Joseph J. Cech

Effects of global climate change on marine and estuarine fishes and fisheries

AbstractGlobal climate change is impacting and will continue to impact marine and estuarine fish and fisheries. Data trends show global climate change effects ranging from increased oxygen consumption rates in fishes, to changes in foraging and migrational patterns in polar seas, to fish community changes in bleached tropical coral reefs. Projections of future conditions portend further impacts on the distribution and abundance of fishes associated with relatively small temperature changes. Changing fish distributions and abundances will undoubtedly affect communities of humans who harvest these stocks. Coastal-based harvesters (subsistence, commercial, recreational) may be impacted (negatively or positively) by changes in fish stocks due to climate change. Furthermore, marine protected area boundaries, low-lying island countries dependent on coastal economies, and disease incidence (in aquatic organisms and humans) are also affected by a relatively small increase in temperature and sea level. Our interpretations of evidence include many uncertainties about the future of affected fish species and their harvesters. Therefore, there is a need to research the physiology and ecology of marine and estuarine fishes, particularly in the tropics where comparatively little research has been conducted. As a broader and deeper information base accumulates, researchers will be able to make more accurate predictions and forge relevant solutions.

Stress-associated impacts of short-term holding on fishes

Most sources of stress in aquaculture, fish salvage, stocking programs, and commercial and sport fisheries may be unavoidable. Collecting, handling, sorting, holding, and transporting are routine practices that can have significant effects on fish physiology and survival. Nevertheless, an understanding of the stressors affecting fish holding can lead to practices that reduce stress and its detrimental effects. The stress-related effects of short-term holding are influenced by water quality, confinement density, holding container design, and agonistic and predation-associated behaviors. Physiological demands (e.g., resulting from confinement-related stresses) exceeding a threshold level where the fish can no longer compensate may lead to debilitating effects. These effects can be manifested as suppressed immune systems; decreased growth, swimming performance, or reproductive capacity; even death. Furthermore, holding tolerance may depend upon the species, life stage, previous exposure to stress, and behavior of the held fish. Water quality is one of the most important contributors to fish health and stress level. Fish may be able to tolerate adverse water quality conditions; however, when combined with other stressors, fish may be quickly overcome by the resulting physiological challenges. Temperature, dissolved oxygen, ammonia, nitrite, nitrate, salinity, pH, carbon dioxide, alkalinity, and hardness are the most common water quality parameters affecting physiological stress. Secondly, high fish densities in holding containers are the most common problem throughout aquaculture facilities, live-fish transfers, and fish salvage operations. Furthermore, the holding container design may also compromise the survival and immune function by affecting water quality, density and confinement, and aggressive interactions. Lastly, fishes held for relatively short durations are also influenced by negative interactions, associated with intraspecific and interspecific competition, cannibalism, predation, and determining nascent hierarchies. These interactions can be lethal (i.e., predation) or may act as a vector for pathogens to enter (i.e., bites and wounds). Predation may be a significant source of mortality for fisheries practices that do not sort by size or species while holding. Stress associated with short-term holding of fishes can have negative effects on overall health and well-being. These four aspects are major factors contributing to the physiology, behavior, and survival of fishes held for a relatively short time period.

Diel movements of bat rays, Myliobatis californica, in Tomales Bay, California: evidence for behavioral thermoregulation?

We used ultrasonic telemetry to examine movement patterns of 11 bat rays, Myliobatis californica, in Tomales Bay, California. Tomales Bay is long (20 km) and narrow (1.4 km), and is hydrographically separated into outer and inner bay regions. The outer bay (the outermost 8 km) is characterized by oceanic conditions while the shallow inner bay (the innermost 12 km) features wide seasonal temperature shifts. Five rays were tracked monthly from October 1990 to November 1991 and six rays (four of which carried temperature-sensing transmitters) were tracked daily from 30 June to 16 July 1992. Mean bat ray movement rate was 8.84 m min−1 (range 4.49 to 13.40 m min−1) and was not significantly affected by size (p=0.592), tidal stage (p=0.610), or time of day (p=0.327). Movement direction was unrelated to tidal stage (p=0.472) but showed a highly significant diel pattern (p<0.001). From 2:50–14:50 h, rays moved toward the warmer and shallower inner bay, while from 14:50–2:50 h they moved toward the cooler and deeper outer bay. These telemetry data, along with known bat ray foraging patterns and respiratory temperature-sensitivity, argue for behavioral thermoregulation as the primary influence on this movement pattern.

Hydropower-related pulsed-flow impacts on stream fishes: a brief review, conceptual model, knowledge gaps, and research needs

The societal benefits of hydropower systems (e.g., relatively clean electrical power, water supply, flood control, and recreation) come with a cost to native stream fishes. We reviewed and synthesized the literature on hydropower-related pulsed flows to guide resource managers in addressing significant impacts while avoiding unnecessary curtailment of hydropower operations. Dams may release pulsed flows in response to needs for peaking power, recreational flows, reservoir storage adjustment for flood control, or to mimic natural peaks in the hydrograph. Depending on timing, frequency, duration, and magnitude, pulsed flows can have adverse or beneficial short and long-term effects on resident or migratory stream fishes. Adverse effects include direct impacts to fish populations due to (1) stranding of fishes along the changing channel margins, (2) downstream displacement of fishes, and (3) reduced spawning and rearing success due to redd/nest dewatering and untimely or obstructed migration. Beneficial effects include: (1) maintenance of habitat for spawning and rearing, and (2) biological cues to trigger spawning, hatching, and migration. We developed a basic conceptual model to predict the effects of different types of pulsed flow, identified gaps in knowledge, and identified research activities to address these gaps. There is a clear need for a quantitative framework incorporating mathematical representations of field and laboratory results on flow, temperature, habitat structure, fish life stages by season, fish population dynamics, and multiple fish species, which can be used to predict outcomes and design mitigation strategies in other regulated streams experiencing pulsed flows.

Gut blood flow in fish during exercise and severe hypercapnia

This paper reviews the effects of exercise and hypercapnia on blood flow to the splanchnic circulation. Brief struggling behaviours are known to decrease blood flow to the gut (GBF). Likewise, prolonged swimming in unfed fish has been shown to reduce GBF in proportion to the increased oxygen uptake. Therefore, the normal postprandial increase in GBF theoretically should be impaired whenever fish are active. However, indirect evidence suggests that GBF is spared to some degree when fed fish swim continuously but at a cost (10-15%) to their critical swimming speed. Severe respiratory acidosis can be created by the new intensive aquaculture settings that use oxygen injection into re-circulated water. The only study so far to examine the effects of severe hypercapnia on GBF and its regulation showed that routine GBF and alpha-adrenergic control of GBF remained normal in unfed white sturgeon (Acipenser transmontanus). However, severe hypercapnia produced a hyperactive state and increased sensitivity of GBF to struggling. As a result, routine GBF was maintained for a short period of time. Thus, environmental changes such as severe hypercapnia can indirectly impact GBF through altered struggling behaviour, but the implications of the overall reduction in GBF to food assimilation have yet to be established.

Time of day and water temperature modify the physiological stress response in green sturgeon, Acipenser medirostris

The effects of time of day and water temperature on the acute physiological stress response were investigated in young-of-the-year green sturgeon (Acipenser medirostris). The response to a 1-min air-emersion stressor was assessed during the day (08.00 h) and at night (20.00 h), as well as after acclimation to either 11 degrees C or 19 degrees C. Blood samples were collected prior to stress and at several times after exposure to the stressor, and plasma concentrations of cortisol, lactate, and glucose were determined. The magnitudes of cortisol (19.1 ng ml(-1) vs. 4.9 ng ml(-1)) and lactate (190.6 mg l(-1) vs. 166.7 mg l(-1)) were significantly higher in fish stressed at night when compared with the day. There were no significant differences in glucose levels between time periods. Although, acclimation temperature did not affect peak cortisol concentrations (56.7 and 50.3 ng ml(-1) at 11 degrees C and 19 degrees C, respectively), the duration of the response was significantly extended at 11 degrees C. Post-stressor lactate increases were similar between temperature groups, but at 11 degrees C post-stressor glucose levels were significantly increased through 6 h, suggesting stressor-induced glycogenolysis and gluconeogenesis or decreased glucose utilization. These data demonstrate that the physiological stress response in green sturgeon is modified by both time of day and temperature.

Effects of short-term management stress and ACTH injections on plasma cortisol levels in cultured white sturgeon, Acipenser transmontanus

Abstract General management practices including capture, handling and transportation in fish hatcheries can induce a stress response indicated by a plasma cortisol increase in many species. However, this phenomenon is not well established in cultured white sturgeon ( Acipenser transmontanus ). We determined resting levels of cortisol and the cortisol responses to two management stressors and to exogenous adrenocorticotropic hormone (ACTH 1–24 ) injections in cannulated mature male white sturgeon. Mean resting cortisol level was 8.6 ng/ml and ranged over 5.8–12.8 ng/ml through a 22-h period. Water reduction and transportation+handling stressors elicited significant cortisol increases above pre-stress and post-stress levels. Exogenous ACTH 1–24 injections of 0.5 and 5.0 μM caused dose-dependent peak cortisol increases above those produced by either the water reduction or transportation+handling stressors.

Osmoregulation in juvenile and adult white sturgeon, Acipenser transmontanus

SynopsisBlood samples from cannulated young adult (2.5–15 kg) white sturgeon, acclimated to San Francisco Bay water (24 ppt) had plasma values of 248.8 ± 13.5 mOsm kg−1 H2O, [Na+] = 125 ± 8.0 mEq 1−1, [K+] = 2.6 ± 0.8 mEq 1−1 and [CL−] = 122 ± 3.0 mEq 1−1. Freshwater acclimated sturgeon had an osmolality of 236 ± 7, [Na+] = 131.6 + 4.4, [K+] = 2.5 ± 0.7 and [CL−] = 110.6 ± 3.6. Freshwater acclimated fish gradually exposed to sea water (increase of 5 ppt h−1) had higher plasma osmolalities than did the bay water acclimated fish. These young adult sturgeon are able to tolerate transfer from fresh water to sea water as well as gradual transfer from sea water to fresh water. Plasma electrolytes in transferred fish are regulated, but tend to differ from long term acclimated fish at the same salinities. There is a gradual increase in the upper salinity tolerance (abrupt transfer) of juvenile white sturgeon with weight: 5–10 ppt for 0.4–0.9 g fish, 10–15 ppt for 0.7–1.8 g fish, and 15 ppt for 4.9–50.0 g fish. The ability of juveniles to regulate plasma osmolality is limited. The young adult fish are able to tolerate higher salinities (35 ppt) than juvenile sturgeon but probably are also characterized by low activity of the necessary ion exchange mechanisms in the gills which permit rapid adjustment of blood electrolytes with graduate change in external salinity.

Growth and reproduction of the mosquitofish, Gambusia affinis, in relation to temperature and ration level : consequences for life history

SynopsisThe allocation of energy to growth and reproduction, in relation to temperature and food availability, was investigated in laboratory experiments with the mosquitofish,Gambusia affinis. At constant temperature of 20, 25 and 30°C and ad libitum feeding, specific growth rates increased with increasing temperature at 1.7, 3.1 and 3.4% dry mass day−1, respectively. Growth rates in a cycling temperature regime (20–30°C,