Spawning Temperature Research Articles

Gametogenesis, spawning behavior and larval abundance of the Pacific oyster Crassostrea gigas in the Thau lagoon: Evidence of an environment-dependent strategy

The Thau lagoon, located at the South of France, provides 10% of the French pacific oyster Crassostrea gigas production. Despite this intensive shellfish production, the larval recruitment of this species within the Thau lagoon is still misunderstood and spat collection remains highly variable; as a consequence, shellfish farmers rely mostly on hatchery”s spat. The present study aimed to describe reproduction features of C. gigas within the Mediterranean, as well as to explore spawning triggers of this species. To achieve this goal, the reproduction cycle from gametogenesis to spawning was followed during two years in several locations within the Mediterranean Thau lagoon. The spawning behavior of C. gigas within the Thau lagoon appeared to be slightly different from the one of the Atlantic Coast, showing several spawning events from June to October. The minimal temperature for massive spawning was 23°C, which is much higher than temperatures mentioned in the literature for this species. A strong relationship was found between phytoplankton communities and gametogenesis, the latter being improved by a higher diatom/dinoflagellate ratio. Temperature was insufficient alone to explain spawning, highlighting other potential triggers such as the moon or lightning strikes. We made the hypothesis of a hierarchy of events triggering spawning, encompassing locking, synchrony and intensifying triggers. Statement of relevanceThis paper is filling in a gap in the literature regarding to reproduction of C. gigas in the Thau lagoon, which is always associated to temperature. However, temperature may not be the only factor involved in oyster reproduction, that is what we tried to show in this paper.

Enhancement of oogenesis/spermatogenesis in meagre Argyrosomus regius using a combination of temperature control and GnRHa treatments

A multiple GnRHa injection method for inducing spawning of high fecundity and quality in meagre was optimized. Specifically, the study (a) examined how long females would continue spawning in response to consecutive, weekly GnRHa injections, if maintained at the natural spawning temperature, and (b) evaluated whether males can produce adequate amounts of good quality sperm for the same period, with the assistance of a GnRHa therapy. Combined with stable temperatures (19–20°C) that are prevalent during the early spawning season (April–May) in the Mediterranean Sea, each weekly GnRHa injection induced ~2 consecutive spawns per week for a period of 17weeks. Fish spawned consistently 2days after treatment and produced high fecundity and egg quality (i.e. fertilization, hatching and early larval development). Maximum mean total fecundity (±S.D.) obtained was 1,415,000±149,000eggskg−1 in 32 spawns, being the highest total season fecundity reported for meagre, and significantly higher than the estimated maximum potential fecundity for the species. At the same time, sperm of consistently high quality (i.e. initial motility, duration of motility and storage survival) was produced in response to treatment with multiple GnRHa implants, though towards the end of the experiment a significant reduction (ANOVA, P≤0.05) in spermatozoa density was observed. This protocol is expected to enhance greatly commercial production of meagre. Statement of relevanceThe present study reports on an optimized protocol for the induction of consistent and repeated spawning in meagre, based on the use of weekly GnRHa injections combined with stable temperatures that are prevalent at the early spawning season in the Mediterranean Sea. This protocol produced eggs of high fecundity and quality (i.e. fertilization, hatching and early larval development) for a period of >4months, and it is expected to enhance greatly commercial production of meagre.

Репродуктивные показатели и экология размножения атлантической атерины Atherina hepsetus (Pisces: Atherinidae) у западного побережья Крыма

Атерины (сем. Atherinidae) — массовые представители прибрежной пелагической ихтиофауны Азово-Черноморского бассейна, в некоторых районах являются объектами промысла. Вместе с тем сведения о биологии и экологии атерин до настоящего времени остаются крайне скудными и фрагментарными. Данная работа посвящена изучению меж- и внутригодовой (сезонной) изменчивости ряда индивидуальных и популяционных репродуктивных показателей атлантической атерины Atherina hepsetus из акватории Черного моря, прилегающей к западному побережью Крыма. Отлов производился ставными неводами круглогодично в течение 2010–2014 гг. с периодичностью 2–3 раза в месяц. В общей сложности изучено 2403 экз. На основе результатов исследования впервые введены понятия общего, популяционного и массового (пик нереста) репродуктивных периодов, установлены межгодовые изменения их продолжительности, а также календарные сроки начала и окончания. Изучены интенсивность нереста и его сезонная динамика, сезонная динамика развития половых желез самцов и самок и определены индивидуальные и среднепопуляционные значения их гонадосоматического индекса. Установлен диапазон изменчивости температуры нереста (8.5–14.5 ℃), выделена зона максимально благоприятной нерестовой температуры (9.0–12.0℃).

Spawning grounds of haddock (Melanogrammus aeglefinus) in the North Sea and West of Scotland

The importance of physical constraints on the spawning distribution of northern shelf haddock was examined using a 2 stage generalized additive model applied to 1st quarter bottom trawl survey data from the North Sea and west of Scotland. In order to consider possible effects of biomass-dependent spatial dynamics on local density, geostatistical aggregation curves and the spaces selectivity index were computed. Local changes in abundance were proportional to changes in annual abundance and therefore density did not confound the estimate of the physical habitat preference of spawning haddock. Model performance was good, with AUC and Kappa values higher than the threshold for good performance and Pearson coefficient scores higher than previous studies of fish spawning distribution. An optimum temperature for spawning of 7°C was evident for North Sea and west of Scotland regions. Spawning haddock preferred high salinity waters in the northern North Sea and shelf edge waters to the west of Scotland. They tended not to aggregate on mud-rich sediments, which was associated with a split in the main spawning areas between the east and west North Sea. The distribution of spawning haddock from this study indicated a shift in the spawning grounds compared to historic reports. By identifying the physical characteristics and persistent use of spawning grounds, the present study provides a guide for future marine developments and an aid to discussions about the utility of spawning closures.

The dependence of the duration of sperm motility in Ob–Irtysh basin coregonidae on temperature

The duration of sperm motility in four whitefish species in the Ob–Irtysh basin, namely, Coregonus tugun, the river and lake forms of C. peled, C. lavaretus pidschian, and C. nasus, has been studied. It is shown that the duration of sperm motility in these species has a statistically significant inversely proportional dependence on the temperature of the water that is used for activation. The total duration of sperm motility at the spawning temperature in the range from 0.1 to 5.0°C amounts to 331 ± 107 s, on average, while the duration of forward movement amounts to 149 ± 44 s, on average. At temperatures that exceed the spawning values (above 7.1°C), these parameters constitute 190 ± 47 and 86 ± 15 s, respectively. The highest interspecific variability in the duration of sperm motility was observed within the temperature range from 0.1 to 2.5 and above 7.1°C. C. tugun shows less dependence of the duration of sperm motility on temperature than the other species under study. At a temperature of 0.7°C, the total duration and duration of the forward movement of C. tugun sperm are 201 and 108 s, respectively. When the temperature was increased to 13.4°C, these parameters decreased by 1.2 and 1.1 times only, i.e., to 172 and 100 s, respectively.

New evidence may support the persistence and adaptability of the near-extinct Chinese sturgeon

Damming the Yangtze River has resulted in a shortened spawning migration distance and time period, created altered and fewer spawning locations, reduced spawning population size, and narrowed the spawning temperature range for the Chinese sturgeon, Acipenser sinensis. No sign of spawning activity was detected in 2013 and 2014, raising concern about the possible extinction of the species. However, the recent discovery of four wild juvenile Chinese sturgeon in the Yangtze Estuary in 2015 suggests that following a short time period when spawning was suspended, a few Chinese sturgeon have resumed spawning at an unknown location in the Yangtze River. This demonstrates that Chinese sturgeon have an extraordinary ability to adapt to environmental changes. However, they appear to have reached their limit in adapting to the drastically changed riverine environment. Innovative conservation efforts are needed to improve the chances for survival of this critically endangered species.

Trends in the Reproductive Phenology of two Great Lakes Fishes

AbstractTo assess potential effects of climate change on Great Lakes fish populations, we evaluated trends in the reproductive phenology of Yellow Perch Perca flavescens (spring spawner) and Lake Trout Salvelinus namaycush (autumn spawner). For Yellow Perch in Lake Michigan, the estimated reproductive midpoint date (50% of mature females ripe or spent, 50% not yet spawned) took place 6.2 d/decade earlier in the spring near Milwaukee from 1988 to 2012 and 1.8 d/decade earlier in Green Bay from 1980 to 2012. At both locations water temperatures at the spawning sites on the midpoint date showed no trends, but mean water temperatures during the spring at the spawning site and midlake increased over the study period. This suggests that Yellow Perch spawning areas were warming sooner in the spring and that Yellow Perch were spawning earlier to maintain a consistent spawning temperature. Lake Trout phenological patterns were more complex. For Lake Trout in Lake Michigan near Milwaukee, there was a marginally significant trend for spawning to take place 2.1 d/decade later in the autumn from 1983 to 2006. However, water temperatures at the spawning site at the midpoint date did not change and autumn temperatures at the site and at midlake did not show a warming trend. For Lake Trout in Lake Superior near the Apostle Islands, the midpoint date did not change from 1988 to 2012. Water temperatures at the spawning site on the midpoint date and during the autumn also showed no trends, but midlake summer and autumn water temperatures increased significantly. Overall, Yellow Perch in Lake Michigan have shifted reproductive timing in a manner consistent with a warming climate, but the relationship of climate change to reproductive phenology remains unclear for Lake Trout in Lake Michigan and Lake Superior.

Climate change and pollution speed declines in zebrafish populations

Endocrine disrupting chemicals (EDCs) are potent environmental contaminants, and their effects on wildlife populations could be exacerbated by climate change, especially in species with environmental sex determination. Endangered species may be particularly at risk because inbreeding depression and stochastic fluctuations in male and female numbers are often observed in the small populations that typify these taxa. Here, we assessed the interactive effects of water temperature and EDC exposure on sexual development and population viability of inbred and outbred zebrafish (Danio rerio). Water temperatures adopted were 28 °C (current ambient mean spawning temperature) and 33 °C (projected for the year 2100). The EDC selected was clotrimazole (at 2 μg/L and 10 μg/L), a widely used antifungal chemical that inhibits a key steroidogenic enzyme [cytochrome P450(CYP19) aromatase] required for estrogen synthesis in vertebrates. Elevated water temperature and clotrimazole exposure independently induced male-skewed sex ratios, and the effects of clotrimazole were greater at the higher temperature. Male sex ratio skews also occurred for the lower clotrimazole exposure concentration at the higher water temperature in inbred fish but not in outbred fish. Population viability analysis showed that population growth rates declined sharply in response to male skews and declines for inbred populations occurred at lower male skews than for outbred populations. These results indicate that elevated temperature associated with climate change can amplify the effects of EDCs and these effects are likely to be most acute in small, inbred populations exhibiting environmental sex determination and/or differentiation.

Elevated temperature enhances normal early embryonic development in the coral Platygyra acuta under low salinity conditions

To better understand the possible consequences of climate change on reef building scleractinian corals in a marginal environment, laboratory experiments were conducted to examine the interactive effects of changes in salinity and temperature on percent fertilization success and early embryonic development of the coral Platygyra acuta. In the present study, a salinity of 24 psu (ambient 32 psu) reduced fertilization success by 60 %. Normal embryonic development was reduced by >80 % at 26 psu (ambient 33 psu) with 100 % abnormal development at 22 psu under ambient temperature. Elevated temperature (+3 °C) above the ambient spawning temperature did not show any negative effects on fertilization success. However, there was a trend for more abnormal embryos to develop at elevated temperature in the 2 d of the spawning event. The interactive effects between salinity and temperature are statistically significant only on normal embryonic development of P. acuta, but not on its fertilization success. Salinity was revealed to be the main factor affecting both fertilization success and normal embryonic development. Interestingly, the much lower fertilization success (76 %) observed in the second day of spawning (Trial 2) under ambient temperature recovered to 99 % success under elevated (+3 °C) temperature conditions. Moreover, elevated temperature enhanced normal early embryonic development under lowered salinity (26 psu). This antagonistic interactive effect was consistently observed in two successive nights of spawning. Overall, our results indicate that, in terms of its fertilization success and embryonic development, P. acuta is the most tolerant coral species to reduced salinity thus far reported in the literature. Elevated temperature, at least that within the tolerable range of the corals, could apparently alleviate the potential negative effects from salinity stresses. This mitigating role of elevated temperature appears not to have been reported on corals before.

Modelling the impact of climate change on South Pacific albacore tuna

The potential impact of climate change under the IPCC AR4–A2 scenario (close to the AR5-RCP8.5 scenario) on south Pacific albacore tuna (Thunnus alalunga) is simulated with the Spatial Ecosystem And Population Dynamics Model (SEAPODYM) and environmental forcing variables provided by the Earth Climate model IPSL-CM4. Parameters controlling the habitat and dynamics of the population were optimized by fitting the model, using maximum likelihood, to a complete fishing data set for the historical fishing period since 1950. Albacore undertake clear seasonal migrations between feeding and spawning grounds, as evidenced by seasonal catch and size composition changes. This seasonality was well predicted by the SEAPODYM albacore simulations. The total biomass estimate of south Pacific albacore was predicted to have decreased from ~1.8 million tonnes (Mt) at the beginning of industrial fisheries in 1950 to 1.25Mt in 2006, in good agreement with an independent estimate from stock assessment analysis. A simulation without fishing indicated an equivalent contribution of environmental variability and fishing to the historical decrease of the stock biomass. The parameterized SEAPODYM model was used to project the dynamics of the population until the end of the 21st century with an average fishing effort based on recent years. Under this fishing and climate change scenario, the population was predicted to decrease and to stabilize after 2035 just below 0.8Mt, i.e., 55% below the initial biomass of 1960. After 2080 however, the trend was reversed when a new spawning ground emerged in the north Tasman Sea. A test simulation highlighted the sensitivity of the model results to projected dissolved oxygen concentration for which there is large uncertainty in the tropical region. A second test simulation showed that genetic selection favouring albacore with preferences for higher optimal ambient spawning temperature would maintain a reduced level of spawning in current tropical spawning areas, suppress the emergence of an area of spawning in the north Tasman Sea and therefore keep stock abundance at low 2035 levels.

Externally driven changes in the abundance of summer and winter flounder

Abstract Marine organisms that utilize nearshore environments for major components of their life histories are subject to both local-scale forcing such as water quality and estuarine degradation as well as large-scale forcing such as fishing and decadal-scale climate variability. Large-scale forcing has the potential to synchronize the dynamics of subpopulations, while local-level forcing can produce asynchronous subpopulation trends. Summer flounder (Paralichthys dentatus) and winter flounder (Pseudopleuronectes americanus) are important commercial and recreational flatfish along the east coast of North America which spend their first year of life in coastal habitats. We found that the two exhibited significant within-species coherence in commercial landings and fisheries-independent surveys across the northeast shelf of the United States, suggesting large-scale external drivers. In laboratory studies, temperature has been found to be an important factor regulating survival during the egg, larva and settlement phases of both species. We reconstructed a 40-year time-series of coastal water temperature for the major spawning and nursery areas to examine changes in the thermally available habitat. Estimates of winter flounder abundance were negatively correlated with the winter water temperature, but not with fishing mortality. Summer flounder abundance, by contrast, was negatively correlated with fishing mortality, but exhibited no link with temperature. In addition, time-varying stock–recruitment relationships indicated that stock productivity declined for winter flounder over time, while summer flounder productivity has varied without a trend. While both species declined in the 1980s and early 1990s due to heavy fishing pressure, the reduction in fishing over the last two decades has led to rebuilding of the summer flounder stock and an expansion of its age structure. Declining productivity due to warming estuarine conditions has kept the winter flounder stock at low levels despite low fishing pressure. The two stocks illustrate the importance of controlling fishing mortality in the management of natural marine resources while also accounting for changes in productivity due to climate variability and change.

Regulated recruitment: native and alien fish responses to widespread floodplain inundation in the Macquarie Marshes, arid Australia

AbstractRivers and wetland ecosystems are degraded by diversions of water upstream. In response, governments have reallocated water to flood wetlands, mimicking natural inundation of habitats known to drive booms in native freshwater fish production. Individual flow events allow the ecological outcomes of restoration efforts to be evaluated, in order to improve ongoing adaptive management. This study investigated the population size and recruitment responses of seven native and three alien fish species to widespread floodplain inundation at 15 sites across the Macquarie Marshes, a regulated wetland in Australia's Murray–Darling Basin. Flooding during the late winter, when water temperatures were 4 to 12.6 °C below the spawning threshold for native fish species present in the system, promoted reproduction and recruitment by alien species, which were significantly more abundant than native species after flooding. Fish assemblage structure also differed significantly between main channel and floodplain habitats, with macrophytes, pH, emergent vegetation, flow velocity and small wood debris accounting for 59% of spatiotemporal variation in fish assemblage structure. Strong correlations were identified between the length of spawning window and post‐flood abundance of young‐of‐year and recruit size classes in the most abundant alien and native fish species. Future environmental flows, particularly those that inundate floodplain habitats, need to be delivered in light of the confounding effects of flow–temperature coupling and the lower spawning temperature thresholds of alien species. Copyright © 2014 John Wiley & Sons, Ltd.

Spatial Ecological Processes and Local Factors Predict the Distribution and Abundance of Spawning by Steelhead (Oncorhynchus mykiss) across a Complex Riverscape

Processes that influence habitat selection in landscapes involve the interaction of habitat composition and configuration and are particularly important for species with complex life cycles. We assessed the relative influence of landscape spatial processes and local habitat characteristics on patterns in the distribution and abundance of spawning steelhead (Oncorhynchus mykiss), a threatened salmonid fish, across ∼15,000 stream km in the John Day River basin, Oregon, USA. We used hurdle regression and a multi-model information theoretic approach to identify the relative importance of covariates representing key aspects of the steelhead life cycle (e.g., site access, spawning habitat quality, juvenile survival) at two spatial scales: within 2-km long survey reaches (local sites) and ecological neighborhoods (5 km) surrounding the local sites. Based on Akaike’s Information Criterion, models that included covariates describing ecological neighborhoods provided the best description of the distribution and abundance of steelhead spawning given the data. Among these covariates, our representation of offspring survival (growing-season-degree-days, °C) had the strongest effect size (7x) relative to other predictors. Predictive performances of model-averaged composite and neighborhood-only models were better than a site-only model based on both occurrence (percentage of sites correctly classified = 0.80±0.03 SD, 0.78±0.02 vs. 0.62±0.05, respectively) and counts (root mean square error = 3.37, 3.93 vs. 5.57, respectively). The importance of both temperature and stream flow for steelhead spawning suggest this species may be highly sensitive to impacts of land and water uses, and to projected climate impacts in the region and that landscape context, complementation, and connectivity will drive how this species responds to future environments.

A Synthesis of Kootenai River Burbot Stock History and Future Management Goals

AbstractIn Idaho, Burbot Lota lota are endemic only to the Kootenai River, where they once provided an important winter fishery to the indigenous people and European settlers. This fishery and that of Kootenay Lake in British Columbia may have been the most robust Burbot fisheries in North America. However, the fishery in Idaho rapidly declined after the construction of Libby Dam by the U.S. Army Corps of Engineers in 1972, and it closed in 1992. Concomitant to the collapse in Idaho was the collapse of the Burbot fishery in Kootenay Lake and the Kootenay River. The operation of Libby Dam for hydroelectric power generation and flood control created major changes in the river's nutrient concentration, temperature, and seasonal discharge, particularly during the winter when Burbot spawn. Libby Dam operations were implicated as the major limiting factor to Burbot recruitment, giving rise to higher winter temperatures and widely fluctuating flows. Because the Burbot in the Kootenai River are at risk of demographic extinction, a conservation strategy was prepared to outline the measures necessary to rehabilitate the Burbot population to a self‐sustaining level. The strategy indicated that operational discharge changes at Libby Dam are required during winter to provide suitable temperature and discharge conditions for Burbot migration and spawning. Studies recommend that the discharge at Bonners Ferry average 176 m3/s for a minimum of 90 d (mid‐November through mid‐February). Furthermore, preferred Burbot water temperatures of about 6°C are necessary for migration and cooler temperatures of 1–4°C for spawning. With each passing year, Burbot stock limitations increasingly constrain rehabilitation. Thus, coordination of intensive culture, extensive rearing, and pen rearing among the Kootenai Tribe of Idaho, the British Columbia Ministry of Environment, the University of Idaho's Aquatic Research Institute, and the Idaho Department of Fish and Game is important for restoration.

Genetic variation underlies temperature tolerance of embryos in the sea urchinHeliocidaris erythrogramma armigera

Ocean warming can alter natural selection on marine systems, and in many cases, the long-term persistence of affected populations will depend on genetic adaptation. In this study, we assess the potential for adaptation in the sea urchin Heliocidaris erythrogramma armigera, an Australian endemic, that is experiencing unprecedented increases in ocean temperatures. We used a factorial breeding design to assess the level of heritable variation in larval hatching success at two temperatures. Fertilized eggs from each full-sibling family were tested at 22°C (current spawning temperature) and 25°C (upper limit of predicted warming this century). Hatching success was significantly lower at higher temperatures, confirming that ocean warming is likely to exert selection on this life-history stage. Our analyses revealed significant additive genetic variance and genotype-by-environment interactions underlying hatching success. Consistent with prior work, we detected significant nonadditive (sire-by-dam) variance in hatching success, but additionally found that these interactions were modified by temperature. Although these findings suggest the potential for genetic adaptation, any evolutionary responses are likely to be influenced (and possibly constrained) by complex genotype-by-environment and sire-by-dam interactions and will additionally depend on patterns of genetic covariation with other fitness traits.

Effect of Release Temperature from Three Gorges Reservoir on the Procreation of Chinese Sturgeons

Chinese sturgeon is the national list endangered fish species. Since the construction of the Gezhouba dam in 1981, the migration of Chinese sturgeon for procreating to upstream of the Yangtze River has been blocked which cause the only spawning ground was left locating in a narrow zone downstream close to the dam site. The procreation of Chinese sturgeons need suitable ecological factors, including temperature, hydrology, sediment and so on, but after impoundment of Three Gorges Reservoir (TGR), the environment have changed a lot that brings a great threaten to the Chinese sturgeons. In this paper, based on previous hydrodynamics and thermal coupled model of TGR, three different scenarios including dry, normal and wet year is simulated to access the influences of release temperature from TGR on procreation of Chinese sturgeons. The result indicates that due to the weak stratification of the TGR, the release temperature changes compared to natural river water temperature, as a result, the time of the procreation is slightly delayed in different scenarios because the release temperature is higher than the upper bound temperature for spawning, of which the days been delayed is about 14 in dry years, 13 in normal years and 5 in wet years, respectively, so temperature becomes a limiting factor to the procreation of Chinese sturgeons.

THE RELATIONSHIP BETWEEN THERMAL REGIME ALTERATION AND SPAWNING DELAY OF THE FOUR MAJOR CHINESE CARPS IN THE YANGTZE RIVER BELOW THE THREE GORGES DAM

Large dams often alter flow and thermal regimes downstream, resulting in fish spawning delays and larval abundance declines. Accurate prediction of the delayed spawning period under changed thermal regime is critical for selecting a correct timing to modify dam operation and to release the environmental flow needed to enhance fish spawning. We used correlation analysis to investigate the relationship between thermal regime alteration and spawning delay of the four major Chinese carps (FMCC) below the Three Gorges Dam in the Yangtze River, China, using a 13-year ecological data series (1997–2009). Eighteen variables were defined to quantify thermal regime and related to two variables representing spawning timing. Our results demonstrate that the start of FMCC spawning has been delayed from early May to middle June since the Three Gorges Dam initiated operation in 2003. Water temperature declines of 2 °C–4 °C in March, April and May (a critical period for gonad development) were the principal reason for the observed spawning delay. The variable most associated with spawning timing was the arrival date of the cumulative temperature needed for gonad development from stages IV to V (DDegDayIV–V), which describes the long-term impacts of the timing, magnitude and duration of thermal regime upon gonad development. Only the cumulative temperature for gonad development and the minimum temperature for FMCC spawning (18 °C) are both satisfied, the occurrence of suitable flow conditions, that is, flow increase or flash flood, would produce a successful spawning event. Consequently, we suggest that the experimental flow increase process of the Three Gorges Reservoir aimed at enhancing FMCC spawning should initiate after 15 June when the requisite thermal regime can be met. Copyright © 2013 John Wiley & Sons, Ltd.

Phylogeny influences the relationships linking key ecological thermal metrics for North American freshwater fish species

Habitat temperature is a major determinant of performance and activity in fish. We summarize published studies of 173 North American freshwater fish species to examine the interrelationships among thermal response metrics associated with three types of individual performance: growth (optimal growth temperature (OGT), final temperature preferendum (FTP)), survival (upper incipient lethal temperature (UILT), critical thermal maximum (CTMax)), and reproduction (optimum spawning temperature (OS), optimum egg development temperature (OE)). We found that all metrics were highly correlated, especially those associated with a specific performance type. Differences in thermal metrics were also significantly linked to traditional thermal guild classifications, spawning season, and strategy. We found an overall decline in correlation strength when we used phylogenetically independent contrasts to control for the effect of phylogeny. This decline was much greater for growth and survival metrics than for reproduction. This suggests that the role of evolutionary history in determining thermal sensitivity at the species level varies greatly across the range of performance types that can be used to characterize the behaviour of an individual.

Optimum and maximum temperatures of sockeye salmon (Oncorhynchus nerka) populations hatched at different temperatures

Temperature tolerance and heart rates were compared among nine sockeye salmon (Oncorhynchus nerka (Walbaum in Artedi, 1792)) populations, whose eggs were incubated at 10, 14, and 16 °C before rearing all hatchlings at a common temperature. Critical thermal maximum (CTmax) significantly differed among populations and temperature treatments. Populations with shorter migration distance and a lower migration and spawning temperature tended to have higher CTmax at 90 days posthatch. However, the relationship was reversed when fish of similar size were compared at 135–214 days posthatch. CTmax at 90 days posthatch was also positively related to body mass, which differed appreciably among populations at this development stage. With growth, the population differences in CTmax diminished from 3.1 to 1 °C. Elevated incubation temperature also decreased CTmax. Arrhenius breakpoint temperature (ABT) for maximum heart rate differed among populations incubated at 14 °C. The Chilko Lake population, which rear at 1.2 km above sea level, had the highest heart rate across all temperatures when incubated at 14 °C, but the lowest ABT among populations. This study provides clear evidence for the local adaptation among sockeye salmon populations with respect to temperature tolerance and cardiac capacity, information that adds to the debate on whether intraspecific variance is adaptive, or a constraint, or both.

Identifying species at risk from climate change: Traits predict the drought vulnerability of freshwater fishes

Trait analysis has potential to identify species that are vulnerable to climate change, but its predictive strength has not been adequately examined. Conditions during the recent ‘Millennium Drought’ in Australia’s Murray-Darling Basin resembled the projected future climate of the region and provided an opportunity to test the ability of traits to predict population responses to a warmer and drier environment. I used data from a large-scale monitoring program to assess how 14 dietary, life-history and physiological-tolerance traits related to changes in occurrence and abundance of 39 of the basin’s freshwater fish species. Species that fared worse under prolonged drought were significantly more likely to have an invertivorous rather than omnivorous diet, a low age at sexual maturity, a small maximum body size, a low spawning temperature, a long spawning season, low fecundity, demersal rather than planktonic eggs, and a low upper thermal limit. Rankings of drought vulnerability of fish species derived from correlations between population changes and traits showed good agreement with a previous assessment of inter-specific variation in resistance to drought, and were corroborated by independent observations of drought responses for some species. Trait analysis should have wide application to identifying species at risk from climate change, provided that sufficient traits are assessed and that adequate consideration is given to variation in trait-vulnerability relationships among different groups of organisms, geographic regions and types of ecosystems.