Time of start of spawning in Atlantic cod (Gadus morhua) females in relation to vitellogenic oocyte diameter, temperature, fish length and condition

Spawning time of female Atlantic cod ( Gadus morhua L.) can be predicted to within 3 days using vitellogenic oocyte diameters measured over the last month before spawning. Simulations show that a l°C drop in temperature during vitellogenesis delays spawning by about 8–10 days. Similar results were obtained with fish on low ration for 4–8 months before spawning. Moderately fed females held over two to four consecutive spawning seasons demonstrated a significant delay (⋍3–40 days) in the date of first spawning as the fish grew older and more fecund. Forecasting studies on spawning migrating Arcto-Norwegian cod gave no evidence of a significant effect of fish length on the time of spawning. Warmer water temperature during vitellogenesis for the larger fish appears to compensate for the negative effect of fecundity On spawning time.     

Linking responses of native and invasive plants to hurricane disturbances: implications for coastal plant community structure

Hurricane disturbances produce significant changes in forest microclimates, creating opportunities for seedling regeneration of native and invasive plant species alike. However, there is limited information on how changes in microclimates and pre-existing forest conditions affect native and invasive plants responses to hurricane disturbances. In this manipulative study, we examined the responses of three common shrub/small stature tree species, two of which are native to the coastal region of the southeastern USA (Baccharis halimifolia and Morella cerifera) and one that is invasive (Triadica sebifera), to two key components of hurricane disturbance (canopy damage and saline storm surge). In a greenhouse, we grew seedlings of these species under a range of shade levels that mimicked pre-and post-hurricane canopy conditions for wet pine forest and mixed hardwood forest, two forest communities common in coastal areas of the southeastern USA. Seedlings were subjected to saline storm surges equivalent to full strength sea water for 3 days. Seedling responses (mortality and growth) to the treatments were monitored for 16 months. All species benefitted from higher canopy openness. Storm surge effects were short-lived and seedlings readily recovered under high light conditions. The storm surge had stronger negative effects on survival and growth of all species when coupled with high shade, suggesting storm surge has greater negative impacts on seedlings where hurricane winds cause minimal or no canopy damage. The invasive T. sebifera was by far more shade tolerant than the natives. Survival of T. sebifera seedlings under highly shaded conditions may provide it a competitive edge over native species during community reassembly following tropical storms. Differential responses of native and invasive species to hurricane disturbances will have profound consequences on community structure across coastal forest stands, and may be regulated by legacies of prior disturbances, community structure, extent of canopy damage, and species’ tolerance to specific microclimates.

     

The inter-spawning interval of the female Three-spined stickleback, Gasterosteus aculeatus

Female Three-spined sticklebacks spawn several times in a breeding season, at intervals of a few days. The changes that take place in females during the interval between successive spawnings were analysed. The average time between spawnings was 87.5 hours. Between spawnings females increased in weight by between 15 and 30%. The bulk of this weight increase was lost when the eggs were spawned. The increase in weight was because of an increase in weight of the ovaries, which showed an increase in both dry matter and water content. After spawning the ovaries formed 8 to 9% of the total body weight, and this increased to up to 24% just prior to the next spawning. The ovaries were maximally hydrated immediately after spawning. There were no significant changes in the calorific value of the ovaries, but the calorific value of the rest of the body was a minimum just after spawning. It was estimated that between spawnings females were making a net gain of energy at an average rate of 2 cal/hour. After spawning, courtship behaviour by the females waned, but recovered over the last half of the interval between spawnings. The inter-spawning interval of the Three-spined stickleback provides a useful situation in which physiological and nutritional aspects of reproduction in a teleost fish can be studied.     

Plasma levels of gonadotropin and 17α,20β-dihydroxy-4-pregnen-3-one in relation to spawning behaviour of rainbow trout, Oncorhynchus mykiss(Walbaum)

Manipulation of the opportunity to spawn was used to investigate the relationship between endocrine events, egg viability and spawning behaviour in female rainbow trout. Females were prevented from spawning by isolating them from males and gravel for up to 21 days after ovula- tion. Blood samples were taken before pairing with a male, at the onset of nesting activity, and at the completion of spawning. Plasma hormone levels of gonadotropin (GtH) and 17α,20β-dihydroxy-4-pregnen-3-one (17,2OP) were measured by specific radioimmunoassays. There were no qualitative or quantitative differences in the spawning behaviour of females paired on the day of ovulation or 7. 14, or 21 days after ovulation. There was a general decrease in the viability of eggs with increasing retention times. In females paired on the day of ovulation, or after 7 or 14 days, GtH levels increased with the onset of nesting behaviour and declined as fish reached the post-spawning condition. By day 21, GtH levels before pairing were significantly higher than prepairing levels in the other three treatment groups, and did not increase at the onset of nesting, or decrease in post-spawning fish. Plasma 17,20P remained high in prepairing and nesting samples of all four groups and declined to low levels in fish in post-spawning condition. In females paired on the day of ovulation there was a significant increase in 17,20P from the prepairing to the nesting stage. These results suggest that 17,20P plays a key role in the synchronization of behavioural and maturational events at the time of spawning.     

The induced spawning of roach, Rutilus rutilus (L.), with the antioestrogens clomiphene and tamoxifen

The induced spawning of gravid roach was investigated using the antioestrogens clomiphene and tamoxifen. Three dose levels ofeach were used: 0·1, l or 10 mgkg^-1, given twice with a 4-day interval to groups of eight fish with saline controls. Running males were randomly distributed. Tamoxifen, when injected at a rate of l mg kg^-1 was found to be most successful. This treatment induced ovulation in five of the six females, and profuse spawning on 3 consecutive days, 4 days after the first injection. Clomiphene induced ovulation and spawning in one of six females at 2 × 10 mg kg^-1, and two of eight females at 2 × l mg kg^-1, respectively 6 and 7 days after the first injection. The eggs produced showed normal devel-opment. No control fish ovulated or spawned. Both drugs probably act by indirect mechanisms, blocking sex steroid feedback inhibition of gonadotropin (GtH) secretion at the pituitary, thereby inducing a plasma GtH surge. The results of this experiment suggest that tamoxifen may be an effective substitute for pituitary preparations in the induced spawning of fish.     

Use of fish behavior in assessing the effects of Hurricane Iniki on the Hawaiian island of Kaua'i

Synopsis Declared the most compact and powerful storm known to have reached the Hawaiian Archipelago, Hurricane Iniki destroyed terrestrial and freshwater habitats island-wide when it struck Kaua'i late on the afternoon of Friday, 11 September 1992. Five weeks after the storm, a research group began underwater studies on the north shore of Kaua'i to assess the physical and biological effects of the hurricane and to track at four-month intervals the recovery of three high quality streams that are home to Hawaii's native and mostly endemic freshwater fishes, mollusks, and crustaceans. Early in the investigation, information on the social behavior of resident fishes showed particular promise for assessing the impact of the hurricane and for tracing the recovery of stream ecosystems. In Hanakapi'ai Stream, the stream damaged most by the hurricane and a subsequent flash flood, two downstream species,Eleotris sandwicensis andStenogobius hawaiiensis, were missing, and members of a third one,Sicyopterus stimpsoni, were sufficiently crowded into the lower section of the stream that aggressive behavior, occasionally resulting in injury, sharply curtailed feeding and prevented all but the earliest phases of courtship. Although the study began in the middle of the spawning season forAwaous guamensis, the few males found were in poor condition and showed neither territorial behavior in response to other males nor courtship when gravid females were encountered. Farther upstream, males ofLentipes concolor directed an inordinate amount of effort toward maintaining territories. Similar, but less dramatic alterations in distribution and behavior were seen in fishes from the less damaged Wainiha River. In Nu'alolo Stream, protected from hurricane winds by nearly vertical valley walls, the behavior was typical for fishes throughout its length except forE. sandwicensis in the damaged section at the stream mouth. Most progress in the return to social behaviors characteristic of pre-hurricane conditions for fishes in Hanakapi'ai Stream and Wainiha River occurred during the first four months of the study, but it was not until October 1993, more than a year after Iniki, that the behavior of the fishes signaled a return to conditions that existed before the storm. The study demonstrated that Hawaii's stream fishes are remarkably capable of rebounding from the effects of hurricanes because of the hardiness of adults and the recruitment of young animals from the ocean as a natural part of each species' amphidromous life cycle.     

Light synchronization of the daily spawning rhythms of gilthead sea bream (Sparus aurata L) kept under different photoperiod and after shifting the LD cycle

Reproduction in most fish is typically a seasonal process, as spawning takes place usually at a given time of the year, depending on the reproduction strategy of the species, to ensure maximal survival of offspring. Nevertheless, fish reproduction cannot be considered an exclusively annual phenomenon, because spawning may also show daily rhythmicity. In this study, we investigated the existence of a daily spawning rhythm in gilthead seabream (Sparus aurata L) exposed to different light-dark (LD) cycles and at different times of the year using an automatic and programmable egg collector. Floatability and fertilization rates were analyzed at different times throughout the 24 h. The results showed a daily spawning rhythm with spanning occurring from 14:30 to 21:30 h, with the acrophase (peak time) being 18:29 and 18:08 h in fish exposed to an artificial photoperiod of 9L:15D in winter and in spring, respectively. Nevertheless, in fish exposed to a natural photoperiod of 12L:12D in spring, the acrophase of the rhythm was recorded later, at 21:28 h. The average fertilization rate was 87%, and no significant differences were found between the different hours of spawning. Moreover, when the LD cycle (9L:15D) was shifted by 12 h, the daily spawning rhythm gradually re-synchronized, resuming a stable phase-relationship after 4-5 transient days, which is characteristic of a endogenous circadian rhythm. Our results clearly demonstrated the existence of a 24 h period of spawning in gilthead sea bream, with a peak anticipating the forthcoming night, and its capacity to gradually re-synchronize after a 12 h shift in the LD cycle, pointing to the endogenous nature of this rhythm. These findings will be valuable for better understanding the reproductive physiology of this species and for optimizing the protocols of egg collection and larvae production in aquaculture.     

Possible biogeochemical response to the passage of Hurricane Fabian observed by satellites

Physical and biogeochemical changes induced by the HurricaneFabian in the Northwest Atlantic in early September 2003 wereobserved using composite satellite images. After the passageof the hurricane, the mean sea surface temperature (SST) alongthe track decreased on average by about 1.3°C with maximumdecrease of 10°C. At the same time, the mean Chl a concentrationincreased by about 42%. Entrainment of cold, nutrient-rich watersby vertical mixing induced by the hurricane seems to have enhancedthe phytoplankton production. Asymmetric distribution of changesin SST and Chl a (strong intensity on the right side of thestorm track) was observed from the satellite data. The storm-inducednitrate increase estimated from the satellite SST, using a localrelationship between nitrate and temperature measurements wasabout 40% on average along the track of the storm. A numericalmodel study and climatological nutrient profile showed an increasein mixed-layer depth of 26 m and nitrate increase of about 0.2µmol L^–1 after the storm passage. In addition toaltering the physicochemical conditions of the water column,physical forcing by the hurricane also changed the taxonomiccomposition of phytoplankton. It is inferred that the dominanceof diatoms after the storm is a result of the increase in nutrientconcentration within the mixed layer due to the wind forcingof the storm.     

Spawning response of mature female sea bass,Lates calcarifer (Bloch), to a single injection of luteinizing hormone-releasing hormone analogue: effect of dose and initial oocyte size1

The effect of various doses of luteinizing hormone-releasing hormone analogue (LHRHa) ranging from 1 to 100 μg/kg body weight on the spawning response of mature female sea bass, Lates calcarifer (Bloch) was tested. A single intramuscular injection of LHRHa resulted in a dose-related increase in the spawning rate (number of spawnings of each fish over four consecutive days) of mature fish. An LHRHa dose of 5 μg/kg and less induced low spawning rates of 16.7% to 37.5% or at least one spawning every four days. However, mature sea bass spawned more than once (43.8–58.3%) in four days at dose levels of 10 μg/kg and above. Hormone treatment within the dose range tested did not influence the number, fertilization and hatching rates of spawned eggs. The influence of initial oocyte size on the LHRHa-induced spawning response of mature sea bass was also examined. Sea bass with an initial oocyte diameter of 0.30–0.39 mm did not respond to the single injection of 100 μg LHRHa/kg. In contrast, LHRHa induced spawning among sea bass with an initial egg size of 0.40–0.49 mm, although two of four sea bass of the same stage of ovarian maturity spawned spontaneously. Fish having an initial oocyte size of 0.50–0.55 mm spawned with and without LHRHa treatment. Spontaneous spawning among saline-injected sea bass occurred at a later time (24–58 h post-injection) compared to fish induced to spawn by a single injection of LHRHa (8–36 h post-injection). The initial spawning response time interval for fish with an initial egg size of 0.50 mm or greater was further reduced to 8–9 h by LHRHa. These results indicate that LHRHa can successfully induce spawning in mature female sea bass which have attained a critical oocyte diameter and that the spawning response interval is reduced with a further increase in egg size beyond the critical oocyte diameter limit.     

The soundscape of Arctic Charr spawning grounds in lotic and lentic environments: can passive acoustic monitoring be used to detect spawning activities?

The aims of this study were to (i) assess the efficacy of passive acoustic monitoring (PAM) for detecting Arctic Charr at their spawning grounds and (ii) characterize the overall acoustic soundscape of these sites. PAM was carried out over three Arctic Charr spawning grounds in the UK, one lotic and two lentic. 24-h cycles of recordings were collected prior to and during the Arctic Charr spawning season, which was determined from data returns by simultaneous net monitoring. Acoustic analysis consisted of manual quantification of sound sources, Acoustic Complexity Index (ACI) calculation and spectral analysis in 1/3 octave band (SPL; dB re 1 μPa). In the lotic spawning ground, prior to the beginning of Arctic Charr spawning, SPL and ACI showed a restricted range of variation throughout the 24-h, while during spawning the night values of SPL and ACI were found to significantly increase, concurrently with the rate of gravel noise induced by fish spawning activities and fish air passage sounds. Both prior to and during the Arctic Charr run, the lentic soundscape was characterized by diel variation due to the daytime presence of anthropogenic noise and the night-time presence of insect calls, while only a few occurrences of fish air passage sounds and gravel noise were recorded. These findings suggest that PAM over Arctic Charr spawning grounds could provide meaningful information to be used in developing management plans for this threatened species, such as determining the location and time of arrival, diel pattern and length of spawning activities.     

Impact of xynthia tempest on viral contamination of shellfish

Viral contamination in oyster and mussel samples was evaluated after a massive storm with hurricane wind named "Xynthia tempest" destroyed a number of sewage treatment plants in an area harboring many shellfish farms. Although up to 90% of samples were found to be contaminated 2 days after the disaster, detected viral concentrations were low. A 1-month follow-up showed a rapid decrease in the number of positive samples, even for norovirus.     

Multispecies spawning sites for fishes on a low‐latitude coral reef: spatial and temporal patterns

Spawning sites used by one or more species were located by intensively searching nearshore coral reefs of Kimbe Bay (New Britain, Papua New Guinea). Once identified, the spawning sites were surveyed repeatedly within fixed 5 m radius circular areas, for > 2000 h of observations ranging from before dawn to after dusk spanning 190 days between July 2001 and May 2004. A total of 38 spawning sites were identified on the seven study reefs distributed at an average of one site every 60 m of reef edge. Pelagic spawning was observed in 41 fish species from six families. On three intensively studied reefs, all 17 spawning sites identified were used by at least three species, with a maximum of 30 different species observed spawning at a single site. Spawning was observed during every month of the study, on all days of the lunar month, at all states of the tide and at most hours of the day studied. Nevertheless, the majority of species were observed spawning on proportionately more days from December to April, on more days around the new moon and in association with higher tides. The strongest temporal association, however, was with species‐specific diel spawning times spanning < 3 h for most species. While dawn spawning, afternoon spawning and dusk spawning species were differentiated, the time of spawning for the striated surgeonfish Ctenochaetus striatus also differed significantly among sites. The large number of species spawning at the same restricted locations during predictable times suggests that these sites are extremely important on this low‐latitude coral reef.     

Effects of overripening on spawning behaviour and reproductive success of Atlantic salmon females spawning in a controlled flow channel

The influence of overripening on salmonid egg quality has often been described in artificial breeding. However, no information exists on the impact of this factor on fish reproducing naturally, although it is likely to be critical, especially in disturbed environments. Pairs of Atlantic salmon in which the size of the male and the female was evenly matched were released in a spawning channel from 1 to 12 days after ovulation. Handling did not affect egg quality. Overripening had a negative effect on egg viability. Egg mortality, infertility and malformations increased with the number of days after ovulation. In females which had just matured, 16·7% of their recovered eggs were dead, 3·1% were unfertilized and 1·7% were malformed, as compared to 25·4, 9·7 and 5·4%, respectively, in females that had been mature for at least a week. Overripening played a role in both female spawning behaviour and capacity to spawn, as females which had been mature for over a week released their eggs more quickly while they retained more ova in their abdominal cavity than early spawning females. Thus, in studies of reproductive behaviour and in particular of sexual selection, it is critical to take into account the maturation status of females since the duration of spawning activity is used by various authors to determine female sexual motivation. Alternatively, overripening may decrease the female selectivity for mates.     

Bioactivity of stored luteinizing hormone-releasing hormone analogue (LHRHa) in sea bass, Lates calcarifer Bloch

The spawning induction activity of dissolved and pelleted (D-Ala⁶, Pro⁹ N ethylamide) luteinizing hormone-releasing hormone analogue (LHRHa) stored for various periods was assessed in mature female sea bass. The spawning response of mature fish was reduced significantly after injection of dissolved LHRHa (20 μg kg⁻¹) stored for more than 90 days in a refrigerator (4–10°C) or for more than 30 days at room temperature (28–30°C). Similar to fish administered fresh preparations of LHRHa, fish spawned successfully after injection of a solution of LHRHa previously frozen, subjected to alternate freezing and thawing, exposed to sunlight or implanted pelleted LHRHa (50 ng kg⁻¹) stored at room temperature for 30–120 days. Loss of hormone bioactivity after prolonged storage may have been due to bacterial growth in solubilized preparations. Injection or implantation of stored LHRHa did not influence egg production among treated sea bass. These results demonstrated the relatively prolonged shelf life of stored LHRHa.     

Spatio-temporal variation in the elemental compositions of otoliths of southern bluefin tuna Thunnus maccoyii in the Indian Ocean and its ecological implication

The elements Na, Mg, Mn, Ca, Sr and Ba in otoliths of southern bluefin tuna Thunnus maccoyii , collected from their feeding ground in the central Indian Ocean and spawning ground between southern Java and north-western Australia were measured by laser-ablation inductively coupled plasma mass spectrometry (LA-ICPMS) and compared among sampling locations and developmental stages. The Na, Mg and Mn to Ca concentration ratios were significantly higher at the larval stage than at the adult stage, and the ratio reached a peak at the first inflection point of the otolith, mean ± s.d. 43·3 ± 4·9 days after hatching and decreased sharply to a low level thereafter. The temporal change of the elements:Ca ratios in the first inflection point corresponded to the life stage transition from larva to juvenile, indicating that the uptake rate of elements from ambient waters was significantly influenced by the ontogenetic change in the fish. The elemental composition at the otolith edge differed significantly in sub-adults on the feeding grounds and adults on the spawning grounds. Thus, the otolith elemental composition can be used as a biological tracer to study the time of the ontogenetic shift and to reconstruct the past migratory environmental history of T. maccoyii . In addition, the elemental composition of the otolith core of the adult was similar between feeding and spawning grounds, indicating that the fish in the Indian Ocean had the same larval origin, which is consistent with the single spawning population hypothesis.     

Light Synchronization of the Daily Spawning Rhythms of Gilthead Sea bream (Sparus aurata L) Kept under Different Photoperiod and after Shifting the LD Cycle

Reproduction in most fish is typically a seasonal process, as spawning takes place usually at a given time of the year, depending on the reproduction strategy of the species, to ensure maximal survival of offspring. Nevertheless, fish reproduction cannot be considered an exclusively annual phenomenon, because spawning may also show daily rhythmicity. In this study, we investigated the existence of a daily spawning rhythm in gilthead seabream (Sparus aurata L) exposed to different light‐dark (LD) cycles and at different times of the year using an automatic and programmable egg collector. Floatability and fertilization rates were analyzed at different times throughout the 24 h. The results showed a daily spawning rhythm with spanning occurring from 14:30 to 21:30 h, with the acrophase (peak time) being 18:29 and 18:08 h in fish exposed to an artificial photoperiod of 9L∶15D in winter and in spring, respectively. Nevertheless, in fish exposed to a natural photoperiod of 12L∶12D in spring, the acrophase of the rhythm was recorded later, at 21:28 h. The average fertilization rate was 87%, and no significant differences were found between the different hours of spawning. Moreover, when the LD cycle (9L∶15D) was shifted by 12 h, the daily spawning rhythm gradually re‐synchronized, resuming a stable phase‐relationship after 4–5 transient days, which is characteristic of a endogenous circadian rhythm. Our results clearly demonstrated the existence of a 24 h period of spawning in gilthead sea bream, with a peak anticipating the forthcoming night, and its capacity to gradually re‐synchronize after a 12 h shift in the LD cycle, pointing to the endogenous nature of this rhythm. These findings will be valuable for better understanding the reproductive physiology of this species and for optimizing the protocols of egg collection and larvae production in aquaculture. (Author correspondence: javisan@um.es)     

Size-selective overwintering mortality in the sand smelt, Atherina boyeri Risso, and its role in population regulation

The fat laid down as a winter reserve by O-group sand smelt, Atherina boyeri , was found to be size-dependent. The larger, earlier-spawned fish lay down more fat prior to the onset of winter. During the winter the fish do not feed for some 100 days and rely on this fat for energy; laterspawned O-group fish (<59 mm s.l. in November) have insufficient fat reserves and starve to death in a normal winter. This loss of the smallest 46% of the O-group is shown as an increase in the mean size of the O-group over the winter period. Older sand smelt age classes have more than sufficient fat reserves for overwintering. There is thus a clear advantage in spawning early in the season, and any restriction on spawning ground availability at that time will result in overall population regulation. This conclusion supports the hypothesis that the density-dependent control on population size in the sand smelt is a limitation on the number of fish which can spawn at the optimum time.     

The secondary immune response of young carp, Cyprinus carpio L., following injection of cortisol

Cyprinus carpio immunized at 9 weeks after hatching with either human gamma globulin or trinitrophenylated sheep red blood cells either fail to respond or respond poorly on secondary exposure at 17 weeks of age. Injection of cortisol either simultaneously with the antigen, or 3 days prior to, or 3 days after antigen, permits the antibody response to proceed upon subsequent challenge. The implication of these results for the ontogeny of the fish immune response is discussed.     

The Barrier Reef sediment apron: Tobacco Reef,Belize

Sedimentological and biological surveys of the back-reef sediment apron of Tobacco Reef, a continuous segment of the Belizean Barrier Reef, reveal five distinct biogeological zones: (1) coralline-coral-Dictyota pavement, (2) Turbinaria-Sargassum rubble, (3) Laurencia-Acanthophora sand and gravel, (4) bare sand and 95 Thalassia sand. These zones parallel the entire 9-km reef. The distribution of these zones is related to the spatial patterns of fish herbivory, the size of bottom sediments, and the stability of the substrate. Sedimentological and hydrodynamic studies indicate that most of the sediments in this area are transported from the reef crest and fore reef during periods of storm or hurricane activity and that their size distribution is largely the result of differential transport by high bottom-water velocities during those periods.     

An accurate tool for ageing Two‐spined Blackfish for use in determining timing of spawning in upland streams in the Brindabella ranges,ACT, Australia

To manage populations of threatened fish species in modified habitats and regulated rivers requires an understanding of their reproductive biology and spawning cues. In particular, accurate information about early life stages in these species can be used to facilitate programmes that maximise recruitment and breeding success. This study aimed to develop methods to accurately age early juvenile freshwater native fish, Two‐spined Blackfish, (Gadopsis bispinosus), to allow the determination of spawning date. This was accomplished through the examination of otolith microstructure in early juveniles. The age at which the first ring was deposited and the relationship between days and number of rings were determined using both field and aquarium trials. Field trials of marked juvenile otoliths revealed daily deposition of rings (1.02 ± 0.02 rings per day for fish sacrificed six days postmarking). The strength of this relationship lessened slightly as juveniles aged (0.92 ± 0.02 rings per day for fish sacrificed 13 days postmarking). The first otolith ring was deposited 7.50 ± 1.09 days after spawning. The enumeration of daily rings combined with knowledge of the commencement of ring deposition enabled accurate estimation of spawning date. The current study is the first to examine otolith microstructure in juvenile Two‐spined Blackfish allowing accurate determination of spawning date. While more research is required to accurately age older juveniles, this technique has the potential to precisely correlate spawning with environmental cues, facilitating better management of temperature and flow during breeding periods, potentially increasing spawning and recruitment of this endangered species.