Cynthia M. Jones

Strontium and barium uptake in aragonitic otoliths of marine fish

Abstract Minor and trace element analyses of fish otoliths (ear stones) may provide a high-resolution reconstruction of temperature histories and trace element compositions of aquatic systems where other environmental proxies are not available. However, before otoliths can be used to reconstruct water chemistry, it is essential to validate the assumption that trace metals in otoliths are deposited in proportion to dissolved concentrations in the ambient environment. We show, using a marine fish (Leiostomus xanthurus) reared in the laboratory under controlled experimental conditions, that otolith Sr/Ca and Ba/Ca ratios are deposited in proportion to their respective ratios in ambient waters. Temperature significantly affected Sr incorporation but did not affect Ba incorporation in otoliths. Sr/Ca partition coefficients (DSr) were 0.182 and 0.205 at 20°C and 25°C, respectively. The partition coefficients for Ba/Ca were 0.055 at 20°C and 0.062 at 25°C. A nonlinearity in the relationship between DBa and ambient Ba concentrations suggested that extrapolation beyond the Ba levels used in the experiment was not justified. On the basis of our results, it should be possible to reconstruct Sr/Ca and Ba/Ca levels in environments inhabited by fish based on otolith chemistry. Furthermore, Sr/Ca thermometry may also be possible using fish otoliths, but validation of the temperature dependence of Sr/Ca in otoliths will be required. We believe otoliths represent an excellent, and as yet underused, record of the physicochemical properties of both modern and ancient aquatic environments.

Catch Rate Estimation for Roving and Access Point Surveys

Abstract Optimal designs of recreational angler surveys may require complemented surveys, in which different contact methods are used to estimate effort and catch. All common methods of estimating catch involve on-site interviews that may either be based on access (complete trip) or roving (incomplete trip) interviews. In roving surveys, anglers to be interviewed on a given day are intercepted with a probability proportional to the length of their completed fishing trip, whereas in access surveys, anglers are intercepted as they leave the fishery and are intercepted with the same probability regardless of the length of their completed fishing trip. There are four complemented survey designs which use interviews at access points (mail–access, telephone–access, aerial–access, and roving–access); there are four corresponding designs which use roving interviews (mail–roving. telephone–roving, aerial–roving, and roving–roving). For all of these surveys, total catch is estimated as the product of total effort a...

Properties of catch rates used in analysis of angler surveys.

Abstract On-site angler surveys commonly yield data on fish catch, fishing effort, and their variances for a sample of anglers. The ratio of catch to effort, or catch rate, often is multiplied by an independent estimate of total effort to calculate total catch (with its confidence interval) throughout the fishery. The most frequently used measures of catch rate are the ratio-of-means estimator (mean catch per angler divided by mean effort per angler) and the mean-of-ratios estimator (mean anglers catch rate). Bias and misleading confidence intervals are associated with use of ratio estimators, and the best catch rate measure for estimating total catch has been uncertain. We used statistical theory and simulation modeling to demonstrate that the most appropriate estimator (least bias, truest confidence interval) depends on the method of sampling. The ratio-of-means catch rate is better when anglers are sampled with equal probability at the completion of their trips (as in access point surveys). The mean-o...

Age under-estimation in New Zealand porbeagle sharks (Lamna nasus): is there an upper limit to ages that can be determined from shark vertebrae?

Annual deposition of growth bands in vertebrae has been validated for many shark species, and is now widely regarded as the norm. However, vertebrae are part of the sharks axial skeleton, and band deposition may stop in old sharks when somatic growth ceases. We aged vertebral sections from New Zealand porbeagle sharks (Lamna nasus) under reflected white light and using X-radiographs. Bomb radiocarbon assays supported vertebral age estimates up to ∼20 years, but not at older ages. The results suggest that older porbeagles were under-aged by as much as 50% from vertebral band counts, presumably because band width declined to a point where it became unresolvable. This has important implications for growth studies on other long-lived sharks. Estimated ages at sexual maturity were 8-11 years for males and 15-18 years for females, and longevity may be ∼65 years. New Zealand and North Atlantic porbeagles differ in these parameters, and in length at maturity and maximum length, suggesting genetic isolation of the two populations.

Can otolith chemistry be used for identifying essential seagrass habitats for juvenile spotted seatrout, Cynoscion nebulosus, in Chesapeake Bay?

We investigated the variability of otolith chemistry in juvenile spotted seatrout from Chesapeake Bay seagrass habitats in 1998 and 2001, to assess whether otolith elemental and isotopic composition could be used to identify the most essential seagrass habitats for those juvenile fish. Otolith chemistry (Ca, Mn, Sr, Ba, and La; δ13C, δ18O) of juvenile fish collected in the five major seagrass habitats (Potomac, Rappahannock, York, Island, and Pocomoke Sound) showed significant variability within and between years. Although the ability of trace elements to allocate individual fish may vary between years, in combination with stable isotopes, they achieve high classification accuracy averaging 80–82% in the Pocomoke Sound and the Island, and 95–100% in the York and the Potomac habitats. The trace elements (Mn, Ba, and La) provided the best discrimination in 2001, a year of lower freshwater discharge than 1998. This is the first application of a rare earth element measured in otoliths (La) to discriminate habitats, and identify seagrass habitats for juvenile spotted seatrout at spatial scales of 15 km. Such fine spatial scale discrimination of habitats has not been previously achieved in estuaries and will distinguish fish born in individual seagrass beds in the Bay.

CALCULATION OF CATCH RATE AND TOTAL CATCH IN ROVING SURVEYS OF ANGLERS

SUMMARY To estimate the total catch in a sport fishery sampled by a roving creel survey, we multiply an estimate of the total fishing effort by the estimated catch rate (i.e., catch per unit of fishing effort). While the statistical theory for estimating the fishing effort from instantaneous or progressive counts is well established, there is much confusion about the appropriate way to estimate the catch rate. Most studies have used the ratio of means or the mean of the ratios of individual catches and efforts. We analyzed the properties of these estimators of catch rate under the assumption that fishing is a stationary Poisson process. The ratio of means estimator has a finite second moment, while the mean ratio estimator has infinite variance. Simulation studies showed that the mean of ratios estimator tends to have high and unstable mean squared error relative to the ratio of means estimator and this is in accordance with empirical observations. We also studied the properties of the mean of ratios estimator when all interviews with people fishing for less than e minutes duration were disregarded for values of e up to 60 minutes. There was typically a marked reduction in mean squared error when the shorter trips were not included. We recommend that the mean of ratios estimator, with all trips less than 30 minutes disregarded, be used to estimate catch rate and hence total catch under the roving creel survey design. It has the correct expectation (at least approximately after the truncation) and almost always had smaller mean squared error than the ratio of means estimates in our simulations.

The Theoretical Basis of an Access Site Angler Survey Design

The theoretical basis is presented for a new design of angler surveys. The design was used in a survey to assess recreational fishing on New Yorks Great Lakes and tributaries. The large geographic area and budget constraints necessitated a survey design that could cover broad areas with the maximum efficiency of a limited number of survey agents. The model for the survey relates the amount of time that a survey agent has the angling partys car in view at an access site with the amount of time the party spent fishing. Geometric inclusion probability functions are developed and equations for estimating fishing effort are given. The special case when access sites are not limited to angler use (the case for many marinas) is also discussed and an estimator for fishing effort developed.

Fitting growth curves to retrospective size-at-age data

Abstract The bones and scales of fish are a rich source of information, for they encode in their microstructure the fish’s age and growth history. The growth history in the hard part is used to estimate the somatic growth history of an individual. This, in turn, is used to estimate the growth of the population. Although straightforward in concept, the estimation of retrospective-growth histories and their subsequent use has been problematic. Fisheries scientists have paid a great deal of attention to the proper techniques to estimate somatic growth from hard-part growth. In contrast, little attention has been paid to the use of these retrospective data to estimate population growth. To date, improper analysis of these estimated growth histories abounds in the literature. This first application of nonlinear repeated-measures analysis of the von Bertalanffy growth function, shows that parameter estimates are accurate and precise. I used retrospective sequences of size-at-age for red grouper, Epinephelus morio , to test bias in the use of nonlinear least-squares (NLLS) regression compared with a repeated-measures approach. An NLLS regression assumes that each datum is independent; when this assumption is violated, the parameter estimates that it produces are biased. The results show that the estimate for asymptotic length L ∞ , increasingly underestimates true L ∞ with increased mean age in the catch through the use of observed and simulated data. Although the bias is not large, use of the correct analytic procedure eliminates this bias entirely. Hence, I strongly recommend the use of repeated-measures analysis of these retrospective-growth histories.

Better Science Needed for Restoration in the Gulf of Mexico

In the wake of the BP oil spill, U.S. agencies need research plans to collect data that will aid in managing and assessing marine species and ecosystems. The 2010 BP Deepwater Horizon oil spill in the Gulf of Mexico (GoM) has damaged marine ecosystems and jeopardized endangered and commercial species under U.S. jurisdiction (see the figure). Agencies that manage protected species—including the U.S. National Marine Fisheries Service and the U.S. Fish and Wildlife Service—are tasked with recovering these populations. But many populations have not been adequately assessed, so recovery cannot be measured. Achieving mandated recovery goals depends on understanding both population trends and the demographic processes that drive those trends. After the 1989 Exxon Valdez Alaskan oil spill, evaluations of effects on wildlife were ambiguous, in part because limited data on abundance and demography precluded detection of change (1). Sadly, the situation in the GoM is similar more than 20 years later. As concluded in the National Commission report on the BP spill (2) released 11 January, “Scientists simply do not yet know how to predict the ecological consequences and effects on key species that might result from oil exposure…” We argue that scientists know how to make these assessments, but lack critical data to achieve this goal.

Geographic Variation in Trace Element Composition of Juvenile Weakfish Scales

Abstract We determined Mg: Ca, Mn: Ca, Sr: Ca, and Ba: Ca levels in scales from juvenile weakfish Cynoscion regalis from five estuarine locations along the Atlantic coast of the United States using laser ablation inductively coupled plasma mass spectrometry. Significant variability in the multivariate elemental signatures was found among sites within an estuary, among estuaries, and between collections from 1996 and 1997. Bootstrapped 95% confidence ellipses on mean scores from a canonical discriminant analysis found that most estuaries were significantly separated in discriminant space in both years. Linear discriminant function analyses (LDFA) were then used to classify individual weakfish to their natal estuary. In 1996, cross-validated classification accuracy ranged from 38% for Delaware Bay to 86% for Pamlico Sound, with an overall accuracy of 67%. Classification accuracy in 1997 ranged from 41% for Chesapeake Bay to 83% for Pamlico Sound, with an overall accuracy of 65%. The use of artificial neural...