variation est susceptible d'influencer l'equilibre energetique et la Strategie de reproduction des individus. Nous suggerons que la comprehension de la plasticite comportementale du phoque gris risque d'etre incomplete si les donnecs sur les populations marginales sont ignorees.

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