Annual Egg Production Research Articles

Seasonal patterns of egg production in field colonies of the termite Reticulitermes speratus (Isoptera: Rhinotermitidae)

This is the first report on the annual egg production patterns in mature termite colonies in the field. Data on the seasonal patterns of egg production in field colonies are very important for understanding the annual colony growth schedule, resource allocation, and population dynamics of the termites. However, collecting the eggs from a sufficient number of colonies is extremely difficult in Reticulitermes termites because their multiple-site nesting makes it difficult to find the reproductive center of the colonies. Here, we first show the seasonal pattern of egg production in the subterranean termite Reticulitermes speratus by collecting the reproductive center of ten colonies each month from April through October. We had to destructively examine dozens of nests to find eggs from enough field colonies each month. Mature field colonies began to produce eggs in late May, soon after the swarming season, and the egg production rate (EPR) reached its maximum in early July. The eggs hatched until late October. The EPR was significantly correlated with the average monthly temperature. Additional investigation of the egg distributions in the nests showed that most eggs were kept around the royal cell, which contained the reproductives. The largest colony had 109 supplemental queens and 94,023 eggs, suggesting that each queen produced an average of 24.7 eggs per day, based on the known mean hatching period of an inseminated egg of 34.95±0.12 (SE) days.

Elasticity Analysis of Green Sturgeon Life History

I provide an analysis of a simplified life history model for green sturgeon, Acipenser medirostris, based on published and recent estimates of reproduction and growth rates and survival rates from life history theory. The deterministic life cycle models serve as a tool for qualitative analysis of the impacts of perturbations on green sturgeon, including harvest regulations based on minimum and maximum size limits (“slot limits”). Elasticity analysis of models with two alternative age–length relationships give similar results, with a high sensitivity of population growth rate to changes in the survival rate of subadult and adult fish. A dramatic increase in the survival of young of the year sturgeon or annual egg production is required to compensate for relatively low levels of fishing mortality. Peak reproductive values occur from ages 25 to 40. An increase or decrease in the maximum and minimum size limits can have a profound effect on the elasticity of population growth to changes in the annual survival rate of age classes specified by the slot, due to changes in the number of age classes of subadults and adults that are available for harvest. This analysis provides managers with a simple tool to assess the relative impacts of alternative harvest regulations. In general, green sturgeon follow life history patterns similar to other sturgeon, but species-specific demographic information is needed to produce more complex assessment and viability analysis models.

Influence of female age, body size and environmental conditions on annual egg production of the bullhead

A population of bullhead Cottus gobio inhabiting a mountainous river network, was examined for the influence of maternal condition (total length, LT, and age class in years) and environmental factors (water temperature and fish density) on fecundity, egg size and net annual reproductive effort (ER, defined as the ratio of total egg production mass to body mass) within several stocks. Regardless of location within the drainage network, bullhead reproduction was synchronous, with only a single batch and fecundity ranging from 69 to 896 eggs per female. As with LT fecundity increased with age, although the difference between age classes 5 and 6 years was smaller than between other age classes. Egg diameter also increased with age from age classes 2 to 4 years, but then tended to decrease for age classes 5–6 years. Multiple stepwise regression was used to examine the effect of female LT, water temperature and fish densities on bullhead egg production for each of the four age classes (2, 3, 4 and 5–6 years) separately. When statistically significant, water temperature always had a positive effect and fish densities a negative effect, on fecundity and egg size. The LT always had a positive effect on fecundity for all the age classes. In contrast, LT had a positive effect on egg size and ER only for female reaching maturity (2 years), whereas intermediate aged females (3–4 years) were insensitive and the oldest fish showed a negative response.

Status of the major lobster fisheries in India

Commercial exploitation of lobsters from the Indian seas began in the 1950s. Annual landings have been declining from a peak of 4075 t in 1985 to 1364 t in 2002. Major fisheries were located on the north‐west, south‐west, and south‐east coasts. Among the 12 species recorded, only four species of spiny lobsters (three littoral and one deep sea) and one species of slipper lobster are commercially important. At Kayalpattinam and Tharuvaikulam, on the south‐east coast, lobster landings sharply declined for the gill‐net fishery. Of the two species that contributed to the fishery, Panulirus ornatus and Panulirus homarus, the latter has been more affected owing to high vulnerability to fishing activities. Catch composition analysis of the trammel‐net fishery showed that 35% of the landings consisted of P. homarus in the size range of 23–50 mm carapace length. On the north‐west coast, the spiny lobster Panulirus polyphagus and the slipper lobster Thenus orientalis are incidentally caught in trawl nets. However, the fishery for T. orientalis in the waters off Mumbai lasted only up to 1994. Large‐scale exploitation of spawning females, which formed 60% of the total catch, might have been detrimental to the recruitment process resulting in rapid decline and total collapse of the fishery. Abundance of P. polyphagus reached its maximum during September, constituting 23% of the average annual landing during 1988–2002. A high exploitation ratio (>0.7) indicated over‐fishing of the stock. Repeated spawning and high annual egg production are probably responsible for sustaining the stock, despite over‐exploitation. Major problems confronting the resource management of the multi‐gear and multi‐species lobster fisheries in India are discussed. An operational project, involving fisher community, has been taken up for creating awareness of the need for sustainable exploitation of the resource. Regulatory measures, such as closure of the fishery during the peak of the breeding season, ban on trammel‐net, mandatory release of egg‐bearing lobsters, and establishment of lobster sanctuaries are suggested to the State Governments for implementation.

Indigenous chicken genetic resources in Bangladesh: current status and future outlook

SummaryLivestock, especially poultry, is a promising sector for poverty reduction in Bangladesh. Approximately 140 millions chickens are scattered throughout 68 000 villages in the country, mostly of indigenous, non-descript type. The production system for indigenous chickens is smallholder backyard scavenging in nature with each family keeping an average of 6–7 chickens to meet family requirements, and from which a cash income can also be derived when necessary. Indigenous chickens produce about 75% of the eggs and 78% of the meat consumed domestically. Among said indigenous chicken genetic resources, non-descript Deshi, Aseel and Naked Neck breeds are noteworthyThe non-descript Deshi chicken constitutes about 90% of the indigenous population. Also known as ‘Murghi’, they have undergone unknown periods of natural selection and are a reservoir of excellent genetic diversity. They show high levels of morphological and phenotypic variability and increased fitness under natural settings. Studies reveal that they may be regarded as one breed or population because of the small genetic distances among them. Deshi chickens are characterized by black (75%) and red (25%) plumage colour; black (39%), yellow (32%) and white (29%) shank color; black (99%) eye color; bright red (59%) and pale (41%) comb colour; white (82%) and yellow (17%) skin colour; no definite (61%) and lacing (17%) feather pattern; medium (70%) and large (19%) body size; single comb (97%) and rudimentary spur (98%); medium egg size (80%); light brown (67%) and white (27%) egg shell colour. Regarding production traits, Deshi chickens have average hatch weight of 29 g; body weight at 4, 8, 12 weeks; weekly weight gain (0–12 weeks) of respectively of 77, 175, 315, 24 grams; age at first egg (175 days); weight of pullet (0.9 kg); mature body weight (1.3 kg); hatchability (52%); fertility (83%); annual egg production (45 -50 eggs); 9% mortality up to 500 days of age.The indigenous chicken population of Bangladesh has been undergoing genetic erosion since the 1960s, following the introduction of improved stock from developed countries. Efforts to sustain commercial hybrid broiler and layer chicken farming under intensive and semi-intensive production models have been tested, but efficiency of systematic characterization, screening, breed improvement and conservation programmes with the indigenous Deshi chickens at the smallholder village levels (in-situ) of Bangladesh are yet to be tested. Such an initiative may help to save these creatures from the grip of thethreat of extinction. This in turn may help to sustain village chicken production system in Bangladesh and could be a useful micro-economic strategy in the on-going poverty alleviation process in the country.

Multiple Clutching in Southern Spotted Turtles, Clemmys guttata

We examined the reproductive output of spotted turtles (Clemmys guttata) from a population in South Carolina. We used radio telemetry, palpation, and x-rays to monitor the reproductive condition of females over two field seasons. We present the first evidence for multiple clutching in a wild population of spotted turtles. Of 12 females with radio transmitters that became gravid, five produced second clutches, and one produced a third clutch. Average annual clutch frequency was 1.2 per female. Clutch frequency was independent of body size. We compared reproductive output among three populations: Ontario, Pennsylvania, South Carolina. Individual clutch sizes varied with latitude. Clutch size was largest in the north (mean = 5.3 eggs), midsized in the central population (3.9), and smallest in the south (2.9). We suggest that this pattern is related to seasonality differences, which result in different selective pressures on body size of females. Total annual egg production (the sum of all clutches within a reproductive season) by gravid females did not differ between the Ontario (5.3 eggs) and South Carolina populations (4.6). These data indicate that, although individual clutch sizes differ between northern and southern spotted turtles, total annual reproductive output is consistent in these widely separated populations.

Investigating spatio-temporal change in spawning activity by Atlantic mackerel between 1977 and 1998 using generalized additive models

Long-term, seasonal and spatial patterns in spawning activity of Atlantic mackerel (Scomber scombrus) along the continental shelf west of Europe were investigated. Stage I egg densities from all eight available international, triennial surveys (1977, 1980, 1983, 1986, 1989, 1992, 1995 and 1998) were modelled using generalized additive models. The data showed that seasonal and spatial patterns of spawning activity varied inter-annually. Total annual egg production peaked in 1989 with minima in 1983 and 1998. Further examination of these trends (1977-1998) showed that the intensity of spawning activity has shifted location, declining in the south and rising in the north. There was no direct link between stage I egg densities and sea surface temperature, although the rate of temperature increase along the shelf edge was strongly related to the total annual egg production by the mackerel.

Annual Egg Production of Seasonal Populations of Japanese Anchovy, (Engraulis japonicus) in Kagoshima Bay, Southern Japan

Annual Egg Production of Seasonal Populations of Japanese Anchovy, (Engraulis japonicus) in Kagoshima Bay, Southern Japan

A Model for Individual Egg Production in Chickens

Our primary objective was to improve on an existing model for the individual weekly egg production curve by modeling the curve as a sum of logistic functions: one for the increasing phase of production and a sum for the decreasing phases. To illustrate the model, we used four data sets from two pairs of individuals.For these data, the model consisted of an increasing phase and a single decreasing phase of production: yt=m k1(1-e-t1+e-t)-m(k1-k2)(1+e-t1+e-(t-c2))where yt is egg production at week t, m is maximum production during a specific time interval, k1 is proportion of maximum production for the increasing phase, k2 is proportion of maximum production for the decreasing phase, and c2 is point of inflection from the upper level of the increasing phase to the lower level of the decreasing phase; thus, c2 is a measure of persistency of egg production.For one pair of individuals, production was about 88% of maximum (k1) for the increasing phase and about 76% of maximum (k2) for the decreasing phase. For the other pair, production was about 91% of maximum (k1) for the increasing phase and about 75% of maximum (k2) for the decreasing phase. Persistency (c2) was about 25 wk for one pair and about 28 wk for the other. Predicted total 52-wk production was within one or two eggs of actual production.The secondary objective was to improve estimation of model parameters by summarizing egg production data by 1-wk, 2-wk, or 4-wk intervals and by using cumulative egg production instead of weekly production. For weekly production, estimates of parameters changed only slightly, as intervals increased from 1 wk to 2 wk or to 4 wk. Predicted total 52-wk production, however, decreased up to five eggs as interval increased from 1 wk to 4 wk.For cumulative egg production by time t, Yt, the model was Yt=7k1[2ln(1+et3)-t]-7(k1-k2)[(1+e-22)Ln(ec2+et1+ecc)-te-c2].For cumulative production, estimates of parameters changed only slightly, if at all, as intervals increased from 1 wk to 4 wk. Predicted 52-wk production, however, approached the actual number as interval increased from 1 wk to 4 wk.Prediction of annual (52-wk) egg production based on part-record production for only the first 22 wk might lead to over-prediction because persistency of production lasted longer than the part record. Genetic gain from selection to improve annual production, therefore, might be increased if selection accounted for persistency of production and for the multiphasic shape of the individual egg production curve, and if data were summarized by 4-wk intervals and cumulated.

Intra- and interspecies comparison of energy flow in North Atlantic flatfish species by means of dynamic energy budgets

The quantitative aspects of growth and reproduction in four flatfish species (plaice, flounder, dab, sole) in terms of energy flow are described on the basis of a dynamic energy budget (DEB theory). This theory consists of general assumptions about energy uptake, storage and utilisation and describes an individual by two state variables: structure and reserve, whereby body size exerts its influence through the ratio between surface area and volume. Comparison between model estimates and field data shows that the DEB model successfully describes the energetics of growth and reproduction in a number of flatfish species. Differences between species could be captured in the same model using different parameter values. Intraspecific differences in growth between males and females are mainly caused by differences in maximum surface area-specific ingestion rates. Differences between species are reflected in the surface area-specific maximum ingestion rate, the energy partitioning over growth and reproduction, and in egg volume. According to these parameters at 283 K (10°C), the species could be ranked as follows: surface area-specific maximum ingestion rate (W m −2) plaice: 56.6; flounder: 54.5; sole: 45.1 and dab: 36.1 W m −2. Fraction of energy allocated to reproduction (–): flounder: 0.35; plaice: 0.15; dab: 0.15 and sole 0.10. As a consequence of these differences in surface area-specific maximum ingestion rate and in the fraction of utilised energy allocated to reproduction, the gonad masses (g) of females of 0.5 kg wet mass differ considerably: flounder: 149 g; plaice: 86 g; sole: 70 g; and dab: 69 g. However, due to differences in egg size between species, the potential annual egg production shows a completely different pattern: dab: 2200 10 3; flounder: 1560 10 3; sole: 343 10 3 and plaice: 130 10 3 eggs.

An application of the annual egg production method to estimate the spawning biomass of cod (Gadus morhua L.), plaice (Pleuronectes platessa L.) and sole (Solea solea L.) in the Irish Sea

The spawning biomass of cod (Gadus morhua), plaice (Pleuronectes platessa) and sole (Solea solea) in the Irish Sea in 1995 was estimated by means of the annual egg production method (AEPM). The area surveyed corresponded to ICES assessment area VIIa. This paper describes the sampling design, methods of analysis, estimates of biomass, and sources of error in the estimates. Estimates are also presented for spatially separated spawning grounds of cod and plaice in the eastern and western Irish Sea, the first time that information at this scale has been available. The AEPM estimates of spawning biomass of cod, sole and plaice exceeded the corresponding estimates from Virtual Population Analysis of data from commercial fisheries and trawl surveys by factors of 2.3, 2.7 and 4.3 respectively. The sources of these large discrepancies are not yet resolved.

Estimating the abundance and egg production of spawning winter flounder (Pseudopleuronectes americanus) in the Niantic River, CT for use in the assessment of impact at Millstone Nuclear Power Station

Abstract The winter flounder is a coastal flatfish with spawning populations associated with specific estuaries or coastal areas. Because of its stock structure, this species is susceptible to localized impacts, including power plant entrainment of larvae. Winter flounder rank second in fish larvae entrained at the Millstone Nuclear Power Station (MNPS), located on Long Island Sound in Waterford, CT, USA. Because of its importance to the state’s fisheries, the population spawning in the nearby Niantic River was selected for impact assessment studies in the early 1970s. Northeast Utilities has consistently monitored annual abundance of adult spawners, characterizing relative abundance by trawl catch-per-unit-effort (CPUE) and absolute abundance using mark and recapture data with the Jolly model for demographically open populations. Trends in these two independent but highly correlated indices provide short-term assessments of winter flounder abundance. Abundance of winter flounder peaked in the early 1980s, but as fishing mortality increased to high levels in the late 1980s, their numbers declined thereafter and presently are very low. Information on sex ratio, length-frequency distribution, and spawning condition allow for calculation of annual egg production using a length-fecundity relationship. This forms the basis for estimating production loss due to larval entrainment, which is used as input to a long-term assessment model of power plant impact, discussed in an accompanying paper ( Lorda et al., 2000 : Lorda, E., Danila, D.J., Miller, J.D., 2000. Application of a population dynamics model to the probabilistic assessment of CWIS effects of Millstone Nuclear Power Station (Waterford, CT) on a nearby winter flounder spawning stock. Environmental Science & Policy 3, S471–S481).

Longevity and resilience of Chesapeake Bay striped bass

Since the early 1960s, the Chesapeake Bay striped bass population has undergone a large cycle of abundance, recovering to record levels during the 1990s. Changes in age structure over this period were examined to determine contributions of old females (>13 yr) to the recovery. In 1992, in a sample of large female striped bass, 10 yr of absent year classes (1972-1981) were observed corresponding to a period of recruitment overfishing. Fishery-independent stock assessments conducted 1985-1990 by Maryland Department of Natural Resources indicated that old females, while present in small numbers, made relatively small contributions to annual egg production during the period of recovery. Abundances, weighted for age-specific fecundity, indicated that older fish were probably the most important contributors to recruitment throughout the 1970s and early 1980s. Egg production after 1986 was principally contributed by young females, those produced after 1981. Demographic analysis also supports the view that a Maryland fishing moratorium designed to protect year classes after 1981 stimulated recovery. Longevities of >30 yr documented in this study suggest that striped bass populations can persist during long periods of poor recruitment due to a long reproductive lifespan. Longevity may have also conferred resiliency against an extended period of recruitment overfishing in the Chesapeake Bay

Effects of winter severity on life history patterns and population dynamics of Hydrobia ventrosa (Gastropoda: Prosobranchia).

Interannual variations in population structure and life history patterns of the mudsnail Hydrobia ventrosa were investigated in relation to winter seventy in a windflat of the Wismar Bay (southwestern Baltic Sea). The population structure of H. ventrosa was studied in the field from 1995 to 1999 and egg production of different year classes was measured in the laboratory during the reproductive season of 1997. Abundance of H. ventrosa ranged between 7,000 and 150,000 ind./m 2 with density fluctuations according to the abundance of juvenile snails. The abundance of adult mudsnails remained remarkably constant with a mean density of about 25,000 ind./m 2 . Recruitment occurred between June and November with two peaks of reproduction in 1995 and a single one in the following years. Accordingly, the year class born in 1995 consisted of two cohorts, whereas the following year classes consisted of a single cohort only. H. ventrosa reached a maximum life span of about two years and a maximum shell height of about 3.5 mm. Shell growth was similar between year classes. According to laboratory experiments, about 95 % of the total annual egg production was contributed by 1-year-old females and <5 % of the eggs were laid by females which had overwintered twice and by young-of-the-year. Egg production decreased from 1.0 eggs female -1 day -1 in spring to less than 0.5 eggs female -1 day -1 in autumn. The annual production of recruits was higher after the moderate winter of 1996/97 than after the mild winters of 1994/95 and 1997/98. The cold winter of 1995/96 resulted in a delay of the reproductive season in 1996 and it is suggested that this delay restricted recruitment.

Egg Size and Annual Egg Production by Female Desert Tortoises (Gopherus agassizii): The Importance of Food Abundance, Body Size, and Date of Egg Shelling

We studied egg production in two Californian populations of desert tortoises, (Gopherus agassizii) in 1992 and 1993. One population inhabited the Desert Tortoise Research Natural Area (DTNA) in the western Mojave Desert, where most of the rain falls in the winter. The second population lived near Goffs, in the eastern Mojave, where annual precipitation is divided more evenly between winter and sum- mer. Due to El Niio conditions, heavy winter rains fell at both sites in both years (1991-1992 and 1992- 1993). Consequently, the biomass of spring annuals and annual egg production by tortoises were high in both years at both sites. There were no differences in reproductive output between years so we pooled data for both years to examine the relationship between egg-laying parameters (clutch size and frequency, annual egg production, egg size, etc.) and female size. Variation in annual egg production was due mainly to variation in clutch size, not clutch frequency. Annual egg production per female was lower at DTNA than at Goffs, because some adult females at DTNA did not produce eggs in some years. Females that did lay eggs produced the same number of eggs per year at both sites, even though females at Goffs were smaller (midline carapace length = 214 mm) than females at DTNA (MCL = 234 mm). Despite correction for these body size differences, the eggs produced at Goffs were smaller in all dimensions than eggs produced at DTNA. Smaller eggs and presumably smaller neonates may be related to the greater predictability of sum- mer rain and consequent greater food supply for emergent hatchlings at Goffs. For adult females, food supply probably limits reproduction only during drought years. How can individual females vary their annual reproductive output? Our more extensive data for DTNA tortoises showed that larger females pro- duced larger clutch sizes. In addition, by statistically removing the effects of body size we showed that larger clutches contained smaller eggs. Moreover, larger females produced eggs earlier in the year giving them a better opportunity to produce a second clutch that year. Thus, timing of first clutch was important Still, much of the variation in reproductive output was not explained. Other characteristics of individuals (e.g, age, genetics, physiological maturity, home range quality, or forage selection) may explain some of the variation in reproductive output

Estimation of the spawning stock biomass of blue grenadier (Macruronus novaezelandiae) off western Tasmania based upon the annual egg production method

Egg production of the blue grenadier, Macruronus novaezelandiae, spawning stock off western Tasmania was surveyed from June through September in 1994 and 1995. In each year, daily egg production rates were calculated for each of three surveys and a normal curve was fitted to estimate annual egg production. The CV for the egg production estimate for the survey at the peak of the 1995 season was 14%. Daily egg mortality was not significant in any survey, but a value of 5% was assumed. The spawning biomass of blue grenadier on the west coast of Tasmania was estimated to be between 83 660 and 100 073 t in 1994 and between 59 727 and 71 376 t in 1995. Confidence limits of the estimates were obtained by a bootstrap where the highly skewed egg density data were resampled. Biomass was approximately inversely proportional to incubation time. Increases or decreases in mortality resulted in slightly smaller increases or decreases of biomass respectively. Uncertainty of the sex ratio between spawning and non-spawning periods caused the largest variation in biomass estimate (~30%). The proportion of the population that spawns each year remains a further uncertainty in the estimate of total stock biomass.

Variability in Stage I egg production and settlement of plaice Pleuronectes platessa, on the west side of the Isle of Man, Irish Sea

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 189:241-250 (1999) - doi:10.3354/meps189241 Variability in Stage I egg production and settlement of plaice Pleuronectes platessa on the west side of the Isle of Man, Irish Sea Richard D. M. Nash*, Audrey J. Geffen School of Biological Sciences, University of Liverpool, Port Erin Marine Laboratory, Port Erin, Isle of Man IM9 6JA, United Kingdom *E-mail: rdmnash@liv.ac.uk ABSTRACT: The variability in Stage I egg production and subsequent settlement of plaice Pleuronectes platessa L. on the west side of the Isle of Man, Irish Sea, was investigated over the period 1992 to 1998. This small spawning ground contributed approximately 0.6% of the total plaice egg production in the northern Irish Sea for 1995. The timing of peak egg production varied between years from approximately the middle of February to the end of March. The timing of peak egg production was related to the mean autumnal water temperature, with earlier spawning in warmer years. Egg production on the west side of the Isle of Man in 1995 was earlier than in the eastern Irish Sea, probably reflecting the slightly warmer water conditions in the central Irish Sea. The estimated Stage I egg production varied considerably between years, differing by a factor of 2.8 over all years. There was a positive relationship between the annual egg production and the numbers of individuals settling in Port Erin Bay. Interannual variation in abundance was greater at settlement than in either Stage I eggs or the size of the juvenile population in July. Higher inter-annual variability in the pelagic phase is dampened during the nursery ground phase. KEY WORDS: Irish Sea · Plaice · Egg production · Settlement · Variability Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 189. Publication date: November 26, 1999 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1999 Inter-Research.

Spatiotemporal modelling for the annual egg production method of stock assessment using generalized additive models

Generalized additive models (GAMs) are used to model the spatiotemporal distribution of egg density as a function of locational and environmental variables. The main aim of using GAMs is to improve precision of egg abundance estimates needed for the annual egg production method. The application of GAMs requires a survey design with good coverage in space and time. If the only results available are from less optimal survey designs, they can be improved by using historical data for spawning boundaries. The method is applied to plankton egg survey data of Atlantic mackerel (Scomber scombrus) in 1995. The GAM-based method improves the precision of estimates substantially and is also useful in explaining complex space-time trends using environmental variables.

Distribution of hoki (Macruronus novaezelandiae) eggs, larvae, and adults off Westland, New Zealand, and the design of an egg production survey to estimate hoki biomass

The winter spawning aggregations of hoki (Macruronus novaezelandiae) off the Westland coast, South Island, support New Zealand s largest trawl fishery. The distribution and abundance of hoki eggs, larvae, and adults from ichthyoplankton and acoustic surveys made during the period 1978-1993 were used to describe the location and timing of hoki spawning off Westland. Hoki spawned primarily in south Westland, around Hokitika Canyon, and south along the outer shelf and slope to Cook Canyon, although spawning biomass appeared to increase in north Westland later in the season. Older stage hoki larvae occurred shoreward of eggs and newly hatched larvae, suggesting onshore advection. The data were used to designate spatial and temporal egg sampling strata that significantly increased egg abundance estimate precision. The egg data were used to estimate annual egg production and, combined with data on fecundity and recruited proportion spawning, to estimate virgin biomass. The historical biomass estimate (1.48 million tonnes, CV = 29.4%) was probably biased down because the plankton tows were too shallow. It appears that a future egg production survey, using appropriate plankton sampling depths, could provide a biomass estimate of Westland spawning hoki sufficiently accurate and precise for management purposes.

Spatiotemporal modelling for the annual egg production method of stock assessment using generalized additive models

Spatiotemporal modelling for the annual egg production method of stock assessment using generalized additive models