Burchard et ai.: Maturity indices and field sampling practices for staging Melanogrammus aeglefmus 
91 
a female developing ovary as “a mixture of less than 
50% yolked eggs and hydrated eggs”; however, accord- 
ing to Murua et al. (2003), the presence of hydrated 
oocytes indicate that the spawning process has begun 
and the gonad is in a “spawning” stage, where “oocytes 
are either in migratory nucleus stage or hydration 
stage.” This discrepancy between indices in the defini- 
tion of a developing ovary could result in different esti- 
mates of fecundity in determinate-spawning species for 
which prespawnmg, when the most advanced oocytes 
in an ovary are in the late vitellogenesis stage, is the 
optimal phase in reproductive maturity for the collec- 
tion of samples for accurate estimation of fecundity. If 
sampling is conducted before this stage, all oocytes des- 
tined to be spawned may not be developed and would 
be left out, and, as a result fecundity would be under- 
estimated. If samples are taken from females that have 
already spawned, the number of eggs that have already 
been released cannot be detected, an outcome that also 
would result in an underestimation of fecundity. 
Another important difference between the matura- 
tion indices of Murua et al. (2003) and O’Brien (1993) 
is the description of a resting ovary. The definition 
of O’Brien (1993) was based on a description by the 
NMFS (1989) and Kesteven (1960) and was similarly 
defined by Waiwood and Buzeta (1989), Tomkiewicz et 
al. (2003), and Vitale et al. (2006). All these authors 
described the resting maturity stage as occurring af- 
ter the spent maturity stage. Conversely, Murua et al. 
(2003) described the resting stage as an in-between 
batch state occurring before the spent stage, when 
some hydrated oocytes from the previous batch may 
remain and further batches of hydrated oocytes are 
still to be produced. Therefore, there was a need for 
greater consistency in definitions and standardization 
in terminology of reproductive maturity stages of fish- 
es. In a recent work by Brown-Peterson et al. (2011), 
a great deal of effort was invested in providing such 
standardization. 
Although certain reproductive traits, such as ma- 
turity phases, are universal among teleost fishes, the 
temporal patterns of these traits vary among species 
(Lowerre-Barbieri et al., 2011). Incorporation of tem- 
poral components into standardized indices potentially 
could produce more accurate staging results for each 
species studied, as well as provide additional informa- 
tion on the reproductive success of a species. A recent 
study by Tobin et al. (2010), published after our sam- 
pling was completed in 2006-07, identified the tim- 
ing and microscopic changes in maturation events of 
female Haddock as they transition from immaturity 
to maturity between summer and winter. That study 
provided evidence that Haddock commit to maturation 
by October or November with the existence of corti- 
cal-alveolar-stage oocytes in the ovaries. Knowledge 
of this maturation commitment can allow research- 
ers to confidently identify females as either immature, 
skipped-spawner, or mature after November, improving 
estimations of spawning stock biomass. 
Haddock is a batch-spawning species with group- 
synchronous ovary organization and determinate fecun- 
dity (Clay 1989; Murua and Saborido-Rey, 2003). This 
collection of reproductive traits is common in demersal 
Northwest Atlantic fishes, including but not limited 
to Atlantic Cod, Yellowtail Flounder ( Limanda ferru- 
ginea), and Atlantic Halibut ( Hippoglossus hippoglos- 
sus; see Murua and Saborido-Rey, 2003). The standard 
number of yolked oocytes immediately before the onset 
of spawning in a determinate-fecundity spawner can 
be considered equivalent to the potential annual fecun- 
dity of that fish (Murua et al., 2003). After the onset of 
spawning, the individual will hydrate several batches 
of yolked oocytes throughout the spawning season. 
The purpose of our study was to develop a standard 
field-proof, macroscopic ovarian maturity index for Had- 
dock that is suitable for use in studies of diel spawn- 
ing periodicity (Anderson, 2011) and conforms to the 
recent standardization guidelines of Brown-Peterson et 
al. (2011). Diel spawning periodicity has been widely 
studied in marine fishes (e.g., Ferraro 1980; Walsh and 
Johnstone, 1992; Wakefield, 2010) and provides details 
on the chronology of reproductive processes in species. 
It has been suggested that diel spawning periodic- 
ity maximizes fish survival and reproductive success 
(Ferraro, 1980; Lowerre-Barbieri, 2011). In addition to 
support for the collection of field data on reproductive 
stages, we also wanted the index to provide guidance 
on sampling techniques for the collection of samples 
for laboratory analysis. First, a staging method devel- 
oped from unpublished observations and a review of 
data published before our sampling in 2006-07 was 
used to stage female Haddock ovaries in the field. The 
resulting maturity index was then revised compared 
with a laboratory histological staging method similar 
to that of Tomkiewicz et al. (2003) for Atlantic Cod in 
the Baltic Sea. New stages were assessed to determine 
whether they could be used in future studies to exam- 
ine diel patterns in spawning (Anderson, 2011). Finally, 
the relative strengths and weaknesses of both the field 
and laboratory approaches were assessed. 
Materials and methods 
Initial field and laboratory indices 
A new field macroscopic ovarian maturity index for fe- 
male Haddock was developed by building on previous 
published indices (Homans and Vladykoy, 1954; Robb, 
1982; Murua et al., 2003; Brown-Peterson et al., 2011) 
and unpublished observations made in the field (Table 
1). The index consists of 8 stages, progressing from im- 
mature to regressing. To move toward use of standard 
phraseology, the terminology follows Brown-Peterson 
et al. (2011). It differs from previously published indi- 
ces with the addition of 3 stages that represent early 
to late progression of oocyte maturation (OM; Brown- 
