Black sea bass physiology and life history in the context of seasonal and long-term climate change
Creators: name: Slesinger, Emily Tess
Publisher: name: No Publisher Supplied
Year: 2022

description: The US Northeast Shelf (USNES) provides habitat for many economically and ecologically important fish species and is one of the most rapidly warming regions in the world. A common response from several fishes to warming has been poleward distribution shifts, potentially including the Northern stock of black sea bass (Centropristis striata). Black sea bass inhabit coastal waters along the USNES from (south to north) Cape Hatteras, NC to the Gulf of Maine during summer and migrate to the southern shelf-slope edge for the winter. Understanding the causes and implications of the distribution shift in black sea bass is important for fisheries management because state-specific quotas are based on regional biomass. Research on these impacts of ocean warming on fish species will help support proactiveness from fisheries management towards the changes in fish population dynamics and distributions, and avoiding future conflicts. Therefore, for my dissertation, I researched the impacts of ocean warming on black sea bass from the individual to population level with a focus on population dynamics and distribution extents as they relate to fisheries management.Chapter 2 used laboratory-based physiological experiments to determine optimal temperatures by measuring metabolic rates and hypoxia tolerance at a range of temperatures. Black sea bass could not acclimate to 30℃, and while 24℃ was technically the thermal optimum, measured as the temperature with highest aerobic scope, 24℃ was suggested to be the maximum tolerable temperature. This decision was determined based on Metabolic Index values reaching limiting values near 24℃, which suggested this temperature may not be optimal. The southern portion of BSB range can warm to &gt;24℃; therefore, temperature is likely a dominant driver of recent distribution shifts, at least in the southern extent of their distribution. Chapter 3 investigated if black sea bass in the northern extent, that has currently been experiencing increasing biomass, utilized spawning strategies suitable for higher latitude regions with shorter summers. I measured black sea bass spawning timing and output, and found spawning duration was shortest in the northern range extent. This result was expected because summers are shorter at higher latitudes, and typically lead to fish populations with contracted spawning seasons. Under this premise, fish at higher latitudes should have higher reproductive output to account for the shorter spawning season. However, for black sea bass, reproductive output was lower compared to their southern range extent, and may lead to reduced recruitment in black sea bass at the northern in the future. Chapter 4 examined the intraspecific differences in energy allocation throughout spawning across the whole distribution of black sea bass. To do this, lipid concentration, energy density and total energies of the liver, gonad and muscle were measured in fish collected from pre- to post-spawning. Male fish invested less energy into reproduction than female fish and were more often similar across the distribution (i.e. similar energy usage throughout the distribution during spawning). Compared to the southern region, black sea bass in the northern portion of their range began spawning with lower energy reserves and lower gonad energy, potentially leading to the lower reproductive output observed in Chapter 3. Chapter 5 investigated distribution shifts for black sea bass and four other US NES fish in relation to laboratory measurements of thermal limits. Metabolic Index was measured for each species across four seasons (winter, spring, summer, and fall) from 1970-2019. The limiting Metabolic Index value was lower for cold water species than warm water species. All seasons saw a decline in Metabolic Index over time, but the effects were most pronounced in summer and winter when the decline allowed some regions to reach limiting values or lower. Future habitat loss based on Metabolic Index critical limits was determined for each species. Warm water species will experience a loss of habitat in the inshore and southern portions of their distributions, while some of the cold water species, such as Atlantic cod, may lose additional habitat within the Georges Bank and Gulf of Maine portions of the USNES. The use of Metabolic Index allows for an analysis of just thermal habitat change without accounting for effects of distribution changes based on other factors such as previous fishing pressure. These values provide a modest account of what may happen into the future. This dissertation fills research gaps for relevant questions the USNES fisheries face now and into the future. Ocean warming will continue to affect fish populations. Providing information about how fish populations will be affected will allow for proactive management and early warning for flexibility in fishermen switching focal harvest species.