Graduate Thesis Research

** From February 2012, needs updating

Responses of esocid fishes to warming temperatures: laboratory experimentation on species metabolic rates


 Three native esocid species reside in the Saint Lawrence River: grass pickerel Esox americana vermiculata, northern pike Esox lucius, and muskellunge Esox masquenongy. Abundances of these species have altered over the past couple decades and a few specimens of a fourth esocid species, chain pickerel Esox niger, have been found in the upper river system beginning in 2008. With the appearance of the non-native chain pickerel, some scientists and fisherman are concerned by a possible invasion of the species. Furthermore, an apparent increase in grass pickerel and substantial long term decline of both apex predators, northern pike and muskellunge, beg the question "What's causing these abundance changes?"

 young of year     grass pickerel                                                        northern pike                                                    muskellunge                                                        chain pickerel

The Saint Lawrence River has been subject to a multitude of changes as far back as the logging and agricultural boom of the late 1800s. Other's include 1930s eutrophication, the Moses Saunders power dam and St. Lawrence Seaway in the late 1950s, Dreissenid mussels and round goby invasions of the 1980s and 2000s respectively, and ongoing climate change.  Since 1981, 6 of the 20 warmest years were observed in the river but none of the coldest (Hudon et al 2010). Additionally, literatures suggests that the mean annual water temperature has increase by 1.3 C from 1960 to 2007. As esocid spawning, growth, development, year-class-strength, and ultimately success depend in part on water temperature, I've decided to focus on thermal regimes for this study.

My graduate research is aiming to investigate warming thermal environments as a mechanism for altering esocid abundances. On a narrower scope, I'd like to determine how closely related species respond to thermal regimes, metabolically.

Hypothesis: at warmer temperatures, pickerel species will have lowest standard metabolic rates (as compared to northern pike and muskellunge)

With lower standard metabolic rates, is higher efficiency. I define efficiency as being able to cope in the environment with the least amount of energy expenditure. With less energy used, more can be allocated to other physiological processes such as growth and development. Thus, I presume specimens with the lowest SMR and highest efficiency at high temperatures to also have the highest potential for success in an environment that is experiencing a warming climate.

I chose to work with young of year specimens as that critial life stage consists of substantial growth (i.e. substantial energy usage, high metabolism). Additionally, young who are born in backwater tributaries may be subject to rapid temperature increases with spring and early summer warm-up.

Standard metabolic rates were obtained in a laboratory setting for the four species by way of individual static respirometry trials.

 
 













Despite my best efforts, size was significantly different over all the temperatures between species (p = .0027). Statistically,  species, temperature, and interaction were all significantly different ( P= <.001, p= <.001, and p= .0225 respectively). But since standard metabolic rate is an allometric measure with weight (smaller individual has a higher SMR per mass unit than a larger individual), the results are skewed. Thus, more data needed to be collected on standardized sizes for each species in order to obtain accurate conclusions.

 


For the second season of data collection a few changes were made. First, three size groups for each species were tested. Three colder temperature treatments were also added. With a wide range of fish sizes and thermal regimes, I'll be able to construct regression models for standard metabolic rate that can be used for comparisons between the species, as well as predictors for hypothetical scenarios. Dissolved oxygen was collected with a new YSI optical probe for precise readings. The inflow and outflow tubing was discarded and fish received longer resting times int he respirometer prior to testing,  both in an effort to improve the study design and obtain sound data.

The results of the season two data will increase the knowledge base on pickerel respiration. As of now, few if any metabolic studies have been performed on any grass or chain pickerel species. A better understanding of metabolic comparisons amongst the four family members will be gained from this research. And, the results may be used to infer esocid behavior in a changing environment, in the St. Lawrence River and extrapolated to areas beyond.


Stay tuned for results from season #2.


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