Estimates of biomass and sustainable catch levels for the
Eastern Jack Mackerel stock in the Small Pelagic Fishery
13 March 2013
Introduction
This paper provides summary information that may assist the Small Pelagic Fishery
Resource Assessment Group (SPFRAG) in making recommendations on sustainable
catch levels in the Small Pelagic Fishery (SPF). This paper may also assist
stakeholders to better understand scientific information regarding Jack Mackerel
(east) population abundance including stock assessments, ecosystem simulations and
catch data. Links to the source documents are provided at the end of this summary.
Estimating spawning biomass using the results of a Daily Egg
Production Method (Neira, 2011)
A common way of estimating population sizes for small pelagic species is a ‘Daily
Egg Production Method’ (DEPM) survey. The DEPM uses the number of eggs
collected in a sample area to estimate to adult populations of fish (spawning biomass).
The study conducted by Neira (2011) used DEPM to estimate the spawning biomass
of Jack Mackerel (east).
The spawning biomass estimate varies depending on which statistical method is used.
Neira (2011) used the following two statistical methods to translate the raw data into
an estimate of population size:
 traditional least squares non-linear regression (NLS) which gave an estimate
of adult population size of 115,000 – 169,000 tonnes; and
 a generalised linear model (GLM) using a negative binomial error distribution
which gave an estimate of adult population size of 130,000 – 134,000 tonnes.
Neira (2011) used this information to estimate the spawning biomass of Jack
Mackerel (east) at between 115,000 – 169,000 tonnes, which gave a mid-range
estimate of approximately 140,000 tonnes.
Re-analysis of mean daily egg production in Jack Mackerel east (Lyle
et al. 2012)
The Institute of Marine and Antarctic Studies (IMAS) undertook a re-analysis of the
reported egg density data using a range of alternative model fitting methods suggested
in the literature. Specifically IMAS followed Ward et al. (2011) who compared
several methods and their application in Australian sardine assessments.
This analysis has highlighted how the choice of model to describe the egg mortality
relationship can significantly influence the estimation of spawning biomass. The
report recommended that the SPFRAG should review the data available on SPF
species along with the DEPM literature to develop recommendations on preferred
methods for estimating each of the DEPM input parameters.
Comments on using daily egg production method to estimate the
spawning biomass of Jack Mackerel east (Lo, 2013)
Lo (2013) evaluates the validity and suitability of the Neira (2011) assessment and
provides comment on the evaluation conducted by Wadsley (2012) and Lyle et al.
(2012). Lo (2013) concludes that the approach adopted in the Neira (2011) assessment
was reasonable; however, other methods of assessment produced lower estimates of
biomass.
Lo (2013) also looked at the seven different ways of analysing raw data collected in a
DEPM to give the estimate of adult populations, as summarised in a paper by Lyle et
al. (2012). These results are shown in the table below, the two highlighted methods
were used in Neira (2011).
Statistical
method
NLS
GLM (negative
binomial error)
GLM1
GLM2
GLM3
GLM4
Log-linear (with
bias correction)
Adjusted
mean egg
production
(Po)
Method 1
4.93
3.92
Estimate of
spawning
biomass
Estimate of
spawning
biomass
168,817
134,218
Adjusted
mean egg
production
(Po)
Method 2
3.36
3.80
4.86
4.00
3.85
0.62
0.84
166,420
136,971
131,835
21,231
28,764
3.37
3.40
3.61
0.49
0.61
115,285
116,311
123,495
16,763
20,867
114,943
130,082
The seven methods in the table above fall into two distinct biomass clusters. The
estimates by Neira (2011) compare favourably with the GLM 1 – 3 methods but are
substantially higher than estimates based on the GLM4 and log-linear models (Lyle et
al. 2012). The spawning biomass estimate (140,000 tonnes) used in 2012 as the basis
for setting the Total Allowable Catch (TAC) for Jack Mackerel (east) is mid-range of
the high and low spawning biomass estimates found in the Neira (2011) assessment.
Ecosystem modelling results
Quantitative ecosystem modelling can also provide an estimate of species population
size. Fulton (2013) used two ecosystem modelling platforms (Atlantis and Ecopath
with Ecosim) to model the south eastern waters of Australia. These models were used
to explore the plausibility of a range of alternative spawning biomass estimates for the
stock of jack mackerel in south eastern Australia. Both models indicated that values of
20,000 – 30,000 tonnes are ecologically implausible and are too low to be consistent
with the food-web observations represented in the model. In contrast spawning
biomasses of 130,000 – 170,000 tonnes are plausible given existing data sets and
ecological understandings of the system.
Historical catches of Jack Mackerel
The fishing history for Jack Mackerel off the east coast of Tasmania provides an
indication of stock size and potential productivity. Over 100,000 tonnes was taken
over three years during the 1980s and catches during the 1990s averaged over 10,000
tonnes per annum. To sustain catches of this magnitude, the unfished biomass of Jack
Mackerel must have been well in excess of 100,000 tonnes (Buxton et al. 2012). This
supports a view that the two much lower estimates in the table above are less plausible
than the cluster of higher estimates.
Other research
Buxton et al. (2012) found that the recent scientific guidelines established by the
Lenfest Forage Fish Task Force on management of small pelagic fisheries (Pickitch et
al. 2012) provide rules to minimise food-web impacts on predators, including the
effects of localised depletion, based on the experience of more than 20 ecosystems
worldwide. The TACs set in the SPF in 2012 were more conservative than those
recommended under these rules.
Summary
AFMA routinely uses a range of techniques to review and validate the scientific
methods that form the basis for TAC setting in Commonwealth fisheries. Using the
information available through historical catch data, ecosystem modelling and testing
of statistical methods, AFMA remains confident that the science used to support TAC
setting in the SPF is sound. There are uncertainties, as there always are, but these are
recognised and the TAC is being applied in the context of close monitoring, further
analysis and an adaptive cycle of assessment and management decisions.
References
Buxton, C, Begg, G, Lyle, J, Ward, T, Sainsbury, K, Smith, T & Smith D 2012, The
Commonwealth Small Pelagic Fishery: General Background to the scientific issues.
IMAS, Hobart.
http://www.afma.gov.au/wp-content/uploads/2010/06/SPF-discussion-paperFINAL.pdf
Fulton, EA 2013, Simulation analysis of Jack mackerel Stock Sizes: Ecosystem model
based plausibility study, CSIRO, Hobart.
http://www.afma.gov.au/wpcontent/uploads/2013/03/Fulton_Jack_Mackerel_stock_size_report.pdf
Lo, N 2013, Comments on using daily egg production method to estimate the
spawning biomass of jack mackerel, trachurus declivis, off south-eastern Australia
http://www.afma.gov.au/wp-content/uploads/2013/03/Report_Lo2.pdf
Lyle, J, Hartmann, K, Buxton, C & Gardner, C 2012, Re-analysis of mean daily egg
production in jack mackerel, IMAS, Hobart.
http://www.afma.gov.au/wp-content/uploads/2012/08/IMAS_reanalysis-ofNeira2011.pdf
Neira, FJ 2011, Application of daily egg production to estimate biomass of jack
mackerel, Trachurus declivis – a key fish species in the pelagic ecosystem of southeastern Australia. IMAS, Hobart.
http://www.afma.gov.au/wp-content/uploads/2012/08/1.-Application-of-DEPM-toEstimate-Biomass-of-Jack-Mackerel-Neira-2011-1.pdf
Pikitch, E, Boersma, PD, Boyd, IL, Conover, DO, Cury, P, Essington, T., Heppell,
SS, Houde, ED, Mangel, M., Pauly, D., Plagányi, É, Sainsbury, K & Steneck, RS
2012, Little Fish, Big Impact: Managing a Crucial Link in Ocean Food Webs, Lenfest
Ocean Program, Washington DC.
http://www.lenfestocean.org/foragefish
Wadsley, A 2012, The Commonwealth Small Pelagic Fishery: Review of estimates of
Jack mackerel biomass,
http://tasmaniantimes.com/images/uploads/Analysis_of_jack_mackerel_biomass_esti
mates_(Wadsley_26Aug2012_updated).pdf
Ward, TM, Burch, P, McLeay, LJ & Ivey, AR 2011, ‘Use of the Daily Egg
Production Method for Stock Assessment of Sardine, Sardinops sagax; Lessons
Learned over a Decade of Application off Southern Australia,’ Reviews in Fisheries
Science, vol. 19, no. 1, pp. 1-20.
http://www.tandfonline.com/doi/full/10.1080/10641262.2010.528711