Over the last decade, ocean temperature on the U.S. Northeast Continental Shelf (U.S. NES) has warmed faster than the global average and is associated with observed distribution changes of the northern stock of black sea bass ( Centropristis striata ). Mechanistic models based on physiological responses to environmental conditions can improve future habitat suitability projections. We measured maximum, standard metabolic rate, and hypoxia tolerance (S crit ) of the northern adult black sea bass stock to assess performance across the known temperature range of the species. Two methods, chase and swim-flume, were employed to obtain maximum metabolic rate to examine whether the methods varied, and if so, the impact on absolute aerobic scope. A subset of individuals was held at 30°C for one month (30 chronic °C) prior to experiments to test acclimation potential. Absolute aerobic scope (maximum–standard metabolic rate) reached a maximum of 367.21 mgO 2 kg -1 hr -1 at 24.4°C while S crit continued to increase in proportion to standard metabolic rate up to 30°C. The 30 chronic °C group exhibited a significantly lower maximum metabolic rate and absolute aerobic scope in relation to the short-term acclimated group, but standard metabolic rate or S crit were not affected. This suggests a decline in performance of oxygen demand processes (e.g. muscle contraction) beyond 24°C despite maintenance of oxygen supply. The Metabolic Index, calculated from S crit as an estimate of potential aerobic scope, closely matched the measured factorial aerobic scope (maximum / standard metabolic rate) and declined with increasing temperature to a minimum below 3. This may represent a critical threshold value for the species. With temperatures on the U.S. NES projected to increase above 24°C in the next 80-years in the southern portion of the northern stock’s range, it is likely black sea bass range will continue to shift poleward as the ocean continues to warm.

46Over the last decade, ocean temperature in the U.S. Northeast Continental Shelf (U.S. NES) has 47 warmed faster than the global average and is associated with observed distribution changes of the 48 northern stock of black sea bass (Centropristis striata). Mechanistic models based on 49 physiological responses to environmental conditions can improve future habitat suitability 50 projections. We measured maximum, resting metabolic rate, and hypoxia tolerance (S crit ) of the 51 northern adult black sea bass stock to assess performance across the known temperature range of 52 the species. A subset of individuals was held at 30˚C for one month (30 chronic°C ) prior to 53 experiments to test acclimation potential. Absolute aerobic scope (maximum -resting metabolic 54 rate) reached a maximum of 367.21 mgO 2 kg -1 hr -1 at 24.4°C while S crit continued to increase in 55 proportion to resting metabolic rate up to 30°C. The 30 chronic°C group had a significant decrease 56 in maximum metabolic rate and absolute aerobic scope but resting metabolic rate or S crit were not 57 affected. This suggests a decline in performance of oxygen demand processes (e.g. muscle 58 contraction) beyond 24°C despite maintenance of oxygen supply. The Metabolic Index, 59 calculated from S crit as an estimate of potential aerobic scope, closely matched the measured 60 factorial aerobic scope (maximum / resting metabolic rate) and declined with increasing 61 temperature to a minimum below 3. This may represent a critical value for the species. 62Temperature in the U.S. NES is projected to increase above 24°C in the southern portion of the 63 northern stock's range. Therefore, these black sea bass will likely continue to shift north as the 64 ocean continues to warm. 65 66 67 likely continue to expand northward as the U.S. NES continues to warm. 132 133 Materials and Methods 134 135

Ocean warming is leading to poleward range shifts for many fish species, and while well described, potential life history phenology differences within fish populations along a gradient from their historic to current distributional range have not been studied. In a rapidly shifting fish population, the Northern stock of black sea bass (Centropristis striata), we investigated spawning phenology and output across the US Northeast Shelf to comprise locations in their historic and more recently occupied range near their northern range boundary. Spawning started later in the northern extreme of our study but also ended earlier, leading to decreased spawning duration from south to north. Spawning phenology was mostly driven by Julian day followed by temperature and latitude. Gonadosomatic index, a proxy for reproductive output, was lower in the northern region, indicating that black sea bass did not compensate for the shorter spawning season there. Hepatosomatic index was lower in the northern regions indicating lower pre-spawning liver energy reserves, potentially leading to lower reproductive output. These results suggest a potential for lower recruitment in the recently occupied range and should be further investigated to predict the impacts of ocean warming and for proactive fisheries management as black sea bass distributional range expands poleward.

Fish reproduction is energetically costly, leading to a suite of energy allocation strategies for maximizing lifetime reproductive potential. Assessing energetic allocation for species that inhabit a wide distributional range can provide insight into different strategies found across individuals and populations. The Northern stock of black sea bass (Centropristis striata) inhabits the U.S. Northeast continental shelf from Cape Hatteras, NC, to the Gulf of Maine, and spawns inshore throughout this distribution from April to October. To assess energy allocation towards spawning, C. striata were collected in four regions across this distribution and throughout their spawning season. By assessing energetic allocation (lipid, energy density and total energy) in muscle, liver and gonad tissues, C. striata were identified as mixed breeders because while they mobilized somatic energy stores towards reproductive development, they also used energy acquired from their diet to sustain reproductive output throughout the spawning season. Unlike male fish, female fish both invested more energy into liver and gonad tissues and exhibited regional differences in energetic values. For both sexes, C. striata in the northern portion of the distribution had lower energetic values both in the somatic stores and towards gonadal development than the fish in the southern portion of the distribution, possibly because of longer migration distance. Overall, the authors found significant spatial variation in energetic constraints that may affect reproductive output and success (recruitment), a relevant result as C. striata are a popular recreational and commercial species throughout this distribution.