Estimating the dynamics of spawning aggregations using biological and fisheries data

Acoustic surveys can provide accurate estimates of biomass at a particular location at a point in time, but provide a negatively biased estimate of the total spawning population unless the proportion of fish that are unavailable to the survey is accounted for. Changes to the ages and maturity stages of fish caught during the spawning season is evidence for turnover of fish during spawning and, along with information on relative abundance, provides a basis for estimating turnover rates. A model is therefore developed that tracks the numbers of males and females by age as they arrive on the spawning grounds, initiate spawning, complete spawning and leave the spawning grounds. This model can be used to determine the proportion of the spawning biomass on the spawning grounds over the spawning season. It is applied to data for blue grenadier, Macruronus novaezelandiae, off western Tasmania, Australia. The results can be used to estimate the average proportion of the population available to an acoustic survey, although this estimate is not likely to be very precise, owing to the high between-year variation in arrival times. However, the model provides a quantitative estimate of turnover rate that was previously not available, and is a rigorous basis for estimating turnover for stock assessment.

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Spawning Dynamics of Golf of St. Lawrence Herring (Clupea harengus)

Canadian Journal of Fisheries and Aquatic Sciences ◽

10.1139/f89-258 ◽

1989 ◽

Vol 46 (12) ◽

pp. 2085-2094 ◽

Cited By ~ 6

Author(s):

Timothy C. Lambert ◽

Shoukry N. Messieh

Keyword(s):

Stock Assessment ◽

Sampling Procedure ◽

Clupea Harengus ◽

Spawning Season ◽

Biological Information ◽

Age Classes ◽

Spawning Grounds

Mean day of arrival of spawning herring (Clupea harengus) in the Gulf of St. Lawrence was calculated for different length groups by region and season. During the spawning season of both spring and autumn groups, herring arrived and deposited eggs on spawning grounds in decreasing order of age and length. Spawning bed surveys at two locations confirmed batch depositions of eggs which were correlated with the presence of dominant age-classes within the spawning population. Due to limitations of the port sampling procedure for collection of biological information routinely used in herring stock assessment, some length groups were underrepresented. This could result in the underestimation of the abundance of recruiting year-classes.

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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

Canadian Journal of Fisheries and Aquatic Sciences ◽

10.1139/f98-048 ◽

1998 ◽

Vol 55 (7) ◽

pp. 1682-1694 ◽

Cited By ~ 1

Author(s):

John R Zeldis ◽

Rob C Murdoch ◽

Patrick L Cordue ◽

Mike J Page

Keyword(s):

New Zealand ◽

Egg Production ◽

Abundance Estimate ◽

Trawl Fishery ◽

Spawning Aggregations ◽

Biomass Estimate ◽

Acoustic Surveys ◽

Newly Hatched Larvae ◽

Estimate Precision ◽

Spawning 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.

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REPRODUCTIVE ASPECTS OF SCALLOPED PERCHLET, Ambassis nalua (HAMILTON, 1822) IN PABEAN BAY INDRAMAYU, WEST JAVA

Jurnal Ilmu dan Teknologi Kelautan Tropis ◽

10.28930/jitkt.v9i1.17921 ◽

2017 ◽

Vol 9 (1) ◽

pp. 113

Author(s):

Nisha Desfi Arianti ◽

M.F. Rahardjo ◽

Ahmad Zahid

Keyword(s):

Sex Ratio ◽

Sampling Period ◽

Spawning Season ◽

West Java ◽

Fish Samples ◽

Length Range ◽

Males And Females ◽

Mature Fish ◽

First Maturity ◽

Somatic Index

ABSTRACTScalloped perchlet, Ambassis nalua, is one of fishes in Pabean Bay, Indramayu. This research aims to determine the reproductive aspects of Ambassis nalua in Pabean Bay Indramayu including sex ratio, spawning season, first maturity, fecundity and spawning pattern. Fish samples were collected by trap net and trammel net at three sites in Pabean Bay from April to October 2015. A total of 424 of A. nalua were caught, consist of 114 males and 310 females; with total length ranged from 38.04 to 112.63 mm and total weight ranged from 0.37 to 25.44 g. Sex ratio of mature fish was 1:1.9. The mature males and females were found in every month of sampling period. The gonado-somatic index (GSI) ranged from 0.40 to 0.83 and 2.36 to 4.54 for male and female, respectively. The peak of spawning season was found in September. The first maturity (Lm50) for male and female were 79.17 mm and 91.25 mm, respectively. The fecundity varied from 3,451–32,465 eggs. Egg diameter distribution shows that spawning pattern of A. nalua was batch spawner. Keywords: Ambassis nalua, spawning season, sex ratio, reproduction

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Simulation of the estimation of ageing bias inside an integrated assessment of canary rockfish using age estimates from a bomb radiocarbon study

Marine and Freshwater Research ◽

10.1071/mf07010 ◽

2007 ◽

Vol 58 (10) ◽

pp. 905 ◽

Cited By ~ 5

Author(s):

Ian J. Stewart ◽

Kevin R. Piner

Keyword(s):

Functional Form ◽

Stock Assessment ◽

Small Sample Size ◽

Small Sample ◽

Assessment Model ◽

Bomb Radiocarbon ◽

Interval Width ◽

Functional Forms ◽

Age Model ◽

Spawning Biomass

The stock of canary rockfish off the west coast of the continental US is currently assessed using an integrated statistical catch-at-age model. The functional form of an ageing bias detected in production ageing (large numbers of ages read for use in stock assessment) from a bomb radiocarbon study with small sample size (n = 16) was estimated externally and used to adjust the age data in the most recent stock assessment. Using simulation methods, the present study evaluated whether integrating the estimation of the ageing bias inside the assessment model would (1) influence the uncertainty in assessment results and (2) improve our ability to differentiate between competing functional forms (linear, linear with intercept and jointed) for specifying the ageing bias. Internal estimation of the ageing bias relationship increased the approximate 95% confidence interval width about the spawning biomass estimate by 1–10% depending on the functional form assumed. The assessment model was not able to reliably distinguish between all competing functional forms of the ageing bias tested, even with increased radiocarbon sample sizes. However, significant under-ageing at the youngest ages was found to be inconsistent with other sources of data in the assessment model. The question of ageing bias form remains important because it had moderate effects on estimates of spawning biomass and assessment model uncertainty.

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Histological analysis invalidates macroscopically determined maturity ogives of the Kattegat cod (Gadus morhua) and suggests new proxies for estimating maturity status of individual fish

ICES Journal of Marine Science ◽

10.1016/j.icesjms.2005.09.001 ◽

2006 ◽

Vol 63 (3) ◽

pp. 485-492 ◽

Cited By ~ 48

Author(s):

F. Vitale ◽

H. Svedäng ◽

M. Cardinale

Keyword(s):

Gadus Morhua ◽

Histological Analysis ◽

Spawning Season ◽

Age Classes ◽

Data Set ◽

Histological Techniques ◽

Stock Biomass ◽

Spawning Stock ◽

Correct Estimation ◽

Spawning Biomass

Abstract Assessment and management of fish populations currently rely on correct estimation of the spawning-stock biomass (SSB), which is based on accurate maturity ogives of the population. Although maturity ogives are usually calculated through macroscopic evaluation of the gonads, histology is generally considered to be more accurate. Here we show that the macroscopic analysis consistently overestimates the proportion of mature females for all age classes in Kattegat cod. The resulting bias showed minimum values for all age classes about a month before the spawning season. Consequently, estimation of the incidence of maturation in females several months before or after the spawning season can only be accurate using histological techniques. Further, the observed bias was used to reconstruct a historical data set of maturity ogives of Kattegat cod. The results showed that female spawning biomass (FSB) might have been overestimated by up to 35%. However, as histological analysis is considered a laborious procedure, proxies of maturity status were sought. It was indicated that the gonadosomatic and hepatosomatic indices may serve as robust proxies for discriminating mature females from immature, thus greatly enhancing the accuracy of the macroscopic maturity evaluation of cod gonads when histological analysis is lacking.

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Hierarchical model-based estimation of population growth curves for redfish (Sebastes mentella and Sebastes fasciatus) off the Eastern coast of Canada

ICES Journal of Marine Science ◽

10.1093/icesjms/fsw195 ◽

2016 ◽

Vol 74 (3) ◽

pp. 687-697 ◽

Cited By ~ 5

Author(s):

Noel G. Cadigan ◽

Steven E. Campana

Keyword(s):

Population Growth ◽

Stock Assessment ◽

Growth Curves ◽

Eastern Coast ◽

Short Term ◽

Large Dataset ◽

Production Models ◽

Sources Of Variation ◽

Males And Females ◽

Sebastes Mentella

Northwest Atlantic (NWA) redfish (Sebastes mentella and Sebastes fasciatus) stocks are currently assessed using survey indicators and age-aggregated production models rather than age-based models because routine age readings are not available due to the difficulty in obtaining reliable measurements for these fish. However, recruitment is highly variable for redfish species so age-aggregated production models are not a good approach to provide short-term harvest advice. Recently a relatively large dataset of validated age readings was published that provide a good basis to model growth and its variability [i.e. population growth curve (PGC)]. In this article we propose a hierarchical random effects growth model that includes between-individual variation to estimate PGCs for 10 NWA redfish stocks and for males and females separately. These growth curves are required to develop age-based stock assessment models. External estimates of measurement error in length and age are included in our model to separate these sources of variation from the PGC variability. The hierarchical approach leads to more realistic growth curves than if each stock and sex are modelled separately. Model results indicated that S. mentella usually grow to larger sizes than S. fasciatus and that females of both these species grow to larger sizes than males. There was little evidence of a change in growth rates over time.

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Reproductive Biology and Fishery-Related Characteristics of the Malabar Grouper (Epinephelus malabaricus) Caught in the Coastal Waters of Mafia Island, Tanzania

Journal of Marine Biology ◽

10.1155/2013/786589 ◽

2013 ◽

Vol 2013 ◽

pp. 1-11 ◽

Cited By ~ 6

Author(s):

Lydia Gaspare ◽

Ian Bryceson

Keyword(s):

Reproductive Biology ◽

Spawning Season ◽

Small Scale ◽

Northeast Monsoon ◽

Independent Research ◽

Spawning Aggregations ◽

Gonadal Histology ◽

Management And Conservation ◽

Sexually Mature ◽

Epinephelus Malabaricus

The reproductive biology and fishery-related characteristics of the Malabar grouper (Epinephelus malabaricus) (Bloch and Schneider, 1801) specimens were investigated. The size of females ranged from 25 to 113 cm total length (LT), with 50% sexually mature at 79 cmLT, and the males (97 cm to 114 cmLT) were larger than the females. Due to the sex ratios and size distribution of the sample, it appeared that the groupers change sex between 97 and 113 cmLT. However, the gonadal histology data lacked specimens in the transitional stage. The spawning peak occurred in November, as defined by the presence of ripe females, and the spawning season lasted from September to February. The size of the fish correlated positively with the water depth at capture, which is also related to oxygen levels in deep water being more favourable for larger fish. Larger specimens (>100 cmLT) were targeted by fishers between December and February, when the northeast monsoon coincides with calmer weather and the spawning season. Fishers were interviewed, and observations were made on fishing gear, vessels, and grounds. There was no indication that small-scale fishers targeted spawning aggregations; therefore, fisheries independent research is recommended in order to verify the time, location, and behaviour of the spawning of Malabar groupers for management and conservation purposes.

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Small-scale spatial and temporal patterns in spawning of Atlantic cod (Gadus morhua) in coastal Newfoundland waters

Canadian Journal of Fisheries and Aquatic Sciences ◽

10.1139/f00-026 ◽

2000 ◽

Vol 57 (5) ◽

pp. 1011-1024 ◽

Cited By ~ 45

Author(s):

Gareth L Lawson ◽

George A Rose

Keyword(s):

Gadus Morhua ◽

Atlantic Cod ◽

Temporal Patterns ◽

Small Scale ◽

Spatial And Temporal Patterns ◽

Spawning Grounds ◽

Acoustic Surveys ◽

Placentia Bay ◽

June July ◽

Timing Of Spawning

Acoustic surveys were used to locate coastal Atlantic cod (Gadus morhua) spawning grounds and examine spatial and temporal patterns of spawning in Placentia Bay, Newfoundland, Canada. The same three grounds were used in 1997 and 1998 (Bar Haven in the inner bay and Cape St. Mary's and Oderin Bank in the outer bay). Grounds had densities >0.1 fish·m-2 over scales of 100 m and >13% of mature females in spawning condition. Ground use and spawning timing differed between years. Mean spawning female densities were highest at Cape St. Mary's in 1997 (1.6 × 10-2 fish·m-2) and Oderin Bank in 1998 (1.0 × 10-2 fish·m-2). At all grounds, spawning peaked earlier in 1997 (April) than in 1998 (June-July). In both years, cod spawned at sub- or near-zero temperatures. "Spawning columns" were observed at sites and times having high densities of spawning females. Sex ratios suggested that males arrived first and stayed later, while females followed when ready to spawn, accompanied by juveniles. Older females spawned earlier and later than younger females. Peaks in density of spawning females and the proportion of females spawning did not coincide. Hence, the location and timing of spawning cannot be quantified solely from the proportions of females in spawning condition.

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Probability of stochastic depletion: an easily interpreted diagnostic for stock assessment modelling and fisheries management

ICES Journal of Marine Science ◽

10.1093/icesjms/fsu127 ◽

2014 ◽

Vol 72 (2) ◽

pp. 428-435 ◽

Cited By ~ 14

Author(s):

James T. Thorson ◽

Olaf P. Jensen ◽

Ray Hilborn

Keyword(s):

Stock Assessment ◽

Biological Effects ◽

Decision Support Tool ◽

Maximum Sustainable Yield ◽

Support Tool ◽

Management Actions ◽

Stock Assessments ◽

Harvest Control Rule ◽

Recruitment Variability ◽

Spawning Biomass

Abstract Marine fish populations have high variation in cohort strength, and the production of juveniles (recruitment) may have persistent positive or negative residuals (autocorrelation) after accounting for spawning biomass. Autocorrelated recruitment will occur whenever average recruitment levels change between oceanographic regimes or due to predator release, but may also indicate persistent environmental and biological effects on shorter time-scales. Here, we use estimates of recruitment variability and autocorrelation to simulate the stationary distribution of spawning biomass for 100 real-world stocks when unfished, fished at FMSY, or fished following a harvest control rule where fishing mortality decreases as a function of spawning biomass. Results show that unfished stocks have spawning biomass (SB) below its deterministic equilibrium value (SB0) 58% of the time, and below 0.5SB0 5% of the time on average across all stocks. Similarly, stocks fished at the level producing deterministic maximum sustainable yield (FMSY) are below its deterministic prediction of spawning biomass (SBMSY) 60% of the time and below 0.5SBMSY 8% of the time. These probabilities are greater for stocks with high recruitment variability, positive autocorrelation, and high natural mortality—traits that are particularly associated with clupeids and scombrids. An elevated probability of stochastic depletion, i.e. biomass below the deterministic equilibrium expectation, implies that management actions required when biomass drops below a threshold may be triggered more frequently than expected. Therefore, we conclude by suggesting that fisheries scientists routinely calculate these probabilities during stock assessments as a decision support tool for fisheries managers.

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Reducing retrospective patterns in stock assessment and impacts on management performance

ICES Journal of Marine Science ◽

10.1093/icesjms/fsx159 ◽

2017 ◽

Vol 75 (2) ◽

pp. 596-609 ◽

Cited By ~ 8

Author(s):

Cody S Szuwalski ◽

James N Ianelli ◽

André E Punt

Keyword(s):

Stock Assessment ◽

Reference Points ◽

Natural Mortality ◽

Time Varying ◽

Management Performance ◽

Population Processes ◽

True Time ◽

Management Advice ◽

Spawning Biomass ◽

Over Time

Abstract Retrospective patterns are consistent directional changes in assessment estimates of biomass in a given year when additional years of data are added to an assessment, and have been identified for a number of exploited marine stocks. Retrospective patterns are sometimes reduced by allowing population processes to vary over time in an assessment, but it is unclear how this practice influences management performance. We simulated stocks in which retrospective patterns were induced by forcing natural mortality, selectivity, or growth to vary over time. We then evaluated the impacts of reducing retrospective patterns by allowing population processes to vary in the assessment. In general, allowing selectivity, natural mortality, and growth to vary in the assessment decreased the magnitude of retrospective patterns in estimated spawning biomass, regardless of whether the true time-varying process was allowed to vary. However, the resulting reference points and management advice were sometimes drastically in error when a process other than the true time-varying process was allowed to vary, and these errors resulted in under-utilizing or over-exploiting the stock. Given the potential for error, identifying the important population processes that vary over time when addressing retrospective patterns should be a priority when providing management advice and may require increased longitudinal life history studies.

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