Using New Approaches to Update and Collect Fisheries Specific Data on Age Determinations of the Spiny Dogfish in the Gulf of Maine

Primary tabs

Project Type: 
Research
Project Number: 
R/MED-8
Inception Date: 
2006
Completion Date: 
2008
Theme Area: 
Fisheries Resources

Participants:

Paul Tsang UNH - Department of Molecular, Cellular & Biomedical Sciences Principal Investigator
James Sulikowski University of New England Co-Principal Investigator
David Koester University of New England Co-Principal Investigator

Students Involved:

Jeff Kneebone UNH - Department of Molecular, Cellular & Biomedical Sciences
Wally Bubley UNH - Department of Molecular, Cellular & Biomedical Sciences
Erin Fagan UNH - Department of Molecular, Cellular & Biomedical Sciences
Amanda Noble University of New England - Biological Sciences
Nathaniel Furey University of New England - Biological Sciences
Marie Quinlan University of New England - Biological Sciences
Devin Flawd University of New England - Biological Sciences
Abstract: 

In the year 2000, the Atlantic States Marine Fisheries Commission implemented an interstate Fisheries Management Plan to protect the overfished spiny dogfish (Squalus acanthias) in the Northwest Atlantic, including the Gulf of Maine. This was a timely decision because some aspects of dogfish life history have not been updated since comprehensive surveys were conducted 20 years ago.

Critical to any fisheries management plan is accurate and current information on life history parameters, such as age and growth, size at sexual maturity, fecundity, and longevity. Furthermore, in the case of the spiny dogfish, current investigations suggest that geographic region is an additional consideration for the development of a management plan. Recent tagging studies indicate that two stock populations of spiny dogfish might exist within the Northwest Atlantic, rather than a single unit stock as previously assumed. As such, previous investigations have not accounted for possible variations in life history traits that may be attributable to environmental changes that accompany changes in latitude across geographic regions.

A defining life history parameter is to determine age at maturity. Due to discrepancies in age determination data among previous studies, recent reports from the Northeast Fisheries Science Center (NEFSC), Atlantic States Marine Fisheries Commission (ASMFC), and National Marine Fisheries Service (NMFS) stress the need for additional research on standardizing age determination techniques so that total length can be reliably converted to age classes. Therefore, the goal of our present proposal is to develop a new method for the accurate determination of age in the spiny dogfish population within the Gulf of Maine.

We will accomplish this goal by comparing the traditional dorsal fin spine method of age determination to the vertebral centrum method of aging spiny dogfish to ascertain which structure produces the most accurate and reliable correlation between age and total length. In addition, we will also examine age at sexual maturity in order to determine if this parameter has changed along with the documented reduction in size at maturity. Our results will provide accurate and updated information on the biology of the spiny dogfish, which will benefit scientists, fisheries biologists and fishermen. Furthermore, the validated age measurements, growth rates and age at sexual maturity information will add credence to future assessment of population dynamics and stock structure of the spiny dogfish.

Objectives: 
Our first objective is to compare the dorsal fin spine method to the vertebra centrum method of aging spiny dogfish to determine which structure produces the most accurate and reliable correlation between age and total length. Age determination will be based on identification of band formation in vertebral centra and in dorsal fin spines. Precision and bias will be evaluated through standard statistical and mathematical techniques. Validation of band formation will be attempted through the use of oxytetracycline and through marginal increment analyses.
 
Our second objective is to examine age at sexual maturity, which will be assessed by gross and histological examinations of male and female reproductive tracts. This will enable us to determine if indeed age at sexual maturity has decreased along with the documented reduction in size at sexual maturity. Together, our findings will provide reliable and updated fisheries data on the relationship between age and length, and age at sexual maturity for the spiny dogfish (Squalus acanthias) population in the Gulf of Maine.
Methodology: 

Age determination will be based on identification of band formation in vertebral centra and in dorsal fin spines. Precision and bias will be evaluated through standard statistical and mathematical techniques. Validation of band formation will be attempted through the use of Oxytetracycline and through marginal increment analyses. Age at sexual maturity will be determined by gross and histological observations of male and female reproductive tracts.

Rationale: 

A Fishery Management Plan (FMP) was adopted in 2000 to protect the overfished spiny dogfish in the Northwest Atlantic. Critical to any FMP is accurate and updated information on life history traits such as age and size relationships, and age at sexual maturity. NMFS, NEFSC, ASFMC reports stress the need for standardizing age determination due to discrepancies in previous aging studies. Thus, by developing a new method of age determination, fisheries biologists and fishermen will benefit from updated and accurate information on the biology of the spiny dogfish, as this information will add credence to future assessment of population dynamics and stock structure for this species.

Accomplishments: 
Researchers Determine Average Age at First Maturity for Spiny Dogfish in Gulf of Maine
Despite the abundance of spiny dogfish in Gulf of Maine waters, very little is known about the life history of this species. Age and growth are particularly difficult to assess on elasmobranchs like the dogfish primarily because they lack many of the hard bony structures typically used to determine age in aquatic organisms. NHSG-funded researchers used a modified histological staining technique to estimate the average age of spiny dogfish using their second dorsal fin spine and vertebrae. In 2012, this method helped determine that in the Gulf of Maine, the age at first maturity for spiny dogfish males is 6.5 years and six years for females of the species. These data will provide updated and more accurate life history information that can be incorporated into future management plans for the species.

A major goal of our N.H. Sea Grant funded project on spiny dogfish is to develop a technique for accurate age determinations using two hard structures, the second dorsal fin spines and vertebrae. We validated that vertebrae processed with the modified histological staining technique of Natanson et al. (2007; Environmental Biology of Fishes, 80:293-308) was not only an appropriate aging structure for spiny dogfish, but it provided better age estimates than those obtained using the second dorsal fin spines.  Based on this modified histological staining technique, we found that age at first maturity for males was 6.5 years, while age at first maturity for females was 6 years.  In turn, our data will provide updated and more accurate life history information (in this case, age and growth), which can be incorporated into a future management plan for these elasmobranchs.

Publications

Available from the National Sea Grant Library (use NHU number to search) or NH Sea Grant

Journal Article

  • Bubley, W., J. Kneebone, J. Sulikowski and P. Tsang (2012). Reassessment of spiny dogfish "Squalus acanthias" age and growth using vertebrae and dorsal-fin spines. Journal of Fish Biology 80(5):1300-1319.

Thesis/Dissertation

  • Bubley, W. (2010). Updated life history and population structure assessment of spiny dogfish, "Squalus acanthias," in the Gulf of Maine. Doctoral dissertation, University of New Hampshire.