Lord C, Brun C, Hautecœur M, Keith P. Insights on endemism: comparison of the duration of the marine larval phase estimated by otolith microstructural analysis of three amphidromous Sicyopterus species (Gobioidei: Sicydiinae) from Vanuatu and New Caledonia.
Ecology of Freshwater Fish 2010: 19: 26–38. © 2009 John Wiley & Sons A/S Abstract –  The microstructure of otoliths of three amphidromous gobies (Sicydiinae) of the genus Sicyopterus has been analysed. One of these species, Sicyopterus lagocephalus has a widespread distribution whereas the other two are endemic (Sicyopterus aiensis, from Vanuatu and Sicyopterus sarasini, from New Caledonia). The microstructural analysis of the otoliths showed that the duration of the marine larval phase is significantly shorter for both endemic species than for the cosmopolitan species (131 ± 3.4 days for S. lagocephalus, 79.2 ± 4.6 days for S. aiensis and 76.5 ± 3.9 days for S. sarasini). These results led us to infer that it could be one of the factors explaining endemism. We have also improved our knowledge on the processes undergone during the marine phase by studying the growth of the otolith. This work allowed us to propose possible migration routes. These species’ reproduction period has also been studied by back‐calculating hatching dates. All these elements improve our understanding of the life‐history traits and dispersion strategies of these species, which is crucial to implementing conservation measures in order to protect them and their environment, both threatened by anthropogenic actions.

International managers use escapement estimates of the Deschutes River, Oregon, population of fall Chinook salmon Oncorhynchus tshawytscha to forecast abundance and assess population health. Fish are externally marked in the Deschutes River, and a subsample of the marked fish is recovered on the spawning grounds to provide data for estimating escapement. Escapement would be overestimated if some of the marked fish exited the Deschutes River prior to spawning (i.e., used this tributary temporarily). We used mark–recapture and radiotelemetry techniques to calculate (1) the proportion of adult fall Chinook salmon that entered the Deschutes River and subsequently exited the river prior to spawning and (2) the effect of such temporary entrances on spawning ground escapement estimates. We used separate criteria to calculate maximum and minimum temporary tributary use rates, which were then used to adjust the escapement estimates made with external‐tag data alone. Over the 3 years of study, the adjusted estimates were approximately 4–29% lower than the unadjusted estimates. We conclude that failure to adjust escapement estimates for temporary tributary use might lead to inflated harvest targets. To partially account for temporary tributary use, the lower 95% confidence limit for an escapement estimate could be used to regulate harvest.

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