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Fishery Bulletin 111(1) 
corded for this species in the Gulf of Maine (34.5 cm; 
Collette and Klein-MacPhee, 2002). The gear type used 
in this study selected for larger fish, and we suspect 
that smaller fish avoided the longline hooks. Although 
to our knowledge skipped spawning (when a mature 
individual skips a year of spawning) has not been ob- 
served in Haddock, it is not uncommon in long-lived 
iteroparous fishes, including Atlantic Cod (Jorgensen 
et ah, 2006; Rideout et ah, 2006; Fig. 1). Therefore, we 
could not have assumed that a female was immature 
if it lacked signs of sexual maturity during the spawn- 
ing season, as was assumed by Waiwood and Buzeta 
(1989) because there is the possibility that the fish had 
skipped spawning that year. 
The use of microscopic analysis or histological ex- 
amination of a tissue sample of the ovary was a reli- 
able way to determine whether the ovary was imma- 
ture or regenerating. Immature ovaries could be dis- 
tinguished histologically from regenerating ovaries by 
the diameter of the primary oocytes (W. Roumillat, per- 
sonal commun.). Immature ovaries contained primary 
oocytes that were equal in diameter, but regenerating 
ovaries had primary oocytes that varied in diameter. 
Additionally, the RE phase can be differentiated from 
the I phase by the following features: RE ovaries 1) 
have a thicker ovarian wall, 2) have more space, inter- 
stitial tissue, and capillaries around primary oocytes, 
and 3) have the presence of late-phase atresia and 
muscle bundles (blood vessels surrounded by connec- 
tive and muscle tissue) (Brown-Peterson et ah, 2011). 
Because of the selectivity of the fishing gear for larger- 
size fish and our limited sampling period, our study did 
not provide adequate data to fully resolve macroscopic 
differences between the RE and I stages. Further work 
should focus on differentiation of a regenerating ova- 
ry from an immature ovary with sampling conducted 
further into the summer with less size-selective gear. 
Proper identification of immature ovaries would great- 
ly reduce the error in calculation of spawning biomass 
estimates and improve accuracy of estimates of length 
at maturity. 
Developing stage 
There was disagreement between D and early OM 
phase, HI (Table 1). We observed that when a Had- 
dock ovary began OM, some oocytes in the initial batch 
completed the process before others within the same 
ovulating batch. Although Haddock ovaries have been 
reported to be homogeneous in structure throughout 
all phases of maturity (Templeman et ah, 1978; Robb, 
1982), our observations indicate that it is not homoge- 
neous in structure during this very early phase of OM 
(HI). This result is supported by Alekseyeva and Tor- 
mosova (1979), who reported that formation of batches 
occurs through asynchronous maturation of individu- 
al groups of oocytes. The histological staging method 
sometimes resulted in HI ovaries being misclassified 
as D, likely because they were sampled during initial 
OM of the first batch of oocytes for the season, when 
there were no histological characteristics present to 
indicate that prior batches had been spawned. Initial 
spawning HI ovaries had so few fully hydrated oocytes 
(because of the asynchronous maturation of the batch) 
that collection of a small tissue sample from a central 
location was sometimes unsuccessful in representing 
all phases of oocytes present. As a single batch pro- 
gresses through OM, evidence that spawning has been 
initiated becomes more pbvious with GVM and yolk co- 
alescence beginning in oocytes (Table 2; Lowerre-Bar- 
bieri et ah, 2011). As the season progresses and the 
ovary initiates OM in later batches of oocytes, a HI 
tissue sample could be distinguished from a D tissue 
sample by the presence of POFs. 
The agreement between macroscopic and histologi- 
cal staging for D and HI ovaries could be improved if 
the method used to take tissue samples from the ovary 
were modified. When ovaries are classified as HI in 
the field, a larger tissue sample or samples should be 
taken from multiple places in the ovary to improve the 
accuracy of the histological results. Our observations 
demonstrate that determination of the maturation of 
an ovary based on histological examination alone may 
not always be accurate. To reduce staging errors based 
on histological analysis in future studies, it is recom- 
mended that each tissue sample be documented with 
a photograph of the whole ovary from which it was 
extracted and with an estimate of the percentage of 
hydrated oocytes observed on the visible surface of the 
ovary. 
Three ovaries classified as D in the field contained 
POFs when analyzed histologically, and, by our defini- 
tion, a D ovary could not have previously spawned that 
season (Table 1; Fig. 1). Therefore, those specimens had 
spawned at least one batch of eggs but had not yet 
hydrated oocytes for the next batch, and the decrease 
in volume of the ovary after spawning a prior batch of 
eggs was not evident in field observations. A closely re- 
lated species, Atlantic Cod, begins to hydrate a batch of 
oocytes 1-2 days before spawning (Kjesbu, 1991). Final 
oocyte maturation in cold-water marine fishes with pe- 
lagic eggs generally lasts 1-2 days (Thorsen and Fyhn, 
1996). Trippel and Neil (2004) reported that Haddock 
had a mean interval of 5.4 days between batches of re- 
leased eggs, and Hawkins et al. (1967) and Alekseyeva 
and Tormosova (1979) reported an interval of 26-40 h. 
These findings combined indicate that there is an in- 
terbatch period between the spawning of a batch and 
the next batch that is beginning to hydrate, a period 
described by Murua et al. (2003) as the resting stage 
(Fig. 1). 
Consequently, there was the possibility that a ma- 
ture ovary could be incorrectly classified as D in the 
field if it was between ovulation events during this in- 
terbatch period. Therefore, we concluded that it is not 
always possible to be certain that an individual has 
begun spawning for the season on the basis of macro- 
scopic observation alone and this uncertainty can pose 
