Latitudinal variation in reproductive biology and growth of female Dover sole (Microstomus pacificus) in the North Pacific, with emphasis on the Gulf of Alaska stock

Dover sole (Microstomus pacificus) have a wide distribution throughout the North Pacific, ranging from southern Baja California (26°N) to the Gulf of Alaska (GOA, 59°N). Prior to this study, our understanding of Dover sole reproductive biology was limited to the stock off the US west coast. This study was initiated to determine the length and age at maturity for Dover sole in the GOA. We also compared the length at maturity and growth rate across latitudes to test the hypothesis that individuals near the northern extent of their range (GOA stock) mature at a larger size than individuals in the southern stock off California and Oregon. Female Dover sole (n=273) ranging in length from 198–663 mm were collected opportunistically around Kodiak Island, Alaska, (55–59°N) from February 2000 to October 2001, with sampling concentrated in the months February-April, June–July, and October–November. All ovaries were examined to determine the maturity stage using standard histological criteria. The spawning season of Dover sole in the GOA spanned at least 4 months, from February to May. Dover sole in the GOA matured at a larger size than those off California and Oregon, with an estimated length at 50% maturity (ML50) of 439 mm. At the same fish length that nearly 100% of Dover sole from California and Oregon waters are mature, Dover sole in the GOA are just beginning to mature. The estimated age at 50% maturity (MA50) for female Dover sole in the GOA was 6.7 years and was similar to the MA50 for cohorts at more southern latitudes. We attribute the latitudinal variation in ML50, combined with the similar MA50 across latitudes, to spatial differences in growth rates.