Otolith Stable Isotope Analyses Research Articles

Reconstructing habitat use, identifying origin and discrimination of the barramundi (wild and farmed) populations using otolith stable isotope analysis

Reconstructing habitat use, identifying origin and discrimination of the barramundi (wild and farmed) populations using otolith stable isotope analysis

Otolith stable isotope micro-sampling to discriminate poorly studied stocks: Crevalle Jack in the eastern gulf of Mexico

Developing conservation and management strategies for species with complex life histories, broad spatial distributions, and long lifespans is notoriously difficult. Too often managers cannot identify critical habitats nor vulnerable life stages because of the sheer scale of migration or uncertainty about connectivity among populations. Advancements in otolith stable isotope analysis, and specifically sampling of discrete otolith layers, have provided opportunities to assess lifetime migrations and connectivity without extensive, long-term field sampling. Here, we compared carbon and oxygen stable isotope values in discrete otolith layers for Crevalle Jack (an unregulated and data-poor species) captured in two isotopically distinct regions (Alabama and the Florida Keys). Our goal was to address vital questions about how broad-scale movement patterns through ontogeny differ between the two regions and whether connectivity occurs throughout the life history. Our results revealed that Crevalle Jack appear to inhabit inshore nursery areas at age-0, before migrating to coastal/offshore habitats between age-1 and age-2. Comparisons between fish collected in northeastern and southeastern Gulf of Mexico regions revealed significant differences in the patterns of stable isotope values throughout the life history and in otolith δ 13 C values. Despite these differences that suggest a separation of the two populations, individual variability was significant, hindering our ability to determine whether fish from the two regions represent separate, self-recruiting stocks. Our research illustrates the potential of otolith stable isotope micro-sampling as a tool for examining broad-scale movement and migration patterns of fishes, and informing future research and management. • Understanding population connectivity is essential to fisheries management. • Otolith stable isotope micro-sampling can help examine movement and connectivity. • Lifetime stable isotopes in Gulf of Mexico Crevalle Jack otoliths were assessed. • Stable isotopes helped elucidate population connectivity and individual variability. • Results will aid in management of an unregulated fish species.

Establishment of invasive Black Carp (Mylopharyngodon piceus) in the Mississippi River basin: identifying sources and year classes contributing to recruitment

Black Carp (Mylopharyngodon piceus) was imported to the USA to control aquaculture pond snails. This species has escaped captivity and occurs in parts of the Mississippi River, several tributaries, and floodplain lakes, which is concerning due to potential competition with native fishes and predation on native mussels, many of which are imperiled. However, Black Carp captures have primarily been incidental by commercial fishers, and evidence of reproduction in the wild is limited. The objectives of this study were to assess relative abundance of aquaculture-origin and wild Black Carp using ploidy and otolith stable isotope analysis, identify spatial extent of natural reproduction using otolith microchemistry, assess age distributions of wild and aquaculture-source Black Carp to infer years in which natural reproduction occurred and timing of aquaculture escapement or introductions, and estimate size and age at maturation to assess whether recruitment to adulthood has occurred. Results revealed that Black Carp are established in parts of the Mississippi River basin based on findings that: (1) non-captive Black Carp primarily consist of fertile, naturally-reproduced fish, (2) reproduction has occurred in several rivers, (3) multiple year classes of wild fish are present, and (4) wild fish have recruited to adulthood. Multiple introductions or escapements of aquaculture-source fish into the wild, including both fertile and functionally sterile individuals, were also inferred. Individual growth appears to be rapid, although considerable variation was observed among fish. Additional study is suggested to refine understanding of where and when Black Carp reproduction is occurring in the Mississippi River basin.

Diary of a bluegill (Lepomis macrochirus): daily δ13C and δ18O records in otoliths by ion microprobe

Otoliths provide information about an individual fish’s environment at ecologically relevant time scales. We used ion microprobe analysis to produce high-resolution δ13C and δ18O time series from two age-4 bluegill (Lepomis macrochirus) otoliths, which provided insight into fish behavior and otolith fractionation processes. Scanning electron microscope images revealed δ13C and δ18O pit diameters of 10 and 15 µm, respectively, corresponding to 1–5 and 2–9 daily increments during rapid otolith growth and 6–9 and 12–25 increments near annual otolith growth checks. Spot-to-spot reproducibility (1 SD) of the calcite standards was <0.2‰ for δ18O and <0.4‰ for δ13C and was small enough to resolve a change in a fish’s ambient temperature of approximately 1 °C. A whole-lake 13C addition experiment elevated the δ13C of the lake’s dissolved inorganic carbon for 56 days during the summer of 2005. Mixing model results indicated that the proportion of dietary carbon in otoliths (M) was similar for both fish (BLG-3, M = 0.45; BLG-12, M = 0.35), but the relation between M and proxies of metabolic rate differed between fish. Otolith stable isotope analysis by ion microprobe can reveal the environmental history of an individual fish and contribute to our understanding of processes that influence isotope ratio fractionation in otoliths.