Repeat Spawners Research Articles

Impact of catch-and-release practices on behavior and mortality of Atlantic salmon ( Salmo salar L.) kelts

Kelts of Atlantic salmon (spent Salmo salar L .) are often caught and released (C&R) by anglers before and during their seaward migration in the river, but the extent of captures and the biological and management implications have not been previously evaluated. In this study, we investigate the impact of C&R on behavior and mortality of kelts by using telemetry. In total 73 Atlantic salmon kelts were tagged with acoustic tags after angling in spring 2008 in the sub-arctic River Alta, Norway. They were tracked manually in the river and recorded during their initial marine migration on arrays of acoustic receivers deployed across the Alta Fjord up to 30 km from the river mouth. To increase the sample size – in order to reliably quantify capture rates of kelts during the recreational angling season – telemetry was combined with mark-recapture. Recapture rates, behavior and survival of the angled and tagged kelts were compared to a control group of salmon ( n = 17) tagged acoustically 7–10 months earlier, and therefore considered unaffected by recent angling and tagging. The recapture rate of the control group kelts (18%) did not differ from the recapture rate of the kelts tagged in spring (14%), and only a small proportion of the tagged kelts (2%) was recaptured more than once the same season. In total, 4% of the kelts died after C&R in the river and 92% migrated out the fjord on average 1 month after catch, tagging and release. The C&R fish descended the river slower than the uncaught control group, but no difference in the start of their marine migration, migration progression or survival was observed between the compared groups. We conclude that (1) C&R affected the post release behavior of kelts only by delaying the river descent, and (2) the delayed post release mortality rate of C&R kelts was not elevated despite the reduced energy levels and physiological condition of kelts. Hence, releasing angled kelts can be a viable management strategy to enhance the return rate of repeat spawners.

Distribution and biological characteristics of escaped farmed salmon in a major subarctic wild salmon river: implications for monitoring

We report the occurrence, distribution, and biological characteristics of escaped farmed salmon in the River Teno in northernmost Europe, which supports one of the largest and most versatile wild Atlantic salmon ( Salmo salar ) populations in the world. Farmed salmon were caught during the fishing season (May–August) when their proportion in the catch varied between 0.0% and 0.7%. Occasional sampling after the fishing season revealed much higher proportions of escapees, up to 47%, indicating a potential for a more severe impact of farmed fish than the in-season monitoring is able to uncover. Peak migration of the wild salmon was in June or July, but that of escaped farmed fish was in August. Up to 88% of the escaped salmon caught in August showed gonad development, and scale analysis indicated that 4.5% of them were repeat spawners. Genetic analyses using microsatellite markers revealed highly significant genetic differentiation between wild salmon and escaped farmed fish (FST = 0.05) caught in the River Teno and a Norwegian farmed strain (FST = 0.10). The heterogeneity of escapees compared with the single farmed strain indicated that escapees apparently originate from multiple sources, which will complicate their genetic identification and the assessment of the level of hybridization with wild salmon.

The role of the maturation‐inducing steroid, 17,20β‐dihydroxypregn‐4‐en‐3‐one, in male fishes: a review

The major progestin in teleosts is not progesterone, as in tetrapods, but 17,20beta-dihydroxypregn-4-en-3-one (17,20beta-P) or, in certain species, 17,20beta,21-trihydroxy-pregn-4-en-3-one (17,20beta,21-P). Several functions for 17,20beta-P and 17,20beta,21-P have been proposed (and in some cases proved). These include induction of oocyte final maturation and spermiation (milt production), enhancement of sperm motility (by alteration of the pH and fluidity of the seminal fluid) and acting as a pheromone in male cyprinids. Another important function, initiation of meiosis (the first step in both spermatogenesis and oogenesis), has only very recently been proposed. This is a process that takes place at puberty in all fishes and once a year in repeat spawners. The present review critically examines the evidence to support the proposed functions of 17,20beta-P in males, including listing of the evidence for the presence of 17,20beta-P in the blood plasma of male fishes and discussion of why, in many species, it appears to be absent (or present at low and, in some cases, unvarying concentrations); consideration of the evidence, obtained mainly from in vitro studies, for this steroid being predominantly produced by the testis, for its production being under the control of luteinizing hormone (gonadotrophin II) and, at least in salmonids, for two cell types (Leydig cells and sperm cells) being involved in its synthesis; discussion of the factors involved in the regulation of the switch from androgen to 17,20beta-P production that seems to occur in many species just at the time of spermiation; discussion of the effects of in vivo injection and application of 17,20beta-P (and closely related compounds) in males; a listing of previously published evidence that supports the proposed new function of 17,20beta-P as an initiator of meiosis; finally, discussion of the evidence for environmental endocrine disruption by progestins in fishes.

Sex-specific patterns of lifetime reproductive success in single and repeat breeding steelhead trout (Oncorhynchus mykiss)

All other things being equal, the lifetime reproductive success (LRS) of iteroparous and semelparous individuals should scale with the number of breeding seasons. Deviations from this relationship may occur for many reasons, including age- or size-related fecundity or life history trade-offs, which may differ between sexes. We used 19 brood years of DNA parentage analysis in a small (N = 4–143 year−1) wild, unexploited population of steelhead trout (Oncorhynchus mykiss) to compare the LRS of individuals that spawned only once [“one time spawners” (OTS), N = 355 male, 371 female] to those spawning twice [“repeat spawners” (RPS), N = 13 male, 49 female]. Female RPS had nearly twice the LRS of female OTS (1.17 offspring per female vs 0.91 offspring per female), whereas male RPS had nearly three times the LRS of male OTS (1.54 offspring per male vs 0.57 offspring per male). Female RPS produced slightly more adult offspring during their second breeding season than their first (0.78 vs 0.82 offspring per female); however, male RPS produced all of their adult offspring in their second breeding season (0 vs 1.54 offspring per male). The additional growth in body size of males between breeding seasons may give them an advantage in their second breeding season, but the lack of offspring produced in their first season suggests a trade-off between survival and future reproduction that was not expressed in females.

Spawning time variation in Icelandic summer-spawning herring (Clupea harengus)

Different fish stocks of the same species are defined by spatial and temporal differences in spawning, though spawning time can vary within and among stocks. Here we address spawning time variation in Icelandic summer-spawning (ISS) Atlantic herring ( Clupea harengus ). We do so by examining influencing factors that include variation in stock size structure, spawning experience (recruit vs. repeat spawners), spawning stock biomass (SSB), sea temperature, and combinations thereof. Our results, based on temporal variation in ovary weight (OW), relative ovary weight (RG), and maturation stage, across a time series of nearly 50 years and eight length classes of ISS herring, show that spawning occurs over a relatively invariant 30-day period defined by day-of-the-year. Logistic regression analyses and temporal development in OW and RG show that maximum spawning invariably occurs on day-of-the-year 200 ± 15 days, and seasonal variation in mesenteric fat content is physiologically consistent with the timing. We show that the smaller recruit spawners tend to spawn ~17 days later, on average, than the larger repeat spawners. Spawning occurs ~7 days later when SSB is greater than the long-term average, and spawning may be delayed by as much as 10 days during periods of colder than average ocean temperature.

Effects of female spawning experience and larval size on feeding and growth of cod larvae Gadus morhua L. reared in mesocosms

The viability, defined in terms of growth and feeding success, of cod larvae from first-time and repeat spawners of similar sizes was studied in two mesocosms. The growth rate of larvae from first-time and repeat spawners were similar from hatching through to 41 days old, when the experiment was terminated. Larvae from first-time spawners were heavier throughout the experiment than larvae of repeat spawners, a difference that might be explained by a difference (although non-significant) in egg size between the two groups. There was a significant difference in growth rate between the two mesocosms, which may be explained by the difference in temperature between the mesocosms. In both mesocosms larvae fed mainly on copepod nauplii during the first weeks of life and started to actively select copepodites at age 20 days post hatch. There was no significant difference in the energy content of the ingested prey at a given age between offspring of first-time and repeat spawners, although there was a significant difference between the two mesocosms. The dry mass of the ingested prey items compared to larval dry mass increased until age 17–27 days post hatch and decreased thereafter.

Length-structured analysis of the reproductive season of anchovy and common sardine off central southern Chile

The anchovy (Engraulis ringens) and common sardine (Strangomera bentincki) are two small pelagic fish which have a similar reproductive strategy off central southern Chile. The seasonal reproductive dynamics of both the species was investigated by taking into account the gonadosomatic index (GSI) and visual maturity data as a function of female size for the period 1993–1999, and also the seasonal pattern in condition factor per size classes. Larger females of common sardine (repeat spawners) have a reproductive peak earlier in the season than younger females at first maturity, while larger anchovy have a reproductive peak delayed as compared with first-time spawners. The condition factor of females exhibited an inverse cycle with the seasonal pattern of GSI, and delayed by approximately 6 months. Although larger females tend to present better and wider condition than smaller females, the condition of females seems to be delayed in larger females probably mediated by the seasonal pattern in food availability. This “energy storage strategy” in spring and summer time seems to be size-dependent and past energetic reserves could also affect the egg production and timing of reproduction. We concluded that the reproductive season of anchovy and common sardine is different and mediated by the length structure in the seasonal upwelling system off central southern Chile.

Use of Parentage Assignment and DNA Genotyping to Validate Scale Analysis for Estimating Steelhead Age and Spawning History

AbstractSound fisheries management depends on understanding life history characteristics, such as age at maturity, migration, and spawning history; hard parts, such as scales and otoliths, are commonly used to estimate values for these traits. Validation of these techniques is often difficult but critical because errors in mean values for a population can result in erroneous estimates of sustainable exploitation rates. In this study, we compared information on age and spawning history derived from genetic analysis with information from scale analysis for 1,836 individual steelhead Oncorhynchus mykiss representing two life history stages (smolt and mature adult); these fish were of hatchery and wild origin and were sampled from two rivers in Washington State over a period of 19 years. Aging error rates were less than 5% for both wild smolts and hatchery adults, but the error rate for wild adults was much higher (13%; 95% confidence interval [CI] = 1.82–29.22%). Adult scale ages were biased; scale readers typically overestimated the ages of younger fish and underestimated the ages of older fish. In addition to the errors in age estimation, repeat spawners were misclassified as virgin spawners 6.5% of the time (95% CI = 0.79–20.26%). The higher error rates obtained in using scales for aging and identifying repeat spawning in wild adults may partly stem from the more complex life history relative to that of smolts or hatchery‐origin adults; these results highlight the need for verification of scale analysis, especially for wild steelhead populations.

Impending collapse of bluefin tuna in the northeast Atlantic and Mediterranean

AbstractThe abundance of bluefin tuna, Thunnus thynnus, in the east Atlantic and Mediterranean has declined in recent decades. The International Commission for the Conservation of Atlantic Tunas (ICCAT), the regional bluefin tuna management authority, has developed a plan to promote recovery by 2022, while still permitting fishing to continue during the period 2008–2010. Here we predict that the adult population in 2011 will likely be 75% lower relative to 2005 and that quotas in some intervening years will allow the fishery to capture legally all of the adult fish. Population demographics (proportion of older fish and repeat spawners in population) indicate that buffering capacity against years of poor reproduction has been reduced. This population is at risk of collapse (90% decline in adult biomass within three generations, the criterion used by the IUCN for defining populations as Critically Endangered), even under the currently agreed recovery plan, unless new conservation measures are implemented in the next few years.

Temporal Shifts in Demography and Life History of an Anadromous Alewife Population in Connecticut

AbstractPopulations of anadromous alewives Alosa pseudoharengus are declining throughout much of the species' range, particularly in southern New England, where fishery moratoriums have recently been instituted in three states. The alewife run at Bride Brook, a coastal stream in East Lyme, Connecticut, was studied from 2003 to 2006 to assess shifts in demography and life history. Annual censuses of abundance and sampling for size, age, and spawning history structure were conducted. These data were compared with similar data from 1966 to 1967 at this site. Recent alewife runs at Bride Brook featured lower abundance and younger, smaller fish that were less likely to be repeat spawners. The 1966 spawning run was dominated by repeat spawners of ages 5–7, while runs in 2003–2006 were dominated by age‐3 and age‐4 first‐spawn fish. Mean length declined by 10% between 1966 and 2006. Alewives are also recruiting to the spawning run at younger ages and smaller sizes, indicating a shift in life history. The first‐spawn portion of the 1966 spawning run was dominated by age‐5 fish, while recent first‐time spawners were primarily age 3. The shifts in demography and life history observed at Bride Brook are consistent with exploitation or predation concentrated on older, larger individuals in the population. The results of this study suggest recent increases in predatory pressure or bycatch mortality as promising hypotheses that merit further investigation.

Estimating the Ratio of Hatchery‐Produced to Wild Adult Steelhead on the Spawning Grounds using Scale Pattern Analyses

AbstractHatcheries produce Pacific salmon and trout Oncorhynchus spp. for many purposes, including fishery enhancement. The genetic integrity of wild populations spawning near such hatcheries may depend on the efficacy of their spatial or temporal separation from hatchery fish. We describe a simple, novel approach based on the examination of scales from an iteroparous species, steelhead O. mykiss, to evaluate whether the ratio of hatchery‐produced adults to wild adults on the spawning grounds met recommended levels. In this river, migrating steelhead are diverted into the hatchery by a weir. Hatchery‐produced fish are manually spawned and killed in the hatchery, whereas wild fish are passed over the weir and allowed to spawn naturally upstream from the hatchery. Therefore, in principle, all hatchery‐produced adults should be captured at the hatchery on their first spawning migration. However, scales from 8.3% (58 of 699) of female and 2.6% (22 of 844) of male hatchery‐produced steelhead adults showed evidence of previous spawning migrations. Although this frequency was lower than the incidence of repeat spawning by wild fish (males, 11.0%; females, 20.3%), these records nevertheless indicated significant reproductive opportunities in the wild for hatchery‐produced fish. Combining these frequencies of repeat spawning with estimates of the survival and numbers of wild fish, we modeled the ratio of hatchery to wild fish on the spawning grounds using data from eight return years. This ratio exceeded the recommended levels under all reasonable scenarios modeled (14.7‐89.6% hatchery fish). Combined with evidence of spatial and temporal overlap, our data suggest that unless changes are made to increase the capture efficiency of adults at Washington State's Forks Creek Hatchery and similar hatcheries relying on segregated stocks, the risks of genetic introgression and ecological interactions with wild steelhead populations will remain high.

Transportation of Steelhead Kelts to Increase Iteroparity in the Columbia and Snake Rivers

AbstractWe tested the feasibility of transporting steelhead Oncorhynchus mykiss kelts (postspawned adults) around hydroelectric dams on the Snake and Columbia rivers to increase the returns of repeat spawners. Altogether, 5,878 kelts were collected, tagged with passive integrated transponder tags, and assigned to transported or in‐river treatment groups at Lower Granite Dam (n = 5,320 [2002–2004]) on the Snake River and John Day Dam (n = 558 [2002]) on the Columbia River. Returns of repeat spawners differed by site and year: 11.1% (62/558) for the John Day Dam sample and 1.4% (27/1,959), 0.5% (6/1,241), and 0.8% (17/2,120) for the Lower Granite Dam samples in 2002, 2003, and 2004, respectively. Transportation tests indicated that kelts transported from the Snake River were approximately 2.3 times more likely to return than fish allowed to migrate in‐river. Transport benefits were greatest for wild‐origin female kelts, a demographic with high conservation value. There was no significant benefit for kelts transported from John Day Dam, although transported fish returned at a slighter higher rate (1.1 times). Comparisons between treatment groups (in‐river versus transport) and locations (Snake River versus Columbia River) indicated that the greatest potential transport benefit may be for Snake River kelts owing to the population's low overall iteroparity rate and numerous potential kelt collection sites. The small sample sizes of returning fish limited our ability to examine more complex trends and environmental effects on return rates. Additional research is needed to fully evaluate the efficacy of kelt transportation in the context of regional steelhead recovery efforts.

Pronounced long-term juvenation in the spawning stock of Arcto-Norwegian cod (Gadus morhua) and possible consequences for recruitment

The oldest and largest individuals are disappearing from many fish stocks worldwide as a result of overexploitation. This has been suggested to impair recruitment through decreasing the reproductive capacity of the spawners and increasing the mortality rate of the offspring. By using a time series on spawners biomass by age class for Arcto-Norwegian cod (Gadus morhua) from 1913–2004, I have documented pronounced changes in the spawning stock, including a trend towards younger fish, a less diverse distribution across ages, and a declining proportion of repeat spawners. Despite the total spawning stock biomass (SSB) being at similar levels now as in 1933, the mean age in the SSB has declined from 10–12.5 years to 7–8 years during the study period, and the percentage of fish of age 10 or above in the SSB has decreased from ~97% to ~10%. Contrary to earlier theoretical and experimental studies, no clear link between age structure and recruitment was found here. Recruitment to the Arcto-Norwegian cod stock may thus be more robust towards spawner juvenation than expected, possibly because of strong recruitment compensation.

The impact of repeat spawning of males on effective number of breeders in hatchery operations

In conservation hatcheries, typically a great emphasis is placed on maximizing the effective number of breeders through spawning an appropriate number of spawners, spawning equal numbers of males and females when possible, and by mating either in a single-pair or factorial fashion. A commonly encountered problem, especially in small operations with anadromous salmonids, is a shortage of males at some point during the season, so that some males need to be spawned multiple times. This has an impact on the genetically effective number of breeders, and the commonly used equations for effective number are not applicable. In this paper I derive a relatively simple equation for effective number of breeders when some males are multiply spawned but reproductive contribution within spawning classes are equal: N b , m ≈ N tot − 1 / μ t ∑ i = 1 k − 1 ∑ j = i + 1 k N i N j ( i − j ) 2 ( ∑ i = 1 k i N i ) 2 + 1 , where i is the number of times a male is spawned, N i the number of males spawned i times, and μ t the mean gametic contribution. I also derive an equation that allows relaxation of the assumption of equal contribution within classes. I then develop a number of simple and accurate approximations for the effective number of breeders. The equations can be applied to any situation in which there are discrete spawning classes in which the average reproductive contribution of any one class can be expressed as a multiple of that of another class.

Temporal variation in abundance, return rate and life histories of previously spawned Atlantic salmon in a large subarctic river

The 30 year time series analyses revealed large temporal variation in the return rates and a recent increase in abundance of previous spawning Atlantic salmon Salmo salar in the River Teno, northern Scandinavia. The mean proportion of repeat spawners was 7 and 4% in the total Atlantic salmon catch and 9 and 22% in multi‐sea‐winter (MSW) catch component for females and males, respectively. Previous spawners constituted on the average 7% of the catch in mass but up to 20%(31 t) and 30%(19 t) in 2003 and in 2004, respectively. In 1975–2000, the proportion of previous spawners varied between 1 and 6%(3–12% of MSW Atlantic salmon), whereas in 2001–2004, they accounted for 8–21%(16–35% of MSW Atlantic salmon) of the total Atlantic salmon catch. The number of previous spawners in the catch correlated significantly with the preceding numbers of respective 1–3 sea‐winter (SW) maiden Atlantic salmon 2 years earlier. The recent increase in the numbers of 1S1 and 2S1 (1 or 2 years at sea followed by first spawning and 1 year reconditioning period at sea) alternate spawning Atlantic salmon was a consequence of higher numbers of maiden 1SW and 2SW Atlantic salmon in the catches and increased sea temperatures. Similarly, the return rate of 1SW Atlantic salmon to second spawning has improved in recent years. Most previous spawners ascended and were captured early in the fishing season. The smolt and sea‐age combinations of repeat spawners comprised 68 age groups contributing with the annual mean of 15 age groups to the great diversity of the River Teno Atlantic salmon population complex.

Spawning Demographics and Juvenile Dispersal of an Adfluvial Bull Trout Population in Trestle Creek, Idaho

AbstractWe utilized a screw trap, trap‐box weir, remote passive integrated transponder tag (PIT) detection weir, and otolith microchemistry to evaluate (2000–2004) spawning demographics and migration patterns of adfluvial bull trout Salvelinus confluentus in Trestle Creek, Idaho, a tributary to Lake Pend Oreille. Annual repeat spawning was more common than alternate‐year spawning. Annual growth, estimated from adult bull trout PIT‐tagged in 2000 and recaptured in 2001, averaged 28 mm. Peak diel movement of adult bull trout occurred after sunset. Emigration of juveniles occurred in two pulses, one in spring that was associated with snowmelt runoff and increasing water temperatures and a second in fall as stream temperatures dropped and fall rains began. Juvenile bull trout moved a mean rate of 455 m per night in 2001 and 423 m per night in 2002. Each year we trapped large numbers of age‐0 bull trout that appeared to be emigrating with high spring flows. Based on otolith microchemistry, most of the 47 adults in the sample had emigrated at age 3 or age 4, and none had emigrated at age 0. This suggests that age‐0 emigrants are not making a significant contribution to adult returns.

Ovary development in Greenland halibut Reinhardtius hippoglossoides in west Greenland waters

Maturity in adult female Greenland halibut Reinhardtius hippoglossoides was studied in three areas in west Greenland waters: the inshore area in Disko Bay and two offshore areas, Baffin Bay and Davis Strait. The aim was to monitor maturity changes in the inshore fjords of Disko Bay over an extended period from winter to autumn and compare these findings with specimens from Baffin Bay and the presumed spawning area in Davis Strait. A significant difference in maturity level was observed in and between the three areas. In Disko Bay maturity indices increased significantly in August and September both with respect to the gonado‐somatic index (IG) and the size in the leading oocyte cohort. In the period February to May no significant changes were observed. Mature ovaries were only observed among fish >80 cm total length and only among a fraction of these large fish. Offshore areas of Baffin Bay, even though poorly sampled, showed similar signs in the maturity indices as in Disko Bay. Relative to Disko Bay and Baffin Bay, female fish in Davis Strait had more progressed maturity indices. Furthermore, almost all fish in Davis Strait showed signs of progressed maturity contrary to Disko and Baffin Bay. A large proportion of the Greenland halibut in Disko and Baffin Bay apparently did not begin the maturation cycle until very late in their life history or were repeat spawners with a multi‐year maturation cycle. These observations could thus support the hypothesis that Greenland halibut have a prolonged adolescent phase. Atresia was highest in the early phases of maturation in Greenland halibut but relatively high levels of atresia were also observed in fish in more advanced maturity phase. The first was ascribed to fecundity regulation while the latter could be linked to the fish's fitness condition but it was not possible to show this with the available condition index.

Effect of fishing regulation on the occurrence of repeat spawners and age distribution of Atlantic salmon in a northern Baltic river

Abstract Upstream migrating Atlantic salmon, Salmo salar L., were trapped annually between 1990 and 2003 at the mouth of the River Simojoki in the northern part of the Gulf of Bothnia, the Baltic Sea, to collect hatchery brood fish. They were also collected between 1996 and 1998 in the river to estimate the number of ascending salmon. These data on spawners were used to study the effect of changing fishing regulations in the Finnish coastal fishery in the mid‐1990s on the structure of the spawning stock. In total, 1.9% of 2290 multi‐sea‐winter adults had previously spawned. The average annual proportion of repeat spawners was 0.5% between 1990 and 1996, but significantly higher (2.8%) between 1997 and 2003. The age distribution also changed significantly, as 4SW and 5SW salmon appeared in the population in the latter years. These changes were most probably due to the application of stricter fishing regulations. The potential of salmon to spawn repeatedly was thus preserved, despite a severe decline in natural production in the 1980s and early 1990s.

Induced spawning, larval development and rearing of two indigenous Malaysian mahseer, Tor tambroides and T. douronensis

The Mahseers (Tor spp.) are highly valued freshwater ¢shes across the Himalayan and South-east Asian regions. Over exploitation of natural stocks because of high demand and the deteriorating environmental conditions have resulted in marked decline of mahseers in the wild. Malaysian mahseers, T. tambroides (Bleeker) and T. douronensis (Valenciennes), locally known as empurau, kelah or belian and semah, respectively, have signi¢cant cultural and economic importance but both species are now threatened in the wild because of environmental degradation and over ¢shing. A captive breeding programme was instigated to attempt to propagate these two species arti¢cially for conservation and aquaculture purposes. Both pond-reared and tank-held T. tambroides and T. douronensis reached sexual maturity in captivity and were successfully induced to spawn using hormone treatments. Ovaprim (0.5 mL kg � 1 ) was the most successful hormone treatment for both species. Pretreatment of ¢sh with Ovaplant (28^68m gk g � 1 ,2 ^7 weeks before spawning induction) greatly improved the success rate of spawning induction. Repeat spawning (within 4 months of initial spawning) was induced in some captive ¢sh. Use of formalin baths improved hatching by preventing fungal infections. Embryonic development and hatching are described. Juveniles were reared in static greenwater ponds. Tor tambroides reached 142^179 g (max 270 g) in 60 weeks. These results represent the ¢rst successful captive spawning and rearing of both species. Options for future research to improve production are discussed.

The effect of temperature and conditioning interval on the spawning success of wild-caught blacklip (Haliotis rubra, Leach 1814) and greenlip (H. laevigata, Donovan 1808) abalone

Wild-caught blacklip (Haliotis rubra, Leach 1814) and greenlip (H. laevigata, Donovan 1808) abalone fed a formulated feed were held at 16 or 18°C for different conditioning intervals ranging from 114 to 235 days and induced to spawn using ultraviolet-irradiated seawater. They were conditioned again for a second identical period before another induction. For H. rubra, mean spawning rate of both sexes was higher in groups held at 18°C than at 16°C, as was the repeat spawning rate. Conversely, animals held at 16°C produced significantly more gametes than those at 18°C. Egg production peaked in groups held at 16°C for ≥ 165 days. While both mean and total sperm production of H. rubra varied significantly, both figures were always high. Unlike H. rubra, the spawning rate, repeat spawning rate and gamete production of both sexes of H. laevigata were higher when cultured at 16°C than at 18°C. Egg production peaked in groups conditioned at 16°C for ≥ 212 days. Both mean and total sperm production by H. laevigata were much lower than for H. rubra. This study demonstrates that year-round hatchery production of seedstock of both species is possible providing broodstock are held under favourable environmental conditions, preferably 16°C. © 2005 Blackwell Publishing Ltd.