Graduation Year

2023

Document Type

Thesis

Degree

M.S.

Degree Name

Master of Science (M.S.)

Degree Granting Department

Marine Science

Major Professor

Heather Judkins, Ph.D.

Co-Major Professor

Ernst Peebles, Ph.D.

Committee Member

Lisa Hendrickson, MS, Northeast Fisheries Science Center, NOAA

Keywords

isoscape, life history, Loliginidae, longfin inshore squid, statolith, West Florida Shelf

Abstract

Doryteuthis (Amerigo) pealeii is a common fisheries squid that occurs in the Gulf of Mexico (GoM) and along the east coast of the United States. These squid are an important link in the food web, linking higher and lower trophic positions (Madsen et al., 2007), and they are also used for human consumption. The migration patterns of D. pealeii populations in the northwestern North Atlantic have been thoroughly studied when compared to those in the GoM. This research aims to combine statolith aging and stable isotope analysis to enhance the understanding of D. pealeii migration patterns throughout their short, sub-annual lifespan along the West Florida Shelf in the GoM. Individual specimens were aged via statoliths, and δ13C and δ15N stable isotopes were analyzed within individual eye-lens laminae of D. pealeii specimens. These were compared to known isoscapes present along the West Florida Shelf to determine overall migration patterns, which were then compared to variables such as specimen age and hatch month to document any potential relationships. Among individual squid, the most common migration patterns observed in this study were northeastward (35%) and eastward (32%) movement. When compared with hatch month, this suggests the D. pealeii in the GoM exhibit similar migration patterns to those off the northeastern coast of the United States – hatching and spending the colder months offshore, then moving inshore during spring and early summer. This study suggests that maternal contribution of isotope ratios is present in the eye-lens cores of specimens, which allows us to make inferences about the spawning grounds from which the specimens included in this study hatched. Core δ13C and δ15N ratios suggest individuals from the most northern National Marine Fisheries Service (NMFS) statistical zone included in this study remain in the same area they were spawned in, while the other NMFS zones included here intermix. The migration patterns of D. pealeii were compared to those of D. plei observed by Meath et al. (2019) to determine any potential overlap in migration patterns between the two species. Over half of those examined for both species exhibited isotope trends that suggested either northeastward or eastward movement over the course of their lives. This research will contribute to the understanding of the migration patterns of the D. pealeii population within the GoM, allowing fishery management to better regulate populations, maximize harvest, and prevent future overfishing in this area.

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