Integrating physiological data with the conservation and management of fishes: A meta-analytical review using the threatened green sturgeon (Acipenser medirostris)

Reversing global declines in the abundance and diversity of fishes is dependent on science-based conservation solutions. A wealth of data exist on the ecophysiological constraints of many fishes, but much of this information is underutilized in recovery plans due to a lack of synthesis. Here, we used the imperiled green sturgeon (Acipenser medirostris) as an example of how a quantitative synthesis of physiological data can inform conservation plans, identify knowledge gaps and direct future research actions. We reviewed and extracted metadata from peer-reviewed papers on green sturgeon. A total of 105 publications were identified, spanning multiple disciplines, with the primary focus being conservation physiology (23.8%). A meta-analytical approach was chosen to summarize the mean effects of prominent stressors (elevated temperatures, salinity, low food availability and contaminants) on several physiological traits (growth, thermal tolerance, swimming performance and heat shock protein expression). All examined stressors significantly impaired green sturgeon growth, and additional stressor-specific costs were documented. These findings were then used to suggest several management actions, such as mitigating salt intrusion in nursery habitats and maintaining water temperatures within optimal ranges during peak spawning periods. Key data gaps were also identified; research efforts have been biased towards juvenile (38.1%) and adult (35.2%) life-history stages, and less data are available for early life-history stages (embryonic, 11.4%; yolk-sac larvae, 12.4%; and post yolk-sac larvae, 16.2%). Similarly, most data were collected from single-stressor studies (91.4%) and there is an urgent need to understand interactions among stressors as anthropogenic change is multi-variate and dynamic. Collectively, these findings provide an example of how meta-analytic reviews are a powerful tool to inform management actions, with the end goal of maximizing conservation gains from research efforts

Temperature and hypoxia tolerance of selected fishes from a hyperthermal rockpool in the dry Tortugas, with notes on diversity and behavior

We documented the physical habitat characteristics and fish diversity of a hyperthermal rockpool on Loggerhead Key in the Dry Tortugas National Park during July 2000. Rockpool temperatures ranged from 30.5 °C to 35.8 °C and oxygen varied from 6.4 to 3.5 mg/L depending on depth and time of day. Seven fish species from five families inhabited the rockpool. Critical thermal maxima (CTMax) and critical oxygen minima (COM) were measured for three species. French grunt Haemulon flavolineatum was the most temperature tolerant fish (CTMax = 37.9 °C), followed by cocoa damselfish Pomacentrus variabilis (36.1 °C), and white mullet Mugil curema (35.0 °C), respectively. Cocoa damselfish were more tolerant of hypoxic conditions (COM = 0.8 mg/L) than either French grunt (1.2 mg/L) or white mullet (1.5 mg/L). French grunt and cocoa damselfish resorted to aquatic surface respiration at respective dissolved oxygen levels of 2.6 and 1.7 mg/L, whereas white mullet did not display this behavior at oxygen concentrations as low as 1.5 mg/L. High-temperature and low-oxygen responses of the three species were not exceptional, suggesting that behavior and not physiology is the major factor allowing Loggerhead Key fishes to exploit hyperthermal habitats

Temperature and hypoxia tolerance of selected fishes from a hyperthermal rockpool in the dry Tortugas, with notes on diversity and behavior

We documented the physical habitat characteristics and fish diversity of a hyperthermal rockpool on Loggerhead Key in the Dry Tortugas National Park during July 2000. Rockpool temperatures ranged from 30.5 °C to 35.8 °C and oxygen varied from 6.4 to 3.5 mg/L depending on depth and time of day. Seven fish species from five families inhabited the rockpool. Critical thermal maxima (CTMax) and critical oxygen minima (COM) were measured for three species. French grunt Haemulon flavolineatum was the most temperature tolerant fish (CTMax = 37.9 °C), followed by cocoa damselfish Pomacentrus variabilis (36.1 °C), and white mullet Mugil curema (35.0 °C), respectively. Cocoa damselfish were more tolerant of hypoxic conditions (COM = 0.8 mg/L) than either French grunt (1.2 mg/L) or white mullet (1.5 mg/L). French grunt and cocoa damselfish resorted to aquatic surface respiration at respective dissolved oxygen levels of 2.6 and 1.7 mg/L, whereas white mullet did not display this behavior at oxygen concentrations as low as 1.5 mg/L. High-temperature and low-oxygen responses of the three species were not exceptional, suggesting that behavior and not physiology is the major factor allowing Loggerhead Key fishes to exploit hyperthermal habitats

Physiological tolerance to hyperthermia and hypoxia and effects on species richness and distribution of rockpool fishes of Loggerhead Key, Dry Tortugas National Park

Rockpools on Loggerhead Key in the Dry Tortugas National Park experience cyclic tidal changes in water quality and physical dimension resulting in ichthyofaunal assemblages that differ markedly from the adjacent coral reef. Within the beach rock formations and areas transitioning to the nearby reef, we observed 45 fish species; however, only four species – schoolmaster, Lutjanus apodus, French grunt, Haemulon flavolineatum, cocoa damsel, Pomacentrus variabilis, and frillfin goby, Bathygobius soporator – were found in all rockpools. All fishes were transient juveniles except for frillfin goby, which was a pool resident. High temperature tolerance, (Critical Thermal Maxima), and low oxygen tolerance, (Critical Oxygen Minima) for schoolmaster, French grunt, cocoa damsel, and frillfin goby were 40.9, 36.2, 37.6, 40.9 °C and 0.56, 0.77, 0.50, and 0.27 mg/L, respectively. All four species demonstrated thermal and hypoxia tolerance values similar to those published for species traditionally noted as abiotic specialists. Although fish distribution patterns in rockpools were likely influenced by structural complexity and spatial limitations, the relationship between pool morphology and species richness was weak, suggesting that physiological tolerance to high temperature and low oxygen among reef fishes may be more influential in determining which species inhabit the rockpools. Harsh thermal and oxic conditions that cannot be exploited by less tolerant species may be beneficial for some Loggerhead Key reef fishes in providing refuge from predators, foraging grounds, or potential nursery areas

Experimental evaluation of the effect of a light-emitting diode device on Chinook salmon smolt entrainment in a simulated river

The entrainment and impingement of fish into water diversion infrastructure is one of the several factors contributing to their decline. Here, controlled experiments assessed the potential for a behavioral guidance device [a light-emitting diode (LED) light array] strobing at various spectra to reduce the entrainment of juvenile Chinook salmon (Oncorhynchus tshawytscha) into a water diversion pipe. Fish were tested during the day and night, and under control conditions (light off) and red, blue, and white spectra strobing at 2 Hz. Fish entrainment into the diversion pipe was evaluated. Results indicated greater entrainment at night compared to day. All trials at night with the LED light strobing had higher entrainment than the control, with blue and white spectra corresponding to greater entrainment than red spectra. During the day, the white spectra treatment was different from the red treatment, with lower entrainment. LED lights employed to repel migratory juvenile salmon away from water intake structures may be ineffectual but there is potential for the light to be used as an attractant to guide fish towards desirable features such as “safe” areas (bypass channels or fishways)