Social learning in fishes: a review

Animals acquire skills and knowledge from other animals, and fish are no exception. There is now strong experimental evidence that many species of fish exhibit social learning and traditional behaviours. Here, we review the literature pertaining to social learning in fish, focusing on (i) antipredator behaviour, (ii) migration and orientation, (iii) foraging, (iv) mate choice and (v) eavesdropping.     

Diel migration patterns of Atlantic salmon smolts with particular reference to the absence of crepuscular migration

Abstract –  The real-time diel pattern of Atlantic salmon smolt migration was observed for 8 years using automatic resistivity counters verified by video surveillance. A clear dominant nocturnal migration was demonstrated early in the migration period, later becoming increasingly diurnal, until rates became approximately equal at day and night. Migration patterns were related to water temperature, such that when mean daily temperatures were below 12 °C, hourly rates of migration were significantly lower during the day than at night. When daily mean temperatures exceeded 12 °C, there was no significant difference between diurnal and nocturnal migration rates. Migration patterns showed a distinct suppression of migration at dawn and dusk throughout the migration period. It is hypothesised that this behaviour is an active decision and/or an adaptive strategy either to take advantage of increased food in the form of invertebrate drift or to reduce predation risk from actively feeding piscivores or both.     

An evaluation of the potential influence of SST and currents on the oceanic migration of juvenile and immature chum salmon (Oncorhynchus keta) by a simulation model

Using a salmon migration model based on the assumption that swimming orientation is temperature dependent, we investigated the determining factors of the migration of juvenile and immature chum salmon (Oncorhynchus keta) in the North Pacific. We compared the predictions of the model with catch data of immature and juvenile chum salmon collected by Japanese research vessels from 1972 to 1999. The salmon migration model reproduced the observed distributions of immature chum salmon and indicates that passive transport by wind‐driven and geostrophic currents plays an important role in the eastward migration of Asian salmon. These factors result in a non‐symmetric distribution of Asian and North American chum salmon in the open ocean. The directional swimming component contributes to the northward migration in summer. The model results indicate that during the first winter Asian chum salmon swim northward against the southward wind‐driven currents to stay in the western North Pacific. This suggests that Asian chum salmon require more energy to migrate than other stocks during the first winter of their ocean life.     

Computer simulations of homeward-migrating Fraser River sockeye salmon: is compass orientation a sufficient direction-finding mechanism in the north-east Pacific Ocean?

Computer simulations were used to investigate whether compass orientation is a sufficient guidance mechanism for sockeye salmon migrating to the Fraser River from their ocean foraging grounds in the north-east Pacific Ocean. Daily surface ocean currents, simulated by the ocean surface current simulations (OSCURS) model, were used to test the influence of currents on the return oceanic migration of Fraser River sockeye salmon. High seas tagging and coastal recover data of Fraser River sockeye salmon were used for the migration simulations. Surface currents were shown to increase the speed of the homeward-migrating sockeye salmon, as well as to deflect the fish in a north-eastward direction. In spite of ocean currents, all Fraser River sockeye salmon were able to reach their destination with a fixed direction and bioenergetically efficient swimming speed when migration was delayed until the last month at sea. Compass orientation alone was shown to be a sufficient direction-finding mechanism for Fraser River sockeye salmon.     

靖海湾和五垒岛湾放流增殖中国对虾的回游与分布

用烧结法标志中国对虾，在靖海湾和五垒岛湾进行增殖放流，研究其回游与分布规律。重捕资料表明，６月中旬幼对虾对湾内河口浅水区生活随体长增长，逐步向深水扩散；８月上，中旬主群陆续游向湾外，按地形走向向西南回游，部分向东或东南；１０月份回游对湾外水域的对虾有向东，东北或东南回游的现象。     

Assessing the opportunities for upstream migration of non-salmonid fishes in the weir-regulated River Vecht

The degree of obstruction posed by weirs to potential upstream movements of non-salmonid fish (predominantly cyprinids) in the River Vecht, the Netherlands, was assessed. This rain-fed river showed high variability in discharge, providing opportunities for passage at high discharge when weirs were free flowing. Daily recorded discharge and water levels between 1960 and 1984, and an analysis of swimming capacities and migratory behaviour, were used to assess whether hydraulic conditions each day and for each species were suitable for ascent. The assessment demonstrated that migratory opportunities along the six weirs were extremely limited. Only 10 of 32 species were able to ascend all weirs in 5–30% of the years. Opportunities were the greatest for large-sized species during November–March at the downstream-situated weirs, whereas small-sized species had no opportunities year-round. The approach used is widely applicable for barrier assessment in other rivers, because it requires only basic hydraulic measurements that are often available.     

Are the long‐term fluctuations in Atlantic bluefin tuna (Thunnus thynnus) population related to environmental changes?

We tested whether synchronous, long‐term fluctuations in Atlantic bluefin tuna (Thunnus thynnus) trap catches, collected from the ancestral Mediterranean and Atlantic trap fishery, might be related to large‐scale environmental change. Nine time series of trap catches of more than 80 yr long were compared with long time series of three preselected environmental variables, i.e. the North Atlantic Oscillation (NAO), the Length of the Day Index (LOD, a proxy of the atmospheric circulation index) and the temperature. Spectral analyses of trap catches, LOD and temperature displayed similar spectra with peaks at low frequencies, whereas those of the NAO exhibited a broad band spectrum. Regression analyses and tests of correlation did not reveal any clear relationship between trap catches on the one hand and NAO and LOD on the other hand. In contrast, long‐term fluctuations in trap catches appear to be closely and negatively related to long‐term trends in temperature. Underlying processes that could explain such a relationship are discussed, with special focus on changes in migration patterns of the Atlantic bluefin tuna.     

Discrimination of the natal origin of young-of-the-year Allis shad (Alosa alosa) in the Garonne–Dordogne basin (south-west France) using otolith chemistry

Abstract –  The otolith composition of age 0+ Allis shad ( Alosa alosa ) captured in two rivers in the Gironde system in south-west France, the Dordogne and the Garonne, was analysed to establish the natal origin of the fish. Inductively coupled plasma mass spectrometry analyses were used to take measurements of 15 isotopes, among which Co, Fe, Sr and Rb were the most important elements in the discrimination process. It was possible to reclassify each sampled fish into its natal river basin (Garonne or Dordogne) with a high degree of accuracy. Linear discriminant analysis correctly reclassified 91.1% of the Garonne samples and 87.8% of the Dordogne samples (mean success in reclassification in 20 runs ± 1 SD: 89.21 ± 8.6%). Artificial neural networks correctly reclassified 90.1% of the Garonne samples and 81.2% of the Dordogne samples (mean success in reclassification after 1000 training cycles ±1 SD: 85.6 ± 9.1%). Using these tools the present results show that it is possible to assign a natal origin to juvenile shad that hatched in the Dordogne–Garonne basin based on the trace elements in the otolith.