Impacts of climate and density on the duration of the tadpole stage of the common toad Bufo bufo

In an ongoing long-term study of a breeding population of common toads Bufo bufo at a pond in southern England, the dates of first spawning have been recorded since 1980, the dates of toadlet emergence since 1984, and the numbers of emergent toadlets estimated since 1988. The dates when spawn was first laid varied considerably between years from the earliest on 2 February 1993 (day 33) to the latest on 19 March 1996 (day 79). The duration of the tadpole stage was negatively correlated with the date of appearance of first spawn and was up to 30 days longer in early spawning years than in late ones. Despite this, toadlets still emerged from the natal pond up to 36 days earlier in early spawning years than in late ones. Significant positive correlations were found between the duration of the tadpole stage and both the proportion of days during the tadpole stage when the minimum ground temperature was at or below 0°C and the proportion of days when 10 mm or more rain fell. Tadpole mortality was positively correlated with the proportion of days during the tadpole stage when the minimum ground temperature was at or below 1.5°C. Evidence was also found to suggest that tadpole mortality was density-dependent, being proportionately higher when initial tadpole numbers were high than when they were low. Received: 7 May 1999 / Accepted: 19 July 1999     

Reproductive migration of brown trout in a small Norwegian river studied by telemetry

The movement of 34 large (39–73 cm standard length) brown trout Salmo trutta was monitored using radio telemetry for up to 74 days in Brumunda, a small Norwegian river (mean annual discharge 3·3 m³ s⁻¹) flowing into the large Lake Mjøsa. The maximum range of movement in the river was 20 km. No clear relationships existed between individual movement and water discharge, temperature and barometric pressure. Brown trout migrated at all levels of water discharge. At low discharge (<2 m³ s⁻¹) movements were nocturnal. A weir 5·3 km from the outlet restricted ascending brown trout at low ( c . 6° C), but not at high ( c . 8° C) water temperatures. Spawning occurred in September to October and tagged individuals spent 2–51 days at the spawning sites. Mean migration speed from tagging to when the fish reached the spawning area, and from when they left the spawning areas and reached the lake was 1·0 and 2·3 km day⁻¹, respectively. All tagged brown trout that survived spawning returned to the lake after spawning.     

Application of otolith analyses to investigate broad size distributions of young yellow perch in temperate lakes

Otolith analyses were used to back-calculate young-of-the-year (YOY) yellow perch Perca flavescens hatch-date estimates to interpret broad length distributions observed within a small Great Lake, Lake St. Clair, and a small inland lake, Lake Opinicon, during 1998. For the Great Lake, the earliest observed hatch date occurred 2 weeks after suitable water temperatures and latest hatch dates occurred the same week temperatures were considered too warm for spawning. For the inland lake, the earliest hatch date occurred 4 weeks after suitable water temperatures and the latest hatch dates occurred 2 weeks after the water temperatures were considered too warm for spawning. It is inferred that spawning in each lake had a duration of >9 weeks. This suggests that natural perch populations can protract their spawning season opportunistically under the appropriate environmental cues. During 1998, these cues involved a shortened winter, earlier spring, and slow warming to typical summer temperatures, caused by the El Niño-Southern Oscillation. Time of YOY hatch determined the absolute opportunity for growth and resulted in a match or mismatch with optimal foraging conditions and contributed to the development of the observed YOY length distributions.     

Spawning migrations of the chub in the River Spree, Germany

Out of 52 chub Leuciscus cephalus tagged with internal radio‐transmitters, 46 migrated to spawning grounds in the River Spree, Germany. All chub started their first spawning migration on 21–22 May in both years of study, 1995 and 1996. They arrived at three different spawning grounds within a day and left after 1 to 6 days to return to their original sites. On 17 and 18 June 1995 and 1996 chub started their second spawning migration with the same pattern as the first. About 60% of all migrating chub moved between 1 and 13 km upstream to the nearest spawning ground. Some exceptions were observed: a few chub did not use the nearest spawning ground, some chub used different spawning grounds at first and second spawning or moved downstream to a spawning ground. Spawning grounds were characterized by 0·4 m s⁻¹ current velocity, shallow depth (0·1–0·8 m) and a stony bottom, where most eggs adhered.     

Duration of larval and spawning periods inPagrus auratus (Sparidae) determined from otolith daily increments

Synopsis Counts of pre-metamorphic and post-metamorphic daily increments in the sagittae of settled juvenilePagrus auratus were used to determine duration of the larval period and to back-calculate spawning dates. The duration of the larval period was 18–32 days, and was longer for snapper spawned early in the spawning season, when water temperatures were low, than for snapper spawned later in the season when temperatures were high. Sagitta size at metamorphosis was unrelated to duration of the larval period or temperature, and mean increment width during the larval period increased with temperature. These results suggest that metamorphosis is size- rather than age-dependent. Back-calculated spawning dates ranged from September to March, and peaked in November-January. Maximum spawning season duration was five months. Spawning onset was earlier when spring water temperature was higher than normal, and first spawning occurred at 14.8–15.6 °C over three seasons, indicating that spawning onset is temperature-dependent.     

Spawning aggregations of Lutjanus cyanopterus(Cuvier) on the Belize Barrier Reef over a 6 year period

Cubera snapper Lutjanus cyanopterus aggregated to spawn at Gladden Spit, a salient sub‐surface reef promontory seaward of the emergent reef and near the continental shelf edge of Belize. Their spawning aggregations typically formed 2 days before to 12 days after full moon from March to September 1998–2003 within a 45 000 m² reef area. Peak abundance of 4000 to 10 000 individuals was observed between April and July each year, while actual spawning was most frequently observed in May. Spawning was observed consistently from 40 min before to 10 min after sunset within a confined area ≤1000 m². Data suggested that cubera snapper consistently formed seasonal spawning aggregations in relation to location, photoperiod, water temperature and lunar cycle, and that spawning was cued by time of day but not tides. The cubera snapper aggregation site was included within the Gladden Spit Marine Reserve, a conditional no‐take fishing zone.     

Spawning characteristics of the anadromous brown trout in a small Swedish stream

The spawning pattern of the anadromous brown trout Salmo trutta was studied in Själsöån, a small stream in Gotland, Sweden, during eight winters between 1992–1993 and 1999–2000. The total length ( L _T) at spawning was normally distributed (185–890 mm) for females and multimodal for males (300, 400 and 550 mm most frequent length classes). Spawning males were significantly younger (2+ to 4+ years) than females (3+ to 5+ years). The sex‐ratio at the beginning and at the end of the spawning season favoured males. The mean ±  s . d . number of spawners was 70 ± 16 individuals per year. Migration into and out of the stream occurred between November and June. The highest number of spawning fish was found in the stream at the end of November or at the beginning of December. Migration mainly occurred during high water flow and at night. The majority of the females entered the stream and spawned the same (29·3% of all the females) or the next night (32·8% of all the females) while males may have stayed for 2 to 3 weeks (21·3% of all the males) in the stream before spawning. Males usually remained much longer in the stream (mean ±  s . d . 45 ± 56 days) than females (16 ± 30 days). Females lost more mass in the stream (mean ±  s . d . 17·3 ± 8·6%) than males (7·7 ± 9·6%). For both sexes, mass loss was positively correlated with the time spent in the stream. Only 7·3% of the males and 5·7% of the females occurred in the stream for >1 year. Spawning took place only during the night.     

Changing temperature regimes have advanced the phenology of Odonata in the Netherlands

Abstract.  1. Responses of biota to climate change have been well documented for a restricted number of taxa. This study examined shifts in phenology of 37 species of the aquatic insect order Odonata in the Netherlands over the last decade.
2. The present study shows that adults of the Dutch dragonflies and damselflies have advanced their flight dates over recent years due to complex effects of changing temperature regimes on the timing of adult flight dates.
3. Flight dates did not respond to changes in autumn/winter temperatures, advanced with increases in spring temperatures of the focal and previous year, and delayed with increases in summer temperatures of the previous year. Climate change consequently advanced the flight dates of the Odonata because only spring temperatures have increased during the study period.
4. The findings imply that climate change can evoke strong phenological responses in aquatic insects. Moreover, shifts in phenology due to climate change are likely to vary both spatially or temporally, depending on the exact nature of climate change.     

Early warning of egg hatching in pea moth (Cydia nigricana)

Female pea moths (Cydia nigricana) kept at 23 ^oC began to lay eggs 2–3 days after emergence, lived for 16–21 days and laid on average 71 eggs. Individuals kept in field cages lived for slightly longer and laid on average 91 eggs. About 85% of eggs were laid during the first 11 days of the oviposition period, usually in the late afternoon and early evening. The relationship between the rate of egg development and temperature was defined. The estimated developmental zero was 9-4 ^oC at constant temperatures and 8-5 ^oC at fluctuating temperatures. Above 28 ^oC mortality increased and above 31 ^oC development was apparently retarded. Development at constant temperatures took 6–16% longer than at fluctuating temperatures with the same mean. Estimates of hatching dates in the field made from temperature data recorded at several sites in and near a pea crop, and 8 km distant, were usually within a day of the observed date. In warm weather, estimated and observed dates usually coincided; in cooler weather hatching was 2–3 days later than expected. Hatching dates predicted from temperature data after only 80% of development had occurred were correct on 28 out of 36 occasions. An example is given to show how the method could be used eventually with a sex attractant trapping system to provide early warning of first hatching and spraying dates.     

The date of spawning in populations of the Common frog (Rana temporaria) from different altitudes in northern England

A series of ponds in the Wear Valley in northern England, ranging in altitude from 46 to 838 m, were visited regularly over a four-year-period, and a record was kept of the dates on which spawn from the Common frog, Rana temporaria , was first seen in each of the ponds. On average. spawning was delayed by six days for every 100 m increase in altitude. The date of spawning at each of the ponds was fairly consistent from year to year; only in 1974 was the date of spawning noticeably different from other years. A theory was proposed which could account for the variation in the date of spawning with altitude and the annual variation in the date of spawning, observed in the present study. It is proposed that frogs from nothern England become sensitive to environmental temperature in the middle of February and emerge in the spring after experiencing a temperature-sum of 106 degree(C)-days. The onset of temperature sensitivity is probably initiated by a circannual endogenous rhythm. The time at which the rhythm switches on the temperature-sensing mechanism in frogs probably varies in different populations, and may well be locally adapted. For spawning to follow emergence, a certain minimum water temperature may be required. In the present study, most frogs in the wild spawned when the water temperature in the ponds was above 7°C, but frogs could spawn at 3·1°C. Alternative theories for the control of emergence and spawning are also discussed.     

The effects of climate change on the phenology of winter birds in Yokohama, Japan

Observations made largely from summer breeding sites in Europe and North America have been used to document the effects of climate change on many bird species. We extend these studies by examining 23 years of observations between 1986 and 2008 of six winter bird species made by citizens at a city park in Yokohama, Japan. Bird species arrive in autumn and spend the winter in the area, before departing in the late winter or spring. On average, birds species are arriving 9 days later than in the past and are departing on average 21 days earlier, meaning that the average duration of their stay in Yokohama is about 1 month shorter now than in the past. Patterns of changes over time varied among species, but departure dates changed for more species than did arrival dates. Dates of departure and arrival were sometimes correlated with monthly average temperatures—later arrivals and earlier departures were associated with warmer temperatures. In addition, interannual variation in arrival and departure dates were strongly correlated across species, suggesting that species were responding to the same or similar environmental cues. This study provides a clear demonstration of the value of using citizens to make observations that contribute to research in climate change biology.     

Availability of and access to critical habitats in regulated rivers: effects of low-head barriers on threatened lampreys

1.  Conservation of freshwater animal populations requires their access to, as well as sufficient availability of, critical habitats, such as those for reproduction. Abundant small-scale barriers may cause extensive fragmentation of freshwater habitat but, by comparison to larger structures their effects are rarely considered by catchment managers. The relationship between the distribution of, and access to, spawning habitat in a regulated river, characterized by abundant small barriers, was examined for river lamprey Lampetra fluviatilis , a threatened migratory fish.
2.  Telemetry of adult lamprey in the River Derwent, North East England was used to quantify upriver migration and access to spawning habitat, together with surveys of spawning habitat availability and spawning activity between 2002 and 2007.
3.  Access in to the Derwent appeared severely restricted by a tidal barrage, beyond which lamprey migrated rapidly in unobstructed reaches. Of all lamprey tagged in the lower 4 km of river, or ascending the barrage, 64% and 17% passed the first and second weirs respectively, with high flows crucial for this. Although over 98% of lamprey spawning habitat occurred more than 51 km upstream, on average just 1.8% of river lamprey spawners were recorded there.
4.  In order to protect or rehabilitate species or species assemblages, greater attention needs to be paid to the relative spatial distribution of low-head barriers and the resultant availability of key habitats within individual catchments. This is particularly important given the renewed emphasis internationally on low-head hydropower solutions as a source of renewable energy, and the rapid growth in numbers of low-head barriers in many catchments.     

Reproductive biology of Vinciguerria nimbaria in the equatorial waters of the eastern Atlantic Ocean

Adult Vinciguerria nimbaria in an area of the Atlantic Ocean (0–5°N; 10–20°W), collected from November 1994 to February 1998, exhibited two different patterns in diel behaviour: 'typical' behaviour which consisted of large diel vertical migration and 'atypical', characterized by concentrations of schools that remained in the surface layers during the daytime. The total life span of V. nimbaria was estimated at 6–7 months. Females were mature when they reached 30·6 mm standard length ( L _S), which corresponded to an age of 85 days. Once the females were mature, spawning was continuous in the population as a whole, and V. nimbaria spawned continuously throughout the year. Spawning took place during two restricted times of the day: typical females spawned at dusk and atypical females spawned at dawn. Using the post-ovulatory follicles method, spawning frequency was estimated at 2 days. Batch fecundity was estimated at 1236 oocytes or 1230 oocytes g⁻¹ of total body mass, and egg size was 650 µm whatever the period of the year. The lifetime fecundity of V. nimbaria was estimated at 9000 eggs (109 000 eggs if mortality rate was not taken into account), and the maximum stock egg production of a theoretical cohort occurred at 37 mm L _S. Young adults thus contributed the most to the reproductive output for the survival of the population.     

Reproductive patterns in seventeen species of warmwater fishes in a Missouri River reservoir

Synopsis The timing of ovarian maturation and spawning of 17 warmwater fish species in Lake Oahe (South and North Dakota) was estimated from changes in the mean ovary indices (ratios of ovary weight to fish length). The onset of vitellogenesis varied within species (up to 2 months). Maturation of the ova took from 7.5 to 10 months, depending on species. Annual variations in the mean date of peak spawning of individual species during 1964–1971 were usually less than a week. There was little overlap of the annual mean peak spawning dates of the 17 species, and an established sequence of spawning among species was shown. A relatively high incidence of atresia in the shovelnose sturgeon, northern pike, and carp indicated that these species had apparently not yet adapted to the altered and variable spawning conditions in this reservoir. Regularity of spawning would seem to provide the best chance for spawning success in variable environments such as Lake Oahe.     

Reproductive biology and recruitment of the white sea bream in the Azores

The life history of the white sea bream Diplodus sargus in the Azores showed a pattern consistent with digynic hermaphroditism achieving sexual maturity during the second year of life, at 16·7 cm L _T. Spawning occurred from March to June at temperatures between 15 and 17° C and the onset and duration of spawning season in the sea bream appeared to be influenced by sea water temperatures. As latitude decreased, both in the northern and southern hemispheres, the spawning season of D. sargus populations started earlier and extended longer, highlighting the potential importance of temperature to the onset and duration of reproduction in this species. Settlement took place from late May to July, and settlers remained in the nursery area for c . 2·5 months. Emigration from the nursery area to join shoals of juveniles occurred from late July to September.     

Migratory behaviour of ide: a comparison between the lowland rivers Elbe, Germany, and Vecht, The Netherlands

Individual movement patterns of adult ide Leuciscus idus , a Eurasian river‐dwelling cyprinid, in two lowland rivers were measured all year‐round during 1997–2000 to assess migratory behaviour and variation between and within these populations. In the River Elbe, a 1091 km long lowland river with a free flowing stretch of 590 km, 24 ide were implanted with radio transmitters. Fish were hand‐tracked all year‐round once a week in the main study area (75 km), and once per 6 weeks in a larger area (321 km). In the River Vecht, a 190 km long highly regulated river with six weirs and fishways in the Dutch section, 25 ide were implanted with transponders. An array of three automatic detection stations covering the entire river width, registered each individual passage continuously. Within population variation in year‐round movement patterns was very high. In both rivers a similar continuum was found from individuals using a river stretch of only a few km for spawning, feeding and wintering, to individuals migrating >100 km. The populations in the two rivers differed, however, in spawning site fidelity. In the River Vecht spawning site fidelity was observed in all individuals and appeared much stronger than in the River Elbe, where individuals moving downstream >60–90 km tended to adopt new spawning sites in the next year. Moreover, some ide in the River Vecht migrated upstream to wintering habitats in autumn, whereas this was not observed in the River Elbe. The results suggest that ide is a flexible species capable of using a wide variety of movement patterns and scales.     

Spawning ecology of flannelmouth sucker, Catostomus lattipinnis (Catostomidae), in two small tributaries of the lower Colorado River

We report the first published accounts of spawning behavior and spawning site selection of the flannelmouth sucker in two small tributaries of the lower Colorado River in the Grand Canyon, Arizona. Spawning was observed on 20 March 1992 and from 28 March to 10 April 1993 in the Paria River, and from 16 to 19 March 1993 in Bright Angel Creek. Flannelmouth suckers exhibited promiscuous spawning behavior–individual females were typically paired with two or more males for a given event and sometimes changed partners between events. Multiple egg deposits by different females sometimes occurred at one spawning site. Flannelmouth sucker selected substrates from 16 to 32 mm diameter in both streams. Spawning occurred at depths of 10 to 25 cm in the Paria River and 19 to 41 cm in Bright Angel Creek. Mean column water velocities at spawning locations ranged from 0.15 to 1.0 m sec^-1 in the Paria River and from 0.23 to 0.89 m sec^-1 in Bright Angel Creek. Water temperatures recorded during spawning ranged from 9 to 18° C in the Paria River and 13 to 15° C in Bright Angel Creek. Spawning flannelmouth sucker ascended 9.8 km upstream in the Paria River and 1.25 km in Bright Angel Creek. Spawning females (410–580 mm) were significantly larger than spawning males (385–530 mm) in the Paria River. The mean size of spawning fish in the Paria River was significantly smaller than the entire stock, averaged throughout the study period (380–620 mm). However, fish spawning in 1992–1993 averaged 53 mm larger than fish spawning in the same reach of the Paria River in 1981, indicating a shift in the size structure of this stock.     

Habitat use and population characteristics of potentially spawning shovelnose sturgeon Scaphirhynchus platorynchus (Rafinesque, 1820), blue sucker (Cycleptus elongatus (Lesueur, 1817), and associated species in the lower Wisconsin River, USA

The goal of this study was to compare the possible locations, timing, and characteristics of potentially spawning shovelnose sturgeon (Scaphirhynchus platorynchus), blue sucker (Cycleptus elongatus), and associated species during the spring of 2007–2015 in the 149‐km‐long lower Wisconsin River, Wisconsin, USA, a large, shallow, sand‐dominated Mississippi River tributary. A 5‐km index station of two pairs of rocky shoals surrounded by sandy areas was electrofished for shovelnose sturgeon and blue sucker in a standardized fashion a total of 40 times from late March through mid‐June, the presumed spawning period. On one date in 2008 and two dates in 2012, all rocky shoals and adjacent sandy areas in the lowermost 149 km of the river were also electrofished for both species. Shovelnose sturgeon and blue sucker appeared to spawn in the limited rocky areas of the river along with at least four other species: mooneye (Hiodon tergisus), quillback (Carpiodes cyprinus), smallmouth buffalo (Ictiobus bubalus), and shorthead redhorse (Moxostoma macrolepidotum), usually at depths of 0.8–2.0 m and surface velocities of 0.4–1.0 m/s. However, apparently spawning shovelnose sturgeon were found only on mid‐channel cobble and coarse gravel shoals within a single 7‐km segment that included the 5‐km index station, whereas apparently spawning blue suckers were encountered on these same shoals but also more widely throughout the river on eroding bluff shorelines of bedrock and boulder and on artificial boulder wing dams and shoreline rip‐rap. Both species showed evidence of homing to the same mid‐channel shoal complexes across years. Blue sucker tended to concentrate on the shoals earlier in the spring than shovelnose sturgeon, usually from late April through mid‐May at water temperatures of 8.0–15.5°C along with quillback and shorthead redhorse. In comparison, shovelnose sturgeon usually concentrated on the shoals from mid‐May through early June at 13.5–21.8°C along with mooneye and smallmouth buffalo. Based on recaptures of tagged fish, at least some shovelnose sturgeon and blue sucker returned to the shoals at one‐year intervals, although there was evidence that female blue sucker may have been more likely to return at two‐year intervals. Most shovelnose sturgeon could not be reliably sexed based on external characteristics. Spawning shovelnose sturgeon ranged from 487 to 788 mm fork length, 500–2400 g weight, and 5–20 years of age, whereas spawning blue sucker ranged from 495 to 822 mm total length, 900–5100 g weight, and 5–34 years of age, although age estimates were uncertain. Females were significantly larger than males for both species although there was overlap. Growth in length was negligible for tagged and recaptured presumably spawning shovelnose sturgeon and low (3.5 mm/y) for blue sucker, suggesting that nearly all growth may have occurred prior to maturity and that fish may have matured at a wide range of sizes.     

Specific gravity and vertical distribution of sprat eggs in the Baltic Sea

During peak spawning of sprat Sprattus sprattus in the Baltic Sea in May–June egg specific gravity averaged ± s . d . 1·00858 ± 0·00116 g cm⁻³ but was significantly higher in the beginning and significantly lower towards the end of the spawning season. A close relationship was found between egg diameter and egg specific gravity ( r ² = 0·71). This relationship, however, changed during the spawning season indicating that some other factor was involved causing the decrease in specific gravity during the spawning period. The vertical egg distribution changed during the spawning season: eggs were distributed mainly in the deep layers early in the season, occurred in and above the permanent halocline during peak spawning, and above the halocline towards the end of the spawning season. Consequently, poor oxygen conditions in the deep layers and low temperatures in layers between the halocline and the developing thermocline may affect egg development. Thus, opportunities for egg development vary over the spawning season and among spawning areas, and depending on frequency of saline water inflows into the Baltic Sea and severity of winters, between years.     

Interannual variation in the reproductive cycle of the New Zealand snapper Pagrus auratus (Bloch & Schneider) (Sparidae)

Changes in reproductive condition in the New Zealand snapper Pagrus auratus (Bloch & Schneider) were monitored in a wild population over three successive years. Recrudescence occurred in spring with spawning beginning in October and continuing for 3 to 5 months. The initiation of spawning varied by up to 3 weeks and was associated with sea surface temperatures of 15–16° C. Theconclusion of spawning was associated with temperatures of 19–21° C but showed greater interannual variation than the onset of spawning. Changes in the gonadosomatic index were accompanied by parallel changes in hepatosomatic index in females but not males, reflecting the role of the liver in vitellogenesis in females.