Morphometics and gonadal development of the hagfish Eptatretus cirrhatus in New Zealand.

Hagfishes have been the target of commercial fisheries in many areas of the world, with the catch processed for leather and for human consumption. A fishery has been operating in New Zealand waters for the last six years, harvesting the bearded hagfish, Eptatretus cirrhatus. The fishery has thus far been unregulated. Based on samples collected dockside over a two-year period, this report expands the morphometric database for this species, provides information on the size and weight of the harvested animals, determines the sizes at the onset of gonadal development and the minimum sizes at sexual maturation for males and females, and indicates that E. cirrhatus, like most other hagfish species, has no specific breeding season. Although females appear in the population at smaller sizes, the sex ratio for mature animals is 1:1 and the sizes of the largest males and females are comparable. The changes observed in sex ratio as a function of TL suggest differences in the timing and rates of gonadal development in females versus males rather than protogyny. Based on the size of the eggs, the number of eggs per female, the proportion of the population that contains large eggs, and the number of postovulatory females, it is clear that E. cirrhatus, like other hagfish species, are potentially vulnerable to overexploitation

A comparison of male and female L:W curves.

<p>The curves are significantly different but parallel, with males heavier than females at all TLs.</p

Growth and changes in proportional measurements.

<div><p>(a) Prebranchial length, as percent of TL, plotted against TL. As the hagfish grow, the relative size of the prebranchial region decreases significantly. </p> <p>[Slope = -0.0069; r²=0.207; Sy.x=1.218; F_(1,176)= 46.01; p<0.05*, significant].</p> <p>(b) Branchial length, as percent of TL, plotted against TL. The relative size of the branchial region does not change with growth.</p> <p>[Slope = -0.0007; r²=0.003; Sx.y=1.142; F_(1,170)=0.484; p>0.05, not significant].</p> <p>(c) Trunk length, as percent of TL, plotted against TL. As the hagfish grow, the relative size of the trunk increases significantly.</p> <p>[Slope = 0.0082; r²=0.063; Sy.x=2.692; F_(1,170)=11.27; p<0.05*, significant].</p> <p>(d) Tail length, as percent of TL, plotted against TL. As the hagfish grow, the relative size of the tail decreases significantly.</p> <p>[Slope= -0.0048; r²=0.039; Sy.x=2.011; F_(1,170)=6.892; p<0.05*, significant].</p></div

Total slime pore count plotted against TL.

<p>The number of slime pores increases significantly as the hagfish grow in length (p<0.05*). </p

The initiation of female and male gonadal development.

<div><p>(a) The percentage of female hagfish with developing ovaries as a function of TL. The assumptions made are (1) that before male gonadal development has been initiated, and sex cannot be determined macroscopically (Stage 0), the genetic sex ratio is 1:1, and (2) the genetic sex ratio within each 50 mm TL intervals remains 1:1 throughout, although the individuals in a given interval may or may not have initiated gonadal development. </p> <p>(b) The percentage of male hagfish with developing testes as a function of TL. This graph is based on the same assumptions as part (a). Males begin gonadal development at a larger TL than females, and males at Stage 0 persist at TLs where all females have initiated ovarian development. </p></div

A scatterplot of reproductive stage vs total length.

<p>Note that all animals above 585 mm TL were readily identifiable as either male or female. </p

Female reproductive parameters.

<div><p>(a) Egg length as a function of TL. There is no signficant relationship here; larger females do not produce larger eggs than smaller females. </p> <p>(b) Egg number as a function of TL. Large female hagfish produce more eggs than smaller females. </p> <p>(c) A regression of the number of eggs as a function of egg length. For all females, the number of eggs under development decreases as the eggs grow larger. </p></div

Gonadal development and sex ratios as a function of TL.

<div><p>(a) The percentage of hagfish at Stage 0 as a function of TL. Data were sorted into 50 mm TL intervals, and the percentage at Stage-0 determined as:</p> <p>(Stage-0s)/(females + males + Stage-0s) </p> <p>The percent values were plotted at the midpoint of each TL interval. </p> <p>(b) Sex ratios (female:male) as a function of TL. Data were sorted into 50 mm TL intervals. The sex ratio decreases from ~4.5:1 to 1:1 as the percentage of Stage 0 animals in the size interval decreases to zero (Figure 13a). </p></div

Growth and changes in slime pore number and distribution.

<div><p>(a) Prebranchial slime pore count plotted against TL. The slime pore count in this region does not change significantly with growth. [Pearson r=-0.046; p>0.05, not significant; R²=0.002, <i>n</i>=178; mean 16.02, median 16].</p> <p>(b) Branchial slime pore count plotted against TL. The number of slime pores in the branchial region increases significantly with growth, as 7 slime pores become more common. [Pearson r=0.447; p<0.05*, significant; R²=0.197; <i>n</i>=178; mean 6.37, median 6.0].</p> <p>(c) Trunk slime pore count plotted against TL. The number of slime pores in the trunk increases with growth. [Pearson r=0.165; p<0.05*, significant; R²=0.027; <i>n</i>=178; mean 49.0, median 49.0].</p> <p>(d) Tail slime pore count plotted against TL. The slime pore count in this region does not change significantly with growth. [Pearson r=0.077; p>0.05, not significant; R²=0.006; <i>n</i>=178; mean 11.69, median 12.0].</p></div

Stages of female sexual maturation (see Table 1).

<p>Stages of female sexual maturation (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0078740#pone-0078740-t001" target="_blank">Table 1</a>).</p