Richard T. Kraus

Life History and Stock Structure of Atlantic Bluefin Tuna (Thunnus thynnus)

Our understanding of the biology of Atlantic bluefin tuna (Thunnus thynnus) has increased profoundly in the last decade, and the progress is attributed to the development and application of a variety of novel tools. Here we provide a comprehensive examination of available data on the life history and stock structure of T. thynnus by re-examining current databases and literature and highlighting findings from recent studies using approaches such as archival tags and natural markers (e.g., genetics, otolith chemistry). The present review provides a detailed synthesis on the reproductive biology, feeding ecology, growth, mortality, migration, and stock structure of T. thynnus. In addition to characterizing key life history attributes and discussing stock-specific (east versus west) differences, the implication of trans-Atlantic movement and mixing are addressed. We also identify significant data needs that still exist and must be addressed to promote effective management and rapid recovery of T. thynnus populations.

Dispersive behaviors of black drum and red drum: Is otolith Sr:Ca a reliable indicator of salinity history?

We tested the hypothesis that strontium:calcium (Sr:Ca) in otoliths are reflective of environmental salinity experienced by two estuarine fishes during early life. Laboratory and field experiments were performed to examine the effects of salinity and temperature on Sr:Ca in otoliths of black drum (Pogonias cromis) and red drum (Sciaenops ocellatus). Otolith Sr:Ca of juveniles reared at four salinities (5‰, 15‰, 25‰, 35‰) differed significantly forP. cromis while no salinity effect was observed forS. ocellatus. Otolith Sr:Ca of both species were not affected by temperature (23°C and 30°C), suggesting that partitioning of Sr in otoliths of these taxa is constant over the temperature range examined. A field verification trial was conducted forP. cromis and a positive relationship between otolith Sr:Ca and ambient salinity was observed, even though the percent variability explained was modest. A series of Sr:Ca point measurements were taken from the core to the edge of the otoliths of wildP. cromis andS. ocellatus, and otolith Sr:Ca chronologies of both species showed conspicuous declines during the first few months of life. While Sr:Ca chronologies of both species suggest that ingress is associated with a reduction in otolith Sr:Ca, inconsistencies in laboratory and field experiments intimate that Sr uptake in the otolith may be insensitive to salinity and regulated by other factors (aqueous chemistry, ontogenetic shifts in habitat, or physiology). Results from early life history transects of otolith Sr:Ca conform to expected patterns of estuarine ingress-egress during early life and indicate that the approach may be useful for detecting large-scale habitat transitions (marine to estuarine habitats).

Seasonal Patterns of Movement and Residency by Striped Bass within a Subestuary of the Chesapeake Bay

Abstract Although often generalized as anadromous, striped bass Morone saxatilis show varying degrees of residency in natal estuaries and exhibit diverse seasonal migration patterns in estuarine and coastal waters. Most coastal striped bass originate from the Chesapeake Bay, but the bay and its subestuaries also harbor substantial numbers of striped bass throughout the year. The degree to which resident striped bass inhabit individual subestuaries was evaluated by use of acoustic telemetry. We investigated seasonal patterns of movement within and outside of the Patuxent River, a centrally located, intermediate-size subestuary of the Chesapeake Bay. A fixed acoustic receiver array was deployed in the Patuxent River, and 42 acoustic-tagged striped bass were monitored for a 2-year period (2008–2009). Seasonal patterns of movement within the subestuary were similar between years and were generally consistent with overall anadromous behavior: striped bass moved downestuary during winter to points outside the P...