Spawning Patterns Research Articles

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 (LT) 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.

Growth Variation, Settlement, and Spawning of Gray Snapper across a Latitudinal Gradient

Abstract Newly recruited juvenile gray snapper Lutjanus griseus were collected each fall for two consecutive years (2000 and 2001) from sites in Florida and North Carolina. Spawning, settlement, and growth patterns were compared across sites based on otolith microstructure. Larval otolith growth trajectories were generally similar for larvae from different sites and years; however, the mean pelagic larval duration (PLD) was 1 d longer for fish from North Carolina than for fish from the more southern sites. As a result, fish were larger at settlement to North Carolina. Estimated juvenile growth rates ranged between 0.62 and 0.88 mm/d and differed across sites and years, growth being generally faster at the southern sites. Water temperature accounts for some of this variability; however, site-specific differences in other factors probably contributed to some of the observed differences in growth. Back-calculated spawning patterns showed a lunar association with the new and first-quarter moons at all sites e...

Non-synchronous spawning behavior in laboratory reared amphioxus Branchiostoma belcheri Gray

Spontaneous spawning in amphioxus ( Branchiostoma belcheri Gray) was observed in a tank and the characteristics of spawning were analyzed by video recording under infrared light conditions during summer of 2001. Everyday when spawning was observed, without exception a male first swam up from the bottom and released sperm near the water at the surface of the tank. The initiation time of the male spawning gradually became earlier as days passed. Spawning males and females individually swam up at various intervals and released gametes. However, at the population level, the spawning pattern of amphioxus was considered to be synchronous because both males and females intensively spawned around 90 min after the spawning of the first male. The act of releasing eggs or sperms of individuals was shorter than 10 min in most of the spawning animals.

Spawning Characteristics of the South African Mudcrab Scylla serrata (Forskål) in Captivity

Abstract Scylla serrata is a potential aquaculture species in Southern Africa. Information about its reproductive biology is required as a prerequisite to establishing hatchery technology. Adult female S. serrata were caught in the Umlalazi estuary on the subtropical east coast of South Africa and kept in captivity to observe and record spawning characteristics. Data collected included crab size and mass, time in captivity prior to spawning, fecundity per batch, relative fecundity, individual egg mass and size, size of zoea 1 larvae, incubation time, and hatch success rate. Of the 119 crabs kept in captivity 83% spawned in the maturation system– most within 40 d of capture. The crabs were highly fecund (mean relative fecundity per batch = 10,655 ± 4,069 eggs/g female) and the majority of the batches hatched within 288 h (12 d) at 27 C. Spawning in captivity occurred throughout the year, with a peak in late winter/early spring. This differs slightly from records of ovarian maturity stages of the crabs in the wild. A pattern of synchronous spawning was recorded where the females were observed to extrude their eggs in groups, commonly within 3 d of one another, separated by long periods of inactivity, suggesting an exogenous spawning cue. A total of 1,374,488 zoea larvae were obtained per kg of female per month. This means that if sufficient mature females can be caught from the wild, these could be used for stocking hatchery operations. The crabs were easy to maintain, mature, and spawn in captivity. This will facilitate future domestication which will eventually reduce the need for wild caught broodstock. The spawning characteristics of South African 5. serrata At in well with those observed for the genus throughout its distribution implying that ecological and fisheries management could be similar.

Reproductive biology of the rosylip sculpin, an intertidal spawner

Rosylip sculpin Ascelichthys rhodorus spawned in the intertidal during the winter in the north‐eastern Pacific. Large numbers of males typically congregated at spawning sites, where females deposited clutches. The mating system of this species was external fertilization and group spawning at specific oviposition sites under boulders in the intertidal, and no alternative male mating strategies. Males were abundant at sites while oviposition was occurring, and most abandoned the sites as spawning tapered off seasonally despite the presence of developing clutches. Experimental removal of males from sites suggested that males provided some short‐term benefits to clutches, with catastrophic loss of clutches significantly lower when males were present. The large number of males at an oviposition site and histological evidence indicating high sperm production and storage of sperm prior to release suggest a high level of sperm competition in this species. This spawning pattern appears to differ in substantial ways from any other reported fish mating system.

Comparison of multiple techniques to evaluate reproductive variability in a marine bivalve: application to the scallop Pecten novaezelandiae

Reproduction and spawning of the scallop Pecten novaezelandiae were monitored at four sites in the Hauraki Gulf, New Zealand, from July 2000 to July 2001. A visual grading system based on the macroscopic appearance of the gonad was developed and tested, and changes in visual grade, quantitative histology, and standardised gonad mass were used to describe seasonal and spatial patterns in gametogenesis and spawning. Visual grade was significantly correlated with histological and gonad mass data (r 2 = 0.74–0.87) and validated as an accurate method for measuring reproduction in P. novaezelandiae. Visual grading facilitates rapid assessment of reproductive condition and can be conducted non-destructively, thus providing a tool allowing long-term studies of individual spawning behavior in relation to environmental signals. Scallops exhibited episodic spawning, with spawning events detected in spring, summer, autumn, and even early winter. Gonad recovery and subsequent gamete development and maturation were apparent between spawnings. Within-season variability in gonad size and condition could be the result of multiple (serial) spawnings during a season. The timing of spawning varied among populations, probably reflecting differences in environmental conditions that influenced reproduction. However, the largest spawning events occurred at all sites in early summer (December/January), coincident with wind-driven upwelling conditions.

Spatial and seasonal variation in reproductive characteristics and spawning of southern calamary (Sepioteuthis australis): spreading the mortality risk

AbstractSouthern calamary (Sepioteuthis australis) in Tasmania form spawning aggregations in Great Oyster Bay on the central east coast of Tasmania during spring/summer; these are targeted by commercial fishers. However, it is not known if there are similar aggregations farther south in Tasmania or at other times of the year, mainly because the species lives for less than a year. Therefore, this study describes and identifies differences in reproductive ecology of southern calamary on the east and southeast coasts of Tasmania, by sampling adults and surveying egg masses at inshore sites in both regions. Inshore populations on both coasts showed a similar seasonal trend of large gonosomatic index, reproductive output, and body size, and of greatest abundance during spring, and lowest in autumn. The number of egg masses was higher on the east coast, where mature calamary formed large spawning aggregations during spring and summer. However, there were no such aggregations during winter or autumn. Along the southeast coast, spawning activity was sporadic, resulting in isolated, low density, egg patches deposited over broader areas during spring, summer, and winter. There was no evidence of areas of seagrass or macroalgae associated with large depositions of egg masses at any time on the southeast coast. It appears that, by adopting different spawning behaviour in different locations and seasons, southern calamary may spread the risk of mortality in both space and time. The biological significance of this is unclear, particularly with respect to understanding the mechanisms that drive the development of spawning aggregations. Both spatial and seasonal spawning patterns appear to result from specific use of inshore sites at certain times of the year.

Linking channel geomorphic characteristics to spatial patterns of spawning activity and discharge use by Atlantic salmon ( Salmo salar L.)

This paper relates spatial patterns of spawning by Atlantic salmon ( Salmo salar L.) to channel geomorphic and hydrologic characteristics in two upland Scottish streams. The full length of each stream was surveyed and classified using a process-based typology. The precise locations of 845 spawning events were mapped over 3 successive years. These locations were classified by reach type, and a location-specific discharge was calculated for each spawning event. Fish used ‘response’ reach types (pool-riffle and transitional pool-riffle/plane bed) preferentially, avoiding ‘transport’ reach types (plane bed and step pool). The spatial distribution of reach types contrasted markedly between the streams, and as a consequence, the distribution of spawning activity differed. In each stream, fish utilised relatively high flows for spawning with almost all spawning occurring at discharges greater than location-specific median annual flows, while optimum discharges (defined as those where values of use most exceeded values of availability) were as high as two to three times greater than reach median flows. In each stream, spawning occurred over a greater flow range in response than transport reach types, primarily as a result of higher maximum utilised flows in the former. Because the channel classification procedure is process based (and therefore transferable to other geographic areas), the present study suggests that reach type may be used to predict the spatial distribution of Atlantic salmon spawning activity within a catchment. Since the data indicate that discharge use by spawning fish is reach-type specific, the results also suggest that channel morphology should be considered when identifying environmental flow requirements.

Patterns of spawning and recruitment of sea bass to Bristol Channel nurseries in relation to the 1996 ‘Sea Empress’ oil spill

Young-of-the-year bass (Dicentrarchus labrax) were sampled from ten Bristol Channel sites during 1996, 1997 and 1998 to investigate whether the pattern of recruitment to south Wales nurseries observed following the ‘Sea Empress’ oil spill in spring 1996 was anomalous. Back-calculated egg fertilization (spawned) dates indicated that early spawning events (February–March) at the Trevose Head spawning area provide recruits to south Bristol Channel nurseries, and that the majority of recruits to south Wales nurseries arise from subsequent spawning events. Recruitment of post-larvae to all nurseries in the Bristol Channel starts in late June–early July. The late recruitment of 0-group bass to all nurseries in 1996 was attributed to lower water temperatures in February and March than in 1997 and 1998, and was not restricted to south Wales. However, 0-group bass were relatively less abundant in 1996 at sites nearest the ‘Sea Empress’ oil spill, suggesting a possible effect of the latter on survival of post-larvae in the nurseries, rather than during the offshore egg and larval stage.

The role of life history in the relationship between population dynamics and environmental variability in two Mediterranean stream fishes

ChubSqualius torgalensisand naseChondrostoma lusitanicum, in a Mediterranean stream, showed important differences in life‐history traits and population dynamics. Both species reached mean maturity at age 2 years. Chub lived up to age 5 years, spawned in March to June, grew at a maximum rate of 0·59 mm mm−1 year−1and showed a low reproductive allocation, with fecundity and egg size increasing with body size. Nase lived up to age 4 years, spawned in January to April, grew at a maximum rate of 0·46 mm mm−1 year−1and showed a high reproductive allocation, with egg size independent of body size. Both chub and nase showed moderate fluctuations in population size during 1991–1998, but differed in factors driving density at age. Density of age 1 year juvenile chub decreased following severe summer droughts and proportionate survival prevailed thereafter. Density of age 2 year adult nase decreased following severe spring floods, but neither environmental nor parental stock effects were detected for juveniles and older fishes. The results illustrated the interplay between life history and environmental variability in driving fish population dynamics, with impacts of both summer droughts and spring floods being contingent on species‐specific patterns of spawning and reproductive investment.

Spatial and temporal patterns of spawning and larval hatching by the horseshoe crab,Limulus polyphemus, in a microtidal coastal lagoon

Estuarine species with wide geographic distributions often experience tidal regimes that vary significantly throughout their range. Plasticity in behaviors associated with the tide is expected to enable synchronization with local tides. The American horseshoe crabLimulus polyphemus typically inhabits estuaries and coastal areas with pronounced semi-diurnal tides that play a role in synchronizing the timing of spawning and larval hatching, but also lives in areas that lack significant tides and associated synchronization cues. We investigated the spatial and temporal pattern of adult spawning and larval hatching ofL. polyphemus in a microtidal coastal lagoon (Indian River Lagoon, Florida, USA). Spawning activity and larval abundance were monitored weekly February 1998–August 2000 at sites spanning 100 km of the lagoon. To identify possible synchronization cues for spawning and hatching success, the presence of adult and larvalL. polyphemus were related to environmental and hydrologic variables using logistic regression. The presence of spawning adults varied significantly among the sub-basins of the lagoon, with the highest densities occurring in the Banana River. Large spawning aggregations were not observed and densities never exceeded 6 m−2. Spawning occurred year-round but varied seasonally with episodes of increased mating activity in the early spring. The occurrence of mating pairs was episodic and was not synchronized among sites. Larval densities were low (4 m−3) and larvae were present at only 12 of the 21 sites. Hatching success was decoupled temporally from spawning activity, with peaks in larval abundance occurring approximately 8 wk after peaks in spawning. Larval abundance was associated with periods of high water. Reproductive activity of horseshoe crabs in the lagoon differs significantly from populations inhabiting areas with semi-diurnal and diurnal tides. These differences are likely due to the lack of periodic tidally-related synchronization cues and regular beach inundation.

Reproductive cycle of two commercial species of sea cucumber (Echinodermata: Holothuroidea) from Caribbean Panama

The reproductive status of the holothuroid species Isostichopus badionotus (Selenka, 1867) and Holothuria mexicana (Ludwig, 1875) was studied over 16 months in Bocas del Toro (Panama), from November 1999 to February 2001. Sexual reproduction was evaluated by the gonad index method, and by histology of gonad development. In addition, population structure was assessed based on sex ratio, minimum reproductive size, and length and weight distributions of males and females. The sex ratio in both species was 1:1, with a unimodal population distribution composed mainly of mature individuals. The minimum reproductive length and weight were 13–20 cm and 150 g, respectively, for both species, although reproductive individuals 10 cm in length were also found. A consistently higher gonad index was observed in H. mexicana, due to a high proportion of mature females and males and high gonad indices in most monthly samples. Gametogenesis and spawning patterns seemed to occur throughout the year, with periods of enhanced activity. Two periods of maximum reproductive activity were tentatively identified: July–November for I. badionotus and February–July for H. mexicana, but neither species had a single, sharply defined annual spawning event. Further work on these exploited holothuroids should examine the relationships between reproduction and environmental factors and between reproductive status and recruitment.

Reproduction of the commercial sea cucumber Holothuria scabra (Echinodermata: Holothuroidea) in the Solomon Islands

Over a 3-year period (1996–1998), reproduction of the commercial sea cucumber Holothuria scabra (Jaeger, 1833) was investigated in the Solomon Islands to determine the spawning pattern and whether gametogenesis is continuous or seasonal. The gonad consisted of a single cohort of tubules that developed uniformly. Macroscopic examination of the gonads revealed that mature gametes were present throughout the year. Individuals with gonads at different stages of maturity were present in most samples. Partly spawned gonads were prevalent in females, whereas mature gonads were prevalent in males. The time at which the peak gonad index was recorded differed among years. Although gametogenesis was continuous, with a potential for prolonged gamete release, a period of enhanced spawning occurred during the dry season, from September to December. Maximum gonad indices were reached prior to and during this period of enhanced spawning. Histology revealed that gametogenesis reinitiated in partly spawned gonads, resulting in the presence of gametes at different stages of development in the gonad. The uniform growth of gonad tubules indicated that H. scabra does not conform to the progressive tubule recruitment model described for holothurian oogenesis. Continuous reproduction in H. scabra and prolonged availability of mature gametes would facilitate use of this species for aquaculture.

Modelling the transport success of anchovy Engraulis encrasicolus eggs and larvae in the southern Benguela: the effect of spatio-temporal spawning patterns

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 250:247-262 (2003) - doi:10.3354/meps250247 Modelling the transport success of anchovy Engraulis encrasicolus eggs and larvae in the southern Benguela: the effect of spatio-temporal spawning patterns Jenny Huggett1,*, Pierre Fréon1,2, Christian Mullon2,3, Pierrick Penven2 1Marine and Coastal Management, Private Bag X2, Roggebaai 8012, South Africa 2Institut de Recherche pour le Développement, 213, rue La Fayette, 75480 Paris, France 3Department of Oceanography, University of Cape Town, Private Bag, Rondebosch 7701, Cape Town, South Africa *Email: jhuggett@mcm.wcape.gov.za ABSTRACT: Recruitment success of anchovy Engraulis encrasicolus in the southern Benguela is thought to depend largely on the passive transport of eggs and larvae from their warm-water spawning area, located in the southern part of their distribution range (Agulhas Bank), to their cold-water nursery grounds located 500 km away on the west coast of South Africa. In order to test this hypothesis, the output of a 3D hydrodynamic model was coupled to a particle-tracking model, allowing the quantification of different factors such as the timing and precise location of spawning activity, the frequency of spawning activity within a month, the level of aggregation of the spawning stock, and the interannual variability of transport due to mesoscale processes. Results from the model indicate that spawning season and area have a major effect on transport success. The most favourable period for spawning was September to March, peaking in November, and the western Agulhas Bank was the most favourable spawning area. A low success rate of passive transport to the core inshore nursery area in the model suggests that additional processes such as swimming or advection are required for larvae to reach this area. In general, there was good agreement between observed spawning patterns and the optimal temporal and spatial strata where particle transport was most successful, suggesting that the spawning strategy of anchovy is mainly the result of an adaptation to the circulation patterns in the region. Nonetheless, some discrepancies were observed between the success of transport and actual spawning patterns, and temperature may also be an important factor to take into consideration to fully explain how this originally temperate species is able to survive in an area of highly contrasting temperatures. KEY WORDS: Individual-based model · Transport success · Anchovy · Ichthyoplankton · Recruitment · Reproductive strategy · Southern Benguela · Engraulis encrasicolus Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 250. Online publication date: March 26, 2003 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2003 Inter-Research.

Influence of wave-induced disturbance on seasonal spawning patterns in the sabellariid polychaete Phragmatopoma lapidosa

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 256:123-133 (2003) - doi:10.3354/meps256123 Influence of wave-induced disturbance on seasonal spawning patterns in the sabellariid polychaete Phragmatopoma lapidosa Daniel A. McCarthy1,2,*, Craig M. Young1, Roland H. Emson2 1Department of Larval Ecology, Harbor Branch Oceanographic Institute, 5600 North, Fort Pierce, Florida 34946, USA 2Division of Life Sciences, King¹s College, University of London, 150 Stamford Street, London SE1 9NN, United Kingdom 3Present address: Smithsonian Marine Station at Fort Pierce, 701 Seaway Drive, Fort Pierce, Florida 34949-3140, USA *Email: mccarthy@sms.si.edu ABSTRACT: The effect of wave-induced disturbance on seasonal spawning patterns of the opportunistic polychaete Phragmatopoma lapidosa (Kinberg, 1867) was investigated by comparing seasonal fecundity, egg size and adult size between intertidal and subtidal worms at Boynton Beach, Florida. Fecundity patterns showed spawning peaks in summer and fall in both habitats, with reduced spawning in late fall and early winter. Subtidal females averaged 1015.2 eggs mm-1 body length (range 0 to 2000 eggs mm-1), while intertidal females averaged 607.4 eggs mm-1 (range 0 to 1520 eggs mm-1). Mean egg diameters were not significantly different between worms from the 2 habitats, ranging between 90.4 µm (SD = 3.7) and 89.5 µm (SD = 4.3) for intertidal and subtidal worms respectively. Inter- and intra-census comparisons of egg diameter, fecundity and adult length revealed few statistically significant relationships, suggesting that intertidal and subtidal worms were the same age. Adult lengths in both habitats did change seasonally. The smallest adult worms were found shortly after massive fall recruitment replaced a large percentage of individuals in both intertidal and subtidal populations. Stepwise multiple regression indicated that 76.2% of the variance in intertidal fecundity was explained by a negative correlation with wave height (40.4%), and a positive correlation with day length (34.7%). In contrast, 85.5% of the variance in subtidal fecundity was explained by a positive correlation with day length (77.4%), and a negative correlation with chlorophyll a concentration (8.1%). While habitat-specific differences in energy available for gametogenesis probably contribute towards the observed fecundity trends, the force of crashing waves could also influence fecundity, as it may affect frequency of spawning in intertidal but not subtidal habitats. KEY WORDS: Phragmatopoma · Polychaetes · Fecundity · Spawning · Reproductive plasticity Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 256. Online publication date: July 17, 2003 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2003 Inter-Research.

Spawning locations and movement of Kootenai River white sturgeon

Summary The Kootenai River white sturgeon Acipenser transmontanus, an endangered species, spawns within an 18-km reach in the Kootenai River, Idaho, river kilometer (rkm) 228.0-246.0. Preliminary observations of adult white sturgeon have shown what appeared to be a progressive upstream movement during the spawning season, spawning over sand substrate seldom reaching the typical sturgeon spawning habitat of gravel and cobble located upstream of rkm 244.6. This behavior may be unusual for a white sturgeon population. The primary objecttive of this paper is to compare, within each spawning season and between seasons, the spatial and temporal pattern of egg collections (as an indicator of spawning location) and the spatial and temporal pattern of suspected spawners, as determined by their movement from 1994 to 1999. Adult white sturgeon were tagged with sonic and radio transmitters. Artificial substrate mats were deployed within three sampling reaches to determine approximate spawning locations and timing in reference to locations of spawners. Eggs were collected 207 different times from 1994 to 1999, including 123 times in the lower reach and 84 times in the middle reach. White sturgeon demonstrated a consistent temporal pattern of shifting spawning location as the season progressed, first spawning in the lower reach and then moving upstream to the middle reach. A total of 1234 contacts of potential spawners were made during May and June for the years 1994-1999. Some spawners were located in as many as four different locations from which eggs were collected within a season. There appeared to be at least five primary spawning locations, most in the vicinity of outside bends. This movement and temporal spawning pattern appears to be unique when compared with published studies on other sturgeon populations. Companion studies indicate that the species is not recruiting despite mitigative measures, and white sturgeon are thought to be spawning in unsuitable habitat. The combination of movement by white sturgeon within this sandy reach during the spawning season and spawning in unsuitable habitat may be contributing to the failure of recruitment. Present measures to recover the population may be inadequate. Further study is needed to determine if this movement pattern is caused by changing water velocities. Also, if historic spawning locations cannot be identified and rehabilitated, then we suggest consideration be given to habitat enhancement measures at the present spawning locations.

Biology and population dynamics of the long-finned squid Loligo plei (Cephalopoda: Loliginidae) in southern Brazilian waters

Population structure and reproductive patterns of the long-finned squid Loligo plei off the coast of Santa Catarina, southern Brazil, were analysed from the biological samples of commercial catches landed in the Itajaı́ harbour from April 1995 to February 1998. The species were recruited to the trawl fishery at 130 mm mantle length (ML) and males were, on average, nearly 1.3 times larger than females. The exponents of males and females ML–weight relationships were 1.89 and 2.07, respectively, and differed significantly between maturity stages. Cohorts of both sexes did not persist into their second year, a feature that, coupled with the scarcity of spent animals, provided evidence for semelparity with nearly 1 year life span. An extended seasonal breeding and spawning pattern was characterised with a large reproduction event concentrated during the summer months extending through autumn and winter. It is suggested that the summer spawners hatch during the summer–early autumn, recruit to the fishery in the spring and reach maturity in the following summer, at the age of nearly 1 year. Squid spawned during the winter will hatch during winter–early spring, recruit to the fishery during the summer and autumn and spawn in their second winter. Between summer and winter spawning events, continuous spawning activity produce several microcohorts detected in trawlers catch. Summer spawners sustain the most important commercial concentrations. The relationship between L. plei population structure, seasonal abundance and the dynamics of environmental conditions off southern Brazil is discussed.

Inhibition of embryonic development and fertilization in broadcast spawning marine invertebrates by water soluble diatom extracts and the diatom toxin 2- trans,4- trans decadienal

Water soluble diatom extracts and the diatom aldehyde 2- trans,4- trans decadienal were assayed on the gametes and embryos of the broadcast spawning polychaetes Arenicola marina and Nereis virens and the echinoderms Asterias rubens and Psammechinus miliaris. Both crude cellular extracts and purified aldehyde were found to inhibit fertilization, embryogenesis and hatching success in a dose dependent manner. Intact diatom cells had no discernable effect on fertilization or development. Extracts of Skeletonema costatum were generally more effective than Nitzschia commutata in inhibiting development and fertilization. There was considerable interspecific variation in terms of toxin sensitivity. The polychaetes were more sensitive to the effects than the echinoderms. Within the polychaetes A. marina was the more tolerant in terms of developmental competence but N. virens had a higher fertilization rate. Echinoid embryos were more tolerant than asteroid embryos. This is the first study to present data on the inhibition of fertilization success by diatom extracts and aldehydes. Our observations are discussed in relation to temporal patterns in spawning and possible adaptive mechanisms to avoid diatom toxicity.

Artificial Selection and Environmental Change: Countervailing Factors Affecting the Timing of Spawning by Coho and Chinook Salmon

Spawning date is a crucial life history trait in fishes, linking parents to their offspring, and it is highly heritable in salmonid fishes. We examined the spawning dates of coho salmon Oncorhynchus kisutch and chinook salmon O. tshawytscha at the University of Washington (UW) Hatchery for trends over time. We then compared the spawning date patterns with the changing thermal regime of the Lake Washington basin and the spawning patterns of conspecifics at two nearby hatcheries. The mean spawning dates of both species have become earlier over the period of record at the UW Hatchery (since the 1950s for chinook salmon and the 1960s for coho salmon), apparently because of selection in the hatchery. Countering hatchery selection for earlier spawning are the increasingly warmer temperatures experienced by salmon migrating in freshwater to, and holding at, the hatchery. Spawning takes place even earlier at the Soos Creek Hatchery, the primary ancestral source of the UW populations, and at the Issaquah Creek Hatchery. Both species of salmon have experienced marked shifts towards earlier spawning at Soos Creek and Issaquah Creek hatcheries despite the expectation that warmer water would lead to later spawning. Thus, inadvertent selection at all three hatcheries appears to have resulted in progressively earlier spawning, overcoming selection from countervailing temperature trends.

Evolutionary individual-based model for the recruitment of anchovy (Engraulis capensis) in the southern Benguela

Evolutionary simulations are developed to explore environmental constraints that select observed spatial and temporal spawning patterns for anchovy (Engraulis capensis) in the southern Benguela. They couple a realistic three-dimensional hydrodynamic model with an individual-based model in which an evolutionary-based reproductive strategy for adult fish and a passive transport for early life stages are implemented. The evolutionary success of spawning is quantified when patterns at the population level emerge after many generations from constraints at the individual level through a selective process. As a result, several self-sustaining populations are identified considering different sets of selective constraints. Simulated spawning patterns better match the observed mean spawning pattern when two selective environmental constraints are associated: a threshold temperature of 14°C, above which the development of early life stages is ensured, and the avoidance of offshore currents that constitute a loss of spawning products. Simulated recruitment patterns are more realistic when considering the constraint of reaching the nursery area. This modeling experience can help to identify, temporally and spatially, environmental factors important for fish recruitment and to establish a hierarchy of these factors. The probable coexistence in nature of several self-sustaining populations of pelagic fishes is shown to be important for recruitment studies.