Investigation of the Reproductive Anomalies of the Spiny Dogfish

Ryan Knotek
Class of 2012

Gillnetting for Spiny Dogfish in the Gulf of Maine

Dissection of a mature female Spiny Dogfish

Embryos at different stages of gestation from Spiny Dogfish in North Carolina

The spiny dogfish is a “k” selected species. Their long gestation period, low fecundity, long life, and late maturation make their populations sensitive to fishing pressures. Groundfish stocks, such as cod, in the late 1980’s became low enough that commercial fisherman began to target spiny dogfish, and from 1987 to 1996 there was almost a ten-fold increase in the amount of landings within the U.S.

In 2000 the species fell to threshold levels. The severity of the situation caused an emergency management plan in 2002, when the Mid-Atlantic and New England fishery Management Councils made the Spiny Dogfish Movement plan, which put into place a 4 million pound quota and lower possession limits. Although the spiny dogfish now had a management plan limiting their population degradation, they were still thought incapable of rebounding until 2020. However between 2005 and 2008 there was a four-fold increase in their biomass, an anomaly never seen or believed to be feasible in any shark species.

The goal of my honors thesis project will be to investigate the potential anomalies in spiny dogfish reproduction and how may have contributed to the four-fold increase in biomass. The current information on the reproduction of spiny dogfish is outdated and has not tracked the dogfish reproduction over the full 22-month gestation period. The hypothesis of this project is that there may be regionally different reproductive cycles, and multiple stocks of spiny dogfish along the U.S. East Coast.

For my project, 150 female dogfish per month will be dissected; 50 each from the Gulf of Maine, New Jersey, and North Carolina. The dissections will include the total length, fork length, and weight of each specimen, as well as the size and number of follicles, total length and sex of pups, embryo sizes, and candle sizes. The data will then be compared to investigate the potential regional differences in reproductive cycles for this species.