ABSTRACT
Marine reserves can protect fish populations by increasing abundance and body size, but less is known about the effect of protection on fish behaviour. We looked for individual consistency in movement behaviours of sea trout in the marine habitat using acoustic telemetry to investigate whether they represent personality traits and if so, do they affect survival in relation to protection offered by a marine reserve. Home range size had a repeatability of 0.21, suggesting that it represents a personality trait, while mean swimming depth, activity and diurnal vertical migration were not repeatable movement behaviours. The effect of home range size on survival differed depending on the proportion of time fish spent in the reserve, where individuals spending more time in the reserve experienced a decrease in survival with larger home ranges while individuals spending little time in the reserve experienced an increase in survival with larger home ranges. We suggest that the diversity of fish home range sizes could be preserved by establishing networks of marine reserves encompassing different habitat types, ensuring both a heterogeneity in environmental conditions and fishing pressure.
ABSTRACT
Alternative reproductive tactics are characterized by the occurrence of discrete alternative morphs that differ in behavioural, morphological and physiological traits within the same sex. Although much effort has been made to describe the behaviour, morphology and physiology of such alternative morphs, less effort has been invested investigating how much overlap there is in the characteristics of such morphs in natural populations. We studied random population samples of the invasive Round Goby Neogobius melanostomus from five different localities in the river Rhine system in the Netherlands. We found two morphologically and physiologically distinct male morphs which likely represent alternative reproductive tactics. Almost all mature males under 9.35 cm total length had a gonadosomatic index > 3%, suggestive of a sneaker tactic, while nearly all males above 9.35 cm has a gonadosomatic index of < 3%, suggestive of a parental tactic. Cheek size and eye diameter alone were sufficient to distinguish the two morphs. Gonads had a different relationship with size in the two morphs, indicating separate growth trajectories. The gonad mass of sneaker morphs would be ca. 7.5 times as high as the gonad mass of parental morphs of the same total length after extrapolation. Few (9%) intermediates were found, suggesting that the expression of alternative reproductive tactics is determined before the first breeding season. This contrasts with studies on other goby species, which show evidence of plastic tactics that can be affected by social circumstances. We conclude that it is possible to distinguish two alternative male morphs in the Dutch Round Goby population using morphological measurements alone. Although behavioural observations are needed to provide conclusive evidence, the difference in GSI between these morphs indicates that these morphs reflect alternative reproductive tactics.
