Jason M. Robinson

Influence of Variable Interannual Summer Water Temperatures on Brook Trout Growth, Consumption, Reproduction, and Mortality in an Unstratified Adirondack Lake

Abstract Stressful water temperatures negatively affect physiological processes in fishes, yet evidence for how elevated temperatures influence population-level characteristics is rare. An 8-year field study of brook trout Salvelinus fontinalis in an unstratified Adirondack lake revealed that an aggregate measure of chronically stressful summer water temperatures strongly influenced brook trout population-level characteristics. We quantified chronic thermal stress using the cumulative degree-days over which bottom temperatures exceeded a range of thresholds (18–22°C) and found that the strongest relationships were with cumulative degree-days over 20°C (DD>20). Across years with similar brook trout densities, warmer summer water temperatures resulted in decreased brook trout growth, but growth was not reduced in a year with high water temperatures and low density. Maximum stomach fullness was negatively related to water temperature. Reproductive activity was negatively correlated with stressful summer ther...

Long-Term Retention and Visibility of Visible Implant Elastomer Tags in Brook Trout

Understanding how juvenile brook trout Salvelinus fontinalis from different sources contribute to fishable populations would be facilitated by a batch mark that could be applied to early life stages and be retained and visible throughout a fishs life. We evaluated visible implant elastomer (VIE) as a long-term batch mark for juvenile brook trout in hatchery and lake environments. Visible implant elastomer material was injected into the postocular eye tissue of 2,350 age-0 brook trout. Marked fish were stocked into three lakes, and an additional group was held in the hatchery. Tissue dissections revealed that VIE tag retention was 100% in both environments after 970 d. Tag visibility in hatchery fish examined under indoor fluorescent light was greater than 95% through 585 d, then dropped to 55-70% between 700 and 900 d. Tag visibility in lake fish examined under outdoor sunlight was 50-72% at 400 d and 0% at 959 d. When these same fish were observed in dark conditions with blue-filtered light and amber glasses, tag visibility was 75% for hatchery fish at 970 d and 100% for lake fish at 959 d. The high retention and increased visibility when viewed in dark conditions with blue-filtered light demonstrates that VIE tags are a suitable long-term batch mark for juvenile brook trout.

Sustainable exploitation and management of autogenic ecosystem engineers: application to oysters in Chesapeake Bay

Autogenic ecosystem engineers are critically important parts of many marine and estuarine systems because of their substantial effect on ecosystem services. Oysters are of particular importance because of their capacity to modify coastal and estuarine habitats and the highly degraded status of their habitats worldwide. However, models to predict dynamics of ecosystem engineers have not previously included the effects of exploitation. We developed a linked population and habitat model for autogenic ecosystem engineers undergoing exploitation. We parameterized the model to represent eastern oyster (Crassostrea virginica) in upper Chesapeake Bay by selecting sets of parameter values that matched observed rates of change in abundance and habitat. We used the model to evaluate the effects of a range of management and restoration options including sustainability of historical fishing pressure, effectiveness of a newly enacted sanctuary program, and relative performance of two restoration approaches. In general, autogenic ecosystem engineers are expected to be substantially less resilient to fishing than an equivalent species that does not rely on itself for habitat. Historical fishing mortality rates in upper Chesapeake Bay for oysters were above the levels that would lead to extirpation. Reductions in fishing or closure of the fishery were projected to lead to long-term increases in abundance and habitat. For fisheries to become sustainable outside of sanctuaries, a substantial larval subsidy would be required from oysters within sanctuaries. Restoration efforts using high-relief reefs were predicted to allow recovery within a shorter period of time than low-relief reefs. Models such as ours, that allow for feedbacks between population and habitat dynamics, can be effective tools for guiding management and restoration of autogenic ecosystem engineers.

Tradeoff between Assessment and Control of Aquatic Invasive Species: A Case Study of Sea Lamprey Management in the St. Marys River

AbstractAllocating resources between the gathering of information to guide management actions and implementing those actions presents an inherent tradeoff. This tradeoff is evident for control of the Sea Lamprey Petromyzon marinus in the St. Marys River, connecting Lakes Huron and Superior and a major source of parasitic Sea Lampreys to Lake Huron and northern Lake Michigan. Larval Sea Lampreys in the St. Marys River are controlled through the application of Bayluscide, which is applied to areas of high larval density. Bayluscide applications are guided with an annual deepwater electrofishing survey to estimate larval Sea Lamprey density at relatively fine spatial scales. We took a resampling approach to describe the effect of sampling intensity on the success of the larval Sea Lamprey management program and explicitly incorporated the economic tradeoff between assessment and control efforts to maximize numbers of larvae killed in the St. Marys River. When no tradeoff between assessment and control was in...

Rainbow trout performance in food-limited environments: implications for future assessment and management

We evaluated the performance of rainbow trout in food-limited lake and hatchery environments using whole-body water content as a proxy for fish energy reserves and lipid content. Relative abundance of rainbow trout stocked in an oligotrophic lake from 2002 to 2006 decreased by 88% in 145 days. Whole-body water content of rainbow trout increased following stocking in the lake and similar increases in water content were observed in fish from a food-deprived hatchery treatment. Water content in the fed hatchery fish was significantly lower than water content observed in stocked lake fish. Traditional metrics of body condition (i.e., Fultons K and relative weight) based on length–weight relationships were insufficient to detect the observed changes in whole-body water content for all lake and hatchery treatments. We conclude that depletion of energy reserves contributed to poor survival and low angling returns of stocked rainbow trout in the study lake.