Recruitment sources of brown trout identified by otolith trace element signatures

Abstract

This study examined whether element:Ca ratios within the otoliths of juvenile brown trout could provide accurate trace element signatures for specific natal tributaries, and attempted to match these to trace element natal signatures found within the otoliths of adult trout caught in the main stem rivers of the same catchment. The trace element signatures of juvenile trout otoliths were analysed from a sample of eight tributaries representing the main sub-catchments of the Motueka River catchment, New Zealand. Trace element signatures were determined using laser ablation inductively coupled plasma mass spectrometry, and differentiated using linear discriminant function analysis with an overall cross-validated classification success of 96.8%. Temporal stability in element:Ca ratios was investigated by repeat collections of juvenile fish over two years. Natal signatures from 11 of 23 adult trout sampled from the catchment main stems were matched to one of the eight tributary signatures showing recruitment sources to be spread relatively evenly throughout the catchment. This study demonstrates the potential of using otolith trace element analysis to determine the natal origins of freshwater fish within a catchment.

Assigning origins in a potentially mixed‐stock recreational sea trout (Salmo trutta) fishery

“…First, we showed that otolith chemistry in juveniles reflects site-specific conditions and can be used successfully to differentiate among anadromous adults later in life. For example, Walther et al (2008) found that only 6% of spawning American shad (Alosa sapidissima) in the York River system in Virginia were produced elsewhere and thus were potential strays from other rivers, and Olley et al (2011) were able to use otolith chemistry to show that recruitment sources for brown trout were spread evenly throughout their study catchment. For example, of the 118 fish harvested in the Renews River estuary over 3 years, 96% were classified as having been produced in that river, whereas only 22% of fish captured at the Chance Cove estuary were clas- CC 10 (100) 0 (0) 0 (0) 0 (0) 10 (100) RR 0 (0) 22 (100) 0 (0) 0 (0) 22 (100) PR 1 (17) 0 (0) 5 (83) 0 (0) 6 (100) PB 0 (0) 0 (0) 0 (0) 10 (100) 10 (100) Total 11 (23) 22 (46) 5 (11) 10 (21) 48 (100) DFA, discriminant function analysis; CC, Chance Cove; RR, Renews River; PR, Port Rexton; PB, Pierre's Brook.…”

“…The use of otolith chemistry is an increasingly common tool to infer stock structure in recreationally important species (Patterson & Swearer 2008;Wells et al 2010;Newman et al 2011;Ramsay et al 2011). For example, Walther et al (2008) found that only 6% of spawning American shad (Alosa sapidissima) in the York River system in Virginia were produced elsewhere and thus were potential strays from other rivers, and Olley et al (2011) were able to use otolith chemistry to show that recruitment sources for brown trout were spread evenly throughout their study catchment. However, to the best of our knowledge, our study was the first to investigate population mixing between catchments in sea run brown trout in a recreational fishery.…”

“…However, the use of these natural tags requires that each stock or population displays unique chemical otolith signatures (Elsdon et al 2008). Olley et al 2011;Ramsay et al 2011). If differences are found among locations, then the juvenile chemical fingerprint can be used as a baseline to facilitate classification of individuals with unknown rearing origins.…”

“…Encouragingly, a number of studies have successfully employed the use of differential otolith chemistries to associate individuals with habitat (Veinott & Porter 2005;Lara et al 2008;Patterson & Swearer 2008;Walther et al 2008;Clarke et al 2010;Cuveliers et al 2010) and to quantify recruitment patterns in freshwater recreational fisheries (e.g. Olley et al 2011;Ramsay et al 2011).…”

Integrated catchment management—a decade of research in the Motueka River catchment

“…Two papers examine fish movements. Olley et al (2011) demonstrate how the microchemistry of trout otoliths (ear bones) can be used to infer patterns of fish movement within catchments and the potential power of this technique for determining critical spawning areas that contribute to the main-stem fishery. Doehring et al (2011) test an acoustic camera for describing juvenile galaxiid (whitebait) movement through tidal floodgates near the river mouth.…”