Measuring reproductive condition in the Greenshell™ mussel Perna canaliculus

The annual reproductive cycle of Perna canaliculus (Gmelin) was investigated for 1 year by collecting monthly gonad samples from an intertidal population. Gonads of 50 animals were dissected and photographically recorded on video before being fixed for histological sectioning. The histological gonad sections were examined both qualitatively, using a classification and scoring system (S) and quantitatively, using image analysis technology. The quantitative measures used were the proportion of: (1) sections comprising follicles (FC); (2) sections comprising gametes (GC); and (3) the proportion of follicles comprising gametes (G/F). Significant consecutive monthly changes in the qualitative and quantitative measures indicated major spawning events. Gametogenesis occurred during winter with a spawning in August‐September. Gonad condition remained low during the spring and early summer until a development period between January and March. A second major spawning event occurred between March and April. There was a high degree of synchrony in reproductive status observed between the sexes. When comparing the four measurement methods using the f statistic as an index of power the GC measure was found to be the most reliable. A gonad visual grading system was developed for rapid assessment of gonad reproductive status and tested. Visual grades of pre‐recorded gonad samples were compared to the histological measures. Increasing visual grade correlated strongly with increases in all of the histological measurements.

The visual grading was a good predictor of the spawning activity of female P. canaliculus.     

Seasonal differences in catches of leptocephali in the East China Sea and Suruga Bay, Japan

The species composition, distribution, and size of eel larvae, or leptocephali, caught near the continental shelf in subtropical and temperate regions of East Asia were compared between two seasons (May–Jun and Oct–Dec) to learn about the seasonality of reproduction of marine eels. There was greater species richness and evidence of spawning by more species of marine eels during the late autumn surveys in both the East China Sea (ECS) and in Suruga Bay along the east coast of Japan. Small leptocephali <10 mm TL and a wide range of sizes of various taxa were collected during both seasons along the outer edge of the continental shelf in the ECS, indicating that some marine eels may spawn there all year. The lack of small leptocephali during the spring survey in Suruga Bay suggested that most eels have a clear seasonal cycle of summer or autumn spawning at the higher latitudes of coastal Japan where there is much greater fluctuation of water temperature throughout the year than in the ECS. At lower latitudes such as in the ECS, and in tropical areas where water temperatures are higher and more constant, some marine eels may spawn all year round.     

Spawning patterns of four species of predominantly temperate pelagic fishes in the sub-tropical waters of southern Queensland

The diverse pelagic fish assemblage of sub-tropical southern Queensland includes fishes with predominantly temperate distributions, such as tailor Pomatomus saltatrix, sardine Sardinops sagax, round herring Etrumeus teres, and Australian anchovy Engraulis australis. The peak spawning seasons of P. saltatrix, S. sagax and E. teres occur during late winter and early spring (June–October). Eggs and larvae of these three species are widely distributed in shelf waters and comprise >50% of the ichthyoplankton assemblage during this period. Mean monthly sea surface temperatures (SSTs) during late winter and early spring range from 21 to 23 °C, and are thus similar to those recorded in southern Australia during summer and autumn, which is the spawning season of these three species in those temperate waters. E. australis eggs occur mainly in inshore waters, and comprise >50% of fish eggs collected during summer and autumn when mean monthly SSTs in southern Queensland exceed 27 °C. E. australis also spawns mainly during summer and autumn in temperate Australia. Hence, water temperature may be less important as a determinant of the spawning season of E. australis than it is for the other three species. The suitability of southern Queensland for spawning by predominantly temperate species during late winter and early spring may contribute to the high diversity of the region's pelagic fish assemblage. Adult P. saltatrix, S. sagax and E. teres appear to migrate northwards into southern Queensland during early winter to spawn, and larvae may be transported southwards into temperate waters by the East Australian Current. This dispersal-migration pattern is similar to those observed for several species, including P. saltatrix, in the western boundary current systems off the east coasts of North America and Africa. Hence, pelagic fishes in ecosystems off the east coast of three continents migrate into sub-tropical waters to spawn, and larvae are transported back into temperate nursery areas by the prevailing current.     

Nursery grounds of Tarakihi (Teleostei: Cheilodactylidae) around New Zealand

Nursery grounds of the tarakihi Cheilodactylus macropterus (Bloch & Schneider) were discovered in 1963–72 mainly off the south‐western coast of the North Island, in Tasman Bay, along the entire eastern coast of the South Island, and around the Chatham Islands. They occurred at depths of 20–100 m, and mostly between 10 km and 30 km from shore. The tarakihi nurseries had a dense and varied invertebrate bemthic epifauna dominated by sponges and small corals. Few signs of nurseries were found in. other New Zealand waters, in spite of the existence of major spawning grounds there. It is not known with which spawning grounds the various nursery grounds are linked.

The Tasman Bay nursery ground is 18–33 km wide and about 75 km long, with a surface area of about 2000 km². There is a rich demersal fish fauna (37 species were recorded) dominated by tarakihi, red gurnard Chelidonichthys kumu (Lesson & Garnot), snapper Chrysophrys auratus (Bloch & Schneider), and leathei'iacket Novodon convexirostris (Guenther). The young tarakihi occur at depths of 20–45 m and concentrate during winter in the warmer deeper water. They first appear in trawl catches in summer, towards the end of their first year (assumed birthdate is 1 March), and stay on the nursery until the age of 3 y. They occur in the deeper water off the nursery during their fourth and fifth year and depart during their sixth year, possibly for the spawning grounds off the west coast of the South Island. The mean lengths at the ages of 15, 27, and 39 months were 12.6, 18.0, and 24.0 cm respectively in 1970. There was some variation in growth rate within the nursery ground, but the age groups could nevertheless be recognised easily from, length frequency modes. Monthly modal lengths showed that growth slows down in winter. Evidence for fluctuations in year class strength was found; year classes 1966 and 1969 were weak and year class 1968 was strong.

The vulnerability of tarakihi less than 4y old to commercial New Zealand trawl gear is low, and the local fishing fleets do no serious damage to the habitat on the nursery grounds. However, a large part of the tarakihi nursery grounds off the east coast of the South Island lies outside the territorial fishing zone. Intensive fishing on these grounds by large foreign vessels using heavy trawl gear could have an adverse effect on the habitat of the young tarakihi in this region.     

Reproductive synchrony in a diverse Acropora assemblage,Vamizi Island,Mozambique

Multi‐specific synchronous spawning has never been documented for East Africa, but coral spawn‐slicks are observed annually around Vamizi Island, Northern Mozambique. We monitored gamete development in Acropora species from July 2012 to October 2013 and from August to September 2014 to describe patterns of reproductive seasonality and synchrony within and amongst species of Acropora. Gamete maturation was highly synchronized within and amongst Acropora species and culminated in multi‐specific spawning events lasting 1–3 nights in each year of the study, in late August or September. In 2013 and 2014, 50% or more of the colonies of over 50% of the species sampled prior to the spawning events had mature gametes. In all years, 91–99% colonies sampled after the spawning events had no visible gametes. The percentage of colonies with mature gametes was up to 100% for some species. In other species, the absence of mature gametes throughout the study period indicates that they might not spawn in certain years. The analysis of a 8‐year record of observations of spawn‐slicks showed that spawning generally occurred once a year for a few consecutive days between September and December, during periods of rising sea surface temperature and low wind speed and rainfall. This study is the first to quantitatively document coral reproduction in Mozambique and multi‐specific synchronous spawning off the coast of Africa. These findings contrast with the asynchronous breeding reported for Kenyan reefs and support the absence of breakdown in coral reproductive synchrony towards low latitudes.     

Spawning strategies and transport of early stages of the two Cape hake species,Merluccius paradoxus and M. capensis,in the southern Benguela upwelling system

Seasonal and short-term variability of environmental parameters influence the spawning strategies of fish species. In this study, the spawning strategies and the transport of early stages of the two Cape hake species off South Africa were investigated. Distribution of eggs and larvae of Merluccius paradoxus and M. capensis was analysed in order to derive more detailed and species-specific information on spawning season, spawning location, and transport of early stages. Samples were collected during three pilot surveys between January and October 2007 and during an extensive survey in September/October 2008 in the southern Benguela upwelling system off South Africa. Eggs and larvae of M. paradoxus were found in greater numbers than those of M. capensis during all surveys. Highest abundances were found from September to October, indicating one spawning peak for M. paradoxus during late austral winter to spring. The western Agulhas Bank was identified as the primary spawning ground, and smaller spawning events occurred on the West Coast. Larvae of both species were mainly distributed in subsurface waters between 25 and 100 m. More than 50% of all larvae caught had a total length between 3 and 4 mm and size increased significantly with decreasing latitude. Merluccius capensis were found closer inshore than M. paradoxus, indicating that early stages of the two species followed separate drift routes. We assume that this distribution pattern most likely evolved from differences in spawning location and phenology. The spawning strategies of M. paradoxus and M. capensis are well adapted to a time-frame of optimal transport conditions favourable for larval survival in the highly variable environment of the southern Benguela upwelling system, but the peak spawning of the two species is separated in time and space.     

The Fish Assemblage of a Newfoundland Estuary: Diel, Monthly and Annual Variation

Twice monthly sampling over two 16 month periods at a shallow site on Newfoundland's east coast showed the fish assemblage to be dominated by four taxa (Gasterosteus aculeatus, G. wheatlandi, Osmerus mordax, Gadus spp.) that accounted for 96% of the individuals collected. Of the 16 479 fish measured, 65% were adults based on the estimated size of first spawning. The fish assemblage was dominated (86%) by species with demersal eggs, several of which spawn at the same shallow sites used by juveniles as nursery sites. Coastal spawning and demersal eggs maintain offspring in coastal nursery areas where survival is thought to be increased. Number of species and number of fish were both correlated with water temperature being highest from mid-summer to early autumn and lowest in winter. Temperature, time of spawning, and movements of juveniles and adults facilitated grouping species into five assemblages based on seasonal abundance: seasonal periodic species (summer and winter), regular species, regular species collected in all seasons except winter, and occasional (rare) species. At the diel scale, two consistent species groupings were observed: species that showed no significant difference between day and night and species caught primarily at night. Number of night species exceeded day species by a factor of two. No seine-caught species in shallow water exhibited significantly higher catches during the day. Observations by SCUBA divers indicated some species were more abundant during day time at slightly deeper depths. This observation in conjunction with day and night seining in shallower water, suggests these species aggregate in deeper water during day and move to shallow waters at night.     

Life Cycle and Population Dynamics of the Polychaete Perinereis cultrifera from the Algerian Mediterranean Coast

Abstract. The polychaete Perinereis cultrifera ( Grube, 1840 ) (Nereididae) is common along Algerian coasts in algal‐covered hard bottoms. An intensive study was conducted from June 2000 to June 2001 to characterise the life cycle of an intertidal and upper subtidal population of P. cultrifera in Algeria near the Tunisian border (30 km). P. cultrifera has a 3‐year life span and reproduces exclusively by epitoky. The reproductive season is short, and spawning occurs in late April/early May when the sea‐water surface temperature starts rising. Female sexual differentiation starts in February in the second year of life; thus, the oocytes take 16 months to mature and their diameter at maturity is approximately 250 μm.     

Fish assemblage structure on sandy beaches with different anthropogenic influences and proximity of spawning grounds

Fish assemblages in an insular (preserved) and a continental (disturbed) sandy beach were compared to assess any changes that could be attributed to anthropogenic influences and/or the proximity of the fish spawning grounds. We expected that the closer geographical position to the spawning grounds and the small amount of anthropogenic disturbance on the insular beach would be likely to provide more suitable conditions for early fish development compared with the continental beach. A total of 192 samples (96 in each beach) were taken, yielding 68 fish species, mostly young‐of‐the‐year. Fish assemblage structure differed significantly between the two beaches. Moreover, the insular beach had higher number of species, number of individuals and biomass compared with the continental beach. The commercially important Clupeiformes Harengula clupeola, Anchoa tricolor and Anchoa januaria, Perciformes Micropogonias furnieri and Mugiliformes Mugil liza were typical species on the insular beach, partitioning the seasonal use of the beach. On the other hand, a few abundant non‐commercial species, mainly the Atheriniformes Atherinella brasiliensis and the Perciformes Eucinostomus argenteus and Diapterus rhombeus, occurred all year round at the continental beach. The high fish richness and abundance and the more conspicuous species turnover across seasons on the insular beach are probable indications of more complex and dynamic organization of the communities favored by better geographical position and less anthropogenic disturbance in the area.     

Reproductive biology of the leatherjacket,Meuschenia scaber (Monacanthidae) (Forster 1801) in the Hauraki Gulf,New Zealand

The leatherjacket Meuschenia scaber is widely distributed in Australasian waters, and is a valued bycatch of inshore bottom trawl fisheries although little is known of its life history. Here, we describe the reproductive biology of the species based on 651 leatherjackets sampled in the Hauraki Gulf, New Zealand, between July 2014 and March 2016. The maximum total length (L_T) recorded for females and males were 320 and 315?mm, respectively, with both sexes present in all size classes. Monthly analysis of gonad condition revealed a clear spawning season from late austral winter to early summer (August–December), and histological analysis of the ovaries revealed that M. scaber is an indeterminate serial spawning gonochorist. The estimated sizes at sexual maturity (L₅₀) for females (189.9?mm L_T) and males (188.4?mm L_T) did not differ significantly. Relatively small testes, sexual dimorphism and underwater observation of nesting suggest that M. scaber is a paired spawner.     

Reproduction in the intertidal limpet Cellana ornata in southern New Zealand

The reproductive cycle of the abundant intertidal limpet Cellana ornata (Dillwyn 1817) was examined over 19 months, covering two breeding periods, on a rocky intertidal platform in southern New Zealand. A gonad index was calculated, and histological sections were used to count the numbers of mature and immature eggs present. Fecundity was estimated using counts of eggs before and after spawning. To determine any variation between sites, the gonad index of limpets at a second site dominated by boulders was examined over 6 months during the second breeding period. C. ornata had a single spawning period annually during summer, with greatest gonad sizes in January‐February. There were significant differences in peak gonad indices between two breeding seasons on the platform. Within the second breeding period, both the timing and magnitude of peak gonad development differed between sites, with lower reproductive output at the boulder site. Fecundity increased with increasing size, but individuals are probably capable of reproducing after their first year on the shore. The life history of this species is discussed in comparison to other limpets in New Zealand.     

Developing yellowtail kingfish (Seriola lalandi) and hāpuku (Polyprion oxygeneios) for New Zealand aquaculture

Two high value species, yellowtail kingfish (Seriola lalandi) and hāpuku (groper, Polyprion oxygeneios), have been identified as suitable new candidates for New Zealand aquaculture. This paper reviews the research by NIWA and collaborators conducted to test the biological, technological and economic feasibility of farming these two species. NIWA now has the capability to produce sufficient kingfish fingerlings per year to meet the needs of the early stages of an industry. Advances in hāpuku aquaculture have also been significant, from spawning in captivity through to the selection of juveniles for improved growth. Recently, the first spawning of captive hāpuku F1 broodstock and production of F2 eggs, larvae and juveniles was achieved. Although hāpuku larval survival remains variable, the ability to close the life cycle, and the availability of domesticated broodstock, provide a significant step forward and increase the chances of this species being commercially farmed.     

Spatial and temporal distribution of landlocked Galaxias maculatus and Galaxias platei (Pisces: Galaxiidae) in a lake in the South American Andes

Galaxiids are present in many of the Andean lakes in southern South America. We studied landlocked Galaxias maculatus (Jenyns) and Galaxias platei Steindachner populations in a deep oligotrophic lake (Lake Gutiérrez, Patagonia, Argentina). Their temporal and spatial distribution, intralacustrine movements (horizontal and vertical), and spawning periods were analysed using several sampling techniques (ichthyoplankton net, seine net, gill net, and baited benthic taps). We identified the early life stages of both species based on their morphology and otolith shape. The free embryos of both species migrate to the limnetic zone, where they coexist as larvae, facing the same food availability and probably the same predation risk. Each species then moves on to its own juvenile and adult habitat: the littoral and benthic zone for G. maculatus and only the deeper benthic zone for G. platei. Their adult habitats and part of their spawning periods partly overlap.     

Gametogenic development and spawning of the razor clam,Zenatia acinaces in northeastern New Zealand

The potential exists for New Zealand to exploit already established markets for razor clams through development of fisheries or aquaculture industries for the New Zealand razor clam, Zenatia acinaces. However, fishery or aquaculture development for Z. acinaces requires an understanding of the reproductive cycle including the timing of gametogenic development and spawning. The reproductive cycle of Z. acinaces was studied over an 11‐month period from May 2000 to March 2001 at Kennedy Bay, Coromandel Peninsula, using qualitative standard histological analysis and quantitative measures of oocytes. Histological analysis indicated that Z. acinaces is dioecious and gametogenic development was synchronous between the sexes. Gametogenesis began in June with gametes maturing quickly and by August/September (late winter/ early spring) most razor clams were ripe. Spawning began as early as September (spring) although spawning mainly occurred during October. By December (summer), nearly all clams were completely spent. From January 2001 most clams could not be sexed as all residual gametes were resorbed. Razor clams remained in this stage during March 2001. Spawning began when the water temperature was around its lowest, c. 15°C. Monthly mean number of eggs/follicle was sensitive to changes in reproductive development, closely following patterns observed in the qualitative stagings. Patterns of monthly mean oocyte diameters did not adequately describe the spawning events observed in qualitative analyses. Sex ratios were equal over the size range (69–99 mm shell length) of clams that could be sexed. The data presented in this study provide valuable information on the timing of spawning events for Z. acinaces, necessary for developing sustainable management strategies and selecting broodstock for aquaculture.     

Revised life history analysis for large grazing copepods in the subarctic Pacific Ocean

Discovery that the subarctic Pacific copepods previously grouped as Neocalanus plumchrus belong to two species required reanalysis of the life histories of both. After correction of the abundance estimates for N. plumchrus s.str., our concept of its life history remains much as previously described, because it makes up about 90% of the summed populations. Fifth copepodites of the new species, Neocalanus flemingeri, descend from the surface layer in late May to early June and mature immediately. Males are only present for about two months, and females carrying spermatophores are found during that period. Throughout the summer and autumn the entire population is constituted of females with small, dormant ovaries. This appears to be a diapause phase. Ovarian development begins in November, and spawning occurs at the end of January. Copepodite stages develop in surface layers from February through May.     

Reproductive biology of horse mackerel Trachurus capensis and Trachurus trecae in Namibia and Angola

Harvest control measures for Namibia and Angola are defined using reference points for spawning biomass, which requires knowledge of spawning potential and dynamics of fishery stocks. The reproductive biology of two species of horse mackerel, Trachurus capensis and Trachurus trecae, in these waters was investigated for spawning distribution in time and space. Samples were collected during two scientific cruises conducted in February and July/August 2007 off the coast of Namibia and Angola. A total of 396 fish ovaries was examined to determine the spawning dynamics of the two species. The ovaries were histologically analysed and their oocyte distributions mapped. The length (TL)–weight relationships of the two species differed significantly. The observed development of oocyte recruitment and absence of a hiatus in the oocyte distribution indicated that these species are indeterminate spawners. Analyses of the data from the NatMIRC database (2001–2004) indicated annual changes in gonadosomatic index (GSI) for T. capensis at different latitudes, but these changes were small. GSI also fluctuated between years and areas, but there were no clear spatial or temporal trends, with averages ≤4.0% at all stations. The GSI of both species was not indicative of the histologically determined development of gonad maturity. Oocyte maturation for T. capensis indicated that smaller and younger fish spawn first. Batch fecundity (F) for T. trecae was best described by F = 4 986 TL (cm) – 99 645 (r ² = 0.83). This study provided the first analyses of oocyte development in time and space for the two species in the region.     

Buoyancy regulation by Microcystis in Lake Okaro

Seasonal changes in ovarian activity were investigated in New Zealand turbot Colistium nudipinnis (Waite 1910) and brill Colistium guntheri (Hutton 1873), collected by commercial trawlers along the west coast of the South Island of New Zealand. Both species demonstrated group synchronous oocyte development, with a capacity for multiple ovulations within a reproductive season. During a 17‐h trawl survey, ovulated turbot were caught between 1500 and 2030 h, indicating a daily spawning rhythm. The turbot and brill spawning seasons were prolonged (late autumn to mid summer). A protracted spawning season confers some advantages in aquaculture.     

Distribution and dispersal of the early larval stages of the Japanese spiny lobster Panulirus japonicus in the East China Sea

The annual distribution and dispersal of early‐stage phyllosoma of the Japanese spiny lobster Panulirus japonicus were examined in the East China Sea and the Sea of Japan off western Japan. Early‐stage larvae were sampled mainly in summer and relatively near the coast off western Kyusyu Island. Few larvae were found in the other three seasons in the East China Sea and the Sea of Japan. This finding suggests that P. japonicus larvae are retained in coastal areas for a few months after hatching until stage V and are transported offshore until autumn, before they grow to stage VI. Examination of archival drifter data off western Kyusyu Island during the spawning season of P. japonicus supported the relatively rapid dispersal of the larvae from the East China Sea near Japan to the Pacific Ocean or the Sea of Japan. Larval transport from the East China Sea to the Pacific Ocean, which is considered to be a main distribution area of middle‐ and late‐stage larvae, would occur in the south at approximately 32–33°N in the East China Sea near western Kyusyu Island.     

Golden perch Macquaria ambigua are flexible spawners in the Darling River,Australia

The role of flow and floodplains for the recruitment of fishes in the Murray‐Darling Basin, Australia, remains a contentious issue. In this context, the reproductive ecology of golden perch Macquaria ambigua, a widespread, high‐profile angling species with a propensity to produce large numbers of semi‐pelagic eggs remains to be resolved. Back‐calculation of spawning dates from otoliths of juvenile golden perch (Macquaria ambigua) collected in August and November 1997 from the Menindee Lakes on the floodplain of the Darling River, in western New South Wales, Australia, advances understanding of spawning of this species in three ways: (1) golden perch spawned at lower temperatures (≤18.8°C) than has previously been reported from the Murray‐Darling Basin; (2) golden perch in the Menindee Lakes can be derived from spawning in all seasons of the year in contrast to what is apparent in more southerly locations of the Murray‐Darling Basin; and (3) spawning can occur in the absence of floods.     

Biology of Evechinus chloroticus (echinoidea: Echinometridae) from different localities

Mean gonad indices of Evechinus chloroticus (Val.) at Kaikoura and Kaiteriteri, South Island, New Zealand, increased during the winter and spring to reach peak values during the summer and then decreased to minimum values in autumn. There was only one major summer peak at Kaikoura, but two at Kaiteriteri. The maximum mean gonad index of Kaiteriteri specimens was little higher than the minimum at Kaikoura. Absolute size of gonads and spawn producton were also lower at Kaiteriteri, perhaps because of less food there.

At both localities gametogenic cycles were correlated with gonad index cycles, progressing from unripe to ripe from late autumn to spring, but Kaikoura urchins held ripe gametes over a longer period than Kaiteriteri urchins. The volume of spawn from females was greater than that from males but males had ripe gametes (and could be artificially induced to spawn) longer. At Kaikoura, some spawning probably occurred throughout summer with a major spawning in late summer or early autumn. Large urchins with small dark gonads were found throughout the year, particularly at Kaiteriteri; these were probably senile individuals.

Although at both localities Evechinus matured at 3–4 years, Kaikoura urchins were larger at maturity.

At Kaiteriteri sex ratios of mature Evechinus did not differ significantly from 1:1, but in some populations at Kaikoura males were significantly more prevalent than females.