Strong relationships between levels of puerulus settlement and recruited stock abundance in the red rock lobster (Jasus edwardsii) in New Zealand

Any demonstrable relationship between levels of settlement and subsequent strength of recruitment to the fishery is of great interest to the managers of rock lobster fisheries. A project to estimate levels of settlement of the puerulus stage of the red rock lobster, Jasus edwardsii, on crevice collectors around the main rock lobster fishing shores of New Zealand has been in place for more than quarter of a century, with considerable temporal variation but also strong temporal and spatial consistencies in settlement. There are significant correlations between settlement level and the fishery catch per unit effort (CPUE) response for most fishery areas, at time lags between settlement and recruitment consistent with what is known of juvenile growth rates. There are also significant correlations when more than one settlement year is correlated against each year of CPUE, to account for variable growth rates between individual lobsters. There was no concurrence between field and fishery model estimates of recruitment for the three fishery areas with sufficient data, revealing a different interpretation of annual rates of recruitment to the fishery between the two approaches. The reasons for the discrepancy are unclear, but one possibility is that the model estimates of recruitment are poor.     

Post-larval settlement of California spiny lobster Panulirus interruptus in Bahía Tortugas,Baja California and its relationship to the commercial catch

Based on data series for 8 consecutive years of settlement of post-larvae of the California spiny lobster Panulirus interruptus, its relationship to commercial catch was examined. The purpose was to establish a database to build a model for prediction of commercial catches of this lobster. The study area is a rocky shelf southwest of the bay entrance of Bahía Tortugas in Baja California Sur. A set of artificial collectors was placed at this site to obtain postpuerulus and early juveniles settlement for each month. Different simple regression analyses were performed on annual series of mean rates of post-larval settlement vs. commercial catches by the Bahía Tortugas fishing cooperative. We tested several delay periods between the series (4–8 years to approximate the age of fishery recruitment) to find the best-fit relationship. The relationship with a 5-year delay showed the highest positive correlation (0.7925) and was statistically significant. This delay period was used to regress the data for the years 1993–2001. The results showed that variations in the abundance of settled post-larvae in a given year are reflected in the commercial catch 5 years later and exhibit the same upward or downward trend. The one exception was the high post-larval settlement rate in 1997–1998, coinciding with the El Niño event, which was not mirrored by a similar increase 5 years later in the 2002–2003 catch. The pre-recruit index seems a very promising tool for predicting catches for this lobster fishery.     

Blue crab (Callinectes sapidus) larval settlement in North Carolina: environmental forcing,recruit–stock relationships,and numerical modeling

Ecosystem‐based fishery management requires an understanding of relationships between fisheries and environmental variability. The purposes of this study were to investigate (1) how environmental forcing drives variability in larval settlement of the blue crab Callinectes sapidus, (2) whether larval settlement data are useful for determining recruit–stock relationships, and (3) whether environmental data can be used to predict settlement. Megalopae settling on passive collectors in the Newport River estuary, NC, were collected nightly from September to November for 13 yr from 1993 to 2009. Observed settlement was compared with winds, tides, and predicted settlement (numerical model derived from environmental data) using cross‐correlation analysis. Weather events associated with settlement pulses were also identified. Recruit–stock relationships were developed by comparing observed and predicted settlement indices to lagged NC fishery data. Settlement was positively correlated with winds from the northeast, southeast and south in 12 of 13 yr and with maximum duration nighttime flood tides in all years. Settlement pulses occurred when high pressure systems formed over the southeast USA (58% of pulses) or hurricanes (25%), and nearly all occurred during nighttime flood tides (85%). Significant recruit–stock relationships occurred between observed settlement and fishery landings (r² = 0.96) and effort (r² = 0.94) in wet years and catch per unit effort (r² = 0.98) during dry years. The timing of settlement pulses, but not the magnitude of annual settlement, was successfully predicted using the settlement model. These results suggest that blue crab fisheries in NC are influenced both by larval settlement and post‐settlement processes (freshwater inflow).     

Experimental suspended culture of mussels (Mytilus edulis L.) in Wales using spat transplanted from a distant settlement ground

Spat of Mytilus edulis L. were transferred 300 km by road on collectors from an area of high and regular spatfall, but unfavourable culture conditions, to a raft at a site deficient in mussel settlement. Spat were collected on coir ropes and fibrous rubberized matting staked to intertidal settlement grounds in Morecambe Bay, northwest England. During January to April, 80 mm circumference ropes could collect 3 000–7 000 spat/m/week, with smaller numbers in other months, and fibrous matting sometimes also caught many spat.Spatted collectors were suspended in the Menai Straits, North Wales. Despite heavy losses from overcrowding, fast currents and turbulence, growth was sufficiently good for some rope populations to produce marketable crops after about 16 months. Mean lengths increased from 1.5–5.0 mm to 47.5 mm in the first year, and to 60 mm after 1.5–2 years. At about 55 mm, attained at ca 16 months, the best crops yielded 10–15 kg/m live weight, corresponding to 2–3 kg of cooked meat/m. Percentage meat yields from 40–50 mm mussels were equally good, suggesting that crops could be harvested below the present marketable size.Economic systems for collecting spat and for on-growing at controlled densities remain to be developed for different hydrographic conditions and scales of commercial operation in Britain.     

Spawning of Pecten maximus (Pectinidae) and the artificial collection of juveniles in two bays in the west of Ireland

The main spawning times of the scallop Pecten maximus (L.) in 1985 and 1986 in Kilkieran Bay were in late May and August in 1985 and in early June and late July in 1986. In the Birterbuy Bay population spawning was mainly in late April and August in 1985 and in late May 1986. Spawning continued at low levels throughout the summer. Fecundity also varied in the 2 years. Settlement on artificial collectors was monitored from June to September 1985 and May to September 1986 in Kilkieran Bay, from June to November 1985 in Birterbuy Bay. Major settlements occurred in June 1985 and in July 1986 in Kilkieran Bay, while only light settlement was recorded in Birterbuy Bay during 1985. Late spawnings in each year did not lead to successful settlements. Spatial variations in settlement intensity in Kilkieran Bay suggest that most larvae settle several kilometres from adult beds. Size-frequency distributions of settled juveniles, however, indicate that silting of some collectors may reduce their efficiency for collection of juveniles.     

Gonad development, larval settlement and growth of Mytilus edulis L. in a suspended population in Hvalfjördur, south-west Iceland

Annual cycles of gamete development in Mytilus edulis L. in south-west Iceland were investigated during 1986 to 1987. Histological preparations of the gonads showed that all individuals were fully mature in the beginning of June in both years and one spawning period was recorded each year at a sea temperature of 10-12^oC. The main spawning took place from the middle of July to the middle of August, and from the middle of June to the end of July in 1986 and 1987, respectively. Redevelopment of the gonads after spawning was observed in February when both food availability, measured as chlorophyll a concentration, and temperature were low. Rapid gonad maturation took place during the spring phytoplankton bloom in March-April. Larval settlement was heavy on the artificial collectors used. The length of the larval period was estimated as being 4-5 weeks and peak settlement occurred in the middle of September. The size of the early plantigrades settling on the collectors during the study period indicated direct settlement of mussel larvae from the plankton onto the collectors. One year after settlement the spat averaged 24.6 mm ± 6.0 (SD) shell length and two years after settlement a market size of 50.8 mm ± 5.7 (SD) was reached. Growth was correlated with food availability, measured as chlorophyll a concentration. The growth season lasted from March to October with the greatest shell growth in late summer. The results showed that the growth of M. edulis was markedly increased by suspending the animals in a more favourable environment than that found on the natural mussel beds.     

Juvenile cod (Gadus morhua) mortality and the importance of bottom sediment type to recruitment on Georges Bank

The demersal settlement of pelagic juvenile fish has been considered a critical period in which the final adjustment is made to the size of a year class. Distribution patterns of pelagic and recently settled juvenile cod (Gadus morhua) were examined from nine surveys on Georges Bank during the summer over 5 years, 1984–1989, to relate juvenile survival to the sedimentary environment. Pelagic juveniles were widespread across Georges Bank in June, and by mid‐July they occurred on all bottom types from sand to gravel on eastern Georges Bank. However, by late July‐early August they were mostly abundant on the northeastern edge gravel deposit, which with its complex relief, provides abundant prey and refuge from predators. A bank‐wide estimate of pelagic juvenile abundance in 1986 and 1987 was used to assess mortality of the recently settled juveniles and to evaluate the relative importance of survivors from the northeastern edge gravel area to recruitment of the Georges Bank population. Settlement mortality rates over 1–2 months on the northeastern gravel area ranged from 3 to 8% day^?1, which compared reasonably with other studies. The seasonal abundance of the pelagic juveniles was almost an order of magnitude higher in 1987 than 1986; however, recruitment at age 1 was similar, indicating that a high mortality of the demersal juveniles occurred in 1987. The limited northeastern gravel area on Georges Bank may represent a survival bottleneck depending on the variability in the distribution and abundance of juvenile cod settlement in relation to that of their predators.     

Spat Collection and Growth to Commercial Size of the Tehuelche Scallop Aequipecten tehuelchus (D'Orb.) in the San Matias Gulf, Patagonia, Argentina

Studies on larval settlement and growth of the commercial scallop Aequipecten tehuelchus were carried out over a 2-yr period in San Matias Gulf, Argentina. Gonadal index was used to indicate spawning and spat collectors were deployed when spawning began. Artificial spat collectors (mono-filament bags filled with thin shrub branches) were placed at a depth of 25 m in two areas of the Gulf during two seasons (1989–1990 and 1991–1992). Maximum settlement occurred by mid-February during the first season and by mid-January in the second season. Larger numbers of spat were found in collectors placed near the sea bottom. After settlement, spat were removed and placed in cages for growout. Scallops reached the average commercial size (60 mm shell height) 16 mo later. Mortality rate during the entire period was 10%.     

Population dynamics of the brown shrimp Crangon crangon L., in shallow areas of the German Wadden Sea

Settlement, growth and mortality of the brown shrimp, Crangon Crangon L., were studied in the north Frisian Wadden Sea over a period of 19 months to fill existing gaps regarding the species' life cycle, and thereby to clarify points related to the fishery. Settlement of postlarval shrimp in the shallow areas occurred in three batches: in May; during summer; and an overwintering batch. Compared with an earlier model based on laboratory-derived data, a new growth model based on field data predicts similar growth rates for the earlier phase of the shrimp life cycle, but higher rates for the later stages of the cohorts. Mean growth rate of the different cohorts over the size range sampled was 0.23 ± 0.08 mm day^?1. Of the factors tested, only temperature significantly influenced growth rates. Preliminary estimates of instantaneous total mortality values for shrimp cohorts from these shallow areas ranged from 0.03 to 0.12 day^?1. Salinity explained most of the variation in mortality rates, but this most likely indicates an indirect effect of depth on emigration. The cumulative effects of growth rates estimated from the new model and lower losses through predation could imply a higher contribution of winter eggs to the autumn fishery. This, however, needs further evaluation to properly quantify the trade-offs between settlement and recruitment to the fishery, as well as the growth and mortality rates.     

Recruitment patterns and early growth of acroporid corals in Manado, Indonesia

A coral settlement device was used to examine recruitment patterns of Acropora at two stations (st.; A and B) in Bunaken Island, Manado. The recruitment timing of Acropora was not determined because of mixing with Isopora. A marine block (MB) was used to observe the growth of settled acroporid corals at st. A. Within a year of settlement (February–May of the following year), the corals which had settled on the MB had grown to a size of 13.4 ± 5.86 mm. They were dominated by Isopora, with a small proportion of Acropora. A supplementary experiment again using the MB was conducted at three other sites (st. C, D, E) where Isopora was not abundant. The size of the corals which settled on the MB was nearly the same as that of the corals at st. A. Juvenile Acropora corals (≤3 cm, encrusting form) were measured on the Manado coast (st. F) between February and May. At this site, Acropora corals were dominant and no Isopora corals were observed; the size of Acropora was 18.5 ± 5.01 mm. Acroporid corals in February and March at st. A appeared smaller than those at st. F and grew to nearly the same size in early April.     

Settlement of the commercial scallop,Pecten fumatus (Reeve) 1855, on artificial collectors in eastern Tasmania

The settlement of the commercial scallop, Pecten fumatus (Reeve) 1855, in artificial collectors was monitored on the east coast of Tasmania over a 4-year period using spat collection techniques similar to those practised in Japan. Major spat settlement occurred in mid-late September but small irregular settlements were observed in late spring and early summer. Information on settlement obtained in the first 2 years of the study was successfully applied in the collection of large quantities of scallop spat during the later years of the study.The number of settled scallop spat and growth of the spat varied with depth. Maximum settlement occurred at depths of 16–22 m, with a decrease in numbers towards the surface and the seabed (depth, 31 m). Growth of scallop spat also varied with depth. Scallops in collectors near the surface grew faster than those in deeper water, the most noticeable change in growth occurring at depths between 16 and 20 m.A considerable percentage (up to 62%) of settled spat were lost from the larger-mesh collectors and most losses occurred when spat detached their byssal threads in late November-mid-December. Further losses are attributed to fish predation and competition with colonising ascidians. Major colonising groups apart from scallops included brown and filamentous algae, ascidians, bryozoans, crabs, shrimps, gastropods, bivalves and fish.     

Impact of wind stress anomalies on the seasonal pattern of southern rock lobster (Jasus edwardsii) settlement in South Australia

Quantified estimates of southern rock lobster (Jasus edwardii) puerulus settlement have been undertaken in the Southern Zone fishery of South Australia since the early 1990s. An analysis of mean monthly puerulus settlement indices from 1995 to 2007 in three monitoring sites revealed a strong seasonal correlation (r > 0.94 between sites) in settlement patterns. Settlement was highest during the winter months of June, July and August with peak settlement in all sites occurring in July. A reduced secondary settlement occurred during February and March. Seasonal trends were correlated with monthly wind stress and direction data in order to investigate possible environmental drivers of settlement. Using monthly averages of wind stress, it was hypothesized that strong along‐shore wind‐stress anomalies (ASWSA) prior to peak settlement would influence puerulus indices. Maximum ASWSA over the December–May period prior to maximum settlement was therefore examined. The results showed significant correlations (P < 0.1, r = 0.51–0.90) between wind stress and puerulus settlement in all but one site. We suggest that storm events, in combination with onshore surface drift during the period of settlement, are the principal physical oceanographic mechanisms influencing settlement patterns within the Southern Zone rock lobster fishery of South Australia.     

Settlement of mussels (Mytilus galloprovincialis Lamarck) on rope collectors in the estuary of the River Krka,Yugoslavia

The 25-km² estuary of the River Krka, Yugoslavia, supports a large natural population of mussels. Artificial culture on hanging ropes is now beginning, and for this it is necessary to know the best areas, depths and times for settlement and collection of seed. In this experiment, plastic rope test collectors were set each month from May 1981 to April 1982 at three sites. After 2 months, settled mussels were removed from collectors. Water temperature and salinity measurements were made weekly at each site. Maximal settlement at the two upstream sites was found in September, when 350 and 485 mussels were recovered from 125 cm² of rope at 2 m depth. However, at the site further downstream, good settlement occurred throughout the year, peaking at 5250 mussels per 125 cm² of rope at 3 m depth during April. Such productive sites will be extremely useful in supplying seed for mussel farms in this area.     

Ontogenetic habitat shift of age-0 Japanese flounder <Emphasis Type="Italic">Paralichthys olivaceus</Emphasis> on the Pacific coast of northeastern Japan: differences in timing of the shift among areas and potential effects on recruitment success

Ontogenetic habitat shift and feeding habits in the shallow (< 15 m) and deep (30–80 m) habitats of age-0 Japanese flounder Paralichthys olivaceus in Sendai Bay, the Pacific coast of northeastern Japan, were examined to understand the mechanisms that potentially enable area-specific high recruitment success. The flounder was able to use the shallow nursery habitat for about 1 year, until the next summer of their settlement (June–August) when they had reached 250 mm total length (TL). In addition, age-0 flounder between 150 and 250 mm TL used both shallow and deep habitats from winter to the next summer of their settlement, where species, size, and availability of potential food and susceptibility to predators are considerably different. These area-specific characteristics in Sendai Bay are clearly different from other areas around Japan that have been described in the literature: shorter residence in the shallow habitat and smaller size at emigration to the deep habitat. The characteristics in Sendai Bay seem to be enabled by prolonged good feeding conditions in the shallow habitat, which result from an abundant food supply and relatively lower temperature that does not exceed the uppermost temperature (25 °C) for maximum growth of the age-0 flounder. We consider that the prolonged better feeding conditions in the shallow habitat in the study area for ca. 1 year after settlement contribute to higher recruitment success.     

Development of new assessment methods for Acropora coral recruitment using coral settlement devices and holes of marine block

We developed new assessment methods for Acropora coral recruitment using coral settlement devices (CSDs) and holes of a marine block. Both devices were deployed in situ before mass spawning of Acropora corals. The CSDs were sampled after 3–4 months of spawning to measure early recruitment, whereas holes of the marine block were observed underwater or MB was sampled to observe holes after 1 year of spawning to measure the recruitment. By combining the results, we would know the recruitment (visually identified underwater) in reefs, including the amount of early recruitment (identified by stereomicroscopic methods), and the environmental condition of the coral reef. These results would help to predict the future of a reef. Nagura Bay had a high early Acropora recruitment; however, due to competition with algae and sedimentation, the recruitment of juvenile corals was extremely low. The reef would possibly be healthy and sustainable at sites where both the early recruitment and recruitment are high. However, if both are low, the reef will be in a critical condition where urgent restoration will be required.     

Settlement and growth of the mussels (Mytilusgalloprovincialis,Lamarck, 1819) on different collectors suspended from an offshore submerged longline system in the Black Sea

A study of spat settlement of a submerged longline mussel culture system was carried out in Sinop area, Black Sea, between May 2008 and May 2009. The effects of six different types of collectors on spat settlement and growth were investigated. Six different types of spat settlement rope were used as polypropylene ropes with 18 mm diameter, 18 mm diameter timeworn silk rope, 22 mm diameter rope made from old hawser (OSR), 22 mm diameter ropes made from old anchovy net without pegs, 18 mm diameter old used nylon ropes and 18 mm diameter tasselled polypropylene ropes. Monthly temperature, salinity, chlorophyll‐a, total suspended matter, inorganic matter and organic matter were determined during the experimental period. The best settlement was observed on the OSR type when measured per metre (3450.00 ± 125.83 ind m^?1). Consequently, the findings showed that settlement preference of spat occurred according to rope structure, and if ropes are designed to combine numerous well‐fixed tassels, spat settlement can increase. Spat growth was affected by environmental factors and rope structure. In addition, the study revealed a negative relationship between density and growth.     

Effects of water depth on survival and growth of <Emphasis Type="Italic">Argopecten purpuratus</Emphasis> (Lamarck, 1819) spat in northern Chile

Collection and suspended culture of Argopecten purpuratus spat in Japanese-type collectors was undertaken in the Rinconada Marine Reserve (Antofagasta, Chile) to determine growth variations between surface and bottom waters. Scallop spat was collected at 16-m depth and grown at 1- and 16-m depths. An initial settlement of ca. 13,000 post-larvae per bottom collector (2 cohorts) was observed on 3 February 2001. Two new cohorts settled in bottom collectors on 3 March, while no spat settlement occurred in surface collectors. The four cohorts exhibited substantial and different mortality rates over the study period, depending on the cohort and on-growing depth. The first and second cohorts exhibited mortality rates of 80.3 and 53.1% in bottom collectors, respectively, versus 29 and 43.6% in surface structures. The third and fourth cohorts exhibited mortality rates of 21.4 and 59.7% in bottom collectors, respectively. Mean shell height of scallop spat after 88 days of culture was 6.46 mm for the first cohort and 4.37 mm for the second cohort in bottom collectors, versus 10.33 and 7.31 mm in surface collectors, respectively. Mean post-larval growth rate in bottom collectors (86 μm day⁻¹) was significantly lower than growth rate in surface collectors (146 μm day⁻¹). Factors explaining the depth-related mortality and growth rates are discussed to improve scallop culture in the Reserve. It was concluded from the results that culture improvement in Antofagasta Bay would require collecting spat in bottom waters and raising it near the surface during initial cultivation stages.     

Use of satellite data to identify critical periods for early life survival of northern shrimp in the Gulf of Maine

The northern shrimp Pandalus borealis is at its southern limit in the Gulf of Maine (GOM), and recruitment success is higher in years with relatively cool water temperature. However, the mechanisms for the temperature effect are not clear. We used rolling window analysis of daily satellite data to identify critical periods for early life survival of the 1998–2012 northern shrimp year‐classes and to investigate the importance of the phenology of the hatch and bloom. Survival was negatively correlated with sea surface temperature (SST) during a 6‐week period around the time of larval emergence (late winter) and during a 4‐week period in late summer when SST and stratification reached annual maxima. Survival was negatively correlated with chlorophyll‐a concentration (chl‐a) during two 5‐week periods centered approximately a month before the hatch midpoint and around the time of settlement to the benthos. A small‐magnitude winter bloom occurred around the time of the hatch in many years, but our results did not reveal a link between survival and bloom‐hatch phenology. The timing of winter and spring blooms were correlated with SST during the preceding 10 months. A survival model including SST and chl‐a during the critical periods explained 73% of the variance in survival. Summer SST increased significantly during the study period; the other critical variables showed no trend. The rolling windows approach revealed sensitive periods in early life history that may not have otherwise been hypothesized, providing a foundation for research towards a greater understanding of processes affecting recruitment.     

Effects of different substrates on settlement and growth of pearl oyster (Pinctada maxima) larvae in hatcheries

Metamorphosis of pearl oyster Pinctada maxima pediveliger is affected by physical and chemical characteristics of the collectors. In the present study, we conducted four experiments to evaluate the effects of collector characteristics on the settlement and growth of hatchery-reared pearl oyster. In the first experiment, black, red, yellow, and white plastic sheets were used as collectors. Settlement of P. maxima larvae in black and red plastic sheets was significantly higher than that in yellow and white plastic sheets (P < 0.05). Mean shell length was not significantly different among the four colored sheets (P > 0.05). In the second experiment, pediveliger larvae were settled onto palm rope and polypropylene rope collectors. The number of spat in the palm rope collector was significantly higher than that of spat in the polypropylene rope collector (P < 0.05). Mean shell length was not significantly different between palm rope and polypropylene rope collectors (P > 0.05). In the third experiment, settlement and subsequent growth were compared between plastic sheets with and without biofilm. The number of spat in the plastic sheets with biofilm was significantly higher than that in the plastic sheets without biofilm (P < 0.05). Mean shell length after settlement were not significantly affected (P > 0.05). In the fourth experiment, pediveliger larvae were stored in tanks with (experimental group) and without collectors (control group). The settlement rate of larvae on the wall was not significantly different between the two groups(P > 0.05). The settlement rates of the larvae on the wall and collectors in the experimental group were significantly larger than those on the wall in the control group(P < 0.05). Mean shell length was not significantly different between the groups (P > 0.05). Our results suggest that appropriate selection of collector types, color, and conditioning can improve the settlement of P. maxima larvae in hatcheries.     

Reproductive cycle of Aulacomya ater [Bivalvia: Mytilidae (Molina 1782)] in Punta Arenas Cove (Antofagasta Region,Chile)

Changes in the condition of broodstock, presence of larvae, and post-larval settlement of A. ater in Punta Arenas Cove (Antofagasta Region, Chile) were used to determine its reproductive cycle. The condition used as a spawning indicator shows that these events occur in three periods throughout the year (May–July, August–November, and December–February). Intense periods recorded in October–November and December–February coincided with periods in which the water temperature descended to less than 13 °C. Simultaneously, plankton samples indicated constant presence of A. ater larvae at this site, with large increases in abundance during August and between October and January, reaching a maximum of 2,192 larvae m^?3 in October. The periods of increase in larval abundance coincide with spawning periods; however, the greatest abundances were recorded before the start of the descent of the spawning indicator of the population under study. Monthly installation and replacement of collectors, after recording the first spawning, showed the permanent settlement of A. ater post-larvae over the course of the study, with a period of greater intensity occurring from the end of August to the end of January, registering peaks in October and November with 5,667 and 4,183 post-larvae × 600 cm² collector^?1, months which also coincide with the greatest larval abundance. The presence of larvae and post-larvae of the mytilids Choromytilus chorus and Semimytilus algosus was also recorded alongside A. ater larvae and post-larvae. Ch. chorus presented a cycle very similar to that of A. ater in both stages, with a maximum abundance of 4,531 larvae m^?3 in November and 13,533 post-larvae × 600 cm² collector^?1 in December.