Ontogenetic differentiation of swimming performance and behaviour in relation to habitat availability in the endangered North Sea houting (Coregonus oxyrinchus)

¹ Fisheries and Maritime Museum, 6710 Esbjerg V, Denmark
² Christian-Albrechts-Universität zu Kiel, Institute for Animal Breeding and Husbandry, 24098 Kiel, Germany
³ Gesellschaft für Marine Aquakultur (GMA) mbH, 25761 Büsum, Germany
⁴ Danish Ministry of the Environment, Ribe Environmental Centre, Water and Nature Division, 6760 Ribe, Denmark
⁵ Technical University of Denmark, Department of Mechanical Engineering, 2800 Kgs, Lyngby, Denmark
⁶ Tassilo Jäger-Kleinicke, 24147 Kiel, Germany
⁷ Fisheries Helmut Schwarten, 23714 Malente, Germany
⁸ Technical University of Denmark, National Institute of Aquatic Resources, Freshwater Fisheries, 8600 Silkeborg, Denmark
⁹ University of Copenhagen, Marine Biological Laboratory, Biological Institute, 3000 Helsingør, Denmark

^a Corresponding authors: sbp@fimus.dk

Received: 11 September 2011
Accepted: 23 May 2012

Abstract

The survival of the highly endangered, anadromous fish species North Sea houting (Coregonus oxyrinchus) depends on the correct timing of downstream dispersal during its early ontogenetic stages. To date, however, no studies have investigated the ontogenetic differentiation of swimming performance and behaviour, including the potential of habitat complexity to influence dispersal rates. By testing larval and juvenile North Sea houting in a laboratory, we examined (1) swimming performance measured as maximum swimming performance (U_max) and routine swimming speed (U_routine) and (2) the potential of habitat complexity (i.e., cover providing shade) to influence dispersal behaviour in an indoor stream channel. The U_max and the U_routine were 9.4 and 4.6cm s^-1, respectively, in the larvae [body length (BL) s^-1: 7.3 and 3.5, respectively], and 25.2 and 16.3 cm s^-1 in the juveniles (BL s^-1: 7.0 and 5.2, respectively). We compared laboratory swimming performance data with water speeds in North Sea houting spawning areas in the Danish River Vidaa. Results showed that the water speeds present in 95% and 85% of the water column caused downstream displacement of larvae and juveniles, respectively. However, areas with slow-flowing water near river banks and river beds could function as nursery habitats. Stream channel experiments showed that cover providing shade caused delayed dispersal in both larvae and juveniles, but the larvae dispersed later and spent less time under cover than the juveniles, a finding that implies ontogenetic effects. Finally, the larvae refused to cross an upstream-positioned cover, a behaviour that was not observed in the juveniles. Therefore, habitat complexity may have the potential to influence dispersal behaviour in both larval and juvenile North Sea houting. Overall, we provided the first evidence of ontogenetic differentiation in the North Sea houting. These findings will be valuable for the development and dissemination of science-based conservation strategies.