Isotopic turnover in aquatic predators: quantifying the exploitation of migratory prey

Abstract

In the tidal freshwaters of Virginia, U.S.A., the blue catfish (Ictalurus furcatus), an introduced piscivore, derives a significant proportion of its nutrition from spawning anadromous fish (genus Alosa, including blueback herring (A. aestivalis), American shad (A. sapidissima), and alewife (A. pseudoharengus)). Because the Alosa are not continually available to I. furcatus, there is an isotopic turnover, defined as change in isotope composition due to growth and metabolic tissue replacement, in I. furcatus tissues associated with the diet switch from freshwater to anadromous fishes. However, isotopic turnover rates for ictalurid fish are unknown. This study determined the maximum isotopic turnover rate of channel catfish (Ictalurus punctatus) tissues and compared this maximum rate with that of I. furcatus captured in the field over the 3-month Alosa spawning run. Maximum turnover rates for 13 C were 0.014 and 0.017‰ per day in muscle and blood. For 34 S, rates were 0.017 and 0.020‰ per day in muscle and blood, respectively. Isotopic turnover of muscle carbon reflected growth rate, but sulfur did not match growth as well. Ictalurus furcatus captured in the field showed no enrichment during the Alosa spawning run owing to slow turnover and variable diet. In aquatic ecosystems that have migrating prey, exploitation by predators may be underestimated using isotopes because of slow tissue turnover.Résumé : Dans les eaux douces intertidales de la Virginie, aux États-Unis, Ictalurus furcatus, un poisson piscivore introduit, retire une proportion significative de son alimentation des poissons anadromes du genre Alosa, dont le l'Alose d'été (A. aestivalis), l'Alose savoureuse (A. sapidissima) et le Gaspareau (A. pseudoharengus), qui viennent y frayer. Parce que les Alosa ne sont pas toujours disponibles à I. furcatus, il se produit un virement isotopique dans les tissus de la barbue, c'est à dire un changement dans la composition isotopique reliée à la croissance et au renouvellement métabolique des tissus consécutif à un remplacement dans le régime des poissons d'eau douce par des poissons anadromes. Cependant, les taux de renouvellements isotopiques chez les poissons ictaluridés sont inconnus. Noua avons déterminé le taux maximal de renouvellement isotopique dans les tissus de la Barbue de rivière (Ictalurus punctatus) et l'avons comparé avec le taux maximum observé chez les I. furcatus capturés en nature durant les 3 mois de la montaison de reproduction des Alosa. Les taux maximaux de renouvellement du 13 C sont respectivement de 0,014 et de 0,017‰ par jour dans le muscle et dans le sang, alors que les taux maximaux de 34 S sont respectivement de 0,017 et de 0,020‰ par jour dans les mêmes tissus. Le taux de renouvellement isotopique du carbone musculaire reflète le taux de croissance, mais celui du soufre ne suit pas la croissance d'aussi près. Les I. furcatus capturés en nature ne font preuve d'aucun enrichissement durant la montaison des Alosa à cause du faible taux de renouvellement et du régime alimentaire variabl...

Tissue-specific turnover rates of the nitrogen stable isotope as functions of time and growth in a cyprinid fish

“…This strong influence of growth on isotopic turnover has also been reported for ectothermic animals more generally (e.g. MacAvoy et al, 2001;Perga & Gerdeaux, 2005;Heady & Moore, 2013) and is attributed to them having lower metabolic activities than endotherms (Bosley et al, 2002;Tominaga et al, 2003). Indeed, Perga and Gerdeaux (2005) suggested that as fish, and other ectotherms, have a discontinuous pattern of growth over the year, the stable isotope values of their muscle might only reflect their food consumed during periods of growth.…”

Stable carbon and nitrogen incorporation in blood and fin tissue of the catfish Pterygoplichthys disjunctivus (Siluriformes, Loricariidae)

“…λ can be defined as the sum of tissue net growth (k gt ) and tissue catabolic turnover (k dt ); thus, λ=k gt +k dt . If an animal, and hence, its tissues, is growing exponentially, then one can measure growth and determine the contribution of growth and tissue catabolic turnover to λ (Hesslein et al 1993;MacAvoy et al 2001;Jardine et al 2004;Sakano et al 2005;Suzuki et al 2005;Guelinckx et al 2007;Vollaire et al 2007;Zuanon et al 2007;Reich et al 2008). Following Reich et al (2008), we assumed that the fractional growth rate of a tissue was equal to the fractional rate of growth of the whole animal (k g ).…”

“…Thus, the use of carbon ( 13 C) and nitrogen ( 15 N) stable isotopes have become commonplace in dietary reconstruction for fishes. Few investigations, however, have determined turnover rates and tissue-diet discrimination factors (ΔX=δX tissue − δX diet ) of fish tissues in the laboratory before gathering animals and tissues from nature (Hesslein et al 1993;MacAvoy et al 2001;Jardine et al 2004;Sakano et al 2005;Suzuki et al 2005;Guelinckx et al 2007;Vollaire et al 2007;Zuanon et al 2007). These investigations suggest that empirically determined turnover rates and tissue-diet discrimination factors are essential for interpreting field isotopic signatures in a range of species.…”

Turnover rates of nitrogen stable isotopes in the salt marsh mummichog, Fundulus heteroclitus, following a laboratory diet switch

“…Most laboratory diet-switch experiments (Hesslein et al 1993;Herzka and Holt 2000;MacAvoy et al 2001;Bosley et al 2002;Tominaga et al 2003) and field studies (Vander Zanden et al 1998;Maruyama et al 2001) show that growth is the primary factor causing stable isotopic change in fish following a diet shift. One field study of larval red drum has found significant metabolic turnover, and the authors suggest that differences between larval energetic requirements in the laboratory and in the field may account for variation between lab and field results (Herzka et al 2001).…”

“…Stable isotopes have been used to determine the placement of mummichogs in food webs (Deegan and Garritt 1997) and estimate habitat use (Currin et al 2003). Knowledge of species-specific and tissuespecific turnover and nitrogen discrimination is important for accurate interpretation of isotopic data because past studies have demonstrated variation between species (Hesslein et al 1993;Herzka and Holt 2000;MacAvoy et al 2001;Bosley et al 2002) and also between tissues of the same species (Tieszen et al 1983;Hobson and Clark 1992).…”