When significant aggregations of fish were detected acoustically, the midwater trawl was set to confirm species identity and to collect approximately 100 individual Atlantic herring. Tows were conducted along the transect line after passing over the fish aggregations. Tow times were generally short in duration (10 - 20 minutes); just long enough to collect the necessary samples. All herring samples were frozen at sea for further laboratory analysis.

Back in the laboratory, herring samples were thawed out for examination. Natural length measurements were taken to the nearest 5 mm, total weight to the nearest 0.1 g, gonad weight to the nearest 0.1 g, sex and International Commission for the Northwest Atlantic Fisheries (ICNAF) gonad development stage (Table 3). In order to account for freezing and thawing of herring samples, length measurements were corrected using Maine Department of Marine Resources' correction equation:

Lmm = 4.1825 + 1.0051 * [Frozen Sample Length (mm)].

Stage Description and Criteria
ICNAF Atlantic herring gonad development stages (from Burnett et al., 1989).

I
Immature: testes and ovaries very small, threadlike, 2 - 3 mm broad; testes grayish
white or brownish red; ovaries pinkish or wine red.
II
Immature fish that will spawn next year: testes and ovaries small, 3 - 8 mm broad;
testes reddish or grayish brown; ovaries orange-red; eggs visible only with
microscope.
III
Ripening, early stage: testes and ovaries occupy about half of ventral cavity, 1 - 2
cm broad; testes grayish or brownish red; ovaries orange-red; eggs small, but visible
and granular.
IV
Ripening, mid-stage: testes and ovaries almost as long as body cavity; testes reddish
yellow with blood vessels clearly visible; ovaries orange-red or pale yellow-red; eggs
larger, opaque with only a few clear.
V
Ripe: testes and ovaries fill body cavity; milt and eggs do not flow, but can be
extruded by pressure; testes yellowish white or milk white with no reddish color and
blood vessels not visible; ovaries yellowish; eggs large and mostly clear.
VI
Spawning: testes and ovaries ripe and emptying; milt and eggs flow freely; testes
white or pale yellowish white with no blood vessels visible; ovaries yellowish; eggs
large and clear.
VII
Spent: testes and ovaries baggy, flabby and bloodshot; testes empty or with residual
milt; ovaries empty or with few residual eggs.
VIII
Resting: testes and ovaries firm and larger than in Stage II; walls striated with blood
vessels prominent; testes brownish red; ovaries wine red; eggs not visible to naked
eye.

herr_spawn_size.csv