Trace elements in otoliths indicate the use of open-coast versus bay nursery habitats by juvenile California halibut

Abstract

Many coastal fishes use inshore nursery habitats as juveniles, but it is often difficult to define which nursery areas supply most recruits to adult populations. We tested whether trace element concentrations in otoliths can be used to identify which of 2 nursery habitats (bays or shallow open coast) were occupied by juvenile California halibut. Juveniles from bays in 1998 had concentrations of Cu and Pb in their otoliths that were higher than those in open coast juveniles of the same year. This broad-scale difference between bay and open coast juveniles remained intact when bay juveniles from 1994 to 1997 were added to the comparison, and juvenile halibut could be assigned to their nursery habitat of origin quite accurately (83%) using otolith concentrations of Cu and Pb. At a finer spatial scale, otolith concentrations of Cu and Pb differed among individual bays, and fish from the same bay could differ among years, precluding their use as markers of nursery habitat use at these scales. Like halibut otoliths, sediments from bays had higher concentrations of Cu and Pb than open coast nursery sites, and this difference was consistent over 11 yr. Otoliths and sediments from individual bays, however, showed no correlation in Cu and Pb concentrations. The concentration of Cu and Pb in sediments and their deposition in otoliths were thus loosely matched at a broad scale, though the underlying cause of this link is not known. A discriminant model, parameterized using Cu and Pb levels in juvenile otoliths, was used to classify prior nursery habitat use by 19 larger halibut (of unknown origin). Eleven of these halibut had high levels of Cu and Pb in the part of the otolith deposited as a juvenile, and were classified as of bay origin. The other 8 halibut had low otolith Cu and Pb levels in the juvenile portion of their otoliths and were classified as having used open coast nurseries. Overall, our results suggest that this approach has the potential to allow identification of nursery habitat use by California halibut at a broad scale (bay vs open coast) but not at a fine scale (individual bays).

Availability, usage and expected contribution of potential nursery habitats for the California halibut

“…The majority of fish within embayments were in Mission and San Diego bays. Our findings concerning nursery habitat contribution show general agreement with the results of Forrester and Swearer (2002), who employed an elemental fingerprinting approach along a 300 km section of southern California to determine nursery habitat utilization. They concluded that approximately 50% of adult halibut had utilized protected embayments as nursery habitats, while the remaining 50% spent their juvenile period in the shallows of the exposed coastline.…”

Large scale-variability in otolith microstructure and microchemistry: The case study ofDiplodus sargus sargus(Pisces: Sparidae) in the Mediterranean Sea

“…This is reflected in an increasing number of published papers that mostly deal with tropical regions and, to a lesser extent, with temperate regions (i.e. Forrester & Swearer 2002;Vasconcelos et al 2007Vasconcelos et al , 2008Standish et al 2008). …”

High resolution micromill sampling for analysis of fish otoliths by ICP-MS: Effects of sampling and specimen preparation on trace element fingerprints

“…These elements are extremely sensitive to any changes in laser and ICP operating conditions (Koch and Günther, 2007) (Newman, 1996). In the analysis of otoliths of juvenile halibut by high resolution ICP-MS, for instance, instrumental results were sporadic for several trace elements, including Ag, Al, Cd, Co, Ni, Sn and Zn, due to the detection problems, therefore, these elements were not considered in statistical evaluations (Forrester and Swearer, 2002).…”

“…In this study, we opted for a different tack on this problem and developed a probe-based method -high resolution micromill sampling -a method that mechanically isolates otolith's core corresponding to the first year of life. A solid phase preconcentration procedure was interfaced to an ICP-MS instrument to enhance the sensitivity since high variability and inaccuracy in instrumental results for trace elements were mainly due to the lack of sensitivity as was observed in the past studies (Milton and Chenery, 2001;Forrester and Swearer, 2002 …”

“…A principal application of otolith microchemistry is to assign widely distributed adults to their natal nursery habitats using otoliths as birth certificates (Secor, 2004) or natural tags (Campana, 2000). Classification accuracy using otolith microchemistry is moderate and often ranges between 60 and 80% (Forrester and Swearer, 2002;Secor et al, 2002;Rooker et al, 2003;Patterson et al, 2004;Arslan and Secor, 2005;Swan et al, 2006). Such classification rates show promise, but are often insufficient for intended applications.…”