Jason J. Schaffler

Fish Species Distribution in Seagrass Habitats of Chesapeake Bay are Structured by Abiotic and Biotic Factors

Abstract Seagrass habitats have long been known to serve as nursery habitats for juvenile fish by providing refuges from predation and areas of high forage abundance. However, comparatively less is known about other factors structuring fish communities that make extensive use of seagrass as nursery habitat. We examined both physical and biological factors that may structure the juvenile seagrass-associated fish communities across a synoptic-scale multiyear study in lower Chesapeake Bay. Across 3 years of sampling, we collected 21,153 fish from 31 species. Silver Perch Bairdiella chrysoura made up over 86% of all individuals collected. Nine additional species made up at least 1% of the fish community in the bay but were at very different abundances than historical estimates of the fish community from the early 1980s. Eight species, including Silver Perch, showed a relationship with measured gradients of temperature or salinity and Spot Leiostomus xanthurus showed a negative relationship with the presence of macroalgae. Climate change, particularly increased precipitation and runoff from frequent and intense events, has the potential to alter fish—habitat relationships in seagrass beds and other habitats and may have already altered the fish community composition. Comparisons of fish species to historical data from the 1970s, our data, and recent contemporary data in the late 2000s suggests this has occurred.

Beyond Zar: the use and abuse of classification statistics for otolith chemistry.

Classification method performance was evaluated using otolith chemistry of juvenile Atlantic menhaden Brevoortia tyrannus when assumptions of data normality were met and were violated. Four methods were tested [linear discriminant function analysis (LDFA), quadratic discriminant function analysis (QDFA), random forest (RF) and artificial neural networks (ANN)] using computer simulation to determine their performance when variable-group means ranged from small to large and their performance under conditions of typical skewness to double the amount of skewness typically observed. Using the kappa index, the parametric methods performed best after applying appropriate data transformation, gaining 2% better performance with LDFA performing slightly better than QDFA. RF performed as well as QDFA and showed no difference in performance between raw and transformed data while the performance of ANN was the poorest and worse with raw data. All methods performed well when group differences were large, but parametric methods outperformed machine-learning methods. When data were skewed the performance of all methods declined and worsened with greater skewness, but RF performed consistently as well or better than the other methods in the presence of skewness. The parametric methods were found to be more powerful when assumptions of normality can be met and can be used confidently when skewness and kurtosis are minimized. When these assumptions cannot be minimized, then machine-algorithm methods should also be tried.

Coast-Wide Nursery Contribution of New Recruits to the Population of Atlantic Menhaden

AbstractThe Atlantic Menhaden Brevoortia tyrannus is a coastal-spawning, estuarine-dependent clupeid that has economic and environmental value along the U.S. East Coast. Atlantic Menhaden spawn offshore and rely on circulation patterns in the ocean to deliver larvae to multiple estuarine nursery grounds for juvenile development before recruiting to the adult stock. Historical estimates of the Atlantic Menhaden nursery contribution by each of the major nurseries along the coast indicate that the Chesapeake Bay produces 69% of the recruits to the adult stock; yet, these estimates are over 20 years old and have never been quantitatively validated. We used otolith chemistry for three cohorts of age-1 Atlantic Menhaden to evaluate nursery contribution and provide updated recruitment rates for each of the nursery grounds for this species. Based on geochemical signatures and a quadratic discriminant function that assigned juveniles to their nursery grounds at nearly 90% accuracy, we classified age-1 menhaden of ...

Documenting utility of paddlefish otoliths for quantification of metals using inductively coupled plasma mass spectrometry

RATIONALE The otoliths of the inner ear of fishes record the environment of their surrounding water throughout their life. For paddlefish (Polyodon spathula), otoliths have not been routinely used by scientists since their detriments were outlined in the early 1940s. We sought to determine if paddlefish otoliths were useful for resolving elemental information contained within. METHODS Adult paddlefish were collected from two wild, self-sustaining populations in Oklahoma reservoirs in the Arkansas River basin. Juveniles were obtained from a hatchery in the Red River basin of Oklahoma. Otoliths were removed and laser ablation, inductively coupled plasma mass spectrometry (ICP-MS) was used to quantify eight elements (Li, Mg, Mn, Rb, Sr, Y, Ba, and Pb) along the core and edge portions, which were analyzed for differences between otolith regions and among paddlefish sources. RESULTS Differences were found among samples for six of the eight elements examined. Otoliths from Red River basin paddlefish born in a hatchery had significantly lower amounts of Mg and Mn, but higher levels of Rb than otoliths from wild paddlefish in the Arkansas River basin. Concentrations of Y, Sr, and Ba were reduced on the edges of adult paddlefish from both reservoirs compared with the cores. CONCLUSIONS This research shows the utility of using an ICP-MS analysis of paddlefish otoliths. Future research that seeks to determine sources of paddlefish production, such as which reservoir tributaries are most important for reproduction or what proportion of the population is composed of wild versus hatchery-produced individuals, appears promising.

Do Alternative Leaders Affect Fish Catch in Pound Nets at the Mouth of Chesapeake Bay

Abstract More than 60 stranded bottlenose dolphins Tursiops truncatus exhibiting marks consistent with interactions with pound nets have been documented in the lower Chesapeake Bay since 1997. Given this high rate of bycatch, action is needed to mitigate bottlenose dolphin mortality. However, for any such modification to the pound net to be acceptable to fishers, a clear demonstration of no reduction in the targeted finfish catch will be required. Working with fishers, we evaluated the effect of an experimental pound net leader on finfish catch. The experimental leader entailed similar or greater catches of finfish than did the traditional leader. Further, catches of Batoidea (cownose ray Rhinoptera bonasus, bullnose ray Myliobatis freminvillei, southern stingray Dasyatis americana and Atlantic stingray D. sabina) and clearnose skates Raja eglanteria were reduced with the experimental leader. This example demonstrates that working with fishers to devise alternative harvest strategies can result in the imp...

Contribution of Nursery Areas to the Adult Population of Atlantic Menhaden

AbstractMuch is known about the life history of the Atlantic Menhaden Brevoortia tyrannus, and yet the impact of multiple nursery grounds on population structure remains a central challenge in understanding this species. Historic estimates hypothesized that the Chesapeake Bay is the predominant contributor of new recruits (age 1) to the adult stock, but no research has been done on which nursery grounds support the adult stock. In this study, we used previously established chemical signatures from juvenile otoliths to evaluate the natal origin of adult Atlantic Menhaden (ages 2–4) that correspond to the 2008–2010 year-classes. We found that, on average across ages, the northeastern, Chesapeake Bay, and southeastern nursery grounds each contribute about 30% of the recruits that persist into older age-classes and that over the 3 years of the study the proportion of nursery contributions from each nursery was relatively stable. This has repercussions for the fishery, as most fish ages 2–3 are fully mature an...